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NBS SPECIAL PUBLICATION

^ QC100 .U57 NO.506 506

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

Workshop on Asbestos:

Definitions and

Measurement Methods
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act of Congress March 3, 1901. The

Bureau's overall goal is to strengthen and advance the Nation's science and technology and

facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in

trade, and (4) technical services to promote public safety. The Bureau's technical work is performed by the National Measurement Laboratory, the National Engineering Laboratory,

and the Institute for Computer Sciences and Technology.

THE NATIONAL MEASUREMENT LABORATORY provides the national system of

physical and chemical and materials measurement; coordinates the system with measurement

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Molecular Science — Analytical Chemistry — Materials Science.

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and measurement capabilities; provides engineering measurement traceability services;

develops test methods and proposes engineering standards and code changes; develops and

proposes new engineering practices; and develops and improves mechanisms to transfer

results of its research to the utlimate user. The Laboratory consists of the following centers:

Applied Mathematics — Electronics and Electrical Engineering^ — Mechanical

Engineering and Process Technology^ — Building Technology — Fire Research —

Consumer Product Technology — Field Methods.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts

research and provides scientific and technical services to aid Federal Agencies in the selection,

acquisition, application, and use of computer technology to improve effectiveness and

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'Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D.C. 20234. 'Some divisions within the center are located at Boulder, Colorado, 80303.

The National Bureau of Standards was reorganized, effective April 9, 1978.
NOV 2 8 1978

Proceedings of Workshop on Asbestos:

^

Definitions and Measurement Methods

Proceedings of a Workshop on Asbestos held at

the National Bureau of Standards,

Gaithersburg, Maryland, July 18-20, 1977

Edited by

C. C. Gravatt, Philip D. LaFleur,

and Kurt F. J. Heinrich

National Measurement Laboratory

National Bureau of Standards

Washington, D.C. 20234

Sponsored by

National Bureau of Standards

of the Department of Commerce

and Occupational Safety and Health Administration

of the U.S. Department of Labor

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued November 1978
I

I

Library of Congress Catalog Card Number: 78-600109

National Bureau of Standards Special Publication 506

Nat. Bur. Stand. (U.S.), Spec. Publ. 506,490 pages (Nov. 1978)

CODEN; XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1978

For sale by the Superintendent of Documents, U.S. Government Printing Office Wastiington, D.C. 20402 - Price .$6.75

Stock No. 003-003-01993-3
FOREWORD

Asbestos is a generic name used to describe a variety of

hydrated silicate materials which exist as fibers. Because

"asbestos" resists heat and acids, is noncombustible, and can

be woven into fabrics, it is a valuable industrial material.

Asbestos has been known and used since ancient times. Today, it

is used in some 3000 commercial applications, from potholders,

to brake linings, to construction materials.

Concern over the use of asbestos has arisen from studies

which indicate an increased incidence of various serious

diseases among people who work with it. Meaningful regulation

requires proper definitions of workplace air concentrations of

asbestos and effective measurement methods for these minerals.

This Workshop was organized to evaluate the existing state-ofthe-art in measuring "asbestos" and is part of an interagency

program dealing with definitions and measurement methods for

asbestos between the National Bureau of Standards of the

Department of Commerce and the Occupational Safety and Health

Administration of the Department of Labor.

Philip D. LaFleur, Chief

Center for Analytical Chemistry

1 1
PREFACE

This Workshop was organized to provide a forum for

representatives of industrial corporations, trade associations,

regulatory and other federal agencies, state and local agencies

and other researchers to discuss asbestos definitions and

measurement methods.

The Workshop was divided into four topical areas:

Mineralogical Aspects, the Relationships Between Chemical and

Physical Properties and Health Effects, Analytical Methods, and

Regulatory Aspects. The format of the Workshop included

presentations of technical papers by invited experts, followed

by verbal discussions. At the conclusion of each session there

was a general discussion of the material presented. The general

discussions served to define those factors for which there is

general agreement, what points of controversy exist, and to

identify additional research that is required to resolve the

remaining problems.

The following protocol was employed for the preparation of

these proceedings. Each author/speaker submitted a written

manuscript based on and containing the material given in the

oral presentation. The questions, answers, and comments which

followed each talk have been transcribed from the tape

recordings made of the Workshop, edited both to remove extraneous material and to improve readability, but without

changing the meaning. These discussion sections are printed

immediately following the manuscript. The general discussions

which followed each session have been similarly transcribed,

edited, and printed at the end of each topic section. In

addition, any questions, answers, comments, or discussion

material which was submitted to the editors in writing has been

inserted in the appropriate section of the Proceedings and the

material has been designated as "submitted in writing - not in

recording of Workshop." I wish to express my gratitude to all

those who, through participation in the Workshop or preparation

of these proceedings, made this undertaking a success. These

proceedings were expertly typed and prepared by

Mrs. Joy Shoemaker and members of her Text Editing Facility and

the assistance of Mrs. Betty Garrigues in correcting proofs was invaluable. The able assistance of Drs. Ryna Marinenko and

John Small in editing the Analytical Methods Session is

gratefully acknowledged.

It is hoped that these Proceedings will provide useful

information to those currently involved in formulating

measurement methods, definitions, and regulatory positions with

respect to asbestos and other fibrous materials.

C. C. Gravatt, Chief

Office of Environmental Measurements

iv
ABSTRACT

This document contains invited papers which were given at

a workshop on "Asbestos: Definitions and Measurement Methods"

which was jointly sponsored by the National Bureau of Standards

of the U. S. Department of Commerce and the Occupational Safety

and Health Administration of the U. S. Department of Labor. The

discussion portions of the Workshop also have been included as has written material appropriate to the topics under

consideration which was submitted to the editors at a later

date. The Workshop covered four major topics: Mi neral ogical

Aspects, the Relationship Between Chemical and Physical

Properties and Health Effects, Analytical Methods, and

Regulatory Aspects. Also included in these Proceedings is a summary of each of these topics. These summaries serve to

define those factors for which there was general agreement at

the Workshop, identify remaining points of controversy, and, in some cases, describe additional research required to resolve

remaining problems.

Keywords: Amphibole; asbestos; fibers; light microscopy;

mineralogical terminology; scanning electron

microscopy; serpentine; talc; transmission electron microscopy.

V
TABLE OF CONTENTS

PAGE.

FOREWORD iir

PREFACE iv. ABSTRACT vj

SECTION I. MINERALOGICAL ASPECTS

Chairman - Brian Mason, Smithsonian Institution, Washington, D. C.

HISTORY OF ASBESTOS-RELATED MINERALOGICAL TERMINOLOGY li' Tibor Zoltai

FIBROUS AND ASBESTIFORM MINERALS ig'

James R. Kramer

THE CRYSTAL STRUCTURES OF AMPHIBOLE AND SERPENTINE MINERALS 3E^ Jack Zussman

THE "ASBESTOS" MINERALS: DEFINITIONS, DESCRIPTION, MODES OF FORMATION, PHYSICAL

AND CHEMICAL PROPERTIES, AND HEALTH RISK TO THE MINING COMMUNITY 4^ Malcolm Ross

GENERAL DISCUSSION OF MINERALOGICAL ASPECTS 6J

SESSION II. RELATIONSHIP BETWEEN CHEMICAL AND PHYSICAL PROPERTIES AND HEALTH EFFECTS

Chairman - Marvin Schneiderman, National Cancer Institute of the

National Institutes of Health, Bethesda, Maryland

EPIDEMIOLOGICAL EVIDENCE ON ASBESTOS 7' W. J. Nicholson, A. M. Langer, and I. J. Selikoff

MEASUREMENT OF ASBESTOS RETENTION IN THE HUMAN RESPIRATORY SYSTEM RELATED TO

HEALTH EFFECTS 91 J. Bignon, P. Sebastien, and A. Gaudichet

EPIDEMIOLOGIC EVIDENCE OF THE EFFECT OF TYPE OF ASBESTOS AND FIBER DIMENSIONS

ON THE PRODUCTION OF DISEASE IN MAN 12 W. Clark Cooper

PATHOPHYSIOLOGY IN RELATION TO THE CHEMICAL AND PHYSICAL PROPERTIES OF FIBERS. . . 13

Paul Kotin

THE CARCINOGENICITY OF FIBROUS MINERALS 14

Mearl F. Stanton and Maxwell Layard

NIEHS ORAL ASBESTOS STUDIES 15

John A. Moore

EPA STUDY OF BIOLOGICAL EFFECTS OF ASBESTOS-LIKE MINERAL FIBERS 16

D. L. Coffin and L. D. Palekar

A STUDY OF AIRBORNE ASBESTOS FIBERS IN CONNECTICUT 17 Leonard Bruckman

GENERAL DISCUSSION OF RELATIONSHIP BETWEEN CHEMICAL AND PHYSICAL PROPERTIES

AND HEALTH EFFECTS 19

vi
ble of Contents Continued

PAGE

:SSION III. ANALYTICAL METHODS

Chairman - K. Heinrich, Analytical Chemistry Division, National Bureau

of Standards

IDENTIFICATION OF SELECTED SILICATE MINERALS AND THEIR ASBESTIFORM VARIETIES ... 201

William J. Campbell

AN OVERVIEW OF ELECTRON MICROSCOPY METHODS 221

Clayton 0. Ruud

IDENTIFICATION OF ASBESTOS BY POLARIZED LIGHT MICROSCOPY 235

Walter C. McCrone

MINERAL FIBER IDENTIFICATION USING THE ANALYTICAL TRANSMISSION ELECTRON

MICROSCOPE 249

D. R. Beaman and H. J. Walker

TRANSMISSION ELECTRON MICROSCOPICAL METHODS FOR THE DETERMINATION OF ASBESTOS. . . 271

Ian M. Stewart

STATISTICS AND THE SIGNIFICANCE OF ASBESTOS FIBER ANALYSES . . 281

J. P. Leineweber

SELECTION AND CHARACTERIZATION OF FIBROUS AND NONFIBROUS AMPHIBOLES FOR

ANALYTICAL METHODS DEVELOPMENT 295

J. C. Haartz, B. A. Lange, R. G. Draftz, and R. F. Scholl

ASBESTIFORM MINERALS IN INDUSTRIAL TALCS: COMMERCIAL DEFINITIONS VERSUS

INDUSTRIAL HYGIENE REALITY 313

John M. Dement

THE DETECTION AND IDENTIFICATION OF ASBESTOS AND ASBESTIFORM MINERALS IN TALC. . . 325

Harold D. Stanley

MISIDENTIFICATION OF ASBESTOS IN TALC 339

Jerome B. Krause and William H. Ashton

AMBIENT AIR MONITORING FOR CHRYSOTILE IN THE UNITED STATES 355

Richard J. Thompson

ENVIRONMENTAL PROTECTION AGENCY INTERIM METHOD FOR DETERMINING ASBESTOS IN

WATER 365

Charles H. Anderson

INTER-LABORATORY MEASUREMENTS OF AMPHIBOLE AND CHRYSOTILE FIBER

CONCENTRATION IN WATER 377

K. S. Chopra

THE STANDARD FOR OCCUPATIONAL EXPOSURE TO ASBESTOS BEING CONSIDERED BY

ASTM COMMITTEE E-34 381

M. Cossette and A. A. Winer

IDENTIFICATION AND COUNTING OF MINERAL FRAGMENTS 387

R. J. Lee, J. S. Lally, and R. M. Fisher

PRACTICAL ASPECTS OF TALC AND ASBESTOS 403

C. J. Parmentier and G. J. Gill

GENERAL DISCUSSION OF ANALYTICAL METHODS 413

vii
Table of Contents Concluded

PAGE

SESSION IV. REGULATORY ASPECTS

Chairman - John Martonick, Occupational Safety and Health

Administration, Washington, D. C. i

INTRODUCTION 421

John Martonick

THE MINING ENFORCEMENT AND SAFETY ADMINISTRATION - REGULATIONS AND METHODS .... 422

Aurel Goodwin

OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION METHODS 431

Willard C. Dixon

FDA PROJECTS AND METHODS W

J. A. Wenninger, I. M. Asher, and P. McGrath

CPSC REGULATION OF NON-OCCUPATIONAL EXPOSURE TO ASBESTOS IN CONSUMER PRODUCTS. . . 45"

Robert M. Hehir, Steven P. Bayard, and June Thompson

IMPACT OF ASBESTOS REGULATIONS ON THE MINING INDUSTRY 46'

C. S. Thompson

GENERAL DISCUSSION OF REGULATORY ASPECTS 46

LIST OF ATTENDEES 47'

Disclaimer:

Certain trade names and company products are identified in order to adequately

specify the experimental procedure. In no case does such identification imply recommendation or endorsement by the National Bureau of Standards, nor does it imply that the products are necessarily the best available for the purpose.

viii
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg , MD, July 18-20,

1977. (Issued November 1978)

HISTORY OF ASBESTOS-RELATED MINERALOGICAL TERMINOLOGY

Tibor Zoltai

Department of Geology and Geophysics

University of Minnesota

Minneapolis, Minnesota 55455

Abstract

Asbestos-related mineralogical terms such as fiber , fibrous , asbesti form , asbestos-l i ke , and asbestos have been misinterpreted and

redefined during the last few years in the literature of environmental

and public health studies. The new definitions are inadequate for the

proper description and study of various mineral particles and, at the same time, are causing considerable confusion in interdisciplinary

communication.

The meaning of these terms is traced through the history of

mineralogy. It is demonstrated that: the use of the term fiber has

always required some resemblance to organic fibers; fibrous has been the

term describing a crystallization habit in which the mineral appears to

be composed of fibers; asbesti form has been used, without exception, to

describe a special fibrous habit in which the fibers have higher tensile

strength and flexibility than crystals in other habits of the same mineral; asbestos was initially the name of an independent mineral

species and gradually became a collective term applied to all asbestiform

varieties Of minerals.

Key words: Acicular; amphibole; asbestiform; asbestos; fiber; fibrous;

fragments; mineralogical; serpentine; terminology.

Introduction

Until a few years ago there was no problem with the asbestos-related mineralogical

terminology. Mineralogists knew exactly what other mineralogists meant when they used terms

like asbestos, asbestiform, fibrous, and acicular, even if some of these terms, like

asbesti form , are not always defined in textbooks. The last syllable of asbestiform (that

is, - form ) is consistent with several adjectives used for the description of textures or crystallization habits (e.g., reniform, filiform, dentiform, colloform). Consequently, it is

understood, without question, that asbestiform is a descriptive term for a certain texture or

i crystallization habit.

This situation of content was suddenly changed less than five years ago, when through

the focusing of public and scientific attention on asbestos pollution this portion of the

nineralogical terminology was picked up by environmental and public health scientists, by

angineers and by lawyers. Unfortunately, they did not adopt the terminology as used by

fnineralogists but have introduced a redefinition of most of the critical expressions, in

spite of the objection of leading mineralogists. The most important of these arbitrary

changes of definitions included:

I

j (1) Asbestos is understood by mineralogists as a collective term referring to the

jUnusual crystallization of certain minerals in the form of long, strong, and flexible

jfibers, aggregated in parallel or radiating bundles from which the fibers can easi ly be

1
separated. The definition accepted by the Minnesota District Court during the trial of

Reserve Mining Co. [63, p. 24],^ however, was a different one:

Asbestos is a generic term for a number of hydrated silicates that, when

crushed or processed, separate into flexible fibers made up of fibrils,

(emphasis by the author)

By this definition all amphiboles and a number of other minerals became possible

candidates for inclusion in the term asbestos. Because of the perfect prismatic cleavage,

upon crushing, amphiboles always produce acicular fragments. Of course, acicular fragments

are not fibers, are not flexible and are not composed of fibrils. However, they may not be

distinguishable from asbestos fibers in routine electron microscopic examination. In order

to get around that problem the term fiber had to be defined in a more practical sense.

(2) The redefinition of fiber (U.S. District Court, District of Minnesota, Fifth

Division, Fall, 1973) that was soon adopted by most environmental and public health

scientists [28, p. 5] states that a fiber is:

j

a mineral which is at least three times as long as it is wide.^>^ 1

This definition of fiber eliminated the difficult task of testing the flexibility and

the presence of fibril composition of submicroscopic particles, and retained only the shape

of the particle as a decisive criterion. Accordingly, all acicular amphibole cleavage

fragments became fibers and as indirectly implied, all amphibole minerals became asbestos.

(3) Leading mineralogists objected to calling amphibole cleavage fragments, asbestos

fibers and amphiboles, asbestos minerals. In order to overcome that objection two less

frequently used terms, "asbesti f orm" and "asbestos-like", were redefined in line with the new definitions of asbestos and fiber. The new definitions were introduced in the Minnesota

courtroom [63], and subsequently in the language of the news media and the environmental

literature:

Asbesti form became a prefix added to the name of any mineral which is known to occur as "asbestos" on occasion and/or produce "fibers" when crushed.

Asbestos-1 i ke was defined as any hydrous silicate particle which is at least

three times longer than wide, that is, which is a "fiber".

Thus, all amphiboles became asbesti form mi neral

,^ instead of asbestos minerals, and

amphibole fragments became asbestos-1 i ke fibers , underscoring its implied relationship with

asbestos.

These new definitions provided a simplified mineralogical interpretation for the complex

and not fully resolved problem of asbestos mineralogy. It simplified the identification of

mineral particles by eliminating the need for distinction between asbestos fibers and

acicular cleavage fragments. A fiber can simply be identified by its shape (>3:1 aspect

^Figures in brackets indicate the literature references at the end of this paper.

^The 3>1 aspect ratio limitation in the description of fibers was used before by some i British and American regulatory agencies. However, this was the first incident when this

fiber description became an asbestos f i ber identification , as the use of the term fiber

implied an identity between appropriately shaped amphibole fragments and amphibole

asbestos fibers. This implicative use of the 3>1 aspect ratio is apparent in most

current envi ronmental studies.

^It should be noted that sedimentologists use the term acicular for the description of

particles "whose length is more than three times its width" [27, p. 5].

^The expression "asbestiform amphiboles" is basically valid. However, in the context of

the new definitions it is erroneous as it includes al 1 amphiboles. According to the

proper mineralogical terminology the same expression is limited to those amphibole

crystals which actually grew in the asbestiform habit.

2
ratio) and if its composition and lattice matches that of an amphibole, that particle can be

called "asbestiform" amphibole, or simply, "asbestos". Consequently, all available data on the health hazards caused by the inhalation of asbestos fibers can be applied to acicular

amphibole fragments, thus eliminating the need for the extensive job of determining the

nature and the extent of the health effects of the actual particles, that is, the acicular

amphibole fragments.

On the other hand, the new definitions created serious problems, probably not forseen by

the promoters of the new definitions. For example, jade became an asbestos in spite of the

fact that jade is the toughest known natural substance [8]. One type of jade (nephrite) is

mineralogical ly actinol ite-tremol ite, and according to the new definitions, it is an "asbestiform mineral" and its acicular fragments are "asbestos-like fibers". The other type

of jade is jadeite, a pyroxene. Pyroxenes are similar to amphiboles as far as both are chain

silicates and break into acicular fragments. The only major difference between these two

groups of minerals, in terms of their qualifications for "asbestos", is that pyroxene is not

"hydrated". Consequently, in terms of the new definitions jadeite is not an asbestos.

However, one could argue whether the presence of OH is really necessary in the definition of

asbestos.^

At the same time the new definitions include many non-asbesti form mineral varieties in

the rank of asbestos, they also exclude a number of other minerals, (e.g., non-hydrous

silicates) which in fact may also crystallize occasionally in asbestiform habit. Most of

these minerals are rare and are not known to constitute commercial deposits. Nevertheless, a mineralogical definition should not be tied to commercial criteria.

The new definitions, of course, magnify the extent of the potential asbestos pollution

'problem by an exponential factor. If all amphiboles are "asbestiform" and their fragments

'are "asbestos-like" then every state in the union has some asbestos in the soils, drifts, and

'bedrocks. Kryvial , Wood, and Barrett show [44, p. 13] the distribution of "high con- centration of asbestiform phases" of rocks in the continental United States. Only a few of

the amphi bol e-beari ng rocks included in that survey contain even a minor fraction of known,

true asbestiform varieties of amphiboles.

The new definitions are not only contrary to mineralogical traditions but are inadequate

for crystal chemical descriptions. They also can lead to ambiguity and contradiction. For

example, Kryvial, et al . in their monograph [44, p. 5] wish to exclude hornblende from the

"asbestiform" category of amphiboles; apparently because hornblende seldom crystallizes in

asbestiform habit. However, the new definition of "asbestiform" does not allow them to use it

in that sense, or to express the same concept in any other non-ambiguous way. They try to get

laround the problem by using the term fibrous in an ambiguous way by stating that hornblende is

"seldom seen in a fibrous form". Yet in page 3 of the paper they state that all amphiboles

, "fragment into fibers", whether they are products of an "acicular form of a fibrous crystal"

•(?) or not. They admit that at a microscopic scale the fragments of hornblende are no different from that of other amphiboles. Apparently, what they are trying to say is that

fibrous is not always fibrous, but the new terminology does not allow them to distinguish

between these two types. The proper mineralogical terminology can do that.

Most mineralogists object to the misuse of the mineralogical terminology. Some

iniineralogists , however, have found themselves in situations where compromise was necessary

and they used the new definition of fiber (>3: 1 aspect ratio) and the term "fibrous" in an .accordingly loose context [42,45,71], sometimes with comments on the disciplinary restric-

:tions of that terminology [11].^

I|i'lt is not entirely impossible that the minute acicular crystals of jade may turn out to

^possess some asbestos properties. In that case minute fragments of jade could approprijately be called asbestiform fibers.

'The authors of [11] accept the new definition of fiber "in the context of studies of

'health hazards".

3
The true background and character of mineralogical concepts and the seemingly complex

definition of the asbestos-related mineralogical terminology can be best illuminated through

a historical analysis of the relevant terms and expressions. That will be attempted in the

fol lowing pages.

Historical Review

Asbestos in history . Asbestos is probably the most unique substance in the mineral

kingdom. To begin with, it does not even look like a stone, but looks more like some organic

wool or cotton. Good quality asbestos is more elastic than other minerals and its high

tensile strength is unique. Asbestos is not only stronger than organic fibers but it is also more durable, is fireproof, and for all practical purposes, amphibole asbestos is chemically

inert.

The peculiar properties of asbestos have attracted the attention of man throughout

history. In early times the use of asbestos was restricted either to the households of

powerful and rich royalties or to special geographic areas. There are records that

Egyptians, Greeks, Romans and even earlier civilizations had knowledge of asbestos and used

it for special purposes. The Egyptians sometimes used coarse asbestos cloth to protect the

embalmed bodies of Pharaohs from the ravages of time. The Romans made cremation wrappings to

collect the unspoiled ashes of emperors. The lamps of the Vestal Virgins were furnished

asbestos wicks which lasted forever. There are also some questionable records that the

Romans threw asbestos and other toxic substances in the river flowing through the besieged

city of Auxium, in order to break the resistance of the defendants. According to legend,

Charlemagne had an asbestos tablecloth which he threw in the fireplace after dinner for the

purpose of cleansing it, to the amusement of his company (fig. 1).

Figure 1. De Boot's [6] illustration of the fire-proof

property and the making of asbestos cloth.

As it can be expected, in addition to the practical uses there were some less logical and more mysterious applications of asbestos in early and in superstitious civilizations. In medieval times, for example, asbestos was used as a major ingredient in an ointment (fig. 2)

intended to cure a number of diseases. Loosely translated De Boot's prescription reads:

"Multiple application, miraculous asbestos ointment for juvenile tinea

(head-fungus?) and shinbone (skin?) ulcer. Take 4 oz. asbestos, 12 oz. lead (oxide?), 2 oz. zinc oxide, and calcinate, thereupon pulverize into

glass while adding vinegar, and agitate it daily for a month; after a month boil it for a quarter hour and let it cure until it becomes clear;

thereafter add some vinegar, mix it with rose-petal oil until it becomes

a homogeneous ointment: then go and smear it over the infant's head, to

promote healing: for itches and shinbone ulcer smear it over the

4
affected area in the evening, for healing. The same mineral, mixed with

aqua vitae and bamboo syrup, when applied in small quantities in the

morning will sooth the pain of female white-menstruation ( 1 eukorrhea? )

,

and wi 1 1 soon heal .

jMiracii- Ex Amianto linimeiirum ad tineam puerorum,

lofumA- & ad ulcera tibiaru miraculofum fit fequenri movit,\nti jIq^ Accipiuntur Ainianti line, quatuor, plumbi

aptdis It- ^j^j J i tutizE unciae dux,ac calcinantur , deindc

nimentu. , . , pulverilataui vitro macerantur cum aceto,ac quotklie per men{em materia agitatur femclj-poft menfcm ebullienda eft unius liora: quadrante , ac quiefcerefiniturjdonccinclarefcat: dcindeillius accti

clari quantitas , cum pari quantitate olei rofacci,

mifcctur, donee bona fiat unio linimenti forma: eo

immqitur caput pucri totuni ut cito fmetur: ad fcabiem', & ulceia tibiarum vefperi partes ungnntur, MuUt. donee flmentur. Si lapis hie cum aqua vita:, & fae- charo folvatur,ae exigua portio mane quotidiemulicri albo mcnftruo laboranti detur,mox fanatur. ^{^^^*

Figure 2. De Boot's prescription for the miraculous

asbestos ointment [6, p. 384-5].

The industrial revolution opened an era yielding rich rewards for imaginative inventions. Asbestos, as other unique minerals, did not escape attention and a large number of

applications were discovered. Some of these were practical and were adopted, such as fireproof suits and other products (fig. 3). Some, on the other hand, were not well received by

the public, like the refillable asbestos cigarette paper introduced in England during the

1880' s [38].

Asbestos Ropc-ladilcr. Portable Anti-thermal and Anti-septic Hat. (Frederick Jones & Co.)

Figure 3. Illustration of some early asbestos products,

Jones [38].

5
Actually, industry was rather slow in adopting asbestos. Even after the discovery o1 the extensive and high-quality Canadian chrysotile deposits, asbestos-industrialists spent

more time promoting their product than manufacturing it,'^ at least for a few decades. After

the turn of the century they began to succeed and asbestos soon became one of the most widely

used industrial minerals.

Asbestos in mineralogy . Although there were several references to asbestos in tht; ancient literature, the first scientific-type descriptions were offered relatively late b\

Dioscorides [20] and Plinius [55]. Dioscorides called it ayiavToo amiantos (meanin;

immaculate, unpolluted) and Plinius added a comment that the Greeks used to call it ao^eoxoa

asbestos (meaning incombustible, unquenchable, inextinguishable). Plinius also used th(

Latin name of 1 i num vi vum for the same mineral as he believed it to be a plant from India; ; plant which grew in a part of the earth burned completely by the sun, thus became accustomec

to that environment and learned to survive in the flame of fire.

During the scientifically dormant Middle Ages the nomenclature of Dioscorides and

Plinius was neither challenged nor modified. Of the two names of asbestos, amiant appeared tdi be the more popular. J

Almost two centuries ahead of the era of the scientific revival, Agricola [1] offered iti 1546 the first criteria for mineral identification. According to Werner [66], Agricolcii

recognized several basic categories of mineral properties such as color, transparency^

(transl ucida) , resplendence (fulgor), luster (mitor), weight (gravitas), hardness

(durities), flexibility (f lexibi 1 itas) , cleavage (fissio), etc., and used descriptive terms

as: globular (figura globi), cyclindrical (figura cycl i ndrica) , conical (figura metae),

hair-like (figura capillorum), star-like (figura stellarum), etc. It is easy to recognize ir Agricola' s expressions the prototypes of some modern terms. Although he did not expand our knowledge of asbestos, he did introduce the descriptive term capi 1 1 ary (haarfdrmig, hairlike) which was adopted later for the description of the shape of asbestos fibers.

The next stage of development in mineralogy was during the 18th century when scientists

began the development of a mi neral ogical system divided into orders, classes and species or the basis of common and distinct external properties. These followed the natural hi stor^

concepts and criteria used in botany and zoology. The first and still relatively crude

classification was offered by Walerius [65] and by Cronstedt [15] and the first significant

improvement of Agricola' s list of external characters of minerals, and its application in mineral classification, was offered by Linneaus [47]. The term fibrous (fibrosum) appeared

in his list of descriptive terms for minerals composed of parallel fibers.

This period was closed by Werner who published the first comprehensive and consistent

system of mineralogfe' in 1774 [66]. He exerted unparalleled influence on the future

development of mineralogy.* His influence extended from the wide-spread acceptance of his

system of mi neral ogy to the establishment of mining schools in many countries and to the

practice of naming new minerals after personal names.

In his classification system, capil lary is to be used for the description of asbestos

fibers and fibrous is used to describe the breakage of bundles of fibers into small fibers.^

He constructed a complete system of minerals of about 300 species. Although never published,

it was spread by his students and fellow mineralogists [34,26], and was. adopted all over the

'Jones' book [38] may have been inspired by similar interests. He writes [38, p. VI]

that "he hopes by this means (writing the book) to ... tend to develop the uses of"

asbestos.

*!f?nc!n^''^H "^T "'"y^^Q^^Q^V determinative mineralogy, after the Greek opvtoa (fossil) and yvwoia (to know).

^Note that there is very little difference between saying that (1) fibrous crystals grow

in bundles of fibers (as we would say it today) and (2) a bundle of fibers breaks down

to fibrous crystals. However, the use of fibrous as a description of breakage was soon changed to a description of texture or habit by Blum [5, p. 30], Thomson [61, p. 256],

Phillips [54, p. XXXVI and LXXII], etc.

6
civilized world, even before his death in 1817. In his system he recognized one asbestos

species, with four subspecies, and two other [26] subspecies, asbestartiger or asbestarticher , one of actinolite and one of tremolite.^^ Werner recognized a number of

other fibrous, but not "asbestartiger" mineral varieties. He called those strahl iger or fasriger . Jameson [36,37] translated Werner's terminology into English as asbestous , prismatic , and fibrous , respectively for asbestartiger, strahl iger, and fasriger. The

comparison of the appropriate portion of Werner's and Jameson's classification are given in

Table 1.

Table 1. Comparison of Warner's and Jameson's classification of asbestos and some fibrous minerals.

Werner, after Freiesleben [26]

ERSTE KLASSE: ERDLICHE FOSSILIEN

3 . Kiesel Geschlecht

Spischaft des Pistazits

52. Anthophyllite

a. strahl icher

Sipschaft des Zeoliths

75. Prehnit

a. fasricher

77. Zeolith

b. Faser — Zeol ith

5. Talk Geschlecht

Si pchaft des Tal ks

137. Asbest

a. Bergkork

b. Amianth

c. gemeiner Asbest

d. Bergholz

Sipschaft des Strahlsteins

138. Strahlstein

a. asbestarticher

b. gemeiner

c. glasicher

d. korn icher

141. Tremolit

a. asbestarticher

b. gemeiner

c. glasicher

Jameson [36]

CLASS II.

ORDER VI. SPAR

Genus I . Schi 1 1 er Spar

5. Prismatic Schiller Spar

or Anthophyll ite

Genus IV. Prehnite

1. Axotomous Prehnite

2d Subsp. Fibrous

Genus IV. Zeolite

7. Prismatic Zeolite

1st Subsp. Fibrous

Genus VIII. Augite

2. Hemi pri smatic Augite

4th Subsp. Actynolite

1st Kind Asbestous

2d -- Common

3d -- Glassy

5th Subsp. Tremolite

1st Kind Asbestous

2d -- Common

3d -- Glassy

6th Subsp. Asbestus

1st Kind Rock-Cord

2d -- Flexible Asbestus

3d — Common Asbestus

4th -- Rock-Wood

The actual names of classification units vary from author to author. In order to avoid

the lengthy comparison of the expressions used by different authors only "species",

"subspecies", or "varieties" are used in the text (instead of "subspecies" and "kinds''

of Jameson, for example).

^^Phillips and Allen [54, p. LXXII] used asbestiform as well as a special term fasciculated

for minerals composed of fibers or acicular crystals occurring in bundles.

7
Jameson's asbestous was soon changed to asbestiform in English mineralogy textbooks:

Thomson in 1836 [61, II., p. 22], Phillips and Allan in 1838 [54, p. 58] and Dana^^ 1857

[17, p. 153].

Haiiy [30] also adopted Werner's basic system and terminology, and translated most of

his German terms into French, although he practiced more flexibility than Jameson did as he

introduced a more chemical classification scheme. However, he makes no apparent distinction

between asbestos and other fibrous varieties and uses the term f i breux for all. He translated Werner's asbestartiger Strahlstein and Tremolit as Actinote fibreux and Grammatite

fibreuse,^^ fasriger Prehnite as Prehnite fibreuse, and straliger Antophyllit as anthophyllite aciculaire. Although he does not distinguish between asbestos and other fibrous

crystals, he seem to restrict the use of fasci cl

, and to a lesser degree fibre , to asbestos

fibers. The term f i 1 amenteux was introduced into the French mineralogical literature by

Brard [7], asbestoid by Beudant [4, p. 389] and asbesti forme by Cloizeaux [13, I, p. 80]

as equivalent expressions for the German asbestartig and the English asbestiform.

It should be noted that all these early mineralogists, including Werner and his

followers, used the term fibrous in a general sense and considered asbesti form (asbestous,

asbestartig, feinfaserig, asbestoid) as a special class of fibrosity. Although none of

them have defined the uniqueness of asbestiform fibrosity, the reason for that distinction

was implied in their recognition of the unique properties and appearance of asbestos,

including the unusual strength of asbestos fibers. Hoffmann (and Breithaupt) [33, lib,

p. 307], for example, pointed out that the asbestiform variety of tremolite is less

brittle, that is, stronger than the common prismatic or acicular variety.

Figure 4. Handcolored illustrations of Schilletnder Asbest (Amianth) and gemeiner

(common) Tremolit in Schmidt's Mineral ienbuch [60].

i2At the bottom of this page Dana gives some exercise questions like: What is the crystallization of hornblende? Mention the characters of the varieties of actinolite - (i.e.,

glassy, radiated, asbestiform, massive).

^^Occasionally, however, he used the German word "asbestartiger" in the French text without

translation.

8
Werner's historical system of mineralogy was used without fundamental modifications for

\/er a century, especially in popularized mineralogy books like that of Schmidt's [60].

srner's strong influence on mineralogy resisted, for some times, the acceptance of the

roposals of a new breed of mineralogists who advocated to change the system of mineralogy

rom the "natural history" type to a more chemical one. Mineralogists like Thomson [61],

sudant [4], Berzelius [57], Rammelsberg [56], and others believed that the chemical

roperties of minerals are much more important than their external and physical properties,

homson was a strong opponent of the classification of minerals on the principles of natural

istory. He was especially critical of Mohs [49] who carried the natural history approach to

jch an extreme that it almost became free of chemistry. Thomson came out to say [61, p. 8]:

"It appears to me, that mineralogy is so closely connected with

chemistry , and so dependent on it for its specific distinctions that it

would be highly injurous to it, and therefore, very unwise to attempt to

deprive it of so important an ally."

In line with the emphasis on chemistry came a new classification and the redefinition of

neral species. All those former species which had no distinct chemical composition were

iscredited. This included the degradation of Werner's one asbestos species to the rank of

iriety. Of course, asbestiform actinolite and tremol ite were already considered variations

)r subspecies) by Werner himself. Asbestos and its subspecies became classified, on the

isis of relatively poor and inconsistent chemical analysis, as variations of amphiboles,

)idote, pyroxenes, talc, and tourmaline by Beudant [4, p. 837], for example. Rammelsberg

(pressed this philosophy of the reclassification of the former asbestos species^^ [56, Part

; , p. 31 3] as:

"Mineral substances described by the name of asbestos (or amiant) do not

appear to constitute an independent species. As their chemical compositions indicate, and it may be more appropriate as noted by Breithaupt,

that the name asbestos represents a condition which can be obtained by

several, thoroughly different kinds of minerals." (emphasis by author)

Berzelius, the Swedish chemist-mineralogist (also the major promoter of the "blowpipe

lalysis" which became one of the major mi neral ogical techniques for more than a century ), was

ie of the most ardent pioneer advocates of this "scientific" system of mineralogy. In his

546 publication [54, p. 213-214] Berzelius states that mineral species as previously defined

)n't exist. He proposed that instead of species, minerals shoul.d be identified and

lassified on the basis of:

"ingredients and different chemical proportions .. .as well as their definite

bonding relationships." (Verbindungsverhal tnisse = ? = crystal structure.)

The transfer of mineralogy from Natural History to Chemistry did not take place as 'oposed by Berzelius and his compeers. Instead, mineralogy developed gradually in that

rection and assumed a unique position among the sciences, a status of transition between

itural history and physical sciences. The concept of species was not fully abandoned

ther. In fact, with the meaning redefined in a chemical context, "mineral species" is still

ed today by some mineralogists, like Berry and Mason [3, p. 272-274]. The classification

' minerals was also changed during the second half of the 19th century from categories of

:ommon external properties" to groups of chemical units. Mineral species or individual

nerals were defined by their chemical composition and crystal structure. Of course,

'ystal structures were not known at that time. Consequently, they had to be substituted for

' the observable consequences of the crystal structure: the crystallography and physicallemical properties of minerals. That is, if two minerals had the same composition but had

fferent crystallography and physical properties they were considered to be two distinct

nerals. That criterion was readily applicable to minerals which occurred in good crystal

)rms. However, the same could not be used for asbestos where there was not crystal 1 ographic

In the same book Rammelsberg recognized Krokydolite (crocidol ite) , named by Hausmann in

1831, as an independent species. That may, at first, look like a contradiction in his

philosophy. However, it is not, as crocidol ite' s parent mineral riebeckite was only

discovered many years later, in 1888, by Sauer.

9
data and the only non-chemical information available was the difference in the tensili

strength and flexibility of the asbestiform versus the compositional ly equivalent non' asbestiform mineral. That difference was considered by many mineralogists to be sufficient!;

distinct to warrant the recognition of some asbestiform varieties as independent minerals

Several dozen asbestos minerals were proposed and accepted during this stage of evolution.

The chemical compositions of most of these asbestos minerals were known and thei

chemical identity with other minerals were recognized. The compositional equivalence o chrysotile and serpentine was realized since Kenngott's publication [40] in 1853. That wa sufficient for some mineralogists to declare chrysotile as a variety of serpentine. Others

however, still considered the differences in physical properties sufficiently significant ti recognize chrysotile (under various names, like: metaxite, schweizerite, etc.) ani serpentine as two distinct minerals. The other two major asbestos minerals, byssolite ani crocidolite, were known to match amphibole compositions, byssolite since Scheerer's 185

analysis [59] and crocidolite since Delasse's 1847 analysis [19]. Crocidolite was firs

believed to be an asbestiform variety of arfvedsonite [50, p. 461] in spite of minor chemica

differences. However, as soon as riebeckite was discovered by Sauer in 1888, crocidolite wa reclassified by Naumann (and Zirkel) [51, p. 707], as its asbestiform (Asbestform in German

variety.

As a consequence of the undecisive significance of differences in physical propertie

versus compositional identities, the classification of asbestos minerals as independen

minerals or as varieties was a function of the individual interpretation of mineralogists

For example, Hintze [31], Groth [29], and Naumann (and Zirkel) [51] recognized chrysotile a a variety of serpentine and crocidolite as a variety of riebeckite; E. S. Dana [16] classifiei

both as independent species; Klockmann [41] and Rogers [58] recognized chrysotile as a independent mineral and crocidolite as a variety of riebeckite.

The asbestos nomenclature was further complicated during the last decades of the 19t

and first decades of the 20th century when asbestos became a major industrial material. Th

industrially useful properties of asbestos obtained from certain deposits differed somewha

from that of others, and on the basis of that some asbestos were given distinct mineral names usually reflecting the name of a mining company or district (for example, bostonite : Bosto

Asbestos Packing Co.; amosite : Asbestos Mines of South Africa; montasite : Montana mine

South Africa; prieskaite : Westerburg mine, Prieska, South Africa). The use of thes

distinct mineral names, of course, provided some promotional advantages. The majority o these commercial mineral names never got into mineralogy text books, and those few which di were subsequently eliminated or discredited. Amosite, for example, was formally discredite

in 1946 [2].

The discovery of x-ray diffraction produced a tool available for crystal structur

determination. As the basic crystal structures of the former asbestos minerals were prove

to be identical with that of compositional ly equivalent major minerals they were al

degrade

to the rank of varieties, without further arguments. For example, the final decision o crocidol ite' s mineralogical identity with riebeckite was provided by Whittaker in 1949 [67

and by Drysdall and Newton in 1960 [22]. The asbestos varieties of minerals were consequent!,

identified by the prefix of fibrous or asbestos-1 i ke [24, p. 578] or asbestiform (see Table

for details). Fibrous^^ was used as a more general term to include both asbestiform and non asbestiform fibrous minerals. However, asbestiform was always restricted to asbesto

varieties, as that was done consistently since Werner's time, 200 years ago.

i^These asbestos mineral names included: Adigenite, agalite, antholite, baltimorite;

beaconite, cyclopeite, dermatite, fibrolite, griquanlandite, hydrophite, ishkyldite,

karachaite, kolskite, kymantine, metaxite, nemalite, picrolite, retinalite, rezhikite.

rhoduzite, schweizerite, vorhausite, williamsite, zermattite, zillerite, xylotite, etc.

^^Ford [24, p. 204] gave a more liberal definition of fibrous than usual. He states thai

"fibres may or may not be separable" in a fibrous mineral.

10
Table 2. Descriptive term| used by mineralogists to distinguish between asbestos and other

types of fibrous textures.

(Frequently in conjunction with fibrous.)

Page number of an example is given.

Werner (Friesleben) asbestartich Naumann [50, p. 324] asbestartig

[66, p. 10]

Naumann (Zirkel) Asbestform

Hauy [30] no distinction [51, p. 707]

Hoffmann (Breithaupt) asbestartig Nicol [52, p. 152] asbesti form

Loo, CD, p. 3ub J

Jameson [36, II, p. 22]

Tschermak [62, p. 444] ? feinfaserig

asbestous

Phillips (Allan)

Groth [29, p. 151] asbestartig

asbesti form

[54, p. 58] E. S. Dana [16, p. 384 asbesti form

ilnomson [bl, 1, p. 48IJ asbesti form Hintze [31 , II , p. 1 195] ? feinfaserig

nA /A n / U i n y~i ^ w% 1 Mons vndiui nger ) asbestous Klockmann [41, p. 567] ? feinfaserig

[49, II, 27]

Beudant [4, p. 387] asbestoide

Doelter [21 , II , p. 589] asbestarti a

Rogers [58] no distinction

Brard [7, p. 206] f 1 1 amenteux

Ford [24, p. 578] asbestos-1 i ke

Blum [5, p. 242] ? feinfaserig

Hurlbut [35, p. 446] asbesti form

Rammel <;hprrf fifi n '^'iftl Kraus, Hunt, Ramsdel

asbesti form

Schmidt [60, p. 358] asbestartig [43, p. 392]

Bristow [9, p. 85] asbesti form Berry, Mason asbestiform

Cloizeaux [13, p. 81]

[3, p. 527]

asbesti forme

Deer, Howie, Zussman asbesti form

J. D. Dana [17, p. 153] asbesti form [18, II, p. 243]

^ French: fibreux; German: faserig.

The term f i ber , in reference to asbestiform fibers, was equivalent to the concept of

organic fibers because the early natural historians believed that asbestos was actually a vegetable. Mineralogists from the 18th century on did not specifically state that the term

fiber is used because of its resemblance with organic fiber. However, that reasoning is

apparent in their description of asbestos fibers as hai r- 1 i ke or capi 1 1 ary or thread- 1 ike , and in the types of names they have given to asbestos minerals, such as mineral-wood, rockcotton, mountain cork, rock-wood. Jones [38] provided extensive details in the description

of the similarity between asbestos and organic fibers (fig. 5) and concluded [38, p. 221]

that:

"The nature of the asbestos fibre is thus so far identical in structures

with the organic fibres."

11
I

No. 1.—Thctford Ore. No. 2.—Ttctford Ore.

Figure 5. Jones' [38] comparison of asbestos and organic fibers.

Although the use of the term fiber has not been restricted to asbestos and included a number of other minerals they all had some characteristics reminiscent of organic fibers. Ir> any case, the term fiber has never been used as a description of the elongated shape of

crystals. For that acicular is the proper mineralogical expression.

The term asbestos was first a species name, as noted earlier it was introduced by Werner

and his school. Later it became a collective term, like cl ays or gems , in reference to

asbestiform varieties of a number of otherwise unrelated minerals. Parallel with the

mineralogical terminology asbestos also became an industrial term for a category of mineral

products containing asbestiform varieties of silicates. However, some commercial asbestos

may be mixed with non-asbesti form acicular crystals or cleavage fragments. The quality of!

asbestos is related to: (a) the extent of the development of the preferred asbestos character

(high tensile strength, flexibility, length of fibers) of the asbestiform fibers, and (b) the

percentage of the less desirable non-asbesti form , acicular crystals or cleavage fragments

present in the product. That is, the mineralogical and industrial definitions of asbestos

are not fully coincident.

The unusual properties of the asbestiform fibers were always recognized by the early users of asbestos as well as by mineralogists. These properties included high tensile

strength [for example, 32,33,38,64], increased flexibility (noticed by all mineralogists),

unexpected optical properties [for example, 53,69] and differences in surface properties,

like surface charges [for example, 28,42,45,72].

12
With the introduction of high-power electron microscopy, a new tool for mineralogical

research and a new area of applied mineralogy was established. Electron microscopes

permitted the examination of extremely small mineral particles and the study of the fiber

of fibril structures of various asbestiform crystals. The long suspected cylindrical

(tubular, scroll-like) structure of the chrysotile fibrils [68] was directly observed by

Maser et al. in 1960 [48] and a more detailed record was offered by Yada [70]. In addition

to the cylindrical fibril structure, Cressey and Zussman [14] reported on a polygonal

chrysotile structure which appears to be the dominating fibril structure in the so called

"schweizerite" and "Provlen-type" chrysotile varieties. Comparable work, although with

less spectacular results, was done on asbestiform amphiboles by several investigators, for

example, Chisholm [12], Franco, Hutchinson, Jefferson, and Thomas [25]. The asbestiform

amphibole fibril structure appears to be more subtle than that of chrysotile. The increased

tensile strength and flexibility may be due to the presence of systematic defects such as faults, dislocations and twinning, and/or to the lack of surface defects. Of course, we

know that defects can interfere with the cleavage and fracture of solids and are frequently

introduced artifically in alloys and other crystals to enhance their strength as it is

elaborated on in the textbook of Kelly and Nicholson [39]. Undoubtedly, time and extensive

research will be needed before the structural causes of the unusual properties of asbestiform amphiboles will be fully explained.

Concl usions

Several conclusions can be drawn from this review of the history of asbestos-related

mineralogical terminology and its current misuse in environmental sciences:

(1) Terms such as fiber, fibrous, asbestiform, and asbestos, have distinct

meanings in mineralogy whether or not we can offer a complete crystal

structural explanation for the development of the properties, reflected

by these terms.

(2) The asbestos-related mineralogical terminology is adequate and clear,

and is not in need of revision. However, its full understanding requires

a relatively comprehensive knowledge of mineralogy. Consequently, a set

of detailed and unambiguous definitions should be prepared for interdiscipl i nary use.

(3) The asbestos-related mineralogical terms have been grossly

misinterpreted in most of the recent literature of environmental

sciences. The implied definitions are inadequate for the description and

discussion of the crystal chemical and crystal physical properties of

minerals, and endanger the success of coordinated, interdisciplinary

studies aimed at the understanding and the solution of the health hazards

created by asbestos pollution.

The presence of any foreign particle in ai r and waters i n excessi ve quantities i

undesirable and i s potential ly harmful . It is imperative that all efforts be made to clean up

the environment starting with one of the most dangerous mineral pollutants: asbestos. This

job requires extensive interdisciplinary cooperation and the establishment of an unambiguous

interdi scipl i nary 1 anguage .

The extensive list of definitions offered in the recent U.S. Bureau of Mines Information

Circular [10] are comprehensive and consistent with mineralogical traditions. The adoptation

of these definitions for the interdisciplinary language of asbestos studies should be

considered.

The following definitions of the four most critical asbestos-related mineralogical terms

are based on their historical review.

13
FIBER

FIBROUS

ASBESTIFORM

An aci cul ar si ngl e crystal , or a simi 1 arly el ongated polycrystal 1 i ne aggregate , whi ch di spl ays some resembi ance to orgam" c f i bers . m

Examples for criteria of "resemblance to organic fibers" are: circular cross section, flexibility, silky surface luster, axial lineation, threaded

appearance, etc. Most of these fiber characteristics cannot be observed at

electron-microscopic scale. Consequently, any elongated particle may be

called a fiber (when fiber used as a shape-descripti ve expression ) provided

that it displays parallel edges and apparently equidimensional cross section.

That is, elongated triangular-shaped or irregular particles cannot be

considered to have the shape of a fiber.

The descriptive term used for a mi neral whi ch i s composed of paral lei , radi ati ng or i nterl aced aggregates of fibers , from whi ch the fibers are usual ly separabl

.

That is, the crystalline aggregate may be referred to as fibrous even if it is

not composed of separable fibers, but has that distinct appearance.

A special type of fibrous habit in which the f i bers are separable, and are more flexible and possess higher tensi 1 e strength than crystal s i n other

habits of the same mineral.

Increased flexibility and higher tensile strength are, apparently, the most

distinct qualities of asbestiform fibers. These properties are undoubtedly

due to certain structural variations and can justifiably be included in the

def i ni ti on.

ASBESTOS A col lective mineralogical term whi ch i ncl udes the asbesti form varieties

of vari ous (si 1 icate) mineral s . TTTTS"

The justification for restricting asbestos to silicate minerals may be

questionable from the mineralogical point of view, as non-silicate minerals

may also crystallize in fibrous habit and the fibers may possess asbestiform

properties. However, these properties are expected to be different in

magnitude from those of the asbestiform silicates and, therefore, from the

health study's point of view, are justifiably excluded from the category of

asbestos.

'^'^The development of fibrous habits must be due to certain unusual conditions which existed

at the time of the mineral's crystallization. These conditions may be accompanied by

structural modifications and by consequent changes in the mineral's physical properties.

These changes, however, are usually not as conspicuous as they are in silicate asbestiform fibers. In fibrous gypsum, for example, the only readily observable change is in

the mineral's fracture pattern. The usually absent ((111)) cleavage plane is perfect in

fibrous gypsum and is responsible for its acicular rather than platy fragments. This

change in the cleavage pattern is probably due to some structural modification. On the

other hand, the conditions of crystallizations may be such that no change in the

mineral's structure and properties is necessary. For example, if a fibrous mineral is

altered to another, the new mineral may show pseudomorphic fibrous appearance. Dana

[16, p. 678] believes that the appearance of fibrous talc is due to its alteration from

enstatite.

^^The industrial quality of asbestos depends, in part, on the degree of development of the

asbestiform fiber structure in the mineral. That is, if more crystals have the scrolllike structure in chrysotile, or the crystals have higher density of defects or twinning

in asbestiform amphiboles or have fewer surface defects, the asbestiform fibers are stronger and more flexible, and thus they are more desirable. A similar relationship

may exist between the degree of development and the density of asbestiform fibers in the

bundles, and their biological activity. That is, the gradation of asbestiform development

in a mineral, from acicular cleavage fragments to asbestiform fibers, may constitute different health hazards.

14
The critical reviews offered by Drs. Edwin Roedder and James H. Stout are acknowledged

with appreciation. This study was in part supported by a grant from the Regional Coppernickel Study, Environmental Quality Council, Minnesota.

References

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[2] Amosite discredited, Am. Mineral . 34, 339 (1946).

[3] Berry, L. G. and Mason, Brian, Mineralogy , (Freeman and Co. , San Francisco, 1959).

[4] Beudant, F. S. , Traite Elementaire de Mineralogie , (Verdiere, Paris, 1824).

[5] Blum, J. R. , Lehrbuch der Oryktognosie , (G. Schweizerbart, Stuttgart, 1833).

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[8] Bradt, R. C. , Newnham, R. E. , and Biggers, J. V. , The toughness of jade, Am. Mineral . 58,

727-732 (1973).

[9] Bristow, H. W. , Glossary of Mineralogy , (Longman et al .

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Superior: Discussion, Canad . Mi neral , 14 , 394 (1976).

[12] Chisholm, J. E. , Planar defects in fibrous amphiboles, J. Material Sci . 8, 475-483

(1973).

[13] Cloizeaux, A., des Manuel de Mineralogie , 2 vols., (Dunond, Paris. 1862).

[14] Cressey, B. A. and Zussman, J. , Electron microscopic studies of serpenti nites , Canad . Mineral . 14, 307-313 (1976).

[15] Cronstedt, A. F. , Forsokti 1 1 en Mineralogie , el ler Mi neral Ri kets Uppstalning , (Stockholm, 1758).

[16] Dana, Edward S. , The System of Mineralogy of James Dwight Dana, Descriptive

Mineralogy , 6th ed. , (J. Wiley and Sons, New York, 1914).

[17] Dana, James D. , Manual of Mineralogy , (Henry H. Peck, New Haven, 1857, new ed. (1871).

[18] Deer, W. A., Howie, R. A., and Zussman, J., Rock-Forming Minerals , 5 vols., (J. Wiley

and Sons, 1962, 1963).

[19] Delasse, A., (analysis of crocidolite) Compt . Rend. 44, 766 (1847).

[20] Dioscorides, P. , nep^ vXnS ^axp^KnS (Materia Medica) , (Approx. 50 A. D.).

[21] Doelter, C. , Handbuch des Mi neral chemie , 3 vols., (T. Steinkopff, Dresden and Leipzig,

1912, 1914, 1918).

[22] Drysdall, A. R. and Newton, A. R. , Blue asbestos from Northern Rhodesia and its

bearing on the genesis and classification of this type of asbestos. Am. Mineral. 45,

53-59 (1960).

15
[23] Engleston, T. , A Catal ogue of Mi neral s and Synonyms , (J. Wiley and Sons, New York,

1892).

[24] Ford, W. E. , Dana' s Textbook of Mineralogy , 4th ed. , (J. Wiley and Sons, New York,

1951).

[25] Franco, M. A., Hutchinson, J. L. , Jefferson, D. A., and Thomas, J. R. , Structural

imperfection and morphology of crocidolite (blue asbestos). Nature 266, 520-521

(1977).

[26] Freiesleben, J. C. , A. G. Werner' s Letztes Mi neral -System , (Craz and Ceroid, Freyberg

and Wien, 1817).

[27] Gary, M. , McAfee, R. , Jr., and Wolf, C. L. , (editors), Glossary of Geology , (Am.

Geol. Inst., Washington, D. C. , 1972).

[28] Great Lakes Research Advisory Board, Asbestos i n the Great Lakes Basi

, (February,

1975).

[29] Groth, P., Tabel 1 ari sche Ubersicht des Mi neral ien , 4te Auf 1 . , (Friedrich Vieweg und

Sohn, Braunschweig, 1898).

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1822).

[31] Hintze, C. , Handbuch der Mineralogy , Bd. 2, (Von Veit, Leipzig, 1897).

[32] Hodgson, A. A., Fibrous si 1 icates , Lect. Ser. 1965 No. 4, (The Royal Inst, of Chem. , 1966).

[33] Hoffmann, C. A. S. , Handbuch der Mi neral (5gie , (after Bd. 2a by A. Breithaupt), 4 vols.

,

(Craz and Ceroid, Freyberg, 1811-1818).

[34] Hoffmann, C. A. S. , (about Werner ' s Mineral System), 17th ed. , Bergm . J. 1, 369 (1789).

[35] Hurlbut, C. S. , Jr. , Dana' s Manual of Mineralogy , (J. Wiley and Sons, New York, 1959).

[36] Jameson, Robert, System of Mineralogy , (Archibald Constable, Edinburgh, 1816).

[37] Jameson, Robert, Manual of Mineralogy , (Archibald Constable, Edinburgh, 1821).

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[40] Kenngott, Adolf, Das Mohs'sche Mineral System , (C. Ceroid, Wein, 1853).

[41] Klockmann, P., Lehrbuch der Mineralogie , (F. Enke, Stuttgart, 1903).

[42] Kramer, J. R. , Fibrous cummingtonite in Lake Superior, Canad . Mi neral . 14 , 91-98 (1976).

[43] Kraus, E. D. , Hunt, W. F. , and Ramsdell , L. S. , Mineralogy , (McGraw-Hill, New York,

1959).

[44] Kryvial, R. J., Wood, R. A., and Barrett, R. E. , Identification and assessment of

asbestos emissions from incidental sources of asbestos , (U.S. Env. Prot. Agency,

EPA 650/2-74-087, Washington, Sept. 1974^^

[45] Langer, A. M. , Approaches and constraints to identification and quantitation of

asbestos fibers, env. Health Presp . 9, 133-136 (1974).

16
[45] Light, W. G. and Wei, E. T. , Surface charge and asbestos toxicity, Nature 265 , 537-

539 (1977).

[47] Linneaus, C. A. , Systema Naturae , (Holm, 1768).

[48] Maser, M. , Rice, R. V., and Klug, H. P., Chrysotile morphology. Am. Mineral . 45,

680-688 (1960).

[49] Mohs, Frederich, Griindriss der Mineralogie , 2 vols., (Dresden, 1822). English:

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1825).

[50] Naumann, Carl F. , Elemente der Mineralogie , 8te Auf 1

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[51] Naumann, Carl F. , Elemente der Mineralogie , 13te Auf 1 . by Ferdinand Zirkel,

(W. Engelmann, 1898).

[52] Nicol, James, Elements of Mineralogy , (A. and C. Black, Edinburgh, 1873).

[53] Peacock, M. A. , The nature and origin of the amphibole asbestos of South Africa, Am . Mineral . 13, 241-285 (1928).

[54] Phillips, William, An Elementary Introduction to Mineralogy (1823), 4th ed. by

R. Allan, (Longman, et al . , London, 1837).

[55] PI inius Secundus , C. , Hi storia Natural is , 27 books (77 A. D.

)

[56] Rammelsberg, C. F. , Worterbuch des Chemischen Thei 1 s der Mineralogie , (C. G. Luderitz,

Berlin, 1841).

[57] Rammelsberg, C. F. , J. J. Berzel i us ' Neues Chemi sches Mi neral System (J. L. Schrag,

Nurnberg, 1847).

[58] Rogers, A. F. , Introduction to the Study of Minerals , (McGraw-Hi 1 1

, New York 1937).

[59] Scheerer, Th. , (analysis of byssolite) Pogg . Ann. 84, 389 (1851).

[60] Schmidt, F. A., Mi neral ienbuch , (Krais and Hoffman, Stuttgart, 1855).

[61] Thomson, Thomas, Outl ine of Mineralogy , Geology , and Mineral Analysis , 2 vols.,

(Baldwin and Cradock, London, 1836).

[62] Tschermak, Gustav, Lehrbuch der Mineralogie , (Alfred Holder, Wein, 1884).

[63] U.S. District Court, District of Minnesota, 5th Division, Supplemental Memorandum , (No. 5-72, Civil 19, Appendix 5, Judge Miles Lord, May 11, 1974).

[64] Vermaas, F. H. S. , The amphibole asbestos of South Africa, Trans . Proc . Geo]. Soc.

South Africa 55, 199-229(1952).

[65] Walerius,!. A., Mi neral -riket , (Holm, 1847).

[66] Werner, A. F. , Ausserl ichen Kennzeichen des Fossilien , (Leipzig, 1774), English: On

the external character of minerals , Transl . A. V. Carozzi (U of 111 . , Press, 1962).

[67] Whittaker, E. J. W. , The structure of Bolivian crocidolite, Acta Crystalloqr. 2, 312-

317 (1949).

^ -

[68] Whittaker, E. J. W. , The structure of chrysotile, Acta Crystal logr , 6, 747 (1953).

.69] Wylie, A., Optical properties of asbestiform amphiboles and their non-asbestiform

analogues, U. S. Bureau of Mines , I. R. (in press).

17
[70] Yada, Keiji, Study of chrysotile asbestos by a high resolution electron microscope

Acta Crystal logr . 23, 704-707 (1967).

[71] Zoltai, T. and Stout, J. H. , Comments on asbesti form and fibrous mineral f ragmenti

(Minn. Poll. Contr. Agency, 1935 W. Co. RoadB-2, Roseville, MN 55113, 1976). ^

[72] Zoltai, T. , Veres, I., Wagner, M. J., and Hammer, R. F. , Surface charges o: asbestiform amphibole fibers, (in manuscript).

J

Discussion

i

M. COSSETTE: Could you tell me if the use of the word asbestoid implies that it is no) quite asbestos?

T. ZOLTAI: Brard and Beudant used it in lieu of asbestartich or asbestiform, that isi the expression is equivalent to asbestiform.

A. BOHMER: Are you suggesting that if a mineral has an asbestiform habit in iti varieties and it has a three-to-one ratio it is asbestos? That is, should we limit qui

classification of asbestiform to those minerals? '

ZOLTAI: Yes.

i

18
'National Bureau of Standards Special Publication 506. Proceedings of the Workshop on

Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued riovember 1978)

FIBROUS AND ASBESTIFORM MINERALS

James R. Kramer

Department of Geology

McMaster University

Hamilton, Ontario L8S 4M1

Canada

Abstract

Asbestiform minerals may be differentiated from other elongate

minerals by comparing their length and aspect ratio distributions in the

greatest percentile level. Individual fiber analyses of UICC and other

well-characterized samples suggest a possible 20-40 percent intensity

ratio variation relative to Si of major cations. There is a very small

amount of evidence to suggest that fibers other than asbestos are toxic.

Key words: Acicular; asbestiform; asbestos; elemental composition;

fibers.

Introduction

The ability to differentiate between acicular minerals, fibrous minerals, and asbestiform minerals is most significant to the work of analysts, health researchers, and

mineralogists. Zoltai [21, p. 13-31]^ defines the terms carefully, discusses the history of

the relevant terms, and shows how the discrepancies in the use of the terms found today has

evolved. In short, the differentiation of the terms asbestos, asbestiform, fiber, fibrous,

and acicular has been obscured in many cases and in different applications. One reason for a large part of the overlap of the usage of the terms is the difficulty in separation of one

term from another on an analytical basis at the scale of the transmission electron

.nicroscope. When enumerating elongate particles at the micrometer scale, in many cases a cleavage fragment can appear similar to a fiber or an asbestiform mineral. Thus the advent of

the transmission electron microscope to identify and enumerate particles on an environmental

monitoring basis has brought certain ambiguities.

The Glossary of Geology [1] defines some of the pertinent terms as follows:

"ASBESTOS: (a) a commercial term applied to a group of highly fibrous silicate minerals

that readily separate into long, thin, strong fibers of sufficient flexibility to be woven,

are heat resistant and chemically inert, and possess a high electric insulation, and

therefore are suitable for uses (as in yarn, cloth, paper, paint, brake linings, tiles,

insulation cement, fillers, and filters), where incombustible, nonconducting, or chemically

resistant material is required, (b) a mineral of the asbestos group, principally chrysotile

(best adapted for spinning) and certain fibrous varieties of amphibole (ex. tremolite,

actinolite and crocidol ite). (c) a term strictly applied to the fibrous variety of

actinolite. syn: asbestus, amianthus, earth flax, mountain flax.

ASBESTIFORM: said of a mineral that is fibrous, i.e. , that is like asbestos.

ACICULAR: (cryst) said of a crystal that is needlelike in form. cf. fascicular,

sagenitic.

^Figures in brackets indicate the literature references at the end of this paper.

19
FIBROUS: said of the habit of a mineral, and of the mineral itself (e.g. asbestos), the

crystallizes in elongated, needlelike grains or fibers."

The more restrictive definition of asbestos (c) is not presently used. Thus asbestifori,

is a restricted usage of fibrous pertaining to asbestos. In the general field of mineralogy

asbestiform has not been a commonly used term.

Taken as a whole, one can easily imagine that overlap at an analytical level among tt"

definitions of acicular, asbestiform, and fibrous definitions could occur. In a bulk sample

the distribution (bundle, fibrils, splitting), fiber length, and concentration of fiber

would be used to distinguish between asbestiform and fibrous in most cases. Acicular would t distinguished from fibrous and asbestiform in that the properties of a fiber (flexibility

bundles, splitting) are not present. When minerals are dispersed, occur separately and ar examined at the micrometer scale, the distinguishing characteristics for these terir

disappear or are highly obscured. At this microscopic level, it is most difficult t distinguish among cleavage fragments, acicular minerals, and fibers. In no cases, however

are cleavage fragments considered to fall into the definitions of asbestiform, fibrous, c acicular.

In another discussion of asbestiform [20, p. 19], it is considered "a type of minera

fibrosity in which the fibers and fibrils possess high tensile strength and flexibility.

Spiel and Leineweber [18] point out that all asbestos minerals have overlapping tensil

strengths; and methods of measurement are difficult "with large variations in results usin

the same and different techniques." Furthermore, there are virtually no tensile strengt

data on other fibers and cleavage fragments. Flexibility is related to the "harshness" o flexural modulus of fibers [18]. It is not clear what differences exist between asbestifor

fibers and cleavage fragments of amphiboles. There is found considerable variation in th

flexural modulus of chrysotile which may be due to the water content, mineral impurities, o orthorhombic and monoclinic crystal forms in the fibers.

Another approach to obtain a working definition and differentiation of asbestos fiber

and other elongate (length/width > 3) mineral fragments is to consider the definitions i terms of their health significance. Length and aspect ratios within certain defined limit

have been proposed as the only important mineral parameters to be considered in respirator

disease. If one accepts this argument with no additional caveats, one could easily extend th

length factor considerations to any elongate particle provided that the length an length/width criteria are met. This argument would then demote the analytica

differentiation of the terms to a mineralogical wrangle; furthermore, there would be littl

necessity to distinguish among the various minerals in most cases. Following the extensio

of the length argument further, one then becomes faced with the conclusion that many mineral

commonly occurring in rocks and soils on the earth's surface would be considered a healt

risk. Cralley [8] suggested that the ubiquity of occurrence of elongate mineral and non mineral particles in autopsies may be related to the ubiquity of occurrence in the moder

environment. He suggests that variable response in the lung may depend upon the chemical an physical characteristic of the fibers, but he does not state what specific characteristic

should be studied. One might therefore conclude that all, or certain sizes of, elongat

particles might be considered with variable response in the lung depending upon th

mineralogy and surface properties. Lists of some of these common fibrous or acicula

minerals are given in Kramer [12] and Zoltai [20].

There is very little epidemiological, animal, or cytotoxicity data on elongate an fibrous minerals other than asbestos. Table 1 summarizes the results obtained for studies o elongate/fibrous minerals other than asbestos from searching TOXLINE, MEDLINE, and Chemica

Abstracts for the past few years. Almost all of the few elongate/fibrous minerals teste

showed some toxicity, and there is some suggestion for endemic lung conditions related t soils. Many equidimensional minerals were not active or as active as the elongate/f ibrou

minerals in hemolytic studies. Almost all of the minerals tested were silicates, so it is no possible at present to generalize to all minerals.

20
Table 1. Toxicity of fibrous minerals other than asbestos.

Mineral System and effect Reference

General soils and endemic pleural plaques 13

Sepiol ite-palygorskite increased enzyme activity 11 lactic acid inhibition

hemolytically active 17

endemic pleural calcifications 4

and soils

tumors in rats, i.p. injection 15

Amphiboles amphibole in soil and 5

pleural plaques

Arfvedsonite i.p. carcinogenicity in rats 16

Vermicullite i.p. carcinogenicity in rats 10

Apatite-nephel ine dust effects 3

i.t. effect, rat lungs 9

Talc (tremolite) hemolytically active 17

Nemalite hemolytically active 17

Gypsum allergic reactions 14

chronic bronchitis 14

There is no specific information on the nature of the surfaces of the minerals, except

that in one study of Schnitzer and Pundsack [17], the hand cut specimens of asbestos and other

fibrous minerals were not hemolytically active. Interestingly, amphibole asbestos is not

hemolyticany active. However, there are very little data available to arrive at any

definitive conclusions. In addition, Webster [19] has noted that in animal studies with

monkeys, non-fibrous nepheline dust has produced interstitial fibrosis. This suggests that

other factors besides fibrosity are responsible for the development of fibrosis.

In summary, there is difficulty at the sub-micrometer level to differentiate asbestiform, fibrous, and acicular minerals. Furthermore, there is no health evidence which might

be used in an alternate classification of elongate particles. The relative response of

different fibrous minerals is not clear.

Since definitive animal studies and epidemiological information exist for asbestos

minerals only, it is pertinent to investigate parameters which might be used to differentiate

between asbestos minerals, other fibers, and cleavage fragments found in the environment.

Length and aspect ratio distributions are examined for occupational asbestos samples and for

environmental samples, and the composition of fibers and intra-fiber composition are examined

to ascertain variations within a sample.

21
Fiber Morphology

The fiber length and often the fiber width are characterized in virtually all toxicity

studies, and the length is often considered the most important factor in health aspects of

fibers. More often than not, the mass-median length or median length is stated in reports of

research. It is not uncommon for the median length of occupational exposures to coincide with

the median length of environmental measurements. Median length does not, however, provide

information of the entire length distribution. Therefore, it is worthwhile to consider what

variations if any exist for the entire length distribution of fibers measured in an occupational exposure and in an environmental exposure.

Figure 1 summarizes length data for both chrysotile and amphibole fibers. Figure la

compares the length distribution of 300 environmental samples of fibers measured in air and

water environments by this laboratory to the length distribution of UICC amosite and

chrysotile measured by this laboratory and to surface and underground mine dusts compiled

from du Toit [9]. Figure lb compares fiber tailings from Lake Superior to UICC amosite

analysis and to occupational exposures from du Toit, and figure Ic compares the distribution

of the longest chrysotile sample measured in urban air in Ontario to UICC and occupational

measurements of du Toit. All three cumulative length plots show that distributions fori

occupational exposure converge with environmental distributions at the 50 percentile level

and that the fiber length from occupational exposures are greater than that fromi

environmental exposures at the 99 percentile level.

2l I » II II I I r—I 1—i

1 |100

E

z

z

UJ

o

99.9

Z

HI3

o

—'—1—•—

AMPHIBOLE

m

—1_ 1 1 B

10

100

. 1

50 95 99 99.9

Figures la and lb. (caption on the next page).

22

01

'I
igure 1. Distribution curves showing the difference in asbestos length and other fiber

length. (a) About 600 analyses of elongate fibers compared to length distribution of UICC samples and from underground (U) and surface (S) dusts from

South African Mines. (b) Comparison of amphibole in taconite tailings from

Lake Superior to UICC amosite and surface and underground mine dust from

South Africa. (c) Comparison of UICC chrysotile and surface and underground

mine dusts with sample from atmospheric environment containing largest fibers.

See figures lb and Ic for figure la labelling of individual distributions.

Occupational and environmental samples show a broad length distribution over almost

hree orders of magnitude, and the only apparent differences in the length distributions are

or the longest fraction. Therefore, characterization of the entire length distribution is

andatory for all studies.

Campbell, et^ aj^. [6, p. 44 ff] have carried out a similar analysis for aspect ratios,

hey show a great deal of overlap of aspect ratio for the milled asbestos form and the milled

on-asbestos form of anthophyl 1 ite and tremolite. Furthermore, they show a distinct

ifference for a commercial milled chrysotile sample and an ambient air sample. In both

ases, the distributions overlap, but the milled asbestos form has a small distribution of

arge length/width aspect ratios that is not found in the milled non-asbestos form, and the

ommercial milled chrysotile has a small distribution of larger aspect ratios that is not

ound in the ambient air sample. The aspect ratio distribution of hornblende is very similar

0 the aspect ratio distribution of the non-asbestos amphiboles. The difference in the

spect ratios between milled asbestos and milled non-asbestos minerals is found for the upper

ive percent or less. This difference in aspect ratio parallels the difference in length

istributions of the largest percentile discussed above for occupational and environmental

amples. In fact, the very large aspect ratios would be measured on the fibers of largest

ength. It may well be that the differences in aspect ratio and of length of the longest

ibers will be most significant in health studies. Figure 2 shows the morphology of six

ifferent samples of cummingtonite-grunerite from the Wabush Lake, Labrador, area. The bulk

omposition and the mineralogy are the same for all six samples, and all of the samples were

aken within about 500 meters of each other. Figure 2a is clearly an asbestiform sample and

igure 2f is clearly equidimensional . The detailed morphology of these samples may show some ignificant toxicol ogical differences. They are now being studied in detail mineralogical ly,

nd for hemolytic and cell activity responses.

23
^^^^

v

Figure 2. Asbestiform and equidimensional cummingtonite-gruneritG from Labrador.

(a) Asbestiform cummingtonite scale units are in cm. (b) - (f) Variations in

fibers, cleavage fragments, and equidimensional cummi ngtonite-grunerite sampled

within 500 meters of each other and the asbestiform variety. Each numbered

scale unit is 0.1 cm.

24
Fiber Composition

Asbestos and other fibers vary in major elemen^ compc^sition due to the substitution of

octahedral coordinating cations (typically Mg, Fe^ , Fe^ , Al), tetrahedrally coordinated

:ations (Si, Al), and coordination of larger cations (Ca, Na, K). Chrysotile is a silicate

sheet structure of nearly fixed composition, Mg3Si205(0H)4 , but the amphibole asbestos

ninerals show more substitution of ma^or ions. H^nce the anthophyl 1 i te-gedrite series

develops with substitution of Mg for Fe^ , Al for Fe^ , and Mg with substitution of Al for Si

nak^s the charge balance; the cummingtonite-grunerite series with substitution of Mg for

Fe^^; the tremol ite-actinol ite series with substitution of Mg for Fe^ and substitution of

Fe^ for Al . "Amosite" is an asbestos acronym for a cummingtonite-grunerite of variable

composition, and crocidolite is the asbestos variety for a glaucophane-riebeckite of variable

composition. There are other less common amphiboles with asbestiform habit. In addition,

there is substitution of trace elements and in some cases other elements (for example, Mn) may

substitute in the amphibole structure to a large extent. Therefore, one may not conclude that

'there is any fixed composition for one asbestos mineral, and it is possible to have variations

in composition within one sample depending upon the history of formation of the mineral. In

addition, other asbestos minerals and other mineral impurities can and do often occur in

asbestos samples.

Normally a fibrous sample from an occupational setting or known single source can be

identified and characterized quite well even at the micrometer size range. This is possible

because there would generally be a limited number of minerals to consider. An environmental

sample, however, poses a most difficult analytical task if available in small amounts. There

can be many common minerals, each of which may have a variable composition, and the net result

is that many minerals may occur with overlap in composition, gross crystal lographic

properties and optical properties.

I Health researchers often use well characterized samples from specific locations for

their experiments. These samples have been chemically analyzed in bulk, but often individual

fibers and variations in composition along a fiber have not been analyzed. UICC samples of

amosite and crocidolite as well as one sample of tailings from Lake Superior and one asbestiform cummingtonite-grunerite sample from Labrador (fig. 2a) were subjected to analysis

using energy-dispersive fluorescence spectroscopy in conjunction with a transmission

electron microscope.

The analytical procedure is similar to that of Beaman and File [2]. Isolated fibers

between 0.2 - 0.8 pm in width were subjected to analysis with an excitation voltage of 80 kV

and a take-off angle of 36 degrees. The excited area was estimated to be about 0.2 pm when

considering scattering effects. Counts were recorded and areas under peaks were estimated

using a computer routine which also adjusted for background. Ratios of peak area of Mg, Fe,

Na, and Ca relative to Si were calculated, and these ratios were adjusted for areal ratios

determined on an adjacent blank portion of the grid. This later correction was normally

negligible. In the following discussion, ratios of areal peaks to Si corrected for

background of analyzer and grid background are reported. Champness et a^. [7] have noted that

the use of intensity ratios should correct for fluorescence variations due to specimen

thickness variations.

Figure 3a shows elemental intensity ratios relative to Si for UICC amosite for 58

analyses on 15 fibers, whereas figure 3b shows similar results for 51 analyses on 15 fibers of

UICC crocidolite. In both figures, the results are given for increasing Fe/Si intensity

ratios, and the values between horizontal lines represent the intensity ratio value for the

particular element. Both samples show a marked variation in elemental intensity ratios with

Between 30-60 percent variation about the mean fjOr the corrected values. With reference to

amosite, assuming all of the Fe is structural Fe^ , there should be a parallel decrease in the

Mg/Si ratio as Fe/Si increases. This is obviously not apparent for the bulk analysis.

Although the surfaces of all fibers were examined prior to analysis for optical density

continuity so that surficial material such as Fe-oxides might be excluded, it is possible

that some of the variation in the Fe/Si ratio is due to surface oxidation of Fe. But this

would not explain the variation in Mg/Si ratios for amosite which, with the exception of two

extreme analyses, varies about 20 percent about the mean of the ratio.

25
A m 0 s I T E (u I CO

2.2 r

2.1 -

Q ^ g \ I ' ' . i I t 1 I . ' ' FIBERS

CROCIDOLITE (UlCC)

1.9 •

1.8

0.5 ^

F I B E RS

Figure 3. Corrected intensity ratios for UICC amosite (a) and UICC crocidolite (b).

Intensity ratios are cumulative with the value for each element depicted

as the difference between adjacent horizontal bars.

26
Crocidolite UICC. samples show similar variations with the Fe/Si ratios with a deviation

of about 15 percent about the mean; Mg/Si varies about 15 percent about the mean, and Na/Si

varies about 25 percent about the mean. There is no relationship between Mg or Na ratios and

Fe ratios, but there is an apparent correlation between Na/Si and Mg/Si. This correlation

could be due to radiation from Na, Mg, and Al

Figure 4 shows elemental intensity ratios for one fiber of UICC crocidolite (4a) and one

fiber of UICC amosite (4b). Variation of intensity ratios along the fiber length is between

5-10 percent, and this is much less than for the range in variation for all mineral fibers.

This is true for all of the eight mineral fibers tested at multiple locations.

CROCIDOLITE (UICC)

(/) 5

Z lij

LiJ CH

o 50-

y 1- UJ

<

Mn

T i K

Ca

_j

<

Ld

LlI _l

UJ

Si

0j060

QP50

Q040

0X)30

Si 0020

OJOOO

Fe/

a900

Si 0.800

czz:

AN ALYZ ED S POTS

(crocidolite fiber I4^m. diameter 0.3pm.)

Figure 4a. Variation along a fiber of UICC crocidolite.

27
AMOSITE (UlCC)

Ih-LU

-Z.(J)

UJUJ

^q:

O -I — Ld

<

Mn

Ti

K

Na

C a

0.050

<

Iz

LU

LU

_l

LU

0020

ni

Mg/ 0090

/

Fe

'Si

0080

1.000

0.950

ANALYZED SPOTS

(AMOSITE FIBER 1 6^m. dia. 0.3^m.)

Figure 4b. Variation along a fiber of UICC amosite.

Figure 5 shows the results of 64 analyses on 14 fibers of asbestiform cummingtonite f

Labrador. There is an approximate 50 percent variation of Fe/Si intensity ratios about

mean, and there appears to be a decrease in the Mg/Si intensity ratio with increasing Fe

ratio with only a few exceptions.

28
C u mmingtonite

FIBERS

Figure 5. Corrected intensity ratios for analysis of 64 asbestiform fibers from Labrador

(figure 2a).

Figure 6 shows two examples of the analysis of different locations on the same fiber for

e Labrador cummingtonite-grunerite sample. Once again there is a much smaller variation

10 percent) of intensity ratios along an individual fiber with the exception of one

cation which showed an extremely high Fe/Si ratio. This very large ratio may be due to

rficial Fe-oxide, although there was no anomalous electron density visible.

29
CUMMINGTONITE

(/) z

^

"l' LU UJ

o 2 cr

< LU

<

H

Z

UJ

UJ

_l

UJ

CO

o

I-

<

<

Iz

UJ

UJ

UJ

Fe.

Mn

Ti

K

Na

Ca

Q200

0.180

0.160

0.800

0.750

0.700

0.650

I

AN ALYZ ED S POTS

(CUMMINGTONITE FIBERS IS^m.dia. 04 ^m.)

CUMM I NG TON ITE

021

Mg/ 019

0.17

0.15

Fe 1.0

Si 0.9

08

0.7

19.6

y

' I I ' ' ANALYZED SPOTS

(CUMMINGTONITE FIBERS I6;jm. di a . 0.2 jjm.)

Figure 6. Variation in intensity ratios for analyzed spots along two asbestiform

cummingtonite-grunerite fibers from Labrador.

30
There appear to be two possible reasons for variations in areal intensity ratios. There

an be a real variation in the composition of individual fibers in an apparently homogeneous

hase, and/or the differences can be due to x-ray adsorption and secondary radiation

specially from Fe in these samples. The fact that analysis on spots on a specific fiber

ivGs an intensity variation less than 10 percent (with one exception in 200 analyses)

ompared to a 30-50 percent variation in bulk is strongly suggestive that the difference in

he two variations (20-40 percent) is the approximate absolute variation in intensity ratio

ue to compositional variation that exists in these samples. If the coefficient relating

ntensity ratios to compositional ratios is not dependent upon other factors, one would

nticipate a real variation in fiber composition of 20-40 percent maximum for the major

lements.

One assumes generally that the composition of fibers within a relatively pure mineralgical phase is reasonably constant in composition. This assumption must be tested by

etailed analysis of many fibers within a specific sample.

Conclusions

It appears that asbestos morphology differs from other elongate acicul ar-fibrous

inerals and from environmental exposures in the largest percentile group. Therefore, the

ntire size distribution should be characterized before carrying on toxicity studies.

The composition of fibers within a well characterized sample may vary in composition,

ence analysis on individual fibers must always be carried out.

Finally the health significance of fibers other than asbestos should be studied,

rimary cytotoxicity and mutagenicity testing of hydrated silicates, anhydrous silicates and

on-silicates may well provide clues for more extensive studies.

Work supported in part by Inland Waters Directorate, Environment Canada. Microscope

nalytical work by 0. Mudroch, and field work by R. Marttila are gratefully acknowledged.

References

[1] American Geological Institute, Glossary of Geology , Washington, D.C., 1972.

[2] B6aman, D. R. and File, D. M. , Quantitative determination of asbestos fiber concentrations. Anal. Chem. , 48, 101-110, 1976.

[3] Borschchevski i

, Y. M. and Konikova, T. S. , Apatite and apatite-nephel ine dust, Nauch.

Tr. , Leningrad Inst. Usoversk. Vrachei , Ub, 108-116, 1973. (Chemical Abst: 080:

078900).

[4] Burilkov, T. and Michailova, L. , Sepiolite content of the soil in regions with endemic

pleural calcifications. Int. Arch. Arbeitsmed, 29, 95-101, 1972.

[5] Burilkov, T. , Michailova, L. , and Babadjov, L. , Amphibole asbestos in the soil and its

significance for the endemic occurrence of pleural plaques, Zh. Gesamte Hyg. Grenzgeb,

18, 802-809, 1972. (HEEP: 74/02556)

[6] Campbell, W. J., Blake, R. L. , Brown, L. L. , Gather, E. E. , and Sjoberg, J. J., Selected

silicate minerals and their asbestiform varieties. Bur. of Mines Info. Circ. 8251, 1977.

[7] Champness, P. E. , Cliff, G. , and Lorimer, G. W. , The identification of asbestos, J. of

Microscopy, 208, 231-249, 1976.

[8] Cralley, L. J., Inhalable fibrous materials, ijn H. A. Shapiro (ed). Pneumoconiosis , Oxford U. Press, 1970, p. 70-74.

31
[9] du Toit, R. S. J., Dust in South African asbestos mines and fiberizing plants, i_n reference 8, p. 13-17.

[10] Hunter, B. and Thomson, C. , Evaluation of the tumorigenic potential of vermiculite by

intrapleural injection in rats, Brit. J. Indust. Med., 30, 167-173, 1973.

[11] Koshi , Kimiko, Hayashi, Hisato, and Sakabe,, Hiroyuki, Cell toxicity and hemolytic

action of asbestos dust, Ind. Health. 6, 69-79, 1968.

[12] Kramer, J. R. , Asbestos: Nomenclature, occurrence and redistribution in water,

in Drinking Water and Health, U.S. Nat. Res. Counc. , 1977 (in press).

[13] Mikhailova-docheva, L. , Hygienic evaluation of the mineral composition of soils in

regions of the People's Republic of Bulgaria marked by the revelence of endemic

pleural calcifications, Gig. Tr. Prof. Zabol., 16, 30-33, 1972. (HEEP: 73/04741).

[14] Owinski, J., Effect of dust pollution and thermal microclimate on the incidence of

chronic non-specific diseases of the respiratory system with regard to the gypsum

workers industry in Gacki, part IV, Radiographic results and symptoms of chronic

bronchitis, Przegl Lek, 32, 265-258, 1975. (MEDLINE).

[15] Pott, F. , Huth, P., and Friedrichs, K. H. , Tumorigenic effect of fibrous dust in

experimental animals. Environ. Health Perspect. , 9, 313-316, 1974.

[16] Pylev, L. N. and lankova, G. D. , Carcinogenic activity of magnesia arfvedsonite

administered intrapleural ly to nonbred rats, Vopr. Onkol., 22, 71-76, 1975. (TOXBIB:

75/104450).

[17] Schnitzer, R. J. and Pundsack, F. L. , Asbestos hemolysis. Environ. Res., 3, 1-13,

1970.

[18] Spiel, S. and Leineweber, J. P., Asbestos minerals in modern technology, Environ.

Res. , 2, 166-208, 1969.

[19] Webster, I., Commentary, i_n reference 8, p. 133.

[20] Zoltai, Tibor, History of asbestos-related mineralogical terminology. This Proceedings, Paper 1

[21] Zoltai, Tibor, Comments on asbestiform and fibrous mineral fragments relative to

Reserve Mining Company taconite deposits, Minn. Pollut. Contr. Agen. , Minneapolis, 37

p + III append.

32
Discussion

C. RUUD: What was the accelerating voltage of your electron beam in all of these

microanalyses?

J. KRAMER: We tried some studies varying it, but the value we used routinely was

80 kv. There are a lot of details of these findings on the analytical part which suggest

problems. I would be happy to discuss these with individuals.

M. COSSETTE: Are you aware of any work with high pressure mercury porosimetry to

differentiate between fibrous length groups?

KRAMER: No, do you have some data or know of some?

COSSETTE: No, I know of some people doing work in the area but nothing published.

A. WILEY: Do you use the polarizing microscope, and, if so, do the clino-amphiboles

show parallel extinction?

KRAMER: Yes, within analytical error, but some of the cummi ngtonite fibers from

Labrador may not show parallel extinction. They may have a small angle (5-10°).

WILEY: Your ordinary varieties do, though?

KRAMER: Yes, I think that this is a very important point to consider; this apparent

optical difference and its significance to fiber morphology.

D. BEAMAN: 0.3 pm is not particularly large for an amphibole. I wonder to what

extent you feel some of these trends may be due to the difference in the size of your

fibers.

KRAMER: Yes, there may well be a size factor. 0.3 pm width is at the threshold

of size effect upon intensity ratios according to your study published in Analytical

Chemistry .

F. MUMTON: I'd like to ask you about your ion exchange measurements of these two types

of materials; you didn't show any data, but yet you say there are differences. What range

are you talking about? What did you do?

KRAMER: First of all, the ion exchange differences will depend upon the composition

of the material. We worked mostly with cummi ngtonite from Labrador. What we are using

basically are these minerals (see figure 2) as an exchange medium to compete against a copper-organic ligand. The procedure is analogous to an ion exchange column but we are

using the minerals. We calibrate the system against known associations such as copperglycine. We carried out the analyses using equidimensional , fibrous and asbestiform

varieties and found little differences in conditional stability constants for the different

varieties of the same composition. In addition, the exchange capacities appear to be very

similar and typical of all silicate minerals (about 3-4 micro-equi valents/meter^).

W. EISENBERG: Have you modified your definition of a mineral species as a result of

the data you've obtained?

KRAMER: No, you noticed I didn't give any definitions. I just quoted other people.

Seriously, I am trying to point out that there are either analytical problems or variations

in composition, or both, at the micrometer scale of a fiber. See Science, 1_98, 359-365 for

some possible reasons.

33

Jational Bureau of Standards Special Publication 506. Proceedings of the Workshop on \sbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued :!ovember 1978)

THE CRYSTAL STRUCTURES OF AMPHIBOLE AND SERPENTINE MINERALS

Jack Zussman

Department of Geology

University of Manchester

Engl and

Abstract

The crystal structures of the two main asbestos-forming minerals,

the amphiboles and serpentines, are surprisingly very different. The

amphiboles are "chain silicates" in which Si04 tetrahedra are linked to

form bands four tetrahedra wide and of very great length. These bands

run parallel to the asbestos fiber axis and are linked laterally by

cations, mainly Ca and Mg in tremolite; Na, Mg and Fe in crocidolite; Mg

and Fe in amosite and anthophyl 1 ite. The tempting correlation of the

chain unit of crystal structure with asbestiform nature is, however, too

facile. Many amphiboles are not asbestiform, and as the serpentine

minerals show, some asbestiform minerals do not have a chain structure.

The serpentine minerals are "layered silicates" in which Si04

tetrahedra are linked to form thin sheets of great lateral extent. The

tetrahedra all point in the same direction and their apical oxygens are part of an (0,0H)-Mg-(0H) sheet which is itself formed by Mg-(0,0H)

octahedra. Thus the fundamental serpentine layer is polar and has a tetrahedral and octahedral component. The mismatch in dimensions of

these two components generally leads to curvature of the layers and in

chrysotile asbestos the layers form either scrolls or concentric

cylinders with very high length/breadth ratio and with length parallel to

the fiber axis. Other forms of serpentine, however, with chemistry very

similar to that of chrysotile, do not exhibit asbestiform morphology.

For all minerals, the physical and chemical properties are important both for industrial usage and environmentally in determining the

nature of the dusts produced in manufacturing processes and in subsequent

abrasion. Factors which may influence properties in addition to the

basic chemistry and "average" x-ray structure are the crystal morphology

and mode of aggregation, and also the abundance and nature of structural

defects.

Keywords: Amphibole; asbestos; chemistry; cleavage; defects; dusts;

environment; fibers; morphology; serpentine; structure.

In this review I would like to describe briefly the crystal structures of the two main

asbestos-forming minerals, the amphiboles and serpentines, to consider what they have in

:ommon and what are their differences, to identify if possible what are the fundamental

:riteria that lead to asbestiform habit, and to observe the crystal lographic features that

nay contribute to their physiological behavior.

35
Amphi boles

These minerals are "chain silicates" in which Si04 tetrahedra are linked so as to form

chains with composition Si40ii as shown in figure 1. The chains are four tetrahedra wide, of

very great length, and they lie parallel to the fiber axis in the asbestiform amphiboles. One

might say that amphibole asbestos is finely fibrous because of the chain structure, but this

is an over simplification. Some amphiboles are not fibrous at all, let alone asbestiform.

(5) OH

Figure 1. Plan and end-view of an idealized Si40ii amphibole chain together with

additional (OH) ions.

No minerals could be formed from Si40ii chains alone and in the amphiboles there are cations linking chains laterally as shown in figure 2. The cations vary from one amphibole to

another. In tremolite Mg ions link chains by means of a strip of Mg(0,OH) octahedra. The

oxygens of this strip are the apices of the Si-0 tetrahedra and the OH ions occur as in figure

1. Calcium ions link the chains across the bases of the tetrahedra. An alternative view of

the structure is one of almost continuous sheets of Mg and Ca polyhedra linked by Si ions.

36
Figure 2. Schematic end-view of amphibole chains linked by cations in X and

Y positions. In some amphiboles the site A is occupied. The

amphibole formula can thus be written Ao_ iX2Y5(Si , Al )8022(0H)2

Other important amphiboles are: - anthophyl 1 ite in which largely Mg ions play the role

Df both Ca and Mg in tremolite; the cummi ngtonite - grunerite series, which contain Mg and Fe

in varying proportions; and riebeckite, in which Mg, Fe and Na are the principal cations in

addition to Si (see Table 1). The above-mentioned compositions are those most relevant to the

:onsideration of asbestos, since in addition to the less common varieties of asbestos,

tremolite and anthophyl 1 ite , there are the two more abundant and commercially more important

»/arieties - 'amosite,' a form of cummingtonite - grunerite, and "crocidol ite" (blue

asbestos), a form of riebeckite.

37
Table 1. Cation distribution in idealised formulae of the amphibole minerals.

Asbestos-forming amphiboles are marked*.

Cummi ngtoni te-Gruneri te*

Anthophyl 1 ite*

Gedri te

Tremol ite*-Actinol ite

Common Hornblende

Tschermakite

X

(Mg,Fe)2

(Mg,Fe)2

Ca2

Ca2

Ca2

(Mg,Fe)5

(Mg,Fe)3Al2

(Mg,Fe)5

(Mg,Fe)4Al

(Mg,Fe)3Al2

Eden ite Na

Pargasite-Hastingsite Na

Richterite

Katophorite

Mboziite

Na

Na

Na

Ca2

Ca2

NaCa

NaCa

NaCa

(Mg,Fe)5

(Mg,Fe)4Al

(Fe)5

(Mg,Fe)4Al

(Mg,Fe)3Al2

CALCIUM

AMPHIBOLES

Sig

Si7Al

SieAlg

ALKALI

AMPHIBOLES

Glaucophane-Riebeckite*

Eckermanni te-Arfvedsoni te Na

Na2

Na2

(Mg,Fe)3Al2

(Mg,Fe)4Al

Sig

Sig

For the sake of completeness at least, though it may also have some indirect importance,

it should be noted here that the amphibole asbestos-forming minerals are monoclinic in symmetry except for anthophyl 1 i te which is orthorhombic. Cell parameters are given in Table 2.

Table 2. Amphiboles. Cell parameters.^

o o o aA bA cA

9.82 18.05 5.28 104°39

9.89 18.20 5.31 104°38

9.56 18.30 5. 35 101°50

9.74 17.95 5.30 103°54

18.56 18.01 5.28 90°

Tremol ite [1]^

Actinolite [2]

Grunerite [3]

Crocidolite [4]

Anthophyl 1 ite [5]

^ These cell parameters relate to particular specimens.

Variations in chemical composition, particularly in Fe/Mg

ratio, can be expected to yield a range of values but

usually within 1 or 2 percent of those given.

^Figures in brackets indicate the literature references at the end of this paper.

38
A well-known physical property of amphiboles is that they generally cleave readily along

{110} planes. Assuming that the Si-0 chain is a strong structural unit, and that the

strongest inter-chain bonding is across the strips of octahedra joining tetrahedral apices,

the probable paths of weakness can be traced as on figure 3, which on a macroscopic scale

results in cleavages intersecting at approximately 120°, as observed.

\ /

/

SI

r

/

Figure 3. Schematic view of amphibole structure as seen down z axis, showing

likely paths of weakness leading to cleavages intersecting at 57°.

Although the good prismatic cleavages explain the readiness of amphibole crystals to

liplinter into elongated particles, this is not necessarily relevant to the unusual physical

lature of asbestos. It would be so if a block of asbestos was a single crystal and the

iroduction of hair-like fibers was the process of splitting off cleavage fragments. However,

III block of asbestos, even when very small, is not a single crystal but an aggregate of singlei:rystals all lined up parallel to the fiber axis but with a range of azimuthal orientations,

he process of stripping fibrils from asbestos is thus more likely to be one of breaking

:rystallites away from the aggregate at the grain boundaries across which there is weak

liohesion.

39
The asbestiform nature of certain amphiboles is thus a consequence of the crystallite

morphology which in turn is influenced by the conditions of crystal growth as well as the

inherent chemical and physical features of a single crystal. The production of a fiber

aggregate as in asbestos must depend upon independent nucleation of each fibril and its

preference for growth along z rather than at right angles to it.

It is perhaps significant that the group of amphiboles loosely referred to as "hornblendes" occur in roughly equidimensional crystal habits and not as asbestos. Table 1 shows a simplified scheme for the chemical compositions of amphiboles and it is seen that the

hornblendes are characterized chemically by having appreciable substitution of Al for Si.

Asbestiform amphiboles show little substitution of this kind. The minerals richterite and

eckermannite , which also have little Al for Si substitution, are not known to occur naturally

as asbestos, but synthetic products have been so described and are at least extremely fibrous

[6,7]. I would suggest therefore that the substitution of Al for Si might be responsible for

increased potential for growth of prism faces relative to growth in the z direction.

Even if true, the above suggestion cannot be the only criterion that governs asbestos

formation since tremolite itself can occur in asbestiform or non-asbestiform habit, each

variety having the same major element chemical composition. In such circumstances other

parameters such as the pressure and temperature conditions, rates of cooling or heating, or minor or trace element concentrations may be critical factors.

The mechanical properties of asbestos and related minerals are of importance both for

the desirable physical attributes of articles made from asbestos, and environmentally in

determining the nature of the dusts produced during the processes of manufacture or during

subsequent abrasion. Factors which can give different mechanical properties are the nature

of the fundamental particles and their state of aggregation (bundles of fibers versus single

crystals). For single fibrils or crystals in the {110} cleavages, and the resistance to

breakage across other planes (roughly perpendicular to fiber length), will help to determine

the morphology of the dust particles produced. Structural defects may also have an influence

on physical properties.

Structural defects

It should be emphasized here that the published crystal structures of amphiboles (and

serpentines), determined by x-ray diffraction, are the content of the "average" unit cell,

the volume of specimen investigated consisting of something like 10^^ unit cells. In real

crystals the unit cells do not repeat perfectly and several kinds of defects may occur. These

departures from the perfect structure are no doubt important in questions concerning crystal

growth and they may well influence physical properties and physiological effects.

The two principal kinds of imperfection in amphibole structures are stacking defects and

Wadsley defects. Stacking defects are illustrated schematically in figure 4. In the normal

monoclinic amphibole, slabs of structure parallel to (100) are stacked alongside one another

with regular displacements. In a faulted structure occasional errors in the direction of

this displacement occur and the frequency of such faults varies from one specimen to another.

When the faults are relatively infrequent the result can sometimes be described as a twinned

crystal. Figure 5 shows a high resolution electron micrograph displaying twin components.

Such defects are also seen in lower magnification electron micrographs and they have

important effects on diffraction patterns. When the faults are frequent and regularly

repeating, they are no longer really faults but are the regular displacement of a structure

with a super-cell and perhaps different symmetry. The latter describes approximately the

relationship between the orthorhombic and monoclinic amphiboles.

40
monoclinic monoclinic twin

orthorhombic

monoclinic with

stacking fault

Figure 4. Illustration of the stacking

of blocks of amphibole

structure to form a) regular

monoclinic, b) monoclinic

twinned, c) monoclinic

faulted, and d) orthorhombic

structures. The fault plane

is (100).

-igure 5. High-resolution electron micrograph of amosite showing faulted and twinned structures. (Electron beam parallel to x) Figure from J. L. Hutchinson et al. [8].

41
Figure 6 illustrates the Wadsley defect by showing how parts of an amphibole crystal

might contain occasional triple or single Si-0 chains distributed among the normal double

chains. In low magnification electron micrographs such defects are seen as linear features

parallel to (010) (fig. 7).

PYROXENE AMPHIBOLE

single chains double chains

triple chain double chain double chain

double chain double chain single chain

Figure 6. Schematic illustration of a) pyroxene structure, b) amphibole structure,

c) amphibole with triple chain Wadsley defect, and d) amphibole with

single chain defect.

Figure 7. Electron micrograph of amphibole with beam perpendicular to y showing

Wadsley defects on (010). Figure from J. E. Chisholm [9].

42
For environmental health considerations we do not yet have a causative understanding of

the harmful effects of asbestos and do not know which properties of asbestos are involved. It

is conceivable therefore that more subtle structural factors than those described above might

be important. Although the structure described is broadly correct for all amphiboles, minor

differences in atomic coordinates occur from one amphibole to another. Structure

determinations have been performed for non-asbesti form tremolite, actinolite, anthophyl 1 ite

and grunerite, but not for asbestiform specimens because of technical difficulties. For

crocidolite, a fiber approaching a single crystal was used rather than a hair- like strand of

asbestos. As part of the details of structure, variations can occur in the way in which Fe

and Mg atoms are distributed amotjig similar but not strictly equivalent octahedral sites. In some amphiboles the role of Fe-^ may be significant in oxidation-reduction processes, and

there is the possibility of Na (or Ca) having a degree of cation exchange capacity.

Serpentine

Chrysotile, another important variety of asbestos is not an amphibole but is a member of

the serpentine group of minerals. Because of its asbestiform character, and repeat distance

in the unit cell of about 5.3 A parallel to the fiber axis (similar to that in amphiboles), it was once thought to have a chain-like crystal structure. Later work, however, showed it to be

a layered silicate with structure analogous to that of the clay mineral kaolinite, but with Mg

instead of Al in its composition. The paradox of how a layered mineral could have asbestiform

habit was solved largely by Whittaker [10,11,12] who deduced from x-ray diffraction patterns

that layers are rolled to form concentric cylinders or scrolls with their long axes parallel

to the fiber. This indirect evidence was supported by electron microscopy of transverse

sections of chrysotile, culminating in the spectacular high-resolution photographs published

by Yada (fig. 8).

Figure 8. High resolution electron micrograph of transverse section of chrysotile

asbestos. Figure from K. Yada [13].

43
The reason for the curving of the fundamental laye rs in chrysotile can be seen by

examination of their chemical composition and structure. Each layer has two components, one

a sheet of linked Si-0 tetrahedra, and the other (joined to the first by sharing apical

oxygens), a sheet of (Mg-0,OH) octahedra. A plan and elevation view of the composite layer,

Mg3Si205(0H)4 , is shown in figure 9. In order to form a flat-layered composite the dimensions

of each component would need to match fairly closely. Reasonable estimates of the repeat

distance of each show that the tetrahedral Si sheet has smaller dimensions than the

octahedral Mg sheet, and this mis-match can be overcome by curvature, with the Mg sheet

outermost, or by some other means of relieving structural strain. This leads to a number of

strange structural configurations in serpentines, one of which is the tube-like character of

chrysoti 1 e.

b=9-2A

oi-i ooooooooooo

Figure 9. Plan and elevation views of idealized serpentine structure.

Electron micrograph studies of chrysotile asbestos show that diameters of natural

fibrils are of the order of 100 to 500 A, and the length/breadth ratios are of the order of;|

100 to 1 or greater. The limitation on growth in the radial direction is more easily|

understood for chrysotile than for amphiboles in that as successive layers are added during*^

the growth process, the radius of curvature increases, eventually deviating too far from its|

ideal strain-free value to be energetically favorable. Thus chrysotile asbestos probably'

forms by multiple nucleation, usually on the walls of veins in massive fine-grained]

serpentinite rock, with relatively rapid growth in the fiber direction and limited growth at

j right angles to it. I

I

It is pertinent in the context of possible environmental problems to consider the

structure and morphology of other serpentine minerals which have very similar composition but are not asbestiform. One such mineral is antigorite. It too has a curved sheet structure,

but the layers are corrugated rather than rolled (fig. 10). The corrugations have a rather

regular wavelength so that quite well-formed crystals result. Sometimes they are equidimensional but they have a tendency to be thin, and lath-like parallel toy. Antigorite

44
is often found associated with other serpentine minerals; it does have a small but distinct

difference in chemistry and is known to form under higher temperature conditions than the

others [15].

Figure 10. The "corrugated sheet" structure of antigorite viewed along the y axis.

After G. Kunze [14].

A third kind of serpentine is the mineral lizardite, which in spite of the difficulties

mentioned above does manage to achieve a more or less flat-layered structure [16]. The

accompanying strain however means that crystals contain imperfections and usually grow only

to very small dimensions. Thus a high proportion of apparently massive serpentine is

composed of lizardite grains too small for optical resolution, but seen by the electron

microscope to have platy morphology. The stacking of successive serpentine layers in

lizardites can lead to 1,2,3,6 and even 9-layer repeats, and whereas lizardite platelets are usually not elongated, some of the multi-layer varieties yield lath-like crystals, and again,

like antigorite a coarse splintery fiber. Cell parameters of serpentine minerals are given

in Table 3.

Table 3. Serpentines. Cell parameters.

o aAo bA

o cA ^ Fiber Axis

clino-chrysotile [10] 5.34 9.25 14.65 93°16' X

ortho-chrysoti le [11] 5.34 9.2 14.63 90° x para-chrysotile [12] S5.3 9.24 14.7 90° 1

lizardite [17] S5.3 =9.2 =7.3 X n 90° X when fibrous

antigorite [14] 43.3^ 9.23 7.27 91.6° y when fibrous

These cell parameters relate to particular specimens. Variations in chemical

composition, particularly in Fe/Mg ratio, can be expected to yield a range of values,

but usually within 1 or 2 percent of those given. For antigorite markedly different

values occur. Lizardites with n = 1, 2, 3, 6, and 9 have been described.

Other large values of a are found.

45
Yet another strange morphology for a serpentine mineral has been discovered

recently [18], and although it has not yet been studied extensively, it does appear to be

quite common in occurrence. In this variety, flat lath-like serpentine layers are arranged to form polygonal prisms, sometimes surrounding a core of tubular chrysotile. A

cross-section is illustrated in figure 11. Typical diameters are of the order of 1000 to

2000 A. Serpentine specimens in which this structure seems to be prevalent are those

which have a coarse splintery fibrous texture. Their fracture fragments are expected to

have, and indeed show, lath- like morphology. Whether this material should be classed as a form of chrysotile or of lizardite is a moot point, and it may be better to call it

"polygonal serpentine" with our present state of knowledge.

Figure 11. Electron micrograph of an ion-thinned serpentine specimen showing

cross-sections of chrysotile tubes and polygonal serpentine.

Figure from Cressey and Zussman [18].

Although for antigorite there is clearly a distinct chemical composition, there is no consistent chemical difference between chrysotiles and lizardites. The latter two can therefore be regarded as polymorphs and would be expected to have distinct (P,T) stability

fields. Attempts to define these have not so far been successful. Examination of the

mineralogy and textures of large numbers of serpentinite rocks have led to the conclusion

that the chrysotile asbestos is formed secondarily from lizardite or antigorite and not

directly from olivine and pyroxene, and that it is formed in a relatively low but rising

temperature regime [19,20].

Concluding Remarks

There have not as yet been extensive tests comparing the physiological activities o asbestiform and non-asbesti form varieties of amphiboles or of serpentines. It would clearly

be useful to know what, in addition to morphology, are the essential chemical and physical

differences between asbestiform and non-asbesti form varieties. These differences might be

46
either consequences or causes of the contrasting morphology. Since, for any mineral,

different specimens show variations in properties even when morphology does not change

significantly, it is not easy to determine which, if any, are absolutely specific to

asbestos. Such differences, if established, might be quite subtle but nevertheless important

for physiological effects, but since the mechanism of the latter is unknown, we have no clues

from this quarter to aid us in the search. If particle size and shape are the only important

factors, then we need not trouble to look further (except as a fascinating geological

problem). If other factors are important, and we do not know what they are, then any material

to which people are exposed on a large scale needs to be tested for its physiological effects.

References

[1] Papike, J. J., Ross, M. , and Clark, J. R. , Crystal -chemical characterization of

cl inoamphiboles based on five new structure refinements, in Pyroxenes and Amphi boles : Crystal Chemistry and Phase Petrology , Min. Soc. Amer. Special Publ . No. 2 117-136

(1969).

[2] Mitchell, J. T. , Bloss, F. D. , andGibbs, G. V., Examination of the actinol ite structure

and four other C2/m amphiboles in terms of double bonding, Zeit . Krist . , 133 , 273-300

(1971).

[3] Ghose, S. and Hellner, E. , The crystal structure of grunerite and observations on the

Mg-Fe distribution. J. Geol

, 67, 691-701 (1959).

[4] Whittaker, E. J. W. , The structure of Bolivian crocidolite, Acta Cryst . , 2, 312-317

(1949).

[5] Finger, L. W. , Refinement of the crystal structure of an anthophyll ite, Ann. Rep. Dir.

Geophys. Lab. , Carnegie Inst. Yr. Bk. , 68, 283-288 (1970).

[6] Fedoseev, A. D. , Makarova, T. A., and Kosulina, G. , Synthesis of fibrous richterite

under hydrothermal conditions. Za£. Vses . Min . Obshch .

, 97, 722-725 (1968).

[7] Goncharov, Yu, I., Balitskii, V. S. , Khadzhi , I. P., and Popova, N. P., Replacement of

phlogopite by amphibole asbestos of the eckermannite-arfvedsonite series in alkaline

hydrothermal solutions, Zag. Vses . Min . Obshch . , 103, 716-718 (1974).

[8] Hutchison, J. L. , Irusteta, M. C. , and Whittaker, E. J. W. , High resolution electron

microscopy and diffraction studies of fibrous amphiboles. Acta Cryst . , A31 , 794-801

(1975).

[9] Chisholm, J. E. , Planar defects in fibrous amphiboles, J. Mat. Sci^. , 8, 475-483 (1973).

[10] Whittaker, E. J. W. , The structure of chrysotile, II., Cl i nochrysoti 1 e , Acta Cryst . 9,

855-862 (1956).

[11] Whittaker, E. J. W. , The structure of chrysotile. III, Orthochrysoti 1 e , Acta Cryst . 9,

862-864 (1956).

[12] Whittaker, E. J. W. , The structure of chrysotile, IV, Parachrysoti 1 e , Acta Cryst . 9,

865-867.

.13] Yada, K. , Study of chrysotile asbestos by a high resolution electron microscope. Acta

Cryst . 23, 704-707 (1967).

[14} Kunze, G. , Die gewellte Struktur des Antigorits, I, Zeit . Krist . 108 , 82-107 (1956).

.15] Evans, B. W. , Johannes, W. , Oterdoom, H. , and Trommsdorff, V., Stability of chrysotile

and antigorite in the serpentinite multisystem. Schweiz min. petrogr. Mitt., 56, 79-93

(1976). —

47
[16] Rucklidge, J. C. and Zussman, J., The crystal structure of the serpentine mineral,

lizardite MggSi 205(0H)4 , Acta Cryst . , 19, 381-389 (1965).

[17] Whittaker, E. J. W. and Zussman, J., The characterization of serpentine minerals by x- ray diffraction, Mineral . Mag . , 31, 107-126 (1956).

[18] Cressey, B. A., and Zussman, J., Electron microscopic studies of serpentines, Canad . Mineral . , T4, 307-313 (1976).

[19] Wicks, F. J. and Zussman, J., Microbeam X-ray diffraction patterns of the serpentine

minerals, Canad . Mineral .

, 1_3, 244-258 (1975).

[20] Wicks, F. J. and Whittaker, E. J. W. , Serpentine textures and serpentinization, Canad . Mineral . ,15 , In press (1977).

Discussion

NOTE: Discussion of this paper was included in the General Discussion at the end of this

session.

I

48
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

THE "ASBESTOS" MINERALS: DEFINITIONS, DESCRIPTION, MODES OF FORMATON,

PHYSICAL AND CHEMICAL PROPERTIES, AND HEALTH RISK TO THE MINING COMMUNITY

Malcolm Ross

U.S. Geological Survey

National Center, 959

Reston, VA 22092

Abstract

The mineralogical description of "asbestos" given here is based on a very special feature common to all forms of commercial "asbestos" - the

property that permits the minerals to separate into long tubes or fibrils

only a few tens of nanometers thick. This separation can be accomplished

by very light grinding or agitation; the common non- fibrous amphi boles do

not separate into such fibrils even after intense grinding. The ease of

such fibril separation may be caused by the special nature of the crystal

structures of the commercial "asbestos" minerals. Repeated twinning on (100) in amosite and crocidolite, the curling of layers of chrysotile to

form tubes, and the presence of triple, quadruple, n-tuple chains

("Wadsley" defects) in amosite, crocidolite, anthophyl 1 ite, and

tremolite, are the structural features that probably promote the

formation of thin fibrils. Stability diagrams in the system MgO-Si02-H20

indicate possible geochemical processes by which commercial "asbestos"

can form.

The relative health risk posed by exposure to the "asbestos"

minerals may be related to the fibril composition, crystal structure,

size, shape, and total surface area. The relative chemical reactivity of

the fibril surface is predicted to be

chrysotile < anthophyl 1 ite < amosite < crocidolite

on the basis of the types of oxidation-reduction and exchange reactions

that may occur. According to epidemiological studies, the relative

health risk appears to be anthophyl 1 ite < chrysotile < amosite < crocidol ite.

"Asbestos" health risks in the mining and milling industry and

environs are reviewed. Health studies done in the chrysotile mining

district of Quebec, Canada, have presented good evidence that realistic

"asbestos" dust standards can be set that not only protect the workers

and residents of the mining areas from undue health risks but probably

allow the industry to operate economically.

Key Words: Actinolite; ambient air; amosite; amphibole; amphibolite;

anthophyl 1 ite; asbestos; asbestos stability; chrysotile; chrysotile

emissions; chrysotile mining; crocidolite; cummingtonite; dust levels;

grunerite; health risk; Homestake Mines, S.D.; hornblende; Hunting Hill

Quarry, Rockville, Md. ; lung cancer; mesothelioma; serpentinite, surface

chemistry; talcbole; Thetford Mines, Quebec, Canada; tremolite; Urals-,

U.S.S.R. ; and Wadsley defects.

49
Introduction

It is generally a rather straightforward, though often time-consuming mineralogical task

to describe the physical and chemical properties of amphiboles and serpentines including

those varieties referred to as "asbestos". Exceptions are minerals such as fibrous tremolite

and fibrous talc that to date do not have adequate mineralogical descriptions. Defining

minerals that constitute an "asbestos" health hazard is an entirely different and a much more complex problem, for it involves many factors not included within the science of mineralogy.

This commentary is concerned with the various definitions of "asbestos" as they relate

to: (1) the medical profession, which must determine which types of mineral particles

constitute an "asbestos" health hazard; (2) the legal and regulatory professions, which must

enact and enforce the laws relating to "asbestos" use; (3) the mineralogical profession,

which must describe the chemical, structural, and physical properties of swch minerals; and

(4) the mining and quarrying industries, which may be affected by these definitions.

What is "Asbestos"?

Three definitions of "asbestos" found in the Glossary of Geology [9, p. 41]^ are quoted

as follows: "asbestos (a) A commercial term applied to a group of highly fibrous silicate

minerals that readily separate into long, thin, strong fibers of sufficient flexibility to be

woven, are heat resistant and chemically inert, possess a high electric insulation, and

therefore are suitable for uses (as in yarn, cloth, paper, paint, brake linings, tiles,

insulation, cement, fillers, and filters) where incombustible, nonconducting, or chemically

resistant material is required, (b) A mineral of the asbestos group, principally chrysotile

(best adapted for spinning) and certain fibrous varieties of amphibole (esp. tremolite,

actinolite, and crocidol ite). (c) A term strictly applied to the fibrous variety of

actinol ite.

The term "asbestos", from a geoscientist' s point of view, applies only to the minerals

chrysotile (one of the serpentine polymorphs), "amosite" (a variety of grunerite),

"crocidol ite" (a variety of riebeckite), anthophyl 1 ite, tremolite, and actinolite when they

are present in sufficient quantity to be commercially valuable for their special physical and

chemical properties, which include fibrous habit, insulation qualities, low electrical

conductivity, fire resistance, and suitability for weaving. Many other minerals sometimes

possess habits described variously as acicular , asbestiform , elongate , fibrous, bladed , lamellar , filiform , pri smatic , or columnar ; for example, minerals of the zeolite group having

acicular habit, fibrous calcite and quartz, acicular wol lastonite, prismatic pyroxenes,

elongate chrystal 1 i tes of attapulgite, and f i 1 iform sepiolite. Since these minerals are not

exploited for the commercially valuable properties listed above, they are not called

"asbestos" by geoscientists.

At present, the most widely used definition of "asbestos" by various groups concerned

with environmental health problems, including the, U.S. Environmental Protection Agency (EPA)

and the U.S. Mining Enforcement and Safety Administration (MESA), is from the notice of

proposed rule-making for "Occupational Exposure to Asbestos" published in the Federal

Register (Oct. 9, 1975, p. 47652, 47660) by the U.S. Occupational Safety and Health

Administration (OSHA). In this notice, the naturally occurring minerals chrysotile, amosite,

crocidol ite, tremolite, anthophyl 1 ite, and actinolite are classified as "asbestos" if the

individual crystallites or crystal fragments have the following dimensions: length - greater:

than 5 micrometers, maximum diameter - less than 5 micrometers, and a length to diameter ratio

of 3 or greater. Any product containing any of these minerals in this size range are also

defined as "asbestos". H

The crushing and milling of any rock usually produces some mineral particles that are within the size range specified in the OSHA rules. Thus, these regulations present a formidable problem to those analyzing for "asbestos" minerals in the multitude of materials

and products in which they may be found in some amount, for not only must the size and shape

of the "asbestos" particles be determined, but also an exact mineral identification must be

made.

^Figures in brackets indicate the literature references at the end of this paper.

50
A wide variety of amphiboles is found in many types of common rocks; many of these

amphiboles might be considered "asbestos" depending upon the professional training of the

person involved in their study and the methods used in mineral characterization. Campbell et

al . [3] have carefully described the differences between the relatively rare fibrous

varieties of the amphiboles and the common nonfibrous forms.

If the definition of "asbestos" from the point of view of a health hazard does include

the common nonfibrous forms of amphibole, particularly the hornblende and cummingtonite

varieties, then we must recognize that "asbestos" is present in significant amounts in many

types of igneous and metamorphic rocks covering perhaps 30 to 40 percent of the United States.

Rocks within the serpentinite belts; rocks within the metamorphic belts higher in grade than

the greenschist facies, including amphibolites and many gneissic rocks; and amphibole-bearing

igneous rocks such as diabase, basalt, trap rock, and granite would be considered "asbestos"

bearing. Many iron formations and copper deposits would be "asbestos" bearing, including

deposits in the largest open-pit mine in the world at Bingham, Utah. "Asbestos" regulations

would thus pertain to many of our country's mining operations, including much of the

construction industry and its quarrying operations for concrete aggregate, dimension stone,

road metal, railroad balast, riprap, and the like. The "asbestos" regulations would also

pertain to the ceramic, paint, and cement industries, and to many other areas of endeavor

where silicate minerals are used.

We do not know whether health investigators will consider other minerals that commonly

possess a fibrous or acicular habit to be health hazards; minerals such as wol 1 astoni te , the

fibrous forms of calcite and quartz, acicular minerals of the zeolite mineral group, the

pyroxenes, the sepiolite minerals including attapulgite, and the calcium silicates found in

Portland cement. Certainly if the common amphiboles such as hornblende, tremolite,

actinolite, gedrite, and cummingtonite with their typical prismatic cleavage are considered

health hazards, the common pyroxenes having similar habits should also be considered health

hazards.

A Mineralogical Description of Commercial "Asbestos"

The commercial deposits of "asbesto^" contain one of the following minerals:

chrysotile, Mg3Si20^(0H)4 ; |mosite, (Fe^ ,Mg)7Si 8022(0H)2 (a variety of grunerite);

crocidolite, NagCFe^ ,Mg)3Fe| Si8022(0H)2 (a variety of riebeckite); "fibrous" anthophyllite, (Mg,Fe)7Si8022(0H)2 ; and "fibrous" tremolite and actinolite, Ca2(Mg,Fe)5Si8022(0H)2.

Tremolite and actinolite are now, as they were in the past, of little economic importance;

anthophyllite is of little economic importance now. About 95 percent of the commercial

asbestos now used in the United States is chrysotile, of which about 90 percent is imported

from Canada. No commercial amosite or crocidolite has ever been mined in the United States.

In addition to being compositional ly different, the five amphibole forms of commercial

"asbestos" have completely different crystal structures from that of chrysotile. The

structure of chrysotile consists of double layers, each consisting of a layer of linked

Si04 tetrahedra that is coordinated to a second layer of linked Mg02(0H)4 octahedra through

the sharing of oxygen atoms; the composite double layer rolls up, like a window shade, to

form long hollow tubes. The diameters of the individual tubes are on the order of 25 nm; the length-to-diameter ratio can vary from 5 or 10 to well over 10,000.

The structures of the amphibole minerals, on the other hand, are composed of strips

or ribbons of linked polyhedra, which join together to form the three-dimensional crystal.

The individual strips are composed of three elements-two double chains of linked (Si,Al)04

tetrahedra that form a "sandwich" with a strip of linked MgOe , FeOe , or AlOg octahedra.

The structural relationship of the upper double tetrahedral chain to the octahedral part

of the strip is shown in figure 1. The three-dimensional arrangements of these strips or "I-beams" [26] orthoamphibole (anthophyllite) and in cl inoamphibole (tremolite, amosite,

actinolite, and crocidolite) are shown in figure 2.

51
re 1. Structural relationship between the

upper double chain of linked

(Si,Al)04 tetrahedra and the octahedra part of the amphibole strip

of "I-beam." The circles represent

Mg, Fe, or Al atoms in octahedral

coordination; at the apices of the

polyhedra are oxygen atoms. Tetrahedral Si and Al atoms are not

shown. The "I-beams" extend

infinitely in a direction parallel

to the c-axis (the fiber axis).

The width of the "I-beam" in the

b-direction is three octahedra.

Figure is modified from Papike and

Ross [26].

ORTHOAMPHIBOLE

Pnma

B

Ta Sin y3 1 ^

7z

7

I- — b —

C LINOAMPHIBOLE C

-^1

Figure 2. Arrangement of the amphibole strips or "I-beams" in (A) orthoamphibole (space

group Pnma ) and (B) cl i noamphibole (space group C2/m). The "I-beams" are viewed end-on (parallel to the fiber c-axis). The central portion of the

"I-beam" is composed of (Mg,Fe,Al)06 octahedra; the upper and lower portions

are composed of double chains of (Si,A104) tetrahedra. The "I-beams" are stacked

in two ways: (1) +++... (cl inoamphibole) , and (2) + -+-... (orthoamphibole).

Figure modified from Papike and Ross [26].

One feature is common to the six "asbestos" minerals: their ready separation into

long fibrils or tubes only a few tens of nanometers in diameter. This separation can be

accomplished by very light grinding or by agitation in water by means of an ultrasonic!

separator. The common nonfibrous amphiboles do not separate into such fibrils even after

intense grinding; instead, they break up along cleavage planes into rather short stubbyl

prisms-though the length-to-diameter ratio may still be greater than 3:1.

52
What causes the special type of fibril separation found in commercial forms of

"asbestos" but generally not in the nonfibrous amphiboles? Three observations are

perti nent:

(1) Chrysotile, which forms individual hollow tubes, can separate into fibrils as thin as the diameter of the individual tube. The chemical bonding between tubes is very

weak and perhaps is due only to van der Waals forces; thus, the tubes are easily separated

from one another.

(2) Amosite and crocidolite "asbestos" from South Africa is repeatedly twinned on (100) as has been observed in electron microscope studies [4,15,25,34]. This "polysynthetic" twinning, which produces repeated planar faults parallel to (100), is extremely

rare in the nonfibrous calcium-rich amphiboles (tremolite, hornblende) and uncommon in

nonfibrous amphiboles of the cummingtonite-grunerite series [30,31,32].

(3) Amosite, crocidolite, fibrous anthophyl 1 ite, and fibrous tremolite have been

shown to possess chain defects, also called "Wadsley" defects [8,15,36,37,38]. These

defects are caused by the formation of expanded "I-beams" that are composed of triple,

quadruple. .. etc. chains of linked (Si,Al)04 tetrahedra rather than the double chains found

in all amphibole crystal structures. If these "I-beams" are expanded indefinitely, the

resulting strip becomes identical with the single talc layer of composition Mg6Si802o(0H)4

recall that the composition of anthophyllite is Mg7Si8022(0H)2 • These expanded "I-beam"

units can intermix with the regular amphibole "I-beams" to form a variety of minerals that

I refer to as "talcboles" in allusion to their hybrid character-between talc and amphibole.

Veblen [38] has described the detailed structures of four of these "talcboles" obtained

from specimens originally described as "fibrous anthophyllite." In these crystal structures, "I-beams" of one or two types form an ordered three-dimensional structure. Veblen

[38] showed evidence, as did Hutchison et al. [15], that disordered arrangements of these

structural units also occur. Hutchison et al. [15] reported the presence of expanded

"I-beam" structures in fibrous tremolite, and Franco et al. [8] reported the apparent

presence of triple-chain lamellae, seen as planar faults on (010), in crocidolite from

Western Austral ia.

Formation of "Asbestos"

How do chrysotile and the "talcboles" form? Modes of origin can be inferred from the

stability relationships among talc, anthophyllite, enstatite, forsterite, antigorite, and

chrysotile given by Hemley et al . , [13]. Their mineral stability fields at 1 kbar H2O, in

terms of crystallization temperature and molality of aqueous silica, are given in figure 3. This figure shows a number of relationships pertinent to the problem of formation of

"asbesti f orm" minerals. As the temperature decreases, forsterite (Mg-rich olivine) can react to form antigorite or chrysotile depending on the silica concentration in the aqueous

solutions to which the ol i vi ne-beari ng rock is exposed. One chemical reaction that may

lead to the formation of brucite-bearing serpentinite is:

2 Mg^SiO^ + 3H2O ^ Mg3Si205(0H)4 + Mg(0H)2 . fosterite chrysotile brucite

This reaction may explain the origin of the very long brucite needles, referred to as "nemalite," that are found in various serpentinites. Thirty-centimeter-long needles of

this mineral were collected by C.E. Brown (U.S. Geol . Survey) from a Quebec serpentinite

locality and were examined by single-crystal x-ray methods (Malcolm Ross, unpub. data).

The brucite needles show hexagonal symmetry, a = 0.315 nm, c = 0.474 nm, and the long

direction of the needles are parallel to the brucite a-direction. The rather marked line

broadening that appears in the x-ray pattern suggests that the brucite needles are composed

of many small crystallites oriented so that their a-axes are parallel to the fiber direction. The brucite needles are intergrown with chrysotile, for chrysotile x-ray reflections

are superimposed on the diffraction pattern of brucite, and extremely long chrysotile

fibrils remain when the brucite needles are dissolved by dilute HNO3.

53
Figure 3. Mineral stability relations in the system MgO-Si02-H20 as a function of log of

molality of aqueous silica and temperature, at 1 kilobar HgO pressure. Figure

modified from Hemley et al . [13].

At higher concentrations of aqueous silica, forsterite may alter to talc by the

reaction:

SMg^SiO^ + SCH^SiO^)^^ ^ 2Mg3Si40^ q(0H)2 + 8H2O .

At silica concentrations near the quartz saturation curve, anthophyl 1 ite can alter directly

to talc by the reaction:

3Mg^Sig022(0H)2 + ^(H^SiO^)^^ ^ 7Mg3Si^0^ qCOH)^ + W^O .

This reaction may be of importance for the formation of fibrous anthophyl 1 ite and talc.

As the temperature decreases and the H2O, Mg^ , and silica activities remain within

geologically reasonable limits, one probable reaction sequence is:

enstatite anthophyl! ite ^ talc.

If the alteration of a chain silicate to talc proceeds by an intragranular reaction,

"tal cbol e-type" phases may form as intermediates between anthophyl 1 ite and talc during

low- temperature alteration [36,37,38]. Figure 4 shows the stability fields of forsterite,

enstatite, anthophyl 1 ite, and talc in terms of temperature and molality of aqueous silica

54
[13]. A stability (or metastabi 1 ity) field for the "talcboles" (labelled "asbestos") is

superimposed on this diagram, overlapping the fields of talc and anthophyl 1 ite. The

fibrous nature of the "talcboles" can be explained if the alteration process of a chain

silicate (anthophyl! ite) to a sheet silicate (talc) proceeds by reforming the double

chains at the unit-cell level. In figure 4, the phase boundary between enstatite (a

pyroxene having the formula Mg2Si20s) and anthophyl 1 ite suggests the possibility of having

mixed single chain (pyroxene) and double chain (amphibole) structures.

2.0-" \ 1 1 8 ' 600 640 ^ 680 720

T C

Figure 4. Adaptation of the enstatite-anthophyl 1 ite-talc-forsterite stability relationships

at 1 kbar H2O to show a possible stability or metastabi 1 ity field of "talcbole

asbestos" (strippled). Figure modified from Hemley et al. [13].

anth. = anthophyl 1 ite.

The fibrous nature of commercial amosite and crocidolite appears to be related to the

crystal growth mechanism; perhaps the crystallites nucleate at many centers and grow as individual fibers only a few tens of nanometers thick (see Franco et al . [8, figures

1,2]). The presence of (100) twinning and "Wadsley" defects may be the result of rapid

growth and, in addition, may hinder growth in a direction perpendicular to the fiber axis.

Properties of "Asbestos" That May Be Related to Health Risk

Health studies suggest that of the four economically important forms of "asbestos,"

crocidolite has been responsible for the greatest health risk, followed by amosite, then

chrysotile, and lastly anthophyl 1 ite [11]. If we assume that the health hazard caused by

the commercial "asbestos" minerals is due to some combination of their chemical, structural,

and physical properties, we can make some predictions about their relative biological

activity.

All commercial "asbestos" minerals separate into very thin fibrils; possible reasons

for this have been discussed previously. The thickness, length, and flexibility of the

fibrils apparently is important in determining how the fibrils lodge in human tissue and

55
how readily they are cleared from the lung areas. The straight fibrils of small diameter,

particularly those of crocidolite, can more readily move to the periphery of the lung,

where they are in a position to penetrate the pleura and thus produce mesotheliomas [11].

That curly fibrils, especially those of chrysotile, are more readily arrested in the upper

respiratory tract is given as a reason for the low incidence of mesotheliomas in chrysotile

miners and millers [11,19,23]. Assessment of the role of fibril size in relation to lung cancer is less clear [11]; however, Gross [12] cited evidence that "asbestos" fibers less

than 5 pm long cause negligible pathogenicity, both of the lung and pleura.

The problem of fibril size in relation to cancer incidence is of some importance, for

the average ambient airborne "asbestos" fiber is shorter than the average fiber in the

whole rock. Brulotte [2] reported that the average concentration of airborne dust particles

in the chrysotile mining district of Thetford Mines, Quebec, was 80,500 ng/m^ during active

mining and 39,600 ng/m^ during a 5-month period when the mines were closed. If we assume

that the rock contains 4 weight percent chrysotile, these measurements suggest a minimum

chrysotile dust concentration in the ambient air of 3220 and 1584 ng/m^.^

The total surface area of the inhaled fibrils and the chemical reactivity of this

surface may have an important influence in the production of cancer.

Researchers have not yet determined whether this surface plays a direct part in the

formation of cancerous tissue, or whether a carcinogenic chemical adheres to the mineral

surface and the chemical itself later reacts with the tissue or in some way catalyzes the

carcinogenic process. The high incidence of lung cancer in men who worked in the "asbestos"

trades (textiles, brake- lining fabrication, insulating) and who also smoked [33] indicates

that carcinogenic chemicals in the tobacco smoke may somehow interact with the "asbestos"

fibrils. If many of the fibrils are not easily cleared from the lung, they may adsorb

these chemicals and hold them indefinitely. Injection of "asbestos" fibrils directly into

the pleura of animals causes a high incidence of mesothelioma [40]. These experiments

suggest a direct relationship between the active fibril surface and production of pleural

cancer. However, other dissimilar substances injected into animals also cause tumors; for

example, nonfibrous hematite (Fe203), sanidine (KAlSisOg), and corundum (AI2O3) [27].

As a generalization, the relative chemical reactivity of the exposed fibril surfaces

of the four important forms of commercial "asbestos" in aqueous solutions is:

chrysotile < anthophyl 1 ite < amosite < crocidolite.

Chrysotile, the least reactive of the four, is composed of rolled-up layers that possess

no broken chemical bonds except where the edges of the layers are exposed at the ends of

the tubes. The three amphiboles, on the other hand, have broken chemical bonds on all

surfaces of the fibrils.

Anthophyl 1 ite can alter to various other silicates in aqueous solutions, as has been

explained above. Similar alteration mechanisms might also exist for crocidolite and amosite

although, to my knowledge, these have not been documented. However, studies of the

^Conversion of these figures (nanograms chrysotile per cubic meter of air) to numbers of

"fibers" per cubic centimeter of air (the value usually given in health studies) is

estimated by using the following relations:

(1) density of chrysotile = 2.5g/cm^ = 2. 5xl0^ng/cm^

(2) volume of 1 ng chrysotile = 4x10 ^°cm^ = 400 pm^

(3) volume of chrysotile fibers in pm^/cm^ = ^"^500^

(4) if a fiber having dimensions 1 pm x 1 pm x 5 pm (5 pm^) is designated as a "standard fiber," then

1 ng chrysotile = 80 "standard fibers"

(5) number of chrysotile "standard fibers"/cm3 = ^"9^^^^

56
geochemistry of silicates indicate that the exposed surfaces of these two amphiboles

present some interesting possibilities for chemical change. Amosite (and also crocidolite)

can undergo oxidation-reduction reactions of the type,

Fe^"^Sig022(0H)2 IFeg'^Fe2"^Sig02202 + H2

Ernst and Wai [6] have demonstrated that this reaction takes place in iron-bearing sodic

amphiboles at 705 °C. The complete reversibility of such a reaction in the chemically

similar silicate mineral biotite, has been demonstrated by Wones [42] and by Takeda and

Ross [35]. In the experiments of Wones, auto-oxidation was accomplished in a neutral

atmosphere (flowing argon) at 500-700 °C. Reduction was accomplished by passing hydrogen

gas over the crystals. Analogous reactions can take place at much lower temperatures

but also at much lower rates.

Cation exchange reactions take place in the amphiboles known as richterites [14];

exchange is accomplished within the A-site of the amphibole structure at 775-850 °C by the

reaction:

(Na)CaNaMg^Sig022(0H,f)2 + K"^ t (K)CaNaMg^Sig022(0H,F)2 + Na"^.

Crocidolite having a partially filled A-site such as that from Bolivia [41] can also undergo

exchange reactions with potassium being replaced by sodium and possibly by oxonium and

ammonium ions. Crocidolite with a partially or completely vacant A-site may undergo exchange

reactions coupled with oxidation-reduction, e.g.:

Na2Fe3'^Fe2^'^Sig022(0H)2 + R"^ + e" (R"^)Na2Fe^^"*'Fe^'^Sig022(0H)2

where R^ = K^, Na^, H^O^, or NH^, and a = a vacant site.

Whether such reactions can take place within animal tissue is not known, but the charged

and reactive surfaces of crocidolite and amosite fibrils appear to offer excellent sites or templates for the initiation of complex chemical changes.

The surface area available for adsorption is, of course, directly related to fibril

thickness or diameter. The specific surface of chrysotile, as measured both by nitrogen

adsorption and permeability, is about twice that of amosite and crocidolite [28]. Because

chrysotile forms hollow tubes, this larger area for adsorption in chrysotile is predictable

if the average fiber thickness is similar for all three minerals.

The strain-free layer of chrysotile has a radius of curvature of about 8.8 nm [5]; thus,

the minimum diameter of the tube should not be much less than 17 nm. The most frequently

measured tube diameter is about 26 nm. Bates and Comer [1] found in a study of chrysotile

from Arizona and Quebec a range of diameters from 11.4 to 85 nm; the average diameter was 25

nm. The fiber size ranges in the other forms of commercial "asbestos" have not come to my

attention, although some crocidolite fibers from Western Australia [8] appear to be on the

order of 50 nm wide.

"Asbestos" Health Risks in the Mining and Milling Industry and Environs

Although a significant health risk for those who work in the "asbestos" trades,

particularly for those who smoke, has been well documented, the risk appears to be much

lower for those in the chrysotile mining and milling industry and for those who reside in areas of such activity. The most detailed study of an "asbestos" mining community is that

of the chrysotile mining areas of Quebec, Canada; the studies were started in 1966 and

continue to the present [20-23]. Similar studies of chrysotile miners on a smaller scale

have been undertaken by Kogan et al. [16] in the Urals, U.S.S.R. , and by Vigliani [39] in

Italy. According to McDonald [17,18] these other studies came to the same conclusions on health risk as the Quebec studies, the latter of which have led the way in making some assessment of the health risk relative to the amount of dust to which the workers were

exposed. Health-risk studies of workers in the "asbestos" trades, for the most part, have

not given reliable dust-exposure figures, or even the relative amounts and types of

"asbestos" inhaled.

57
Chrysotile has been mined in the Thetford Mines, Black Lake, and asbestos localities of

Quebec for nearly a century, beginning in 1886. Production has increased steadily since

then, reaching 907,000 metric tons in 1956 and 1,500,000 metric tons in 1976. A tremendous

amount of ambient dust has been generated over the years both by mining activities and by the

winds blowing over the huge tailings piles. Even in 1974, when dust-emission controls had

much improved over those of the earlier years (72 million particles per ft^ in 1950 to 4

million particles per ft^ in 1975 [20]) as a result of wet drilling, watering of haul roads,

etc. , emissions of particles from chrysotile mining and milling operations in the Province of

Quebec amounted to 140,000 metric tons, of which about 4 percent (5600 metric tons) was "asbestos" dust [2]. The ambient dust levels for this region have already been discussed.

Is there a high incidence of cancer of the lung and pleura among the 35,000 residents of

the Thetford Mines area of Quebec, 10 percent of whom are employed in the chrysotile industry?

According to McDonald et al . [17-23], the cancer incidence for the male employees in the

Quebec chrysotile industry is similar to that for Canada as a whole and only detectably raised

in those with moderate to high levels of exposure. In Table 1 is given the proportional

mortality from lung cancer and mesothelioma for the Quebec and North Italian chrysotile

miners and millers, and also for the entire populations of various countries in the year 1970.

In the period 1936-1973, seven cases of mesothelioma have been reported in the Quebec mining

and milling industry [19, Table 12]. The worldwide incidence of mesothelioma in those who

worked in the chrysotile mining and milling industry for the period 1958 to 1976 is 11 cases

[19, Table 4]. The Canadian studies do show an increased incidence (2.1 to 3.6 times) ^f lung cancer for those workers exposed to the highest concentrations of dust -- 400 to 800 mpcfyr^, but little evidence of health risk from this disease at levels below 200 mpcf-yr.

An unusually high number of deaths caused by lung cancer in Homestake gold miners during

the period 1960 to 1973 has been reported by Gil lam et al . [10]. The cohort consisted of 440

individuals who in 1960 had worked 5 years or more underground. Gillam et al . attributed the

high incidence of lung cancer to inhalation of cummi ngtonite amphibole. They did not specify

whether the hornblende amphibole, also present in the rock being mined, contributed to health

risk. In rebuttal to this work, McDonald et al . [24] reported on a health analysis of a cohort of 1321 Homestake miners whose working period was from as far back as 1937 to the end

of 1973; each of the miners had more than 21 years mining service. Deaths resulting from

malignant neoplasm were very close to those expected (93 observed, 90.5 expected); this

includes the subcategories of malignant neoplasm -- respiratory, gastro-intestinal , and

"other" cancers. The excess death found in the Homestake miners was due in fact to silicosis,

silico-tuberculosis, and heart disease. McDonald et al . [24] stated, "The pattern of

mortality of men with long employment in this industry indicates a serious pneumoconiotic

hazard characteristic of hard rock miners, but not of cancer."

Fears [7] has made an epidemiological study of cancer risk, including respiratory

cancer, in 97 U.S. counties in 22 states known to be mining chrysotile or amphibole

"asbestos." He found no excess of cancer mortality compared with cancer mortality

rates in 194 demographically matched counties in which such minerals are not known to be

mined; cancer mortality in both groups of counties was significantly below the national

average.

^This unit expresses (in millions) the average number of particles (including approximately

4 percent chrysotile) contained in each cubic foot of air inhaled during a worker's career

in the mines or mills times the number of years the worker was employed. If the dust is

assumed to contain 4 percent chrysotile, then working for 50 years at a dust level of

16 mpcf (800 mpcf-yr ) is roughly equivalent to inhaling 23 chrysotile particles for every

cm^ of air taken into the lungs during the employment lifetime. A figure of 200 mpcf-yr

is roughly equivalent to 6 particles of chrysoti 1 e/cm^. Conversion from dust particle

measurements to chrysotile fibers per cm^ is difficult because chrysotile abundance varies

from place to place.

58
Table 1. Proportional mortality from lung cancer and mesothelioma for selected

male populations.

Cohort Deaths

Group No. men All causes % lung cancer % mesothelioma

General population ^

Canada (1970) 82,052 5.3 0.03

USA (1970) 988,620 5.1 0.03

Finland (1970) 22,332 7.1 0.04

Italy (1970) 252,795 4.7

England - Wales (1970) 278,617 8.9 0.06

Chrysotile mining-milling ^

Quebec (1936-73) 10,951 3,938 5.7 0.18

N. Italy (1932-70) 1,098 270 2.2 0

Anthophyl 1 i te mini ng-mi 1 1 i ng

^

Finland (1936-67) 900 216 9.7 0

"Asbestos" trades

Insulators 26,505 2,137 19.6 6.7

Asbestos factory 10,781 1,422 15.0 3.1

^ Entire male population over 24 years of age [19, Table 13],

[19, Table 12; 20, p. 525].

^ [19, Table 12].

^ Composite figures [19, Table 12].

At present, people are concerned about the possible health hazards associated with

the quarrying of serpentine rock at Hunting Hill quarry near Rockville, MD, and its use as

a surface material for roads, playgrounds, and parks. The rocks being quarried here are very similar geologically to those of the chrysotile mining localities of Quebec, except

that they contain much less chrysotile - about 0.5 weight percent. Rohl et al . [29] from

Mount Sinai Hospital reported chrysotile fiber abundances of 500 to 4700 ng/m^ of air

sampled adjacent to roads and a parking lot paved with loose crushed stone from the

Hunting Hill quarry. The highest figures were measured during "moderate" motor vehicle

use. The Mt. Sinai figures are equivalent to 0.2 to 1.9 |jm^ of chrysotile per cm^ of air

or 0.04 to 0.4 "standard fibers" per cm^ of air. Air samples taken near the perimeter of

the Hunting Hill quarry gave chrysotile mass concentrations of from 0.02 to 64 ng/m^

or 2 X 10 ^ to 5 X 10 ^ "standard fibers" per cm^ of air (U.S. Bureau of Mines, State of

Maryland, and McCrone Assoc., unpublished data). The present U.S. Government limits for

"asbestos" content of air are 2 fibers/cm^ (OSHA) and 5 fibers/cm^ (MESA) where a fiber

is defined as longer than 5 |jm, less than 5 |jm wide, and having a length-to-width ratio

of 3: 1 or greater.

The publicity about the possible health risk because of dust emission from the

Hunting Hill quarry and its rock products had caused the quarry to lose about 30 percent

of its business by July 1, 1977. Montgomery County, MD, expected to pay about $2.3 million

in its initial effort to seal the roads so as to reduce dust emissions and to remove loose

stone from the parks (The Counci 1 Report , Montgomery County, vol. 6, no. 22, July 1,

1977). Apparently, other mining and quarrying operations along the "serpentine belt" of

the eastern U.S. from Maine to Alabama also will be considered health risks to the general

public [29]. Rohl et al . [29] suggested that exploitation of crushed amphibolite rock

also raises the possibility of contamination of the air by "asbestos"-l i ke minerals.

59
Discussion

The cancer incidence among those employed in the chrysotile mining and milling industry

does not appear to be excessive when compared to national populations (Table 1). However,

the incidence of cancer among those employed in the "asbestos" trades is very high (Table

1 )

; incidence of lung cancer being 3 to 4 times that of the average population, incidence

of mesothelioma being 130 to 220 times that of the average population. The "asbestos"

trades generally utilized a variety of "asbestos" minerals including amosite and/or

crocidolite, sometimes mixed into a paste for lagging. If we consider that about 90

percent of all the commercial "asbestos" ever mined was chrysotile, and that there is a low

incidence of cancer in the chrysotile mining industry, we are led to conclude that either

amosite and crocidolite are very hazardous or that there is an additional factor relating

to health risk in the "asbestos" trades which has not yet been discovered. Previously, I have discussed some reasons why these two minerals may be more chemically reactive than

chrysotile. Definitive epidemiological studies of the amosite mining regions of South

Africa and the crocidolite mining regions of South Africa, Bolivia, and Australia appear

to be lacking; such studies are needed in order to understand the high cancer incidence in

certain trades utilizing these minerals. It is important to point out that the "asbestos"

minerals should be considered separately when analyzing their effects on the worker's

health. Reasoning by analogy is dangerous; high cancer incidence associated with one form

of "asbestos" in a particular occupation does not necessarily mean that there will be the same incidence when utilizing another form of "asbestos" in that or another occupation.

Unfortunately, this type of reasoning has led many to assume that any amphibole in any

environment will cause high cancer mortality.

The operational problems in defining and characterizing fine mineral particles and

the unknown health effects on humans by minerals not generally regarded as "asbestos"

appear to be causing more and more investigators to accept rather broad definitions for

"asbestos." The present analytical techniques used by the EPA and OSHA do not distinguish

between amphibole cleavage fragments and the minerals geosci enti sts generally consider to

be true "asbestos." In fact, if electron diffraction is not used expertly, many pyroxenes

might be called "asbestos." For example, bronzite, a common orthopyroxene having the

composition (Mg , Fe)8Si 3624 , is very similar chemically to amphiboles of the cummingtonitegrunerite series, (Mg,Fe)7Si8022(0H)2. Also, orthopyroxene gives an electron diffraction

pattern similar to that of cummingtonite--both patterns possess 0.26 nm spacings between

the diffraction row lines in the ho£ reciprocal lattice net. A full interpretation of the

patterns is necessary for positive identification. Similarly, calcic pyroxenes might be

confused with amphiboles of the tremol ite-acti nol ite series or with hornblende. Cummingtonite (and possibly hornblende) is considered an "asbestos" health hazard by health

investigators from the National Institute of Occupational Safety and Health (OSHA), as reported by Gil lam et al . [10]. The Mt. Sinai group [29] suggested that crushed amphibolebearing rocks (amphibol ite) used as road-surfacing material may result in widespread

"asbestos" contamination of community air.

Along with the general use of broader definitions of "asbestos" is a trend toward

setting lower and lower limits on the acceptable amount of "asbestos" permitted in the

environment (at present the OSHA standard is 2 fibers/cm^; the MESA standard is 5 fibers/cm^, but it will soon be changed to the OSHA value).

A more stringent "asbestos" health standard is presently being proposed by the

National Institute for Occupational Safety and Health (Reexamination and Update of

Information on the Health Effects of Occupational Exposure to Asbestos , December 1976;

document prepared by NIOSH for transmittal to OSHA, as requested by the Assistant

Secretary of Labor). This document states (p. 92-93): "Evaluation of all available human

data provides no evidence for a threshold or for a safe level of asbestos exposure."

"In view of the above, the standard should be set at the lowest level detectable by

available analytical techniques ."

"Since phase contrast microscopy is the only generally available and practical

analytical technique at the present time, this level is defined as 100,000 fibers >5 pm

in length/m^ (0.1 fibers/cc) ."

60
A definition of "asbestos" to include many amphiboles, chrysotile, and possibly other

minerals that appear fibrous or acicular in the electron microscope coupled with a fiberconcentration standard of 0.1 fibers/cm^ should serve to shut down a large number of our

hard rock mines and quarries. Also, nothing has yet been said about the effect of such

standards on construction workers building highways, tunnels, bridges, or dams on amphibolebearing rock, nor of the agricultural workers who are exposed to fiber-containing dust

while working the croplands. If the present concept of low or "zero threshold" health

risk and broad use of "asbestos" definitions continue, much of the crust of the earth

could be considered a health hazard.

A way of minimizing the effect on the mining industry of the present and proposed

"asbestos" standards, yet still maintaining a good level of health safety, is presented by

the Canadian studies of the Quebec chrysotile workers. Here J. C. McDonald and his

colleagues G. W. Gibbs, A. D. McDonald, M. R. Becklake, J. Siemiatycki, C. E. Rossiter,

F. D. K. Liddell, 0. A. El Attar, A. Harper, and many others [17-23] have undertaken not

only to delineate areas of health risk in the Quebec environment but also to assess the

exposure limits of rock dust where the incidence of cancer and other diseases is at an acceptably low level. No occupation can be considered to have a zero health risk. It

would seem that similar studies in this field would be of value in the United States.

References

[1] Bates, T. P., and Comer, J. J., Further observations on the morphology of chrysotile

and halloysite. Clays Clay Min . , 6, 237-247 (1959).

[2] Brulotte, Raynald, Study of atmospheric pollution in the Thetford Mines area, cradle

of Quebec's asbestos industry. Atmospheric Pol 1 ution , M. M. Benarie, ed. , Elsevier

Sci. Pub., Amsterdam, 447-458 (1976).

[3] Campbell, W. J., Blake, R. L. , Brown, L. L. , Cather, E. E. , and Sjoberg, J. J.,

Selected silicate minerals and their asbestiform varieties: mineralogical

definitions and identification-characterization, U.S. Bureau of Mines Information

Circular 8751 , 56 pp. (1977).

[4] Champness, P. E. , Cliff, G. , and Lorimer, G. W. , The identification of asbestos, J. Microscopy , 108 , 231-249 (1976).

[5] Deer, W. A., Howie, R. A., and Zussman, Jack, Rock-formi ng Minerals , vol . 3, Sheet

Si 1 icates , Longmans, Green, and Co. Ltd., London (1962).

[6] Ernst, W. G. , and Wai , G. M. , Mdssbauer, infrared, x-ray, and optical study of cation

ordering and dehydrogenation in natural and heat-treated sodic amphiboles. Am . Mineral . . 55, 1226-1258 (1970).

[7] Fears, T. R. , Cancer mortality and asbestos deposits. Am. J. Epidemiology , 104 , 523-

526 (1976).

[8] Franco, M. A., Hutchison, J. L. , Jefferson, D. A., and Thomas, J. M. , Structural

imperfection and morphology of crocidolite (blue asbestos). Nature, 266 , 520-521

(1977).

[9] Gary, Margaret, McAfee, Robert, Jr., and Wolf, C. L. , Glossary of Geology , (Am.

Geological Inst., Washington, D. C. , 1972).

[10] Gillam, J. D. , Dement, J. M. , Lemen, R. A., Wagoner, J. K. , Archer, V. E. , and

Blejer, H. P., Mortality patterns among hard rock gold miners exposed to an asbestiform mineral. Annals. N.Y. Acad . Sci. , 271, 336-344 (1976).

[11] Gilson, J. C. , Asbestos cancers as an example of the problem of comparative risks,

Inserm Symposia Series , 52, lARC Scientific Publications No. 13, Environmental

Pollution and Carcinogenic Risks, 107-116 (1976).

61
[12] Gross, Paul, Is short-f ibered asbestos dust a biological hazard? Arch . Envi ron . Health , 29, 115-117 (1974).

[13] Hemley, J. J., Montoya, J. W. , Shaw, D. R. , and Luce, R. W. , Mineral equilibria in the

MgO-Si02-H20 system: II Talc-antigorite-forsterite-anthophyll ite-enstatite stability

relations and some geologic implications in the system. Am. J. Sci . , 277 , 353-383

(1977).

[14] Huebner, J. S. and Papike, J. J., Synthesis and crystal chemistry of sodium-potassium

richterite, (Na,K)NaCaMg5Si8022(0H,F)2: A model for amphiboles. Am. Mineral . , 55,

1973-1992 (1970).

[15] Hutchison, J. L. , Irusteta, M. C. , and Whittaker, E. J. W. , High-resolution electron

microscopy and diffraction studies of fibrous amphiboles. Acta Cryst . , A31 , 794-801

(1975).

[16] Kogan, F. M. , Guselnikova, N. A., and Gulevskaya, M. R. , The cancer mortality rate

among workers in the asbestos industry of the Urals, Gig . Sanit . 37, 29-32 (1972).

[17] McDonald, J. C. , Cancer in chrysotile mines and mills. Biological Effects of Asbestos , Lyon, International Agency of Res. on Cancer, 189-194 (1973a).

[18] McDonald, J. C. , Asbestosis in chrysotile mines and mills. Biological Effects of

Asbestos , Lyon, International Agency of Res. on Cancer, 155-159 (1973b).

[19] McDonald, J. C. , and McDonald, A. D. , Epidemiology of mesothelioma from estimated

incidence. Preventive Med . , 6, 426-446 (1977).

[20] McDonald, J. C. , and Becklake, M. R_. , Asbestos-related disease in Canada, Hefte z. Unfal 1 hei 1 kunde , 126, 2. Deutsch-Osterreichisch-Schweizerische, Unfalltagung in

Berlin 1975, Springer-Verlag, Berlin, 521-535 (1976).

[21] McDonald, A. D. , Harper, A., El Attar, 0. A., and McDonald, J. C. , Epidemiology of

primary malignant mesothelial tumors in Canada, Cancer , 26 , 914-919 (1970).

[22] McDonald, J. C. , McDonald, A. D. , Gibbs, G. W. , Siemiatycki, J., and Rossiter, C. E. , Mortality in the chrysotile asbestos mines and mills of Quebec, Arch . Envi ron . Health , 22, 677-686 (1971).

[23] McDonald, J. C. , Becklake, M. R. , Gibbs, G. W. , McDonald, A. D. , and Rossiter, C. E.

,

The health of chrysotile asbestos mine and mill workers of Quebec, Arch. Envi ron . Health , 28, 61-68 (1974).

[24] McDonald, J. C. , Gibbs, G. W. , Liddell, F. D. K. , and McDonald, A. D. , Mortality after

long exposure to cummi ngtoni te-grunerite (abstr.). Am. Rev . Resp . Pi sease , Supp . , 115 , No. 4, 230 (1977).

[25] Nord, G. L. , Jr., "State-of-the-Art" of the analytical transmission electron microscope, in Proc. Symposi urn on El ectron Microscopy and x-ray appl i cations to envi ron- mental and occupational health analyses , Ann Arbor Sci . Publ . , in press (1978).

[26] Papike, J. J., and Ross, Malcolm, Gedrites: Crystal Structures and intracrystal 1 ine

cation distributions. Am. Mineral . 55, 1945-1972 (1970).

[27] Pott, F. and Friedrichs, K. H. , Tumoren der Ratten Nach I. P. Injektion faser formiger

Staube, Naturw . , 59, 318 (1972).

[28] Rendall, R. E. G. , The data sheets on the chemical and physical properties of the

U.I.C.C. standard reference samples, in Pneumoconiosi s , H. A. Shapiro, ed.

,

Oxford U. Press (1970).

[29] Rohl , A. N. , Langer, A. M. , and Selikoff, I. J., Environmental asbestos pollution

related to use of quarried serpentine rock. Science, 2%, 1319-1322 (1977).

62
[30] Ross, Malcolm, Papike, J. J., and Weiblen, P. W. , Exsolution in cl inamphi boles,

Science, 159, 1099-1102 (1968a).

[31] Ross, Malcolm, Smith, W. L. , and Ashton, W. H. , Triclinic talc and associated

amphiboles from the Gouverneur Mining District, New York, Am. Mi neral . , 53, 751-769

(1968b).

[32] Ross, Malcolm, Papike, J. J., and Shaw, K. W. , Exsolution textures in amphiboles as indicators of subsolidus thermal histories, in Mineral . Soc. Am. special paper no . 2, J. J. Papike, ed. , pp. 275-299 (1969).

[33] Selikoff, I. J., Hammond, E. C. , and Churg, Jacob, Asbestos exposure, smoking, and

neoplasia, J. Am. Med. Assoc .

, 204, 106-112 (1968).

[34] Seshan, K. and Wenk, H.-R., Identification of faults in asbestos minerals and application to pollution studies, in Proc . El ectron Microscope Soc . Am . , 34th annual meeti ng , G. W. Bailey, ed. , 616-617 (Claitor's Pub. Div. , Baton Rouge, LA, 1976).

[35] Takeda, Hiroshi and Ross, Malcolm, Mica polytypism: Dissimilarities in the crystal

structures of coexisting IM and 2Mi biotite. Am. Mineral . , 60, 1030-1040 (1975).

[36] Veblen, D. R. and Burham, C. W. , Triple-chain biopyriboles: Newly discovered intermediate products of the retrograde anthophyl 1 ite-talc transformation, Chester, Vt. , (abstr.). Trans . Am. Geophys . Union , 56, 1076 (1975).

[37] Veblen, D. R. and Burnham, C. W. , Biopyriboles from Chester, Vermont: The first

mixed-chain silicates (abstr.), Geol . Soc. Am. Abstracts with Programs 8, 1153 (1976).

[38] Veblen, D. R. , Triple-and mixed-chai n biopyriboles from Chester , Vermont , Ph.D.

thesis, Harvard University, Cambridge, Mass. (1976).

[39] Vigliani, E. C. , Asbestos exposure and its results in Italy, in Proc . International

Conf. on Pneumoconiosis , Johannesburg , Oxford U. Press, 192-196 (1970).

[40] Wagner, J. C. , Berry, G. , and Trimbrell, V., Mesothel i omata in rats after inoculation

with asbestos and other materials, Brit . J. Cancer, 28, 173-185 (1973).

[41] Whittaker, E. J. W. , The structure of Bolivian crocidolite. Acta Cryst . , 2, 312-317

(1949).

[42] Wones, D. R. , Physical properties of synthetic biotites on the join phlogopite annite.

Am. Mineral . 48, 1300-1321 (1963).

Discussion

NOTE: Discussion of this paper was included in the General Discussion at the end of this

session.

63

National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

GENERAL DISCUSSION OF MINERAL08ICAL ASPECTS

L. SWENT: Homestake Mining Company management is very aware of the implications that

the Homestake mine study referred to by Mr. Ross will have for industry. We believe that

we have a serious responsibility to see that a study is done and that it is a properly

done study.

The first study, done by NIOSH without consultation with Homestake Mining Company, was published in June 1976, and contained a number of serious defects of procedure, assumptions,

and reasoning, which make its conclusions invalid.

As a result, NIOSH and Homestake Mining Company have entered into a cooperative

arrangement for a second study. The mortality analysis part of the study has been con- tracted to SRI International. NIOSH has begun the environmental sampling work in the

mine, and SRI has started reviewing the Homestake personnel records for the mortality

study.

Anyone interested in reading a critique setting forth the defects which invalidated

the conclusions of the first NIOSH study may obtain a copy by writing to: L. W. Swent,

Vice President-Engineering, Homestake Mining Company, 650 California Street, San Francisco,

California 94108.

W. DIXON: I wanted to ask Malcolm Ross if he has studied fibers which are intermediate between talc and anthophyl 1 i te in their characteristics and composition?

M. ROSS: Yes, that is the work of Veblen, Buseck, and Burnham; their papers on this

will be coming out within the next few months (Science, Vol. 198, p. 359-365). These

minerals are intermediate chemically and structurally between anthophyl! ite and talc.

They have been found in two or three places; I'm sure we'll probably find more.

DIXON: I'd like to make a general request that if anyone participating in this

conference has comments to make on the toxicity of those types of materials mentioned

above I would be glad to hear of any information that might be available.

NOTE: No response was received to this request. (CCG).

R. LEE: I would like to make a comment on a couple of things. First is the outward

morphology of amosite versus cleavage fragments; it's generally been written in the

literature, which I've seen, that they're indistinguishable. This is, I think, the way a lot of people look at it. We've been doing some studies on amosite, penge amosite versus

grunerites, and we find that indeed in the amosite it's generally a (100) face when you

get a single crystal diffraction pattern near 0,0 on your microscope. In the grunerites,

they tend to lie about 28° away from this, which puts them on a (110) face, in other words

a cleavage plane. The second comment is that our studies on the size distributions of

airborne particles show that the aspect ratio of airborne serpentines and very fibrous

amphiboles tend to be much, much larger than the size distribution of the corresponding

cleavage fragments which were airborne. Something like a minimum of 30 to 1, or an average of 30 to 1 for the particles we observed in an electron microscope, versus about 7 or 8 to 1 for amphibole fragments. But the point I want to make is that we should not

only be looking at the health effects, we should be making sure that we know whether we

are looking at cleavage fragments or at amosite.

ROSS: To add to this, Ann Wiley brought up one clue as to whether amosite or grunerite is really similar to the penge amosite from South Africa. Do the minerals have

parallel extinction at the very highest optical magnification? Most of the garden variety

cummingtonite-grunerite minerals have inclined extinction; even for the individual

crystallites. The parallel extinction is caused by small lamellae randomly oriented about

the fiber axis. Optically the specimen looks orthorhombic; optical observation is the

65
first technique to use in order to get an idea whether an amphibole may be similar to the

known commercial asbestos.

N. TATE: I wonder if you know of Judge Bowder's investigation among the miners in

Quebec, where he's found very heavy incidence of disease which was not previously

reported. Figures range from 45 percent among workers, nonsmokers with low exposures,

up to 70 percent lung changes in workers with heavy exposures. I also had the opportunity

of talking to Prof. McDonald just before I left London. He has a new study which will be

published shortly; he says he's found excess disease among the miners at Thetford, half

of it the normal asbestos diseases and half of it shows that asbestos workers have lower

resistance to all disease. These are two studies which I think should be taken into

account.

ROSS: Certainly, that's why I want to bring out the Canadian work. It should be

taken into account; but you have to recall that these men have been exposed to heavy dust.

Friends of mine who go there on geological field trips tell me that up until recently

people would hose down the windows in the morning to see out of them, that's how thick the

dust was up there. They have, in the past, gotten tremendous amounts of dust in their

lungs. Now what the Canadian study is attempting to do is to divide the workers into what

they consider low, intermediate, heavy, and very heavy exposure levels to see if they can

see a difference in health risk. Now the reports I've seen indicate that below 200 mpcfyr there's a very low health risk, but all I know is what I read in their papers. I want

to point out that somewhere we have to find a tolerable health risk or we'll have to close

down the surface of the earth.

A. SUNDARAM: Dr. Ross, I'm wondering how you graded the various types of asbestos in

relation to the toxicity or pathogenicity? There are at least four distinct types of

pathogenicity arising from asbestos exposure: asbestosis, lung cancer, mesothelioma, and cancer of the gastrointestinal track; also it is claimed in other organs. When you graded

it so easily: crocidolite, amosite, anthophyl 1 ite , and chrysotile, did you do the gradation

yourself or are you quoting any paper?

ROSS: I 'm quoting Gilson.

SUNDARAM: And is the gradation based on animal data or epidemological data?

ROSS: I can give you the reference (Inserm Symposia Series 52, p. 107-116 (1976));

it's a summary paper by Gilson where he suggested this generalization. Perhaps you can find something wrong with it, but it was a generalization. I made an additional generalization that the chemical activity of these four minerals seemed to be similar in that

crocidolite can undergo on the surface more chemical reactions than amosite, and amosite

more than anthophyl! ite, and chrysotile being the least chemically reactive. I'm just

pointing this out as a generalization, something to start from; maybe it might give some clues for the formation of cancer, I don't know. It may not be that it is the only factor,

because the shape and the aerodynamics are apparently very important, and the lung clearance

functions are very important, so there are many parameters that have to be taken into

consideration. The chemical reactivity of the surface is one of them. I believe that the

chemical reactivity of the surface is important. Consider a standard fiber 1x1x5 pm in

size. There will be 100 times more surface area if you divide a standard fiber into

10,000 smaller fibers. So one big fiber might be a 100 times less effective, as far as the surface chemistry is concerned, than 10,000 small ones - yet they both would have the same weight in nanograms.

SUNDARAM: So you mean to say that the gradation is based on chemical reactivity and

not on any toxic parameter?

ROSS: Well, I'm saying chemical reactivity may enter into the toxic parameters.

What causes lung cancer? Does the fiber interreact with a chemical such as in tobacco

smoke and then with the human tissue, and so forth? Does the fiber interreact directly

with the human tissue chemically? I'm basically getting down to a chemical answer in the

end.

66
B. WHITE: As you know we are in the process of putting together so called emergency

regulations, relative to the Rockville Quarry. Now these regulations deal primarily with

the containment of the crushed stone. You're inferring that you feel that this sort of

approach is not indicated based on the Canadian work?

ROSS: The Canadian work would suggest there is not a health danger with this level

of asbestos dust. Now all the data are not in. What we would need is ambient air

measurements in the Rockville area. Dr. Selikoff suggested, at the National Institutes of

Health hearing on this a few weeks ago, 45 nanograms is the limit in ambient air. What

level of ambient air do you want to have for chrysotile? I haven't seen an ambient air

figure for the Washington, D.C. area. I don't know what it is. I'm really pointing out

that we can shut down all the serpentinite quarries on the East Coast. If it's

serpentinite it is going to have some chrysotile in it. But then, where do we go from

there? We also have tremolite; we can shut down other mines because of tremolite or because of fibrous hornblende and on and on and on. Now I think that I'm pointing out,

from a mineralogical and geological point of view, that this is an immense problem. EPA

is now getting set up to get crusher runs on mines and quarries all down the East Coast.

It's going to run into millions of dollars. It's already running into millions in the

Montgomery County area. Now I think that the health people have got to get together and

decide what they're going to call asbestos, what dust levels are going to be considered

dangerous, and what sort of mining operations they think they are going to have to shut

down. You can shut down a mining operation very easily by putting so many requirements on

it that the contractors say, "heck with it, I'll go to Frederick and get carbonate rock."

I'm pointing out it's an immense problem, it's economic, it's political, it's health, and

so forth.

WHITE: I agree with you very much; our intent is certainly not to close down the

mine, and I agree also that the health people must come to grips with the issue of the

ambient air. Now obviously since there are no standards, our approach is purely on the

mechanical side of this, which is trying to reduce the dust emission as much as possible

and, quite frankly, I feel until there is more data on the amount that can be floating

around in the air that this is a very sensible approach, a preventive approach actually

of dealing with the problem. Even though there is nothing that one can hang the hat on from the health side, I personally think that to allow the crushed rock to be used

indiscriminately is just simply not a good approach to preventive medicine. Thank you.

R. DAVIS: We live in a complex world and you pointed out that contractors might use carbonate stone. A number of the state highway departments have shown that carbonate

contributes to lower skid resistance. We are faced with the problem of how many people

are going to die from cancer from the chrysotile type of material and how many are going

to die from lowered skid resistance on the highways. These are very complex problems.

ROSS: What makes it so frightening is if you pull a string and all of a sudden a lot more string comes out, you don't know whether you've increased health risk or decreased

it. You've decreased it in one area and perhaps increased it in the other. One possibility

is that people would be so scared of asbestos, they won't use it for anything. Asbestos

has saved many lives when used for fi reproof i ng. We could carry on with fiberglass which

has a lot of similarities to asbestos, or we can get rid of fiberglass, and we can insulate

with organic chemicals, like some that form carbon monoxide and HCN when they burn. The

total picture is a big one and I think that we all should try to get a feeling for the

entire situation, and consider some of the problems that could arise.

E. COX: I'd like to ask M. Ross or Dr. Zoltai if you could tell us when the first

commercial mining of asbestos took place, what type it was, and where it was?

T. ZOLTAI: About a couple of thousand years ago; on a commercial scale the major

mines started in the late 19th century.

COX: About 1880-1890?

ZOLTAI: Yes.

COX: And where were they, sir?

67
ZOLTAI: In Canada.

COX: In Canada, and what were they?

ZOLTAI: Chrysotile.

K. HEINRICH: I'd like to ask Malcolm Ross if you have information of the size

distribution of chrysotile in Thetford and if it is similar to that in Montgomery County?

ROSS: Tom Bates did a size study of chrysotile from the Thetford area, Canada, and

also on the beautiful chrysotile from Arizona. I have^the figures in my paper but I think

in the Canadian chrysotile he had a minimum of 110 A outside diameter and a maximum of

several hundred with an average of about 250 A. I think the Arizona chrysotile had a generally larger diameter. You meant length, I'm sorry, I was thinking of width. I don't

know that, I don't have that figure. Some of the Canadian chrysotile was in beautifully

long fibers. This material set the chrysotile industry off, because in 1886 they found

these exceptionally good types of asbestos. I imagine some of it was very long fiber

material, but of course much of it would be short fiber also as the Rockville chrysotile is.

J. ZUSSMAN: I have two comments and one question. One is the point about when some commercial use of asbestos started. I believe there is some record of something industrial

in Italy with products like asbestos paper. There is also mention of the manufacture of

asbestos socks and gloves at a place in Russia. These were both before the start of large

scale mining at Thetford.

Another comment is in connection with Dr. Ross's remarks about the reactivity of

various forms of asbestos, in which he put chrysotile low down on that scale. In one sense perhaps chrysotile is high up in the scale of reactivity in that it is less resistant

to acid, and quite dilute acids can attack and start to dissolve away chrysotile. It has

a rather exposed layer of magnesium hydroxide and this is obviously going to be quite

reactive to dilute acids. I am not sure whether its reactivity in this sense makes

chrysotile less or more physiologically harmful.

I'd like to ask one question of Dr. Ross about the synthesis. I was very interested

to hear of his colleague Dr. Hemley's work on stability fields of the serpentine and

amphibole minerals, and I would like to ask whether or not the chrysotile or amphibole

formed was asbestiform or not. Quite a lot of work has been done on the stability fields

of amphiboles and serpentines in general, but rather little pinpointing when long thin

chrysotile fibers form and when other serpentines like lizardite and antigorite form; also

when asbestiform and when non-asbestiform amphiboles form. I wonder if the products of

those experiments were identified as asbestiform or not.

ROSS: Yes, Dr. Hemley's work, I think, was really one of the outstanding contributions we've had in this area of geochemistry this year. These experiments were very

difficult; they are run at relatively low temperatures, so his run times were many weeks

duration. Concerning the stabilities of the individual polymorphs of serpentine, he

attempted to define an antigorite and chrysotile field. He did some electron microscopy,

I believe, and found pi aty-serpenti ne , which he called antigorite. I asked Julian Hemley - "if you injected some chrysotile into the human blood stream or into the lung, what would

you expect to happen?" He thought about the various parameters in the human body that

might affect that system and he said, "I don't think anything would happen." Nevertheless,

chrysotile is very soluble in dilute acids, and Dr. Langer will agree ingested chrysotile

in the stomach should decompose quite readily. Hemley did not think that the pH range of

the human body, other than the stomach, would contribute to any appreciable dissolution of

the chrysotile. He suggested it would last and last.

0. MENIS: Being a chemist, I would like to ask the mineralogist why they have

neglected the OH group, the hydroxyl ation process. I wonder if Prof. Zussman and others

would like to comment on the role of the OH, the potential of local pH values of these

materials, and the ease of the hydroxyl ation which is known from thermal data where you

have a great difference between the various amphiboles and chrysotile.

68
ZUSSMAN: I look to my colleagues because I really don't know much about it, and I don't know that very much is known about the comparative effects of the hydroxy! in these

different minerals. Certainly in the amphi boles, and crocidolite in particular, some work

has been done on oxidation-reduction phenomena, because there you have not only the hydroxyl

but you have the ferric ion and the combination of the two is conducive to chemical reac- tions going on. I don't know of any work which has examined the effect of OH in the

grunerites or very much in serpentine except with regard to decomposition. If you heat

them, then they break down at different temperatures, and you mentioned the question of

differential thermal analysis giving different results. I think one has to be very

cautious about this because it's notoriously easy for a variety of results to be obtained

in the decomposition temperatures by DTA methods, which may or may not be significant. In

the amphi boles, hydroxyl is there, and so is fluorine (I hadn't mentioned that because

there was a limit to the complication that one could go into in the time available for my

paper), but it's quite possible that the ratio of hydroxyl to fluorine, the presence of

fluorine or the presence of chlorine could be relevant. These are all minor variables and

there has not been much systematic study of how many of these variables are relevant to

the comparison of asbestos and non-asbestos amphiboles or serpentines, and their effects.

Malcolm Ross may have some comments on this.

ROSS: If you pass hot, inert gas over grunerite crystals, hydrogen will be removed

and you'll get two atoms of trivalent iron. This is quite reversible, at least in other

similar phases. Ernst and Wai have done this experiment with sodic amphiboles. Repeated

experiments on biotite by Wones shows complete reversibility of this oxidation-reduction

reaction. In amosite as well as crocidolite, the iron may be oxidized by removal of

hydrogen. This can go very readily at higher temperatures. It is unknown whether this

can go on in the human lung, but it is a possible chemical reaction. Also another reaction

is ion exchange in crocidolite. You can oxidize or reduce the iron, and exchange oxonium,

ammonium, potassium, or sodium in the vacant site. Thus there are some very interesting

possibilities for chemical change on the surface of these crystals.

J. KRAMER: I might make a comment. I think back to the original question on chemical

reactivity. One of the ideas of looking at surface reactions in the amphiboles originally

was that these crystallites forming the asbestos form of the amphibole may be hooked

together with OHO bonds, and we thought we might see some differences here. Our type of

measurements which I quickly alluded to, are crude. They're gross and are in no way domain

measurements. We didn't find any differences. The other thing is of course that chrysotile

versus the amphiboles has a much different zero point of charge, quite a bit different

double layer in terms of surface reactions. One might want to compare these two groups in

order to look at reactions involving the hydroxyl groups. But I think maybe Dr. Zoltai

may like to comment upon some of his surface charge measurements because I think these are much more specific to the individual fiber. I'd like to hear your comments.

ZOLTAI: Actually we haven't done any sophisticated work to be able to answer a question of that level. All I can say is that what we were trying to do was to detect

surface charges at the level of single fibers rather than in bulk quantities of fibers.

By using distilled water containing positive or negative labelling sols in suspension, we

tried to detect the surface charges of amosite from South Africa and non-asbesti f orm cummingtonite. In other words, there was only one experiment, and in that case the asbestiform material appeared to have much higher negative surface charge. However, the two

specimens came from two different localities, besides being only one test that could not

be considered very meaningful. Actually, the reason we did that was to see whether the

technique is applicable to asbestos. It would be very nice to have a technique where you

can get an indication of the surface charge at the scale of single fibers.

KRAMER: Did you notice any domains pertinent to your technique?

ZOLTAI: Occasionally, yes.

UNKNOWN: I'd like to ask Dr. Zussman a question. Have you any way of estimating

what fraction of the total amphibole structure might be defective, what are the length

dimensions of the defects, and how much of a chemical variation would you expect to be

associated with the defects that you outlined?

69
ZUSSMAN: The little work that has been done on this shows the frequency of defects

in the limited number of samples that have been looked at and, in some of the ones I can remember, the defect occurred about one every 50 cells, so it was a small proportion in

that particular sample. Other samples may show a much higher density of defects, but I think just not enough samples have been looked at in that respect. As to the importance

of defects, they could be very important in terms of crystal growth, and in terms of

mechanical properties. Perfect crystals without defects have very different tensile

strengths and other mechanical properties compared with crystals from the same substance

but with defects, and it's conceivable that chemical reactivity may be concentrated at the

sites of defects. It's an area which is not being looked into to my knowledge; perhaps

somebody else can say otherwise. Added after meeti ng : My answer above about the density

of defects was related to Wadsley defects. I omitted to say that the other kind of defect

(stacking and twinning) have been reported as very abundant in crocidolite, amosite and

tremolite asbestos. Only the Wadsley type of defect would have a direct effect on chemical composition, but it would be rather small if there are relatively few of them.

SUMMARY: Dr. Mason, the session chairman, indicated that he felt the General Discussion

provided a very adequate summary of the mineralogical aspects.
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

EPIDEMIOLOGICAL EVIDENCE ON ASBESTOS

William J. Nicholson, Arthur M. Langer, Irving J. Selikoff

Environmental Sciences Laboratory

Mount Sinai School of Medicine of the City University of New York

One Gustave L. Levy Place

New York, New York 10029

Abstract

Data on the human health effects from occupational and

environmental exposure to asbestos will be presented with special

emphasis on the role of different asbestos minerals. Further, human

tissue burdens of fibers and their association with asbestos related

diseases will be discussed. Experimental animal data from various

species and utilizing different routes of administration will also be

presented, again with emphasis on differing fiber types.

Key Words: Asbestos; cancer; epidemiology; fibers; mesothelioma;

occupational exposure.

PART I. HUMAN HEALTH EFFECTS

We have already heard in the session on mineralogical aspects of asbestos considerable

comment and speculation about health effects. What I would like to do here is present some data on human health effects associated with different forms of asbestos, and to discuss

briefly some of their meaning in terms of ambient air concentrations.

The modern history of asbestos disease dates from the turn of the century, when two

reports were published documenting the effects of uncontrolled conditions in asbestos

textile factories. One, the testimony of Dr. H. Montague Murray at a compensation hearing,

described severe pulmonary fibrosis found at autopsy, in 1900, in the last survivor of a group of ten workers first employed 14 years previously in a carding room [1]^. The second

was the description by Auribault of deaths during the early years of operation of an asbestos weaving mill established at Conde-sur-Noireau, France, in 1890 [2]. During this

period 50 men died, including 16 of 17 recruited from a cotton textile mill previously

owned by the factory director.

Subsequently, cases of pulmonary fibrosis following inhalation of asbestos were published in the medical literature, including one by Cooke, who gave the disease its current name, asbestosis [3]. A 1929 study of asbestos textile operations by the British

Factory Inspectorate revealed the existence and extent of a continuing problem [4]. In a clinical survey of mill employees, 80 percent of those employed for 20 years or more had

x-ray evidence of asbestos disease. This finding stimulated the Factory Inspectorate to

require the introduction of extensive environmental control technology in the industry and

the establishment of an ongoing medical surveillance program.

Conditions in the United States were not improved significantly until the 1960's and in

recent years the prevalence of abnormal x-rays among workers with 20 or more years of

occupational exposure to asbestos has been high. Table 1 lists data of such abnormalities

found among insulation workmen employed in the New York and New Jersey area prior to 1960

[5]. Most x-rays of the group were normal until 20 years, and if abnormal usually showed

^Figures in brackets indicate references at the end of each part of this paper. There is

also a set of references following the discussion.

71
Table 1

Onset of

exposure (yrs.)

40+

30-39

20-29

10-19

0-9

Total

X-ray changes in asbestos insulation workers.

Asbestosis (grade)

No.

121

194

77

379

346

1 ,117

Percent

normal

5.8

12.9

27.2

55.9

89.6

Percent

abnormal

94.2

87.1

72.8

44.1

10.4

1

35

102

35

158

36

366

51

49

17

9

0

126

28

18

4

0

_0^

50

changes only of minimal extent. However, after 20 years most had abnormal x-rays and, when

abnormal, often of significant degree. Thus, long term observations are required to obtain

a valid assessment of lung scarring associated with asbestos exposure. Analysis of shortterm data can be highly misleading.

Asbestosis was the only disease known to be present among occupational ly exposed workers

until 1935, when it was suggested that lung cancer might be associated with asbestos

exposure. In that year and again in 1936 a clinical report was published of lung cancer in an asbestos worker who had died with evidence of pulmonary fibrosis [6,7]. While such

reports were not sufficient to causally relate asbestos exposure to lung cancer, the possibility was raised. In 1947 it was confirmed by substantial data, which showed that 13

percent of individuals who died with asbestosis in Great Britain also had bronchogenic

carcinoma [8]. Mesothelioma, a rare tumor of the lining of the abdomen or chest, was described in an asbestos worker in 1953 [9], found frequently to have followed potential

asbestos exposure in 1960 [10], and unequivocally related to such exposure in 1965 [11].

Gastronintestinal cancer also was found to be in excess among asbestos insulation workers in

the United States [12].

In 1975, three-quarters of a century after the first identification of asbestos-related

deaths, society continues to be plagued by their presence, unfortunately, in ever increasing

numbers. Moreover, the population at risk from the several asbestos-related cancers has

expanded from those directly handling the mineral to those working nearby the application

or removal of asbestos materials, and, finally, to those who simply live in the vicinity

of an asbestos operation or in the household of an asbestos worker.

High Exposure Effects

The full spectrum of disease from asbestos exposure is best manifest in the data of

Selikoff, Hammond, and Seidman on the mortality experience of 17,800 asbestos insulation

workmen [13]. Table 2 shows the expected and observed deaths among this group of workers

from January 1, 1967, through December 31, 1976. Among those individuals who have died, one

in five deaths was due to lung cancer, about 5 percent to gastrointestinal cancer, approximately 7 percent to mesothelioma (a tumor so rare in the general population that it may

account for only one in ten thousand deaths in the absence of exposure to asbestos), 10

percent to other cancers, and 7 percent to asbestosis, the disease first characterized seven decades earlier and wished away numerous times subsequently. The data on the mortality

experience of this group of workmen are also sufficient to suggest that cancer at sites

other than those mentioned above may also be increased from asbestos exposure. Here,

however, the malignancies are less common. Overall, comparing the frequencies of deaths

from the cancers and asbestosis with those among the general population, nearly 40 percent

of the deaths in this group of workers can be attributed to their occupational exposure to

asbestos.

72
Table 2. Deaths among 17,800^ asbestos insulation workers in the United States and Canada.

January 1 , 1967 - December 31, 1976

Number of men Man-years of observation

17,800

166,855

Expected Observed Retio

Total deaths, all causes 1,660.96 2,270 1.37

Total cancer, all sites 3 1 y . yu yy4 0. 1 1

Lung cancer 105.97 485 4.58

Pleural mesothelioma b 66 —

Peritoneal mesothelioma b 109 --

Cancer of esophagus 7.01 18 2.57

14.23 22 1 .55

Panrpr of rol on . rectum 37.86 59 1 .56

All other cancer 154.83 235 1.52

Asbestos is b 162

All other causes 1,351.06 1,114 0.82

^ Expected deaths are based upon white male age specific mortality data of the U. S. National Center for Health Statistics for 1967-1975 and extrapolation to 1976.

^ These are rare causes of death in the general population.

From: Selikoff, I. J., Hammond, E. C. , and Seidman, H., Mortality experience of

insulation workers in the United States and Canada, 1943-1977, to be

published, Ann . N.Y. Acad . Sci .

Asbestos related disease has also resulted from exposures in asbestos factories. A

study of production employees of the largest asbestos products manufacturing facility in the

United States again demonstrated the presence of significant excess disease [14]. In this

study, the mortality experience of all 689 individuals who were working on January 1, 1959,

and who were first employed prior to 1939, was analyzed. From 1959 to 1976, it was expected

that 188 deaths would have occurred in this group. Instead, 274 died, 46 percent more

than anticipated. About 40 cancers were expected; 99 were observed. As shown in Table 3,

the anticipated asbestos-related tumors were found in excess - bronchogenic carcinoma,

nesothel ioma, and gastrointestinal cancer.

73
Table 3. Expected and observed deaths among 689 factory workers, employed before

January 1, 1939, during the seventeen years from January 1, 1959 through

December 31 , 1 975.

1959 - 1975

Observed Expected Obs./Exp.

All causes 274 188.19 1.46

Cancer, all sites 99 39.93 2.47

Lung cancer 35 12.53 3.91^

Pleural mesothelioma 14 n.a. —

Peritoneal mesothelioma 12 n.a. —

Cancer of esophagus,

stnmflrh colon and rectum

15 7.99 1 .88

Cancer all other sites 23 19.40 1.19

All respiratory disease 42 12.16 3.45

Asbestosis 35 n.a.

Other respiratory 7 b

Al 1 other causes 133 136.11 0.98

Person-years of observation 9,646

^ Pleural mesothelioma included with cancer of bronchus in calculating ratio

since expected rates are based upon "cancer of lung, pleura, bronchus, trachea."

^ This rate is virtually identical with that of "all respiratory disease."

n.a. = not available.

From: Nicholson, W. J., Case Study 1: Asbestos-the TLV approach, Ann. N. Y. Acad . Sci., 271, 152-169 (1976).

Time Effects - Lapsed Period

If one considers the time from onset of exposure to the clinical evidence of disease,

one finds, just as with asbestosis, that there is a long-lapsed period from first exposure to

appearance of asbestos related cancers. Data from the group of insulators illustrate this

point in figure 1, where the excess cancer risk, calculated for equal but not aged standardized populations within each ten-year time interval, is plotted. A significant increase in

risk is seen only after 25 years for lung cancer and after 30 years for mesothelioma. An

increase in the ratio of observed to expected cases of the various asbestos cancers occurs prior to 20 years, but the total number of such cancers is small, as the population is

relatively young.

This long-lapsed period creates significant difficulties in attempting to establish

dose-response relationships. The disease seen today is from exposures decades past when few

measurements were made of asbestos concentrations. Thus, we can only estimate past exposures, based on current knowledge. Further, such estimates can be unreliable, and the

determination of the efficacy of standards based upon them cannot be made with certainty,

until further decades have past. If we then find serious misjudgments have been made,

asbestos disease will continue to plague us well into the twenty-first century.

74
TIME FROM ONSET OF EXPOSURE (YEARS)

Figure 1. The excess, asbestos-related mortality rates for lung cancer and mesothelioma

according to time from onset of asbestos disease.

75
Another aspect of time in the identification of carcinogens is seen in the data from

the study of New York and New Jersey insulation workers over the period 1943 through 1973

[15]. Table 4 shows the mortality experience of 623 insulators, all with 20 years since

first exposure in different time periods. One notable feature in these data is the deficit

of deaths of all causes in the first 10-year observation period; an excess of total mortality appears only after several years from first observation (and 30 years from onset of

exposure). It is common to observe such a deficit, often as great as 25 percent, in studies

comparing the mortality experience of working groups with that of the general population

the "healthy worker effect"). This results in part because identified groups of workmen

are healthier than a corresponding age group in the general population, which would include

terminally ill individuals and others unable to hold a job because of disability. However, even in these early years, the excess asbestos cancers can be seen, although they are not

yet the dominant contribution to total mortality.

Synergistic Effects

A second important concern is increasing evidence that many cancers may have a multiple

factor etiology. For example, lung cancer in asbestos workers is strongly associated with

cigarette smoking. In the large cohort of 17,800 insulators observed by Selikoff and

Hammond, the smoking habits were obtained on the majority of workers in 1967 [16]. Table 5 illustrates the effect of cigarette smoking on lung cancer mortality of these workers.

Among 2,066 non-cigarette smokers, only eight lung cancers were seen in a ten-year period,

where 1.82 were expected, based on American Cancer Society data on the risk of lung cancer

death in non-smokers. Inhalation of asbestos by insulators appears to multiply the risk by

four or five times. Considering the data for men with a history of smoking, among 9,591,

325 deaths were observed versus 66.78 expected, also a fivefold increase. However, since

cigarette smokers already have a ten to twenty times greater risk of lung cancer deaths than

non-smokers (depending on cigarette consumption), the multiplicative effect of the asbestos

exposure increases the lung cancer risk up to 100 times for smoking asbestos workers

compared to non-smokers unexposed to asbestos. This was also shown by the experiences of a cohort of New York and New Jersey insulators [17]. Hence, it was estimated that the risk

of dying of lung cancer for cigarette smoking asbestos workers was more than 90 times that

of individuals who neither smoked nor worked with asbestos.

Indi rect Asbestos Exposure |

In 1968 it was pointed out by Harries that shipyard workers other than insulators were

at risk from asbestos disease [18]. Among Devonport Dockyard employees, five cases of

mesothelioma were found among men who had not been "asbestos workers" but had followed other

trades in the yard. These men presumably had been inadvertently exposed to asbestos merely

by working in the same shipyard areas where asbestos had been used. Continuing to follow

this group. Harries later documented 55 cases of mesothelioma in this shipyard alone,

only two of which occurred in asbestos workers [19], one, a man who had previously sprayed

asbestos. A study of the distribution of all verified cases of mesothelioma found in

Scotland between the years 1950 and 1967 is also revealing [20]. Of 89 cases available for

study, 55 were in shipyard employees, dockers, or naval personnel. Of the 55, again only

one was an asbestos insulation worker.

m

A third important study of workers in British shipyards is that of John Edge, who

reviewed x-rays of former shipyard workers in Barrow [21]. A prospective study was conducted of 235 men whose x-rays, taken between 1955 and 1969, showed abnormalities characteristic of asbestos exposure (pleural plaques, scarring of the covering of the lung or lining of the chest), but no parenchymal fibrosis (scarring of the lung tissue). Most of

these x-rays were of individuals (riggers, welders, carpenters, electricians, machinists,

steamf itters , etc.) who had not worked directly with asbestos, but who could have sometimes

been nearby when asbestos was used. In tracing the individuals who had such x-ray changes,

it was found that 70 had died from 1970 to 1973. Of these 70 deaths, 13 were of lung

cancer, two and one-half times the number expected, and 17 were of mesothelioma (none, of

course, were anticipated).

76
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77
Table 5. Deaths of lung cancer among asbestos insulation workers in the United States and

Canada, 1967-1976; influence of cigarette smoking.

Expected deaths^

Observed deaths

- b

U. S. Smoking specific

1

History of cigarette smoking 325 60.07 66.78

Current smokers 228 31.87 39.69

Ex smokers 97 23.29 13.34

2. No history of cigarette smoking 8 14.11 1 .82

Never smoked 5 8.49 0.98

Pipe/Cigar 3 5.63 0.84

3. Unknown history of cigarette smoking 152 31 .80 11.93

Total 485 105.97 66.78

^ Age, year and sex specific.

^ Based upon age, specific data of the U. S. National Center for Health Statistics,

cigarette smoking not considered.

^ Based upon American Cancer Society's Cancer Prevention Study, 1967-1972.

I

From: Hammond, E. C, Selikoff, I. J., and Seidman, H. , Cigarette smoking and mortality

among U. S. asbestos insulation workers, to be published in Ann . N.Y. Acad . Sci .

Environmental Asbestos Disease I

In 1960 Wagner reviewed 47 cases of mesothelioma found in the Northwest Cape Province,

South Africa, in the previous five years [10]. Of this number, roughly half were in people

who had worked with asbestos. Virtually all of the rest, however, were in individuals who

had, decades before, simply lived or worked in an area of crocidolite asbestos mining (one

lived along a roadway in which asbestos fibers were shipped). This germinal observation

demonstrated that asbestos exposure of limited intensity, often intermittent, could cause mesothelioma. The hazard was further pointed by the findings of Newhouse[l 1 ] , who showed

that mesothelioma could occur among people whose potential asbestos exposure consisted of

their having resided near an asbestos factory or in the households of asbestos workers.

Twenty of 76 cases from the files of the London Hospital were the result of such exposure,

31 were occupational in origin, and asbestos exposure was not identified for 25.

A recent extensive study of the effects of household exposure has been conducted by

Dr. Henry Anderson and his colleagues of the Mount Sinai School of Medicine [22]. In a clinical survey of 489 family contacts of former factory workers, it was found that the

x-rays of 36.2 percent of these individuals showed abnormalities characteristic of asbestos

exposure. It did not matter greatly what the relationship to the worker was; the asbestos

dust in the household could affect any resident - wife, sons, daughters, parents. While

almost all were currently asymptomatic, and while most would perhaps suffer no impairment

from their past exposure, others may be stricken with an asbestos-related cancer as a result

of past household asbestos exposure. During the initial phase of the survey of deaths,

mesothelioma had been identified in this group of family contacts.

78
Asbestos Fiber Types : Relation to Disease

Canadian asbestos mine workers by the McGill group has already been mentioned earlier

in these proceedings. In the initial publication of their mortality study [23], a favorable mortality experience was reported with lung cancer and gastrointestinal cancer

being found in excess only in the higher exposure categories. While this study was comprised of 11,788 individuals, it should be noted that nearly half (4,818) were in the

lowest dust category (virtually no exposure) or had been employed in the mines and mills

for less than one year. Further, many others would have had relatively recent employment.

Thus, the potential for dilution of asbestos-related health effects exists. A concomitant

study of x-ray changes among mine and mill employees may suffer even more from the disadvantage of short-term periods of observation [24]. Overall, 12.5 percent of 11,207

individuals were found to have abnormal x-rays. However, many of these had less than 10

years of employment and the x-ray that was read was the last maintained by the company of

employment.

We have also conducted studies of Canadian mine and mill employees, but of individuals

who had been employed for at least 20 years [25]. Table 6 lists the x-ray abnormalities

found among 1,120 such individuals. As can be seen, extensive asbestos-related x-ray

changes were present in this group of currently employed workers. Overall, 61 percent had

abnormal x-rays. Table 7 presents the mortality experience of 535 men who were first

i employed in the mines and mills before 1941 and followed from 1961 [26]; 16 percent of the

deaths were from asbestosis and 15 percent from lung cancer. One case of mesothelioma was

found, considerably less than would have been expected on the experience of U. S. insulation

workers or factory employees. The reason for this is unclear at this time. It may be

related in part to the physical characteristics of the chrysotile fibers in the mine and

mill environment, the fibers here being of a longer length than that encountered in

! manufacturing and end product use.

Table 6. X-ray changes among 1,120 Quebec asbestos mine and mill employees

by time from onset of exposure.

Time from onset of Percent abnormal

exposure (years) Normal x-ray Abnormal x-ray within category

20 - 24 83 46 35.7

25 - 29 99 104 51,2

30 - 34 122 182 57.6

35 - 39 76 170 69.1

40+ _58 180 75.3

Total 438 682

79
Table 7. Expected and observed deaths among 544 asbestos miners who were at least

20 years from onset of asbestos mining work at start of observation, 1961

through August 1977, by calendar years.

Total deaths

Total cancer, all sites

Lung cancer

Pleural mesothelioma

Peritoneal mesothelioma

Cancer of stomach

Cancer of colon, rectum

Cancer of esophagus

Al 1 other cancers

Asbestosis

Other non-infectious respiratory

All other causes

Man years

Expected

159.92

36.73

11 .10

b

b

3.65

5.03

0.87

16.08

b

6.69

116.50

Total, 1961-77

Observed

178

49

28

1

4

6

10

26

4

99

7,408

Ratio 0/E

i.n

1 .33

2.52

1.19

0.62

0.60

0.85

^ Expected deaths are based upon age-specific death rate data for Canadian white

males.

^ Death rates not available but these have been rare causes of death in the general

population.

Data are also available on exposure to amosite asbestos. From 1941 to 1954 a factory

producing amosite insulation materials operated in Paterson, New Jersey. The mortality

experience of individuals employed at any time between 1941 and 1945 is shown in Table 8. The usual asbestos diseases are seen to be present. Lung cancer is six times expected and

10 of 298 deaths are from pleural or peritoneal mesothelioma. An important aspect of this

study is that individuals with relatively short exposures are shown to have an increased

risk of death from asbestos-related causes. Table 9 shows the expected and observed deaths

from lung cancer, mesothelioma, gastrointestinal cancer, and asbestosis according to time of

employment in the plant. All time categories less than one year are elevated, and while a single one-month category does not have statistical significance, the longer periods up to

six months do.

80
/

Table 8. Deaths among 933^ workers employed in an amosite asbestos factory, starting

five years from onset of work 1941-1945 to December 31, 1974.

Deaths 1946-1974

Cause of death Expected Observed Ratio

All causes 285.62 483 1 .69

Cancer, all sites 50. 10 157 3.13

Lung cancer 12.45 83 6.67

G.I. cancer 12.05 24 1 .99

PI PI 1 1^;^ 1 mpc ni" hp 1 "i nma hU

i;

Peritoneal mesothelioma b 5

"Asbestos" cancer 24.50 117 4.78

Other cancer 25.60 40 1.56

Asbestos is b 28

All other causes 235.52 298 1 .27

Expected deaths are based upon white male age-specific death rate data of the L). S. National Office of Vital Statistics, 1949-1972. Rates were extrapolated for

1946-1948 from rates for 1949-1955 and for 1973-1974 from rates for 1968-1972.

128 workers were omitted from these calculations: 33 had prior asbestos exposure;

38 died in the first five years after onset of employment. 49 were not completely

traced; and eight had other asbestos employment after the five year from onset

point.

^ U. S. death rates not available but these are rare causes of death in the general

population.

81
\

Table 9. Deaths of all "asbestos disease" among 933^ workers employed in an amosite

asDestos Tacuory,

December 31, 1974.

srarLing Tive years trom onset ot

Effect of duration of exposure.

wor K 1 1 - 1 Q/l tr.1 u lo

Death of "asbestos disease 1 y+D- 1 y /

Diiratinn of emolovment No. Expected Observed Ratio

<1 month 62 3.47 6 1 .73

1 month 92 3.73 8 2.14

2 months 79 3.73 11 2.95

3-5 months 145 5.98 17 2.84

6-11 months 129 4.15 21 5.06

1 year 105 3.74 20 5.35

2 years 77 2.91 24 8.25

3-4 years 51 2.36 15 6.36

5+ years 65 2.88 34 11.81

Total 805 32.95 156 4.73

^ "Asbestos disease": asbestosis and chronic pulmonary insufficiency, lung cancer,

pleural, and peritoneal mesothelioma, cancer of esophagus, stomach, colon-rectum.

128 workers were omitted from these calculations: 33 had prior asbestos exposure;

38 died in the first five years after onset of employment. 49 were not completely

traced; and eight had other asbestos employment after the five year from onset

point.

Finally, if one considers the fiber type that insulation workers were exposed to, data

from manufacturers have indicated that it was only to chrysotile and amosite. No crocidolite was ever used as thermal insulation materials [27]. Further amosite was used in

significant quantities only from 1940 through the early 1960's. As neither the period of

use nor the incidence of mesothelioma among amosite workers listed above can account for

the high frequency of this cause of death among insulation workers, it is clear that

exposure to chrysotile asbestos is of importance here as well.

Summary

Accumulated human health data indicate that all major commercial varieties of asbestos,

chrysotile, amosite, and crocidolite, produce significant disease. Lung cancer, asbestosis,

mesothelioma, and gastrointestinal cancer are in significant excess among factory workers

and insulators, while lung cancer and asbestosis are dominant causes of death among mine

and mill employees. Further, evidence exists that environmental exposures, such as in the

homes of workers or in the vicinity of mines and factories, have been sufficient to produce

mesothelioma. Workers indirectly exposed to asbestos in their work, as shipyard workers,

can be at significant risk.

Currently no data exist that would indicate a threshold for asbestos related cancers. Prudence would suggest that exposures to all asbestos fibers be reduced to the minimum

commensurate with feasible environmental controls. Considerable data exist that most work

environments can maintain concentrations well below the current asbestos standard. I believe the issue is not that reduction of standards will result in the closing down of the

surface of the earth, as was suggested earlier in this symposium, but that reduction in

standards, with feasible control measures, will allow us to use the surface of the earth

safely.

82
References

[1] Murray, H. M. , Report of the Departmental Committee on Compensation for Industrial

Disease, London, H. M. Stationary Office, p. 127 (1907).

[2] Auribault, M. , BulJ. del ' Inspect , du Travail , p. 126 (1906).

[3] Cooke, W. E. , Pulmonary asbestosis, Br. Med. J., 2, 1024-1025 (1927).

[4] Merewether, E. R. A. and Price, C. V. , Report on effects of asbestos dust suppression

in the asbestos industry. Part I. , London, H. M. Stationary Office (1907).

[5] Selikoff, I. J., Personal communication.

[6] Lynch, K. M. and Smith, W. A., Pulmonary asbestosis III: Carcinoma of lung in asbestosilicosis. Am. J. Cancer , 24, 56-64 (1935).

[7] Gloyne, S. R. , A case of oat cell carcinoma of the lung occurring in asbestosis.

Tubercle , 18, 100-101 (1936).

[8] Merewether, E. R. A., Annual Report of the Chief Inspector of Factories, London,

H. M. Stationary Office (1907).

[9] Weiss, A., Pleurakrebs bei 1 ungenasbestose, in vivo morphologisch gesichert, Medi - zinische , 3, 93-94 (1953).

[10] Wagner, J. C. , Sleggs, C. A., and Marchand, P., Diffuse pleural mesothelioma and

asbestos exposure in the northwestern Cape Province, Br. J. Ind. Med. , J7, 260-271

(1960).

[11] Newhouse, M. L. and Thompson, H. , Mesothelioma of pleura and peritoneum following

exposure to asbestos in the London area, Br. J. Ind . Med. , 22, 261-269 (1965).

[12] Selikoff, I. J., Churg, J., and Hammond, E. C. , Asbestos exposure and neoplasia, JAMA , 188, 22-26 (1964).

[13] Selikoff, I. J., Hammond, E. C. , and Seidman, H. , Mortality experience of insulation

workers in the United States and Canada, 1943-1977, to be published, Ann. N.Y. Acad . Sci

[14] Nicholson, W. J., Selikoff, I. J., Seidman, H. , and Hammond, E. C. , Mortality experience of asbestos factory workers: effect of differing intensities of asbestos

exposure. Environ . Res. (in press). For earlier data, see: Nicholson, W. J., Case

study 1: Asbestos - the TLV approach, Ann. N.Y. Acad. Sci- , 271, 152-169 (1976).

[15] Selikoff, I. J., Hammond, E. C. , and Seidman, H. , Cancer risk of insulation workers in

the United States, In Biological Effects of Asbestos, Bogovski, Gilson, Timbrel 1, and

Wagner (eds.), Lyon, lARC, pp. 209-215 (1973).

[16] Hammond, E. C. , Selikoff, I. J., and Seidman, H. , Cigarette smoking and mortal ity among

U. S. asbestos insulation workers, to be published in Ann . N.Y. Acad . Sci . For earlier

data see: Hammond, E. C. and Selikoff, I. J., Relation of cigarette smoking to risk of

death of asbestos-associated disease among insulation workers in the United States, in

Biological Effects of Asbestos , Bogovski, Gilson, Timbrell, and Wagner (eds.), Lyon,

lARC, 312-317 (1973).

[17] Selikoff, I. J., Hammond, E. C. , and Churg, J., Asbestos exposure, smoking, and

neoplasia, J. Am. Med. Assoc., 204, 106-112 (1968).

;i8] Harries, P. G. , Asbestos hazards in naval dockyards, Ann. Occup . Hyg . , 1

, 135 (1968).

19] Harries, P. G. et al.. Radiological survey of men exposed to asbestos in naval dockyards, Br. J. Ind. Med., 29, 274-279 (1972).

83
[20] McEwen, J., Finlayson, A., Mair, A., and Gibson, A. A. M. , Mesothelioma in Scotland,

Br. Med. J. , 4, 575-578 (1970).

[21] Edge, J., Asbestos-related disease in Barrow-in-Furness, J. Environ . Res. , IJ, 244-247

(1976).

[22] Anderson, H. A. et al . , Household contact asbestos neoplastic risk, Ann. N. Y. Acad.

Sci .

, 271, 311-323 (1976).

[23] McDonald, J. C. , McDonald, A. D. , Gibbs, G. W. , Siemiatycki , J., and Rossiter, C. E.

,

Mortality in the chrysotile asbestos mines and mills of Quebec, Arch . Environ . Health , 22, 677-686 (1971).

[24] Rossiter, C. E. , Bristol, L. J., Cartier, P. H. , Gilson, J. G. , Grainger, T. R. , Sluis-Cremer, G. K. , and McDonald, J. C. , Radiographic changes in chrysotile asbestos

mine and mill workers of Quebec, Arch . Environ . Health, 24, 388-400 (1972).

[25] Comite d'etude sur la salubrite dans I'industrie de I'amiante: rapport pre! iminaire,,

Beaudry, R. , Lagace, G. , and Juteau, L. (eds.) (1976).

[26] Nicholson, W. J., Seidman, H. , and Selikoff, I. J., (to be published) Ann. N.Y. Acad . Sci . (Proceedings of Science Week).

[27] Selikoff, I. J., Hammond, E. C. , and Churg, J., Mortality experiences of asbestos

insulation workers, 1943-1968, in: Shapiro, H. A. (ed.), Pneumoconiosis , Proceedings

of the International Conference , Johannesburg 1969 , Cape Town , Oxford University Press,

pp. 180-186 (1970).

PART II. EXTRAPOLATION TO OTHER INORGANIC FIBERS

Current Status of the Asbestos Problem

Part I of this contribution discusses essential elements and factors related to asbestos

fiber exposure and associated human disease. The historical perspective presented, in

conjunction with recent data, may help define the emerging problem area concerned with the

biological potential of inorganic fibers as a class of compounds. These may be outlined

as fol lows:

The Time Required to Define the Asbestos Problem was Decades Long:

(

Asbestosis, the disease characterized by scarred lungs due to the inhalation of asbestos

fiber, was first described over 70 years ago [1]. It was not until the 1930's and 1940's

that an accumulation of evidence suggested that asbestos fiber inhalation was also associated

with increased neoplastic risk, specifically carcinoma of the lung [2-5]. This effect was

not anticipated, and was overlooked for extraordinarily long time periods. Problems

focussing on the activity of mineral fibers , other than asbestos , may require lengthy time

periods to define . This may be for 1 ung scarring , an obvious effect associated with inhala- tion , and especial ly so for neoplasms .

The Different Asbestos Fiber Types Produce Similar Disease Patterns:

The disease stigmata produced by asbestos fiber inhalation are similar for the different

fiber species. Inhalation of all commercial asbestos, chrysotile [6], amosite [7],

crocidolite [8], anthophyl 1 ite [9], and mixtures of these fibers [10] produce both scarring

and various forms of malignant disease. A range of mineral species with different physical

and chemical properties can produce disease patterns in humans which are similar and

occasionally indistinguishable. It should be stressed that the major difference in biological effects noted are the relative risks associated with each fiber type for each disease

entity. Because the many varietal forms of asbestos fibers produce disease , and the

non-asbestos fibrous minerals are similar structural ly and chemical ly , any mineral entity

which can be inhaled should be studied for health effects.

84

1
Extra-Pulmonary Organs in Humans are Involved in Asbestos Disease:

The disease patterns associated with asbestos exposure are complex. Although inhalation is the primary route of exposure to the individual in the workplace, extra-pulmonary

organs may be affected as well. For example, asbestos fiber exposure has been associated

with the development of intra-abdominal and gastrointestinal tumors [11,12]; excess malignancies of the buccal cavity, pharynx, larynx, esophagus, and stomach have also been

reported [13,22]. Therefore, multiple organs and cell types are targets of asbestos fiber

action. Importantly, hundreds of thousands of man-years of observation were required to

statistically verify that excesses of less common tumors occurred in these workers. Organs

other than 1 ungs should be considered targets for other mineral fibers as wel

.

Occasionally, Multiple Primary Tumors May Simultaneously Occur in the Same Host:

Multiple primary tumors may occur in the same individual who had been occupational ly

exposed to asbestos fiber. Contributing causes of death, as wel 1 as the cause, are important

in defining the extent of disease associated with mineral fiber exposure .

The Clinical Latency Period for Asbestos Disease is Extensive:

There exists a long latency period between the onset of exposure to asbestos fiber and

the first clinical appearance of neoplastic disease. These stigmata have different lapse

time intervals for manifestation, e.g., mesothelioma is greater (30-40 years) than for lung cancer (20-30 years) [15,16]. This time lapse works against the establishment of an etiological link between the agent and the disease; it may confound exposure history by

implicating several "agents." It therefore requires many years of retrospective-prospective

study to determine , qual itati vely and quantitatively , the relationship between mineral

exposure and disease .

Fiber Exposure Continues Throughout the Life of the Exposed Individual:

Although a long time period may elapse between the cessation of exposure to asbestos

fiber and the appearance of disease, these materials tend to be retained in both lung

parenchyma and extra-pulmonary tissues of exposed workmen [17-21]. Therefore, exposure in

these individuals continues for their lifetime in that particles are often present,

continuously interacting on the cellular level. Removal of an i ndi vidua! from immediate

exposure to mi neral fiber does not si mi 1 arly remove him from "organ exposure . " Thi s concept holds for al 1 inorganic fibers which are not readi ly soluble i n vivo .

Fiber Dose-Response is a Function of both Duration and Intensity of Exposure:

Both the duration and intensity of exposure to asbestos fiber appear to influence the

relative risk of developing the different asbestos diseases, and markedly influence the

length of the clinical latency period in which the disease becomes manifest [22]. For

example, a study of workers employed in an asbestos factory utilizing amosite fiber demonstrated that exposure to high concentrations of amosite for as little as three months

significantly increased the relative risk of developing lung cancer (3.87x=SMR) [13,22].

Exposures in this instance were extremely high. However, if one were to establish an average threshold limit value based on man-years of exposure (average fiber levels

multiplied by number of years employed at such levels), such levels would be only 0.1 to

0.2 f/mL, generally considered to be a "safe" level for prevention of asbestosis by today's

OSHA standard. This would essentially ignore short-term, high-level exposures which

evidently carry significant disease potential. As counterpart, those workers employed for

short time periods (less than one year) required longer clinical latency period before their

diseases became manifest. This dose-response relationship is likely to hold for mineral

fibers other than amosite. Peak exposures may be more important than long-term exposures

and , on the other hand, low exposures may requi re longer periods of observation to f ul ly

def i ne neopl astic ri sk .

85
Co-Factors Exist in Asbestos Disease:

Cocarcinogenic and other synergistic factors are important in the production of asbestos

disease. The importance of cigarette smoking has been demonstrated by evidence that

carcinoma of the lung synergistical ly increases in cigarette-smoking asbestos workers [23-

25]. However, present data indicate that cigarette smoking is important only for carcinoma

of the lung, not for other malignancies. Lung cancer, cigarette smoking and inhalation of

other i norganic particles , e.g. , uranium mining , has been shown to be i nterrel ated i n the ; past . Therefore , such a synergi sm may exi st for mineral s other than asbestos .

The asbestos problem required decades of time to define through hundreds of thousands,

of man-years of observations. A range of materials produces similar disease patterns,

acting singularly or in concert with other biologically active agents. The clinical latency

period is long, target organs are many, and exposure related in part to fiber retention.

No known safe level of exposure exists for the prevention of malignant disease. It may bei

logical to assume at present, that lessons learned from the study of the asbestos problemi

may be applied to other inorganic fibers as well; that these findings may be used as a model

to guide and delineate in new and important areas.

The Nature of Mineral Fibers

Asbestos is the term which categorizes a specific group of natural silicate minerals

which occur in fiber form. The term fiber indicates, by definition, that the mineral

species grew with this morphology. It also indicates, by definition, that the plane

surfaces which define the external symmetry of the mineral are crystal faces resulting!

from growth. Asbestos fiber consists of a polyf i lamentous bundle of intergrown crystal

units. The breaking open of such a fiber purportedly is brought about by separation alongi

the juxtaposed crystal faces. The same mechanical treatment, as during grinding, of a non- asbestos, single crystal fiber, produces acicular cleavage fragments. The surfaces so'

formed are cleavage planes rather than crystal faces. It is generally considered that the

majority of cleavage surfaces normally follow crystal face morphological development, in that

both tend to occur parallel to "low energy" planes within the mineral [28]. Some investigators, however, considered that there may be significant physical-chemical differences

between crystal faces and cleavage planes (see T. Zoltai, this Conference). If so, such i differences between crystal faces and cleavage planes may result in different biological

activities of these materials. This fundamental difference prevents direct extrapolation

from asbestos fiber (bound by crystal faces) to fibrous rock- forming silicates (bound by

cleavage planes).

In addition to the differences in surface character, some difference in other properties may exist as well. Asbestos minerals possess physical-chemical properties which are unique. Some of these properties, such as high fiber tensile strength and flexibility, are not observed in other mineral or synthetic fibers. These properties have been described in a number of recent documents [26,27]; their mineralogical character is detailed by others at

this meeting (see, e.g., M. Ross, T. Zoltai, A. Goodwin). It is of very great importance to

note that differences between asbestos fiber and other silicate fibers are based on mega

scopic properties, that is, those physical properties determined on bulk samples. The

question arises as to whether or not these characteristics which distinguish asbestos from

non-asbestos mineral fibers are derived from molecular properties (e.g., twinning). If

they are, then these characteristics must also exist on the submicroscopic level as well

On the other hand, if these characteristics are determined by the physical nature of fiber

bundles, that is, derived by properties related to the manner in which the units are inter

grown, then separation of these units upon comminution destroys the "unique characteristics.

Single fibers on the submicroscopic level, of asbestos or other mineral fibers, are often

indistinguishable on the basis of morphology, structural characterization (by selected area electron diffraction), and chemistry (as determined by an electron microprobe technique).

Since mechanical properties cannot be measured on the microscopic or submicroscopic levels,

it is unknown at the present time if the "asbestos properties" carry through to the submicroscopic level. This focuses directly on the issue concerning the disease potential of

fibrous silicates other than asbestos. If the "asbestos property" is only megascopic in

nature, then size reduction of asbestos produces fibers essentially identical to acicular

cleavage fragments of rock- forming silicates. The nature of the mineral fiber entity, on the submicroscopic level, prevents direct extrapolation concerning the biological activity;

86
of other fibrous silicates. However, some extrapolation is currently possible on the basis

of existing data.

Data Which Suggest Inorganic Fibers Other than Asbestos are Biologically Active

Small fibers of various chemical compositions may form stable aerosols, persist in the

work environment (with an accompanying increased inhalation potential), penetrate deep into

the alveolar portions of the lung, and tend to be retained in tissues for long time periods.

It has been suggested that such factors as fiber chemistry, trace metals, adsorbed hydrocarbons, etc. are not important in terms of carcinogenic potential. It has also been

suggested that any fiber species in contact with the mesothelial lining of the chest, or lung, may produce mesothelioma, possibly by means of an "Oppenheimer" effect [29]. Experimental work conducted with such materials as fibrous glass has demonstrated that even these

man-made fibers may induce tumors when implanted at the mesothelial surface [30,31].

Clinical human evidence suggests that all varieties of asbestos fibers can produce disease,

and that any sub-species of a single variety can also produce disease. If certain forms of

mineral species, commonly referred to as asbestos, are active biologically, what factors are responsible for this activity? Currently, only the size and shape of fiber are common to

all mineral species which have been demonstrated to produce disease.

It has been suggested that amphibole "fibers" observed in some industrial talcs are "acicular cleavage fragments" and therefore not asbestos per se.^ This argument carries

with it the unsupported argument that since these particles are not asbestos, they are therefore not biologically active. However, a literature exists which implicates "fibers"

in talc as a factor in human disease. These fibers are commonly asbestiform fibers

(acicular cleavage fragments). Although these latter forms cannot be easily distinguished

from each other, studies have indicated that these common contaminants of industrial grade

talcs are the agents responsible for human disease. The disease stigmata are as follows:

fibrosis, with patterns identical to asbestosis [34-38]; occurrence of uncoated fibers and

asbestos bodies in lung tissues of workmen with interstitial lung scarring, and

accompanied by other asbestosis stigmata (e.g., pleural plaques in workers with

"talcosis") [37,39-41]; and excess malignancies, some of which are markers for asbestos

exposure, e.g., mesothelioma [42]. One may cautiously accept that there are biologically

active fibers contaminating industrial grade talcs. This might also carry with it, with

some caution, that crystal faces and cleavage planes have the same biological potential in

terms of producing human disease.

Current Status

It has taken 70 years to define the asbestos problem. The work of defining the human

hazards associated with exposure to fibrous minerals, other than asbestos, will require at

least as much effort and time.

The varietal nature of asbestos, its broad range of mineralogical properties,

suggests that other non-asbestos silicate fibers may be active as well. The argument

centering on crystal face and cleavage plane difference extrapolated to biological

potential requires study. The fact that a mineral fiber is non-asbestos does not

extrapolate to its being non-active biologically.

^True asbestos, defined on the basis of mineral phase and its physical-chemical properties

(flexibility and high tensile strength) does occur occasionally in talc deposits [32].

Asbestiform is defined as "formed-like or resembl ing asbestos...." This term refers to

rock-forming fibrous silicates which are not flexible, do not have high tensile strength,

yet when comminuted are identical to size-reduced asbestos. The term fiber in the present

context is used to mean a morphological form, not necessarily the result of conditions of

growth and therefore not necessarily bound by crystal faces. Since these characteristics

cannot be easily measured on submicroscopic "fibers," the distinction if presently academic.

87
References

[1] Murray, H. M. , In: Report of the Departmental Committee on Compensation for Industrial

Disease , Minutes of Evidence, Appendices and Index, c.d. 3495 - c.d. 3496, London,

Wyman and Sons (1907).

[2] Lynch, K. M. and Smith, W. A. , Pulmonary asbestosis. III. Carcinoma of lung in

asbestos-silicosis. Amer. J. Cancer , 24 , 56-64 (1935).

[3] Gloyne, S. R. , Two cases of squamous carcinoma of the lung occurring in asbestosis,

Tubercle , 17, 5-10 (1935).

[4] Wedler, H. W. , Asbestose und Lungenkrebs , Dtsch med . Wschr. , 69, 575-576 (1943a).

[5] Wedler, H. W. , Uber den Lungenkrebs bei Asbestose, Dtsch. Arch, kl i

, Med . , 191 , 189-

209 (1943b).

[6] McDonald, J. C. , Becklake, M. R. , Gibbs, G. W. , McDonald, A. D. , and Rossiter, C. E.

,

The health of chrysotile asbestos mine and mill workers of Quebec, Arch, envi ronm . Hith . , 28, 61-68 (1974).

[7] Selikoff, I. J., Hammond, E. C. , and Churg, J., Carcinogenicity of amosite asbestos.

Arch, environm . Hlth . , 25, 183-186 (1972b).

[8] Wagner, J. C. and Berry, G. , Mesotheliomas in rats following inoculation with asbestos,

Brit . J. Cancer , 23, 567-581 (1969).

[9] Meurman, L. 0. , Koviluoto, R. , and Hakama, M. , Mortality and morbidity among the working

population of anthophyl 1 ite asbestos miners in Finland, Brit . J. industr . Med . , 31 , 105-112 (1974).

[10] SeliKoff, I. J. , Hammond, E. C. , and Seidman, H. , Cancer risk of insulation workers in

the United States , In: Bogovski, P., Gilson, J. C. , Timbrell, V., and Wagner, J. C. , eds. Biological Effects of Asbestos, Lyon, International Agency for Research on Cancer

(lARC Scientific Publications No. 8), pp. 209-216 (1973).

[11] Keal , E. E. , Asbestosis and abdominal neoplasms. Lancet , pp. 1211 (1960).

[12] Selikoff, I. J., Churg, J., and Hammond, E. C. , Asbestos exposure and neoplasia, J. Amer. med. Assn., 188, 22-26 (1964).

[13] Selikoff, I. J., Epidemiology of gastrointestinal cancer, Environm . Hlth . Perspect .

,

9, 299-305 (1974).

[14] Dohner, V. A., Beegle, R. G. , and Miller, W. T. , Asbestos exposure and multiple primary

tumors, Amer. Rev. resp . Dis. , 112 , 181-199 (1975).

[15] Selikoff, I. J., Hammond, E. C. , and Churg, J., Mortal ity experiences of asbestos

insulation workers , 1943-1968 , In: Shapiro, H. A. , ed. , Pneumoconiosis , Proceedings of

the International Conference, Johannesburg 1969 , Cape Town, Oxford University Press,

pp. 180-186 (1970).

[16] Selikoff, I. J., Lung cancer and mesothelioma during prospective surveillance of 1249

asbestos insulation workers, 1963-1974, Ann. N.Y. Acad . Sci. , 271 , 448-456 (1975). |^

[17] Pooley, F. D. , An examination of the fibrous mineral content of asbestos lung tissue

from the Canadian chrysotile mining industry, Environm . Res . , VZ, 281-298 (1976).

[18] Langer, A. M. , Rubin, I. B. , Selikoff, I. J., and Pooley, F. D. , Chemical characterization of uncoated asbestos fibers from the lungs of asbestos workers by electron microprobe analysis, J. Histochem . Cytochem . , 20, 735-740 (1972b).

88
[19] Fondimare, A. and Desbordes, J., Asbestos bodies and fibers in lung tissues, Environm . Hlth . Perspect . , 9, 147-148 (1974).

[20] Sebastein, P., Fondimare, A., Bignon, J., Monchaux, G. , Desbordes, J., and Bonnaud, G. , Topographic di stribution of asbestos fibers in human 1 ung in relation with occupational

and non-occupational exposure , In: Walton, W. C. , ed. , Inhal ed Particles and Vapours , IV , New York, Pergamon (in press).

[21] Langer, A. M. , Inorganic particles in human tissues and their association with

neoplastic disease, Environm , Hlth . Perspect . , 9, 229-233 (1974).

[22] Selikoff, I. J., Cancer ri sk of asbestos exposure , In: Hiatt, H. H. , Watson, J. D. , and Winsten, J. A. , eds. , Origins of Human Cancer , Cold Spring Harbor, N.Y. , pp. 1765-

1784 (1977).

[23] Selikoff, I. J., Hammond, E. C. , and Churg, J., Asbestos exposure, smoking and

neoplasia, J Amer . med Ass. , 204, 106-112 (1968).

[24] Doll, R. , The age distribution of cancer: implications for models of carcinogenesis,

J. roy. Stat . See. , 134, 133-166 (1971).

[25] Berry, G. , Newhouse, M. L. , and Turok, M. , Combined effect of asbestos exposure and

smoking on mortality from lung cancer in factory workers. Lancet , ij, 476-479 (1972).

[26] lARC Monograph Series: Evaluation of Carcinogenic Risk of Chemicals to Man, V. 14,

Asbestos WHO-IARC Lyon, 1977, 106p.

[27] Langer, A. M. and Wolff, M. S. , Asbestos Carcinogenesis , In: Schrauzer, G. , ed. , Inorganic and Nutritional Aspects of Cancer, Plenum Press, N.Y. , pp. 29-55 (1977).

[28] Langer, A. M. , Rohl , A. N. , and Wolff, M. S. , The nature of mineral surfaces and their

role in biological interactions, Soc. Occup . and Environ . Hlth . , Wash., 1977 (in

press).

[29] Oppenheimer, B. S. , Oppenheimer, E. T. , Stout, A. R. , Danishefsky, I., and Eirich,

F. R. , Malignant tumors and high polymers. Science , 118 , 783-784 (1953).

[30] Stanton, M. F. and Wrench, C. , Mechanisms of mesothelioma induction with asbestos and

fibrous glass, J. nat. Cancer Inst. , 28, 797-821 (1972).

[31] Stanton, M. F. , Some etiological considerations of fibre carcinogenesis . In: Bogovski, P., Gilson, J. C. , Timbrel 1, V., and Wagner, J. C. , eds.. Biological Effects

of Asbestos , Lyon, International Agency for Research on Cancer (lARC Scientific Publications No^ 8), pp. 289-294 (1973).

[32] Ford, W. E. , Dena's Textbook of Mineralogy, N.Y. Wiley, 4th Ed. , 678p (1957).

[33] Bureau of Mines, Dictionary of Mining, mineral and related terms, ed. P. W. Thrush,

Washington, D. C. , U. S. Government Printing Office (1968).

[34] Dreessen, W. C. , Effects of certain silicate dusts in the lungs, J. Indust. Hyq. , 15,

66-78 (1933). " —

[35] Dreessen, W. C. and Dalla Valle, J. M. , The effects of exposure to dust in two Georgia

talc mills and mines, Publ Health Repts . , 50, 1405-1415 (1935).

[36] Siegal, W. , Smith, A. R. , and Greenburg, L. , The dust hazard in tremolite talc mining,

including roentgenological findings in talc workers, Am. J. Roentgenol., 4, 11-29

(1943). — - -

[37] Daymon, H. , Latent silicosis and tuberculosis, Am. Rev. Tuberculosis, 53, 554-559

(1946). — —

89
[38] Porro, F. W. and Levine, N. M. , Pathology of talc pneumoconiosis with report of an autopsy, North . N. Y. State Med. J. , 3, 23-25 (1946).

[39] Hobbs, A. A. , A type of pneumoconiosis, Am. J. Roentgenol . Radiol . Therap . , 58, 488-497

(1950).

[40] McLaughlin, A., Rogers, E. , and Dunham, K. C. , Talc pneumoconiosis, Br. J. Indust . Med . , 5, 184-194 (1949).

[41] Porro, F. W. , Patton, J. R. , and Hobbs, A. A., Pneumoconiosis in the talc industry, Am.

J. Roentgenol . , 47, 507-524 (1942).

[42] Kleinfeld, M. , Messite, J., Kooyman, 0., and Zaki , M. H. , Mortality among talc miners

and millers in New York State, Arch, Environ . Health , 14, 663-667 (1967).

Discussion

M. SCHNEIDERMAN: You talked about short term exposures and problems of peak exposures.

Then you divided an exposure by 20 years and that came out to some very small number,

and you said that small number is substantially below the standards now set. Have you any

information on the difference between biological results from peak exposures and long term

exposures or should we consider only integrated exposures totaled over time and not consider

problems of peak exposure?

A. NICHOLSON: We don't have good data on the effects of peak exposures per se. They

may in fact be proportionally greater than an amount averaged over a longer period of

time. Insulation workers' exposures are very peaky-like. That is, they tend to spend

most of their time working in conditions that would have very low ambient air concentrations. The material is wet or else they're not using asbestos, but at times when they were mixing cement, cutting block, or doing something like that they had very high concentrations. This may be a factor. We just have no way of obtaining data on that particular

item separately from the integrated exposures that we can make some estimate of.

E. COX: Dr. Nicholson, you mentioned an amosite exposure study of very short term

nature and then went on to correlate that to the safe exposure over a long period of time.

I believe your figures were three deaths, contrasted with an expected 1.34, from lung cancer for a person who was employed in that plant for one month or less. Was there any

correlation with smoking done in that study?

NICHOLSON: No, there was not, and the number of deaths in each single category were

small. The consistency over each of those month by month categories, though, was strong.

That is, if you looked at all months together over the period of time for less than one month through five months, the results are of statistical significance. In terms of

cigarette smoking, we know it is strongly correlated with asbestos exposure. What

asbestos does, in essence, is multiply whatever existing risk of death from lung cancer

that is already present. If an individual has a high risk from cigarette smoking, then

additional asbestos exposure can multiply that from five to ten times. If he has a very

low risk of death from lung cancer because he's a non-smoker, it can be increased perhaps

five times by the asbestos exposure.

COX: Thus, there wasn't any correlation done. Now the other question would be with

Dr. Langer's work, and perhaps you could answer it. It deals with the concentration of

uranium involved in the mining danger. Langer had a chart, that went by rather rapidly,

of the different things that are particularly dangerous and one was mining where uranium

was involved.

NICHOLSON: Uranium mining produces a very high risk of lung cancer.

COX: Yes, I wonder if you could speak about the concentration of uranium? The

amount of uranium in the ore body is the thing of interest to me.

90
NICHOLSON: Well, most ore bodies in the Southwest have two or three percent uranium

oxide.

COX: Well, let me be more specific. Phosphate mining in Florida where the yield is one pound of uranium per ton of H3PO4, would that be dangerous?

NICHOLSON: It would depend on what the air concentration of the material is. I couldn't answer the question directly.

COX: Al 1 right, thank you.

L. SWINT: I'd like to clear up that question on uranium mining. Actually the cancer

is caused by radon daughters which come from the radium, which is a decomposition product

of uranium. The amount of uranium in the ore has nothing to do with the lung cancer.

It's really a function of the exposure to radon daughters rather than the amount of uranium

present.

Although radon gas and radon daughters are decay products in the uranium decay series

which, when in equilibrium, would be present in direct proportion to the amount of uranium

present, for practical purposes they are independent because there are many events which

occur that keep equilibrium of randon daughters and uranium from being established. Uranium

and radium, the direct parent of radon, may be out of equilibrium due to differential

leaching by groundwaters, since uranium is much more leachable than radium. The porosity

and permeability of the rock affect the rate at which the rock will release radon gas into a mine atmosphere. Thus, the amounts of radon gas and radon daughters present in a mine

atmosphere are not completely controlled by the amount of' radium or uranium in the rock.

The grade of uranium ore mined in the U. S. through 1973 averaged between two and three

tenths of one percent 1)308, but since 1973 this grade has steadily declined to fifteen

hundredths of a percent in 1976.

SCHNEIDERMAN: In fact, in some of those studies, the hard rock miners who would have

similar exposures to the kinds of things that Dr. Nicholson was talking about were used

as controls so that one might measure whether it was the radioactive material or the

fibrous material that was of consequence. Those might have been inappropriate controls

now that we know better, but hard rock miners were used as controls.

NOTE: The following notes were sent following the meeting and were not part of the verbal

discussion at the end of the session.

P. GROSS: Dr. Langer's presentation suggested that fiberglass is carcinogenic to man. Epidemiologic studies as well as experimental studies in which animals inhaled fiberglass

or were injected intratracheal ly with it have provided evidence that glass fibers were not

carcinogenic. Only when glass fibers of a special thinness and length are placed in the

chest cavity (not the lungs) or injected into the abdomen of rats do cancers develop.

According to a recent publication (Money Causes Cancer: Ban It, by G. E. Moore and

W. N. Palmer, JAMA 238, 397, August 17, 1977), sterilized dimes placed into the abdomen of

rats caused more than 25 percent of them to develop cancer within 14 months. The proclivity

of certain rodents to develop cancers in response to various insoluble, solid materials

embedded in their tissues is well recognized as "Solid-State Carcinogenesis" and should not

be extrapolated to man.

A. LANGER: During my presentation I voiced concern that among fibers other than

asbestos, synthetic insulation fibers, e. g. , fibrous glass, when inhaled, may be biologically active. This concern has been raised by a number of investigators, in different

laboratories, based on observations made during more than 20 years of experimental work. As

early as 1955, Schepers and Delahant [1], utilizing the inhalation route of administration,

exposed guinea pigs and rats to 6-micron diameter fibrous glass. These animals were serially

sacrificed for time periods up to two years, and progressive pulmonary changes followed.

Guinea pigs were observed to develop pneumonia, lung abscesses, emphysema, and systemic

neoplasms. Rats, in addition to these alterations, also formed pleural plaques, a stigma

normally associated with asbestos fiber inhalation. "Severe parenchymal changes" were

91
observed in both animal populations. In the same year, Schepers [2] published additional

experimental data concerning the biological effects of intratracheal ly injected and inhaled

glass wool. He observed persistence of glass in animal lung for up to 18 months after

cessation of exposure. Glass wool fibers were observed in multinucleated giant cells and in areas of incipient atrophic emphysema. Epithelial hyperplasia was commonly observed.

Inhalation experiments, conducted simultaneously with the same animals, produced epithelial

hyperplasia and cellular desquamation; papillomas were observed in bronchioles. Focal

cellular pneumonitis and other effects, such as alveolar wall thickening, were noted.

Schepers considered some of these as "remarkable lesions" and suggested that " glass is

not f ibrogenic when retai ned i n 1 ung ti ssue . At the same time the gravi ty of the type of

bronchiole lesion provoked necessitates caution i n di smi ssi ng glass wool as i nnocuous . Indeed it shoul d be regarded as a potenti al ly harmful substance i n ci rcumstances 1 eadi ng to

the inhalation of large quantities of the type of products studied in these experiments .

It should be stressed that this early study did not provide a control group; however, one

amy cautiously accept these findings considering the nature of the diseases and the extent

to which the animal colony succumbed.

In a number of animal studies which followed (e.g., Gross et al . , 1959 [3]; Gross

et al . , 1970 [4]), pulmonary changes from a variety of synthetic fibers, in a number of

animal models, appeared to occur. However, faced with some experimental caveats, these

workers interpreted the results as not excl usi vely indicative of biological activity of

the fibers. It was not until 1972 that Stanton and Wrench [5] demonstrated the ability of

fibrous glass to induce malignant mesothelioma in experimental animals with appropriately

vigorous control groups. This was substantiated further by Stanton in 1973 [6] and Pott

et al . , 1974 [7]. Further work by Wright and Kuschner, in 1976 [8] unequivocally demonstrated the ability of fibrous glass to act in a manner similar to asbestos fibers in animal

tissues (formation of scar tissue). Finally, Wagner et al . , 1976 [9], were able to produce

mesotheliomas in Wistar rats, after intrapleural inoculation of glass fiber into chest

cavities.

The extent and even the histopathic nature of induced lesions may not be so marked as those from asbestos; nevertheless, many reports in the experimental pathology literature

unequivocally demonstrate the potent activity of synthetic fibers in animal models [10].

Dr. Gross is correct in suggesting that the ability to induce tumors in the experimental

model may well be related to the "Oppenheimer effect" (solid state carcinogenesis).

Extrapolating to humans, this may indeed be the very same reactions which evokes mesothelial

tumors. Hence, it has often been said that mesothelioma merely requires the physical

presence of a fiber at the pleural surface. If this is so, then the chemistry of the fiber,

and its physical state, are secondary in terms of this particular biological response.

Therefore, if inhalation of thin asbestos fibers (of any variety) produce mesotheliomas,

the inhalation of thin glass fibers, which may also penetrate to the mesothelial lining of

the lung, may produce the same response. The subject is still one which requires animal

studies, and certainly human studies. It is an open issue.

Discussion References

[1] Schepers, G. W. H. and Delahant, A. B. , An experimental study of the effects of glass

wool on animal lungs. Arch. Ind. Health , T2, 276-279 (1955).

[2] Schepers, G. W. H. , The biological action of glass wool. Arch. Ijid. Health , 1_2, 280-

287 (1955).

[3] Gross, P., Westrick, M. , and McNerney, J. M. , Glass dust: a study of its biologic

effect, Arch . Ind . Health , 16, 10-23 (1959).

[4] Gross, P., Kaschak, M. , Tolker, E. , Bobyak, M. , and deTreville, R. T. P., The pulmonary

reaction to high concentrations of fibrous glass dust, Arch. Environ . Health , 20,

696-704 (1970).

[5] Stanton, M. and Wrench, C. , Mechanisms of mesothelioma induction with asbestos an fibrous glass, J. Nat. Cancer Inst . , 48, 797-821 (1972).

92
[6] Stanton, M. , Some etiological considerations of fiber carcinogenesis, In: lARC Mono.,

Biolog. Effects of Asbestos, Bogovski, P., et al . , Eds, Sci . Pub . No. 8, Lyon, pp

289-294 (1973).

[7] Pott, F. , Huth, F. , and Friedrichs, K. H. , Tumorigenic effect of fibrous dusts in

experimental animals, Eny. Health Perspect . , 9, 313-315 (1974).

[8] Wright, G. and Kuschner, M. , The influence of varying lengths of glass and asbestos

fibers on tissue response in guinea pigs. In: BOHS-Inhaled Particles and Vapours , IV,

Edinburgh (1976), in press.

[9] Wagner, J. C. , Berry, G. , and Skidmore, J. W. , Studies of the carcinogenic effects of

fiber glass of different diameters following intrapleural inoculation in experimental

animals. In: Occupat. Exp. to Fibrous Glass, A Symposium - HEW - NIOSH, Univ. Maryland,

June, 1974, U. S. Govt. Printing Office, Wash. p. 193-204 (with discussion).

[10] Occupational Exposure to Fibrous Glass : A Symposium , HEW - NIOSH, Univ. Maryland,

June, 1974, U. S. Govt. Printing Office, Wash. 404 p.

93

National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

MEASUREMENT OF ASBESTOS RETENTION IN THE HUMAN RESPIRATORY SYSTEM RELATED TO HEALTH EFFECTS

J. Bignon, P. Sebastien, and A. Gaudichet

Universite Paris-Val de Marne - Institut de Recherche sur 1' Environnement

Centre Hospital ier Intercommunal

94010 Creteil , France

and

Laboratoire des Particules Inhalees

Direction Departmental e de 1' Action Sanitaire et Sociale

75013 Paris, France

Abstract

The retention pattern of asbestos fibers in the human respiratory

system is related to four mechanisms: penetration into the respiratory

tract deposition on the surface of respiratory epithelium, clearance,

and intra-tissular translocation of asbestos fibers. Knowledge of such

retention pattern for people exposed to asbestos dusts could provide

useful information concerning the role of these mechanisms and the

pathogenicity of fibers. So, asbestos fibers content has been assessed

by light and electron microscopy in different samples from the

respiratory tract: sputum, broncho-alveolar washing fluid, lung

parenchyma, parietal pleural, and mediastinal lymph nodes from people

diversely exposed to asbestos dusts and affected by various asbestosrelated diseases. In each sample, asbestos fibers, identified as chrysotile or amphibole, have been counted and measured (length and

diameter).

It has been shown that asbestos fibers found in sputum and in

broncho-alveolar washing fluid by light and electron microscopy were

reliable for the assessment of inhaled asbestos fibers in the workplace

or in the environment.

Analytical data concerning asbestos burden in respiratory tissues

can be summarized as follows:

- despite the fact that most of the consumed asbestos is of

chrysotile type, amphibole was more frequently found in lung parenchyma

than chrysotile, in most cases;

- most of the fibers retained in lung tissues were less than 0.20 \jm

in diameter and shorter than 5 |jm. The intra-alveolar fibers were

shorter (3.3 pm) than fibers found in lung parenchyma (4.9 pm). Fibers

encountered in mediastinal lymph nodes were shorter (2.5 pm) and of

amphibole type, whereas fibers encountered in parietal pleura were the

shortest (2.3 pm), and thinnest (0.06 pm in diameter) and mostly of

chrysotile type.

The signification of these data concerning the topographic

variation in the fiber type and size are discussed in relationship with

adverse health effects, particularly carcinogenesis.

Key Words: Asbestos; carcinogenesis; fibers; pathogenicity; respiratory

tract.

95
Introduction

The factors relevant to the assessment of public health risks of exposure to asbestos

have been recently reviewed in two documents [1,2]^. It is now well documented that

exposure to asbestos dust can lead to the development of lung fibrosis, bronchogenic

carcinoma, pleural plaques, pleurisy, mesothelioma, gastro-intestinal tumors, and perhaps

other unexpected diseases. The most critical point today is the establishment of doseresponse relationship. Regarding cancer, adequate data to establish a threshold limit are

not yet available. "The existence of a theoretical no-effect level may even be doubted;

however, there may exist a practical no-effect level, below which any excess incidence

cannot be adequately established" [1].

As far as asbestos is concerned, because of the various possibilities of exposure, it

is difficult to define retrospectively sharp conditions of exposure. So, the exposureeffect relationships are not very reliable and greater reliance should be put upon

biological monitoring. Asbestos metrology in human samples could provide information

about the most important questions arising for the assessment of dose-effect relationships

and for the subsequent definition of prevention practices:

A. Is there any relationship between one or several body-burden parameters at

autopsy and the cause of death, sex, age, and possibilities of exposure? The problem is

that the latency period of asbestos-induced diseases can be very long (up to 30 or 40

years). As the accumulation of fibers in man occurs in a dynamic way (related to

inhalation and clearance mechanisms), only the residue-burden can be investigated at

autopsy. Research is needed to establish eventual relationships between autopsy residueburden and burden at the time of disease onset.

B. What is the most suitable external indicator of body-burden during life? Such a contamination indicator, if it exists and if available for monitoring, could be very

helpful for the detection or the survey of exposed people. If relationships could be

established with related diseases or with any biological test, this kind of survey should

be specifically relevant to biological monitoring.

C. What is the biological significance of physical and chemical properties of fibers

(length, diameter, elemental composition, associated pollutants...) regarding the

induction of diseases (particularly tumors)?

Recent experimental data using intrapleural implantation [3] or intraperitoneal

injection [4] of fibers of different sizes indicated clearly that the size parameters are

the most important for inducing cancer and that the most carcinogenic fibers, whatever the

chemical composition, are those with diameters of less than 0.5 or 0.25 pm, and length more than 5 or 8 pm [5]. How can information provided by asbestos measurements in human

respiratory tissues be correlated with these recent findings?

D. These studies on body-burden correlated to environmental monitoring could lead to more appropriate standards or quality guides for the future, in relation to the prevention

of asbestos-related cancers.

General Considerations Related to Asbestos Retention

A. What Could Be the Definition of Body-Burden for Asbestos .

The actual amount of pollutants in humans at any time is called retention. The

retention of particles in humans occurs in a dynamic way and reaches an equilibrium level

depending on the relative rate constants of deposition and clearance processes. The model

of lung retention, based on the ICRP Task Group report [6], is suitable for describing the

general scheme of deposition, clearance, penetration, and translocation of fibers in

humans, as shown in figure 1. So far, the penetration and retention of asbestos fibers

through the gastro-intestinal tract have not been intensively investigated [7].

^Figures in brackets indicate the literature references at the end of this paper.

96
DusI" in inspired and expired air

Blood

t

Nasopharynx comparl-nnenl- 5put"unn

Trocheo _ bronchial

connparl"nnenl"

Alveolar connpart"nnen|-

f f } f } T

' ? ^ f } } } } } } ///

/ / / / - / / /'Parenchymal \\ss\aq jj/'' /'

Pulmonary lymph

vessels and nodes

7

'M.

Gas^roinl'eshnal

fract"

Pleural hssue Feces

Figure 1. General scheme for deposition, clearance, translocation and retention of

fibers, derived from the ICRP lung model [6]. (Heavy arrows : deposition;

light dotted arrows : clearance pathway; light arrows : translocation

pathways.

)

As asbestos measurement in tissues requires a destructive process, the retention of

asbestos fibers cannot be controlled continuously. Measurement of asbestos in organs will

provide information on asbestos retention at a very definite time: time of death for

autopsic material, or time of surgical intervention for biopsic samples. So far, few

attempts have been made for monitoring asbestos retention in alive people either by means

of external magnetic procedure involving no sampling [8], or by means of relating bodyburden to the amount of asbestos in sputum [9,10], in gastric juice [11], and in feces

[12].

B. Deposition .

Distinction has to be made between the two pathways for human exposure to asbestos:

the pulmonary tract (PT) and the gastrointestinal tract (GIT).

Timbrel 1 has reviewed the mechanisms by which particles deposit in the respiratory

system and has addressed specifically to the problem of fibers deposition [13]. He

identified settling, inertial impaction and Brownian diffusion as deposition mechanisms

which operate for both compact particles and fibers. In addition, he listed a fourth

mechanism, direct interception, which is of little significance for compact particles but

which may be of marked importance for fibers. In this view, a model for deposition of

fibers in the human respiratory system has been described [14]. The effectiveness of

these deposition mechanisms depends on the anatomy of the respiratory tract, the effective

aerodynamic diameter of the particles (size, shape, density), and the breathing pattern.

Asbestos fibers can also deposit in the gastrointestinal tract (GIT) either directly

(because of the presence of asbestos in water, beverages and food) or indirectly (fibers

coming from the respiratory airways and being swallowed). So far, there is little or no

i direct information regarding the way of fiber deposition at the surface of the human GIT.

97
It is obvious that accurate quantitative information on the deposition of asbestos

fibers in humans is difficult to be obtained because of clearance and translocation

mechanisms occurring simultaneously during lifetime. What we measure in the human body

results from all these associated mechanisms!

C. Clearance .

Fibers which are deposited on the muco-ci 1 iated blanket of the trachea and bronchi move toward the pharynx. The clearance of inhaled particles by this mechanism is believed

to be more than 98 percent effective for most deposited particles [6]. However, the

direct toxic effect of asbestos on the ciliated cells, as shwon recently [15], must impair

the effectiveness of this clearance mechanism.

The fibers deposited at the surface of the alveoli are either taken by alveolar

macrophages or entrapped within the alveolar lining film. From there, some of them are cleared towards the ciliated airways while others should penetrate the alveolar membrane.

The clearance is different according to the type of asbestos; for chrysotile, the

clearance is important, since Wagner et al. [16], Morgan et al. [17] found that a large

percentage of chrysotile asbestos entering the lungs of rats may be removed from the lungs

within 58 days; but we do not know the mechanisms involved. However, most of the cleared

fibers must reach the GIT as demonstrated by the study of Evans et al. [18] using inhaled

neutron activated asbestos; up to 73 percent of this asbestos was found in the feces

within 30 days.

Measurements related to clearance in human have been carried out in several kinds of

samples: sputum [10,19,20], gastric juice [11], and feces [12]. Generally, the finding

of asbestos in such samples was related to past exposure, pulmonary burden or pathological

features. The feasibility of using such samples as indicators of body-burden will be

discussed later.

D. Penetration and Translocation of Asbestos Fibers in the Human Body .

Measurements in tissues using the transmission electron microscope (TEM) have

revealed the presence of numerous fibers and fibrils far more than was ever imagined when

the fiber population was evaluated by light microscopy alone. These findings, occurring

even in case of moderate exposure and long elapsed time from last exposure, suggest a very

high penetration and retention rate for TEM size fibers. In humans, asbestos fibers have

been found by TEM in lung parenchyma by many authors [21,22,23, 24,25,26,27] and also in

bronchial tissue, lymph nodes [28], parietal pleura [25,26], pleural fluid [29,30],

peritoneum [31], liver [24], stomach [32,33], bowel walls [34], and colon [35]. These

findings suggest the penetration of asbestos in the human tissues and their migration

throughout the whole body.

Experimentally, penetration of fibers across the alveolar epithelium has been

described in TEM by Suzuki [36]. The extreme tendency of asbestos fibers to migrate has

also been demonstrated experimentally after subcutaneous injection [37], intrapleural or intraperitoneal inoculation [38,39,40], or after ingestion [41].

However, the penetration of ingested fibers through the wall of the gastrointestinal

tract is still in discussion. This point is mostly relevant to asbestos-related extrathoracic cancers, such as peritoneal mesothelioma, ovarian carcinoma, kidney carcinoma,

etc. Some authors pointed out that there was no penetration [42]. However, an experiment

in progress in our laboratories has shown that ingested chrysotile and crocidolite fibers

did cross the intestinal barrier in the rat, being recovered in the lymph of the thoracic

duct [43]. J

98
Analytical Data Related to Asbestos Body-Burden in Humans

A. Samples Studied as Indicators of Asbestos Body-Burden .

So far, most of the samples studied in this laboratory for estimating asbestos bodyDurden in humans were collected from the respiratory tract. We will only focus on data

obtained from measurements in 3 kinds of samples: lung washing fluid (LWF) obtained by

Droncho-al veolar lavage (BAL), sputum collected on alive people, and respiratory tissues

[lung parenchyma (LP), parietal pleura (PP), and mediastinal lymph nodes (LN) sampled at

autopsy).

According to the model shown in figure 1, it has been assumed that asbestos fibers

Found in LWF were related, on one hand to the intra-al veolarly deposited fraction of

inhaled fibers, and on the other hand to the fraction cleared from the deep lung whereas

those found in sputum must be related to the fibers cleared from the deep lung and from

the tracheo-bronchial compartment [20]. The fibers detected by destroying lung parenchyma

:orrespond to intra-al veolarly deposited fibers and intra-tissularly retained fibers at

the time of autopsy.

The point is to know if LWF and sputum can be used as external indicators of asbestos

3ody-burden. In this view, a systematic comparative study of fibers encountered in LWF,

in sputum and in lung tissue has been carried out and is still in progress.

B. Analytical Procedures .

For this study, the patients were classified according to their past asbestos

exposure. A meticulous history was obtained by questioning each patient in detail about

their successive occupations since leaving school. When a history of asbestos exposure

^/as found, the duration of this exposure and the lapse-time since last exposure was

recorded (expressed in years). Thus, the degree of exposure was estimated on one hand in

terms of its duration and on the other hand according to the type of work done by the

Datients.

All the biological samples were collected within 10 percent formalin. For autopsic

lungs, the formalin was injected i ntratracheal ly. Pieces of tissue samples were cut and

their volume measured. Typically, 1 cc of tissue was prepared for analysis.

Each sample to be analyzed was put in a glass vessel containing sodium hypochlorite.

Fhis digestive procedure was performed at room temperature during one or two hours. Then,

the mixture was directly filtered through a 0.4 pm pore size Nuclepore membrane filter

Dreviously coated with a carbon layer.

At this stage the filter was scanned under the light microscope looking for

ferruginous bodies.

For TEM study, a second carbon layer was deposited upon the filter and the particles,

entrapped in a double carbon-film, were transferred to TEM grids. The preparations were

scanned at X 30,000 direct magnification, looking for fibers. Each fiber encountered was

identified on the basis of its morphological features and its electron diffraction pattern

jnd was called chrysotile, amphiboles, or non-asbestos fiber. The length and diameter of

?ach asbestos fiber was measured using a calibrated mark on the viewing screen. For each

jrid square scanned, the data (number, mi neralogical type, and size of fibers) were

recorded directly on a computer. Several grid squares were scanned until the variation

around the mean calculated for numerical concentrations was less than 30 percent.

Concentrations of fibers were expressed in terms of number per sputum, number per

total lung washing fluid recovered, and number per cc of tissue.

Identification of associated non-fibrous particles has been assessed by means of

electron microprobe analysis [44], but quantitative information concerning numerical or

tiass concentration of such particles has not been obtained.

99
An i ntercompari son study between two laboratories (The University College of

Cardiff - F. D. Pooley and Laboratoire des Particules Inhalees, Paris - P. Sebastien) has

yielded very similar results concerning the assessment of asbestos fibers in tissues,

using the procedure previously described [45].

C. Lung Washing Fluid (LWF) .

The possibility of assessing the asbestos endo-al veolar content by means of bronchoalveolar lavage is now under investigation in diversely exposed people. Such a technique

has been used by different workers in order to collect free cells and proteins from the

human lung [46,47] and it has been shown in the baboon that pulmonary washing was an efficient procedure for the recovery of particles deposited in the alveolar compartment of

the lung [48].

1 . Material and Method

Up to date, this type of investigative procedure has been used in 26 cases (Table 1).

The cases studied were divided in 4 groups:

Table 1. Groups of 26 patients investigated by broncho-alveolar lavage.

Nb Cases

Group 1

Group 2

Group 3

Control

Asb. Exposure

Definite

Heavy

Definite

Moderate

Diseases

Suspected

Moderate

None

Asb : 9

PI PI : 5

Br Ca : 1

PI PI : 2

Silico-Asb :

Sm irr op : 1

Chr bronch :

Fibrosis +

PI PI : 1

PI PI : 1

Chr bronch :

Lar Ca : 1 tuberculosis

fibrosis : 1 histiocyt, x Chr bronch :

Abbreviations; Nb = number; Asb = asbestosis; PI PI = pleural plaques;

Br Ca : bronchogenic carcinoma; Sm irr op = small irregular

x-ray opacities; Chr bronch = chronic bronchitis;

Lar Ca = larynx carcinoma.

100
Group 1 included 9 cases with definite heavy asbestos exposure (DH), subdivided into

7 insulation workers, 1 asbestos-cement worker, and 1 asbestos-textile worker. Lung

asbestosis from 0/1 to 2/2 was diagnosed by x-ray according to the ILO U/C International

classification of radiographs of pneumoconiosis 1971. Asbestosis was associated with

bronchial carcinoma in one case and with pleural plaques in 5 cases (Table 1).

Group 2 included 5 cases with definite moderate asbestos exposure (DM), confirmed by

minutious occupational inquiries. The occupation and associated diseases are indicated in

Tables 1 and 2.

Table 2. Occupations, associated diseases, and mineralogical results in cases of Group 2.

(definite moderate exposure)

Results LWF in Group 2 (definite moderate exposure)

Cases Occupation

Years

occupation

Years since

asb. exp. Diseases

Nb coated

fibers

Nb

fibers % A

MOU... Boiler Fitter 10 19 PI PI 10 + 0

GAN. .

Glass Blower 27 0 PI PI 0 0

MAR... Asbestos

Plate Cutting

19 11 Sil icosis

± Asbest.

0 + 50

ESS... Plumber with

Welding, Brazing

18 3 Small Irr

Opacities

0 0

BOD... Isolation of

Central Heating

3 24 Chronic

Bronchitis

0 0

Abbreviations: PI PI = pleural plaques; Years occupation = years of occupational exposure;

Nb = number; LWF = lung washing fluid; % A = ratio of amphiboles number/

amphiboles number + chrysotile number. (See Table 1 also.)

Group 3 included 3 cases with suspected (but not proven) moderate asbestos exposure

(SM) according to the past occupational history of the patients. The occupation and

associated diseases are indicated in Tables 1 and 3.

Cases

ABD. .

MON. ..

DEC...

Table 3

Results LWF in Group 3 (suspected moderate exposure)

Occupation

Automobi le

Worker

Wood

Worker

Plumber

Years

occupation

10

10

25

Diseases

Chronic

Bronchitis

Fibrosis

+ PI PI

PI PI

Nb coated

fibers

0

0

0

Nb

fibers % A

0

0

Abbreviations: See Table 2,

101
The 9 control cases included patients without specific dust exposure.

The method used for broncho-alveolar lavage (BAL) has been extensively described

elsewhere [49]. It was assumed that the volume of the lung washed by this procedure

corresponded to about one segment. For mineralogical analysis, a 10 mL sample was taken

from the whole lavage before the centrifugation was performed for cells recovery.

2. Results

No asbestos fibers have been detected by LM and TEM in the LWF of the 9 control

cases. Some other no fibrous mineral particles have been encountered in 50 percent of

these cases, identified as chlorite, calcite, quartz, aragonite, phlogopite, magnetite,

and Al metal

In the group 1 of heavily exposed patients (Table 4), the mean number of fibers was 12.1x10^ per lavage. The mean number of alveolar macrophases (AM) was simultaneously

estimated to be 12.6x10^ per lavage. However, there was no correlation between the number

of fibers and the number of AM. Asbestos fibers were mainly of the amphibole type in

insulation or asbestos cement workers. The highest fiber count (50x10^), only of the

amphibole type, was observed in the patient working in an asbestos-cement plant. By

contrast, in the case of having worked in an asbestos-textile plant, all the fibers were

of the chrysotile type. The percentage of coated fibers was low, less than 1 percent in 7

out of 9 cases. The mean length and diameter were 3.3 and 0.13 pm respectively.

Table 4. Mineralogical studies of lung washing fluid (LWF).

Results LWF in Group 1 (definite heavy exposure)

Cases

Exp.

type

Yrs

exp.

Yrs since

last exp. Diseases

Nb

A.M.

106

Nb

fibers

106

%

coated

fibers % A

Mean

length

ym

Mean

diam

ym

CHA. .16 2 A 7.6 21 5 100 3.9 0.15

KRE. .

10 4 A 24.6 5 0.3 100 4.04 0.12

FRA. .

11 3 A 26.1 6 0.5 100 3.02 0.14

CHE..

10 11 A + B, CA 2.4 0.15 100 2.9 0.10

BEN.. . 15 4 A 3.8 0.9 99 3.2 0.15

LAI..11 0 A 9.7 11.4 2 90 3.05 0.12

MAA... 14 3 A + PI PI 7.3 7 0.8 100 2.07 0.15

MAR..AC 19 0 A 10.7 50 0.001 100 2.07 0.15

FAL... AT 4 1 A 2.4 3 0.02 0 5.6

Avera ge 12.2

±4

3.1

±3.1

12.6

±8.4

12.1

±14.4

1 ±1.5

3.3

±1

0.13

±0.1

Abbreviations: Exp type = type of exposure; I = insulator; AC = asbestos-cement plant

worker; AT = asbestos-textile plant worker; NB A.M. = number of alveolar

macrophages per lavage; Nb fibers = number of asbestos fibers per lavage;

% A = see Table 2; diam = diameter.

102
In the group 1, two parameters, duration of exposure in years and lapse-time since the

last exposure, have been assessed and correlated with the fiber count in the LWF. The two curves show that the number deposited within the alveolus increases with duration of

exposure, whereas this number decreases when the time since the last exposure increases

(figure 2).

Nbfibers

- 10

+ Yrs of exposure • Yrs since the last

exposure

10

I

15 20 Yrs

Figure 2. Relationship between fiber count in lung washing fluid and exposure patterns

for cases of group 1 (definite heavily exposed people). The fiber count

increases with the duration (years) of exposure; it decreases when the

delay since the last exposure increases.

In this group, the fiber yield obtained by BAL and by collecting one sputum has been

compared (Table 5). The numbers of coated and uncoated fibers were one or two orders of

magnitude higher in LWF than in sputum. Moreover, the fibers were shorter in LWF (mean

length 3 pm) than in sputum (5 pm). Elsewhere, the proportion of amphibole type fibers

was less in sputum.

By contrast, in groups 2 and 3, with moderate exposure, the asbestos fiber count in

LWF yielded less significant results (Tables 2 and 3). In some cases, both LM and TEM

analysis were negative. In others, only a few fibers were found, but at a level not

allowing a significant count to be expressed.

103
Table 5. Comparison of asbestos fibers in sputum and lung washing fluid (LWF)

from cases of Group 1 (9 cases).

Sputum

(one sample)

LWF

(whole lavage)

Coated Uncoated % amphibole Mean Mean

f i bers f i bers type fibers length diameter

ym ym

7.10^ 1.10^ 65 5 0.16

3.10^ 5.10^ 88 3 0.13

In groups 2 and 3, the comparison of asbestos fibers found in sputum and LWF yieldedl

the following results: in many cases, the numerical concentration was low or null; ini

other cases, one or the other sample showed some fibers. The asbestos content either ini

sputum or in LWF was similar, within the ranges: 0 to 10 for coated fibers and from not:

detectable to 5x10^ for TEM size fibers, mostly of chrysotile type.

D. Sputum .

It has been demonstrated in this laboratory [9,11] and by others [10] that the amount

of coated fibers or ferruginous bodies (FB) in the sputum was significantly related to the

asbestos exposure and to the amount of FB in lung parenchyma further measured at the

autopsy time [11]. This test is very simple and can be used as a retrospective proof of

asbestos exposure, even in the case of long lapse time after the end of exposure. Another

advantage is that the coating around the fibers is the evidence that the fibers have

stayed in the lung.

The study of sputum can also be good in the case of light exposure if the TEM is

used. As an example, in this laboratory the sputum has been studied from 45 people

working inside buildings insulated with sprayed asbestos containing material. The TEMi

examination has shown the presence of TEM size asbestos fibers, only of the chrysotile

type, in 13 cases (29 percent) (Table 6). The influence of duration of exposure on the

presence or not of fibers in sputum has not been demonstrated. Chrysotile fibers were mostly short microfibrils (0.5 to 2 |jm long) and forming clumps, probably entrapped in mucus (figure 3).

Table 6. Sputum monitoring for asbestos in 45 people working

in asbestos-sprayed buildings.

Mean duration

TEM study Nb Percent of exposure (yrs)

Presence of

Fibers 13 29 8.3

Absence of

Fibers 32 71 8.1

104
Figure 3. Electron micrographs showing chrysotile type fibers isolated from

sputum in people resident inside asbestos sprayed buildings.

E. Respiratory Tissues .

1 . Lung Parenchyma

Lung parenchyma samples from 27 autopsic cases diversely exposed to asbestos and with

different malignancies have been studied by TEM. Four blocks of parenchyma were sampled

in different sites of the same lung: central upper lobe, peripheral upper lobe, central

lower lobe, and peripheral lower lobe, as described elsewhere [25]. The geometric mean of

fiber count in the 4 sites has been calculated and then the cases have been classified in

groups according to the asbestos lung burden (Table 7). The proportion of cases having

more than 10^ fibers/cc of lung parenchyma was 8 out of 10 for the asbestosis + respiratory cancer group, 5 out of 11 for the mesothelioma group, 0 out of 2 for the lung cancer (without associated lung fibrosis) group, and 2 out of 4 for the other malignancies

group.

105
Table.

Pathological

features

Asbestosis ± Respiratory

Cancer

Mesothel ioma

Lung Cancer

Others

Mai ignancies

Asbestos fibers burden in lung parenchyma according to

pathological features.

Fiber concentration in the lung, Nb cm

<10^

6

2

10^ - 10^

3

0

>10'

2

0

-3

Total

10

11

2

Total 12 10 27

The mineralogical type of fibers encountered in lung parenchyma has been assessed by

TEM and the results are expressed in Table 8 by the percentage of amphibole/all asbestos

fibers. The parenchyma retention of amphibole type fibers has been found important in

most cases, the amphibole proportion increasing with fiber concentration in all

pathological groups. Moreover, whatever the fiber concentration in lung parenchyma, the

highest mean proportion of amphibole type fibers was observed in the mesothelioma group.

Table 8. Mineralogical type of fibers in lung parenchyma:

ratio amphiboles/(amphiboles + chrysotile) x 100.

Pathological

features

Asbestosis ± Respiratory

Cancer

Mesothelioma

Lung Cancer

Others

Maligancies

Fiber concentration in the lung, Nb cm'

<10^

38

53

4

12

lo"-

59

70

10' >10'

69

89

Average

58

64

41 26

Several size parameters have been assessed: mean length, mean diameter, and

proportion of fibers longer than 8 pm. The results are shown in Tables 9, 10, and 11 respectively. The main figures are: 1) the size of fibers increases when the

concentration increases; 2) the mean diameter never exceeds 0.16 pm; 3) the mean percentage of fibers longer than 8 pm does not exceed 20.8 percent.

106
Table 9,

Pathological

features

Asbestosis ± Respiratory

Cancer

Mesothel ioma

Lung Cancer

Others

Malignancies

Size of fibers in lung parenchyma: mean length (ym)

-3

Fiber concentration in the lung, Nb cm

<10'

3.7

4.8

1

2.8

10^ - 10^

5.4

5.7

>10'

5.5

4.1

2.3

Average

5.1

4.9

1

2.6

Table 10.

Pathological

features

Asbestosis ± Respiratory

Cancer

Mesothelioma

Lung Cancer

Others

Malignancies

Size of fibers in lung parenchyma: mean diameter (ym).

-3 Fiber concentration in the lung, Nb cm

<10"

0.11

0.09

0.05

0.09

10^ - 10^

0.13

0.13

>10'

0.16

0.12

0.13

Average

0.13

0.11

0.05

0.11

Table 11. Size of fibers in lung parenchyma: proportion of fibers longer

than 8 ym (%).

Pathological

features

Asbestosis ± Respiratory

Cancer

Mesothelioma

Lung Cancer

Others

Mai ignancies

Fiber concentration in the lung, Nb cm

-3

<10"

11.6

13.1

0.7

1.6

10^ - 10^

20.1

20.5

>10'

20.8

11.4

6.3

Average

18.6

15

0.7

4.1

107
2. Asbestos Fiber Parameters According to Sampl ing Sites in Respiratory Tissues : Parenchyma , Parietal Pleura , Mediastinal Lymph Nodes .

Besides lung parenchyma samples,, parietal pleura samples were available in 13 cases

and mediastinal lymph node samples in 4 of these cases.

The comparison of fiber concentration in lung parenchyma and parietal pleura is'

indicated on figure 4. The absence of correlation between asbestos fiber content in:

parenchymal and pleural tissue is emphasized. It is noteworthy that in some mesothelioma

cases, even with high concentration inside lung parenchyma, the fiber concentration in the

parietal pleura was very low. By contrast, a correlation seemed to appear between the

fiber concentration in parietal pleura and in lymph nodes (figure 5).

10^ 10^

LUNG PARENCHYMA

FIBERS IN LUNG AND

PLEURA (Nh cni3 \

<

A

M. Mesothelioma

LU M A . Asbestosis — Lung — 10^

PARIETAL

PI M

A M

M

A

Cancer

- 10^

10^ M MM M

Figure 4. Correlation between asbestos fiber concentration in lung and in parietal

pleura (see text for comments).

108
FIBERS IN PLEURA AND

LYMPH NODES (Nb.cm^)

10

_L

PARIETAL PLEURA

10« 10

Figure 5. Correlation between asbestos fiber concentration in parietal pleura and

mediastinal lymph nodes.

The comparison of mineralogical types has been carried out in the same way. The most

riking features were:

a) Most of TEM fibers encountered in parietal pleura were of chrysotile type even

en the proportion of amphibole/amphibole + chrysotile type fibers was higher than 0.5 in

e lung parenchyma (figure 6).

b) By contrast, so far in the few cases studied, most of the fibers encountered in

mph nodes were of amphibole type (figure 6).

The fiber size has been compared in the different sampling sites (Table 12). The

ngest fibers were found in the lung and the thinnest in the parietal pleura. Mean fiber

ngth was of 4.9 pm for lung parenchyma, 2.3 pm for parietal pleura, and 2.5 pm for lymph

des.

109
Ratio (Amphiboles/Amphiboles + Chrysotile) x 100

100

PARIETAL

PLFIIRA

-50

^

50 100

LUNG PARENCHYMA

100 y

X LYMPH

NODES

-51

50 100

1

Figure 6. Ratio of amphiboles count/total asbestos fibers count in lung parenchyma compared

to the ratio in parietal pleura (top) and to the ratio in lymph nodes (bottom).

110
Table 12. Fiber size in lung parenchyma, parietal pleura,

and lymph nodes.

Lung

parenchyma

Parietal

pleura

Lymph

nodes

Mean Length

pm

4.9 2.3 2.5

Mean Diameter

ym

0.13 0.06 0.16

Proportion of Fibers

Longer than 8 ym

percent

15 2 3

Discussion

The contribution of this metrologic study of asbestos dusts in the human PT is

relevant to three major points relating to the pathophysiology of fibrous particles:

It allowed a check of the reliability of monitoring asbestos in sputum and lung

washing fluid for the assessment of asbestos exposure.

- It provided a better understanding of the partition of fibers in the different

compartments of the respiratory system, which allows hypothesis about the translocation of

fibers in the PT.

- It yielded quantitative data concerning the actual fiber dimensions in humans in

different diseases, including pleural mesothel iomata, which have to be discussed in view

of recent experiments concerning the mesothelial response in relation to fiber dimension.

A. External Indicators of Asbestos Lung Burden .

The present work demonstrated that the study of sputum and LWF by LM and TEM was very

reliable for the assessment of asbestos exposure in heavily exposed people. The advantage

of LWF over sputum is that it yields a greater amount of fibers which are most

representative of the alveolarly deposited fraction. This technique, which requires that

the patient accept a fiberoptic bronchoscopy, might help to diagnose asbestos-related

diseases. However, this possibility has some limitation. Indeed, the information

provided by BAL carried out in moderately exposed people was much less reliable than the

study of lung parenchyma. This can be easily understood since we will discuss later on that the percentage of i ntraal veol ar fibers is very low compared to the fibers retained in

lung parenchyma.

However, it seems that LM and TEM study of sputum is an excellent tool for detecting

and following exposed people [9,11]. A cytological control of the sputum looking for AM

is needed to be sure that it represents the mineral content of the deep lung. It is

possible that the measurement of asbestos fibers in other biological samples could be

better indicators of asbestos body-burden, as discussed elsewhere [50]. Thus the search

for asbestos fibers in feces appeared to be a very sensitive method, allowing detection of

low intake of asbestos fibers [12].

B. Translocation of Asbestos Fibers in the Respiratory System .

The figure 7 summarizes all the mean data concerning number, length, and diameter of

fibers in four sites of the respiratory system: alveoli, LP, PP and LN. Moreover, the

figure 8 gives the distribution of length fibers in these four sites.

Ill
Figure 7. Diagram comparing the mean number (Nb), mean length (L) and mean diameter

(d) of asbestos fibers in 4 sites of the respiratory system. Numbers have

been estimated for the whole lung for parenchyma (Par) and alveoli (Alv),

while they are given per cc of tissue for pleura and lymph nodes (LN).

112
percent

30

20

10

30

20

10

30

20

10

30

20

10

LUNG PARENCHYMA

16 32 fim

PARIETAL PLEURA

1

LYMPH NODES

Figure 8. Distribution of fibers length in parenchyma, parietal pleura, lymph nodes

and alveoli. Note that long fibers, more than 4 pm in length, are less

frequent in pleura, lymph nodes and alveoli than in parenchyma.

113
For LP and alveoli, the fiber counts have been integrated for the whole lung

distinguishing intra-al veolar fibers assessed by the BAL and intra-parenchymal fiber,,

assessed by destroying LP. Thus, the fraction corresponding to LP totalizes fiberi

entrapped in the pulmonary interstitial tissue (plus fibers inside blood vessels?) ar fibers within the alveolar compartment. For that estimation, the volume of total lung ha

been assumed to be 5000 mL and the fraction of alveolar spaces washed by the BAL to t 1/20 of the whole lung volume. Thus, the figure 7 shows that the i ntra-al veol ar fractic

of all intra-parenchymal fibers would only represent about 1 percent of all the fiber

retained in lung tissue, when assumed that BAL recovered all intra-al veolarly deposite

fibers.

The mineralogical type of alveolar and interstitial asbestos dusts did not diffe

significantly, as indicated on one hand by the electron diffraction pattern and on tH other hand by the measurement of fiber diameters, identical in both sites (0.13 pm in meo diameter).

I

Elsewhere, it is noteworthy that the intra-al veolar fibers were significantly shorten'

(3.3 pm in mean length) than the interstitial fibers (4.9 pm in mean length for I fibers). This difference must even be more important, because the mean length c interstitial fibers is probably reduced by adding the 1 percent of short alveolar fibe»

to the interstitial fibers when LP is studied; on the other hand, it is possible that t\ mean length of intra-al veolar fibers is increased by the addition of longer fiber

deposited at the surface of the peripheral airways and washed out during the BAL. Indeec

the mean length of fibers in sputum was found to be 5 pm (Table 5). These results clear"

indicate a shorter length of fibers inside alveoli compared to pulmonary interstiti;

tissue. This can be related to two mechanisms, more or less associated (figure 9); eith(

long fibers might penetrate more easily across the alveolar membrane or small fibers ai more easily cleared from the interstitial tissue toward the alveolar spaces? As will t discussed, sizing of fibers in pleura and in lymph nodes brings a clue in the favor of tl last hypothesis.

Indeed, in these two sides (PP and LN), the asbestos fibers were significant'

shorter than in lung parenchyma (2.3 pm in PP; 2.5 pm in LN compared to 4.9 pm in LP; These findings are additional clues to the greatest translocation effectiveness of sho)

fibers. The migration of fibers was found even more selective in this study, since most"

chrysotile fibers were found inside the PP, with a mean diameter of 0.06 pm, where;

mostly amphibole type fibers with a mean diameter of 0.16 pm were found in mediatinal Lf This selective migration of fibers might be mostly related to their dimension, as if on" short and very thin fibers could be entrapped in the PP tissue (figure 9).

C. Fibers Dimension Related to Carcinogenicity .

The aforementioned recent animal experiments after implantation of fibers in tl pleura [3,5] reinforced the idea that the carcinogenicity of fibers depends only ( dimension of fibers, whatever the chemical composition is, in such a way that tt probability to induce pleural cancer reaches 100 percent when all the fibers are less th;

0.25 pm in diameter and more than 8 pm in length (see Stanton et al. , this meeting).

In humans, as demonstrated by this work and by others [24,26,51], all the asbest(

fibers encountered in different sites of the respiratory system were found to have

diameter less than 0.25 pm. By contrast, the present study has clearly demonstrated th. the mean length of fibers was always less than 8 pm in all sites (figure 7). However,

certain percentage of fibers was longer than 8 pm, especially in lung parenchyma ( percent) (see Table 12 and figure 8). The point is to understand how such few fiber

distant from the parietal pleura, might induce the carcinogenetic transformation ( mesothelial cells, or if other mechanisms specific to humans are to be considered.

114
Figure 9. Diagram showing the hypothetic different selective translocation pathways

of fibers in the respiratory system. The longest fibers are retained

within the lung parenchyma (LP) with more amphi bole- type fibers than

chrysoti le-type fibers (A > C). The shortest fibers migrate either towards

the parietal pleura (Par PI) and mostly of chrysoti le-type (C), or towards

the lymph nodes (LN) and mostly of amphibole-type (A). The fibers are shorter within the alveoli (Alv) than in lung parenchyma (LP); this must be

due to the selective translocation of short fibers from the pulmonary

interstitial tissue (?).

The microprobe analyses have been carried out in the Laboratoire de Biophysique

idicale (Pr P. Galle) in collaboration with J. P. Berry.

Part of this work has been supported by the Ministere de la Qualite de la Vie and by

ie Institut National de la Sante et de la Recherche Medicale.

115
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241-252 (1974).

117
[37] Roe, F. J. C. , Carter, R. L. , Walters, M. A., and Harington, J. S. , The pathological

effects of subcutaneous injections of asbestos fibers in mice: migration of fibers

to submesothel ial tissues and induction of mesothel iomata. Int. J. Cancer 2, 628-638

(1967).

[38] Karacharova, V. N. , Olshvang, R. A., and Kooan, F. M. , On changes of certain organs

after intraperitoneal administration of asbestos containing dust in experiment,

Byull . Eksp . Biol . Med. 67, 117-120 (1967).

[39] Morgan, A., Holmes, A., and Gold, C. , Studies of the solubility of constituents of

chrysotile asbestos in vivo using radioactive tracer techniques. Environ . Res . 4,

558-570 (1971).

[40] Friedrichs, K. H. , Hilscher, W. , and Sethi, S. , Staub und gewebe untersuchungen an rattennach intraperitonealer injektion von asbest, IjTt. Arch. Arbeits . Med . 28, 341-

354 (1971).

[41] Cunningham, H. M. and Pontrefact, R. D. , Asbestos fibers in beverages, drinking

water, and tissues: their passage through the intestinal wall and movement through

the body, J. AOAC J6, 976-981 (1973).

[42] Gross, P., Harley, R. A., Swinburne, L. M. , Davis, J. M. G. , and Green, W. B. , Ingested mineral fibers. Arch. Environ . Health 29, 341-347 (1974).

[43] Bignon, J., Masse, R. , and Sebastien, P., Unpublished data.

[44] Berry, J. P., Henoc, P., Galle, P., and Pariente, R. , L' empoussierage pulmonaire:

etude par microscopie electronique, microanalyse par sonde ectronique,

microdi f fraction d'electrons, J. Microscopie 17 , 11-18 (1975).

[45] Pooley, F. 0. and Sebastien, P., Asbestos fibers from mesothelioma cases. Results of

an intercomparison program (1976).

[46] Reynolds, H. Y. and Newball, H. H. , Analysis of proteins and respiratory cells

obtained from humans lung by bronchial lavage, J. Lab. Clin . Med. 84, 559-573 (1974).

[47] Daniele, R. P., Altose, M. D. , and Rowlands, 0. T. , Immunocompetent cells from the

lower respiratory tract of normal human lungs, J. Clin . Invest . 56, 986-995 (1975).

[48] Nolibe, D. , Metivier, H. , Masse, R. , and Lafuma, J., Therapeutic effects of pulmonary

lavage, in vivo, after inhalation of insoluble radioactive particles. Fourth

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September 1975 (in press).

[49] Basset, F. , Soler, P. , Jaurand, J. C. , and Bignon, J. , Ultrastructural examination of

broncho-alveolar lavage for diagnosis of pulmonary histiocytosis X, Thorax 32, 303-

306 (1977).

[50] Bignon, J., Sebastien, P., and Bientz, M. , Review of some factors relevant to the

assessment of exposure to asbestos dusts. International workshop on biological

specimen collection, Luxembourg 18-22 April 1977 (in press).

[51] Pooley, F. D. , Oral communication. Meeting on the biological relevance of fiber

parameters, lARC June 30-July 1, Lyon (1977).

118
Di scussion

R. FISHER: I noticed you used the term amphibole in your tables. Since I believe

these were insulation workers, you mean amosite rather than the general mineral group?

J. BIGNON: The identification of asbestos fibers has been done only by the morphology

in TEM and by electron diffraction. As we did not use microanalysis to identify the

different type of amphibole, and as we did not get accurate inquiries about the material

used by patients, I cannot answer your question.

FISHER: But these were insulation workers, am I correct?

BIGNON: Yes. These workers sprayed a mixture of asbestos and other material; but as the material used by these workers changes from time to time, it is difficult to identify

by a questionnaire the type of asbestos fibers to which the patients have been exposed.

FISHER: The type of amphibole used would be one that would be considered a commercial

form of asbestos and would only be useful for that purpose if it did have the long fiber

length that you showed in your tables. I am trying to distinguish between this type of

amphibole and the more general, more widely occurring forms. I think that's an important

point.

M. SCHNEIDERMAN: Is your question related to the fact that the type of amphibole

used by the insulation workers is in some manner different from what one has in some other

kinds of general exposures; is that what you're driving at?

FISHER: Exactly, yes.

SCHNEIDERMAN: Yes, I think Prof. Bignon agrees with you.

G. WRIGHT: I have one question which is becoming increasingly bothersome. In looking

at old materials from autopsies, the question of whether or not the material that was used

for fixing the lung contains asbestos fiber is beginning to be raised. I would ask whether

the materials you used in fixing the lung had been demonstrated to be asbestos fiber-free?

The other is a comment, because your study, I think, demonstrates rather well the following: the lung apparently is a concentrator of long fibers. In most occupational

exposures, the ratio of fibers longer than 5 pm to those that are shorter is of the order

of 20 to as much as 50 or 100 to 1 . So if you find 17 percent of the residual fibers in

the parenchyma are longer than 8 pm, this strongly suggests that the lung preferentially

concentrates the long fibers. There is very recent evidence by Arthur Morgan, in experimental animals, of precisely what you've shown. In acute experiments lasting for several

months, the animal rather rapidly clears the short fibers and retains the long ones. So

it's a very nice confirmation of your observations.

BIGNON: The liquids we have used for lung fixation and processing were constantly

filtered through 0.5 pm Millipore filters.

119

National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

EPIDEMIOLOGIC EVIDENCE OF THE EFFECT OF TYPE OF ASBESTOS AND FIBER DIMENSIONS

ON THE PRODUCTION OF DISEASE IN MAN

W. Clark Cooper

Equitable Environmental Health, Inc.

Berkeley, California 94704

Abstract

There is epidemiologic evidence to indicate that all types of

commercial asbestos, i.e., chrysotile, crocidolite, amosite, tremolite

asbestos, and anthophyl 1 ite asbestos, when inhaled, can cause pulmonary

fibrosis and increase the risk of lung cancer. All but anthophyl 1 ite

asbestos have been associated with malignant mesothelial tumors. There

is also strong evidence to support a decreasing gradient of pathogenicity

as one proceeds from crocidolite to amosite to chrysotile, but this

evidence does not clearly rule out the interrelated influence of fiber

dimension, shape, and co-factors.

Clear-cut epidemiologic evidence related to differing fiber

dimensions is scanty. Such information is critically needed. The most

pressing need is to determine the pathogenicity of ultrafine fibers in

the electron-microscope size range, and for fibers shorter than 5

micrometers, whether inhaled or ingested. It is suggested that there be

expanded epidemiologic studies of populations which have been exposed to

such fibers, without the presence of long fibers. This will probably

occur where the exposures are incidental to operations other than

commercial asbestos production. It is also recommended that there be

systematic study of the fiber content of human lungs and other tissues,

as related to causes of death.

Key Words: Asbestos; asbestosis; carcinoma; epidemiology; fine

particles; mesothelioma.

When the seriousness of the problem of asbestos-related disease became generally

recognized 15 to 20 years ago, it was regarded as arising solely from commercially-produced

asbestos. Most evidence had been obtained from workers exposed during the mining, processing, or use of commercial chrysotile, amosite, crocidolite, anthophyl 1 ite asbestos, or tremolite asbestos, so studies logically focused on these types.

The scientific and practical importance of determining whether all these types of

asbestos were equally hazardous became apparent. One of the first recommendations made by

the Working Group on Asbestos and Cancer, under the auspices of the International Union

against Cancer, meeting in New York City in October, 1964, was "that the importance of

fiber type on the risk of developing asbestosis, carcinoma of the lung, and mesothelial

and other tumors be investigated" [1]^.

Eight years later, meeting in Lyon, the Advisory Committee on Asbestos Cancers to the

International Agency for Research on Cancer [2], the successor to the subcommittee that

arose out of the 1964 Working Group, answered its own question: "Are all commercial types

of asbestos able to cause lung carcinoma?" as follows:

^Figures in brackets indicate the literature references at the end of this paper.

121
"Yes. Since 1964 the evidence of a causal relationship has been

increased by epidemiological studies showing exposure-response relations

for the incidence of lung carcinomas. The production of lung carcinomas

in certain animals by all types of asbestos supports this conclusion.

The epidemiological evidence in man, however, shows that there are clear

differences in risk, with type of fibre and nature of exposure."

With respect to mesothelioma, the Committee's report stated that,

"There is evidence that all commercial types of asbestos except

anthophyl 1 ite may be responsible. Evidence for an important difference

in risk in different occupations and with the type of asbestos has

increased. The risk is greatest with crocidolite, less with amosite, and

apparently less with chrysotile. With amosite and chrysotile there

appears to be a higher risk in manufacturing than in mining and milling."

The Committee then made specific recommendations for projects assessing excess cancer

risks following exposure to only one type of fiber, mentioning chrysotile, amosite, and

chrysotile, with special emphasis on differences between those engaged in mining and

milling and those engaged in the manufacture and use of these types of commercial asbestos.

It was further recommended that there be investigation of "talc-exposed groups in

mining and manufacturing to establish any differences in morbidity or mortality which

might be related to the amount and shape of the fine respirable particles."

In a related recommendation pertaining to experimental work, recognition was given to

the need for more information about the role of fine particles, especially the influence

of fiber size in the induction of tumors:

"These studies should be extended to include fibres other than asbestos.

A subcommittee should be established to review the need for, and arrange

the distribution of, standard samples of asbestos and other fibres in

addition to the UICC reference samples."

Another pertinent recommendation was: "There is an urgent need for the quantitative

assessment, size analysis, and characterization of particles and fibres in the lungs and

other organs.

Participants in the present workshop are engaged in the continuing search for answers

to the foregoing questions, and it is apparent definitive answers are not easy to obtain.

There is an expanded appreciation of the ubiquity of mineral fibers with shapes resembling

those of commercial asbestos, with diameters extending into a range below detectabi 1 ity by

light microscopy, and with lengths below 5 micrometers (pm), now arbitrarily used as the

lower limit for occupational standards. Decisions on pathogenicity for man are urgently

needed with respect to these, the asbestiform varieties of many minerals, and for all

durable fibers in the range below light microscopic detection, i.e., below 0.4 or 0.5 pm

in diameter, and which are very short, i.e., less than 5 pm in length. How can epidemiologic

evidence contribute to these decisions?

Epidemiologic studies cannot stand alone. They fit into a network of observations

from many sources, including theoretical and observed information on the aerodynamic

properties of particles, vitro tests, studies in experimental animals, and isolated

clinical observations. They are nevertheless, by definition, the final source for quantitative information in man, and ultimately must be the basis for establishing and evaluating

environmental controls.

Some of the effects in man which lend themselves to quantitative study and correlation

with occupational or non-occupational exposures include:

(1) Evidence of asbestosis, such as fibrosis of the lung parenchyma, fibrosis

or thickening of the pleura, calcification of the pleura, and other non- malignant reactions as demonstrated by radiography, functional tests,

physical examination, or study of tissues.

122
(2) Evidence of malignancy, notably carcinoma of the lung, mesothelioma of

the pleura or peritoneum, or cancer of the gastro-intestinal tract,

larynx, or other sites.

(3) Evidence of past exposures, as demonstrated by fibers in various tissues,

sputum, or urine.

It is generally accepted that fiber characteristics probably operate differently with

respect to different pathologic effects, so that asbestosis, lung cancer, mesothelioma,

and other malignancies will follow differing dose-response curves as we consider different

types and dimensions of fibers. Hopefully, we can obtain useful epidemiologic evidence by

considering the patterns of disease, as related to different types and dimensions of

mineral fiber, in groups identified as follows:

(1) Populations whose preponderant exposure has been to one type of asbestos

or the asbestiform variety of a mineral, whether by inhalation,

ingestion, or both, which can be observed for periods of at least 30

years and preferably 50 years after exposures began, and which can be

compared with groups having little or no exposure to the same or related

fibers;

(2) Populations with suspect diseases, whose past exposures can be

reconstructed by history, records, place of residence, or body burdens of

fibrous particles, and which can be compared with a matched series having

some disease unlikely to be asbestos-related. This case-study method is

most useful in relatively rare diseases, such as mesothelioma.

(3) Populations having differing concentrations, types, and sizes of mineral

fibers demonstrated at autopsy, to determine whether or not the patterns

of pathology and causes of death correlate with differing tissue burdens

of fibers.

What evidence have we gathered to date, using the foregoing approaches?

Types of Asbestos Used Commercially

There is unequivocal evidence that chrysotile, amosite, crocidolite, tremolite asbestos, and anthophyl 1 ite asbestos can produce asbestosis and increase the risk of lung

cancer. All but anthophyl 1 ite have been associated with an increased risk of mesothelioma. Grading the relative biologic activity of these several types of asbestos, in terms

of the production of each type of asbestos-related disease, is more difficult. As Margaret

Becklake [3] pointed out in her excellent review, it is not easy to control precisely for

dosage and cofactors. Fiber diameter, length, and shape are highly interrelated with

asbestos type and may be more important than chemical and crystal structure.

The consensus that crocidolite is the most hazardous commercial asbestos has been

derived from a number of studies, but these do not all rule out an influence of shape and

size. Emphasis on crocidolite as being particularly hazardous arose from its early association with mesothelioma in the Northwestern Cape Province of South Africa, as first described

by Wagner et al . [4]. Although the relative absence of mesothelioma in the crocidolite

areas of the Transvaal reported by Sluis-Cremer [5] was at first questioned because of the

exclusion of black and colored miners, Webster [6] has confirmed that there is a much

lower incidence of mesothelioma in the Transvaal. Timbrel 1 [7,8] has offered as an explanation the fact that crocidolite in the Northwest Cape is of smaller diameter (therefore

more respirable) and shorter (therefore more likely to avoid interception in the airways)

than the crocidolite of the Transvaal. It should be emphasized that although the Transvaal

fibers averaged three times as long as the Northwest Cape fibers, both samples had many

fibers above 5 pm in length. Webster [6] on the basis of pathologic observations of the

distribution of fibers in the lungs has questioned the foregoing explanation. He has

suggested that possibly concurrent exposures to iron and manganese in the Northwest Cape

may have an influence.

123
With respect to lung cancer, Enter! ine and Henderson [9] compared the experience of

workers making asbestos cement pipe, where both crocidolite and chrysotile were used, with

that of others exposed only to chrysotile. Those whose exposures included crocidolite had

6.1 times the expected number of deaths due to lung cancer, while those exposed only to

chrysotile had 1.4 times the number expected.

Weill et al. [10] carried out comparative studies of two populations of workers, one making asbestos shingles containing chrysotile, and the other making shingles, flooring,

and asbestos-cement pipe and exposed to both chrysotile and crocidolite. Those exposed to

crocidolite had more small irregular opacities by x-ray, more pleural thickening, and

significantly greater reduction in pulmonary function.

Despite the consensus that crocidolite is probably the most hazardous type of

commercial asbestos, the evidence does not appear strong enough to support a 10-fold

stricter standard for a time-weighted average, or a 60-fold stricter standard for 10-

minute exposures, as applied in the United Kingdom [11].

Amosite has been positively identified as responsible for pulmonary fibrosis, lung

cancer, and mesothelioma. Selikoff et al. [12] found a 10- fold excess of lung cancer, as well as 5 deaths from mesothelioma, in a population of 230 men who had been previously

employed in an amosite-using plant, during the period 1960 to 1971. This has been one of

the few opportunities in the United States to study workers without mixed exposures. The

high rates of asbestosis, lung cancer, and mesothelioma in asbestos insulation workers

have been in men with mixed exposures, to both amosite and chrysotile. The foregoing

experience in an amosite-using industry is in striking contrast to that reported in the

amosite mines in South Africa. Webster [6] states that of 232 confirmed cases of

mesothelioma diagnosed in South Africa between 1956 and 1972, 78 had been in miners, but

practically all had been exposed to Cape Blue crocidolite, with only two having had

exposures only to amosite. As pointed out earlier, the fact that Transvaal amosite shared

with Transvaal crocidolite the property of being thicker and longer than Northwest Cape

crocidolite makes it impossible to ascribe the difference to type alone. Men exposed to

crocidolite in the Transvaal also had relatively few mesotheliomas.

Chrysotile has been rated the least pathogenic type of the three major forms of

commercially-produced asbestos on the basis of relatively few studies in which exposures were limited to this type. Most such studies have been in workers engaged in the mining

and milling of chrysotile, in Canada, Italy, Russia, and Cyprus. A report by Braun and

Truan [13] indicated that the incidence of lung cancer in chrysotile miners and millers in

Quebec, while slightly elevated, was not nearly as great as had been described in asbestos

workers in the United Kingdom or in U.S. insulators. These studies have been criticized

for methodologic flaws, but it would now appear that they reflected a lower risk in

chrysotile miners. More recent studies of Quebec miners and millers by McDonald et al.

[14] show an excess of lung cancer, 5 times expected, only in the highest exposure group.

Only 5 deaths from mesothelioma were found among 3,270 deaths. A more recent estimate by

McDonald [15] gives the proportion of mesothelioma deaths as 8 out of 4,000 deaths. This

is far less than the proportion found in U.S. insulation workers, where, for example,

Selikoff found 77 of 1,092 deaths due to mesothelioma. Weiss [16] has recently studied

the mortality in a group of 264 employees hired during the period 1935-1944 in a plant

manufacturing chrysotile products, and who worked one year or more. The Standard

Mortality Ratio (SMR) for lung cancer was only 0.93. Although the design of the overall

study did not permit strict comparison with the study by Selikoff et al . [17] in an asbestos insulation material producing plant, comparison of groups with similar intervals

from first exposure to end of operation indicated a significantly lower lung cancer risk

in the Weiss study. These reports, combined with those of Weill et al. [10] and Enterline

and Henderson [9] previously reported, suggest that chrysotile is less pathogenic than

crocidolite or amosite. But, as Timbrel 1 [8] has pointed out, the curliness of chrysotile

fibers influences their deposition and transmigration, so shape and size may be more important than chemical composition per se.

The evidence on anthophyl 1 ite asbestos comes almost entirely from Finland, where this

form of asbestos was commercially developed until recently, and where there have been

widespread non-occupational exposures. The extraordinary incidence of pleural

calcification associated with low level exposures is well-documented (Kiviluoto) [18].

Kiviluoto and Meurman [19] and Nurminen [20] have shown in studies of workers exposed to

124
anthophyl 1 1 te asbestos that they have an increased risk of asbestosis and lung cancer, but

mesotheliomas have not been reported. Meurman et al. [21] analyzed 248 deaths in 1,092

anthophyllite miners and millers. There were 21 deaths from lung cancer, where 12.6 were

expected; no mesotheliomas were reported.

Studies of workers exposed to tremolite asbestos without associated exposures to

other fibers are not sufficiently well documented to permit placing them in a gradient of

response with other commercial types of asbestos. The same is true for actinolite

asbestos.

Other Asbestiform Minerals

What is the evidence for the pathogenicity of mineral fibers other than the types of

asbestos commercially exploited? It is almost non-existent because, in the absence of

commercial development and occupational exposures, contacts have been incidental to other

operations and have been poorly documented and usually of less magnitude. The best of

such studies have been associated with commercial talc operations. The presence of

tremolite asbestos, anthophyllite asbestos, and chrysotile in many talc deposits has

confirmed the potential of these types to produce fibrosis, pleural plaques, and to

increase the incidence of lung cancer. There are no studies to indicate that ribrous

talc, in the absence of asbestos of the types mentioned, can produce disease in man, but

one would predict that such fibers in the right size ranges would be pathogenic. Nonfibrous talc is apparently hazardous only if there is concurrent silica exposure. Rubino

et al. [22] reported on the mortality pattern in 1,346 talc miners and 438 talc millers,

in which there were 931 deaths. Although there was an' increased incidence of silicosis

and silico-tuberculosis, they reported no excess in cancer. They did not indicate any

fibrous talc being present.

A promising source of information on a non-commercial asbestiform variety of mineral

has been the population of the Homestake gold mine in South Dakota, where there have been

exposures to amphibole fibers, described as predominantly in the grunerite series similar

to those found in the Mesabi range of Minnesota, extending back for over 100 years.

Unfortunately, results to date are far from conclusive, despite a published mortality

analysis by Gillam et al. [23] and an environmental report by Dement et al. [24]. Gillam

et al. reported a statistically significant excess of lung cancer deaths (10 contrasted

with 2.7 expected) in 440 gold miners identified by the Public Health Service in a 1950

silicosis study. However, a more recent report by McDonald et al. (1977) covering deaths

between 1937 and 1973 in 1,321 employees of the same mine who were members of the

Homestake Veterans Club, and had worked 21 years or more, showed no excess lung cancer

deaths. There were 660 deaths for analysis. There was an excess of deaths from

pneumoconiosis and pulmonary tuberculosis. This, and the excess of non-malignant

respiratory disease deaths reported by Gillam et al . is not surprising, since 39 percent

quartz had been demonstrated in settled dust. Records kept by the mines since 1937 showed

dust concentrations ranging from 11 to 25.5 million particles per cubic foot (mppcf)

before 1952, greatly exceeding standards for free silica. The miners who died of non- malignant respiratory disease had begun work as early as 1916. Even if an excess of lung cancer were proven in the Homestake mine, attributing it to low concentrations of mineral

fibers would not be justified without careful consideration of what is known of smoking

histories and concurrent exposures to arsenic and radon daughters. Asbestiform minerals

almost certainly cannot be held responsible for the excess deaths from non-malignant

respiratory disease, in view of quartz exposures and death certificates which in most

cases had diagnoses of silicosis. It is absurd to attribute fatal pneumoconiosis in such

a situation to grunerite fibers at levels approximating one-tenth the current standard for

asbestos.

Swent [25] has critically reviewed the Gillam study and documented ventilation back

to 1916 and dust counts to 1937 which show that the assumption that past exposures to

silica, arsenic, radon daughters, and fibers were the same as those found in a 1972 survey

is untenable.

As matters now stand, the Homestake study cannot be regarded as supporting the

pathogenicity of grunerite fibers. One awaits the results of new studies being supported

125
by NIOSH, which may establish the mortality patterns with more certainty and hopefully

will permit more accurate estimates of past exposures.

Influence of Fiber Dimensions

Throughout consideration of types of asbestos, it is apparent that type cannot be

separated from shape and size. This is true even when exposures are characterized solely

on the basis of fibers in the light microscopic range (i.e., with diameters greater than

0.4-0.5 pm) and those greater than 5 pm in length. It has been demonstrated in recent

years, however, that neither in standard reference samples of commercial asbestos (Langer)

[26], nor in air and water samples, nor in lung tissue, are fibers mainly in the light

microscopic size range. Furthermore, as Pooley [27] has shown, even chrysotile miners and

millers contain large numbers of amphibole fibers, most of them in the microfiber range,

in their lung tissues, so their exposures are mixed.

When we turn to consideration of epidemiologic evidence on fiber dimensions, either

within a given species of commercially used asbestos, or in the asbestiform varieties of

minerals not used commercially, there is relatively little to report. There is suggestive

but not conclusive evidence from South Africa [7] that relatively short and fine fibers

are more likely to produce mesotheliomas than longer and thicker fibers, but these are within the range of light microscopy and longer than 5 micrometers. There are no conclusive studies in man to support the strong evidence from animal studies that very

short fibers (under 5 pm) are non-pathogenic.

In considering the influence of fiber size, the question of the ultrafine fiber must

be separated from the question of the very short fiber.

The ultrafine fiber is defined as one below the level of resolution by the light

microscope, i.e., less than about 0.4 pm in diameter, down, to the size of the smallest

chrysotile fibril, of the order of 0.025 pm or 250 Angstrom units. Evaluation of such

ultrafine fibers is of great importance because:

1) diameter has a strong inverse relationship to falling speed, so such

fibers remain airborne for long periods and are highly respirable,

although their capture and retention will vary not only with diameter,

but also with length;

2) they are found in large numbers in lung tissues, both in individuals

occupational ly exposed and those without such exposures, but seldom to

the exclusion of large fibers [28];

3) they have been found to be widespread in community air [29] and in

association with the quarrying and use of serpentinite rock [30];

4) they are not included in fibers counted by the methods currently

recommended for monitoring work environments, and are not covered by

current standards;

5) data are not being systematically collected on the numbers of ultrafine

fibers in the air nor how their concentrations relate to the

concentrations of larger fibers found in various occupational and

environmental situations.

There are no epidemiologic studies in which ultrafine fibers are an isolated variable.

All studies of populations exposed to commercial asbestos have involved heavy exposures

within the light microscope range, i.e., to fibers larger than 0.5 pm in diameter, so the

contribution of ultrafine fibers cannot be determined. On the evidence from studies in

animals, it is likely that such fibers, when longer than 5 or 10 pm, would be pathogenic.

126
The problem of the very short fiber is more critical:

1) studies in animals strongly suggest a decreasing gradient of fibrogenic

risk and carcinogenic potential (at least for mesothelioma) for fibers

shorter than 5 to 10 micrometers;

2) samples of naturally occurring chrysotile, amosite, and crocidolite have

been shown to contain a majority of fibers shorter than 5 pm in length

[28];

3) lung tissue contains a high proportion of short fibers;

4) samples of ambient air in many areas, such as those collected near taconite mining operations in Minnesota, and associated with crushed

rock in Montgomery County, Maryland, are predominantly short fibers

[30];

5) since current monitoring methods for the occupational environment

exclude fibers shorter than 5 pm, data are not being systematically

collected.

The biologic activity of short fibers in man is not known. By analogy with studies

in animals one would not expect fibers shorter than 5 pm or 10 pm in length to produce

asbestosis or mesothelioma. The only epidemiologic study in which fibrosis and excess

lung cancer has been attributed to exposures which were predominantly too short, ultrafine

fibers is that of Gil lam et al. [23] in the Homestake mine. Here 94 percent of fibers

were less than 5 pm in length, the median diameter was 0.13 pm, and the median length was

1.1 pm. For reasons pointed out earlier, these exposures, which were described as consisting largely of grunerite with some fibrous cummingtonite and hornblende, are inconclusive. Neither the actual mortality experience nor the past exposures are well

enough defined to be used as scientific evidence.

The case report by Miller et al. [31] in which a 63-year old man who died with

extensive interstitial pulmonary fibrosis was found to have had large numbers of

ultrafine, short fibers in his lungs cannot in itself establish a causal relationship, nor does it indicate how often such an association might occur. It is analogous to an earlier

report by Miller et al. [32] who made a somewhat similar finding in a man who had been

exposed for many years to talc in a rubber products plant and whose lungs showed enormous

numbers of submicroscopic talc particles (non-fibrous). Both reports suggest that

overwhelming concentrations of a reactive dust may in some individuals produce generalized

interstitial fibrosis. It does not tell us how often such might occur, nor provide any

information on relationships with malignancy.

The essentially negative evidence as to health effects from the airborne fibers

associated with taconite mining operations in Minnesota, and the negative evidence from

Duluth (Masson et al . ) [33] with respect to the ingestion of ultrafine, short fibers in

Lake Superior water are reassuring, but it is too soon to rule out effects with long

latent periods, i. e. , 25 years or more.

In summary, no populations whose exposures have been confined to ultrafine fibers,

short fibers, or fibers which are both ultrafine and short, have been defined or studied

long enough to permit epidemiologic evaluation.

There have been several studies in recent years in which the concentrations of fibers

in lung tissue have been guantitated and described, with some attempt at correlation with

pathologic changes. That of Ashcroft and Hepplestone (1973) [34] was limited to 35

individuals with asbestos bodies detected in histological sections, and all but one had

definite or probable histories of occupational exposure. The authors found that from 12

to 30 percent of the fibers were optically visible, the rest being detectable only by

electron microscopy. (They did not describe fiber lengths.) There was a general

correlation between fiber concentration and asbestosis, up to the level of moderate

asbestosis. Another study, by Doniach et al . [35], was limited to optically visible

asbestos bodies in a London necropsy series. The study by Pooley [27] of the lungs of

127
individuals with asbestosis who had been employed in the chrysotile mining industry in

Canada, and in 30 individuals who died with mesothelioma, provided valuable information on the relative proportions of chrysotile and amphibole fibers and on the large numbers of

EM-sized fiber present, but no detailed data on lengths and diameters of fibers were

presented. Its most interesting feature was the large number of amphibole fibers that were found in chrysotile miners. In short, we know of no large series of cases in which

the numbers and sizes of fibers in tissues have been correlated with causes of death.

Studies Which Are Needed

How can the necessary epidemiologic evidence be obtained? It can be accepted without

reemphasis that injection and inhalation studies in animals, testing various types of

asbestos and asbestiform varieties of other minerals in appropriate size ranges, must be

done. It is not likely that further study of individuals who mine, mill, process, or use commercial asbestos will do more than tune more finely what we already know. Even though

this is desirable and necessary, it is not likely to answer questions about very fine or very short fibers, since the nature of commercial asbestos is such that long fibers are always present. Only if dust control measures preferentially increase very greatly the

proportion of short fibers in the electron microscope range would studies in commercial

asbestos operations provide useful information regarding fiber size.

We must turn to other populations, where exposures have been incidental to non- asbestos industrial operations but which liberate or disperse asbestiform varieties of

minerals in the electron microscope range below 5 pm in length. The Homestake mine has

had this type of population, but here a positive finding would lead to a need to consider

several confounding variables. On the other hand, an absence of serious risk would be

highly reassuring, if past exposures were found to have been high. Other populations

which might be studied are those in association with taconite mining and milling

operations, where, in some areas, the airborne mineral fibers are predominantly less than

3 pm in length and do not represent any form of commercial asbestos.

There are many sections of the United States where chrysotile and amphibole fibers

are present in the natural rock and have been present in air or drinking water for long

periods of time. Careful search should be made for areas which might permit comparisons

of malignancy patterns as related to such exposures. The work of Fears (1976) [36], who

found no excess of cancer in U.S. counties with known asbestos deposits, needs to be

refined to concentrate on census tracts contiguous to operations which actually increase

fiber concentrations in the air or water.

A second approach which should be expanded is the large scale study of the fiber

content of human lungs and other tissues, with determination of fiber concentrations and

fiber dimensions, for comparison with causes of death. This has been periodically

suggested but never actively pursued. Stanton (1974) [37] stated,

"There is perhaps one way to determine the hazards of fibers without

waiting the many years necessary for the effects of even massive exposure

to become evident. Unlike most carcinogens, fibers that are a threat are sufficiently durable to remain in the tissues from which cancers are derived. Since carcinogenic response can be related to doses of sized

fibers in experimental animals, it may be possible to equate the number

and size distribution of fibers in human tissues to cancer in man. Although much has been accomplished in assessing large, protein-coated

fibers in human lungs, surprisingly little has been done in assessing the

size distribution and total quantity of all fibers in human tissues.

This would be a tedious job, but it might determine the true significance

of fibers as carcinogens in man."

It is believed that the design and organization of such a major study is long overdue.

Without the information it might provide, environmental decisions involving ultrafine and

ultrashort asbestos fibers or the asbestiform varieties of other minerals will continue on

a very uncertain and often emotional basis. When one considers the tremendous outlays

involved in containing or capturing such fibers in mining and quarrying operations, as well as in asbestos-using industries and in waste disposal, the cost of such studies would

128
appear a prudent investment. As Rohl , Langer, and Selikoff observed in their recent

report [30] providing data on fibers found near Montgomery County roads where serpentinite

rock had been used,

"The evaluation of the possible health hazard that may be associated with

this exposure requires information that is not yet known in the

scientific community: (i) the biological activity of short chrysotile

fiber, (ii) the level of exposure to asbestos which is safe insofar as human cancers are concerned, if a safe level exists, and (iii) the

biological activity of asbestiform silicates, not necessarily asbestos."

"he same comment applies to numerous other environmental situations currently under

;crutiny. We do not know what fiber concentrations expressed in nanograms per cubic meter

)r in total fibers per unit volume, when detected by electron microscopy, mean in terms of

luman health. Unfortunately, epidemiology does not yet provide the answers.

Summary and Conclusion

There is epidemiologic evidence to indicate that all types of commercial asbestos,

i.e., chrysotile, crocidolite, amosite, tremolite asbestos, and anthophyl 1 ite asbestos,

/hen inhaled, can cause pulmonary fibrosis and increase the risk of lung cancer. All but

inthophyl 1 ite asbestos have been associated with malignant mesothelial tumors. There is

ilso strong evidence to support a decreasing gradient of pathogenicity as one proceeds

"rom crocidolite to amosite to chrysotile, but this evidence does not clearly rule out the

interrelated influence of fiber dimension, shape, and co-factors.

Clear-cut epidemiologic evidence related to differing fiber dimensions is scanty.

)Uch information is critically needed. The most pressing need is to determine the

)athogenicity of ultrafine fibers in the electron-microscope size range, and for fibers

shorter than 5 micrometers, whether inhaled or ingested. It is suggested that there be

expanded epidemiologic studies of populations which have been exposed to such fibers,

without the presence of long fibers. This will probably occur where the exposures are

incidental to operations other than commercial asbestos production. It is also

'ecommended that there be systematic study of the fiber content of human lungs and other

tissues, as related to causes of death.

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[3] Becklake, M. R. , Asbestos-related diseases of the lung and other organs: their

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[4] Wagner, J. C. , Sleggs, C. A., and Marchand, P., Diffuse pleural mesothelioma and

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[5] Sluis-Cremer, G. K. , Asbestosis in South African asbestos miners, Environ . Res.,

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[7] Timbrell, V., Griffiths, D. M. , and Pooley, F. D. , Possible biological importance of

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[12] Selikoff, I. R. , Hammond, E. C. , and Churg, J., Carcinogenicity of amosite asbestos,

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[13] Braun, D. C. and Truan, T. D. , An epidemiological study of lung cancer in asbestos

miners, Arch. Ind. Health , U, 634-653 (1958).

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The health of chrysotile asbestos mine and mill workers of Quebec, Arch. Environ . Health , 28, 61-68 (1974).

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[17] Selikoff, I. J., Hammond, E. C. , and Seidman, H. , Cancer risk of insulation workers

in the United States, in Biological Effects of Asbestos , Proceedings of a Worki ng

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[18] Kiviluoto, R. , Pleural calcification as a roentgenologic sign of non-occupational

endemic anthophyl 1 ite-asbestosis , Acta Radiol . Suppl . , 194 , pp. 1-67 (1960).

[19] Kiviluoto, R. and Meurman, L. , Results of asbestos exposure in Finland, in. Pneumoconiosis: Proceedings of the International Conference , Johannesburg , 1969 , H. A. Shapiro, ed. , (Cape Town, Oxford University Press, 1970).

[20] Nurminen, M. , The epidemiologic relationship between pleural mesothelioma and asbestos

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working population of anthophyl 1 ite asbestos miners in Finland, Brit . J. Ind. Med.,

31, 105-112 (1974). "

[22] Rubino, G. F. , Scansetti , G. , Piolatto, G. , and Romano, C. A., Mortality study of

talc miners and millers, J. Occup . Med. , 18, 186-193 (1976).

[23] Gillam, J. C. , Dement, J. M. , Lemen, R. A., Wagoner, J. K. , Archer, V. E. , and

Blejer, H. P., Mortality patterns among hard rock gold miners exposed to asbestiform

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[24] Dement, J. M. , Zumwalde, R. D. , and Wallingford, J. M. , Discussion paper: Asbestos

fiber exposures in a hard rock gold mine, Ann. N. Y. Acad . Sci .

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[25] Swent, L. W. , Herrin, G. R. , Waterland, J. K. , and Bell, R. F. , Mortality patterns

among hard rock gold miners exposed to an asbestiform mineral - a critique. Presented

at American Industrial Hygiene Conference, New Orlenas, LA, May 25, 1977.

[26] Langer, A. M. , Mackler, A. D. , and Pooley, F. D. , Electron microscopical investigation

of asbestos fibers, Environ. Health Perspectives , 9, 63-80 (1974).

[27] Pooley, F. D. , An examination of the fibrous mineral content of asbestos lung tissue

from the Canadian chrysotile mining industry, Environ . Res. , VZ, 281-298 (1976).

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New York City, International Union of Air Pollution Prevention Association's Second

International Clean Air Congress, Washington, D.C., December 6-11, 1970.

[29] Nicholson, W. J. and Pundsack, F. L. , Asbestos in the environment, in Biological

Effects of Asbestos , Proceedi ngs of a Working Conference , Lyon , 1972 , P. Bogovski,

V. Timbrell, J. C. Gilson, and J. C. Wagner, eds. , lARC Scientific Publications

No. 8, Lyon, pp. 126-130 (International Agency for Research on Cancer, 1973).

[30] Rohl , A. N. , Langer, A. M. , and Selikoff, I. J., Environmental asbestos pollution

related to use of quarried serpentine rock. Science , 196 , 1319-1322 (1977).

[31] Miller, A., Langer, A. M. , Teirstein, A. S. , and Selikoff, I. J., "Nonspecific"

interstitial pulmonary fibrosis: association with asbestos fibers detected by

electron microscopy, N. Engl . J. Med. , 292, 91-93 (1975).

[32] Miller, A., Teirstein, A. S. , Bader, M. E. , Bader, R. A., and Selikoff, I. J., Talc

pneumoconiosis: Significance of sublight microscopic mineral particles. Am. J. Med. , 50, 395-402 (1971).

[33] Masson, T. S. , McKay, F. W. , and Miller, R. W. , Asbestos-like fibers in Duluth water

supply. Relation to cancer mortality, J. Amer . Med . Assn . , 228, 1019-1020 (1974).

[34] Ashcroft, T. and Heppleston, A. G. , Asbestos fibre concentration in relation to

pulmonary reaction, in. Biological Effects of Asbestos , Proceedings of a Working

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eds., lARC Scientific Publications No 8, Lyon, pp. 236 (International Agency for

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[35] Doniach, I., Swettenham, K. V., and Hathorn, M. K. S. , Prevalence of asbestos bodies

in a necropsy series in East London: Association with disease, occupation, and

domiciliary address, Brit. J. Ind. Med., 32, 16-30 (1975).

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526 (1976).

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1 131
DISCUSSION

J. DEMENT: I'd like to make several observations dealing with a couple of points.

First of all, Dr. Cooper pointed out that the Homestake mine study dealt with exposure to

very short fiber lengths, and that's certainly true. However, you failed to point out

that in most industrial settings, as high as 99 percent of the fibers, of chrysotile

especially, are shorter than five pm in length with very typical lognormal distributions

which follow closely to the Homestake study. Secondly, a couple of comments with respect

to the Homestake study. In its publication, NIOSH did in fact recognize the possible

contributory effects of free silicate exposures for non-malignant respiratory disease.

Our study ascribed the cancers predominantly to fibrous grunerite exposures. With regard

to the McDonald study, I'd also like to make a couple of comments. First of all, it was a group from a Veterans Association with 21 years minimum employment at Homestake, but not

necessarily underground mining. The copy of the Homestake paper, which I have been given,

does not indicate whether or not they were miners or surface workers. Homestake operates

several above-ground facilities. One must question whether or not 21 years requirement

isn't a selective population, especially with regard to the data we saw from Dr. Nicholson

today where he indicated that even one month carries with it an excess risk. Thirdly, we

at NIOSH of course do realize the importance of the study as evidenced by our increase in

the scope of the study, mainly to get a larger cohort to study. I would like to express a bit of gratitude for your pointing out that lack of evidence should not be taken as lack

of effect.

W. COOPER: With respect to the proportion of individuals underground, I can't answer

that question. I think that the criticism of limiting it to individuals who had worked

for 21 years or more is not a valid criticism. Actually, these were not retired miners,

and even a study of retired miners is not necessarily a bad study; Enterline has developed

the arguments pro and con very well. The fact that members of this club had been there

for 21 years is not very different from the basis that Selikoff and Hammond used in

selecting their population of insulating workers, which was limited to those who had their

initial exposures, or rather had been insulators, 20 years or more. The same processes of

selection which keep an insulating worker working for 20 years keep a miner working 21

years; I do not think that this is a valid criticism. As to whether or not the paper

ascribes the non-malignant respiratory disease to asbestos or to silica, I think it is

unmistakable. The paper, as I recall, does not use the word "silicosis," except in

describing the population as having come from a Public Health Service study of silicosis.

I will read from the conclusion: "The observed excess of malignant respiratory disease

can therefore be attributed to asbestos, singly or in combination with cigarette smoke,

and that of non-malignant respiratory disease can therefore be ascribed to asbestos with a possible additive role from low exposures to free silica dust." That's a direct quotation

from the report, so I think the implication is that the non-malignant respiratory disease

is asbestosis.

132
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

PATHOPHYSIOLOGY IN RELATION TO THE CHEMICAL AND PHYSICAL PROPERTIES OF FIBERS

Paul Kotin

Johns-Manvil le Corporation

Denver, Colorado 80217

Abstract

The array of asbestos-related diseases are reviewed in relation to

their pathogenesis, pathology, and natural history. Biological availability following host entry is especially critical for the biological

effect of asbestos. Experimental data consistently demonstrate that

hazard is related to the geometry of fibers, with fiber diameter and

fiber length being primary determinants. Controversy exists as to the

extent of influence of the two major classes of asbestos fiber:

chrysotile and amphibole. Considerations affecting the anatomic and

metabolic fate of asbestos fibers are also discussed.

Key Words: Asbestosis; fibers; lung cancer; mesotheliomas, pathophysiology; toxicology.

Any postulated role for exogenous agents in the etiology (cause) and pathogenesis

(development) of tissue change or clinical disease is critically dependent on the

biological availability of the agent. Biological availability is defined here as,

"possessing chemical, physical, and steric properties that allow reaction with receptor

sites in the living system at the host, organ, tissue, cell, and macromolecule levels."

In consequence, the environmental presence of a potentially toxic agent need not inevitably

assume an adverse biological effect. For example, fly ash, no less than soot, contains

carcinogenic hydrocarbons; yet the latter may be carcinogenic to man whereas the former is

harmless since it cannot be respired. A low dose of a chemical may be metabolized to a harmless metabolite, while by an alternative biochemical pathway a higher dose may yield a proximate carcinogen, as, for example, with vinyl chloride. Perhaps nowhere does biological

availability play a greater role in the pathogenesis of disease than in relation to fibers.

Clinical and epidemiological studies describing the asbestos-related diseases have

already been presented, and later in this workshop Dr. Mearl Stanton will report on his

elegant experimental studies on fibers. My presentation will attempt to describe in an omnibus and therefore relatively superficial fashion the continuum of environmental and

host factors that result in pathology and disease due to exposure to excessive concentrations of asbestos.

To accomplish this, I will formulate a series of questions and let the answers provide

the desired overview. Before doing this, however, let me emphasize now, and elaborate

throughout my remarks, that the adverse effects of asbestos, like those of all environmental

agents, occur in accordance with recognized toxicological principles. The chronic effects

of asbestos exposure-asbestosis, mesothelioma, lung cancer, and possibly gastrointestinal

cancer, if it indeed is truly related to asbestos exposure-are characterized by four relatively common aspects of environmental response:

1. A long latent period ensues following onset of exposure for either

stigmata of exposure or clinical disease to appear. For the latter, time

is measured in decades or segments of the total life span.

133
2. Exposure is in accord with recognized principles of dose-response in

relation to disease development and appearance. Dose, the product of

concentration or intensity of exposure multiplied by duration of

exposure (time), is clearly the indispensable element in any current

hazard analysis and in future projection. Dose-response considerations

apply at all levels of response from the single cell to the intact host.

3. A no-effect level of exposure or threshold (if that particular word does

create argument) exists for asbestos-related disease.

4. Multifactorial etiology plays a role for some of the asbestos-related

diseases. The issue of the determinant and the modifier in a multicausation situation is a critical one. It appears to be that

cigarette smoking is the determinant for lung cancer. The data on the

role of cigarette smoking in the development of asbestosis, though a factor, are too recent to permit any conclusions even though a modifier

role appears reasonable.

Now, the questions that can be used to provide an overview of our subject are:

1. Inasmuch as asbestos is a generic term for a group of fibrous crystalline

hydrated silicates, which of the spectrum of characteristics of this

group are of relevance to the initiation of asbestos-related disease?

The mineralogy and chemistry of asbestos have been reviewed in detail in this

morning's session. Of the two major sets of characteristics, chemical and physical, fiber

chemistry appears at this time to play only a minor role, if in fact any role at all, in

relation to asbestos-associated disease. Physical characteristics, specifically fiber

size, surface character, internal architecture and substructure, are all related in

varying degrees to biological effect.

Prior to addressing the second question, a brief description of the gross and microscopic anatomy and the physiology of the respiratory tract is necessary. As can be seen

in figure 1, fibrous particles enter the lungs via the trachea following inhalation

through the nose or mouth and are distributed throughout the tracheobronchial tree,

ultimately reaching the alveoli or air sacs. These air sacs are like the spaces in

sponges and are lined by thin membranes in which the capillaries and venules flow.

The entry and penetration of fibers into the lung is governed by physical laws. For

those particles which get into the tracheobronchial tree, some will settle on the lining

and they will move upward (on the mucociliary escalator) where they will be unconsciously

swallowed or spit out. Particles small enough to reach the alveoli will settle out on the

lining of the air spaces where they may be engulfed by phagocyte cells (macrophages) which

may neutralize them or carry them up to the mucociliary escalator so they can be removed.

The mechanism whereby uningested fibers penetrate the lining of the tracheobronchial tree

or the air spaces so that they may reach the pleura is largely unknown. Thus it is the

mucociliary escalator and the macrophages that are the primary defense mechanisms of the

lung. Of particular interest is the fact that cigarette smoke is the most potent and

ubiquitous of all inhalants in its capability to neutralize or destroy the effectiveness

of the lung defense mechanisms.

134
Bronchial

tubes

Bronchiole

Alveolar- sac

Figure 1. Anatomy of the respiratory tract.

135
The second question in relation to fiber effect is:

2. Following host entry, which of the anatomic and physiologic characteristics of the respiratory tract that I have just described affects the

anatomic fate of the inhaled fiber? What is the algebraic summation of

deposition, retention, parenchymal local ization . and mobilization as factors governing lung clearance?

With respect to the chemical characteri sties of fiber, there appears to be no consistent

identifiable effect of chemical composition after host entry of fibers by inhalation.

With respect to physical characteri sties the following effects are noted:

Size . Fibers greater than 5 pm in diameter are virtually entirely lodged in the nose and do not penetrate the respiratory tract. Fibers greater than 3 pm and less

than 5 pm in diameter enter the trachea but do not reach the conducting airways

deeply enough to be retained in the lung. Fibers less than 3 pm and more than one micron can penetrate to the smaller bronchi. Fibers in the millimicron range in diameter

are deposited in the peripheral airways and air spaces through Brownian movement. All

these dimensions are very close approximations.

Length is probably less critical than diameter in relation to anatomic localization

but it is of great importance in relation to biological effect. One possible measure of

localization is the length of fibers found in the lungs in both experimental animals and man following environmental exposure. There are few fibers longer than 100 microns. There

are virtually none longer than 200 pm. The majority are less than 50 pm in length.

We can conclude that only fibers thinner than 3 pm and shorter than 200 pm are of

significance in eliciting a biological response in intact animals.

Shape . Chrysotile asbestos is curly and spiral, whereas amphibole is harsh and

rigid. It is imperative to emphasize that in relation to interception and deposition on the wall of air-conducting passages a curly or a spiral fiber behaves like a straight

fiber having the diameter of the spiral fiber's maximum dimensional curl. Timbrell [1]^

concludes from his studies that chrysotile fibers (curly, pliable) do not penetrate into

the deeper and more peripheral portions of the lung to the extent that the more rigid

fibers of crocidolite and amosite do. More recently, using isotopically labeled fibers,

Morgan [2] has obtained data that tend to question this generalization.

It seems, then, that as a major determinant of biological localization and effect,

shape is still an open question.

Surface Character and Internal Architecture . Surface charge and leaching

characteristics have not been identified to date as being of major importance in relation

to question two. Time may change this.

In contrast, internal architecture has been shown to be relevant. In fact,

chrysotile stands in sharp contrast to the amphiboles. The long, pliable fibers are readily split longitudinally into progressively finer fibrils and this feature may be

critically related to biological effect. An unanswered yet crucial question is the one of

durability of fibers in living systems. Quantitative data on the splitting of fibers and

their solubility in relation to persistence of fibers are an urgent need.

In summary, size and shape are the major determinants of anatomical localization and

retention.

^Figures in brackets indicate the literature references at the end of this paper.

136
Now let's move on to question three and see what can or may follow when fibers set up

residence in the lung:

3. During and subsequent to anatomic localization, what characteristics

affect the biological fate of asbestos fibers at physiological,

pharmacological, and biochemical levels, and what is the sequence of the

morphogenetic events and altered morphology resulting from asbestos

exposure at cell, tissue, and organ level sites?

It is clear that as desirable as data from man might be in assessing the importance

of the chemical and physical variables of asbestos in relation to asbestos-associated

disease, reality forces the conclusion that observations on humans, alive or dead, are incapable of providing all the information necessary for this purpose. Most of our current knowledge is derived from laboratory experimentation, and it is to this resource

that we must turn for our needs.

Experimental data have been derived from research in which animal models have been

exposed (a) in chambers to clouds of asbestos fibers (the most physiological method and

the most analogous to human environmental exposure experience); (b) by intratracheal

installation of the test material (less physiologic but highly useful and informative); or

(c) by intracavitary installation (the least physiologic and the most arti factitious

inasmuch as this method "forces" biological availability where, in fact, in the human

situation none may exist; this method is useful as a tool for studying in-site cellular

responses and mechanisms).

Chemical composition of the several forms of asbestos can be dismissed as a major

factor in the pathophysiology of asbestos, not because fiber chemistry may not indeed play

a role, but because at our current level of ignorance we have no proven concept of what

such a role might be. In support of eliminating chemical composition as a factor is the

consistent observation that in experimental models all forms of asbestos can produce

asbestosis, lung cancer, and mesothelioma depending on the mode of exposure. The report

on the federally supported asbestos feeding study, to be presented later during this

workshop, may shed more light on this mode of exposure.

The size of the fiber, in sharp contrast to chemical composition, is the most clearly

documented physical characteristic that determines biological effect. Data on the fiber

size and cause-and-effeet relationship are virtually entirely derived from the laboratory,

since, in human experience, exposure has been in a mixed length and diameter milieu,

thereby rendering epidemiological data worthless for assessing single size fiber effect.

If only one axiom were permissible in my remarks it would be that on the basis of the

dynamics and kinetics of the behavior of ai rborne fibers , and in accordance with our know- ledge of biological aval lab i 1 ity both anatomical ly and pathophysiological ly , fibers thicker

than 3. 5 microns and longer than 200 microns , or thicker than 3. 5 microns and shorter than

5 microns are devoid of biological effect . Inhalation experiments have confirmed this

anatomically, and intrapleural studies support the conclusion pathophysiological ly.

Three studies can be cited to challenge this statement:

1. Holt [3] reported the production of pulmonary fibrosis in animals exposed

; in chambers to a cloud of predominantly short fibers. However, his own

[ data record the contamination of his sample with long fibers (greater

than 10 microns).

2. King [4] is silent on the percent of longer fibers contaminating his

short fiber sample when he reports fibrosis produced in animals. He says

the sample was almost all short fibers, but he used a technique for

sample preparation that in the hands of others (experienced fiber

researchers) consistently fails to yield a "pure" short sample.

3. Pott and Friedrichs [5] recently reported the production of peritoneal

mesothelioma with samples made up of fibers shorter than 2 microns. This

is a serious challenge to the long-thin concept. I can suggest possible

137
factors confounding their experiment and conclusions, but at present

suffice it to say that we are reviewing their findings in great detail.

This controversy would be rhetorical were it not that, except for the above, all

physiological studies and research reports on biological mechanisms are compatible with

experimental bioassay in relation to the role of fiber size. Briefly, the sequence of

events is as fol lows:

Respired particles can settle at levels of the tracheobronchial tree which are covered by a mucous blanket that is constantly being propelled cephalad toward the pharynx

by the ciliated cells. Clearance of the particles from the lung by this mechanism is

brisk, rapid (minutes to hours), and effective. Particles can also penetrate to the

distal bronchioli and air sacs (the nonciliated regions). They can be cleared here also,

provided they do not penetrate but remain on the surface. This clearance is slow (days to

years), moderately effective, and the particles may need help via phagocytosis to decrease

penetration and to migrate up to the mucous escalator.

The importance of size can be demonstrated at this stage. Allison [6] and others

have shown that short fibers (those less than 5 pm) appear to be readily and completely

phagocytosed, whereas long fibers are not, even when simultaneously attacked by more than

a single macrophage. This process may lead to cell fusion and the formation of giant

cells which are usually found in abundance at the site. Estimates as to the efficiency of

the combined clearance mechanisms range up to 95 to 98 percent. It is especially noteworthy,

though, that mucociliary clearance is minimally affected during exposure to fibers, even

in patients with asbestosis, while it is maximally affected by cigarette smoke.

The swallowing of fibers subsequent to their escalation to the throat is postulated

as the mechanism for the reported low- level increased risk to gastrointestinal cancer in

asbestos workers. When the term "ingestion" is used in relation to occupational risk to

gastrointestinal cancer, it is this passive form of ingestion that is meant. I will say

nothing about penetration of asbestos through the wall of the gastrointestinal tract

because the data are meager and are truly conflicting.

The next step in the sequence of events depends on what happens to the retained

fiber. One of two things may occur:

1. The short fibers, and to a certain degree the long fibers, are engulfed

by pulmonary phagocytes or macrophages, the latter often fusing to engulf

large fibers. These fibers then become coated with an iron/protein

complex. On the basis of animal studies, coating is now believed to be

an intracellular process and follows the engulfing of particles by

macrophages to which they adhere. These coated fibers are what have

traditionally been called "asbestos bodies"; now they are called

"ferruginous bodies" because they are not necessarily limited to

asbestos exposure and they take a positive iron stain due to the

iron/protein complex coating the fiber. There is evidence to suggest

that the coating of a fiber renders it nonf ibrogenic.

2. A majority of the fibers, approximately 75 percent, will remain uncoated,

which can facilitate effective penetration and retention of thin fibers,

or the breakdown of thicker fibers into thinner fibrils. These fibers

tend to accumulate in the peripheral regions of the lower lobes, the site

of early fibrosis (asbestosis). The fibers remain j_n situ (static) for

long periods of time. Some may migrate nakedly through the lymphatic

channels, while others may follow the migration paths of the cells they

have entered.

There is no entirely satisfactory or universally accepted explanation for fibrogenesis. Suggested mechanisms have included (a) simple irritation, (b) leaching out of

metal ions or silicic acid, and now (c) the immune mechanism.

138
There are, however, cellular data that suggest a reasonable mechanism, and this

mechanism assumes that fibrogenesis is evoked through the macrophage response. Such an explanation is attractive since:

1. It is compatible with the observation that long-thin fibers are the

hazardous ones.

2. Macrophages tend to aggregate in the peribronchial area, site of the

earl iest fibrosis.

3. The cumulative effect of exposure is nicely explained by the repetitive

and constant response of macrophages to asbestos exposure.

The sequence of fibrosis and its relation to other asbestos-associated diseases is

unknown except for the mechanical impairment of cardiopulmonary function by the scarring.

Fibrosis produces interference with lung function through replacement of the air spaces

(alveolar septa) with scar tissue and by restricting the normal excursion of the lining

during breathing.

Asbestos may affect anatomical sites in the following ways:

1. First and foremost, the gas exchange area or distal segments of the

tracheobronchial -alveolar tree of the lung may be partially replaced by scar tissue, with resulting decreased lung function, x-ray changes,

changes in physical findings, and blood gas changes.

2. The pleura (visceral and parietal) may thicken with the formation of

plaques; pleural effusion may fill the chest cavity with fluid; or mesothelioma may spread and infiltrate all layers of the lung and chest

wall. The peritoneum may also be affected, although how the fibers reach

this site is unknown.

3. Lung cancer or bronchogenic cancer may result. The role of cigarette

smoking and its impact on the mucociliary apparatus is a critical factor

in the development of lung cancer.

4. Gastrointestinal cancer may occur through entry of fibers into the

gastrointestinal tract by pharyngeal transpassage from the trachea.

The development of cancer, or carcinogenesis, is a multistage process in which the

chemical interaction between the carcinogenic agent and the DNA is a necessary but

certainly an insufficient step in itself for the development of clinical cancer. The

issue of dose-response and no-effect level cannot be pursued in appropriate depth here,

but suffice it to say that a synthesis of experimental and epidemiological data clearly

supports a no-effect level.

The experience with asbestos has, very appropriately, given rise to concern that

other fibers to which man is exposed may also represent a potential hazard to health.

Organic fibers and manmade mineral fibers are in common use. I will limit my comments to

manmade mineral fibers:

1. The dynamics of fiber entry, clearance, retention, and localization

apply to manmade mineral fibers as they do to asbestos.

2. The concept of long-thin fibers as the source of potential hazard, as given for asbestos, also appears to be applicable to the chronic

biological effect of manmade mineral fibers.

3. In relation to chemistry, however, manmade mineral fibers differ from

asbestos. While chemistry may be dismissed in relation to asbestos,

solubility, fiber integrity, fiber fracture, and fiber persistence in

manmade mineral fibers are most logically related to the chemistry of

manmade mineral fibers. For example, glass does not seem to split

139
vertically; rather it fractures horizontally. It is soluble, and in some exposure studies it seems to have disappeared from predicted sites of

localization. A natural fibrous material like gypsum disappears so rapidly that it cannot be detected even at the site of administration

after a very short interval. These facts are well recognized.

Lest one become overly sanguine as to the ease or speed with which critically

necessary information about manmade mineral fibers can be obtained, it is sobering to

reflect that despite our extensive knowledge of asbestos and asbestos-related disease,

the following issues are still unresolved and subject to controversy:

1. Relation of fiber type to asbestos-associated disease.

2. The role of host factors (immunological state; peculiarities of

respiratory tract architecture; concurrent or antecedent disease) in

susceptibility to asbestos-related disease.

3. Progression of asbestos-related disease subsequent to cessation of

exposure to asbestos and the specific etiological influence on cancer of

the lung or gastrointestinal tract in the absence of asbestosis or other

anatomic evidence of exposure to asbestos.

I can best conclude by reiterating that there are special characteristics of

asbestos that, though specific and not unique, to the best of our knowledge, invoke

no mystique. The principles of asbestos-related disease are those of environmental

biology, specifically toxicology and carcinogenesis.

References i

[1] Timbrell, V., Aerodynamic Considerations and Other Aspects of Glass Fiber, ini

Occupational Exposure to Fibrous Gl ass - Proceedi ngs of a Symposium , pp. 33-50 (HEW/

publication NO. (NIOSH) 76-151, Washington, 1976). i

[2] Morgan, A., Progress report to lOEH/QAMA, Montreal, Canada (1976).

i [3] Holt, P. F. , Mills, J., and Young, D. K. , Experimental asbestosis with four types of'

fibers: Importance of small particles, N.Y. Acad. Sci. 132, 87 (1965).

[4] King, E. J., Clegg, J. W. , and Rae, V. M. , The effect of asbestos, and of asbestos

and aluminum, on the lungs of rabbits. Thorax 1 , 188 (1946).

[5] Pott, F. , Friedrichs, K.-H., and Huth, F. , Results of animal experiments concerning

the carcinogenic effect of fibrous dusts and their interpretation with regard to the

carcinogenesis in humans, Zbl . Bakt. Hyg. , I_^ Abt. Orig. B 162 , 467-505 (1976).

[6] Allison, A. C. , Lysosomes and the toxicity of particulate pollutants, Arch. Internal

Med. 128 . 131-139 (1971).

Discussion

A. SUNDARAM: Dr. Kotin, I really enjoyed your talk. I would appreciate it if you

could answer two simple questions that bother me. One, do you believe that fibrogenesis or fibrosis is an essential process that has to occur as a precarcinogenic lesion before you

could find cancer? Two, do you think that fibers actually have to reach a parietal pleura

before pleural mesothelioma can occur, or do you think it can be an indirect outcome of

other toxic efforts?

P. KOTIN: Let me answer your second question first. I would say that the occurrence

of parietal mesothelioma does not inevitably demand the presence of asbestos fibers.

140
For the first question, I would have to give you two answers. Fibrogenesis as a lathogenetic prelude to broncogenic carcinoma, certainly not; as a temporal prelude, yes. or fibrogenesis in relation to mesothelioma, I would be hard put to think of how you

fouldn't get some preliminary benign or even non-neoplastic fibrous tissue response before

'ou got some malignant fibrous tissue response. So the answer to the question is yes,

hat there has to be some fibrosis, but really it's gall for me to answer that one with

lerle Stanton sitting here who's had just eons of experience in this area.

M. ROSS: I still would like to get out into the open what you would consider a lealth risk. You're a high official at Johns-Manvi 1 le. We have heard Dr. Nicholson speak

if the horror of asbestos exposure to insulation workers, he's also mentioned Canada. We

ire now faced with the closing down of small quarries and mining operations because of

imall, peripheral asbestos hazards, for instance, the local quarry here in Rockville.

low, what is your opinion on this? Johns-Manvi 1 le produces quite a bit of asbestos. You

^ould think from what Nichsolson is saying, that eventually we would say asbestos in

leneral has to be banned, not only in mining but in use, unless we can come up with a evel of health risk, a level of exposure, that we can accept. But I can see that the

imall mining industry is going to be wiped out because they can't handle this sort of

:hing as far as financing sample analysis and so forth. Could you address yourself to

;hat problem?

KOTIN: Really, prudence says I should keep quiet, but I've never been prudent.

Sasically, I would agree with Bill Nicholson to the extent that I would say lung cancer md mesothelioma are horrible diseases. The inevitable corollary of that is not that

ixposure to asbestos is horrible. It can be; in the past it has been. I don't think it is

low, at least in areas that I know anything about and I think that's important. The

lorrors of asbestos are the horrors of asbestos-related diseases, particularly lung cancer

ind mesothelioma. As to the question of the ubiquity of asbestos and so on, I'm glad you

isked, since it gives me an opportunity to repeat what I said. I'm unaware of anything or my body of data that suggests that there isn't a dose-response relationship for asbestos;

;hat just as for all hazardous agents there are non-hazardous levels and circumstances of

jxposure. Whether, indeed, the quarry situation is one such circumstance, I really can't

;ay. I would suspect, however, it's a question that can be analyzed in terms of

:raditional dose-response considerations; you don't have to blaze any new trails.

J. SAUNDERS: We've heard earlier of some very elegant work on the identification of

sbestos bodies in tissue and some measurements of their quantities in the various tissues

nvolved the pleural lining, also. Your scheme of clearance from the lung, I think has

een discussed previously, and I think you made some reference to perhaps some fiber

irectly penetrating the air sac from the aveola. My question to you is, do you believe

hat this is the site of biological activity or can you see from your mechanisms re-entry

f the particle?

KOTIN: I think you have to discuss pathogenesis on the basis of the disease of which

ou're speaking. I believe that's the mechanism for the evolution of the disease,

sbestosis, yes. For bronchogenic cancer, I think it's entirely different. I think

ronchogenic cancer is caused by more than one thing. I think the attenuation of the

efenses by concomitant cigarette smoking is indispensable to the evolution of the

isease. Let me say it differently; for all practical purposes, I don't think there would

e an asbestos-lung cancer link if by some divine mechanism cigarette smoking were to

isappear from the face of the earth.

J. SAUNDERS: Perhaps I don't understand the answer. The question was do the fibers

irectly penetrate the lining?

KOTIN: Yes, they can penetrate.

SAUNDERS: Do you believe these are important agents in the genesis of the disease?

KOTIN: Of fibrosis only.

141
A. WILEY: Could you state again the fiber sizes, length, and width that you felt were

of biological importance?

KOTIN: I will say it in microns; it took Dr. George Wright a year to get me to say

micrometers. Fibers thicker than 3.5 |j in diameter and longer than 200 are nonpathogenic,

and that is an arbitrary number. The only reason I say 200 is because that is the maximum

length of fibers that have been detected in lungs.

Up to 200 p and thinner than 3.5 p is the critical size range. If the diameter is

thicker than 3.5 p length is irrelevant, because the fiber is not going to get down to the

lower airways and air sacs.

WILEY: Question was inaudible.

KOTIN: What she is saying is, I am not convinced that 3 to 1 is necessarily the right

ratio. I agree. While 3 to 1 is a very handy rubric, there is nothing sanctified about it.

142
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

THE CARCINOGENICITY OF FIBROUS MINERALS

Mearl F. Stanton

Laboratory of Pathology

and

Maxwell Layard

Biometry Branch

National Cancer Institute

National Institutes of Health

Public Health Service

Department of Health, Education, and Welfare

Bethesda, Maryland 20014

Abstract

The carcinogenicities of 37 different dimensional distributions of seven different durable fibrous materials were correlated with fiber

dimension. Optimum correlation was attained with fibers that measured

<0.25 pm X >8 pm. Morphologic studies suggested that fibers in this

dimensional range lie free in interstitial tissues, while fibers of

smaller dimension are readily phagocytosed and fibers of larger

dimension are sequestered by adherent phagocytes and fused phagocytic

giant cells. Fibers that are fine and long may be more carcinogenic than

others, simply because they are uncompromised by phagocytic activity.

Keywords: Aluminum oxide; asbestos; carcinogenicity; Dawsonite; fibers;

fibrous glass; phagocytosis; potassium octatitanate.

For the past several years we have been interested in the question of how asbestos

causes cancer once a fiber reaches susceptible tissues. We have approached this problem

with the simple device of introducing various types of particles into the pleural space

of rats and observing the resultant tumors during the subsequent two years. The methods

that we have used can be summarized briefly [1,2,3].^ A standard 40 mg dose of particles

is applied by open thoracotomy directly to the left pleural surface of young female

Osborne-Mendel rats. In each experiment, 30 to 50 rats are followed for two years and

those surviving at two years are killed. All rats are necropsied and all pathological

lesions examined histologically. Tumors that resemble the mesenchymal mesotheliomas of man generally develop after the first year. For the sake of precision we have called these

tumors pleural sarcomas. During the second year, rats die at various times with and

without pleural sarcomas; consequently, we have used actuarial computation to arrive at a valid estimate of the incidence of pleural sarcomas which takes into account differences in

life-span [4]. Probability of pleural sarcoma has ranged from 0 to 100 percent depending

on the materials used. Pleural sarcomas have not been observed in several thousand

untreated controls; however, pleural sarcomas have occurred in rats treated only by

simple thoracotomy. Our best estimate of these non-specific, background pleural sarcomas

in treated controls is in the range of 2-4 percent. This is important to keep in mind

since it makes interpretation of low level response unreliable with small numbers of

animals.

^Figures in brackets indicate the literature references at the end of this paper.

143
There are two separate features of asbestos particles that merit consideration as potentially carcinogenic. First, the chemical nature of their constituents and contaminents, especially those with a known potential for carcinogenicity such as the polycyclic

hydrocarbons and heavy metals. Secondly, the physical structure of asbestos particles

which in their fibrous fineness are somewhat unique in the natural world. It is our contention that it is the latter property, namely the simple quality of being an exceptionally fine, long, durable fiber, that is most critical to carcinogenicity. The supporting evidence for this hypothesis is derived primarily from the type of experiments

described above, as carried out by us and others [1,2,3,5,6,7]. It can be summarized

briefly as fol lows:

(1) Vigorous extraction of natural and contaminating hydrocarbons from asbestos does not

alter its carcinogenicity.

(2) Hand-cobbed, hand-milled asbestos that is free of metallic mill contamination is no less carcinogenic than machine-milled asbestos.

(3) Naturally occurring or contaminating carcinogenic metals such as nickel, cobalt,

chromium, iron, magnesium, and silica, or hydrocarbons such as benzo(a)pyrene, of

comparable quantity to that in asbestos, when attached to inert non-fibrous particles

of a size comparable to asbestos, do not show the carcinogenicity of asbestos.

(4) The carcinogenicity of asbestos is greatly reduced if implanted as whole unseparated

sheets of fibers or implanted as very short submicroscopic fibrils.

(5) The carcinogenicity of asbestos is greatly reduced if asbestos is heated sufficiently

to increase its fragility or if pulverized to non-fibrous particles.

(6) Finally, between the various types of asbestos, particularly crocidolite, amosite,

tremolite, anthophyl 1 i te , and chrysotile, there are wide variations in chemical,

crystalline, and molecular structure. Nevertheless, when similar dimensional distributions of these asbestoses are applied directly to the pleura their carcinogenic

response is similar.

If the carcinogenicity of asbestos depends on its dimensional configuration, two

corollary hypotheses are suggested. First, durable fibers of other materials if in the same dimensional range as asbestos should be as carcinogenic as asbestos. Secondly, there

should be an optimal dimensional range of fibers relevant to carcinogenicity.

The data which I would like to present today relates to these two corollaries.

Table 1 lists 37 experiments with seven different durable fibrous materials, each of

differing dimensional distributions, but at or near the size distribution of asbestos. We

have listed these in order of their probability of inducing pleural sarcomas, and as you can see the range runs the gamut from 0 to 100 percent. Asbestos fibers of a standard size

characterized by a working group of the Unio Internationale contra Cancer would fall in

the range of 65-80 percent [8].

The problem that follows is that of determining the dimensional distribution of the

particles in each sample. To do this we used the straightforward method of measuring

length and diameter from montage photographs of typical samples of the particles implanted.

A minimum of 1000 particles were tabulated at magnification of 3000X to 29,000X. Subsequently, in samples containing large particles, magnifications of lOOOX were used to

tabulate fibers inadequately represented on electron micrograph grids. The proper ratio

of microscopic to submicroscopic particles yielded a representative sum of measured

particles which was then entered into an IBM System 370 computer. From the density and

the sum of the calculated volumes, the weight of the counted samples could be obtained and

the distribution of particles per microgram of the sample estimated. For convenience, the

numbers of particles per microgram were grouped into 34 dimensional ranges as indicated in

Table 2. Table 2 illustrates the tabulation of six of the experiments with different

samples of glass. By simple inspection the six examples show an apparent relationship

between tumor probability and particle distribution that has held for all of the fibers

tested thus far. The examples suggest that particles in relatively thin (diameter

<0.25 pm) and long (length >8 pm) dimensional categories are associated with the higher

tumor probabilities.

144
Table 1. Cumulative list of experiments arranged by percent

probability of pleural sarcoma.

Percent

1. DIHYDROXY SODIUM ALUMINUM CARBONATE V 100

2. POTASSIUM OCTATITANATE I 100

3. POTASSIUM OCTATITANATE II 100

4. SILICON CARBIDE GTC #1 100

5. DIHYDROXY SODIUM ALUMINUM CARBONATE I. . . 95

6. BOROSILICATE GLASS (MOL) 85

7. BOROSILICATE GLASS (M6D) 77

8. BOROSILICATE GLASS + BINDER (KL) 74

9. BOROSILICATE GLASS (M6L) 72

10. ALUMINUM OXIDE -HC 70

11. BOROSILICATE GLASS + BINDER (KW) 69

12. DIHYDROXY SODIUM ALUMINUM CARBONATE VII 68

13. DIHYDROXY SODIUM ALUMINUM CARBONATE IV . 66

14. DIHYDROXY SODIUM ALUMINUM CARBONATE III 66

15. BOROSILICATE GLASS (M6W) 64

16. ALUMINUM OXIDE #3 44

17. ALUMINUM OXIDE #4a 41

18. ALUMINUM NITRIDE + OXIDE #6a 28

19. ALUMINUM OXIDE #2 22

20. BOROSILICATE GLASS + BINDER (KCP) 21

21. BOROSILICATE GLASS - BINDER (KUP) 19

22. BOROSILICATE GLASS {M8L) 14

23. ALUMINUM OXIDE #4 13

24. DIHYDROXY SODIUM ALUMINUM CARBONATE VI 13

25. DIHYDROXY SODIUM ALUMINUM CARBONATE II 12

26. BOROSILICATE GLASS (MOS) 8

27. BOROSILICATE GLASS + BINDER (K2P) 8

28. MINERAL WOOL (Hi-Ca, Mg){02P) 7

29. BOROSILICATE GLASS + BINDER (KFP) 6

30. BOROSILICATE GLASS + BINDER (Y2P). ... 6

31. HIGH CA-NA (P2P) 6

32. BOROSILICATE GLASS (M8S) 5

33. ALUMINUM OXIDE #5 5

34. ALUMINUM OXIDE-LC (non-fibrous) 3

35. BOROSILICATE GLASS (YW) (vehicle) (n=270) 2

36. BOROSILICATE GLASS (M6S) 0

37. NICKEL TITANATE 0

145
Table 2. Six example experiments illustrating fiber distribution into 34

dimensional categories by common log of the number of particles

per microgram in each size category.

MOL

85.3%

KI73.9%

>0.8

>4. 0-8.0

>2. 5-4.0

>1.5-2.5

>.50-1.5

>.25-.50

>.10-.25

>.05-.10

.01-. 05

2.23

3.08

2.93

2.53 3.

3.35

3.93

3.46

23 3.08

3.95

4.53

4.79

4.65

55

03

85

03

45

95

16

16

4.09

3.73

0.67

0.67

2.40

3.33

3.76

3.03

0.67

1.52 0.97

2.03 2.19

.42 2.

3.63

3.03

3.25

3.03

74

KCP

21 .5%

M8L

14.3%

>8.0

>4. 0-8.0

>2. 5-4.0

>1.5-2.5

>.50-1.5

>.25-.50

>.10-.25

>.05-.10

.01-. 05

3.00

3.24

3.24

2.50

2.20

1.44

2.05

3.59

3.38

3.28

2.90

2.98

1.81

2.05

2.17

3.17

10

10

0.97

2.01

1.81

2.31

1.81

0.97

,85 2.01

2.55

2.50

0.77

1.49 1.12

2.60 1.45

1.85

1.73

2.11

2.35

2

1

0.17

2.02

2.27

2.42

.38

,85

1.85

2.67

MOS

8.3%

YW

2.8%

>8.0

>4. 0-8.0

>2. 5-4.0

>1.5-2.5

>.50-1.5

>.25-.50

>.10-.25

>.05-.10

.01 -.05

3.88

4.34

4.43

5.90

6.77

2.97

3.43

3.91

4.02

3.88

4.19

4.63

2.46

2.99

2.37

76

69

2.72

1.76

1.17

2.46

3. 37

0.89

0.92

0.80

T.OO

T.IO

0.34

0.40

0.30

0.11

0.41

01-1 >l-4 >4.8 >8-64 >64 .01-1 >1.4 >4.8 >8-64 >64

Length pm

Diameter ym

146
<0.25 jjm) and long (length >8 [jm) dimensional categories are associated with the higher

tumor probabilities.

Statistical regression techniques afford a method of analysis that can use a variety of explanatory variables to determine the best correlations between tumor

probability and size distribution. The logit transformation [9] was applied to the

estimated tumor probabilities (p) according to the formula:

logit = log

Then, linear regression methods which find the best fitting function of the form

logit = a + b^x^ + b|^X|^

were used to compare the common logarithm of the number of particles per microgram in

various size categories to the probability of pleural sarcoma. After analyzing various

dimensional ranges that might have narrowed the optimum tumor inducing size range, it was determined that the best fit was with the dimensions <0.25 pm x >8 pm. The estimated

regression equation was:

logit = log = -1.31 + .424x

with a correlation coefficient of 0.9. The regression curve for this dimensional range is

illustrated in figure 1. Figure 1 also indicates clearly that none of the seven different

types of fibers show consistently greater deviations from the curve than any other, and

that the curve's steepest slope is between 3-4 log particles per microgram. There was no correlation with particles less than 8 pm in length, but relatively good correlations were

also noted with numbers of fibers >8 pm in length and up to 1 . 5 pm in diameter (correlation

coefficient 0.52 to 0.74). Figure 2 illustrates the 34 parameters used for carcinogenicity

correlation and those categories in which relatively good correlation was obtained. It

should be remembered that absence of correlation does not preclude a low level of tumor

response outside these ranges.

Histologic observations suggest the reason for the difference in response to fine,

long fibers and those fibers that are either very short or very thick. The lesions in

those experiments with a low probability of pleural sarcoma were highly cellular, being

composed primarily of f ibroblast-laden vascular granulation tissue with a relatively low

collagen content and an abundance of macrophages. In lesions from low tumor probability

groups in which virtually all fibers were less than 10 pm in length, the fibers seemed

completely contained within macrophages. On the other hand, in those lesions from low

tumor probability groups in which the fibers were virtually all of large diameter, the

fibers seemed sequestered from adjacent tissue by both macrophages and multinucleated

giant cells that closely invested the fiber surface. In contrast, the high tumor probability lesions were relatively acellular, with an abundance of collagen at the site of

implantation and the fine long fibers lay free in the interstitial tissues unaffected by

phagocytes. In ancillary experiments with non-fibrous particles that stimulate collagen

such as talc, silica, or carrageenin, collagen deposition equal to that of the high tumor

probability lesion has been observed without the subsequent development of tumors. Therefore it seems evident that collagen itself is not the critical factor in carcinogenesis.

However, the fact that the fine, long fibers were unaffected by phagocytic activity in the

high tumor probability groups suggests that fibers that are fine and long may be more

carcinogenic than others simply because they are uncompromised by phagocytic activity.

147
O A

LOG NUMBER PARTICLES /MICROGRAM

A = SIC • = GLASS

A = AL2O3

O = DAWSONITE

D = POTASSIUM OCTATITANATE = NICKEL TITANATE

PARTICLE SIZE -< 0.25 Mm X > 8 Mm CORRELATION = o.9 COEFFICIENT

Figure 1, Regression curve relating tumor probability to the common logarithm of the number of particles per microgram with

diameters <0.25 ym and lengths >8 ym.

148
149
References

[1] Stanton, M. F. , Layard, M. , Tegeris, A., Miller, E. , May, M. , and Kent, E. , Carcinogenicity of fibrous glass: Pleural response in the rat in relation to fiber

dimension, J. Natl . Cancer Inst . 58, 587-603 (1977).

[2] Stanton, M. F. and Wrench, C. , Mechanisms of mesothelioma induction with asbestos and

fibrous glass, J. Natl . Cancer Inst . 48, 797-821 (1972).

[3] Stanton, M. F. , Some etiological considerations of fibre carcinogenesis i_n Biological

Effects of Asbestos (Bogovski, P., Timbrel 1, V., Gil son, J., et al., edsTX Lyon

,

France, World Health Organization, International Agency for Research on Cancer,

Publication No. 8, 1973, pp. 289-294.

[4] Armitage, P., Statistical Methods in Medical Research, New York, John Wiley & Sons,

1971 , pp. 376-377, 410-414.

[5] Wagner, J. C. , The pathogenesis of tumors following the intra pleural injection of

asbestos and silica i_n Morphology of Experimental Respiratory Carcinogenesis

(Nettesheim, P. , Hanna, M. G. , Deatherage, J. W. , eds. ). Oak Ridge National

Laboratory, Oak Ridge, Tennessee, Atomic Energy Commission Symposium Series No. 21,

1970, pp. 347-358.

[6] Smith, W. E. , Miller, L. , and Elasser, R. E. , Tests for carcinogenicity of asbestos,

Ann . N/(^ Acad. Sci. 132, 456-488 (1965).

[7] Timbrel!, V., Physical factors as etiological mechanisms i_n Biological Effects of

Asbestos (Bogovski, P., Timbrell, V. , Gilson, J. C. , et al . , eds. ). Lyon, France,

World Health Organization, International Agency for Research on Cancer, Publication

No. 8, 1973, pp. 295-303.

[8] Timbrel!, V. , Gilson, J. C. , Webster, I., UICC standard reference samples of asbestos,

Int. J. Cancer 3, 406-408 (1968).

[9] Cox, D. , Regression models and life tables, J. R. Stat. Soc. (B) 34, 187-220 (1972).

Discussion

A. SUNDARAM: These pleural sarcomas, are they localized? If you leave them for a duration of time do they metastasize?

M. STANTON: Yes, this is real cancer, but they do not metastasize early.

A. LANGER: You allow your animals to live only two years, whereas Wagner allows his

rats to live three years. Have you had any control groups run for the duration of the

animals' lives? In those animals which you are reporting here, you are reporting frank

malignancy? How many of the other animals had hyperplastic lesions?

STANTON: It is difficult to detect precancerous lesions in mesenchymal tissues, so that it really is difficult to say what might be precancerous. We find that after two

years plus the twenty weeks the animal has aged by the time we treat them, most rats are

in their terminal stages. These rats do not have normal lung capacity and so they do not

survive as long as the untreated rat does. By the end of the two years there is only a small percentage of the rats left.

P. KOTIN: This business of assuming that hyperplasia carries with it as a corollary,

or is even indicative of subsequent malignant transformation or neoplasia, particularly in

mesenchymal tissue, has no substance at all. Now I am speaking as a pathologist. The

other thing is, there is a tendency to denigrate experiments which are terminated for the reasons you said, when in fact the confounding findings which arise in the last six to

eight months of a rat or any experimental animals, are such as to muddy up the results.

I'd like your comment on this. The elegance of the observation occurs before you get into

150
the agonal state, where the exposure of the animal probably has little as anything to do

with what he ultimately gets and dies from.

STANTON: No further comment on that.

J. WARREN: Our firm recently completed a report for OSHA, "The Economic and Inflationary Impact Study for the Effects of a Proposed Standard for Asbestos in Construction,"

and in the process of doing this report for OSHA we had to talk to a lot of your firms,

universities - everybody from environmentalists to producers, maybe not some of you in

here personally. This type of meeting is needed. We need people not just talking to each

other, but with each other, and I think you have seen this today. You got one group over

here saying, "Lookout! we are going to put out of business x number of people." Another

group says you have to protect the worker - the worker comes first even at zero exposure.

The only way we are going to resolve this problem, and it is a very sticky problem, is by

everybody talking together. So that is just a comment; we found there is not enough

talking to each other; even if you don't agree you can still talk. Has anyone looked at

the possibility of using experimental animals other than rats, say a primate? Would this

change results or give better data if we had an animal that would live longer? Has

anyone used a rat that has been exposed to cigarette smoke at the same time?

STANTON: Yes, other species have been used. Dr. Bill Smith is here today who has

been using hamsters for many years and has some very elegant data with hamsters. We

ourselves have used mice, and have been successful with mice as well as rats. I don't

think that unless there was an exotic species that we would particularly contribute a great deal more by using another species. Chickens have been used and various other types

of birds with some interesting results.

151

National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

NIEHS ORAL ASBESTOS STUDIES

John A. Moore

National Institute of Environmental Health Sciences

P. 0. Box 12233

Research Triangle Park, North Carolina 27701

Abstract

Epidemiologic data clearly associate inhalation of asbestos with an increased incidence of cancer. In addition to pulmonary and thoracic

neoplasia, there are data which associate an increased incidence of

gastrointestinal and peritoneal tumors. Controversy exists as to

whether these latter types of neoplasia result from asbestos fibers that were ingested subsequent to clearance from the respiratory system.

Exposure to ingested asbestos does occur in the general population

through the presence of fibers in water and food.

The NIEHS oral asbestos studies in rats and hamsters represent a systematic attempt to assess the biological effects associated with

primary ingestion of selected asbestos fibers. The objectives of the

studies include: assessment of biological (carcinogenic) effects as a consequence of exposure to one of several types of asbestos; assess if an interaction may exist between a chemical carcinogen which is known to

produce bowel cancer, and ingestion of asbestos. The specific

experimental design of this series of ongoing studies will be presented.

Key Words: Asbestos; bowel cancer; cancer; epidemiology; fibers.

There is strong evidence that associates occupational exposure to chrysotile amosite,

and crocidolite to a resulting high incidence of lung cancer. Exposure to these forms of

asbestos has also been observed to result in an increased incidence of pleural and peritoneal mesothelioma and an excess risk of gastrointestinal cancer. Environmental exposure

to asbestos through living in the neighborhood of asbestos factories or mines or through

residing in households of asbestos workers also correlates with increased mesotheliomas [1].^

It is plausible to speculate that the increased incidence of gastrointestinal cancer

in occupational ly exposed populations may be a consequence of asbestos fiber ingestion.

Fiber ingestion in these circumstances may result through the swallowing of fibers cleared

from the nasal or tracheobronchial tree. Direct ingestion of fibers deposited in the oral

;cavity also occurs.

i Exposures of the general population to asbestos occurs through ingestion of materials

?and substances that contain fibers. For example, several million fibers per liter were

:found in Canadian tap water [2]; Great Lakes and St. Lawrence River water showed average

concentrations of about 1.7 million asbestos fibers per liter [3]; water collected from

the north shore of Lake Superior in the Silver Bay/Duluth region were found to have even

higher fiber levels. A number of studies have reported the appearance of asbestos fibers

in commercial beverages such as beer, vermouth, and soft drinks [2]. The fibers found in

these products may be a result of the use of asbestos filters used in their preparation

[2]. Food may contain asbestos through the use of asbestos filters or the use of talc,

which has an asbestos impurity [4,5].

^Figures in brackets indicate the literature references at the end of this paper.

153
In response to a growing concern about the possible biological effects of ingested

asbestos, a conference was held in 1973, co-sponsored by the National Institute of

Environmental Health Sciences and the Environmental Protection Agency. The meeting

confirmed that the preponderance of biological data concerning exposure to asbestos focused

on the inhalation and not the ingestion route of exposure. A consensus of that international conference was that research was needed on health effects associated with asbestos

ingestion. A Subcommittee of the DHEW Committee to Coordinate Toxicology and Related

Programs (CCTRP) subsequently reviewed the existing data, recommended that additional

research be undertaken, and prepared a draft research protocol that it felt would be

responsive to the scientific needs. This protocol was widely distributed for comments both

within and outside the Government. Based on the comments received, a final protocol was developed and submitted as part of its final report. In response to the Subcommittee's

report, Congress appropriated specific funds directing the National Institute of Environmental Health Sciences to research the effects of oral asbestos ingestion. The NIEHS is

conducting this research primarily through its research contracts program. The Environmental Protection Agency also contributed funds for these studies. The design of these

studies is in concert with the recommendations of the CCTRP Subcommittee. The basic

design of the studies provides for an evaluation of chrysotile, a serpentine asbestos; and

amosite and crocidolite, fibers representative of amphibole asbestos; plus a non-fibrous

tremolite, which does contain low levels of asbestiform fibers.

The studies call for asbestos to be fed continuously in the diet over the entire

lifespan of the test animal. Each form of asbestos is contained at a one-percent level

in a pelleted rodent diet of constant ingredient formulation (NIH Feed 31). The proposal

to incorporate the asbestos within a pelleted diet form was approved only after studies

indicated that the pelleting process did not alter the physical integrity of the fiber.

The utilization of an asbestos diet in a pelleted form has obvious advantages: it

minimizes fiber aerosols which would occur with greater ease in a non-pelleted form; it

minimizes variations of asbestos concentration in the diet due to segregation of fibers

that would occur during shipping, handling, and feeding. Incorporating asbestos into food

rather than water eliminates settling and subsequent uneven distribution.

All materials are being fed to the F-344 strain of rat; whereas two forms of asbestos,

chrysotile and amosite, are also to be tested in hamsters. Golden Syrian hamsters represent

a second test species and are being fed a serpentine or amphibole form of asbestos. All

studies encompass the lifespan of the animal, which is defined as the age at which the

animal begins eating solid food until its death. To insure asbestos ingestion at a young

age, these studies are initiated by feeding the asbestos diet to a nursing mother, which

is removed once the pups are weaned. These latter animals that begin eating asbestos at

two weeks of age constitute the test generation.

In the basic studies, the test group size is 500, composed of equal numbers of males

and females. In each of the rat and hamster studies, there is a composite total of 1000

animals that receive diet which does not contain asbestos and serve as controls. The

experimental group size allows one to detect a statistically significant increase in

gastrointestinal tumors in the treated groups at a two percent increase above the control

population.

In another rat experiment, two subsets of 200 animals each are to receive asbestos

from the first to the 28th day of life by gastric intubation. The rat pups received

2.35 mg of an aqueous asbestos suspension daily. At weaning, the rats are placed on the

appropriate asbestos diet for the remainder of their lifespan. One subset of 200 animals

is to receive chrysotile while another subset is to receive amosite. The objective of

these experiments is to see if a possibility exists that neonates may be a special risk

population.

There is also scientific interest in determining if asbestos in the diet alters the

expression of intestinal neoplasms induced by a known chemical carcinogen. Studies of this

type are performed in rats that are fed either chrysotile or amosite. A similar study will

be conducted in hamsters receiving the chrysotile diet. There are 350 animals in each of

these three groups. The chemical carcinogen to be utilized was selected after a series of

dose-ranging experiments of one-year's duration was performed in each species. In these

dose-ranging studies, both dimethyl hydrazine and methyl azoxymethanol were evaluated. The

154
results indicated that dimethyl hydrazine was the chemical carcinogen of choice due to lower

toxicity and greater specificity of intestinal tumor response. The dose selected is one that will produce approximately a 10 percent incidence of intestinal tumors. That dose for

hamsters is 4 mg/kg, whereas for rats it was 7.5 mg/kg and 15 mg/kg in male and female

rats, respectively. The dimethyl hydrazine is administered by gavage once every fourteen

days until five doses have been administered. The initial dose was administered at six

weeks of age. Tables 1 and 2 summarize the design of the animal study. The animal testing

phase of the experiments commenced in late 1975. Since the natural lifespan of the F-344

rat is 26-30 months and 18-23 months for the hamster, definitive interpretation of these

studies is several years away.

Table 1. NIEHS oral asbestos study.

Golden Hamster

Chrysoti le

Intermediate

Chrysoti le

Short Range Amosite

Asbestos diet 500^ 500 500

Asbestos diet plus dimethyl hydrazine^ 350 ND ND

Control diet'' 500 250 250

Control diet plus dimethyl hydrazine^ 250 ND ND

^ Number of animals (equal numbers of each sex).

^ Control allocations are descriptive only. Experimental response will be evaluated

against total controls (1000). Subsets of control will reflect temporal differences in

commencing phases of study which is expected to be aggregates of 250-350.

ND - Not done.

Studies conducted by Illinois Institute of Technology Research Institute, Chicago, Illinois.

155
Table 2. NIEHS oral asbestos study.

F-344 Rat

Chrysotile Chrysotile Amosite

Intermediate Short Range Intermediate Croc idol ite Tremol ite

Asbestos diet 500^ 500 500 500 500

Asbestos diet plus

dimethyl hydrazine^ 350 NO 350 ND ND

Preweaning asbestos

gavage plus asbestos

diet 200 ND 200 ND ND

Control diet^ 175 175 175 175 175

Control diet plus

dimethyl hydrazine^ 250 ND 250 ND ND

Number of animals (equal numbers of each sex).

^ Control allocations are descriptive only. Experimental response will be evaluated

against total controls (1000). Subsets of control will reflect temporal differences in

commencing phases of study which is expected to be aggregates of 250-350.

ND - Not done.

Studies conducted by Hazleton Research Laboratories, Vienna, Virginia.

All animals receive a thorough pathologic evaluation at time of autopsy. In con- formance with the NCI Carcinogen Bioassay protocol, some thirty tissues in addition to

any gross lesions will be examined under light microscopy.

The rat studies are being performed through a contract with Hazleton Research

Laboratories, Vienna, Virginia; whereas the hamster experiments are being performed by

the Illinois Institute of Technology Research Institute, Chicago, Illinois.

As a biologist, I wish to emphatically state that the most difficult decision in the

design of these studies was determining the types and specific forms of asbestos that were

to be fed. The literature clearly indicated that some previous studies were flawed due to

unwitting physical violence imposed upon the asbestos during its preparation. In some cases, there was concern about contamination by organic chemicals. In medical research

circles, the issue still rages with respect to the size of fiber that may be associated

with observed neoplastic response. It is necessary to relate size that produces optimal

biological response to the distribution of fiber sizes to which there is general human

population exposure. The common fiber found in municipal water supplies represents one of

serpentine origin. From a numerical standpoint, the preponderance of these fibers is of the

low micron and submicron lengths. To accommodate to these circumstances, it was decided

that there would be two chrysotile asbestos materials used in the rat and hamster studies.

These are referred to as the NIEHS short-range chrysotile and the NIEHS intermediate-range

chrysoti le.

NIEHS short-range chrysotile was mined from the New Idria deposits in California.

This chrysotile is of very small fiber length and diameter. It is a single lot produced by

Union Carbide and is referenced by them as COF-25. The NIEHS intermediate- range chrysotile

originated from the Johns-Manvi 1 le Jeffrey Mine in Canada. This material has general

analogies to their Plastobest 20.

156
One method of comparing these two chrysotile samples is by comparing surface area

determinations. Table 3 presents the results of such tests; the UICC chrysotile surface

area values are listed for comparison. The UICC samples have been the asbestos source for

the majority of biological studies over the past several years. As can be seen from the

table, the NIEHS intermediate-range chrysotile compares quite favorably with the UICC

Canadian chrysotile. The -two-fold increase in surface area of the NIEHS short-range

chrysotile compared to its intermediate- range counterpart reflects the much smaller fiber

size found in this sample.

Table 3. Comparison of UICC and NIEHS chrysotile samples.

2 2

Asbestos Identification UICC Value (m /g) IITRI Value (m /g)

UICC Rodesian Chrysotile 21.3 ± 1.5 22.35

UICC Canadian Chrysotile 26.8 ±0.7 27.7

NIEHS Intermediate Range Chrysotile 27.8 ±2.7

NIEHS Short Range Chrysotile 59.0 ±6.2

The amphibole samples, amosite and crocidolite, were prepared by the Ontario Research

Foundation under the direction of the U.S. Bureau of Mines' College Park Laboratory. This

asbestos, purchased commercially, has been processed by air jet milling to better standardize the range of fiber size contained in the material.

The tremolite sample was mined and milled to -325 mesh by the R. T. Vanderbilt

Company, Balmat, New York. It was subsequently blended by the U.S. Bureau of Mines

personnel to insure homogeneity of the sample.

All test materials are being extensively characterized as to chemical and fiber size

characteristics. The characterization data include x-ray diffraction parameters, chemical

composition, DTA, TGA, optical constants, density, and surface area. These studies are being performed by the U.S. Bureau of Mines. Exhaustive electron microscopic characterization of each material as to fiber length, fiber diameter, surface area, distribution of

fiber size, and selective pore volume measurements are being performed by the Fine Particles

Laboratory of the Illinois Institute of Technology Research Institute, Chicago, Illinois.

The characterization studies on tremolite and the short-range and intermediate-range

chrysotile are nearly complete. The characterization of amosite and crocidolite are scheduled for completion by the end of the year.

Two recent ingestion studies that have been reported within the past year yielded

variable results. In a British study, a group of 32 Wistar rats were fed 100 mg per day

of UICC Canadian chrysotile prepared in milk powder on a f ive-day-a-week schedule for a total of 100 days of ingestion. There were 16 control animals which were fed only the

malted milk. The animals were then allowed to live out their lifetime, which was a mean

survival of 619 days for those animals on chrysotile versus 641 days for the controls. One

gastric leiomyosarcoma was observed in the chrysotile group. No tumors of this type were

found to occur in the controls [6].

In a study reported in the East German literature, a statistically significant

(p <0.01) increased incidence of malignant tumors occurred in rats that received asbestos

filter material in the diet [7]. The exact composition of the asbestos filter material

was not given in this paper. In this study, 25 male and 25 female Wistar rats were given

50 mg/kg body weight per day of asbestos filter material which contained approximately 52

percent chrysotile asbestos. This asbestos containing filter material had been previously

157
powdered and added as a water suspension to the diet. In the group of animals which

received the asbestos filter material, the average survival time was 441 days. Untreated

controls had an average survival time of 702 days. Of the 42 treated rats available for

pathologic evaluation, 12 malignant tumors were found. This is to be compared to seven tumors (two liver cell carcinomas and five mammary fibroadenomas) observed in 49 control

animals. The tumor types observed in the animals fed the asbestos filter material included

four kidney carcinomas, one lung carcinoma, three reticulum cell sarcomas, and four liver

cell carcinomas. Two mammary fibroadenomas, as well as a lung adenoma, two cholangiomas

,

and two forestomach papillomas were also observed.

The NIEHS Oral Asbestos Studies should provide controlled data from large enough

sample sizes to allow for initial formulation of basic principles as to the biological

effects of exposure to ingested asbestos.

References

[1] lARC Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Man, Asbestos,

Volume 14. International Agency for Research on Cancer, Lyon, France (1977).

[2] Cunningham, H. M. and Pontefract, R. D. , Asbestos fibers in beverages and drinking

water. Nature (Lond. ), 232, 332-333 (1971).

[3] Cook, P. M. , Glass, G. E. , and Tucker, J. H. , Asbestiform amphibole minerals: detection and measurement of high concentrations in municipal water supplies, Science , 185, 853-855 (1974).

[4] Merliss, R. R. , Talc and asbestos contaminant of rice, J. Amer . Med . Assoc . , 216 , 2144 (1971).

[5] Wolff, A. H. and Oehme, F. W. , Carcinogenic chemicals in food as an environmental

health issue, J. Amer. Vet. Med. Assoc . , 164 , 623-629 (1974).

[6] Wagner, J. C. , Berry, G. , Cooke, T. J., Hill, R. J., Pooley, F. D. , and Skidmore, J. W.

,

Animal experiments with talc, in Inhaled Particles and Vapours , IV , W. C. Walter, ed.

,

New York, Pergamon (in press).

[7] Gibel, W. , Lohs,.. K. , Horn, K.-H., Wildner, G. P., and Hoffmann, F. , Tierexperimentel le

Untersuchungen Uber eine kanzerogene Wirkung von Asbestif i Itermaterial nach oraler

Aufnahme, Arch. Geschwul stforsch , 46, 437-442 (1976).

Discussion

M. SCHNEIDERMAN: Dr. Moore completed his paper considerably earlier than the time

allotted. Are there some questions concerning this particular elaborate set of

experiments, and the experiment design? Are there some suggestions that people would

have? When the results come in from these experiments, what kinds of doubts will exist in

your mind? What sorts of things would you like to see answered that these are not going to

answer? I hope that there are people here that have thought about these and might have

some questions.

V. WOLKADOFF: Evidently Dr. Moore has brought up chrysotile, the short size range

sample from Edra and the intermediate size sample from Jeffry, and an evaluation of the

size by specific surface area. Amosite was size fractionated by air-jet milling, and

tremolite, evidently by milling of some type, to minus 325 mesh. The chrysotile more or

less has been characterized by specific surface area. Do you have information, within

each of these categories, as to the crystal 1 inity of the individual fibers, the four

categories versus degradation of the crystal 1 inity of individual fibers by the method of

preparation, or is it too early to say? You mentioned data by x-ray diffraction, DTA, and

optical microscopy. I also wanted to know if you are going to include the electron

diffraction results in your studies.

158
J. MOORE: I think I mentioned the electron diffraction work as part of the study,

and I'd rather let the Bureau of Mines personnel, who are here, or the IITRI personnel, answer your question with regard to the crystal 1 i nity. I'm sure it has been looked at,

but I don't know if the data are in such a stage to make any comment about it.

WOLKADOFF: What about air- jet milling of amosite, do you have any data now?

MOORE: No, if I did, I would have presented it.

WOLKADOFF: The tremolite data also, you don't have anything then?

MOORE: No sir, it's not in complete form. As I mentioned in the paper, the

characterization of the two chrysotile samples and the tremolite sample should be

available within the next couple of months, and we would expect that the similar types of

studies characterizing the amosite and the crocidolite will be done by the end of the year.

WOLKADOFF: Thank you very much.

W. CAMPBELL: All the data has been completed on tremolite, including optical microscopy, SEM, TEM, chemical data, and surface area. On chrysotile, the optical data is

finished, the SEM data is about completed, and the TEM is about completed. So in answer

to your question there are very extensive data available on the optical properties, the

morphology, the crystal 1 i nity, the trace metals, and so forth. Surface area is just one

of the many parameters being investigated.

MOORE: I may have misled you in my presentation by only showing the slide on surface

area; I did that one because it did show a distinction between the two chrysotiles. I would point out that we do not wish to infer that there is a clear separation of fibers

between these two materials. Certainly the intermediate range chrysotile sample does have

fibers that are well into the size range of fibers that are found in the short range

sample. The distinction between the two is the proportion of fibers that may exceed, with

respect to length and diameter, those that were found only in the short range.

G. WRIGHT: You quite properly pointed out that the kind of occupational exposure

which has led to what we know about tumor incidence is quite different from what's found

in water supplies. In fact, the differences are very striking. On the other hand, in

occupational exposure generally, and I say would say almost without exception, the percent

of the total fibers that exceeds eight to ten and even five pm in length is of the order

of less than five percent, and in many situations is only one or two percent. In the

animal experiments that have been done by inhalation of asbestos, in general, the clouds

created contained only one or two percent of what we call long fibers. For this reason, I think that to look at your samples in terms of percent, inferring that one, two, or three

percent of long fibers present in a sample is acceptable when you're talking about short

fiber samples is erroneous. We need to get around to the number of long fibers, not the

percent. Now also I would like to ask if these experiments are designed to look at the

occupational experience or at the water experience?

MOORE: I would hope that they would have relevance in both areas.

WRIGHT: What percent or what number of long fibers are still present in your so- called short sample?

MOORE: Well, at what length do you want to consider as a long fiber?

WRIGHT: Anything over 5 pm, because in water, you've said, it is under 5.

MOORE: I recall the raw data that are available on that; about 90 percent of the

samples in the short range chrysotile would be below that.

WRIGHT: In other words, ten percent are still above 5 pm?

MOORE: Right.

159
WRIGHT: Well, that's essentially what the occupational exposure is. I don't think

you're looking at water related exposures.

W. BANK: I'll change the subject slightly. There have been some animal nutrition

studies going on since 1965 in Japan, and more recently in the U.S., in which fibrous

material, namely certain zeolites, have been fed to these animals. The results were that

the animals gained weight faster, certain diseases seemed to disappear, and so on. It's

recognized, however, that there is a possible long-range pathological effect that might be

involved because of the fibrous materials. Have you heard or do you know of any such

information?

MOORE: I'm not aware of that work coming out of Japan.

C. COOPER: I strongly support the observation made by George Wright that the 10

percent or even 5 percent of long fibers in your short fiber samples would leave serious

doubts as to whether the results of these experiments would be applicable to water

supplies. Another question that has bothered a number of people is whether or not

consideration was given, in the design of this experiment, in the choice of samples, to

actually including a sample of the material that has contributed a great deal to this

whole controversy. That is, the amphiboles that are found in Lake Superior water, in the

size distribution in which they were found. I can see the difficulties in doing this, but

I wonder just what the course of reasoning was that led to this type of material not being

incl uded?

MOORE: We were advised, and I must say we also subscribe to the opinion, that with

regard to injestion studies we might, in an initial series of experiments, be better off

by using materials that are known to have biological effects in test species. This is

where we opted to go with the amosite, for example; it's probably the closest thing we

have to being representative of a cummingtonite/grunerite which is the Lake Superior type

of sample. The other problem that we had when we did discuss the possibility of using

something from the water in that area, was the complete lack of agreement among people we talked to with regard to what actually should be the sample that would come out of that

area. In addition there was the logistics of trying to get that sample; it was just that

simple. I would also state that with regard to fiber size, maybe having too many fibers

above 5 pm to permit direct relevance or extrapolation to municipal water supply samples,

as was pointed out by Dr. Wright and yourself, I assume you gentlemen would accept a negative.

A. SUNDARAM: You quoted Dr. Gibel's paper from East Germany. Do you believe that

study was well conducted, showing a significant effect of asbestos by oral ingestion?

MOORE: All I can comment on is the information which was available in the reprint,

which brings questions to mind which certainly aren't explained in the materials and

methods. For example, how they prepared the material, actually what was the other 48

percent since they inferred that 52 percent of the material was chrysotile. I think this

sample size data may have some problems as well.

SUNDARAM: I agree to that, but in addition there is a significant point worth

noting. The paper never mentions the number of animals affected over the control. There

should be a significant increase in the number of animals that had tumors, not a significant increase in the number of tumors, because it may be one animal that had twelve

tumors or it may be 12 animals that had 12 tumors. So it is the number of animals that were affected that's more important than the number of tumors. This paper has been quoted

many times even though it just appeared in 1976. So many people quote it, and I thought

it's better to point out this significant question that we should not miss.

MOORE: I thank you for your point, because the paper does not indicate as to

whether, for example, the 12 malignant tumors found in 42 treated animals came from 12

separate individuals, or whether it was one or more animals which may have had multiple

tumors.

160
D. ALTON: I am really wondering whether a dosage of 100 milligrams per day per unit

weight of rat for the lifetime of a rat is comparable to the ordinary ingestion of

asbestos fibers by man. Is there any relationship between those two figures for rat and

man.

MOORE: I don't remember quoting 100 milligrams per rat per day, but suffice it to

say that the level of asbestos that's in a diet at the 1 percent level certainly is in the

high range of exposure.

COOPER: I have a very crass and practical question to ask. I know it's a matter of

public record what a study of this magnitude costs, what kind of investment it involves,

but I think the group would be interested in knowing just how much a major study like this

represents in cost.

MOORE: It's estimated that by the time the studies that I have outlined are completed, which will include the characterization of the materials as well, it will

probably be somewhere around 3-4 million dollars.

161

National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued Wovember 1978)

EPA STUDY OF BIOLOGICAL EFFECTS OF ASBESTOS-LIKE MINERAL FIBERS

D. L. Coffin

EPA Health Effects Research Laboratory

Research Triangle Park, North Carolina 27709

and

L. D. Palekar

Health Effects Research Laboratory

Northrop Services, Inc.

Environmental Sciences Group

Research Triangle Park, North Carolina 27709

Abstract

A large amount of the earth's crust is composed of rock containing

mineral fibers which resemble asbestos to varying degrees in their

physical and chemical properties. Consequently, such materials are likely to be encountered inadvertently during the extraction of various

ores, the extraction of rock for commercial purposes, and even from rock

moving operations encountered during highway construction, and the like.

Because the air and water may become contaminated by these fibers,

it is of interest from the standpoint of environmental protection to know

how the biological effect of such material compares with that of

asbestos. Consequently, a study has been instituted by EPA to

investigate the relative biological potency of such materials. The

project is being approached on both i_n vivo and i_n vitro levels. The

minerals being studied at the outset are fibrous amphiboles from a taconite mine, but it is the intent to broaden these studies as soon as possible. The animal studies are being conducted in pathogen-free rats

by intratracheal instillation (with and without interacting organic

carcinogens) and by intrapleural injections. The end points are tumor

induction and other chronic diseases. Attention is also being given to

early pathogenic sequences.

The ijri vitro studies consist of red cell lysis, pulmonary macrophage

systems, and various biological and chemical studies connected with the

influence of these agents on cell membranes and interaction with mutagens

and carcinogens. The prime objective is to compare the biological effect

of the minerals studied to the corresponding asbestos species to

determine the comparative influence of such co-variables as fiber

length, trace element content, surface area, zeta potential, and the

like, on the biological outcome. Thus, the study will relate biological

activity to mineralogical characterization so that generalization can be

made on the basis of such factors.

Key Words: Alveolar macrophages; hemolysis; intrapleural injections;

intratracheal instillation; multinucleated giant cell; PMP I; PMP II;

Polyp.

163
The hazards for human health associated with the extraction and handling of various

members of the commercial asbestos series are now well known. However, a new issue has

recently come to the forefront of environmental toxicology concerning the possible health

hazard from inhalation or ingestion of fibrous silicate minerals, not asbestos per se,

that contaminate the air and water. Such silicate materials are ubiquitous in the earth's

crust where amphibole-bearing rocks may serve as a potential source for a number of

mineral species, for example, fibers from the cummi ngtonite-grunerite series, hornblende,

etc.

When the above-mentioned facts became known, there was a tendency to class all of

these materials as "asbestos" and to try to make inferences concerning their potential

health effects in man merely on the basis of supposed analogy to commercial asbestos. We

know now, however, that there is an enormous variation in these materials; some closely

resemble the corresponding asbestos, and others do not. It would be folly, therefore, to

base the threat to human health solely on such a crude determinant. This is particularly

true since, despite the great number of epidemiological and biological studies carried out

with asbestos, much remains to be learned concerning the exact causal mechanisms of the

various lesions attributed to such exposure. For instance, one cannot safely postulate a common etiological mechanism for the usual lesions of asbestos exposure such as pulmonary

fibrosis, carcinoma of the lung, and mesothelioma, and the possible role of asbestos for

tumors in other locations which at this time is largely unexplored.

Because of these issues, the Environmental Protection Agency (EPA) has taken the

initiative to study these matters to determine if a threat to health exists from non- asbestos minerals, and if it does, by means of its quantification, to determine how best

to control it on the basis of health benefit versus cost. EPA is conducting a study of

the relative pathogenic potential of such minerals compared to asbestos, silica, and other

particulate substances of known toxicity. The prime purpose of these experiments is to

relate biological effects to the physiochemical properties of the minerals. Beginning

with the convening of an advisory committee, the following approach evolved, which

includes mineralogical as well as biological studies.

Mineralogical Studies

Intensive study was made from 50 large rock specimens removed from a taconite mine.

After preliminary lithological examinations, two of these were selected for employment in

biological experiments, which are designated as PMP I and PMP II. Fibers were separated

from the rock by such means as mechanical vibration, hand cobbing, air jet milling,

spinning, and riffling. The final specimens were subjected to a detailed analysis by means of optical and electron microscopy, x-ray emission spectroscopy, and x-ray

diffraction. Computations of surface area and determination of extractable organics were

made. Comparisons were also made on the basis of the above parameters with UICC amosite

(fibrous grunerite) and airborne material collected in the vicinity of the mine and the ore processing plant. On the basis of the above measurements, a decision was made to

prepare a large amount of this material suitable for biological experimentation.

Figures 1 through 8 and Tables I-III illustrate various mineralogical characteristics

of the samples chosen from the mine for biological studies, as well as samples from the

airborne material in the vicinity of the mine and ore-processing area. Figures 1 and 2 represent electron micrographs of air samples from mine and processing areas respectively.

The chemical analysis of air samples revealed that in addition to magnetite and

quartz particles there were predominantly two other types of minerals in both areas. The

electron microscope x-ray analysis revealed the presence of Mg, Si, Ca, Mn, and Fe in one sample (fig. 3), whereas the second sample contained only Mg, Si, and Fe (fig. 4). Data

from a careful analysis of size distribution of the air samples are presented in Table 1,

showing two samples from each of the processing and mine areas. The majority of the

particles in both areas were found to be less than 5 pm in length and less than 1 pm in

diameter. A small percentage of particles were between 5 and 10 pm in length, with

varying diameters. Air samples from the processing areas contained 66 to 70 percent

fibers with diameters less than 0.5 pm as compared to 52 to 55 percent in the mine area. This may suggest that further fibrillation of the rock occurs during the processing.

164
Figure 1. Air sample from mine area showing long and straight

fibers (lO.OOOx).

Figure 2. Air sample from the area

of processing plants also

showing long and straight

fibers (lO.OOOx).

Figure 3. Electron microscope x-ray

spectra of air sample

indicating the presence

of Mg, Si, Ca, Mn, and Fe.

En DO ,ao Co aaoaal

165
Figure 4. Electron microscope x-ray spectra of air sample

indicating the presence of Mg, Si, and Fe.

Table 1. Summary data of size distribution of mineral fibers in ambient air samples, --------- Lengths by Percent Number in Microns ---------

<0.50

0.51-1.00

>1.00

Total

<0.50

0.51-1.00

>1.00

Total

<0.50

0.51-1.00

>1 .00

Total

<0.50

0.51-1.00

>1 .00

Total

93%

<1

Air Sample No.

9

0

1 10

-<

Air Sample No. 2

8

0

0

8

< 89%

Air Sample No. 3

5

0

0

5 85%

Air Sample No.

9

0

0

9

1-5

71

12

0

83

66

13

2

81

55

21

4

80

52

21

3

76

5-10

5

2

0

7

2

16

9

2

4

8

14

5

3

5

13

>10

0

0

0

0

10

12

0

0

1

1

0

0

2

2

Total

100

100

100

100

85% 15%

Below 5 ym Above 5 ym

Diameter by Percent Number in Microns

166
.3 6 f J

Figure 5. Electron micrograph of PMP I showing long and straight

fibers with acicular

particles (lOOOx).

^ 1- r

4 10 ]jm

Figure 6. Electron micrograph of PMP II indicating long and straight

fibers and particles (lOOOx).

The electron microscope x-ray emission spectra of the fibers collected from the two

rock samples revealed the presence of Mg, Si, Ca, Mn, and Fe on PMP I (fig. 7); and Mg,

5i, and Fe on PMP II (fig. 8). The size distribution of the samples is given in Tables 2

and 3. The data indicate that the majority of the fibers are less than 5 |jm in length and

less than 0.5 pm in diameters in both samples.

Figure 7. Electron microscope x-ray

spectra of PMP I showing

the presence of Mg, Si,

Ca, Mn, and Fe.

J !• I I I I I I ' T I '!- I 1 "

167
Figure 8. Electron microscope x-ray

spectra of PMP II showing

the presence of Mg, Si,

and Fe.

En OD.OD Ca Hmnpfi

Table 2. Size distribution of PMP I sample.

Lengths in Microns (ym) - -

0.00 - 0.50 0.51 - 1.00 1.01 - 5.00 5.01 - 10.00 10 01 - 25.00 Total

0 00 - 0. 50 1.47 8.09 68.38 2.94 0.73 81.6

0 51 - 1. 00 0.00 0.00 5.88 2.94 0.00 8.8;

1 01 - 2. 00 0.00 0.00 4.41 0.73 0.73 5.8

2 01 - 5. 00 0.00 0.00 0.00 0.00 2.94 2.9'

5 01 - 10. 00 0.00 0.00 0.00 0.00 0.73 0.7;

< 88.23 > < 11 .74 99.9;

Below 5 ym Above 5 ym

Diameter by Percent Number in Microns

Table 3. Size distribution of PMP-2 sample.

Lengths by Percent Number in Microns

<1 1 - 5 5 - 10 10 - 15

0.00 - 0. 50 27.06 41.53 0 0

0.51 - 1

00 0 18.01 5.50 1.80

>1.00 - 10 0 0.80 3.90 1.80

27.06 60.34 9.40 3.60

^—— 87% y ^ 1 3%

Below 5 ym Above 5 ym

Diameter by Percent Number in Microns

168
Figure 9. Fibrous grunerite (UICC amosite)

showing the general shape of the

particle which is long and

straight (lOOOx).

STnee^the air samples and the rock samples seem to be representative of the grunerite

amily, a fibrous grunerite, namely UICC standard reference amosite, with known biological

iroperties, was selected as a possible control for the studies, and characterized. The

ilectron microscope x-ray analysis of amosite indicates the presence of Mg, Si, and Fe

fig. 10). Size distribution data for this material are presented in Table 4. Eightyeven percent of the fibers were found to be less than 5 pm in length and 1.5 pm in

liameter.

1 -

!

10 z 0 .50 , i

•

1 OCT It

II 1 1 L il en aa.aD Co 000039

Figure 10. Electron microscope x-ray

spectra of fibrous grunerite

(UICC amosite) indicating the

presence of Mg, Si, and Fe.

Table 4. Size distribution data of UICC amosite by IITRI method. ______ Lengths Distribution (by percent number), in Microns

.00-1 .10

.10-0.40

.40-1 .50

0.2-0.5 0.5-1 1- 2 2--5 5-10 10-25 25-50 50-100 100- 200 Total

15.90 3.48 1. 64 1 80 0.57 0.20 23.39

8.69 13.49 18. 24 16 40 5.16 1.68 0 41 0.20 0. 01 64.28

2. 54 4 75 1.31 1.84 2 69 0.20 12.93

87% 7%

^ — 6% — >•

iameter by Percent Number in Microns

169
The air samples, the fibers obtained from rocks, and amosite fibers were examined by

electron microscope for their general shape. All samples contained straight and long

fibers and acicular particles (figs. 5, 6, 9). These photographs are not representative

of the size distribution.

Biological Studies

Toxicity evaluations are proceeding both iji vivo and J_n vitro. Whole animal experiments are being carried out to determine the comparative effect of the above-mentioned

mineral fibers in inducing lesions such as pulmonary fibrosis, lung cancer, and pleural

mesothelioma. Basically, a comparison between a test amphibole of the cummingtonitegrunerite family, UICC amosite, and an inert particle is intended. These studies are being conducted in Fisher 344 pathogen-free rats during their life span. The particles

are administered to the animals by intratracheal instillation and intrapleural injections.

In vitro studies are conducted on sheep blood erythrocytes and rabbit alveolar

macrophages. The cytotoxicity is evaluated by quantitation of red cell hemolysis and cell

death respectively.

In Vivo Studies

The doses for the intratracheal instillations were determined by an initial rangefinding study. Several doses of the particulates were administered to the animals and the

highest tolerated dose was determined. Two series of intratracheal studies are planned.

Innoculation of the animals in the first series is complete. The second series will be

initiated in the near future.

Chronic Intratracheal Testing of PMP Amphibole

The first series will determine whether the particles alone cause significant toxicity

to animals. The regimen for this series is as follows:

Series I: Unknown Sample - PMP I Amphibole 600 animals

Asbestos Control - UICC Amosite 200 animals

Negative Control - Saline and Gel ....... .200 animals

Chronic Interaction Studies by Intratracheal Instillations

The purpose of the second series is to determine whether the particles will interact

with a known carcinogen to produce a higher incidence of tumors. A known amount of

benzo(a)pyrene (BaP) will be coated on the particles to compare the synergistic effect of

the carcinogen with amosite, the test amphibole, and hematite. The regimen of this series

is as fol lows:

Series II: PMP I Amphibole + BaP 300 animals

UICC Amosite + BaP 300 animals

Iron Oxide + BaP 300 animals

PMP I Amphibole 200 animals

Iron Oxide 200 animals

BaP 200 animals

Chronic Intrapleural Testing of PMP Particles

Intrapleural studies employing 20 mg of particles injected once into the pleural

cavity are being carried out as follows:

Series III: Unknown Sample - PMP I Amphibole 150 animals

Asbestos Control - UICC Amosite 150 animals

Negative Control - Saline 150 animals

170
In addition to the lifetime experiments, exploration of the pathological sequences

induced by these materials in the lung is in progress by experiments in which sequential

sacrifices are being carried out. Figures 11 and 12 demonstrate epithelial polyps and

fiber-containing giant cells observed in the parenchyma of rats treated with 12 weekly

injections of 1 mg of amosite or the test sample PMP I, 50 days after the last innoculation. The polyps essentially consist of several multi-nucleated giant cells covered with

columnar epithelium.

Figure 12. Multinucleated giant cell containing fibers (lOOOx).

171
In Vitro Studies

The second part of the biological studies consists of in vitro investigation to

determine cytotoxicity of the particles. Two techniques are employed, namely, sheep

erythrocyte hemolysis and rabbit alveolar macrophage destruction. A comparison was made

between several commercial asbestos samples of known biological properties, PMP I and non- fibrous grunerite. The data presented in figure 13 suggest that the amphiboles are not as hemolytic as chrysotile fibers, requiring large doses to achieve 50 percent hemolysis.

Among the amphiboles, anthophyl 1 ite , PMP I, and tremolite are similar in their effect.

Crocidolite and amosite seem to be less hemolytic. In contrast, non-fibrous grunerite is

non-hemolytic. In the rabbit alveolar macrophage study, amosite and PMP I caused marked

depression of cellular viability, whereas non-fibrous grunerite showed no significant

change in cellular viability (fig. 14). The sample PMP II is not yet tested.

A second advisory committee was convened to consider further investigations to

increase our understanding of the mechanisms of mineral interactions with the biological

systems. It was the opinion of the committee that the comparative study of minerals

should be started as soon as possible. On the basis of the existing data, produced by

different laboratories throughout the world, the problem of contamination of the

environment with inorganic fibers may pose a significant health threat. Indeed, it may

shed significant light on existing problems, e.g., asbestos in potable water supplies,

asbestos released from degraded asbestos cement water pipes, natural sources, etc.

The selection of minerals and bioassays are as follows: fibrous and non-fibrous

grunerite will be collected from different geological localities and their biological

properties will be compared. The careful mineralogical analysis and bioassays may

indicate whether there is some influence in terms of the crushing process that may create

new fiber surfaces not present when communiting materials from other areas.

>

-Io

LUI

100

80

60

40

20 -

~~1 \ \ CHRYSOTILE

(RHODESIA-UICC)

TREMOLITE (INDIA)

PMP

ANTHOPHYLLITE

(S. AFRICA-UICC)

AMOSITE

(S. AFRICA-UICC)

-I \—I—

A CROCIDOLITE

(S. AFRICA-UICC)

y GRUNERITE

(NON FIBROUS)

0.01 0.02 0.05 0.10 0.20 0.50 1 2 5

CONCENTRATION (mg/ml)

10 20

Figure 13. Hemolysis of sheep erythrocytes by various minerals.

172
1—I I 1 1 MM 1—I I I 1 1 III 1 I I 1 1 nil 1—I I I 1 1 II

AMOSITE (UlCC-S. AFRICA)

I

I I t I I I Mil I I I I I i III I I I I I nil I I I I! I II

0.01 0.05 0.10 0.20 0.50 1 2 5

CONCENTRATION (mg/ml)

Figure 14. Cytotoxic effect caused by various minerals when exposed to rabbit

alveolar macrophages.

For a proper comparison, a standard reference sample of fibrous grunerite (UICC

jmosite) containing particles of mixed sizes, and another sample specially prepared with

short fibers will be used. Since relatively short fibers are observed in Lake Superior,

the information obtained from these fibers will be useful.

Fibrous cummingtonite with a high magnesium content from several geological localities will also be studied for comparison to determine if different processing methods may

liter surface properties and, in turn, affect the biological properties. In addition,

linerals of known biological properties, such as UICC anthophyl 1 ite , UICC chrysotile A,

:hrysotile RG 144, UICC crocidolite, Indian tremolite, UICC actinolite, antigorite,

ibrous glass, and quartz will be studied for comparison. Several assays will be employed

.0 evaluate the biological properties of the minerals. The direct toxicity of the

•articles will be tested by hemolysis of sheep red blood cells, viability of rabbit

ilveolar macrophages, human lung fibroblasts such as strain WI-38 and perhaps the mouse

iscitis tumor cell line P3881 . The possible mutagenic effects of these materials will be

valuated in well-established mutagenesis test systems, such as the Ames test and the

.5178Y mouse lymphoma cell assay. Neoplasm induction will be tested by the use of

racheal transplants, as well as transformation of Syrian hamster embryo (SHE) cells, or

jouse fibroblasts, such as the C3H lOTij or BALB/c 3T3 cell lines.

173
Concl usion

Preliminary i_ri vitro tests show that both fibrous grunerite and PMP I amphibole are lytic to sheep erythrocytes and depress the viability of rabbit alveolar macrophages,

while non-fibrous grunerite is inactive in both systems. The biological significance of

these studies is at this time unclear. Hopefully the proposed investigation will

contribute sufficient information to correlate mineral properties to health hazards

associated with inhalation and/or ingestion of minerals other than the known commercial

asbestos.

Mineralogical characterization was done by Illinois Institute of Technology, Chicago,

Illinois. Contract #68-02-2451.

Discussion

C. COOPER: I want to congratulate Dr. Palekar for the description of what is getting

under way, and the great care that has been taken apparently to obtain test materials that

at least resemble some of the fibers in the taconite areas. I think an important question

is how representative this is of the entire Mesabi range and I personally don't have figures

available to me as to whether or not the size distributions found at the Peter Mitchell

pit are representative of a larger area. I wonder if anybody in the audience here, or

Dr. Palekar herself, have data on other areas in the Mesabi range to answer the question

as to whether or not 15 percent, approximately, of the fibers are longer than 5 micrometers

in length, because the representativeness of this sample is going to be, I think, an important issue in the future, and I wonder if anybody could address themselves to that?

L. PALEKAR: I don't have a clear-cut answer to your question, but if somebody in

the audience wants to answer that. .

A. LANGER: You mean the representativeness of the Peter Mitchell fibers?

COOPER: Yes.

LANGER: It's unlike anything in the rest of the Mesabi.

COOPER: Are there air samples in other areas with this same distribution?

LANGER: No there are not. Unfortunately for the Reserve Mining Company, the situation

at the Peter Mitchell pit is unique for the Mesabi range. The mineral fibers have been

originated through contact metamorphism with the Duluth Gabbro, which metamorphose the

pre-existing materials here. Now Malcolm Ross is here, who has done work on the amphiboles

in the area. He knows a great deal about the geochemistry of the amphi bole/pyroxene phases;

this is a high temperature metamorphic assemblage, while the rest of the Mesabi range, the

rest of the Biwabik iron ore formation, are generally considered to be low temperature

iron silicates. They do have problems with fibers, but these may not be as important

biologically as the asbestiform amphiboles in the Peter Mitchell pit. This is just unique

for that particular area.

W. NICHOLSON: In looking at the fiber distribution in other than the Reserve Mining

areas, they are of a smaller size distribution and tend, rather than being regular fibers,

(that is with collinear sides) to be chips of fibrous length. They are irregular fragments

rather than the natural fibers that we've been hearing of, and they are in general of a size distribution somewhat smaller than that which has been described here, but there are many fibers (that is defined by a 3 to 1 length to width ratio) that are present in other

areas.

P. GROSS: I would like to comment on the two microphotographs of tissue which Dr.

Palekar showed. I was most interested in the visualization of fibers at that magnification, which indicated that the fibers were quite long, much longer than 5 microns. As

a matter of fact, one of the fibers that I saw, where one of the giant cells was, was as

174

1
long as a giant cell, which probably was in the neighborhood of 100 fjm in length. Also

the photomicrograph of the bronchial-polyp, this sort of picture has been produced in my

laboratory with long fibers of any kind: glass, silicon carbide, aluminum silicate, as well as asbestos. Again, it suggests the presence of a fairly considerable number of long

fibers, and it seems to me that may be a reflection of an exceedingly high dosage

administered even though your long fibers were less than 15 percent of the total.

PALEKAR: Yes sir, we administered the highest tolerable dose. The animals received

twelve weekly injections of 1 mg.

A. WILEY: Since there seems to be a good deal of controversy about what's a fiber

and what's not a fiber, I was interested in your characterization of a grunerite sample as non-fibrous and I'd like to know what you meant by it.

PALEKAR: The particles are not completely characterized at this time and it was presumptuous on my part to present the data. This is really a very preliminary study and

no conclusions can be drawn at this time. We have asked our colleagues from IITRI to

analyze this properly. Thus far I have just taken their word for the non-fibrous nature

of the particles.

G. NORD: Yesterday we saw a great deal about the mineralogy of amphiboles. One of

the things that was brought up was the defect structure of amphiboles. Amosite has a very

high defect density; it's polysynthetically twin on a unit cell scale. The grunerite that

you used, or I should say the minerals that you used from the Mesabi range sample, may

have an entirely different defect population. Is there going to be any attempt to

characterize this defect population? That could also go for the characterization of the

samples discussed by the previous speaker. I have one other comment: It's not enough to

characterize a fibrous mineral strictly by an energy-dispersive analysis. You cannot tell

the difference between a low calcium pyroxene and a low calcium amphibole. It is not

enough to characterize a low calcium amphibole merely by knowing its chemistry. It also

has a different structure; you have orthorhombic amphiboles and you have monoclinic

amphiboles. Grunerite/cummingtonites are monoclinic. You also have anthophyl 1 ites which

are orthorhombic. If one is to characterize these samples adequately so one can separate

out the very small differences, perhaps in the experimental data, you will have to do a great deal more work.

PALEKAR: Well, this paper is by no means the entire story. I never said that this

is it, that this is the only thing we are going to do. We are open to ideas and we are going to characterize many more minerals more thoroughly; this is just the beginning and

we intend to do further analyses.

B. SMITH: Dr. Palekar, I believe you said that the EM measurements that you had on a standard reference sample of amosite, UICC amosite, was showing about 87 percent of the

particles shorter than 5 pm, and that the measurements that you had on the preparation,

the PMP preparation that you made from taconite rock, showed about 85 percent of fibers

running below 5 pm. Now, as I looked at the photographs you showed, the photographs of

the taconite preparation had a micron scale on them, so we were looking at fibers that

were being compared with a 1-micron scale. They didn't seem to be more than, or only a little bit more than the scale. They looked to me about 2 or 3 times the size of the

scale, so I guess they were fibers that were about 2 or 3 pm long. In comparison, the

photograph you showed of the UICC amosite was fitted with a 10-micron scale and there were

an enormous number of fibers visible in that photograph that were much longer than the 10-

micron scale. This presents a problem that has puzzled me many times in samples that I've

looked at, where we've gotten electron microscopy measurements that are telling us that

two samples really are about the same as far as the mean fiber length is concerned. When

I look at them with an optical microscope, it's very apparent to me that there are an enormous number of long fibers that I can easily see at say 400X in one sample, and with

the other sample that electron microscopy figures are telling me is about the same, I have

a tough time seeing any fibers. Now how do we get around this problem?

PALEKAR: Yes, I agree with you wholeheartedly and I had the same questions to our

mineralogist. The electron micrographs of the fibers are not representative. It is known

that there is a tremendous variation between samples. One must make an effort to use the

175
same sample for mineralogical analysis and biological evaluations to establish a proper

relationship between the two.

D. WALIA: I don't have a question but I'd like to address myself to some of the

comments regarding the preparations and characterizations that we did for Dr. Palekar.

The comment that electron microscopy is not the only criteria to distinguish one fiber from

another is true, and we did not depend only on that. Instead we picked up the fibers from

the filter samples, mounted them on glass fibers, and then performed x-ray diffraction

studies on them. We then compared the data with the known fibers from the taconite mines,

and also with the ASTM standards, and from that we were able to identify or pinpoint their

identity as to the mineral species. Second, regarding the size distribution comments, if

you remember the tables Dr. Palekar showed, in the case of UICC amosite, where we have

compared our size distribution data, which is both by diameter and by length, you get a comparison within ±6 percent. I believe this is a good comparison and from the table you

see that UICC amosite has fibers which are as long as 200 pm. When we look at the

taconite samples, which we have prepared, and the size distribution data, you see that there

is no fiber greater than 20 pm. To my knowledge, from all the taconite rock samples I've

seen, I've never come across any mineral fiber which, even using this ambiguous three-toone aspect ratio criteria, that I can say is 200 pm in length. Another comment I'd like to

address myself to is about the non-fibrous grunerite we used. This non-fibrous grunerite,

which has some preliminary results that Dr. Palekar showed, was the one we got from bawabush

iron ore formations in Canada, and the non-fibrous nature of this is based on the lack of

flexibility of the fibers which you commonly see in UICC amosite type materials.

NOTE: The following notes were sent following the meeting and were not part of the verbal

discussion at the end of the session.

GROSS: Dr. Palekar' s description of the bronchial lesions that develop in animals

following the intratracheal injections of long-fibered asbestos as "polyps" deserves

explanation.

A polyp is generally conceived to be a tumor - a neoplasm. The intrabronchial lesions

developing in animals after intratracheal injections of asbestos are not tumors. The

lesions are composed of inframmatory tissues that surrounds impacted, aggregated asbestos.

The inflammatory tissue extends (often in a finger- like manner) into the bronchial lumen

and, in time, becomes covered by normal -appearing bronchial epithelium - hence its resem- blance to a polyp.

R. BLEIFUSS: The reports submitted by the Illinois Institute of Technology Research

Institute (IITRI) regarding the origin of the sample materials to be used in these

biological studies indicates that the source material represents an unusual situation

within the Peter Mitchell Pit (PMP) of Reserve Mining Company. The original sample

material represents a unique occurrence within the PMP in the same sense that the PMP may

be said to be unique to the rest of the Mesabi Range. IITRI personnel collected more than

100 samples in their initial survey on which they carried out extensive mineralogy studies

to characterize the ore. Based on this initial information the sample location from which

they extracted the fibers for the biological study was selected as described below.

"On October 2, 1975, approximately 750 lbs of high fibrous content ore were located and collected. It was found that the ore containing rich

fibrous veins was a very localized phenomenon. Such samples were available only near the incursion of the Duluth Gabbro and occurred only in

two very localized areas within approximately 100 m of each other."

^IITRI Report No. C5321C02-11, Final Report, Contract No. 58-02-1687, "Amphibole Mineral

Study to Complement the Ongoing Characterization of Finely Particulate Environmental

Contaminants for Biological Experimentation."

176
"Fibers were separated from fiber-rich rocks using several methods. Both

hand and vibratory cobbing were used to separate fibrous material ("^-l.S

kg) in veins. Several rocks were found to consist almost entirely of

soft, light green or brown fibrous material. These rocks were crushed,

ground, and sieved (<35 mesh) to produce a material (^'3 kg) with a high

fibrous-to-non-fibrous ratio.

"These separated fibrous materials are not necessarily representative in

all respects of the majority of the fibers in the ore in the Reserve Mine

or in the tailings from the magnetite extraction at Silver Bay,

Minnesota. However, this method was used as large quantities of

materials with a large fibrous fraction could be produced more easily

than by separating fibers from the ore or the tailings."

The mineral composition of the sample prepared from this "high fibrous" ore, which has

been encapsulated for the biological studies, was determined by x-ray diffraction. The

minerals "definitely present" include cummingtonite, riebeckite, and rich(t)erite. Minerals

"present as trace material" were tremolite and crocidolite. However, the basic mineralogy

studies on the 100 original samples include no mention of riebeckite, richterite, or crocidolite. Both the riebeckite^ and crocidolite^ have been described in the literature

and are present only in trace amounts in the Peter Mitchell Pit. The sodium in these two

minerals is considered to be of metasomatic origin. Richterite was not reported by previous

workers in the area which suggests that it may be the result of local hydrothermal activity.

Thus the sample prepared for these biological studies contains three minerals which were

either unreported or considered to be present in trace amounts by previous authors. These

minerals are all commonly reported to be of metasomatic origin, meaning that some of the

critical elements (sodium) for their formation was introduced from outside the iron formation. The occurrence of these minerals in veins further suggests that they are related

to metasomatism.

The sample which was finally selected and processed to produce the fibers for biological studies appears to have a unique metasomatic origin, or at least some of the minerals

in that sample are related to metasomatism. The sample is certainly not representative of

the potential tailings from the PMP. It cannot be classified as typical since three of the

finer most important mineral components are certainly atypical in the PMP area. The sample

was selected to provide a high "fibrous" to "non-fibrous" ratio that was unobtainable from

representative taconite samples.

Biological experiments on this sample will contribute little to the resolution of the

problem pertaining to the possible carcinogenic nature of taconite tailings. The argument

that it is a means of establishing a bridge between a known carcinogen (amosite) and a possible, or suspected carcinogen (cummingtonite in taconite tailings) is not realistic.

The direction of the sampling program was to obtain a fibrous sample as analogous to amosite

as possible. In so doing it is so far removed from being representative, or typical, of

taconite tailings as to make the final outcome essentially meaningless.

^Gundersen, J. N. and Schwartz, G. M. , The Geology of the Metamorphosed Biwabik IronFormation, Eastern Mesabi District, Minnesota. Geological Survey Bulletin No. 43, 1962.

^White, D. A. , The Stratigraphy and Structure of the Mesabi Range, Minnesota. Minnesota

Geological Survey Bulletin No. 38, 1954, 92 pp.

177

National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

A STUDY OF AIRBORNE ASBESTOS FIBERS IN CONNECTICUT

Leonard Bruckman

Air Compliance Unit - Engineering Section

Connecticut Department of Environmental Protection

Hartford, Connecticut 06115

Abstract

The following discussion describes actions taken by the Connecticut

Air Compliance Unit for the purposes of studying the danger to public

health associated with excessive airborne asbestos fiber concentrations.

In Connecticut, the criteria of mesothelioma was selected as the

basis for developing an ambient air quality standard for asbestos (i.e.,

30 r\g/m^ or 30,000 fibers/m^, 30-day average) and compatible mass emission standard (i.e., 24 g/day) in lieu of EPA's qualitative asbestos

regulations. An ambient air asbestos survey indicated that asbestos

concentrations contiguous to manufacturing sources of asbestos emissions

exceed Connecticut's proposed standard. Furthermore, asbestos levels

adjacent to toll plazas were also elevated relative to levels removed

from manufacturing sources, implicating vehicle brake lining

decomposition as a significant source of airborne asbestos fibers. In

addition to the aforementioned air asbestos survey, a preliminary study

of mesothelioma was conducted. There were 133 Connecticut residents

diagnosed with mesothelioma between 1935 and 1972. Although subject to

diagnostic error, available statistics suggest that the combined sex age-adjusted mesothelioma incidence rate (AAR) per 100,000 Connecticut

population has exhibited a possible 10-fold increase since 1935, rising

from 0.02 during 1940 to 0.25 from 1960 to 1969. The trends for both men

and women also showed sharp increases over the same time period (1940 to

1970). The rapid rise in Connecticut's mesothelioma incidence rate

closely follows the increase in the State's cumulative asbestos

consumption and suggests a linearly increasing cause-effect relationship

which warrants further investigation.

Key Words: Air pollution; air quality data; air quality monitoring; air

quality standards; asbestos; health effects; toxic substances.

Introduction

In 1973 the Federal EPA, recognizing the need to control the emission of asbestos

ibers into the ambient air, promulgated National Emission Standards for Hazardous Air

ollutants (NESHAPS) - asbestos, mercury, and beryllium [1,2]^. After an extensive review,

Connecticut's Air Compliance Unit found EPA's asbestos regulation to be inadequate for the

urposes of protecting public health in Connecticut and, consequently, developed its own

I sbestos regulation [3,4]. While EPA's asbestos regulation was written in rather general

jerms (i.e., "...no visible emissions or application of the best available control

jechnology. .

. ") , Connecticut proposed a numerical ambient air quality standerd of 30 r\g/m^

r 30,000 total asbestos fibers (determined by electron microscopy) per cubic meter of air,

0-day average, and a compatible mass emission standard of 24 g/day, at public hearings held

n July of 1973. In the judgment of the Connecticut Air Compliance Unit a "no visible

I Figures in brackets indicate the literature references at the end of this paper.

179
emission" asbestos air quality standard does not provide the State's residents with an adequate degree of protection from this carcinogenic substance. In addition, Connecticut

also proposed to more stringently control the demolition of asbestos-containing structures.

In order to define the magnitude of the environmental hazards posed by airborne

asbestos fibers in Connecticut, prior to the promulgation of the State's asbestos standard,

the Air Compliance Unit conducted an ambient air asbestos survey along with a study of

asbestos-induced mesothelioma incidence [5,6]. The following discussion describes actions

taken by the Connecticut Air Compliance Unit for the puuposes of studying the danger to

public health associated with excessive airborne asbestos fiber concentrations.

Sources of Airborne Asbestos Fibers in Connecticut

Outdoors, the principal source of airborne asbestos fibers in Connecticut is the

manufacture of the many asbestos-containing products (e.g., friction products, gaskets).

It is estimated that almost 10 tons of asbestos fibers might be released into the

Connecticut atmosphere annually as a result of manufacturing operations, assuming

reasonably efficient (i.e., 95% asbestos removal efficiency or greater) control equipment

is employed. Another major source of airborne asbestos fibers is the erosion of asbestoscontaining brake linings and clutch facings. This accounts for approximately two

additional tons of airborne asbestos fibers each year [3,4]. Notwithstanding EPA's

current regulations covering the demolition of asbestos containing structures, perhaps the

largest potential future source of asbestos emissions might be the demolition of buildings

which have been insulated and/or fireproofed with asbestos materials. The portion of the

NESHAPS regulation pertaining to the demolition of asbestos-containing structures does not

clearly state what requirements a demolition operator must meet in order to ascertain

whether a structure to be demolished does or does not contain friable asbestos materials.

The inherent difficulty in determining whether a building to be demolished contains any

asbestos materials, and the associated costs involved in removing such materials if

present, necessitate some type of formalized testing procedure. Briefly, such a test

might entail taking samples from the walls, the insulation covering load-supporting

structural members and the floor and ceiling tile, from at least one floor of the

candidate structure, in addition to the insulation covering the boiler and pipes. A

composite sample could then be created and analyzed to determine its asbestos content

using relatively inexpensive techniques (x-ray diffraction). It is important that the

asbestos content of floor and ceiling tiles be ascertained since these non-friable

asbestos materials might be pulverized during the demolition of a structure creating a potentially serious asbestos air pollution problem, especially if the technique known as "explosive demolition" is used. The amount of asbestos fiber dust released into the

outdoor air during the demolition of an asbestos-containing structure is unknown at this

time, but would appear to be potentially large since there are over 2,000 demolitions in

the State each year, and should thus be quantified as soon as possible.

Indoors, many do-it-yourself home projects create asbestos dust due to the mixing of

dry, loose asbestos with water and subsequent application of such mixtures for the

purposes of insulating and/or fireproofing boilers, pipes, etc..., and the cutting and

sawing of asbestos-containing wallboard, ceiling, and floor tile. Perhaps the most

serious public health hazard posed at this time by excessive asbestos fiber exposure has

been created by the release of asbestos fibers from asbestos-containing surface coatings,

which were applied indoors to walls, ceilings, exposed structural steel, air ducts,

plenums, return air spaces, for insulating, decorating, and fireproofing purposes indoors.

As a result of such activities, appreciable amounts of asbestos fibers may be released

into the air indoors, during the application, again as the surface coating deteriorates,

and finally, when the building is demolished. The asbestos fibers resulting from the

spraying operation itself, as well as those released from the coating over a period of

time due to its friable nature, should be of primary health concern. At least one state

(i.e., New Jersey) and one local municipality (i.e.. New Haven, Connecticut) have already

promulgated regulations for the purposes of controlling and/or prohibiting the future use

of spray-on asbestos surface coatings indoors. NESHAPS currently prohibits the use of | such asbestos-containing spray-on insulation and fireproofing materials outdoors; a recent \ amendment to NESHAPS proposes to prohibit the future use of any type of spray-on asbestos

coating indoors [7].

180
Ambient Air Asbestos Standard

The approach taken in developing Connecticut's proposed ambient air quality standard

for asbestos was to derive a numerical standard which should not be exceeded at this time.

In other words, all assumptions were made such that the standard could not be criticized

as being too strict. Setting standards should be viewed as a dynamic process in that any

value must be reviewed and revised periodically as additional pertinent information

becomes available. Even a preliminary air quality standard is valuable because it

provides some quantitative idea as to what health risk is associated with varying

pollutant levels. Such a standard can be especially useful in developing a set of

priorities for correcting environmental problems created by certain pollutants. For

example, areas which are well below the standard need no immediate attention, while areas

well above the standard require that some sort of corrective action be taken as soon as possible. Such an approach is particularly needed for toxic multi-media environmental

pollutants, such as asbestos. In this manner limited resources can be effectively

directed at solving the more serious aspects of the problem and, at the same time, actions

based solely on emotional decisions by poorly informed administrators can be minimized.

Connecticut's proposed asbestos standard should be viewed in this light; i.e., this

standard is a first attempt at quantifying the adverse health effects posed to the general

public by excessive airborne asbestos fibers. Hopefully, any questions raised by the

rationale used in developing this standard will be answered by future studies using varied

approaches.

Mesothelioma incidence was selected as the foundation for developing Connecticut's

proposed air quality standard for asbestos for the following reasons [8-10]:

The high frequency of lung cancer in the general population makes it

difficult to relate a given case of bronchiogenic carcinoma to asbestos

exposure with the high degree of probability that exists for

mesothel ioma.

Some investigators suggest that the smaller asbestos fibers (i.e., those

less than 5 p in length) most likely encountered in the ambient air may

be incapable of inducing lung cancer, however, it has not been

demonstrated that these shorter asbestos fibers are incapable of

producing mesothelioma.

Most of the information available on the adverse health effects caused by excessive

asbestos fiber exposure has been collected in occupational environments (Table 1) [11-17].

Table 1. Incidence of mesothelioma and asbestos concentrations in occupational

environments [11].

Industry

Cohort^

number of

individuals

Mesothel ioma

incidence

percent Reference

Highest^

concentration

fiber/cm^

Lowest

concentration

fiber/cm^

Insulation 689 2.18 [n] 74.4 0.1

Shipyards 3000 0.73 [11], [14] 8.7 0.3

Construction 632 0.63 [11], [15] 7.1 0.9

Textile plants 716 1.50 [11], [13] 29.9 0.1

1300 1.00 [11], [13], [16] 29.9 0.1

'V.1300 1.20 [11], [12], [17] 29.9 0.1

Most of the individuals in these studies had been followed for 20 years or longer.

Concentrations for NIOSH document [18].

181
Unfortunately, quantitative dose-response relationships concerning environmental asbestos

exposures and mesothelioma incidence in different industrial settings are not available. In 1973, the National Institute for Occupational Safety and Health (NIOSH) monitored asbestos

concentrations in a number of occupational environments [18]. While these short-term fiber

concentrations are of recent origin and, therefore, cannot be directly related to

epidemiological studies of mesothelioma incidence, they can be used to obtain an estimate of

the range of occupational asbestos exposure likely encountered in different industrial

settings. For example, Selikoff and co-workers reported that for workers in the construction

industry (followed for 20 years or longer) 0.63 percent contracted mesothelioma [15]. The

variation in asbestos fiber exposure for the construction industry from the NIOSH study

ranged from 0.1 to 29.9 fibers/cc which corresponds to a hypothetical probability of contracting mesothelioma of 63/10,000 (i.e., 0.63%). In a like manner, occupational mesothelioma

incidence (provided by studies appearing in the open literature) and corresponsing estimates

of the range of asbestos fiber exposure (provided by the aforementioned NIOSH report) were

used to construct a first generation occupational asbestos fiber exposure-mesothel ioma

incidence envelope (Figure 1).

Figure 1. Expected incidence of contracting mesothelioma as a function of industrial

air asbestos exposure (8 hr day, 5-day week).

182

I
Only asbestos fibers greater than 5 |j in length with an aspect ratio of 3:1 (as

iewed by phase contrast light microscopy; 430X magnification) are monitored in industrial

nvironments. These longer asbestos fibers account for approximately two percent of all

sbestos fibers present (by number) [19]. Expressed in another manner, there are pproximately 50 asbestos fibers for every 5 p size fiber. Furthermore, it has been

stimated that there are approximately 1,000 asbestos fibers per nanogram of asbestos

3,20,21]. Consequently, 20 "industrial size" asbestos fibers are equivalent to

pproximately one nanogram of asbestos. Other investigators have reported similar

elationships between industrial size asbestos fibers, total asbestos fibers and their

eight equivalents [3,19]. In addition, occupational exposure concentrations based on a -hour day, 5-day week should be related to general population ambient exposure levels,

his can be accomplished by dividing occupational concentrations by 4.2 (i.e., 24-hour/8-

our X 7 day/5 day = 4.2) [22]. Now the occupational mesothelioma incidence envelope

epicted in Figure 1 can be converted to a general population mesothelioma incidence

nvelope (as a function of both weight and number of asbestos fibers per volume of air),

rom which an ambient air quality standard for asbestos can be selected (see Figure 2).

sing the minimum line a level of 30 r\g/m^ or 30,000 fibers/m^, which is projected to

nduce 150 mesotheliomas nationwide or 2 in Connecticut, was chosen. The use of the

inimum line, which reflects the smallest probability of an individual contracting

esothelioma for a given exposure level, is consistent with the aforementioned objective

f developing an asbestos standard which would be difficult to criticize as being too

trict; the use of either the maximum or some average line would have yielded an asbestos

tandard some 2 orders of magnitude more restrictive (lower) than the proposed standard

or the same response. The chosen standard should result in about 1/10 the yearly

atalities from airplane accidents and approximately the same number of deaths as from

rain mishaps (see Figure 3) [3].

= 10 y—

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2 . Proposed

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10^ 10 10^ 10

150

Nationwide Expected Cases Of Mesothelioma

igure 2. Nationwide expected cases of mesothelioma as a function of ambient air asbestos

exposure (assumed population of United States was 230 million people).

183
o

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Figure 3,

Plane

Train

Nationwide Expected

Cases Of Mesothelioma, Ambient Air

Asbestos Conceritratlon Of 30ng/m^

Activity

Nationwide mortality statistics due to different modes of travel

and expected cases of mesothelioma.

The subject asbestos standard is equivalent to an occupational asbestos level of

0,0025 fibers (>5 p)/cc, well below the newly proposed occupational standard of 0.5 fibers

(>5 p)/cc [23]. This strongly suggests that the aforementioned proposed occupational

asbestos standard is not yet low enough to adequately protect the worker exposed to

asbestos fibers from contracting mesothelioma.

Connecticut's ambient air quality standard for asbestos is based on a 30-day average

sampling period instead of the more common 24-hour duration because a 1-month averaging

time is more manageable from a monitoring standpoint and is not sensitive to short-term

perturbations in air asbestos emissions, but at the same time provides the public with a high degree of protection from the adverse health effects caused by excessive asbestos

fiber concentrations. Compliance with the proposed standard can be easily and accurately

evaluated using Connecticut's low-volume particulate sampler (lo-vol) [6,24].

184
In certain instances it may be necessary to impose asbestos emission standards on manufacturing and other sources of airborne asbestos fibers in order to attain the desired

ambient air asbestos standard. A mass emission standard of 24 g/day (for an isolated point

source of asbestos emissions) is consistent with the 30 r\g/m^ (30,000 fibers/m^) proposed

standard. The development of this emission standard, in addition to a possible stack

sampling train, are explained elsewhere [3,4].

Mesothelioma Incidence in Connecticut

The mesothelioma incidence trend in Connecticut men mounted through the 10 year

period covering 1960 to 1969 from an age-adjusted rate (AAR), obtained using the indirect

method, of 0.04/100,000 Connecticut population for the interval between 1940 and 1949 to

0.37/100,000 from 1960 to 1969. No mesotheliomas were diagnosed in Connecticut women until

the period 1950 to 1959 when 12 were reported yielding an AAR of 0.1/100,000. The trend for

females increased slightly to 0.15/100,000 in 1960 to 1969 (Figure 4). The combined sex AAR

0.4

D

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O

C

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c

e

o

o

CO

(/) <I <

o

a

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3O

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c

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o

O

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O

o

o

Q.

0.3 _

0.2 _

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1940-49 1950-59

Period

1960-69

Figure 4. Connecticut mesothelioma incidence by 10-year period.

185
rose from 0.02/100,000 during 1940 to 0.25/100,000 from 1960 to 1969, over a 10-fold

increase. The increase in cases over the years may in part reflect an increased awareness

of this type of tumor and an attempt by pathologists to classify all malignancies. Though

increases in both occupational and non-occupational asbestos fiber exposure are expected to

have occurred over the last 40 years, only four people were reported with known exposure to

asbestos. Eight others were felt to have experienced some exposure. Occupation at the time

of diagnosis was obtained from hospital admission records and the usual occupation from

death certificates. It was found that 44 individuals (33.0%) worked in the home or in like

occupations. Thirty-six (27.1%) were reported to have worked in manufacturing industires.

Nineteen (14.3%) worked in offices as professionals or clerical employees. Of the remaining

individuals it is interesting to note that one person was listed as a toll collector. Unfortunately, complete occupational histories of each of those individuals afflicted with

mesothelioma are not available at this time [5].

Cumulative United States asbestos consumption has increased rapidly since the beginning

of the 20th century and is projected to exceed 60 million tons by 1980; [25] Connecticut's

asbestos consumption has been estimated by proportionally allocating total U. S. consumption

using the appropriate Connecticut to United States population ratio. A plot of both

cumulative U. S. and Connecticut (estimated) asbestos consumption and Connecticut's combinedsex mesothelioma AAR/100,0G0 population as a function of time suggests that the sharp

increase in mesothelioma incidence closely followed the rapid rise in the State's cumulative

asbestos consumption for comparable intervals (i.e., 1940 to 1970) (Figure 5). This apparent

cause-effect relationship warrants further investigation.

10*

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10^

10^

United States

10'

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o

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Period

Figure 5. Cumulative asbestos consumption and Connecticut mesothelioma

incidence as a function of time.

186
Air Asbestos Survey

An ambient air asbestos survey was conducted during late 1975 and early 1976 to

define the magnitude of the health hazard posed by airborne asbestos fibers in Connecticut

prior to the promulgation of the State's asbestos standard. The newly developed low

volume particulate sampler (lo-vol) (see figure 6), which operates continuously for a 30-

day interval at an air sampling flow rate of approximately 4 cfm, was used to collect

ambient TSP samples. The lo-vol was equipped with special membrane filters (8" x 10",

Gelman Metricel GN-6 0.45 (j pore size, non-nylon reinforced). The filters were analyzed

for chrysotile asbestos by the Battel le-Columbus Laboratories using transmission electron

microscopy in conjunction with electron diffraction (to confirm a minimum of 10 chrysotile

asbestos fibers) [6].

Sampling

Shelter

Filter

Transition

Piece

High -Volume

Pump

Timer

Dicl<son

Flow

Recorder

Sampling

Shelter

Filter

Transition

Piece

Stainless

Steel

Adapter

Temperature

Compensating

Dry Gas

Meter

Gast Rotary

Vane Pump

High-Volume Sampler Low-Volume Sampler

Figure 6. High volume (hi-vol) and low volume (lo-vol) TSP samplers.

Approximately 30 monitoring sites were selected; locations included "typical" urban

sites removed from known sources of asbestos emissions, rural -background sites and

stations contiguous to four industrial users of asbestos (i.e., manufacturers of friction

products, insulated wire and cable, ammunition and molding compounds, respectively) and

three toll plazas situated at various locations along Interstate 95. Ambient chrysotile

asbestos levels removed from asbestos emission sources in both urban and rural location

were below 10 r\g/m^. However, chrysotile asbestos concentrations above the 30 qg/m^

proposed standard were measured near each of the industrial users of asbestos (i.e. , 32 qg/m^

at a public works building located near the friction products manufacturer; 33 r]g/m^ at a junior high school located adjacent to the insulated wire and cable and ammunition manu- facturer combination; 33 qg/m^ at a private home near the molding compounds manufacturer).

187
Each of the subject point sources are in compliance with NESHAPS and other existing state

and federal air quality regulations.

Ambient asbestos levels adjacent to the three toll plazas on 1-95 were also elevated

(in the 10 r\g/m^ to 25 qg/m^ range), implicating asbestos emissions from vehicle brake

lining decomposition as a significant source of airborne asbestos fibers. Asbestos

concentrations at the rural toll plaza (11,000 cars/day eastbound lane; 12,000 cars/day

westbound lane) were 10 ng/"i^ (eastbound lane) and 14 r[g/m^ (westbound lane); there are no known industrial users of asbestos near this rural toll station. Asbestos levels at one

of the urban toll plazas (28,000 cars/day eastbound lane; 27,500 cars/day westbound lane) were 3 nng/m^ (Administration Building, south side of highway) and 25 r\g/m^ (westbound

lane). The asbestos concentration at the other urban toll plaza (27,000 cars/day eastbound

lane; 28,000 cars/day westbound lane), which is also located near one of the largest

industrial users of asbestos in Connecticut (i.e., the aforementioned friction products

manufacturer), was 41 r\g/m^ (Administration Building, south side of highway); this was the

highest concentration measured during the subject survey. The ratio of the maximum asbestos

concentration measured at the first urban toll plaza to that at the rural toll station was approximately equal to the ratio of the number of cars/day passing through each toll plaza

(i.e., 1.8 versus 2.3) during the sampling interval. All of the aforementioned measured

asbestos levels were 30-day average values, except the 41 r\g/m^ concentration, which was approximately a 20-day average value (due to a sampler malfunction).

In addition to the ambient air asbestos survey described above, asbestos levels were

also measured indoors at the boy's swimming pool located in the University of Connecticut's

field house. The ceiling covering this pool was sprayed with an asbestos-containing insulating compound in 1955 and then re-sprayed some 10 years later. Chunks of this coating

have been falling from this exposed ceiling for some two years. Analyses of a bulk sample

of the ceiling material by the Connecticut State Department of Health revealed evidence of

asbestos fibers (between 10-30%) within fiberglass and binding material. Subsequent electron

microscopic analyses of the ceiling material by the Battelle-Columbus Laboratories indicated

that the asbestos was of the amphibole variety. Four (4) long-term (i.e., 30-day) air

samples were collected at various locations at the pool. Identical sampling techniques

were used for both the indoor and outdoor air asbestos surveys. These indoor samples are being analyzed for amphibole asbestos using transmission electron microscopy and energy

dispersive electron-diffraction by Walter C. McCrone Associates, Inc. The results of this

indoor asbestos survey will be reported at a later data [26].

Conclusions and Recommendations

Connecticut's studies to-date indicate the existence of a potential health hazard

posed by airborne asbestos fibers which warrants further investigation. Firstly, additional

ambient asbestos monitoring should be performed as soon as possible to:

1) define the month-to-month variations in ambient asbestos levels at

various locations, primarily in densely populated areas contiguous

to manufacturing sources of asbestos emissions and especially those

locations which already exhibited asbestos concentrations in excess

of Connecticut's standard,

2) further quantify, asbestos levels near toll stations, the relationship between traffic counts and ambient asbestos concentrations,

and determine how asbestos levels decline with increasing distance

from a tol 1 plaza,

3) define ambient asbestos concentrations contiguous to different

types of demolition operations and how rapidly these levels

approach background concentrations after the demolition activity is

completed, and

4) quantify the hazard posed by asbestos concentration indoors where

it is suspected that asbestos-containing spray-on materials are fraying and flaking.

188
Secondly, the relationship between asbestos consumption and mesothelioma incidence in

Connecticut should be investigated in more detail. A thorough epidemiological study of

the 133 reported cases of mesothelioma (as of 1972) should be performed as soon as possible

to identify those cases which are likely associated with non-occupational asbestos fiber

exposure. A prospective study of school children exposed to asbestos fibers indoors as a result of the spray-on application and deterioration of asbestos-containing surface coatings

should be conducted to accurately quantify the health hazard posed by this type of asbestos

fiber exposure.

It is recommended that Connecticut's standard be promulgated and applied both outdoors

and indoors. The routine monitoring of asbestos levels should be initiated as soon as possible. The resulting measured concentrations (along with the populations exposed)

should be compared to the standard so that a rational program and set of priorities can be

formulated to minimize the health hazard posed by airborne asbestos fibers. This seems to

be the most logical way to objectively determine how best to allocate the people's money in

implementing sensible ways of controlling contamination of the environment by airborne

asbestos fibers.

References

[1] National emission standards for hazardous air pollutants (asbestos, beryllium, and

mercury), Federal Register , 38 , 66 (April 6, 1973).

[2] Asbestos and mercury (proposed amendments to national emission standards). Federal

Register , 39, 208 (October 25, 1974)

[3] Bruckman, L. and Rubino, R. A., Rationale behind a proposed asbestos air quality

standard, J. Air Poll . Control Assoc . 25, 1207 (1975).

[4] Bruckman, L. , The Environmental Impact of Asbestos in Connecticut, Internal report

issued by the Connecticut Department of Environmental Protection, Air Compliance Unit,

Engineering Section, March 12, 1973.

[5] Bruckman, L. , Rubino, R. A., and Christine, B. , Asbestos and mesothelioma incidence

in Connecticut, J. Air Poll . Cntr. Assoc., 27, 121 (1977).

i [6] Bruckman, L. and Rubino, R. A., Monitored asbestos concentrations in Connecticut,

paper presented at the 70th annual meeting of the Air Pollution Control Association,

Toronto, Ontario, June 20-24, 1977.

[7] National emission standards for hazardous air pollutants; proposed amendments to

asbestos standard. Federal Register , 42, 41 (March 2, 1977).

[8] Health effects and recommendations for atmospheric lead, cadmium, mercury, and

asbestos, Illinois Institute for Environmental Quality, Environmental Health Resources

Center, Report No. EQ-73-2, Chicago, Illinois, 1973.

, [9] Gross, P., Is short-fibered asbestos dust a biological hazard. Arch. Environ . Health,

29, 115 (1974).

illO] Gross, P., deTreville, R. T. P., and Mailer, M. N. , Asbestos versus nonasbestos fibers.

Arch. Environ . Health , 20, 571 (1970).

[11] Health effects and recommendations for atmospheric lead, cadmium, mercury, and

asbestos. Environmental Health Resources Center, State of Illinois Institute for

Environmental Quality, Report #IIEQ-73-2, Chicago, Illinois, 1973.

[12] Lewinsohn, H. C. , The medical surveillance of asbestos workers, Roy . Soc . Health J.,

92, 69-77 (1972).

[13] Newhouse, M. L. , Berry, G. , Wagner, J. C. , and Turok, N. E. , A study of the mortality

of female asbestos workers, Brit. J. Ind. Med. , 29, 134 (1972).

189
[14] Stumphuis, J., Epidemiology of mesothelioma on Walcheren Island, Brit . J. Ind. Med.,

28, 59 (1971).

[15] Selikoff, I. J., Churg, J., and Hammond, E. C. , Asbestos exposure and neoplasia,

J. Am. Med. Assoc . , 188, 22 (1964).

[16] Newhouse, M. L. , A study of the mortality of workers in an asbestos factory, Brit . J. Ind . Med. , 26, 294 (1969).

[17] Knox, J. F. , Holmes, S. , Doll, R. , and Hill, I. D. , Mortality from lung cancer and

other causes among workers in an asbestos textile factory, Brit . J. Ind. Med. 25,

293 (1968).

[18] Criteria for a recommended standard for occupational exposure to asbestos, U. S. Department of Health, Educationa and Welfare, Public Health Service, Health Services

and Mental Health Administration, National Institute for Occupational Safety and

Health, HSM #72-10267, Washington, D. C. 1973.

[19] Lynch, J. R. , Ayer, H. E. , and Johnson, D. L. , The interrelationships of selected

asbestos exposure indices, Amer. Ind. Hyg . J., 32» 598 (1970).

[20] Thompson, R. J. , personal communication, preprint R. J. Thompson and G. B. Morgan,

Determination of asbestos in ambient air. May 2, 1973.

[21] Wesolewski, J. J., Asbestos in the California environment. Air and Industrial Hygiene

Laboratory Report, AIHL #164, California State Department of Health, Berkeley,

California, May, 1974.

[22] Fulkerson, W. and Goeller, W. E. , (eds.), Cadmium: the dissipated element, Oak Ridge

National Laboratory, Report #0RNL-NSF-EP-21 , Oak Ridge, Tennessee, 1973.

[23] Occupational exposure to asbestos; notice of proposed rulemaking, Federal Register , 40, 197 (October 9, 1975).

[24] Bruckman, L. , Hyne, E. , and Norton, P., A low volume particulate ambient air sampler,

paper presented at the Speciality Conference: Measurement Accuracy as it Relates to

Regulation Compliance, New Orleans, Louisiana, October 1975.

[25] Clifton, R. A., Asbestos, preprint from the 1972 Bureau of Mines Minerals Yearbook,

U. S. Department of the Interior, Washington, D. C. 1975.

[26] Bruckman, L. , Monitored asbestos concentrations indoors, paper presented at the

Fourth Joint Conference on Sensing of Environmental Pollutants, November 6-11, 1977,

New Orleans, Louisiana.

Discussion

NOTE: Discussion of this paper was included in the General Discussion at the end of this

session.

190
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued Movember 1978)

GENERAL DISCUSSION OF RELATIONSHIP BETWEEN CHEMICAL AND PHYSICAL PROPERTIES

AND HEALTH EFFECTS

Editor's Note: This session was actually conducted on two days. The

papers through Dr. M. Stanton's were given the first day and were followed by a general discussion. The remaining papers were presented

the next day, followed by a second general discussion. These two general

discussions have been combined below and are followed by a summary given

by the Session Chairman, Dr. S. Schneiderman, at the start of the second

day's papers. (CCG)

A. SUNDARAM: I would like to address this question to Dr. Kotin. He mentioned that

he believes that there exists a no-effect level for asbestos. Assuming that he is right,

what are the future steps that industry is going to take? Are they going to conduct

animal studies at various dose levels, come up with a no-effect level, extrapolate to the

human situation, and have a TLV? Alternatively, are they going to do more epidemiological

studies and come up with a no-effect level which can directly apply to humans? If we do

these two types of studies, we are still faced with the problem of variability of susceptibility between different groups of humans as well as between animals and humans.

P. KOTIN: The answer to the first part is obviously that industry has a responsibility

to support studies at all levels, from fundamental mechanisms to bioassay. My own bias is

that there is a no-adverse effect level. The question of what will demonstrate the no- adverse effect level is one that is going to require a fundamental understanding of carcinogenesis. I think there are occupational asbestos exposures of sufficient duration where,

to the best of our knowledge as of now (and you always have to put that in), there seems to

be a level of exposure to asbestos not associated with asbestos-related disease. I will

say, in advance, I am aware of and accept all the caveats that just as the rats have not

lived three years, these people have not been exposed for forty years, and maybe at that end

of the distribution curve some evidence of some response may come. There is no answer to

your question, and I wish that there were, other than to say that industry has a responsibility and would be incredibly shortsighted and incredibly stupid if it were not on the

leading edge of supporting all research in relation to fiber and its relation to any adverse

human effect.

M. SCHNEIDERMAN: Dr. Nicholson, would you care to comment on the no-adverse level

problem since you presented information on individuals exposed one month?

W. NICHOLSON: In fact, I was going to ask Dr. Kotin to elaborate on that. I recall

seeing a quote from you that was made sometime in the late sixties before some congressional

committee, when you were Director of the NIH. You felt at that time that there was no evidence that would indicate that a threshold exists. If you could elaborate on that,

particularly on the hard data that exist for asbestos. As one knows, you need enormous

populations in order to see what the dose-response is at lower levels of exposure. I am in

complete agreement with you that there is a dose-response effect at the levels we are speaking of; as you go down in exposure and dose, you certainly go down in effect, but to

my knowledge the difficulty of finding the existence of a threshold exceeds our capability

either in animals or in man.

KOTIN: The answer to your second part is the degrees of reliability that you are willing to accept in terms of the totality of any response. Let me elaborate a little

more. First of all, indeed I did say that, not only before a congressional committee but

before numerous congressional committees. I only have two comments: (a) I'm smarter now,

and (b) I will send you reprints of three articles published in 1954 where I say, on the

basis of what is now known, air pollution is infinitely more important to the evolution of

bronchogenic cancer than cigarette smoking. If I am dumb initially, at least give me credit

191
for not being cast in concrete in opinion. No, the answer to your question is that there

are no absolute data that a no-adverse effect level exists, because of the heterogeneity of

man. So what I have chosen to do is look at the sequence of events that are necessary for

the evolution of a cancer, and I have not used asbestos as a model but I have used other

carcinogenic agents, such as aromatic amines and hydrocarbons. There is no such thing as a threshold for carcinogenesis, there are a series of thresholds. I am prepared to say that

at the molecular level you may have a threshold, but in terms of clinical cancer and particularly in the laboratory, one can quantify the exposure to carcinogenic agents and

predictably get a carcinogenic response, including no tumor formation within the normal life

span of the animal, with no evidence of any abnormality. This is a mumbojumbo answer

because it is not a clear thing, otherwise we would just have to go to the blackboard and

make this a seminar on just chemical carcinogenesis, which I would be delighted to do, and

then get down to specifics rather than these generalizations. Cancer is not a simple

process. It is a highly complex sequential process, with sequential steps dependent on the

antecedent step, and the sequential steps capable of occurring or not occurring on the basis

of what happened in the immediate antecedent step and this can be quantified beautifully.

NICHOLSON: I don't think I want to pursue this, except to make one comment. Some of

the extrapolation and theoretical predictions that one might make on the basis of chemical

carcinogenesis, as opposed to asbestos carcinogenesis, may not be that direct. Let me ask

a question of Dr. Stanton which has to do with relative risks of fibers of different lengths

(as with the issue of threshold; it is a relative risk at different doses): finding in

human tissue and in air samples the vast preponderance of fibers of the shorter sizes, less

than 5 pm (we have had some air exposures where 99.5% are under 5 pm in length, others may

be 98% or 95% depending upon the particular process), at what level can you say, or at what

length can you say, that the shorter fibers are ten times or fifty" times, or some rough

estimate, less carcinogenic than the longer ones. Certainly your 8 pm value is not a sharp

cut off. How might it go down with length, in other words just how does the response go

down with dose?

M. STANTON: Any correlation data are simply that. It doesn't say that only certain

fiber sizes are carcinogenic, nor does it say that short fibers are not carcinogenic. Correlation suggests that long, fine fibers are more carcinogenic than short fine fibers.

There is no sharp demarkation line. I think, if anything, one should go back to the pathological data again, and I've been impressed by the fact that fibers up to 30 pm in length

can be picked up and effectively handled by a phagocyte. So it may be that we are far under

what can be considered very hazardous. Maybe only fibers over 30 pm in length are more

hazardous. Now, what happens if you overload phagocytes? What happens if there are no phagocytes or they are inadequate to handle these fibers in individuals who have compromised

the reticuloendothelial system? It may be the short fibers in such situations can be just

as carcinogenic as long fibers. There is some suggestion that if the reticuloendothelial

system is overwhelmed by foreign bodies, then perhaps short fibers can also be highly

carcinogenic. What we are saying simply is that long, fine fibers seem to be the most

carcinogenic; we are not saying that any fiber is non-carcinogenic.

W. SMITH: Question for Dr. Stanton: The experiments that we have had a chance to hear

about this afternoon certainly present an animal model for asking questions and gathering

information that would be extremely hard to get at through more complicated procedures such

as inhalation exposures; but. Dr. Stanton, what do you think about extrapolation of informs- j tion gained from intrapleural studies over to situations more comparable to human exposures

that could be approached by inhalation studies? We have done a number of experiments by

intrapleural exposure of another species, the hamster, to different kinds of minerals. With

long thin fibers we have been getting tumors, and with short fibers we have not. One of the

materials that has given us a great many tumors has been a preparation of long, thin glass

fibers that have dimensions approximately like those that induce tumors in some of the

experiments that you just described. However, Dr. Gross, I believe, has exposed rats to some very similar types of fibers by inhalation exposures, and these fibers gave him no tumors at all on the inhalation tests. So here we have a problem of how to extrapolate data i from the intrapleural situation, where the fibers are trapped, to the inhalation type of

exposure, where they are subject to physiologic clearing mechanisms.

192
STANTON: Clearly, our experiments are designed to find out what happens once the

fibers get to the tissue that is going to respond. It doesn't take into consideration all

the extraneous problems that might arise in the fiber getting to that tissue, which is what

Bill Smith is saying. What about inhalation? There is no doubt about it; inhalation

studies are the only ones that will really give us some reasonable means of extrapolating

to human experience. Those experiments have not been adequately done, and there are not

enough of them to really get a good handle on what's happening. Dr. Gross has done about

the only experiments that have been done up to this point, with the exception of some that

Chris Wagner did; he has shown that tumors develop in the lung from various types of

asbestos inhalation. Glass has not been studied, or only studied as a large fiber or as non-fibrous material. Dr. Gross is in the audience and I am certain he would be pleased

to tell us about his experiments with glass fibers.

P. GROSS: We exposed rats and hamsters to fibrous glass dust for a period of two

years. The fibrous particles had an average diameter of 0.5 pm and a range of lengths 5 to

20 pm. Inasmuch as the average fiber length was 10 pm, one-half of the fibers were 10 to

20 pm long and the rest were shorter. Since the dust concentration was "^-lOO mg/M^, the

exposure included ~50 mg/M^ of fibers 10 to 20 pm in length. Thin mineral fibers of this

length have been found carcinogenic when implanted in the abdomen or thorax of rats.

However, long-term exposure by inhalation of these long, thin glass fibers resulted

neither in pulmonary fibrosis, lung cancer, nor mesothelioma in any of our animals. These

were allowed to live out their lives.

I. ASHER: We are concerned about parenteral drugs, and we are wondering if anyone

has any information about subcutaneous or intravenous injection of solutions that contain

asbestos or fiberglass fibers?

EDITOR'S NOTE: No reply was received to the above question. (CCG)

R. LEE: Questions for Dr. Palekar: First, what is the unknown amphibole, PMP 1?

Second, I'd like to point out that there were at least three or four people very familiar

with scanning microscopy who picked up a possible trace quantity of potassium in what you

called a non-calcium amphibole. It would t3e very surprising if that particular non-calcium

amphibole x-ray spectrum looked just like that, and it was a grunerite! Next, I was wondering if PMP 1 is a mineral characteristic of the Peter Mitchell pit, and is that a fibrous or non-fibrous variety of material? Finally, what was the set of aspect ratios

measured and particle sizes measured for the non-fibrous "grunerite?" Were they cleavage

fragments or typical of amosite?

L. PALEKAR: Yes, PMP 1 is the unknown sample. We did some analyses of the air samples

in the taconite mine and it happens to be Peter Mitchell pit; that's correct. There were

two samples, one had calcium and the other didn't. The first sample I believe had calcium

and the second didn't. I wasn't aware of the fact that there was a potassium peak on it.

According to our mineralogist colleagues from IITRI, the studies were done by using several

other techniques, and they didn't find any potassium.

LEE: In that particular spectrum you showed something which had at least, on a con- servative estimate, one percent and possibly two percent potassium.

PALEKAR: I will have to take that into consideration. Your second question is

whether we did any analysis on non-fibrous minerals. So far, we have not, but we intend to

do it in the near future.

LEE: Was the sample identified as PMP 1 characteristic of the grunerite minerals

that are found in the Peter Mitchell pit?

PALEKAR: Yes.

' K. HEINRICH: I would suggest that there is a subject that hasn't been discussed,

although it is of great practical importance. We frequently characterize particles by their

shape, and grinding is a very common industrial process. This process will change the

shapes, and the question is this: I have heard isolated statements here which range from

the suggestion that a massive material on grinding acquires characteristics equal to natural

193
fibers, to the statement that you have to be careful in grinding asbestos because it loses

its properties. Could we have a discussion of what the biological implications of grinding

are and how one has to handle this situation?

A. LANGER: Dr. Heinrich has touched upon an extremely important problem which concerns

the biological activity of small particles. The origin of the theory concerning grinding

and subsequent alteration of the activity of minerals dates back some 25 years to

Great Britain, to its Pneumoconiosis Research Unit. At that date, this unit boasted of

having the finest laboratory of its kind in the world. They are remembered for their fine

work. At that time, the pathologists in the group observed that the smaller the size of

quartz particles, the more biologically active the dust was. Indeed, a 5 pm quartz particle

was relatively "inert," if you can use that word, but a 3 pm particle of the same composition was a thousand times more active. A 1 pm quartz particle was a thousand times more active than the 3 pm particle, and a 0.1 pm quartz particle was yet more active. At that

time this unit was interested in the interaction mechanism of the silica particles in

biological systems. One such proposed mechanism involved the generation of silicic acids

in tissue. These acids were thought to be the agent in the production of the response

called silicosis. Production of silicic acid is enhanced as quartz is made soluble.

Grinding of quartz produces a more "soluble" material. To "prove" this theory, workers

ground quartz in a mortar. The ground powder was split into two equal parts. One aliquot

was then washed in hydrofluoric acid and a strong alkali, removing all of the surface

layers, including the Beilby layer, which is the surface disrupted layer. This disrupted

layer on the surface may be demonstrated by x-ray diffraction techniques. There was x-ray

line-broadening produced in the ground material, without "treatment," and a very sharp

x-ray pattern generated by the material that was acid and alkali "washed." These two

preparations, both quartz, were then instilled into animals. According to theory, the

solubility theory, the materials which had not been "washed" should have been more active.

The reverse was found to be the case. It was found that the materials that had the

amorphous layers on the surface had less biological activity as compared to those materials

which had been "washed." They observed the "fresh" surface to be more biologically

active. This has been re-established in many experimental models.

If we carry this concept into the asbestos problem, one sees the extrapolation to the

different sizes of the asbestos fibers and their different biological activities. The early

investigators in this field were divided into two camps. One group demonstrated biological

activity with short asbestos fiber; the other group demonstrated a lack of activity. The

question may be asked as to how the same animal model, the same route of administration,

and the same laboratory could produce conflicting sets of data? When one examines the

process by which the experimental pathologists size reduced thei r material s , the explanation

is there. These pathologists mechanically milled these materials to shorten the fiber

length. They are not only dealing with short fiber, but also with milled fiber. We have

looked at these reports in the literature, dating back to the 60' s, many of which indicate

that milling was used to reduce fiber length. Milling of chrysotile fiber produces a material with a disrupted surface. We have observed this with x-ray diffraction and

electron microscopic studies. We have taken chrysotile asbestos so prepared and have

examined it by x-ray diffraction step scan technique. We've followed the line-broadening

and decreased crystal 1 inity. We've looked at this material by infrared spectroscopy for

specific structural changes corresponding to different molecular groups within the structure. We have examined the material in hemolytic test systems for altered membrane

activity. We have looked at these materials in regard to the ability to reduce free

radicals. We've looked at these milled fibers by many, many techniques and have observed

that those fibers that are produced as "short" fibers show a progressive decrease in

surface activity. I think that it is the preparation technique which alters the surface

of the material. The experimental pathologist may indeed be working with materials that

are not "truly" asbestos. The circumvention of the problem may be brought about by,

instead of using mechanically milled materials, using air-jet milling, or if not air-jet

milling, water sedimentation techniques to separate small fibers. Wagner's group in

Penarth uses sonifi cation methods, air- jet milling, and water fractionation to separate

and collect small fibers. They produce biologically active small fibers.

G. WRIGHT: The inference has been made by Dr. Langer that the experiments using

short fibers have no validity because the surface has been altered by grinding. I would

like to report that Dr. Kuschner and I have used contrasting fibers prepared synthetically

194
and not involving any grinding. The short fibers produced no fibrosis, but from the same batch permitted to grow long, we got well developed, extensive pulmonary fibrosis from

intratracheal injection into guinea pigs.

LANGER: Several years ago we ordered synthetic chrysotile from a company in Pennsylvania. The materials were obtained for animal work. We examined these materials very

carefully; the material was half talc and half poorly crystallized chrysotile. I think when

one talks about chrysotile grown in a thermal bomb in someone's laboratory, one has got to

characterize it extremely well because the crystallization process is very difficult and

very often one does not produce chrysotile. I see Julie Yang here in the audience who's

done a great deal of work at Johns-Manvi 1 1 e growing chrysotile. They had to use a number

of compounds to grow really good chrysotile fibers. It is extremely difficult to do.

J. LEINEWEBER: I would just like to comment that the synthetic chrysotiles that were

made in our laboratory were the ones referred to by Dr. Wright. I've also had the opportunity to see the samples that were made by Tempress. Julie Yang can comment on the great

divergence in quality between the two samples. Ours were good. I did want to say that the

synthetic chrysotiles that were prepared in our laboratory were of good quality crystals

and this is absolutely important.

J. YANG: I worked for Johns-Manvi 1 1 e making synthetic chrysotile. The synthetic

chrysotile we made for Dr. Wright is the pure synthetic chrysotile; there was no mineralizer

added. I think the electron micrograph shows the size distribution; it's all fibrous

material

LANGER: Julie, didn't you use cobalt or nickel in the preparation of those materials?

YANG: No, that's for a different purpose. When we put nickel or cobalt or iron into

it, at that time, was for a different group of tests where we were trying to figure out

whether or not any heavy metal substitution would cause carcinogenic effects. We also

prepared the pure ones with no additives.

LANGER: I think that another important issue should be raised. There were many

discussions of a number of studies in which short fibers produced no biological signs of

activity. There is for every study which shows no activity, another one which does indeed

show that small particles are active. As a matter of fact one of the first studies of

short chrysotile fiber, which is cited extensively in the literature, is probably the most

unread paper in the field today (Durkan, Vorwald, and Pratt on the biological activity of

small fibers). These workers were interested in fiber length as related to biological

activity. At that time they were impressed with the work to come out of Great Britain

demonstrating that the small silica particles were far more active than the large silica

particles. They of course used various size fractionated materials of chrysotile and in

their paper stated that, although they saw no "increased effect" of short fiber they

reported "more limited" activity of the short fiber. Mineralogical analyses of the dusts

used experimentally showed the "short dust material" consisted of only some 17 percent

chrysotile, the rest being other materials.

J. MOORE: I want to raise a question. Dr. Wright, is it possible for you to give me

a reference for that work or to provide the audience with the data if it is not published?

G. WRIGHT: With regard to the comment that Dr. Langer made about the work of Vorwald

and others at the Saranac Lake Laboratory - I was working there at the time and, in the

samples which produced fibrosis, at least five percent of the fibers were of the long, or greater than 10-micrometer, variety. In answer to the question for a reference to the

work by Dr. Kuschner and myself, this has been published recently, in part, in Proceedi ngs

of an International Symposi um on Inhaled Particles , IV , held at Edinburgh in September of

1975. It is edited by Walton and published by Pergamon Press.

195
W. DIXON: I would like to ask about the toxic activity of several kinds of fibers:

(1) partially coated asbestos fibers, for example asbestos fibers which have an organic

coating, (2) talc fibers (I have seen true talc fibers, just as fibrous looking as any

asbestos fibers), (3) fibers which are intermediate between talc and anthophyl 1 ite asbestos

in composition, (4) substitute mineral fibers such as wollastonite which are used in place

of asbestos.

EDITORS NOTE: No response was made to the above question by anyone in attendance or

in writing. (CCG)

P. LEBER: I was interested in the macrophage work of Dr. Palekar. Do you have any

information on the mechanisms of the site of toxicity? I'm thinking particularly whether

you have any information supporting the cell membrane puncture ideas of Dr. Kotin, with the

release of lysozymal enzymes or any organal changes that might occur after ingestion of

these particles, or whether ingestion of particles is actually necessary for cytotoxicity?

L. PALEKAR: Well, the data that I presented was very preliminary and I don't want to

make any conclusions. We performed some standard tests for acid phosphatose and lactate

dehydrogenase and we did find release of these two enzymes into the medium as well as within the cell itself.

J. KRAMER: I have two questions. The first one is addressed to the taconite study.

There were various comments earlier voicing concern about the characterization of the

sample. I would like to add a few additional comments. First of all, I think that you will

find that there is a large variation in the composition of both the tremol ites-actinol ites

and the cummingtonites (Bonnichsen, 1969, Mineral . Soc . Amer . Spec . Paper 2; Kramer, 1976,

Canad. Mineral, 1_4, 91-98), and I believe that you must be aware of these variants when

you characterize your sample. You may wish to determine the cell constants, and there is

literature relating cell volume to composition (Finger, L. , 1967, The crystal structures

and crystal chemi stry of ferromagnesian amphi boles , PhD thesis, Univ. Minnesota). There

are other factors to consider. The cummingtonites contain variable amounts of manganese,

for example. There are a large number of mineralogical factors that you may wish to

consider prior to your animal studies. Also I would suggest that if you look at the

tailings you will be able to ascertain these mineralogical variations.

My second question regards the Connecticut survey. I think that there is one assumption that needs careful consideration, and that is the constant relationship between fiber

number and mass. If this assumption is not valid, then your mass basis is not valid.

Fibers appear to have size distributions over about two orders of magnitude. Therefore,

the mass can be determined by a very small percentage of the fibers. In other words, if you

consider one-lOG \^m fiber out of 100-1 pm fibers, you change your count by only one percent,

but you change your mass by a factor of five or more times. Therefore, the size distribution of the largest few percentile of fibers will be most significant in your mass/fiber

ratio. Why are you using a mass basis and not a count basis?

L. BRUCKMAN: There are many problems in developing that envelope besides what you

just said, which are obviously important. What we were trying to do was to take today's

information and develop some type of standard and again try and make it such that it would

not be criticized as being too strict, and while we were studying and refining the relationships between dose-reponse, we'd at least have a standard. Now we have places in

Connecticut which are above that level, and pretty much everybody has said that there are

some problems with it, but the level looks basically reasonable and I think that it should

be promulgated as a first step. It's a lot better than a no-visible-emission standard. I forgot the second part of your question.

KRAMER: No, it was basically related to why you used a mass standard rather than a count standard.

BRUCKMAN: At the time that we were doing our analysis, the procedures available which

were basically developed by Dr. Thompson at EPA, were based on mass measurements of chrysotile. When we went out and did our ambient survey back then, and it took some time to get

it done, that was the technique that was readily available. As we continued on, in order

to get comparative numbers, in other words to say whether the levels were twice as high or

196
twice as low, we continued doing the same type of analysis through Battel le. I'm probably

not the one to comment on which way is the best way to do it, but when Battel le did the work

for us, their ma^s analysis, based on activated chrysotile samples, was ±50 percent. It's

a kind of reproducible, gross measurement of the amount of asbestos in the air, but it

doesn't give you any information at all about fiber count. But mass was one way of relating

back to our standard. The standard could also be expressed in terms of total asbestos

fibers; I believe it's 30,000 total asbestos fibers for a cubic meter of air sampled. So

if you do do a number determinations, you could still relate that back to the standard.

Battelle does a mass analysis and that was the way we have been doing it all along.

C. COOPER: I also want to comment on Dr. Bruckman's very practical approach to an environmental problem. I'm not going to comment on the audacious assumptions that went into

it, because I think he'd be the first one to say that was the case. My comments are twofold, that is, I saw two important things. One was that the bottom line (and it was the

literal bottom line in his graphs) was a probability of certain events occurring. This cut

right back to the dialogue between Dr. Nicholson and Dr. Kotin yesterday afternoon. It

assumed a no-threshold response; a straight line relationship, but it acknowledged that at some point that the straight-line relationship reached a probability, or a level of risk,

that was very, very low. There's a great deal of difference between a 1 in 10 risk of

getting something, and a 1 in 100 million risk. I think Dr. Bruckman at least faced up to

this important question, regardless of the validity of the assumptions that went into

determining the actual values. The second comment I wanted to make was that using his 30

nanogram limit, the levels of 12 and 25 did not seem particularly alarming. Since he was basing his original case on 168 hours of exposure during a week, probably what one might

call a time-weighted average would be well within the 30 nanograms that was proposed. I was struck by how low these observed concentrations were, using the assumptions in scale.

R. BLEIFUSS: I want to return to the Peter Mitchell mine again and a sample prepared

by IITRI for the EPA. If you read the IITRI reports, it is apparent that the sample site

selected represents unique geological situation within the Peter Mitchell mine, in the same sense that the Reserve operation is unique on the Mesabi Range. It does not really appear to

be typical of the taconite in that area. The sample represents a local segregation of a rather unusual mineral suite and it is doubtful that we should use such a sample on health

studies. I really think we should go back and provide you with a better starting material

for the kind of work you are proposing.

0. MENIS: I would like to address my question to Dr. Bruckman. I appreciate the

advance of this mass measurement and simplification. I just have a question about the total

volume of sample in which this was determined, and what kind of weight basis that was. What

was the total sample of your low volume sampler that was used to establish the 40 nanograms

or 10 nanogram levels that you distinguish between borderline cases and significantly high.

BRUCKMAN: If I understand you right, it's just a different type of sampling equipment

that we developed for this purpose. If you wanted to get a 30-day average sample with a high-volume sampler, which only runs for one day, you'd have to collect 30 samples. Thirty

samples at $500 a throw is a lot of money.

MENIS: My question was, what was the total weight of the collected dust during that

period of time?

BRUCKMAN: We didn't do that determination, because there are problems in getting

total weight with cellulose nitrate membrane filters. They are very hygroscopic and that

presents a lot of difficulty, but that would not affect the amount of asbestos there. So

there were no total weight measurements made, only chrysotile asbestos determinations. We

don't know what the total weights were. We did do total weight for one sample. It looked

like we were getting reasonable numbers, therefore we didn't continue it.

M. COSSETTE: I have a comment that I'd like to address to Dr. Bruckman. One author,

Mr. Rutner, has published a paper on 19 cases of mesothelioma in Switzerland. And of these,

only two were related to asbestos exposure. Also, in experimental animal studies, mesothelioma has been produced with many other materials. In the case of your survey of mesothelioma in Connecticut, did you make any attempt to relate mesothelioma to anything besides

asbestos?

197
BRUCKMAN: We only did a very preliminary study based on hospital records and death

certificates. We'd like to get some money to do a detailed epidemiological study, a complete case history, occupational exposure, and whether these were relatives of people

who worked in asbestos industries. We aren't able to do that. We haven't got any funds at

all to do any of these studies, and it's impossible to carry them on without funding. We

just haven't been able to get into it. Hopefully, the data that I reported on concerning

mesothelioma incidence will be updated. My study was only up to 1972. It should be

updated and maybe other types of potential causes, like fiberglass exposure or something

like that, will come out of this.

COSSETTE: Thank you. The data that you showed indicates that the number of mesothelioma cases has gone up dramatically in the last few years. Do you think this may be

partially due to the fact that it's more easily found now, that we have better determination techniques.

BRUCKMAN: I think that's definitely a contributing factor. I would say yes.

M. ROBERTS: A question for Dr. Palekar: Going back to the presentation of the

slides, the slide with the 1 pm scale showed an electron micrograph of ambient air at the

process plant and at the mine, as compared to the slide with the 10 pm scale showing the

preparation, that you have apparently prepared for your inhalation studies. On the slide

from the ambient air at the plant and mine there was very few fibers more than 1 pm long,

which was the scale shown on that slide, whereas the second preparation, on the 10 pm

slide, showed considerable material that was over 10 to 15 pm. You have replied to a previous question that the rock selected to be used in your preparation was representative,

and I would like to ask how this was selected? Can you give a complete history as to the

location and selection of this material? Further, if these studies are to reflect the

pulmonary response of exposure to the dust from these ores, should not the rock be prepared

from a blind selection of typical mine ore? The principal question here is how the sample

was selected, and can you give some detailed history of where and how this was selected?

PALEKAR: The purpose of this study was to evaluate the biological effects of the

fibers which were emitted in the taconite mine. The air samples were procured from the

mine area and the processing areas. Several samples were collected on filter papers and

proper size distributions were made. I can understand the confusion here between the size

distribution tables presented and the electron micrographs, and I would like to emphasize

again that the electron micrographs are not truly representative of size. The tables

presented are more accurate. Quite a few fibers were counted, and I think that the fiber

size that I presented in those tables are more representative. Now, originally we selected

air samples and characterized them, then we went back to the rocks. Several rocks were

collected, about 50 or so, out of which we selected two rocks which represented the air

samples and the processing area, as well as in the mining areas. We are studying the

biological properties of these two samples. Currently we are not doing inhalation studies,

we are doing intratracheal studies and intrapleural studies. In the future we plan to do

inhalation studies.

LANGER: I wonder if I could add something to this. I think that everyone is missing

a very obvious point: It appears that the regulatory agencies operate in a "management by

crisis" mode, and everytime some new material is dumped into a lake or a river or is thrown

into the air, a few million dollars is then invested in investigating the biological

activity of that particular substance. It is the consensus of workers in the field that

something should be known concerning the properties of fibers in terms of the mechanisms of

interaction. Whether or not one could get pure Peter Mitchell pit fiber, whatever that is,

is an academic point. There are many lithologies in this mine, as described in Gunderson

and Schwart and the Beven French monographs. Whether a "representative" fiber exists is

probably unlikely. It was then decided that the Environmental Protection Agency should

investigate a fibrous rock-forming silicate which was not asbestos per se. The materials

which were fibrous and "pure," yet not exactly characteristic of the cummingtonite/

grunnerite within the Peter Mitchell pit, occurred in localized veins. They were fibrous

on a megascopic level and when comminuted they resembled asbestos fibers. But they were

not asbestos per se. These were rock-forming fibrous amphiboles. I think that if these.:

198
materials induce changes in biological test systems, then we shall go further and investigate others. We must know something about the mechanisms of interaction. If they are not

active, then everything else is academic.

SCHNEIDERMAN: RECAP OF SESSION. The session yesterday afternoon seemed to me vigorous

and active and ended on quite a high note. This morning's session is a continuation of

that, and in view of the speakers we have this will be at least as exciting and as interesting as yesterday's session. At this time I would like to give you a very short summary

of what I thought happened yesterday. In the instructions that were given to the Chairmen,

we were asked to summarize what things people agreed on, what things were learned or said or now accepted as fact, what things were questioned, and where further work should be done.

I made some notes on this during the course of the day and I made some notes yesterday

evening after having gone out to Wolftrap to hear the Preservation Hall "Jazz Band." The

last number they always play is "As the Saints Go Marching In" and I think that if anyone

tries to tell you what people fully agree on he has to be a saint, or as you know, fools

walk is where angels fear to tread. I'm going to be foolish and try to tell you what people

agreed upon. But as I looked at my list, I discovered that that list of agreements was really quite small, and my list of disagreements was quite long and, therefore, the list of

further work to be done is even longer. Any of you that are involved in the funding

agencies, I want you to hear that work to be done is quite long. It seemed to me, in the

agreements, from the notes I have for myself, are that asbestos, whatever it might be, in

many of its subclasses and subdivisions, whatever they are called, is a material which can

have adverse health effects. We talked a lot about the carcinogenic effects and talked

about how some of these might be different or have less intensity for certain forms of this

mineral than for others. The discussions were tempered by the fact that some people said

what looked like very sharp differences in the past don't look like such sharp differences

any longer, and these materials have effects that now appear to be closer to each other.

All through that, there was an undercurrent that we really don't know this because we have

great problems of determining doses to which people were exposed. There was also the undercurrent, although a great deal of emphasis was on cancer, that there are other health

effects, and we have to talk about those. There were questions during the day, as you may

recall, as to whether the cancer effects were dependent upon some of these other effects

having occurred. Whether these were independent, or whether these ran parallel with each

other. Do you have to have hyperplasia, for example, as a necessary component? Was it a pre-cancerous condition? The major questions that people raised during the course of the

afternoon were questions concerning two things: first, questions concerning particle

size. What are the particle size variables with respect to health effects? What are the

particle sizes necessary in order to produce health effects? Are there particle sizes that

are safe? Are there particles that don't produce these kinds of effects? To address

themselves to these questions, Dr. Bignon of Paris showed us information on distribution of

particle size found in the lungs and tissues of individuals with various diseases associated

with asbestos and showed for us - at least in the trapped particles, the remaining

particles, the particles that are still there - a tremendous overlap of the particle size in

persons with illness and persons without illness. This is not necessarily indicating that

these particle sizes that he found (by the way you will recall he found rather smaller

particle sizes than most people have indicated) were necessary to induce certain of these

illnesses. He made it clear, this was not to say that these smaller particles were the ones

that induce the illness. It may very well be these were the only ones that remained, these

were the ones that were trapped, but that is what he found. Dr. Kotin, in a rather elegant

lecture that he labeled as a kind of lecture in pathology that one would give to sophomore

medical students (I rather think it was more elegant than one would give to sophomore

medical students, having taught sophomore medical students myself), gave us a lovely theoretical discussion of physiology of the lung and a lovely theoretical discussion on what

might be going on in the pathogenesis of illness induced by, supported by, and/or

stimulated by asbestos particles. Dr. Kotin remarked that he would attempt to be

controversial; he succeeded at least in asserting the existence of thresholds, with which,

as you know, there is a great deal of difference of opinion. He in turn was challenged on

this by Dr. Nicholson, who had earlier presented data showing relatively very low levels

of exposure. He was also challenged by Dr. Sunderlin of Canada and also a gentleman from

the State of Maryland. The discussion, seemed to me, at one point got really highly

theoretical, and I think Dr. Kotin and other people indicated that there would certainly

be a need for a full scale discussion of this issue. There was one, by the way, in

199
Heidelburg last year; a whole meeting devoted to the problems of threshold. In relation

to problems of particle size, Dr. Stanton and his colleague Dr. Layard described certain

experiments they had done to see v/hether the carcinogenic effect that we found in these

various materials was a carcinogenic effect peculiar to asbestos or whether it was an effect one would get from any particles of that size and of the same dimensions. The

animal studies that Dr. Stanton described would seem to indicate that the very long, thin

particles, longer than 8 p (I did not make a note of the diameter), but long thin

particles, were the most carcinogenic. Stanton very carefully, it seemed to me, said

these are (in answers to questions) the most carcinogenic, but he did not find a line

below which you find materials which are not carcinogenic, that you could be certain that

they are not carcinogenic. He said no he could not find such a line. It was just that

these were more carcinogenic than others; the carcinogenicity fell off as the particles

got shorter and stubbier, but he did not find any sharp line of of demarcation. Now, this

is a problem for the regulatory agencies because they have set a measure relating to the

size of the particle.

There was then discussion concerning the sort of thing that Stanton had done, because

he installs these particles where they can have their effect. People raised many

questions about asbestos in the ambient air and problems that would be associated with

such things as ubiquitous asbestos, most of which are smaller particles than the ones people are industrially exposed to. The questioning addressed - what about inhalation

studies? The remark was made that with very few exceptions, the inhalation studies were

not particularly well done. A nice reference was made to Dr. Gross saying that his

studies were well done, and the remark further carried that the inhalation studies had not

shown the same sorts of effects as the installation studies had shown. This bring to my

mind the similar problem we have with tobacco carcinogenesis, where again in the

inhalation studies, unless done in some very peculiar way, by slitting the trachea in the

neck of the dog and having the dog smoke through the slit, nobody has produced, so far as

I know, lung cancers in any of the experimental animals. So the inhalation studies still

have some serious difficulties with them. A question was raised by Dr. Ross, a geologist,

about these ambient materials and the problems that strict standards would raise for small

businesses. I think Dr. Ross' hope is that one could establish that there were particles

sizes or materials or levels that were in some sense absolutely safe. These economic

problems might not be loaded on the small businesses. It seemed to me what we had was a general agreement on the carcinogenesis of these materials, and their capability of

causing other illnesses and a very large set of statements of all kinds of things we just

don't know, and all kinds of things that we still need to have some work on. I have tried

to list those for you.

200
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (November 1978)

IDENTIFICATION OF SELECTED SILICATE MINERALS AND THEIR ASBESTIFORM VARIETIES

William J. Campbell

Particulate Mineralogy Unit, Bureau of Mines

College Park Metallurgy Research Center

College Park, Maryland 20740

Abstract

The problem of asbestiform particulates with its environmental and

health implications has been compounded by the lack of precision with

which the term "asbestos" has been used. In many instances, non- asbestiform mineral particles have been identified as microscopic fibers

of asbestos-related minerals. This lack of precision in identifying

these particulates not only works to the disadvantage of the minerals

industry, but is also a handicap to rational science-based decision

making by regulatory agencies.

This presentation summarizes methods and terminology suggested by

the Bureau of Mines for the identification and characterization of

asbestiform minerals and also sharpens the distinction between common

serpentine and amphibole minerals and their relatively rare asbestiform

varieties.^ The continuing effort of the Bureau's Particulate Mineralogy Unit is to characterize mineral particles by morphological,

compositional, and structural data using various instrumental analytical

techniques and by developing new methods for identification and

characterization.

Keywords: Asbestos; cleavage fragments; fibers; silicate minerals.

Introduction

The objective of this paper is to present a general introduction on the identification

and characterization of asbestos-related minerals. Detailed discussions of specific

analytical techniques are given in other papers presented at this workshop. At present

there are three types of identification-characterization to supply the needs of regulatory

agencies, medical researchers, and mineral scientists. It is hoped that through interactions such as this workshop a common mineralogical-based procedure can be developed that

meets the needs of all concerned groups.

Until recently, emphasis in the United States was placed on occupational exposure of

employees manufacturing or using asbestos products for insulation and other applications.

Regulatory procedures were adopted from those used in Great Britain. The industrialhygiene identification procedures were acceptable to industry, health, and regulatory

organizations because the concern was restricted to several mineral products known

collectively as asbestos. Although light optical microscopic procedures counted only the

larger particles collected on the air filters, the procedure was adequate for correlating

^This paper is an abbreviated version of the sections on mineral identification and characterization in Bureau of Mines Information Circular 8751 - Selected Silicate Minerals and

Their Asbestiform Varieties: Definitions and Identification-Characterization, 1977, 56 pp.

authored by W. J. Campbell, R. L. Blake, L. L. Brown, E. E. Cather, and J. J. Sjoberg.

Copies of IC 8751 are available upon request to W. J. Campbell.

201
health effects to the number of fibers observed. Exact definitions for asbestos-related

mineralogical terms were essential since all three groups (industry, health, and

regulatory) clearly understood what was being counted and regulated.

The light optical microscopic procedures used by industrial hygienists were designed

for control of asbestos-processing operations in which the chrysotile and asbestiform

amphiboles are present as bundles of fibers as well as individual fibers [1]^. These

bundles may have an average diameter of 0.75 to 1.5 pm for chrysotile and 1.5 to 4.0 pm

for the amphibole asbestos [2]. Particulates of these sizes can be readily observed at a magnification of X 450 to X 500. In contrast, samples from ambient air and personnel air

monitors may consist of individual fibrils or small bundles of chrysotile 0.02 to 0.1 pm

in diameter, and/or amphiboles 0.1 to 0.2 pm in diameter [3]. Fibrils and small fibers in

this size range are not visible with the conventional light optical microscopic

procedures. Therefore, the identif icaiton procedures currently used for regulating the

U. S. mineral producing and consuming industries must be reexamined to insure that they

are both mineralogical ly correct and applicable to the size range of the particles being

regul ated.

This discussion will be limited to the selected silicate minerals and their

asbestiform varieties listed in Table 1. The objective is to point out the particle size

at which the minerals can be identified and characterized by various analytical techniques

[4]. Detailed descriptions of the various analytical and characterization techniques are available in numerous publications and textbooks.

Table 1. Selected silicate minerals and their asbestiform varieties.

Mineral Asbestiform variety

AMPHIBOLE GROUP

Anthophyllite asbestos.

Cummirigtonite-grunerite asbestos.

Tremol ite-actinol ite asbestos.

Crocidol ite.

SERPENTINE GROUP

Serpentine: Chrysotile.

%Si40io(OH)3

Anthophyl 1 ite:

(Mg, Fe^^)^ Sig022(0H,F)2

Cummingtonite-grunerite:

(Mg,Fe''^)7 Sig022(0H)2

Tremol ite-actinol ite:

Ca2{Mg,Fe'^^)5 Sig022(0H,F)2

Riebeckite:

Na2Fe3^ Fe2^ Sig022(0H,F)2

^Figures in brackets indicate the literature references at the end of this paper.

202
A crystalline mineral is defined primarily by its crystal structure and by its

definite composition or range of compositions. Therefore, any system of mineral

identification should be based principally on crystal structure and chemical criteria.

Additional characteristics have to be determined to distinguish varieties. These

varieties have similar basic crystal structures and composition, but are usually

differentiated macroscopical ly by the characteristic habits and/or other specific features

of the varieties. The objective is to summarize the methodology for identifying the

mineral first by mineral group (such as serpentine and amphibole), then by mineral

(actinolite, anthophyll ite, or chrysotile), and finally by mineral variety.

Macroscopic Samples

At the macroscopic level (easily visible by the unaided eye), the obvious feature of

the asbestiform varieties is the presence of fibers that can be easily separated, while

the nonasbestiform varieties have a massive, blocky, bladed, or columnar appearance.

Although chrysotile does occur very rarely in a nonasbestiform habit, in general the

distinction between chrysotile and serpentine can be based on the presence or absence of

separable fibers. In some serpentine samples where an obvious asbestos texture is not

displayed, the distinction between serpentine varieties may require more specialized

techniques [5,6]. The distinction between serpentine and amphibole minerals at the

macroscopic level can be made by elemental analysis, differential thermal analysis, and

x-ray diffraction techniques. For essentially pure samples, these techniques should also

be sufficient to identify the individual amphibole minerals based on the elemental composition corresponding to the various members of the solid solution series.

Many macroscopic samples of interest to the occupational and environmental health

personnel may contain low percentages of asbestiform minerals (for example, chrysotile in

serpentine and tremolite asbestos in talc). As a supplement to optical microscopy, the

presence or absence of serpentine or amphibole minerals can be determined in 10- to 100-mg

samples by instrumental techniques such as x-ray diffraction, differential thermal

analysis, or infrared spectrophotometry. In general, the sensitivity of these

instrumental methods is approximately 1.0 weight-percent. Sensitivity is significantly

affected by the presence of other minerals that give a response at or near the response

peak of the serpentine and amphibole minerals. It is important to note that these methods

usually only distinguish between mineral groups; light optical or electron optical

microscopy is required to obtain morphological characteristics necessary to identify

varieties of the same material.

Chemical characterization is generally necessary to assign a specific mineral name to

an amphibole whose structure is known. The amphiboles have been described [7] using ;^he

structural formula Wo_iX2Y5Z8022(0H,0,F)2. Generally, W = Na, K; X = Na, Ca, Mg, Fe 2,

Mn; Y - Al , Fe ^ , Ti ; and Z - Si, Al . In addition to the variation implied by the

structural formula, a chemical analysis must take into account inclusions of other

minerals that may be present. In contrast to the more formidable task of chemical

characterization of amphiboles, the serpentine minerals generally show little deviation

from the formula Mg3Si205(0H)4. For either structural or chemical characterization of a macroscopic sample, sufficient time must be spent in sample preparation to insure that

relatively pure minerals are being examined.

Microscopic Samples

The petrographic microscope provides a general method by which particles larger than

5 pm can be characterized. By observing the optical properties characteristic of the

structure and chemistry of a mineral, an experienced microscopist can distinguish

amphiboles from serpentines and, in some cases, distinguish individual minerals within

these groups [8]. The refractive indices are sufficiently different for the serpentine

and amphibole groups to make a distinction between groups by using the appropriate index

oil (Table 2). There is significant overlap in the range of the three refractive indices

among the amphiboles, but a specific index (for example, a, p, or y) can be determined to

aid in identifying the amphibole species. Optical relationships can be confused, however,

if the particle consists of fiber bundles or is some other form of crystalline aggregate.

203
Table 2. Refractive indices for the serpentine group and

selected amphibole minerals.

Refractive index Range of values

Chrysoti 1

a 1

493 1560

B 1

, 504 _1. 550

1.,517 -

1.,562

Anti gori te~ 1 i zardi te a 1

. 538 1. 564

Y 1

, 546 _

1. 573

Anthophyl 1 ite a 1

. 596 1.652

B 1..605 1..662

Y 1

. 615 _1 . 676

Actinol ite-tremol ite a 1

. 599 1. 668

B 1

. 612 1

. 680

Y5 1

. 622 _

1

.688

Cummi ngtonite-grunerite a 1 .635 1 .696

P

1 .644 1 .709

V 1 .655 1 .729

Riebeckite a 1 .654 1 .701

P 1 .662 1 .711

1 .668 1 .717

The well-known parallel extinction of the commercial asbestos known as Amosite can be used

to distinguish that variety from the nonasbesti f orm varieties of cummingtonite and

actinol ite. A method of using extinction angles and cleavage directions to distinguish

specific asbestiform and nonasbesti form amphiboles has been described [9]; however, this

technique is limited to particles with diameters greater than about 5 pm and cannot be

universally applied to all amphiboles. There are many other optical parameters such as pleochroism, sign of the elongation, and color that are easy to obtain. Other parameters

such as optic axial angle, optical orientation, and optic sign are relatively more difficult to obtain.

Except for the asbestiform variety, serpentines are usually massive, while amphiboles

range from fine-grained massive to columnar or radiating aggregates of prismatic or acicular crystals. Amphiboles in acicular habit may appear to grade into the asbestiform

varieties. The characteristic features of this habit may still be seen by electron

microscopy. Terms such as "acicular" or "prismatic" may still be applied when seen, but

the term "asbestiform" begins to lose its usefulness. For example, how may flexibility be

demonstrated in a 2-pm bundle of fibers? As particle size decreases, the inability to

manipulate the mineral grains restricts the use of the term "asbestiform" without altering

the original sense of the word. High magnification necessitates the use of strictly

dimensional terms such as size and aspect ratios to accurately describe the morphology of

the amphiboles and serpentines. The degree of morphologic characterization possibly will

depend on the magnification being used. An asbestos particle being described as a single

fiber at low magnification may be seen to be a bundle of fibers at some high

magnification. Therefore, the magnification must be stated in the description.

Morphologic characterization using light microscopy can be accomplished on particles as small as a few micrometers. Electron optics can be used to characterize a wide range of

sizes extending down to a few angstroms. Morphologic characterization alone wi 1 1 not

identify a mineral without supplemental structural or chemical data .

Structural information on individual particulates can be obtained by use of a transmission electron microscope (TEM) in the selective area electron diffraction mode

(SAED). The inclination of the single crystal fragments to the electron beam is very

critical since a slight tilt of the crystal may change a relatively simple reciprocal

204
lattice pattern into a very complex one. Consequently, a special goniometer or tilting

stage is necessary to obtain easily interpretable diffraction patterns. For the

identification of the mineral, a goniometer or tilting stage is even more essential since

dependable conclusions cannot be made from measurements on one reciprocal lattice plane.

The quality of the SAED pattern is a function of fiber diameter. The larger diameter

fibers (>0.5 pm) strongly absorb the 60- to 100-keV electrons used in a conventional TEM,

while the very small-diameter fibers (<0.2 pm) do not give sufficient electron-diffraction

intensity. A second problem with small-diameter fibers is the degradation of the singlecrystal pattern by diffraction lines from nearby particles. A higher energy TEM, with the

resultant greater penetration of the electron beam, can be utilized for large-diameter

particles. However, these costly instruments are not widely available.

Although the magnitude of the characteristic C, the distance between the conspicuous

layer lines for chrysotile and the amphiboles, is similar in direct space (dooi ~ 5.3A),

the chrysotile pattern has very prominent streaks on these layer lines compared with the

spot pattern for the amphiboles [10]. Researchers indicate that the ability to distinguish

between the fibrous and nonfibrous variety of amphiboles by SAED is still to be resolved.

At the very high magnification available with a TEM, chrysotile' s hollow-tube

(scroll-like) structure, approximately 5 nm in diameter, is visible (fig. 1). This

hollow-tube structure, together with chemical and structural data regarding the sample, is

sufficient to identify the mineral variety. However, the hollow-tube structure is only

visible for individual fibrils; fibers (composed of several fibrils) will not display this

characteristic because of stacking of the fibrils.

Figure 1. Chrysotile, showing individual fibrils, at two magnifications: X 18,000 (left)

and X 35,000 (right). The hollow-tube structure is visible at the higher

magnification. (TEM microphotographs.

)

205
The elemental composition of microscopic grains is determined by either wavelength or energy-dispersive x-ray spectrography in conjunction with scanning or transmission

electron microscopy. Extreme care must be taken in the calculation of elemental con- centrations from x-ray spectral intensities because the spectral line intensities (FeKa,

MgKa, CaKa, relative to SiKa) are dependent on particle diameter for small fibers [3].

Energy-dispersive x-ray spectral calibration data for each scanning or transmission

electron microscope must be made using relatively pure standard minerals analyzed by

accepted chemical-instrumental techniques. The analyst should be aware that other nearby

grains may be contributing to the characteristic x-ray lines because of either penetration

of the electron beam through the particles or secondary excitation of nearby particles

from primary x-rays generated in the particle being measured. Modern electron optical

instruments have electron beam diameters of 0.1 to 0.01 pm; however, the sphere of

excitation can be several micrometers in diameter as a result of scattered electrons and

primary x-rays generated in this particle. Conversion of intensity into concentration

using accepted computer programs such as "MAGIC" is limited in accuracy because these

programs are designed for use with grains or particles several micrometers in diameter or larger, whereas the average mineral fiber diameter is less than 0.5 pm for chrysotile. A

good example is the diameter size distribution of chrysotile fibers in ambient air samples

(Table 3). The important point to note is that approximately 95 percent of these

chrysotile fibers are 0.12 pm or less in diameter. Therefore, quantitative correction

procedures applicable to large particles will be of limited value in mineral-fiber

identification because the relative x-ray spectral intensities are dependent on fiber

diameter below 0.2 pm.

Table 3. Frequency distributi

fibers in ambient-ai

Diameter of chrysotile

fibers, pm

0. 02 - <0. 04

0. 04 - <0. 06

0. 06 - <0. 08

0. 08 - <0. 10

0. 10 - <0. 12

0. 12 - <0. 14

0. 14 - <0. 16

0. 16 - <0 18

0. 18 - <0 20

0. 20 - <0. 22

0. 22 - 0. 24

>0 24

on of the width of chrysotile

r samples, percent. ----- Sample -----

1 2 3 4 5 6

10 70 57 17 15 17

47 24 28 29 33 49

24 5 8 28 20 15

14 1 2 12 26 6

2 0 1 7 3 6

0 0 2 3 1

1 0 1 2 1

0 0 0 1 0

0 0 0 0 1

1 0 0 0 0

0 0 1 0 0

1 0 0 1 0

Samples

quarry. were collected 1-2 miles from a serpentine rock

Another problem with

poor signal-to-background

the elemental characterization of

ratio. Longer counting times

very

wi 1

reliability of the measurement, but the best approach is to

small particles is the

help to improve the

minimize the continuum

background resulting from the interaction of the electron beam and the sample substrate.

206
Applying Mineral Terminology to the Identification and Characterization of Particulates

This section addresses the practical considerations and limitations encountered when

applying nomenclature and identification-characterization procedures to regulatory and

environmental samples.

Applying Morphological Terminology

One of the obvious features of minerals and their particulates is their morphology or

shape. The need for precise definitions of terms such as "asbestiform," "fiber,"

"cleavage fragment," and "fibril" was explained in IC 8751. These definitions were carefully structured to eliminate ambiguity and to be technically correct. Applying the

definitions to samples requires careful thought as to what limits must be placed on interpretations resulting from the use of these terms and other mineralogical concepts.

The underlying problem, recognized by both medical and regulatory personnel, is classifying the mineral particle as the asbestiform or nonasbestiform variety. In a mineralogical sense, the source of the mineral particulates must be considered, as explained in the following discussion.

Particulates From A Known Asbestiform Serpentine or Amphibole Source

The definition of asbestiform minerals includes three aspects: morphology, structure,

and chemistry. Morphologically, asbestiform mineral varieties separate into flexible

fibers or flexible bundles of fibers. Flexible fibers bend readily and only break across

the fibers into distinct pieces with some difficulty. Structurally, the asbestiform

minerals are limited, in common practice, to the serpentine and amphibole mineral groups.

Chemically, these minerals are all hydroxylated silicates; the term "hydroxyl ated" is

preferred over "hydrated" because these minerals contain OH ions rather than water of

crystallization. The serpentines contain approximately 13 weight-percent water; the

amphiboles, approximately 2.5 weight-percent water.

For the purpose of this discussion, assume that a hand specimen meeting these

requirements is correctly identified as an asbestiform mineral. If this sample is crushed

and its fragments examined at various magnifications, its fibrous nature would be

apparent. These elongated fragments would be termed "fibers" and "bundles of fibers," and

with the other available information would be called "asbestiform." As these asbestiform

particles are examined at increasing magnification, smaller particles become visible,

while the image of large fibers and fiber bundles may exceed the field of the microscope.

At increasingly smaller sizes, while fibers or bundles of fibers are still the predominant

shape, a few of the fibers are observed to have broken into shorter and shorter segments.

These very short fiber segments are no longer described as fibers, but would be classified

as fragments of fibers, or cleavage fragments if one or more cleavage planes govern their

shape. Therefore, a known asbestiform sample would show an increase in the ratio of fiber

fragments to fibers with a decrease in particle size.

Particulates From A Known Nonasbestiform Serpentine or Amphibole Source

If the hand specimen discussed previously does not separate into flexible fibers or bundles of fibers, the mineral would not be considered asbestiform. However, the specimen

would be classified as serpentine or amphibole if the specific mineral is identified on

the basis of optical properties, chemistry, and structure.

If crushed fragments of this known nonasbestiform mineral are examined at various

magnifications, the particles would be primarily cleavage fragments, or irregularly broken

fragments if cleavage does not govern breakage. However, a few elongated particles may

resemble a fiber in appearance to the degree that they may be indistinguishable

morphologically from fibers derived from an asbestiform mineral sample.

What can be stated morphologically about particles derived from crushing a known

nonasbestiform mineral is that most of the particles are cleavage fragments with non- asbestiform texture; a few are fibrous in appearance, particularly at low magnification;

and all of the particles are known to be derived from a nonasbestiform source.

207
Comparison of Particulates From Known Serpentine and Amphibole Minerals and Their

Asbestiform Varieties

The appearance of particles generated by milling known serpentine and amphibole

minerals and their asbestiform varieties is shown in figures 2 to 5. The samples shown in

figures 2 to 4 were photographed using light optical microscopy at three magnifications to

show that, at decreasing size (depicted by increasing magnification), the original habit

generally persists. For the nonasbesti form amphibole minerals, there were a few elongated

particles from the riebeckite and tremolite. Elongated particles of this type are typical

of the prismatic cleavage of amphiboles. To increase optical contrast, the serpentine

group samples were dispersed in an immersion oil considerably below the refractive indices

for the serpentine.

Figure 2. Light optical photomicrographs of chrysotile and antigorite-1 izardite at

three magnifications. Chrysotile (left) at A, X 100; B^, X 500; and C,

X 950. Antigorite-1 izardite (right) at D, X 100; £, X 500; and F, X 950.

208
Figure 3. Light optical photomicrographs of crocidolite and riebeckite

at three magnifications; Crocidolite (left) at A, X 100; B,

X 500; and C, X 950. Riebeckite (right) at D, X 100; E,

X 500; and F, X 950.

209
Figure 4. Light optica! photomicrographs of tremolite asbestos and

tremolite at three magnifications. Tremolite asbestos

(left) at A, X 100; B, X 500; and C, X 950. Tremolite

(right) at D, X 100: E, X 500; and F, X 950.

210
Figure 5. SEM photomicrographs of crocidolite and riebeckite at three

magnifications: Crocidolite (left) at A, X 500; B, X 2,500;

and C, X 10,000. Riebeckite (right) at D, X 500; E, X 2,500;

and £, X 10,000. Rectangles indicate the area shown at the

next higher magnifications.

211
Riebeckite and crocidolite particles are compared at higher magnifications in figure 5. The outlined areas in the scanning electron micrographs indicate the area displayed at the

next higher magnification. Again, note the presence of a few elongated cleavage fragments

of riebeckite visible at the higher magnification. In contrast, the aspect ratio of the

crocidolite will decrease with decreasing particle size because the individual fibers

cannot cleave further along the fiber axis; they can only break into shorter segments.

Aspect Ratio

Existing regulatory standards are based on counting specific mineral particulates

with aspect ratios of 3 to 1 or greater. The aspect ratio has little mineralogical

significance for individual particulates but is applicable statistically to a large number

of particles. A few relatively long thin particles are produced as cleavage fragments

from the crushing and grinding of many nonasbestiform minerals. Conversely, similar

milling treatment will result in a few short segments of true fibers from the asbestiform

varieties. However, statistically, the length-to-width characteristics of the milled

amphiboles and serpentine and their asbestiform varieties are significantly distinct, as shown by the data in figures 6 to 9.

Figure 6. Frequency polygons for the aspect ratios of anthophyllite

and anthophyllite asbestos.

212
213
CHRYSOTILE

50 r

1:1 3:1 5:1 10:1 20:1 50:1 100:1 200:1 500:1 1000:1

ASPECT RATIO °' "'"^^

H 10,603 CP

Figure 9. Frequency polygons for the aspect ratios of commercial -grade

chrysotile and chrysotile in ambient air.

Figures 6, 7, and 8 show the frequency polygons of the aspect ratio distribution for

milled samples of the normal nonasbestiform variety of three amphiboles--anthophyl 1 ite,

tremolite, and hornblende, respectively. Note that in all three examples, approximately

70 percent of the particles have an aspect ratio of less than 3 to 1 , and 95 percent of

the particles have a length-to-width ratio of less than 10 to 1. The frequency distribution maxima of the aspect ratios for milled anthophyl 1 ite asbestos and tremolite

asbestos are significantly higher than those for the normal, nonasbestiform variety.

Thirty to forty percent of the asbestiform particulates are in the 10-to-l -or- longer

class, with a significant number of particles having an aspect ratio greater than 20 to 1.

Figure 9 shows the distribution frequencies for a milled commercial grade of

chrysotile asbestos and for chrysotile particulates collected on ambient air filters in

the vicinity of a serpentine rock quarry. For the commercial-grade chrysotile, over 50

percent of the particles have an aspect ratio greater than 50 to 1 , whereas the frequency

distribution for the ambient air sample has a maximum between 10 to 1 and 20 to 1 . These

results are anticipated because the higher aspect ratios for the commercial-grade

chrysotile are characteristic of the significantly longer starting material.

All of the aforementioned samples except the ambient air were milled, then dispersed

in water for collection on a suitable substrate. The samples were then measured using

electron microscopy at magnifications of 5,000 to 10,000. The ambient air sample,

collected near a serpentine rock quarry, was measured using a TEM with magnifications of

X 5,000 to X 32,000.

Based on these data, one test for distinguishing the presence or absence of the

asbestiform variety of a mineral could be an examination of the frequency distribution of

the aspect ratio for that mineral. Assuming positive identification of the mineral type,

then the designation of variety would be based both on particle morphology and the

frequency maximum of the aspect ratio. Cleavage fragments will generally have a frequency

maximum less than 3 to 1 , whereas the asbestiform varieties will fall between 10 to 1 and

20 to 1 or higher, depending on the characteristics of the mineral and the history of the

sample, particularly the type and degree of milling. If any shape or size 1 imits are placed on characterizing mineral particulates , such 1 imits should be based on medical

evidence or on some 1 imitation of the characterizing technique and so stated .

214
Particulates From Unknown Sources

Samples such as environmental airborne or waterborne mineral particulates collected

at a considerable distance from a possible source are examples of particulates from an unknown source. The samples could have been collected at a location so distant from a known source that other mineral particulates originating from other sources compose most

of the sample.

The source of the particulates in an environmental sample may be located by taking

additional samples at selected intervals in the direction of, and closer to, the suspected

source. However, several factors must be considered: The direction of air and water

currents with respect to the suspected source, and the proximity to and direction of other

sources with regard to the suspected source. One study found very low concentration of

airborne chrysotile upwind from a source compared with a concentration two orders of

magnitude greater downwind [11]. Another important consideration is the level of natural

or human disturbances of particulates; for example, strong versus weak winds, or heavy

versus light vehicle traffic. In some instances, it may be possible to identify the source if the mineral particulates of interest have unique trace elements or combinations

of elements that are specific to the probable mining or milling operation emitting the

particulates. Detailed elemental analysis using the X-ray spectral capabilities of an SEM

or TEM is required on both the suspected source and the particulates.

Appl i cations

The following examples illustrate the application of mineral terminology and

identification-characterization procedures to three types of problems: (1) chrysotile

determination in ambient-air samples collected near a serpentine rock quarry, (2) identification of asbestiform minerals in ceilings and walls of public buildings, and (3)

characterization of a mineral product. These examples illustrate, in order, the need for

higher magnification than available with the light optical microscope, the use of various

characterization techniques to screen and identify asbestiform minerals, and the judgment

of the analyst in distinguishing cleavage fragments and asbestiform particles.

Ambient-Air Samples Collected Near Serpentine Rock Quarry

The Bureau of Mines is working with State and Federal officials to measure mineral

particulates in ambient-air samples collected in the vicinity of a serpentine rock quarry.

Optical microscopic procedures at about X 500 are limited to the identification of mineral

particulates longer than 5 [^m with an aspect ratio of 3 to 1 or larger (criteria set by

the Mining Enforcement and Safety Administration and the Occupational Safety and Health

Administration). The mineralogist can further identify the particles as belonging to the

serpentine, amphibole, or other mineral group with index oils (Table 2).

The serpentine rock in the quarry is interlaced with small veins of chrysotile

(figure 10). Optical microscopic procedures used for industrial hygiene are adequate for

the detection of large chrysotile fiber bundles. These fiber bundles of commercial -grade

chrysotile can be several micrometers or larger in diameter. In contrast, the mining and

crushing operations in the quarry plus transport of particulates over a distance breaks

bundles of fibers down to fibers or fibrils with diameters of 250 to 1,000A (Table 3).

215
Figure 10. Macrophotograph showing chrysotile veins in

serpentine rock (X 1).

Figure 11 is a series of SEM photomicrographs of a mixture of chrysotile and non- asbestiform serpentine handpicked from a small vein in the serpentine rock quarry. Note

that at X 450 (corresponding to the optical microscope magnification), only one or two

bundles of chrysotile are faintly visible; the predominant particles are the

nonasbestiform serpentine. As the magnification is increased, the high concentration of

chrysotile fibers becomes readily visible. The fiber diameter size data in Table 3 indicate that more than 95 percent of the chrysotile fibers in these ambient-air samples

are below the limit of resolution of the optical microscope. Although many other

scientists have pointed out the 1 imitation of the optical procedures for chrysoti le i_n ambient air , there is need for conti nuous emphasis that higher magnification techniques

are necessary for environmental and regulatory samples .

216
Figure 11. Mixture of nonasbestiform serpentine and chrysotile at five

magnifications: A, X 450; B, X 2,250; C, X 1,800; D, X 9,000;

and £, X 18,000, Rectangles indicate the area shown in the

next panel

.

217
Asbestos in Ceiling and Wall Materials

A possible environmental hazard is the release of asbestos from ceilings and walls in

homes, churches, schools, and various other public and commercial buildings. Because of

the very high number of potential samples to be examined by various State or Federal

agencies, a rapid and reliable screening procedure is necessary to identify those samples

that warrant further test. Three complementary analytical methods for screening, identification, and semi-quantitative estimate of the asbestiform mineral concentration are x-ray

di f fractometry , differential thermal analysis, and microscopy (light optical and scanning

electron).

The screening identification procedures can be relatively simple because chrysotile

is the principal asbestos mineral used for building insulation materials, with amosite

used to a much lesser extent. In 18 samples from a midwestern municipal health

department, chrysotile was a major constituent (>50 weight-percent) in 2 samples, a minor

constituent (1 to 10 weight-percent) in 12 samples, and not detected in 4 samples. Other

minerals present in various concentrations in these samples were calcite, quartz, gypsum,

and mica. Amosite was found as a major constituent in the ceiling of an older building

located on a university campus.

The presence of either serpentine or amphibole minerals in the insulation materials

can be used as a probable indication of asbestos. Therefore, screening tests are based on the presence or absence of characteristic differential thermal analysis or x-ray

diffraction peaks of either serpentine or amphibole minerals. For the positive samples , confirmation of the presence of the asbesti form variety requi res some type of microscopic

exami nation because the thermal and x-ray di f fraction methods do not identify the mi neral

variety .

Some samples will be composed of a mixture of synthetic and natural fibers, such as the mixture of fiberglass and chrysotile shown in figure 12. Generally, it is not

difficult to identify the synthetic fibers based on their larger diameter and the more

•mi form appearance.

Asbestos-related health regulations are having a significant impact on the domestic

talc industry from occupational exposure at the mines and mills and at various

manufacturing plants that use talcs in their operations. Certification that the talc does

or does not contain asbestiform minerals is important because the occupational health

Figure 12. Sample from university building, showing a mixture

of chrysotile and fiberglass (X 140).

Amphiboles and Talc

218
requirements are much more restrictive if the talc is designated as containing asbestiform

serpentine or amphibole minerals.

Talc is both the name of a specific mineral, Mg3Si40io(0H)2 , and a commercial

term for a mixture of minerals ranging from essentially 100 percent talc to blends

where the mineral talc is a minor constituent [12,13]. Semi-quantitative estimation

of the serpentine and/or amphibole mineral concentration, if present, can be obtained

by x-ray diffraction and differential thermal analysis. Several talc deposits contain

a variable amount of tremolite. Therefore, the essential question faced by the analyst

is whether or not the tremolite is fibrous. Judgment required of the analyst is

illustrated by the sample shown in figure 13. This sample consists of platy talc, cleavage fragments of an amphibole, and minor to trace amounts of fibrous amphibole. For

this latter sample, the 3-to-l aspect-ratio criteria would greatly overestimate the

number of fibrous amphibole particles collected on air filters or other monitors.

Figure 13. Platy talc, tremolite cleavage fragments, and

a fibrous tremolite particle (A) (X 400).

References

) [1] Journal of the American Industrial Hygiene Association. Recommended Procedures for

Sampling and Counting Asbestos Fibers. Vol. 36, pp. 83-90 (February 1973).

I [2] Berger, H. , Asbestos Fundamentals. (Chemical Publishing Co., New York) 171 pp.

(1963).

f [3] Beaman, D. R. and File, D. M. , Quantitative Determination of Asbestos Fiber

I Concentrations. Anal . Chem . , 48, pp. 101-110 (January 1976).

; [4] Langer, A. M. , Approaches and Constraints to Identification and Quantification

' of Asbestos Fibers. Environmental Health Perspectives , 9, pp. 133-136 (1974).

[5] Cressey, B. A. and Zussman, J., Electron Microscopic Studies of Serpentinites.

Canadian Mineralogist , T4, pp. 307-313 (1976).

I [6] Mumpton, F. A. and Thompson, C. S. , Mineralogy and Origin of the Coalinga Asbestos

Deposit. Clays and Clay Minerals , 23, pp. 131-143 (1975).

I [7] Ernst, W. G. , Earth Materials (Prentice-Hall , Inc. , New York, 1969).

219
[8] Deer, W. A., Howie, H. A., and Zussman, J., Rock Forming Mineral

. (John Wiley &

Sons, Inc. , New York, 1963) 5 v.

[9] Wylie, A., Optical Properties of Asbestiform Amphiboles and Their Nonasbestiform

Analogs. Available from A. Wylie, Bureau of Mines, College Park, Maryland 20740.

[10] Ruud, C. 0., Barrett, C. S. , Rissell, P. A., and Clark, R. L. , Selected Area Electron

Diffraction and Energy Dispersive X-Ray Analyses for the Identification of Asbestos

Fibres, a Comparison, Micron , 7, pp. 115-132 (1976).

[11] John, W. , Berner, A., Smith, G. , and Wesolowski, J. J., Experimental Determination

of the Number and Size of Asbestos Fibers in Ambient Air. Calif. State Department

of Health, Rept. AIHL/SP-1, 36 pp. (January 1976).

[12] Hamer, D. H. , Rolle, F. R. , and Schelz, J. P., Characterization of Talc and Associated

Minerals. J. American Industrial Hygiene Association , 37 , pp. 296-304 (May 1976).

[13] Rohl, A. N. , Langer, A. M. , Selikoff, I. J., Tordini, A., Klimentidis, R. , Bowes, D. R. , and Skinner, D. L. , Consumer Talcums and Powders--Mineral and Chemical Characterization. J. Toxicology and Environmental Health, 2, pp. 255-284 (1976).

Discussion

J. LEINEWEBER: You brought up the question of cleavage fragments vs fibers, and

asbestiform vs non-asbestiform varieties. I would like to ask why you attach so much

significance to this. I think Dr. Kotin couched it most directly yesterday: the body

doesn't have a dictionary. When we see fibers, if they are in the size range and if we accept this philosophy, does it matter where they come from?

W. CAMPBELL: I think all health data has been based on commercial asbestos, correct?

LEINEWEBER: Not necessarily commercial asbestos, but fibers of one type or another.

CAMPBELL: OK, fibers.

LEINEWEBER: Man-made mineral fibers or natural mineral fibers.

CAMPBELL: There has been little medical studies made upon cleavage fragments. Now

these may be just as harmful as fibers, but until you find this out you should call them

by their proper names. To call a cleavage fragment a fiber does not help anybody.

LEINEWEBER: I don't see any reason for muddying the waters with the semantic differences .

CAMPBELL: I think there is some dispute whether or not there is a difference between

a fiber, based on surface properties and a much larger length-to-width, and a cleavage

fragment. Until you find this out you should call it either a fiber or a cleavage

fragment. They may be equally harmful if they are both 20:1 and 0.5 pm in diameter, but

this really has not been studied. The whole problem with the Lake Superior region was the

debate whether or not the cummingtonite fragments were the same as the amosite asbestos.

LEINEWEBER: This, in that context, was an argument based on the shenanigans that

normally take place in the court of law, and here we are in a scientific environment.

CAMPBELL: I am not a medical scientist. Obviously I don't know if a cleavage

fragment is the same harmful particle as an asbestiform particle, but until you find this

out; you just call it by the proper name. It does not help to call them both the same when they may be different.

220
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

AN OVERVIEW OF ELECTRON MICROSCOPY METHODS

Clayton 0. Ruud

Denver Research Institute

University of Denver

Denver, Colorado 80208

Abstract

According to a recent National Academy of Sciences Report, animal

deposition model studies have shown the fiber size has some effect upon

the toxicity of mineral microfibers, the long thin ones appearing to be

most active [l]-"^. However, the extrapolation of these results to the

relative carcinogenicity in humans must be tempered by the consideration

that an experimental animal model has not been established. Moreover,

the size range to be considered long, thin microfibers is not clearly

defined, that is to say, the shortest length may be on the order of one micrometer or ten micrometers. For this and other reasons most

scientists in the field consider that it is necessary to obtain data on length and width, as well as on concentration and species of mineral

fiber fragments in the environment.

Due to these considerations, microscopy methods are necessary for

mineral fiber analysis, and because of the small size of the particles,

electron microscopy is necessary. This paper will describe the methods

and techniques of electron microscopy which are most generally applied.

These are the transmission electron microscope-selected area electron

diffraction (TEM-SAED) and the scanning electron microscope-energy

dispersive x-ray spectroscopy (SEM-EDXS) methods. The advantages and

disadvantages of these two techniques will be discussed, including their

relative proficiency in detecting sub-micrometer fiber fragments. Their

ability to identify the species of mineral, sample preparation

techniques, statistical considerations and the cost of analysis will

also be reviewed.

The application of various techniques and methods based upon the

TEM-SAED or SEM-EDXS systems will be discussed, including situations

where one or the other is the optimum method. The advantages of combined

systems, scanning transmission electron microscopy with SAED and EDXS,

will be discussed. Also new approaches of combination and computer

controlled methods using both TEM and SEM will be described.

In conclusion, the state of the art will be discussed in terms of

general considerations necessary for the selection of an electron

microscopy technique for mineral fiber analysis.

Key Words: Amphibole asbestos; asbestos; chrysotile; electron

diffraction; energy-dispersive x-ray spectroscopy; mineral microfibers;

scanning electron microscopy; selected-area electron diffraction;

transmission electron microscopy.

^Figures in brackets indicate the literature references at the end of this paper.

221
Background

Collection of mineral particles for identification and counting is usually done by

filtering the medium, air or water, through cellulose ester membrane (Millipore) or perforated polycarbonate (Nuclepore) filters, thereby concentrating them through deposition

on the filter's surface. The effective minimum particle collection size is always less

than one half a micrometer.

The optical microscope is used extensively for counting mineral fibers collected from

occupational environments, but it is generally agreed that this is a matter of expedience

and not due to adequacy. By far the greatest number of asbestos mineral fibers found in

the environment, including occupational environments, are below the resolving power of the

optical microscope. Since neither epidemiology nor animal studies on the relative toxicity

of mineral microfiber have shown conclusively that those less than 0.5 pm in diameter or width are innocuous, it has been considered prudent to count, size, and identify all

particles with an aspect ratio greater than 3 to 1 which are tens of micrometers in length

and shorter. Although the long thin fibers seem to be more active in animal depositionmodel studies, the shortest active fiber length has not been established [1]. Also,

because a number of mineral and man-made microfibers are suspected of producing varying

degrees of adverse health effects, the identification or classification of a mineral

fiber as to species is important.

Until the effect of size, morphology, species and other properties of microfiber can

be related to toxicity, it will be necessary for the analyst to characterize the

distribution of a number of these parameters from environmental samples.

Electron Microscopy

The group of analytical instruments which provides more of what are considered the

important parameters mentioned above is that of the electron microscopes. Both

transmission and scanning electron microscopy have been used extensively for mineral fiber

identification, sizing and counting, and both types of instruments and their related

characterization techniques have their place.

The transmission electron microscope (TEM) with selected area electron diffraction

(SAED) is considered the most widely applicable instrument, although it has some disadvantages which will be discussed. This technique requires that the image forming

electrons travel through the sample and therefore the sample matrix must be transparent to

the high kinetic energy (usually about 100 KeV) electrons. SAED also requires that the

electrons travel through the matrix as well as some part of the microfiber to be identified. SAED is used to characterize the crystal structure of the particle of interest

and is valuable for the identification of the type or class of fiber, e.g., serpentine

asbestos, amphibole asbestos, non-crystalline or non-asbestos.

Scanning electron microscopy (SEM) can be compared with reflected light microscopy.

However, images are formed electro-optical ly, usually by secondary electrons produced by a focused electron beam in the sample. The technique usually employed for species

identification is energy dispersive x-ray spectroscopy (EDXS) which determines the energy

of x-rays emitted from the sample. This emitted x-ray energy spectrum is caused by the

electron beam interaction with the sample and can be used to qualitatively and semiquantitatively identify the elemental content of a microfiber.

A third type of instrument which combines the advantages of both the TEM and SEM is

the scanning transmission electron microscope (STEM). This instrument has been used by a number of laboratories, most of which have procured it specifically for asbestos

microfiber counting and identification. Essentially it is a transmission electron

microscope equipped with scanning and focusing coils so that a focused beam of electrons

can be scanned over the sample or pinpointed in a particular area. The most general mode

of application is to obtain a shadow image as with the TEM, then perform SAED and/or EDXS

as desired. The focused beam should produce a brighter SAED pattern for particle

identification than in the TEM, and if an elemental analysis is desired this may be

obtained from the same particle without transferring the specimen to another electron beam

instrument.

222
There is another type of electron microscope which has been used only sparsely for

asbestos mineral fiber analysis. This instrument is an SEM with an electron detector

below the specimen for transmission imaging. This allows a transmitted electron image to

be formed and the instrument might be called a transmission scanning electron microscope

(TSEM). Application of this technique will be discussed in a subsequent section.

Needless to say, combinations of SEM and TEM instruments have been and are being used

for microfiber analysis also.

Appl i cations

There are four important considerations in the selection of an electron microscopy

method for the counting and characterization of microfibers. These are: observability,

specificity, sample preparation and analysis cost.

Observabi 1 ity

Observability is concerned with the sharpness and contrast of the microfiber image

against the matrix. This controls the relative ability of the microscopist to find

microfibers, measure them, and characterize their morphology. Flinckinger and Standridge

[2] compared fiber counts with SEM and TEM from water samples and concluded that for small

fibers TEM gave much higher counts, about an order of magnitude or greater. Ruud et al.

[3] showed the relative clarity of SEM and TEM images illustrating the superior contrast

of the latter (see figure 1). The highly magnified shadowgraph obtained in transmission

electron microscopy is for the most part an accurate representation of the length and

width or diameter of the fiber. Chrysotile fibers are usually circular bundles of fibrils

or round single fibrils. Often the fibrils can be distinguished in a TEM image by the

fact that they are tubular and the hollow center can be seen in the electron microscope

image [3]. While this tubular appearance is characteristic of chrysotile, it is not

always present so that if a fiber does not appear to be hollow this does not rule it out

as chrysotile. Amorphous material can be attached to the surface and fill the tubes,

thereby giving the appearance, as far as density is concerned, that the fiber is solid

[4]. At any rate it is well to have an identification method in addition to morphology

for chrysotile and it is imperative for the amphibole minerals since non-asbestos material

can appear in the electron microscope to be fibrous, i.e., they may have a 3:1 length-towidth ratio. Also, many chain silicate non-asbestos minerals fracture in the same general

way as the asbestos minerals so that morphology does not lead to a reliable

identification. See figure 2 from Ruud et al. [3]. The most effective additional

identification method is selected area electron diffraction, which will be discussed

subsequently.

223
Figure 1. Comparison of SEM and TEM image clarity for

a microfiber form an environmental sample.

Top is SEM image and bottom is TEM image.

The marks in the upper left corner of each

micrograph are 1 micrometer apart.

224
Figure 2. A TEM micrograph of the mineral wollastonite

The superior image contrast of small microfibers and the clarity of internal voids in

the TEM can be understood when the mechanism of image production and resolution of the two

types of instrumentation is compared. The TEM relies upon the electron opacity of the

microfibers which depends upon the thickness but which is invariably several times higher

than that of the specimen substrate. SEM relies upon the production of secondary

electrons for imaging and the relative difference of their efficiency of production

between microfibers and substrate is often rather slight. In spite of these

considerations, a recent report issued by the EPA [5] judged the two techniques as equal

with respect to fiber counting. However, the sample type and analytical procedure covered

in that report were very specific and not what may be generally expected or applied in

envir'onmental samples. The sample source was a laboratory prepared and dispersed Canadian

chrysotile. The TEM sample preparation was one which is seldom if ever used in TEM

preparation because it is complicated and prone to fiber loss and contamination. This

report therefore cannot be used as justification for the general use of SEM for microfiber

sizing and counting.

The electron microscope magnification used to locate and measure microfibers is an important concern and generally varies from 4000 to 20,000 times. It should be obvious

that the lower the magnification used to find microfibers consistent with sharp contrast,

the higher the likelihood of missing very fine ones. At 10,000X a 0.1 micrometer fiber

would appear to be 1 mm wide and at 4000X it would be 0.4 mm wide. On the other hand,

the lower the magnification used to search for microfibers the larger the area of electron

microscope specimen observed, thereby improving counting statistics for a given amount of

analysis time.

Specificity

Specificity is concerned with the identification of a microfiber species. In the

SEM, clues as to the elemental content may be obtained by EDXS, and these can sometimes be

used to identify the microfiber. With the TEM, SAED is usually employed for speciation.

SAED produces a pattern which is indicative of the crystal structure of a microfiber.

This crystal structure can then be related to the type or species of fiber. Usually only

classification is possible, but in the case of chrysotile asbestos it is usually readily

identified by SAED.

225
The basis for SEM-EDXS is that electron beam microchemical analysis may sometimes be

used to distinguish particles of various minerals [6,7,8]. The most common method

presently in use is the energy dispersive x-ray system (EDXS) attached to an SEM. X-ray

wavelength dispersive analyzers and the conventional electron microprobe have been used;

however, their routine application is negligible in asbestos microfiber analysis because

the high electron beam currents required may damage the specimen and the microanalysis

procedure is relatively time-consuming.

Semi-quantitative electron beam x-ray microchemical analysis in the electron

microscope is based on the fact that a beam of high energy electrons incident upon a particle generates x-rays with energies that are characteristic of the elements present in

that particle. Only those elements heavier than sodium (atomic number 11) can be

practically detected. An EDXS detector placed in the electron microscope sample chamber

close to the specimen converts the energy of the x-ray photons to voltage pulses which are amplified, digitized and stored in a multichannel analyzer or a minicomputer.

In the EDXS identification of microfibers, ambiguities can arise from x-rays produced

by adjacent or adhering particles, from instrumental uncertainties in determining the

exact chemical composition of a particle [9], or from the fact that a given mineral can exist over a wide range of compositions [10]. As much as a 10 percent variation in the

element x-ray intensity can be expected from any one mineral sample [7] or even a single

microfiber [11]. To further confuse the matter we have observed many mineral particles

that are often associated with asbestos materials which show a 3:1 length-to-width ratio

and give EDXS spectra that cannot be distinguished from the asbestos types. Figure 3

shows an example of SEM-EDXS data from an anthophyl 1 ite microfiber and a lizardite

cleavage fragment with a greater than 3:1 aspect ratio. Anthophyl 1 ite is an amphibole

asbestos mineral and lizardite is a non-asbestos polymorph of chrysotile. However, the

EDXS spectrum from the two are indistinguishable. A number of examples of this type of

possible misidentification of mineral microfiber appear in Ruud et al . [3].

In spite of the above considerations, a number of researchers have surmised that each

of the asbestos minerals can give x-ray spectra that usually are characteristic enough,

when combined with fiber morphology, to allow their mineral identification [6,7,12].

Visual observation of the semi-quantitative fiber x-ray spectrum is the usual method of

fiber identification; however, three-component diagrams have been used after subtracting

the continuous background from the semi-quantitative x-ray spectrum for further

extrapolation of the data [6]. For these analyses, matrix corrections are rarely used.

Typically, iron, magnesium, and silicon are plotted on the three component diagram and

compositional boundaries for the asbestos minerals established. In addition to the major

shortcomings mentioned in the previous paragraph, this added refinement suffers from its

failure to use all compositional data obtained such as presence or absence of sodium,

calcium, aluminum, and manganese which might aid in identification [6].

As has already been discussed, observation of proper elemental intensities by energydispersive x-ray analysis is generally not sufficient for positive identification of

fibers. For example, chrysotile, anthophyl 1 ite, and fibrous talc, which have similar

elemental compositions, may be difficult to differentiate [3,6].

These considerations make the sole use of SEM-EDXS unreliable in its general application to the identification of fibers and microfibers. There are specific cases where

the source of the sample is well characterized and the absence of particles of nearly

similar chemical composition has been confirmed that it may be useful.

Considering the uncertainties in SEM application to the identification of microfibers, it is understandable that transmission electron microscopy coupled with selected

area electron diffraction has been selected by many researchers as the most viable method

for identifying and counting asbestos fibers [1]- Although this method has some disadvantages, the overriding advantage is that usually it is specific with respect to the

identification of chrysotile or amphibole microfibers and it permits accurate size

measurement of particles even when that size is on the order of fractions of micrometers

in diameter.

226
Selected area electron diffraction can be readily accomplished on a modern

transmission electron microscope and a pattern observed in about 10 seconds and recorded

usually in less than two minutes. However it usually requires an experienced microscopist

and some fine manipulation of the specimen in the SAED mode for production of a clear

oattern. The two-dimensional SAED pattern of diffraction spots has the advantage, in the

case of some asbestos microfibers, that it contains certain outstanding characteristics

that can be recognized at a glance. This is particularly true for the more common type of

asbestos, the serpentine mineral chrysotile [4,13], figure 4.

227
The SAED pattern of a single chrysotile fiber or fibril is analogous to a rotating or oscillating crystal x-ray diffraction pattern in which the long dimension of the fiber

tends to lie parallel or nearly parallel to the supporting membrane and therefore is

perpendicular to the incident beam corresponding to the axis of rotation being normal to

the beam in the usual type of rotating crystal x-ray exposure. This analogy is also

228
artially true for amphibole fibers. In x-ray patterns the spots are arranged in lines,

niversally called "layer lines," with the spacing between the lines dependent upon the

eriodicity of the crystal structure in the direction of the axis of rotation (see, for

xample, Barrett and Massalski [14]). The analogous layer lines in SAED are also very

rominent and their spacing reveals the crystal periodicity in the direction of the fiber

xis. From a quick view of the layer line spacing one cannot distinguish between

hrysotile, tremolite, and amosite which all have layer line spacings corresponding to a eriodicity of approximately 0.53 nm, but this group of materials can often be

istinguished from some others of interest, for example wol lastonite, lizardite,

ntigorite, albite, hedenbergite, or diopside [3].

Fortunately there is no need for a detailed study of the pattern in order to

ositively identify chrysotile. The chrysotile diffraction pattern has very prominent

treaks on layer lines other than the central one, and some streaking also may be seen on

he central one [13]. Some spots of normal sharpness also occur; these are on the central

ayer line and alternate ones (2nd, 4th, etc.). The streaks are seen on the pattern in

igure 4 and can also be seen on the fluorescent screen of the electron microscope. The

eometry of the pattern is known for orthochrysotile, clinochrysotile, parachrysotile and

ixed ortho plus clino varieties [15], and the origin of the streaks is now well

nderstood as resulting from disorder in the stacking of the prominent layers in the

rystal (the hydroxy 1 , magnesium oxygen-hydroxyl , silicon and oxygen layers). The series

f researches beginning with Warren in 1941 and extending through many studies by

hittaker in 1956, have shown that the layered structure is curved cyl indrical ly around

he axis of the fiber, the axis with 0.53 nm periodicity in clino and ortho varieties,

his is called the c axis in some of the papers [16], but is called the a axis on others

15]. There is x-ray evidence [16] that the layers are wrapped in a helical cylindrical

anner and this is confirmed by electron microscopic views of the cross-section of the

hrysotile tubes by Yada [17]. This curvature of the structure accounts for the presence

f the prominent layer lines, which are perpendicular to the length direction of the

iber.

Amphibole minerals exist in both asbestiform and massive varieties. Numerous names

ive been given to varieties of the amphibole groups, and the many different types of

:oms substituted in the different members of the groups [18] add to the natural

ifficulties of identifying them. It is not surprising that the Joint Committee on Powder

iffraction Standards x-ray powder data file contains many cards of diffraction patterns

iffering from each other by small amounts.

SAED patterns prepared in this laboratory of known samples of the amphibole asbesiform minerals tremolite, crocidolite and amosite have prominent rows of spots which

jsemble the layer lines of rotating crystal x-ray patterns and which we will also call

layer lines.' There are especially closely spaced spots on each of these layer lines,

ir more closely spaced than they are in the rows of spots from the minerals hedenbergite,

Ibite or wol lastonite, for example [3]. We have rarely observed any non-asbestos

iterial exhibiting the characteristic layer line spacing and spot patterns within the

lyer lines displayed by asbestos mineral fibers. However, this author has recently been

iformed that pyroxenes have been observed to produce asbestos-like SAED patterns.

Although chrysotile is usually readily distinguished from the asbestiform varieties

r amphibole (crocidolite, amosite^, anthophyl 1 ite , tremolite and actinolite), it is not

isy to distinguish one variety of these amphiboles from another because the spacing of

"eminent rows of spots in these are the same, and the differences occur only in the

"rangement of spots along the rows. However, an experienced microscopist can learn to

istinguish on sight a pattern usually characteristic of an asbestos fiber from the

Jtterns of most non-asbestos minerals commonly associated with them. Crystalline

Jterials that exist in the form of thin plates also produce SAED patterns with many

)ots, but these in general are arranged in a two-dimensional array in which there are not

jch prominent layer lines in a single direction.

\mosite - a discredited term.

229
As mentioned above, SAED is used extensively as the major criterion for the

identification of mineral microfibers [1,2,3]. However, it should be mentioned that the

method is empirical and has not been rigorously tested. The possibility exists that some species of non-asbestos mineral fibers or microfibers may produce a high incidence of SAED

patterns characteristic of chrysotile or the asbestos amphiboles. An example of this, which

has been mentioned, is pyroxenes.

Transmission electron microscopes and STEM equipped with an energy dispersive x-ray

detector are available which allow simultaneous observation of morphology, crystal

structure and elemental composition. These microscope systems have been used to study

fibers of known asbestos origin as well as environmental and material samples [12,19].

It would be highly advantageous if a thorough crystal lographic examination of the

SAED pattern could be performed in the few seconds in which patterns are now cursorily

examined. This is technologically possible, but requires the building of a TEM or STEM

with a television camera in place of the fluorescent screen coupled to a computer

programmed to index and classify the pattern with respect to standard or calculated

patterns. These facilities are extremely expensive and few laboratories will be so equipped in the near future. However, studies of the patterns with respect to mineral

type, cleavage and fiber orientation are needed.

Sample Preparation ^

As previously mentioned, samples for electron microscopy analysis of microfibers are generally collected on cellulose ester membrane (Millipore) or perforated polycarbonate

(Nuclepore) filter media [5,19]. For analysis by the SEM the latter medium, due to its

smooth surface, is preferred. SEM preparation is usually done by coating the surface

directly with an electrical conducting material, e.g. gold, silver, carbon or silicon

monoxide [5]. More complicated methods have been used for SEM preparation of samples

collected on Millipore [9]. These filters with their rough surface are not generally

suitable for direct coating for SEM because small fibers may be masked by protrusions of

the surface.

In TEM, STEM, and TSEM analysis, the matrix must be nearly electron transparent to

electrons of about 100 KeV energy. This requires that the filtrate (particles) be mounted

upon electron microscope grids with very thin, on the order of 100 Angstroms, carbon or metallic substrates and the filter material dissolved away. Several dissolution

techniques are used, including the Jaffe wick and condensation washing. Generally these

techniques are relatively simple and maintain the original particle size distribution and

relative particle location. Some investigators have reported particle losses as high as 60 percent with the condensation washing technique compared with less than 10 percent with

the Jaffe wick method [20]. Coating the filter and filtrate with a conductive layer prior

to dissolution has been proposed as a technique to minimize particle loss [19,21]. Also,

careful control of the condensation washer can reduce filtrate loss to much less than 10

percent. Most laboratories apply a second carbon, metallic or silicon monoxide coating to

the filtrate after filter dissolution to reduce the probability of particle loss. The

choice of conduction coating is varied; however, many laboratories have been considering

fine grained metallic coatings because of superior contrast and the fact that a reference

pattern is provided on the SAED patterns.

The general preparation technique discussed in the previous paragraph is known as the

"direct transfer" method. A variety of more complicated techniques include the direct

transfer procedure as the last few steps. This includes ashing of the sample which is

required when a considerable amount of organic material is collected with the inorganic

microfibers or sometimes is used as a preliminary step to redistributing the filtrate for

a more uniform or more suitable concentration. Dissolution of the collection filter

substrate and subsequent refiltering has also been used. Needless to say, whether TEM or STEM is performed, the particulates must be distributed as uniformly as possible on the

filter sample. This is a vital consideration in the statistics of analysis which will be

covered by another author in this publication. Ashing can be performed in a low

temperature oxygen plasma device or at high temperatures in a muffle or tube furnace.

There are pros and cons to all redistribution procedures which must be considered by the

analyst; however, it is always highly desirable to process control specimens, i.e.,

230
blanks, when preparing samples for fiber counting and analysis. These blanks confirm a clean preparation environment or bear witness to laboratory contamination.

Another preparation technique which has been used off and on is the so-called "rubout" technique. This was used early in the electron microscopy analysis of microfibers

and has been applied by the Mount Sinai group [22]. High particle losses and the

idestruction of the true particle size distribution to produce only a mass concentration

are cited as disadvantages with this technique. Other techniques have also been cited as viable, including that in a recent EPA report [5]. However, most have been discarded in

favor of the direct transfer method alone or preceded by ashing only when necessary.

The added specimen handling necessary for transmission electron analysis has often

Ibeen cited as a serious disadvantage to TEM, STEM and TSEM analysis. However, experienced

laboratories have developed preparation routines and techniques which make particle

losses, contamination and labor time negligible. The usual amount of time lag in

preparation of a transmitted electron sample is about four hours.

Analysis Cost

The amount of electron microscope time necessary for an analysis is the major

consideration affecting cost, and is dependent upon many factors, not the least of which

is the sample from which the specimen was produced. The size distribution, particle

loading and uniformity of distribution are just three of these. If a very limited amount

of microscope time requires that the analyst use only a low magnification, e.g., 4000X,

then the small microfibers may be missed. Computer image analysis has been used by a few

laboratories [9] and can be applied directly on an electronic image as produced in the

SEM, STEM and TSEM or on photomicrographs produced by an electron microscope. Direct

computer image analysis is also possible with suitably modified imaging devices mounted

into TEM's. This technique can greatly reduce the amount of microscope time required for

microfiber searches but is prone to certain errors, especially where high concentrations

jof microfibers and other particles are present.

j The application of microfiber identification techniques affects the microscope

time as well as imaging. The TEM image is essentially instantaneous, whereas an SEM image must be acquired with time and takes several seconds to form. Furthermore,

on a typical SEM the time for one EDXS analysis is 100 or more seconds. As a conse- quence most analysts working with SEM and STEM only obtain analyses from selected

microfibers, not all of those found. SAED usually requires 10 to 30 seconds to form

an image suitable for recognition by the microscopist and is usually performed on all

microfibers found. Recording of this image is done selectively on a few microfibers

and usually requires 100 to 200 seconds. The beam focusing feature available on all

STEM and some TEM can reduce the recording time by producing a brighter SAED pattern.

Technique Development

A number of laboratories are evaluating the various electron microscopy techniques

iused in the analysis of microfibers. That this is necessary is evident from the wide

discrepancy in results produced on similar samples by different laboratories and/or

microscopists [23]. No two laboratories perform sample preparation or microfiber

analysis exactly the same and some are markedly different. However, over the past three

years a number of laboratories have markedly improved their analytical reliability in

ispite of the overwhelming statistical uncertainties.

F This author is aware of some new approaches to the identification, counting and

measurement of microfibers. United States Steel Research Laboratories are applying

[a specially equipped TSEM with an EDXS detector located for a very high x-ray take-off

angle, higher than possible in a standard unit. This sytem is computer controlled

using criteria from the transmitted electron image data at lO.OOOX magnification

processed through an image analyzer to locate microfibers. The geometry of the system

and the sample and x-ray detector distance (less than 1 cm) are such that a very

adequate EDXS spectrum can be accumulated an order of magnitude faster than with

standard electron microscopes, SEM or STEM. After a statistically significant number

231
of microfibers are found and EDXS data obtained from each, they are classified with

respect to aspect ratio and EDXS spectrum. The specimen is then transferred to a TEM, a 1200 KeV instrument in this case, where some microfibers in each EDXS classification are selected and an SAED pattern obtained for identification. It is recognized that a 1200 KeV TEM is not readily available; however, the SAED could be

performed on most TEM instruments with 80 to 100 KeV.

The advantage in the transmitted image over that usually produced in an SEM is

greater visibility of particles, as has previously been stated. Moreover, the technique has a great advantage over those presently applied from the standpoint that a large number of microfibers are analyzed at least through classification and this is a tremendous statistical advantage.

Concl usion

In conclusion there are a few points that should be made.

1. The transmitted electron image is generally accepted as being superior for counting

and measuring microfibers as compared with a secondary or backscatter electron image.

2. Selected area electron diffraction is generally accepted as the best criterion for

the identification of asbestos mineral microfibers, although a few non-asbestos

minerals may be mistaken for asbestos.

3. The statistical consideration affecting electron microscopy of microfibers is a source of considerable error and new techniques are being and must be developed to

relieve these problems.

4. There are a few specific situations where the SEM can be applied to the counting of

microfibers, especially where the source and species mixture are well characterized.

5. Although the TEM-SAED method of asbestos mineral microfiber counting and identification is not absolute, it is the best compromise of accuracy and cost available.

The author would like to thank C. S. Barrett and J. M. Dement for their contribution

to this paper.

References

[1] National Academy of Sciences, "Drinking Water and Health," Part I, 1977.

[2] Flinckinger, J. and Standridge, J., Identification of fibrous material in two public

water supplies, Env. Sci. and Tech . 10, No. 10, 1028-1032 (Oct. 1976).

[3] Ruud, C. 0., Barrett, C. S. , Russell, P. A., and Clark, R. L. , Selected area electron

diffraction and energy dispersed x-ray analysis for the identification of asbestos

fibers, a comparison. Micron 7, 115-132 (1976).

[4] Mumpton, F. A., Characterization of chrysotile asbestos and other members of the

serpentine group minerals, Siemens Review XLI, 7th Special Issue, 75-84 (1974).

[5] Gerber, R. M. and Rossi, R. C. , Evaluation of electron microscopy for process control

in the asbestos industry, EPA-600/2-77-059 (Feb. 1977).

[6] Rubin, I. B. and Maggiore, C. J., Elemental analysis of asbestos fibers by means of

electron probe techniques, Env. Health Perspect . 9, 81-84 (1974).

232
[7] Ferrell, Jr., R. E. , Paulson, C. G. , and Walker, C. W. , Evaluation of an SEM-ES

method for identification of chrysotile. In Proc. 8th Annual SEM Symposium, Johari

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0. and Corvin, E. (eds.). IIT Research Institute, Chicago, 111., 537-546 (1975).

[8] Langer, A. M. , Rubin, I., and Selikoff, I. J., Electron microprobe analysis of

asbestos bodies, Histochem . Cytoe hem . J. 20, 735-740 (1975).

[9] Pattnaik, A. and Maakin, J. D. , Development of scanning electron microscopy for

measurement of airborne asbestos concentration, U.S.E.P.A. , Office of R and D Pub.

No. EPA 650/2-75-029. Research Triangle Park, N.C., (1975).

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166-208 (1969).

11] Pooley, F. D. , The identification of asbestos dust with an electron microscope

microprobe analyzer, Norelco Reporter , 23, No. 2 , 5-9 (Oct. 1976).

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13] Clark, R. L. and Ruud, C. 0., Transmission electron microscopy standards for

asbestos. Micron 5, 83-88 (1974).

14] Barrett, C. S. and Massalski, T. B. , Structure of Metal

, (McGraw-Hill, New York,

654, 1966).

15] Zussman, J., Brindley, G. W. , and Comer, J. J., Electron diffraction studies of

serpentine minerals, Amer . Mineralogist 42, 133-153 (1957).

16] Whittaker, E. J. W. , The structure of chrysotile, Acta Cryst . 27, 659-664 (1956).

17] Yada, K. , A study of microstructures of chrysotile asbestos by high resolution

microscopy. Acta Cryst . 9, 855-857 (1971).

18] Deer, W. A., Howie, R. A., and Zussman, J., Rock Forming Minerals , (Wiley, New York,

Vol. 3, p. 270, 1963).

19] Cook, P. M. , Rubin, J. B. , Maggiore, C. J., and Nicholson, W. J., X-ray diffraction

and electron beam analysis of asbestiform minerals in Lake Superior waters. In

Trans. Inst. Electrical Electronic Eng. (in press) (1974).

20] Beaman, D. R. and File, D. M. , The quantitative determination of asbestos fiber

concentrations. The Dow Chemical Company, unpublished report (1975).

21] Oriz, L. W. and Loom, B. L. , Transfer technique for electron microscopy of membrane

filter samples. Am. Ind. H^. Assoc. J., 423-425 (1974).

22] Rohl , A. N. , Langer, A. M. , and Selikoff, I. J., Environmental asbestos pollution

related to use of quarried serpentine rock, Science , 196 , 1319-1322 (17 June 1977).

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233
Discussion

J. LEINEWEBER: I would like to make one comment with regard to Clay Ruud's remark

about using the central channel of the chrysotile fiber for identification. This is good

a reasonable percentage of the time, but you can run into chrysotile fibers such that this

channel is not very visible and may be pretty well filled up with the non-cystal 1 i ne material. So, it cannot be used as positive identification.

C. RUUD: I know.

R. FISHER: I want to get clarification whether you advocate visual identification

from the diffraction patterns and visual counts in contrast to recording micrographs. It seems to me desirable to have your data in a form that others can confirm, look at your

diffraction patterns, look at your counts, and not rely on visual observations that are just recorded in a pad or notebook.

RUUD: I hear what you say, and I would like to record every pattern or every micrograph that is projected on the screen, but I can't afford to do this; my sponsor won't

stand for it. So, what we do is, we record typical SAD patterns we see in particular

samples or sets of samples. When we see something different than that, something unusual,

strange, we record it. I agree that it would be nice to have everything recorded for

posterity, but it takes too much time.

FISHER: Well, at this stage it is essential to have records that can be accepted by

others, I am afraid. I agree the costs are high, and people will have to pay them, but I think that any data that are not recorded for confirmation and detailed examination are going to be challenged in all kinds of situations.

RUUD: As I say, we record typical ones; we save the samples and since the samples

are on finder grids any grid can be found and the data confirmed.

J. ZUSSMAN: I'd like to make three comments concerning Dr. Ruud's paper. One

concerning electron diffraction patterns. I think he has very much underplayed the variations and variability one can get in electron diffraction patterns, depending very much

upon the orientation of the grain, the way it lays on the stage. If you look at these

patterns carefully, you see enormous numbers of different effects; I would have made this

comment anyway; I make it still much more strongly now, having heard a lot of judgments

are made perhaps without even taking photographs. From looking down on the screen you can certainly not see the subtle variations which are nevertheless important, produced by

orientation effects. i

Secondly, you mention the scanning electron microscope as being best for chemical

analytical purposes. I don't think it is capable of an accuracy that can be obtained by

the transmission electron microscope with suitable attachments, or STEM, which brings me

to the third point. You showed that lizardite and anthophyl 1 ite were not distinguishable

from their x-ray fluorescence spectra, and this is surprising. The magnesium-to-silicon

ratio for lizardite is 1.5 to 1 in atomic ratio, the other ratio is 0.9 to 1, and I think

there is a detectable difference. The reason why we may not pick up this difference is

that your crystal has the wrong kind of thickness so that the crude ratios of peak height

are not indicative of concentration. The crystal has to be of a suitable thickness for

this to be so.

RUUD: Regarding the last comment, we can rotate the fiber or change the position in

the microscope, and get different ratios, and, as someone pointed out yesterday, just be

going along the fiber you may get different ratios. So, that's one reason why I do not

have too much confidence in energy-dispersive x-ray spectroscopy. The first comment had

to do with selected-area diffraction and the variability of patterns. We do not study

them that carefully. We do not try to distinguish between the various amphiboles,

amphibole asbestos materials. We do not have the time to study individual patterns that

carefully. We looked at the possibilities of trying to get good d-spacings from them; it seems like it is a good possibility if we could connect the computer into a vidicon or a camera tube in the bottom of a TEM or STEM and put it directly into a computer; I think

that would be great. But, so far I know of only one microscope equipped that way, and it

is not used for asbestos analysis.

234

i
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

IDENTIFICATION OF ASBESTOS BY POLARIZED LIGHT MICROSCOPY

Walter C. McCrone

(Paper presented by John G. Delly)

McCrone Associates, Inc.

Chicago, Illinois 60616

Abstract

A number of analytical tools can be used to characterize and

identify asbestos: infrared absorption, x-ray diffraction, DTA, SEM,

TEM, and the light microscope. Each has advantages and limitations. The

polarized light microscope (PLM) has many advantages, and the only

disadvantages are 1) the asbestos particles must be at least a micrometer

in largest dimension, and 2) considerable training in optical

crystallography is needed.

PLM, on the other hand, is very sensitive (ppm range), extremely

rapid (1-5 minutes to identify all components of most samples) and, of

all the methods, only PLM will identify the individual amphiboles.

Keywords: Amphiboles; asbestos; dispersion staining; microscopy.

There are a number of analytical methods useful for the identification of asbestos.

These include infrared absorption (IR), x-ray diffraction (XRD), differential thermal

analysis (DTA), scanning electron microscopy (SEM), transmission electron microscopy

(TEM) with or without electron microprobe analyzer (EMA), and polarized light microscopy

(PLM) with or without dispersion staining (DS). Each has advantages and disadvantages.

Every analyst uses and should use the techniques in which he has the required

training and with which he feels confident. At the same time, every sample should

ideally be analyzed by the most suitable technique. Occasionally, of course, it may be

wise to use two or more techniques and this is certainly true for asbestos. We would like

to summarize our attitude toward the various techniques for asbestos and describe in more

detail the technique we feel has many advantages and is under-utilized; this is polarized

light microscopy, especially when supplemented by dispersion staining. First, however,

the advantages and disadvantages of each technique:

TEM is most useful for the detection and identification of asbestos fibers smaller than

the resolving power limit of the PLM. This is usually the case for water or beverages in

general. Quantitative procedures are available so that the number, size, and identity of

asbestos fibers per unit volume can be accurately determined. Identification by TEM depends

on selected area electron diffraction (SAED). Occasionally energy or wavelength dispersive

detectors are fitted to the TEM to make possible elemental analysis of individual fibers.

Nothing can compete with TEM for the analysis of samples containing subpicogram particles.

SEM has no advantage over TEM except that it takes prettier pictures. It will also

fail to see the smallest fibers, and lacking SAED it cannot identify all fibers. The

energy dispersive detector on most SEMs is not as effective as the wavelength dispersive

detectors on some TEMs and SEMs.

XRD is a useful method since it can be made quantitative. However, it cannot tell

size or shape, is not very sensitive (about 1 percent or a bit better), and does not

differentiate between most of the amphiboles. At best it supplements other techniques.

235
IR and DTA can also be dismissed for all except routine samples containing high

percentages of asbestos.

This brings us to PLM and DS on which we wish to spend more time because of our conviction that, of all the microanalytical techniques for asbestos, it is by far the most

effective. It is the only method depending on the unique optical crystal lographic

properties of the various crystal phases in the sample. These properties - refractive

indices, dispersion of refractive indices, birefringence, sign of elongation and extinction angle - are unique to the crystalline state and therefore unequivocally identify

chrysotile, anthophyl 1 ite, tremolite, actinolite, grunerite, cummingtonite, etc.

The background for dispersion staining has been adequately covered elsewhere [1]-^.

Very briefly, it imparts color to any transparent particle mounted in a liquid whose

dispersion curve intersects the dispersion curve for the particle in the visible. The

colors, related to this matching wavelength, characterize and identify any given substance. With polarized light, isotropic substances show a single characteristic color, but

anisotropic substances show different colors corresponding to the different refractive

indices in different orientations. Chrysotile, for example, shows blue and blue-magenta

colors, crosswise and lengthwise respectively, for each needle crystal when mounted in

Cargille high dispersion liquid n^^ = 1.550.

The colors shown by the various types of asbestos and a few other associated minerals

are indicated in Figures 1-20 by the wavelengths on each crystal view. These are the

wavelengths at which the liquid indicated and that direction in the crystal have the same refractive index. This matching wavelength, A,^, determines the dispersion staining colors.

TALC

Mg„(Si„0„^)(OH),

IQ 1.55 (H.D.): n's(D, H, Z)*

Q= 1.539-1.550

13 = 1.589-1.594

y= 1.589-1.600

6 =0.05 (-)

This sample (Vermont):

a= 1.546

/3 = 1.588

y= 1.589

6 = 0.045 (-)

* Deer, Howie and Zussman.

Figure 1. Dispersion staining colors shown by talc crystals in Cargille high dispersion

liquids Hp. = 1.550 and n^. = 1.580.

^Figures in brackets indicate the literature references at the end of this paper.

236
CHLORITE

(Mg, Al, Fe)^2[(^i'^)8°20l^°"^16

In 1.55 (H.D.):

pale yellow to golden yellow

n 1.580 (H.D.):

Figure 2. Chlorite.

/3 = 513 nm

n's (D, H, Z)

a= 1.57-1.66

13 = 1.57-1.67

y = 1.57-1.67

5 = 0-0.01

The sample (California):

a= 1.586

j8 = 1.587

y= 1.596

5 = 0.010 {+)

Figure 3. Chrysotile.

CHRYSOTILE

In 1.550 (H.D.):

660 nm

530 rnn

iS = 556 nm

= 530 nm 13

n's (D, H, Z)

0-= 1.532-1.549

p = 1.540-1.553

y= 1.545-1.556

5 = 0.013-0.007 (-)

King's Mine, Quebec Sample -»fv= 1.5444

/3 = 1.5525

y= 1.5555

5 = 0.0111

ANTIGORITE

Mg3(Si^O^)(OH)^ Figure 4. Antigorite.

In 1.550 (H.D.):

a= 520 nm

468 nm"

n's (D, H, Z)

a= 1.558-1.567

)3= 1.56 -1.57

y= 1.562-1.574

5 = 0.004-0.007 (-)

This sample:

a= 1.555

j8 = 1.559

y= 1.561

6 = 0.006 (-)

237
LIZARDITE

In 1.55 (H.D.):

520

=^494 nm

a = 690 nm

494 rnn

undulose extinction

n's (D, H, Z)

a= 1.538-1,544

7= 1.546-1.560

6 = 0.016-0.008

This sample:

Q?= 1.545

)3= 1.555

7= 1.557

6 = 0.012 (-)

Figure 5. Lizardite.

TREMOLITE

Ca^CMg, Fe^^g(Sig022)(OH, F)^

(low Fe)

In 1.580 (H.D.):

a = 439 nm

i/3 = 385 nm

'irU' y"=300 nm j

n's (D, H, Z)

a = 1.604-1.619

/3 = y= 1.627-1.642

6 = 0.021-0.023 (-)

In 1.605 (H.D.)

a= 678 mn This sample:

0-= 1.599

/? = 1.610"^

y = 1.621

6 = 0.022 (-)

Figure 6. Tremolite.

238
ACTINOLITE

Ca2(Mg, Fe)g(Sig022)(OH, F)^

(20-80% Fe & 80-20% Mg)

In 1.605 (H.D.):

a- 436 nm

7 < 400

1

, j8 < = 385 nm

y'< 400

In 1.640 (H.D.):

|, 0= 658 nm — = 578 nm

540 nmj

n's (D, H, Z)

a= 1.619-1.668

13 = y = 1.642-1.687

6 = 0.023-0.019 (-)

This Sample (Virginia):

a= 1.633

/3 = 1.641

y = 1.647

6 = 0.014 (-)

Figure 7. Actinolite.

ANTHOPHYLLITE

(Mg, Fe^^^(Sig022)(OH,F)2

In 1.580 (H.D.):

P

= 370 nm

y = 300 nm

» 0=421

*l» y =30

ima = 300 nm

n's (D, H, Z)

a= 1.596-1.694

/3 = 1.605-1.710

7= 1.615-1.722

6 = 0.013-0.028

(+) (-)

In 1.605 (H.D.):

j8 = 465 nm

7 = 395 nm

a= 598 nm

7 = 395 nm {

This sample (Pine Mt. , Ga

a= 1.601

/3 = 1.618

7= 1.628

6 = 0.027 (-)

Figure 8. Anthophyll ite.

239
ANTHOPHYLLITE

(Mg. Fe^^)^(Sig022)(OH,F)2

In 1.640 (H.D.):

(Mg>Fe)

13 = 438 nm

y = 409 nm

»

Q= 463 nm

y = 409 nm [

n's (D, H, Z)

a= 1.596-1.694

i3 = 1.605-1.710

7= 1.615-1.722

6 = 0.013-0.028

(+) (-)

In 1.67:

633 nm

557 nm

= 730 nm

= 557 nm

This sample (Connecticut):

a= 1.659

13 = 1.666

7=1.674

5 = 0.015 (+)

Figure 9. Anthophyll ite.

GRUNERITE

(Fe''^,Mg)^(Sig022)(OH)2

(high Fe)

In 1.670: n's (D, H, Z)

a= 1.663-1.686

13= 1.681-1.707

7= 1.697-1.729

6 = 0.034-0.043 (-)

In 1.700:

a » 700 nm

'Vs660 nm

jS » 700 nm

This sample:

a= 1.669

/3 = 1.684

7= 1.697

5 = 0.028 (-)

Figure 10. Grunerite.

240
CROCEDOLITE

+2

(no Mg, contains Fe )

In 1.670:

13 = 396 nm

rnn

7 = 380 nm

T a - 415"] nm

n's (D, H, Z)

q;= 1.654-1.701

i3 = 1.662-1.711

7= 1.668-1.717

6 = 0.006-0.016 (-)

In 1.700:

/3 = 555 nm

0^604^nm

519 qm

This sample (Orange River,

South Africa):

a= 1.698

13 = 1.703

7=1.708

5 = 0.010 (-)

Figure 11. Crocidolite.

APATITE

Cag(PO^)g(OH,Cl,F)

oj = 408 nm

408 nm

n's (D, H, Z)

e = 1.624-1,666

0) = 1.629-1.667

6 = 0.001-0.007 (-)

IQ 1.64 (H.D.):

e = 715 nm

40 nm

CO = 640 nm

= 640 nm

This sample:

e = 1.6295

o) = 1.6357

6 = 0.0062 (-)

Figure 12. Apatite.

241
FORSTERITE

Mg2SiO^

In 1.640 (H.D.):

nm

nm

n's (D, H, Z)

a= 1.635*-1.827**

i3= 1.651 -1.869

y= 1.670 -1.879

5 = 0.035 -0.052 {+) (-)

*pure forsterite

**plus Fe^"^ replacing Mg

giving fayalite, Fe^SiO^

This sample:

0-= 1.643

/3 = 1.663

y= 1.682

5 = 0.039 (-)

Figure 13. Forsterite.

HORNBLENDE

(^^'^)0.1-0.7^^2^^^'^^''''^^'"''^^>5(''6-7'^2-lV(°^'^>2

In 1.605 (H.D):

L

a = 424 nm

y fJ^60 nrcj

6* ' -- ^

jS = 390 nm

y'= 370 nm

n's (D, H, Z)

a= 1.615-1.705

/3 = 1.618-1.714

y= 1.632-1.730

6 = 0.014-0.026 (+)

a= 570 nm

In 1.640 (H.D); This sample:

a= 1.643

)8 = 1.650

y= 1.660

6 = 0.017 (+)

Figure 14. Hornblende.

242
WOLLASTONITE

Ca(SiOg)

In 1.580 (H.D.):

I tt= 412 nm

-^/3 = 340 nm

V y s 300 nm

= 340 nm |

n's (D, H, Z)

o;= 1.616-1.640

13 = 1.628-1.650

y = 1.631-1.653

6 = 0.015-0.013 (-)

In 1.605:

a= 532 nm

|8 = 429 nm

110 nm

This sample:

q;= 1.612

/3 = 1.628

7= 1.632

6 = 0,020 (-)

Figure 15. Wol lastonite.

CALCITE

CaCO„

In 1.64 (H.D.): n's (D, H, Z)

700 nm

460 nm

e = 1.486-1.550

CO = 1.658-1.74

5 = 0.172-0.190 (-)

This sample:

€'= 1. 525

e = 1.486

GO = 1.653

6 = 0.167 (-)

Figure 16. Calcite.

243
DOLOMITE

(Ca,Mg)COg

111 1.64 (H.D.): n's (D, H, Z)

In 1.67:

Figure 17. Dolomite.

MAGNESITE

MgCO„

Li 1.670: n's (D, H, Z)

e =-- 1.509-1.563^

Gj = 1.700-1.782

6 = 0.190-0.218 (-)

*with Fe replacing Mg

In 1.700: This sample:

00 = 1.694

Figure 18. Magnesite.

244
QUARTZ

SiO^

In 1.550 (H.D.): n's (D, H, Z)

CO = 682

= 682 rnn

oj = 1.544

e = 1.553

5 = 0.009 (+)

This sample:

00 = 1.544

G = 1.553

Figure 19. Quartz.

ORGANIC FIBERS (1. 550 liquid)

Paper fiber

Figure 20. Organic fibers.

Although we speak of dispersion staining colors as specific for a given substance in

a given liquid (at a given temperature) we sometimes observe closely similar colors for

other substances. We must, especially when this possibility exists, make sure that we observe enough data to be able to state with certainty that the substance is, say,

chrysotile. It is not sufficient to observe the proper color in one direction - both

chrysotile and paper fibers can show the same blue color perpendicular to their lengths.

Nor is it sufficient to observe the two colors on a single view of a crystal - both quartz

aad chrysotile can have two colors in common. If all colors shown by the crystal in all

orientations correspond to the known data for a given substance, and if the crystal

morphology shows the colors to be oriented properly, there is then very little chance of

mis identification.

245
Another serious complication, especially with minerals, is the eff_ect of substitutional solid solution oji the optical properties. The substitution of F for OH , Fe^

for Mg2 , or Ca^ for 2Na can drastically change the optical properties of many minerals.

One of the most serious in this respect is anthophyl 1 ite. Nominally Mg7Si8022(0H)2

,

anthophyl 1 ite forms a continuous series of solid solutions with iron replacing magnesium

(Table 1) with corresponding changes in the refractive indices and dispersion staining

colors. Anthophyl 1 ite can also have up to 14 percent MnO, 10 percent ZnO, or 15 percent

AI2O3 with corresponding variations in the optical properties. Figures 8 and 9 show the

dispersion staining properties for two different anthophyl 1 ites , one from Connecticut and

the other from Georgia. In spite of the wide differences between these two anthophyl 1 ites

,

both samples show parallel extinction, a unique characteristic among the asbestos minerals,

and the birefringence values, y-p, p-a, and y-a, as well as the optic axial angle remain

quite uniform or change progressively and uniformly as the composition changes. If, for

example, one observes refractive indices in the anthophyl 1 ite range, the possibility of

tremolite, actinolite, ferroactinol ite, or cummi ngtonite should be considered. The index

range will tell which is present, and all of the latter differ from anthophyl 1 ite in that

they show oblique extinction, usually about 20° rather than parallel extinction. In other

words, anthophyl 1 ite is orthorhombic ; all other amphiboles (and chrysotile) are monoclinic.

Table 1. Optical properties in the anthophyl 1 ite

solid solution series.

- Refractive indices -

% Fe a § 1 2y

0 1,.596 1.608 1.615 120(-)

20 1,,622 1.632 1.642 91(-)

40 1,.641 1.650 1.665 68(+)

•

^ From Deer, Howie

,

and Zussman, "An Introduction

to the Rock-Forming Minerals," Longmans, London

(1966), pages 156-7.

Many interfering substances are just not fibrous, hence they can be ignored if only

asbestos is the target. Quartz has only two refractive indices, 1.544 (w) and 1.553 (e),

but these fall within the range of chrysotile, a = 1.544 and y = 1.558. However, chrysotile

is very fibrous whereas quartz is usually flakes or chips. Chrysotile shows three refractive indices a, p, and y and a low 2V = 30-35° (+) and always shows nearly the maximum

birefringence, 0.014 or 0.012. Quartz can show any birefringence value between 0.000

(u)-u)) and 0.009 (e-iu) depending on orientation. Even a thin sliver of quartz oriented to

show e and u) (and therefore chrysotile colors) can be bounced into other more nearly

isotropic orientations by tapping on the coverslip with a needle.

Organic fibers are not generally confused with asbestos because they have obvious

morphological differences, e.g. , pits, twists, central lumens, nodes, cross-over marks,

etc. However, if mechanically broken down into tiny fibrils they lose this obvious

morphology and some, e.g. , wool and other animal hairs, may closely resemble chrysotile in

optical properties. A careful examination of such fibers morphologically and optically

will usually, however, end any confusion and permit certain identification.

Glass or mineral wool may happen to show a color near the chrysotile range but these,

of course, are isotropic and morphologically quite distinctive.

With careful application, dispersion staining is capable of rapid certain identification of any transparent substance whose optical and morphological properties are known.

It also quickly differentiates between fibrous and nonfibrous minerals and detects traces

of any substance in extraneous mixtures.

246
Reference

[1] Brown, K.M. , McCrone, W.C., Kuhn, R. and Forlini, L. , Microscope 13 311; 14 39

(1963).

Discussion

J. ZUSSMAN: I enjoyed this very beautiful demonstration of the method. This is an academic question, but I think I remember a phenomenon called "form birefringence" which

is supposed to be effective in giving peculiar results for very fine particles of small

dimensions. If you have a very fine piece of an isotopic material, there is a shape

factor which can make it appear to be anisotropic. I wonder if you get any anomalies with

this method coming up, particularly with chrysotile, with fine fibrils, because of form.

I think it is called form birefringence.

J. DELLY: To answer your question, yes, there is an effect, but we don't apply this

technique to a single isolated fiber, so there is not really much chance of being wrong on

that. I agree with you, it is extremely fascinating academically, but in a practical

sense with a bulk sample there are so many fascinating things associated with it that one

spends actually a great deal of time with any one sample playing with colors.

R. DRAFTZ: We have been using some of the techniques, and run into a problem with

paper fibrils, especially with parenteral contaminants. I wonder if you tried the

dispersion technique with chrysotile and with paper fibrils and perhaps found some similarities in color since the refractive index range is about the same.

DELLY: You will see that the highest reported value of y of chrysotile (Deer, Howie,

Zussman) is 1.556. Ao in 1.550 HD refractive index liquid is about 515 nm. Figure 20 of

the article shows that paper fibers in liquid 1.550 will show a Xo of 450 nm parallel to

the fiber. This wide difference in wavelengths should be easily discerned by most people.

In any case, the microscopist is in the enviable position of settling the matter finally

by resorting to the familiar cuoxam test to detemine whether a given fibril is cellulose

or not.

J. LEINEWEBER: I appreciate your very elegant description of the technique, and it

has aroused a lot of questions in my mind about how the dispersion staining really works,

but I would also appreciate a comment or two on the advantages of this technique over ordinary petrographic techniques for fiber identification, and also the size limits that

you are confined to in working with particular particles.

DELLY: Those are a couple of very good questions. First one: The major advantage

is speed. For somebody who does primarily dispersion staining, he can complete an analysis in, probably, under five minutes. It is cheap and it is fast. It is a very

quick survey type of thing, a very quick confirmation. I think that is probably the

primary advantage of the technique. But the lower limit is a bit tricky. The abstract

says that the major dimension should be one micrometer, which, if you are going to use

3:1, makes it about 0.3 pm or 0.25 pm for the minimum. This technique does not depend on resolving power. It could not; otherwise you would not put all these stops in the back

focal plane that deliberately destroy the resolving power. But, the spread of the light

is all you are really looking for. You don't want to see the particle. So, that the

lower limit is probably nominally around 0.3x1 pm. The reason I say nominally is, as with

any other technique, when you go to the limits of any instrumental technique, the art

starts coming in as well as the science. There is no reason though, why you could not

apply this technique with higher-aperture objectives as well and still carry it further

down. I have not personally done it.

V. WOLKODOFF: I just cannot see the advantage of this particular technique compared

to classical techniques. For example, even if crocidolite does or does not show the blue

color, you can pick it up immediately under crossed polars. We have no difficulty

whatever using classical methods for the time element or whatsoever the case may be.

And as one gentleman pointed out, for paper fibers or textile fibers we can pick that up

instantaneously. Also, we are looking for the resolution, and, as you well know, materials

247
containing asbestos fibers contain other materials as well. I must agree that the slides

are extremely glamorous and picturesque, but I really believe that there is just no substitute for the classical petrographic or optical mineralogy when it comes to solid

solutions that exist in several of these asbestos series. I just want to go on record

on that.

DELLY: Dispersion staining methods do not exclude classical methods; indeed, they

are used simultaneously. The commercial form of the dispersion staining objective has

three positions of use: a central stop, an annular stop for dispersion staining, and a position free of any stops which is used for classical methods in conjunction with

dispersion staining.

I

248

i
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

MINERAL FIBER IDENTIFICATION USING THE ANALYTICAL TRANSMISSION ELECTRON MICROSCOPE

D. R. Beaman and H. J. Walker

The Dow Chemical Company

Midland, Michigan 48640

Abstract

In a transmission electron microscope equipped with an energy

dispersive spectrometer (EDS), it is possible to obtain the high resolution morphology, crystal structure, and elemental composition of submicron mineral fibers, particulate, and thin films. The reliability of

fiber analysis is enhanced when fiber identification is based on the

nearly simultaneous determination of these three characteristics because

each of the individual modes can yield ambiguous information. Energy

dispersive spectrometer data can be converted to elemental fiber

compositions using known standard spectra or relative sensitivity

factors which can be calculated or experimentally determined for a given

instrumental configuration. Calculated and experimental sensitivity

factors are found to agree within 15 percent for photon energies above

1.5 keV. The relative error in composition calculated from EDS spectra

will generally be better than 10 percent, but only if the TEM column and

components have been properly modified to reduce the effects of

extraneous x-ray generation and electron scattering. The sources of

these problems are described and a procedure for minimizing the effects

outlined. Proper aperturing, collimation, selection of materials of

construction, and operating conditions can provide useful mineral

spectra. It is often necessary to correct for x-ray absorption even in

fine mineral fibers, and this may be done using reference standards or sensitivity factors corrected for absorption. The effect of absorption

increases rapidly as the difference between the mass-absorption

coefficients of the elemental constituents of the mineral increases.

Carbon contamination which degrades both EDS spectra and electron

diffraction patterns can be minimized by using low current density and

short analysis times.

Less than 15 percent of the chrysotile fibrils in a standard

provided positive selected area electron diffraction patterns (SAED),

but up to 50 percent did have the correct layer line spacing. The

fraction of fibers providing good diffraction increases rapidly as the

number of fibrils in a fiber increases. The reported differences in SAED

quality arise primarily because investigators use differing criterion

for defining a positive SAED pattern and the fiber size distribution

examined varies. Sample preparation methods were reviewed and it was found that condensation washing is only reliable if loss corrections are applied, particularly in the case of amphibole fibers. In spite of the

many problems, inter- laboratory and multiple sample reproducibility in

the measurement of fiber concentrations can be ±30 percent when using

good procedures.

Key Words: Carbon contamination; electron diffraction; mineral fibers;

transmission electron microscope; x-ray spectroscopy.

249
Introduction

The need to identify and determine the concentration of small mineral fibers in

environmental samples provided motivation for the development of the analytical transmission electron microscope (ATEM) which consists of a conventional transmission electron

microscope (CTEM) equipped with energy dispersive spectroscopy (EDS) and possibly scanning

transmission electron microscopy (STEM) capabilities. In such an instrument it is possible

to obtain from very small volumes of material high resolution morphology in the TEM or STEM mode, elemental data using the EDS, and structural information for crystalline

materials in the selected area electron diffraction (SAED) mode. When identification is

based on the nearly simultaneous determination of three quantities-morphology, elemental

composition, and crystal structure-the reliability of the analysis is significantly

improved because the individual modes sometimes yield ambiguous information. The limitations of each mode have been discussed previously [1,2]^. All modes are adversely

affected by the presence of adjacent non-fibrous debris and overlaying films. Fibers that

are too thin or too thick do not provide sufficiently good SAED patterns for positive

identification by comparison with standards. Less than 15 percent of the chrysotile

fibrils in a particular standard gave positive SAED patterns. Chrysotile diffraction is

further degraded by electron beam bombardment and instrumental contamination. Energy

dispersive spectrometry is not a panacea because there are different minerals with similar

compositions and elemental substitution is common. Morphology is often compromised by the

environment and interfering solids. The hollow-core or tubular appearance of chrysotile

is distinctive but often absent and degraded during analysis. It is difficult to establish

a protocol for basing identification on three criteria, but when this is done the quality

of the analysis is significantly improved.

This paper describes some of the difficulties associated with fiber counting in the

ATEM with the goal of circumventing the problems. The data from an energy dispersive

spectrometer can be converted to chemical concentrations but there is a need to calibrate

the instrument and correct for x-ray absorption even in very fine fibers. There are instrumental limitations which degrade EDS spectra but can, to some extent, be avoided.

Contamination seriously affects both the EDS spectra and SAED patterns, but there is

little that can be done to avoid it in existing instruments other than to understand the

problem. The reasons for the controversy concerning the quality of SAED patterns from

mineral fibers are examined and criteria suggested for classifying chrysotile SAED

patterns. Sample preparation methods are reviewed and some results of inter- laboratory

reproducibility are presented.

Sample Preparation

The three methods of water sample preparation that are commonly used are summarized

in table 1 and references 1-6. Water is vacuum filtered through 0.22 pm Millipore or

0.1 pm Nuclepore filters. Nuclepore has the advantage of being smooth and therefore not

generating a replicated structure when carbon coated; it has the disadvantages of being

prone to fiber loss during handling and sporadic occurrences of non-uniform solids

deposition during filtration. Millipore retains fibers well but generates a structured

background if carbon coated prior to destruction of the filter structure.

In the method of condensation washing [1,2,6], TEM grids with carbon-coated Formvar

films are positioned on the Ni support screen of the cold finger in a condensation washer.

A piece of Whatman filter paper placed between the TEM grid and the Ni support screen has

been shown to reduce fiber loss during solvent extraction [7]. The grids are preconditioned by the application of a few drops of acetone beneath the Ni support screen

to prevent warping of the filter section. The filter sections are placed, sample side

down, on the TEM grid immediately following pre-conditioning. The Millipore is removed in

10-50 minutes of acetone vapor extraction. The complete procedure and sources of errors

are described elsewhere [1,2].

^Figures in brackets indicate the literature references at the end of this paper.

250
Table 1. Method of preparing liquids for ATEM analysis.

Method Jaffe-fusion Jaffe-wick Condensation washing

reference

filter medium

pre-treatment

fiber fixation by vacuum evaporation

of carbon

pre-conditioning

extraction

configuration

solvent

duration of

extraction

3,4

0. 22 ym Mill ipore

fused in acetone

vapor for

5-10 minutes

yes

none

filter section on grid on polyurethane in

enclosed petri

dish

acetone

12 hours

5,6

0. 1 ym Nuclepore

none

yes

10 yL droplet of

solvent onto sample

positioned on grid

filter section on grid on wire mesh

on several layers

of filter paper in

enclosed petri dish

chloroform

10-24 hours

1,2,6

0.22 ym Mi 11 ipore

none

no

acetone wetting of

grid without

filter

filter section on grid on cold finger

in reflux column

acetone

10-50 minutes

,^ In the Jaffe-wick method [5,6], the Nuclepore filter is carbon coated after

filtration to fix the solids in place prior to filter extraction. The TEM grid is

positioned on a wire mesh placed on several layers of filter paper in a petri dish. The

j carbon coated filter section is positioned on a grid and a 10 |j1 droplet of chloroform is

added to prevent warping. The layers of filter paper are saturated with chloroform and

the Nuclepore extracted slowly (10-24 hours) in the covered petri dish.

( In the Jaffe-fusion method [3,4], a portion of the Millipore filter is attached to a glass slide and placed for 5-10 minutes in acetone vapor. This short pre-treatment in

acetone destroys the structure of the Millipore and therein avoids the formation of a replicated network structure during carbon coating which would interfere with fiber

counting. The fused Millipore on glass is carbon coated and then extracted using acetone

in the same manner as in the case of the Jaffe-wick method.

One of the prime sources of error in the analysis is the fiber loss which occurs

during sample preparation. Condensation washing is a popular method of preparation, but

it introduces variability in the results and yields higher fiber losses than Jaffe-type

methods [1]. While some investigators have obtained good results with condensation

washing [8,9], there are a sufficient number of technique problems [1,2] so that serious

differences occur in i nter- laboratory comparisons. It is possible to correct for the

losses associated with condensation washing using partially-extracted Jaffe samples to

determine the total fiber concentration [1]. This requires additional preparation time

and TEM analysis. Fortunately the chrysotile losses associated with condensation washing

are usually below 20 percent [1] and can be considered insignificant if the duration of

wash is less than an hour in a properly controlled washer. We have obtained reproducible

results using Jaffe extraction of carbon-coated Nuclepore [2] and loss corrections in

conjunction with condensation washing.

251
All of the above discussion refers to water samples. In preparing air samples it is

preferable to low- temperature ash the filter because of the heavy filter loading

associated with air sampling. The ash is then suspended in water and processed as a water

sample. Because the ash tends to be clumped, it is necessary to subject the suspended ash

to ultrasonic treatment.

Instrumental Limitations

|

Instrumental problems arise when using energy dispersive spectrometers, because TEMs were never intended to be used in quantitative chemical analysis and ATEMs have been

constructed by retrofitting EDS and STEM capabilities to existing systems. There are two

prime sources of the instrumental problem: 1) the EDS is not a focusing spectrometer and

is insensitive to the location of the x-ray source and, thus, will detect all x-rays with

a 1 ine-of-sight path to the detector [3]; 2) in a typical CTEM column there is, in a confined volume, a high density of hardware such as pole pieces, apertures,

anti-contamination surfaces, sample grids, samples holders and associated clips. These

two features combine to yield remote x-ray generation, i.e., x-radiation originating from

regions outside of the volume excited by the primary electron beam. This causes: 1)

spectral peaks unrelated to the sample to appear in the EDS spectrum leading to

quantitative inaccuracy and errors in identification; 2) increased background radiation

which raises the detectabi 1 ity limits; and 3) a loss in spatial resolution. The sources

of the problem are secondary fluorescence by characteristic and continuous radiation

generated in the column apertures, backscattered electrons from the sample and its

support, and scattered primary electrons.

The use of high voltages to penetrate thin samples and retain good spatial resolution

leads to the generation of characteristic and continuous radiation in column apertures.

The second condenser (C2) variable aperture, which is the last aperture above the sample,

poses the most serious problem. The maximum in the generated continuum at a beam energy

of 100 keV and PtKa characteristic radiation both have wavelengths of about 0.2^ and are readily transmitted by thin Pt apertures, e.g., over 40 percent of the O.2A Pt radiation

is transmitted by an 100 pm thick Pt aperture. Most of this radiation will be dissipated

by absorption in the column but any that does reach the sample area can generate secondary

fluorescence at and near the sample which is unrelated to primary electron beam

excitation.

Because almost all primary electrons are transmitted by thin films and small

particles, the backscattered electron fraction is small as indicated for Au films in

figure 1 [11]. If the beam voltage is high and the sample thin, less than 5 percent of

the incident electrons will be backscattered. Any electrons that are backscattered toward

the detector can penetrate the 7.5 pm Be window of the EDS because they will, for the most

part, have energies close to the incident beam energy. Eighty percent of the 100 keV

electrons can penetrate 7.5 pm of Be and in so doing lose less than 5 percent of their

energy. Most backscattered electrons do not reach the detector because they are confined

by the strong objective lens field. They can, however, excite remote particulate matter

and the support grid.

f

252
Figure 1. The percentage of backscattered electrons as a function of

incident electron energy for two different thicknesses of

Au. The data are from Philibert and Tixier [11].

Scattered electrons in the column cause electron beam tailing [12] which leads to

excitation of areas in the sample immediately adjacent to the region of primary beam

excitation. This effect is due to improper alignment and scattering by column components

and increases in severity as the beam voltage is lowered.

The following list indicates some steps that may be taken to alleviate these

instrumental problems. The magnitude of the problem and, therefore, the effectiveness of

these alterations will vary appreciably from one instrument to another because of

differences in electron optical configurations, alignment procedures, column cleanliness,

aperturing (sizes, materials, thicknesses, and location), and operating mode (TEM vs. STEM).

I. Reduce the generation in and transmission of radiation by column apertures.

a) Use thick apertures [13]

b) Use Pt apertures rather than Mo or Ta [12,14]

c) Use column inserts somewhere between C2 and the sample [15]

d) The use of low acceleration potential reduces this problem, but promotes beam

tailing, backscattering, and absorption effects

e) Determine if performance depends upon the emission current for the instrument

being used and the type of sample being studied

II. Reduce the excitation of material remote to the sample.

a) Specimen holders, specimens clamps, and supp.ort grids should be made of low

atomic number materials (Be, graphite, or polymer) or coated with such

materials [1,13,16]

b) Use support grids with maximum open area [13]

253
c) Coat components near the specimen such as anticontamination devices and sample

support rods with low atomic number materials (Aquadag®)

d) The objective aperture must be removed during EDS data acquisition

e) The sample support film should be as thin and have as low an atomic number as possible

f) Operate at as low a tilt angle as will provide adequate EDS intensities (less area of grid exposed to excitation)

III. Optimize the EDS detector configuration.

| a) Use the greatest Si(Li) crystal -to-sampl e distance that will provide adequate

count rates [17]

b) Colli mate the detector with a low atomic number material

|

c) The collimator should be thick enough or shielded with sufficient material (high

z) to absorb any stray radiation [18]

IV. Minimize electron scattering (

a) Use a small (100 pm) condenser aperture [14]

b) Operate at high acceleration potential

| c) Have the column clean and properly aligned

These effects of extraneous radiation can best be examined by comparing spectra

obtained on and off the edge of a thin film or fiber or by comparing the spectra obtained

with the beam positioned in a hole (hole-count) [12] with spectra obtained on the sample.

In performing on- and off-film measurements on a Sn-Cu-Cr film, 3 percent of the Cr

intensity was attributable to Cr plating on the sample hold-down clip while the Cu TEM

grid was responsible for 15 percent of the Cu signal. Insertion of an aperture just

beneath the variable C2 aperture on a Philips EM300 operated in the TEM mode increased the

Cu peak-to-background ratio and reduced the off-film Cu by 35 percent. The maximum peakto-background ratios have been achieved using a column insert (1 mm ID x 2.57 mm OD x 3mm

thick) in the lower end of the vacuum tube through which the variable C2 aperture passes.

Kyser and Geiss [18] have found that operation in the STEM mode reduces the extraneous

background by about a factor of two.

Even after these precautions have been taken, it is still advisable to subtract the

off-fiber spectrum from the fiber spectrum and to use as dilute a sample as feasible. A

high density of solids on the grid may reduce the analysis time required to find fibers,

but it seriously degrades the quality of SAED patterns and EDS spectra.

Quantitative Analysis

There are two aspects to quantitative fiber analysis of environmental samples in the

ATEM, namely, the proper identification of the fibers coupled with the accurate determination of the number of fibers per unit area. When the concentration of a specific mineral

is sought the best procedure is to compare unknown spectra and diffraction patterns with

those obtained from wel 1 -characterized standards in the same instrument using constant

operating conditions. When unknown samples are encountered, it is advisable to compare

ATEM data with the results of x-ray diffraction, infrared spectroscopy, and x-ray fluores- cence in conjunction with a careful consideration of the mineralogy of the problem. When

the fibers, particles, or films of interest are thin, the following expression, originally

proposed by Duncumb [19] and pursued by Cliff and Lorimer [20] and Russ [21], can provide

good results:

254
(P-B)^

'AB iray (1)

B

where I is the net peak intensity corrected for background and peak overlap and S^g is a

relative sensitivity factor, i.e., the ratio of the detected intensities (Ig°/I^°) for two

pure thin standards of the same mass thickness. Absorption, secondary fluorescence, and

backscattering effects must be negligible for eq. (1) to be applicable. S^g is most easily

measured on multi-element thin standards of known composition.

There are not many experimental data and the bulk of what is available has been published by Cliff and Lorimer [20] and Sprys and Short [22]. S^g can be calculated from the

following expression which is fully discussed elsewhere [21,23,24]:

'AB

B

lO^Z^g

^A

C,B

^CA^^Pv p Be

In / ^0

X,A ^C,B V p Be

13.9x10

-4

13.9x10'

(2)

The subscripts A and B refer to the elements A and B. A is the atomic weight, z is the

atomic number, G is the fractional emission in the line of interest, e.g., G(Kai2) = ^(^12

intensity/(Kai2 intensity + Kp intensity), is the acceleration energy in keV, is

the excitation energy in keV, and p/p Beis the mass absorption coefficient for A or B

radiation by the 7.5 pm Be window on the EDS detector.

Note that this expression shows no dependence on the instrumental configuration.

However, S^g values determined in different instruments may differ from each other and

from theoretical values because: 1) the contribution of secondary fluorescence, backscattering, and beam tailing may be vastly different in different instruments; 2) the Be

window thickness and detector efficiencies may be different and, in some instances, the Si

dead layer and Si crystal thickness may be significant; and 3) the samples used to measure

S^g may not be truly thin with respect to absorption.

Figure 2 compares the values calculated from eq. (2) obtained using the Reed and Ware

[25] values for G with the experimental values of Cliff and Lorimer [20]; the ratios are relative to Si, i.e., B = Si. As noted by Goldstein et al . [23] the agreement is poor

below 2 keV and good above 2 keV. Table 2 also compares calculated and experimental S

AB

values. For S.'Mg Si' ^Al Si' ^Ti Si'

^"'^ ^Fe Si' agreement in the experimental values

is generally better than 13 percent (fractional standard deviation or coefficient of

variation), notwithstanding the variation in experimental configuration and conditions.

With the exception of the S^^ and S^^ the agreement between theory and experiment

is better than 15 percent. The S^^ value determined from eight different mineral fiber

standards using the data of Beaman and File [1] was 1.7 ± 0.2 (± 14 percent). This variation is primarily due to inaccuracies in the bulk chemical analysis of the mineral fibers.

If IC = 1 and the S values are all relative to Si,

(3)

255
Table 2. Calculated and experimental values of the relative sensitivity factor,

^A-Si radiation.

Investigator and

Conditions

Experimental S^,^^ Values

^Na-Si ^Mg-Si ^Al-Si ^Ti-Si ^Fe-Si \u-Si

Cliff & Lorimer[13]

EMMA-4 100 kV 5.77

0=0° ^=45°

amphibole particles

Beaman & File[2]

EM300 80 kV

0=39° 1'=26°

asbestos fibers=0.1 ym

Sprys & Short[41]

EM300 100 kV

silicide particles

Morgan et al . [30]

EM300 80 kV 3.92

1^=42°

3 ym i so-atomic drops

Suzuki et al.[42]

JEOL lOOC 400 kV

0=0°

mineral fibers

2.07 1.42 1.08

1.7 ± 0.2 1.4 ± 0.2

1.55

1.7

1.22

1.16

1.08

1.13

1.3

1.27

1.25

1.30

1.38

2.5

1.58

Calculated S^_^^ Values

Goldstein et al.[22]

100 kV.

This report Eq.[ll]

100 kV

Russ[4]

100 kV

1.66

1.52

2.01

1.25

1.13

1.39

1.12

1.09

1.12

1.16

1.07

0.95

1.33

1.22

1.12

1.59

1.46

1.34

0 = tilt angle ^i* = x-ray take-off angle

256
Figure 2. Relative sensitivity factors, , for Ka radiation as a function

of the atomic number of element A. The curves are calculated from

eq. (2) and the points are experimental values from Cliff and

Lorimer [20]; from Beaman [24].

Other relative sensitivity factors can be calculated from the Si values because

S /S = S

If the S values are not relative to Si

V^^A-^^^g^i.A^)-

o We measured the composition of a 3000A thick Cu-Sn-Cr film on a Cu TEM grid using

Philips EM300 CTEM at 80 keV and a Cameca electron probe operated at 25 keV. The results

are shown in Table 3 and compared with bulk chemical results. The ATEM results are seriously degraded by the secondary fluorescence and electron scattering as evidenced by

the high Cu value resulting from the use of a Cu TEM grid. Off-film spectra were subtracted

from the film measurements. The Cr/Sn ratio which is independent of the scattering problems

is in good agreement with the chemical data (relative error = 11 percent). The Cu grid

was used to demonstrate the difficulties associated with quantitation in the ATEM. As

indicated previously, the results will be improved by using low atomic number grids and

grids that do not contain any of the elements present in the sample. The results obtained

in the electron probe, where scattering problems are minimized by the instrumental configuration and the use of low acceleration potential, are excellent (relative error <10 percent).

From these limited data and other reported results on thin films [20,26], we conclude that

the thin film model of eq. (1) is valid and capable of providing relative errors of less

than 10 percent when using experimentally determined S^g values. This represents reasonably

good performance when compared with the 5 percent relative error obtained using EDS

systems and bulk samples [27]. However, it must be stressed that this will only be

attained in CTEMs after taking the precautions described previously. The accuracy will be

best when measuring concentration ratios. The presence of oxide films or organic contamination on the surface and the tendency for surface segregation and particle inhomogeneity to occur complicates and degrades quantitative results.

257
Table 3. Experimental composition of a 3000 A thick Cu-Sn-Cr film.

Method Element

Composition in weight percent

Cu Sn Cr Cr/Sn

Neutron activation

ATEM at 80 keV

with S.r, values

Mb

Electron probe at 25 keV

with S^g values and

absorption corrected

Electron probe at 25 keV

with S-D values but

HD

no absorption correction

14.6

27

15.6

16.4

77.6 7.8

67

76.7 7.6

76.3 7.3

0. 101

0.090

0.099

0.096

Correction of Quantitative Data

It has generally been assumed that if the sample was transparent to electrons, i.e.,

structure was visible in the TEM image, then the sample was sufficiently thin so that the

only consideration necessary in quantitative analysis was the variation in x-ray generation

by the primary electron beam. The loss of ionization through backscatteri ng will generally

be negligible for sub-micro diameter mineral fibers, if the acceleration potential is

above 80 keV. From figure 1, it is seen that for an lOOoA film of Au the voltage could be

as low as 50 keV and the backscatter fraction still below 10 percent, whereas over 50

percent would be backscattered by a bulk material.

1 s t«lnegligible and

[j/p is the mass

f 1 uorescence

B line

al loy

material. It is not presently

Philibert and Tixier [11] have found that continuous

that characteristic fluorescence will be negligible if p/p

absorption coefficient for the exciting radiation, B, by the

clear how significant the characteristic fluorescence correction is for thin films because

the limited accuracy of the analysis in most CTEMs obscures the effect of characteristic

fluorescence. In order to make any corrections to the data, it is necessary to know the

thickness which certainly complicates the analysis and detracts from the simplicity of

standardless correction. However, for particles and fibers the thickness can often be

accurately estimated from the TEM image.

Absorption effects in the analysis of mineral fibers were reported by Beaman and File

[1] and figure 3 shows the dependence of I^/I^^. on fiber size for various minerals. The

ratio of intensity ratios at one fiber radius (r^) to those at another fiber radius (rg) can be determined from Beers law.

258
1.0

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Figure 3. Elemental intensities ratioed to the Si intensity as a function of mineral

fiber diameter. The scales for chrysotile, grunerite, and amosite are on the left and on the right for ferroactinol i te and hornblende.

Si / r.

Si / r.

exp

exp

exp

exp

m

Pm "^1

Si

m

^m "^2 ^

CSC ^ m

Si

m

r^ CSC ijjj

(5)

where p/p is the mass absorption coefficient for x or Si radiation by the mineral, p

is the mineral density, ^ is the x-ray take-off angle and (I °/lr^°)^ /(Iv°/^ct 71.

X ol T2 I

X oT the ratio of the generated intensities which is independent of r. to be generated at the center of the fiber. Rearranging yields

The intensity is assumed

Im ^

R2

csci|j(r2-r^

)

(6)

259
This expression provides a satisfactory fit (± 10 percent) to the experimental data

in figure 3 except in the case of contamination at small fiber diameters [1]. Equation 6

illustrates that it is the difference between the mass absorption coefficients that determines the magnitude of the absorption effect. When p/p

Si

mi neral

» p/p

X

mi neral

a decrease

in I^/I^^j occurs with decreasing size because the relative increase in emission will be

greater for the element with the larger absorption coefficient.

is a greater relative increase in Si emission (p/p

Fe

(p/p

grunerite

Thus, in grunerite there

1455) than in Fe emission

grunerite

~ ^""^ ^ subsequent 25 percent decrease in I(Fe)/I(Si) as the diameter

decreases from 1.5 to 0.15 pm. When p/p

Si

mi neral mi neral

I /IcX Siincreases with

decreasing size because the relative increase in emission is greater for x than for Si.

Thus in grunerite, where p/p 3460 and p/p

Si

grunerite

= 1455, there is a greater

Mg

gruneri te

relative increase in Mg emission and a subsequent 50 percent increase in I(Mg)/I(Si) as the size decreases from 1.5 to 0.15 pm. The easiest way of correcting for such effects is

to use calibration curves of the type shown in figure 3.

Combining eqs. (1) and (5) shows that (^^g)^^ y' (Sy^^g)^^ = R2/R1 where t is the film

thickness (r = t/2). In the case of a very thin film or fiber, taking the limit in eq.

(6) as t approaches zero gives:

, ^AB(not-so-thin) _ t /y B y A \

which is in accord with the expression published recently by Goldstein et al . [23]. The

S„ c • . S(- c- 3nd S„ values used to calculate the Cu-Sn-Cr values were corrected for

Cu Si Sn Si Cr Si

absorption using S^g (not-so-thin) values from eq. (7), and in all cases the relative error in concentration decreased as shown in Table 3. Figure 4 can be used as a guide to

determine when an absorption correction is advisable. When the absorption coefficient

difference for a given particle radius or film thickness is above the line, the absorption

correction will be greater than 10 percent and should be taken into account. Many of the

amphibole fibers with diameters of 0.2 pm and over require absorption corrections [1].

260
10,000

5000

-5.- 1000

<

500

100

0.2 jum diameter amosite (Mg/Si)

— 0.4 /L/m diameter crocidolite (Fe/Si)

Do Not Neglect

Absorption

Neglect

Absorption

100 200

Pfiimtfiim/2 in Mg/cm2

300

Figure 4. A(y/p) = y/p

B line

film m/p

A line

film.

(pt) film

film mass thickness.

When the value of A(y/p) for a particular film thickness is below

the line, the absorption correction will be less than 10 percent.

The absorption correction will exceed 10 percent for values above

the lines. The values shown for amosite and crocidolite indicate

that the absorption correction is significant for relatively thin

fibers.

Instrumentally Induced Contamination

Superimposed on the absorption effects just described is the sample contamination

which occurs when the hydrocarbons from the vacuum pump fluids are decomposed by the

electron beam and deposited on the sample surface [10]. The deposited thickness can, in

time, represent an appreciable portion of the total sample thickness. The magnitude of

the problem depends upon: 1) the cleanliness of the vacuum system; 2) the electron beam

current density; 3) the duration of the analysis; and, 4) the difference in absorption by

carbon for the x-ray lines of interest. The magnitude of the latter effect can be estimated

from the following expression:

In

(I

^ /I f^^^

X Si ^contamination

/y ,j \without

^ X Si 'contamination

t^ CSClp ^

SiK ]i_ C " p (8)

261
where is the density of carbon and t^ is the thickness of the carbon deposit in cm.

Figure 5 shows the observed variation of ^^g/^^^ "in chrysotile with time for different

current densities. The analysis of small (300-400A) chrysotile fibers often requires a small electron beam (higher current density) and a longer analysis time (>5 minutes) to

generate credible counting statistics. Even though p/p

Si

- p/p

Mg

C

is 800, the rapid

decrease in I„ /!(.. can only be partially accounted for by contamination implying other

rig o I electron beam induced effects. When the difference in absorption coefficients is small,

contamination is not a serious problem as indicated in figure 5 for the Cu-Cr-Sn film.

CuKa

5

CrKa

14

SnLa

51

MgKa

1170

SiKa

360

CO

inC

1.0

Chrysotile Fibers 3.7 ;um Beam

Chrysotile Fibril 0.5 pim Beam

Ic/'sn Cu-Sn-Cr Thin Film 0.7 jum Beam

10 20 30

Time In Minutes

40 50

Figure 5. Elemental intensity ratios as a function of the duration of electron

bombardment in an ATEM operated at 80 keV.

^fvjg/^si

""^^ ^Cr^^Sn

are plotted for chrysotile asbestos fibers and a Cu-Sn-Cr thin film

respectively. The beam diameter for each analysis is indicated on the curves. The mass absorption coefficients for the indicated

radiation by carbon are also shown.

Optimum Conditions for Analysis

In thin films, theory predicts [24] that the peak-to-background ratio should vary

approximately as In U with E , increasing rapidly at low U and then more slowly, where U

is the over-voltage ratio, acceleration potential/excitation potential. This is not

always observed experimentally as shown in Table 4. The failure to increase continuously

with voltage is, in part, due to the background contribution from extraneous radiation

which varies from instrument to instrument. The superiority of the STEM (vs. TEM) configuration is indicated in Table 4 where the two STEM instruments have their best peak-tobackground ratios at the highest voltage. Unfortunately, fiber or particle counting in

the STEM mode is not practical [2]. When column modifications are completed, the optimum

operating conditions should be experimentally determined for each instrument. Note that

low voltage operation will promote absorption and backscatter effects and reduce the

effectiveness of SAED on thicker fibers.

262
Table 4. Experimental determinations of the

maximum peak-to-background ratios

acceleration

in the ATEM.

potential providing the

Investigator Instrument and mode X-ray line

F^ inIII keV rWdV for I \j I maximum iiiu /\ 1 1 1 1 i_i 1 1

peak to background

This report EM 300-TEM CuK 60

This report EM 300-TEM SnL 40

Russ[39] EM 300-TEM FeK 50

Joy & Maher[25] JEOL lOOB-STEM MgK 100

Mizuhira[29] JEOL lOOC-TEM Na-CIK 20-40

Galle et al.[19] Cameca-TEM AlK, Au 20

Geiss & Kyser[27] EM 301 -STEM Fe and CuK 100

While there are some mineralogical ambiguities that cannot be resolved by EDS, a well-designed ATEM with the appropriate column modifications used in conjunction with good

analytical procedure can provide distinctive mineral spectra that are of great utility in

fiber identification.

Selected Area Electron Diffraction

Vastly differing claims have been published as to the utility of SAED in the identification of mineral fibers: Ampian [28] finds that positive identification using SAED is

only forthcoming from carefully indexed patterns yielding accurate lattice parameters.

Ross [29] found SAED patterns of asbestos minerals difficult to obtain and interpret and

that 200 keV was required to have distinct patterns. Beaman and File [1] reported that

only about 10 percent of the chrysotile fibrils examined in a standard gave distinct

patterns (40 percent were crystalline). Biles and Emerson [30] reported that most

chrysotile fibers in beer did not give identifiable patterns. Samudra [31] reported that

99 percent of the chrysotile fibers in the size range of 200-1200 A provided good patterns.

Much of this variation can be accounted for.

A distinctive SAED pattern for chrysotile: 1) has a characteristic layer line spacing;

2) is streaked in alternate layer lines; and 3) shows some characteristic reflections,

e.g., those in the second row from center are often quite distinctive. We classify as positive only those fibers exhibiting all of these characteristics. Fibers showing only

the correct layer line spacing as determined visually on the fluorescent screen are classified as ambiguous; the streaking or characteristic reflections are not sufficiently

distinctive to permit positive identification. Patterns without systematic reflections or distinctive layer lines are classified as unknown and the sum of positive, ambiguous, and

unknown is termed crystalline. The percentage of fibers in each category has been determined as a function of fiber size using different instruments, standards, and sample

preparation methods.

Droplets of 10 |jL volume, prepared from the dispersion of a high purity chrysotile

standard [32] in water, were placed on carbon-coated formvar films on TEM grids. The

samples were examined at 0° tilt in a Philips EM300 at 80 keV and a JEOL lOOB at 60 and

100 keV. Fiber searching was carried out in the selected area mode with the diffraction

aperture in position and focused to minimize the time lapse between finding a fiber and

obtaining a SAED pattern. The aperture size at the specimen level was 1-2 pm, the camera

length was minimized, and the SAED patterns were focused with the diffraction and objective

lens controls.

263
Figure 6 shows that less than 15 percent of the individual chrysotile fibrils (300-

400 K in diameter) provide positive SAED patterns. A significantly larger portion (20-50

percent) do exhibit the correct layer line spacing (positive + ambiguous) as observed on the fluorescent screen. For the fraction of positive fibers to exceed 50 percent, the

fibers must contain over 3 fibrils.

1 2 3 4 5 6 7

No. of Chrysotile Fibrils in Fiber

Figure 6. The percentage of chrysotile fibers in a standard providing the indicated

quality of the SAED pattern is shown to depend upon the number of fibrils

in the chrysotile fiber. The results obtained on two different instruments

are plotted along with previously reported results [1]. All samples were prepared using 10 yLl water droplets containing suspended chrysotile.

The results obtained in instrument B were similar at 50 and 100 keV. The lower two curves in figure 6 compare the present results with earlier work [1]. The differences are due to the present use of slightly more stringent requirements for positive identification

and possibly to the use of different standards (Wards in reference 1 vs. Union Carbide).

Figure 7 illustrates that the percentage of fibers providing diffraction patterns in every

category is lower when using samples prepared by the Jaffe extraction of carbon-coated

Nuclepore as compared to water droplets. This is presumably due to the carbon coating

and/or the presence of some residual Nuclepore. Note that the positive fiber category is

not significantly affected by sample preparation.

264
1 2 3 4 5 6 7

No. of Chrysotile Fibrils in Fiber

Figure 7. The percentage of chrysotile fibers providing the indicated SAED

pattern quality is shown to depend, to some extent, on the method

of sample preparation. The results for 10 pL water droplets are compared with those obtained after Jaffe extraction of a Nuclepore

filter in chloroform. All samples were examined in instrument A.

The primary reasons for the differing claims are the use of different criterion for

classifying a pattern as positive and differences in the fibril content of the fibers

being examined. A rigorous definition of positive SAED is needed if identification errors

are to be avoided and interlaboratory agreement achieved. Figure 6 shows that over 70

percent of the fibers containing three fibrils show the correct layer lines spacing

(positive + ambiguous category). Most published SAED patterns are not from single fibrils

as indicated by the presence of partial rings and diffraction spot smearing or multiplicity [28,33]. To a lesser extent, the reported variation is due to differences

in: 1) standard source and treatment; 2) sample preparation methods; 3) instrumental

capabilities; 4) operator judgment; and 5) diffraction technique.

In the river, tap water, and lake samples we have studied, the chrysotile has

consisted predominantly of fibers with 3 or less associated fibrils with single fibrils

appearing most frequently. The fibers in 50 percent NaOH produced from chlorine cells

using chrysotile asbestos diaphragms are predominantly fibrils and 80 percent have lengths

less than 2 pm and 95 percent have lengths less than 5 pm. Identification based on morphology or SAED alone in these cases has not been particularly reliable because less

than 20 percent of the chrysotile fibers had a tubular appearance and only 5-30 percent

gave positive SAED patterns. Those fibers identified as chrysotile had EDS spectra and

fibril diameters characteristic of chrysotile.

265
In counting fibers with the ATEM, searching with the diffraction aperture in place isi not practical because the field diameter is decreased from about 7 |jm to 1 (jm. Wheni

counting in the TEM mode, the fiber is subjected to more electron beam bombardment before'

a diffraction pattern can be obtained. When searching with the diffraction aperture in: position, the SAED patterns from chrysotile fibers containing three or less fibrils,

generally fade within 30 seconds to such an extent as to be unidentifiable. This electron

beam induced change is due to dehydroxyl ization [28] and carbon contamination.

Reliability of the Method

If a sufficient number (typically 60-100) of fibers are analyzed [1,2], the method!

will generally provide concentrations that are accurate within a factor of two. The

reproducibility is considered to be represented by the coefficient of variation or lOOa/mean fiber concentration. Inter-laboratory reproducibility between two different Dow

laboratories measuring chrysotile in 50 percent NaOH, which is a relatively clean sample,

has recently been better than 20 percent (see Table 5). This is reasonably goodi

performance for the small^ amount of material being detected as shown in Table 5. Theidentification of an lOOOA long chrysotile fibril corresponds to the detection of 3 X' 10 grams of material [24]. The results will not be this good for a series of laboratories using a variety of sample preparation techniques and differing criteria for

fiber identification.

Table 5. Experimentally measured asbestos concentrations.

Sample

Concentration in

millions of fibers

per liter

Mass of asbestos

in parts per billion

by weight

Midland, MI Tap Water

Waste Water Effluent^

50% NaOH^

Duluth Tap Water^

0.6

10-400

50-5000

25

0.001

0.2-10

0.5-40

25

50% NaOH sample 1

50% NaOH sample 2

50% NaOH sample 3

50% NaOH sample 4

Dow Lab A

380

380

530

1900

Dow Lab B

380

300

520

1500

Chrysoti le

Amphi bol

In order to achieve good reproducibility, we adhere to the following:

1. Use a sample preparation method with proven low fiber loss such as the

extraction of carbon-coated Nuclepore [2,5,6] or apply a fiber loss correction to each

sample [1,2].

2. Count only samples that have a uniform distribution of solids on the TEM grid,

i.e. , the fibers per unit area shoul d not f 1 uctuate widely [1,2].

266
3. Count until a sufficient number of fibers (generally 60-100) have been detected

so that number of fibers per unit area does not change significantly with additional

counting [1,2].

4. Use a sample volume that provides a particulate density with minimum interferences from non-fibrous solids.

5. Modify the TEM column to reduce electron scattering and secondary fluorescence.

6. Subtract off-fiber EDS spectra from fiber spectra.

7. Correct for absorption, when present, using standards or relative sensitivity

factors.

8. Minimize contamination rates, when possible, by the use of low current density

and short analysis times.

9. Experimentally determine the optimum acceleration potential which often differs

for EDS and SAED performance, necessitating a compromise.

10. Use a reasonable and consistent scheme for classifying fibers.

The authors wish to thank L. Sturkey and W. A. Knox of The Dow Chemical Company,

Walnut Creek, California, for helpful discussions concerning selected area electron diffraction and R. H. Geiss and D. F. Kyser of 1MB, San Jose, California, for their comments

and critical review of the manuscript. The assistance of D. J. Peterson of Dow Chemical

of Canada Ltd. and E. B. Bradford of Dow, Midland, in performing the experimental measurements is also gratefully acknowledged.

References

[1] Beaman, D. R. and File, D. M. , Anal . Chem . 48, 101 (1976), also in Proceedings

Microbeam Analysis Society 10th Annual Conference, paper 31 (1975).

[2] Beaman, D. R. and Walker, H. J., in FDA Symposium on Electron Microscopy of

Microfibers (Aug. 1976) in press.

[3] Ortiz, L. W. and Isom, B. L. , in 32nd Annual Proceedings of EMSA 554 (1974).

[4] Zumwalde, R. , In FDA symposium on Electron Microscopy of Microfibers (Aug. 1976) in

press.

[5] Cook, P. M. , Rubin, I. B. , Maggiore, C. J., and Nicholson, W. J., in Proceedings of

International Conference on Environmental Sensing and Assessment Section 34-1

I.E.E.E. Las Vegas (1976).

[6] Anderson, C. H. and Long, J. M. , Preliminary Interium Procedure for Fibrous Asbestos,

U.S. Environmental Protection Agency, Athens, GA (1977).

[7] Benefield, D. , The Dow Chemical Company, Freeport, Texas, private communication

(1977).

[8] Millette, J. R. , in FDA Symposium on Electron Microscopy of Microfibers (Aug. 1976)

in press.

[9] Stewart, I., in FDA Symposium on Electron Microscopy of Microfibers (Aug. 1976) in

press.

267
[10] Beaman, D. R. and Isasi, J. A., Electron Beam Microanalysis , STP506, American Societyi

for Testing and Materials, Philadelphia (1972).

[11] Philibert, J. and Tixier, R. , in Physical Aspects of Electron Microscopy andi

Microbeam Analysis ; Seigel , B.M. and Beaman, D.R., Eds John Wiley and Sons New YorkT

333 (1975). i

[12] Bolon, R. B. and McConnell, M. D. , in Scanning Electron Microscopy/IITRI/SEM/76, Part

1 (1976).

[13] Russ, J. C. , in Scanning Electron Microscopy/IITRI/SEM/77 1 335 (1977).

[14] Joy, D. C. and Maher, D. M. , in Scanning Electron Microscopy IITRI/SEM/77 1 325

(1977).

[15] Zaluzec, N. J. and Eraser, H. L. , in Proceedings Microbeam Analysis Society,

11th Annual Conference, paper 14 (1976).

[16] Packwood, R. H. , Laufer, E. E. , and Roberts, W. N. , in Proceedings Microbeamn^

Analysis Society, 12th Annual Conference, paper 115 (1977).

[17] Geiss, R. H. and Huang, T. C. , X-ray Spectrometry 4 196 (1975).

[18] Kyser, D. F. and Geiss, R. H. , in Proceedings Microbeam Analysis Society,

12th Annual Conference (1977) paper 110; also private communication with

R.H. Geiss (1977).

[19] Duncumb, P., J. de Microscopie 7, 581 (1965).

[20] Cliff, G. and Lorimer, G. W. , J. Microscopy 103 , 203 (1975).

[21] Russ, J. C. , in Proceedings Microbeam Analysis Society, 8th Annual

Conference (1973) paper 30; also in Edax Editor, 5, 11 (1975); also

J. Submicr . Cytol . , 6, 55 (1974).

[22] Sprys, J. W. and Short, M. A., in Proceedings Microbeam Analysis Society,

11th Annual Conference (1976) paper 9; also private communication with

Sprys, J.W. (1977).

[23] Goldstein, J. I., Costley, J. L. , Lorimer, G. W. , and Reed, S. J. B. , in Scanning

Electron Microscopy IITRI/SEM/77 1_, 315 (1977).

[24] Beaman, D. R. , in Modern Techniques for the Detection and Measurement of

Environmental Pollutants, 10th Rochester International Conference on Environmental Toxicity (May 1977) in press.

[25] Reed, S. J. B. and Ware, N. G. , X-ray Spectrometry 3, 149 (1974).

[26] Rao, P. and Lifshin, E. , in Proceedings Microbeam Analysis Society, 12th

Annual Conference, paper 118 (1977).

[27] Beaman, D. R. and Solosky, L. F. , in Proceedings Microbeam Analysis Society, ] 9th Annual Conference, paper 26 (1974). !

[28] Ampian, S. G. , in FDA Symposium on Electron Microscopy of Microfibers

(Aug. 1976) in press.

[29] Ross, M. , in FDA Symposium on Electron Microscopy of Microfibers (Aug. 1976) in

press.

[30] Biles, B. and Emerson, T. R. , Nature , 219 , 93 (1968).

[31] Samudra, A. V., in Scanning Electron Microscopy IITRI/SEM/77 2 (1977).

268
'32] Union Carbide chrysotile standard provided by K.S. Chopra, Union Carbide Corp.,

Niagara Falls, NY (1977).

'33] Mueller, P. K. , Alcocer, A. E. , Stanley, R. L. , and Smith, G. R. , Asbestos Fiber

Atl as , Environmental Protection Technology Series, EPA-650/2-75-036 (1975).

Discussion

K. HEINRICH: When you showed the variation of intensity with fiber diameter, was the

|cale in micrometers?

D. BEAMAN: Yes.

P. McGRATH: What can be done to develop criteria to reduce the energy-dispersive

interferences so that we can develop criteria for asbestos?

' BEAMAN: We can do much better with the EDS spectra than in the past by making column

edifications and by subtracting background spectra from the fiber spectra.

Question (inaudible):

I BEAMAN: You can make an identification in the STEM mode, but you cannot count fibers

asily. It would be difficult to continuously switch from TEM to STEM.

I C. PARMENTIER: I would like to make a comment concerning TEM-SAED and the lack of

-spaces and difficulty in measuring them for single-fiber chrysotile or amphibole asbestos

n small particulates; we run into the same problem of rapidly decreasing signal intensity,

e have used a cold finger with liquid nitrogen which allows d-spacings to be resolved on

he screen, photographed, and subsequently measured and indexed directly on the negative,

lO we come up with very accurate d-spacings. The second point I'd like to make is in the

pectrometric measurement of Mg-Si ratios. Have you seen varying Mg-Si ratios from

hrysotiles of different locals, and is this taken into account in your analysis?

I

j BEAMAN: We have used two chrysotile standards, but the chemical differences are mailer than data reproducibility. We could not detect any trend. We, of course, use a old finger but still observe the rapid deterioration of SAED patterns in the case of

;hrysotile. Amphibole patterns on the other hand do not tend to fade.

1

269

National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

TRANSMISSION ELECTRON MICROSCOPICAL METHODS FOR THE DETERMINATION OF ASBESTOS

Ian M. Stewart

Walter C. McCrone Associates, Inc.

Chicago, IL 60616

Abstract

Three 'criteria are given for the identification of a mineral

fragment as asbestos: morphology, crystallography, and chemistry. The

derivation of this information in the transmission electron microscope

is discussed.

Quantification of asbestos fiber content in an environmental sample

is considered and currently practiced techniques for quantification both

by mass and by number are reviewed.

Key Words: Analysis; amphibole; asbestos; electron diffraction;

electron microscopy; fibers; transmission electron microscopy; x-ray

energy analysis.

The first meeting on methodology for determination of asbestos by electron microscopy

was held almost exactly seven years ago. Sponsored by, as it then was, the National Air

Pollution Control Administration, it was attended by about a dozen people. The explosion

of interest in asbestos has led to a series of methodology meetings, particularly over the

last two or three years, culminating in the massive attendance at the present meeting. It

is clear, therefore, that there is considerable interest in asbestos and in particular,

asbestos methodologies. There is thus no need to reiterate the reasons for this interest

here.

What may be less obvious however, is why there should be such a necessity for the

development of electron microscopical methods. Figure 1 shows an electron micrograph of a standard suspension of an ul trasonerated chrysotile sample which has been prepared to

simulate material shed from asbestos filters used for parenteral drugs. The size range

represented is quite wide and very closely approximates that which has been found in

liquids filtered through an asbestos filter. If such a sample were to be characterized

entirely by light microscopical methods, much of the material which can be seen in the

alectron microscope, for example fibers A and B in Figure 1, would be completely omitted.

Figure 2 is an environmental sample, taken approximately three miles down stream from an asbestos plant and here again we have material below the detection range of the light

Tiicroscope. The level of asbestos fibers determined by electron microscopy in this case

ivas of the order of 10^ - 10^ fibers/liter, several orders of magnitude higher than would

have been determined if the light microscope was used. Again, in water samples from the

Ouluth and Silver Bay areas, the number of asbestos fibers that were identified by light

microscopy was virtually zero, fewer than one dozen fibers being detected in over fifty

samples by this method. Nevertheless, transmission electron microscopy, as shown in

Figure 3, established that there were indeed high levels of fibrous amphiboles in these

samples. Clearly then, in order to satisfactorily characterize the asbestos content of

such samples, electron microscopy is a necessity.

271
Figure 1. Ul trasonerated chrysotile suspension simulating size

distribution of fibers shed from asbestos filters

used for parenteral drugs — 3200 X.

272
Figure 2. Filtered river water 3 miles downstream from an asbestos processing plant - 20,000 X.

273
Figure 3. Water from western arm of Lake Superior — 12,600 X.

Before discussing methods of preparing samples for examination in the electron microscope or for counting them, it is necessary to be sure what information we need to deriv(

from the electron microscope in order that we can characterize a particular particle as ai asbestos fiber. If one accepts the Federal Register definitions of asbestos and, from « legal standpoint, that is all that one can use at the present time, then to determine at asbestos fiber, one must show first that the material is fibrous, that is, that it has ai aspect ratio of greater than 3:1 and, second, that it is a mineral of the type which i« classed as asbestos by the Federal Register. The determination of the aspect ratio ij

quite straightforward. One measures the length and the width of the particle. The

determination that the particle is indeed asbestos, however, is not so straightforward;

There are basically two criteria which must be satisfied for a positive identification;

certainly on the amphiboles, although for chrysotile perhaps only one of these criteria

will suffice. These criteria are, firstly, that the particle in question belongs to the

correct crystal lographic system and has the correct crystal lographic parameters for one oi

the asbestos minerals. Because of the unique structure of chrysotile, which will not be

discussed here, the diffraction pattern of chrysotile can be regarded as sufficiently

definitive without the addition of chemical information (Figure 4). In the case of the

amphiboles, the diffraction patterns are less characteristic and careful diffraction work

must be performed to establish that the particle is indeed an amphibole. Having

established that it is an amphibole, one must then differentiate which of the several

274
amphibole types it may be. This can best be performed by chemical analysis in the

electron microscope. At the present time the most popular method of determining this

analysis is by use of an energy dispersive x-ray analyzer, fitted to the transmission

electron microscope. Figures 5 and 6 show, respectively, the electron diffraction pattern

and the energy dispersive spectrum of an amphibole fiber which can be tentatively

identified as the commercial asbestos "amosite" - actually a fibrous grunerite. The word

'tentatively' is used deliberately since there are many problems associated with the

interpretation of both the diffraction pattern and the energy dispersive spectrum. Thus,

in general, it is prudent only to classify an amphibole as being within a certain series,

such as the tremol ite-acti nol ite series, or the cummingtonite-grunerite series.

Figure 4. Chrysotile diffraction pattern.

275
Figure 5. "Amosite" diffraction pattern.

SI

•*

t

\! ««

*

1

1

*

1 •

',

,

1

• • L> Wwtyi^..^,.// 'Am -n

©7.07 .00 cw ooap w

Figure 6. "Amosite" energy dispersive x-ray spectrum.

276
In order to determine these parameters simultaneously in the electron microscope,

ome idea should be given of how this information is derived. The morphology is obvious;

,his follows from the normal operation of the microscope as an image producing instrument,

lowever, like all optical systems, the laws of diffraction apply in the transmission

ilectron microscope. Thus, given an object with a periodic structure, the image of this

bject in the back focal plane of the objective lens will be a diffraction image related

,0 the periodicity of the structure. In the transmission electron microscope, this image

lay be observed at higher magnification by adjusting the strength of one of the projection

enses, such that the back focal plane of the objective lens is in focus at the final

iewing screen. As was stated above, the chemical nature of the particle under

nvestigation can also be determined in the microscope by an energy dispersive x-ray

ystem. This is because striking a target with a high energy electron beam will result in

he emission of x-rays whose wavelengths or energies are characteristic of the chemical

pecies at the point of impact. By suitably focusing the incident beam it is possible to

solate individual particles in the microscope and to either analyze their energies by an

inergy dispersive spectrometer or their wavelengths by a wavelength spectrometer. In

iractice the energy dispersive spectrometers are more common. They have the advantage

,hat they detect all elements simultaneously from about sodium upwards in atomic number

ind they are also considerably cheaper to install on an instrument than the wavelength

lispersive system which, although having a better signal to noise ratio, suffers a major

lisadvantage for rapid analysis in that it is sequential, analyzing only one element at a

;ime. There are many factors which may interfere with or disturb the energy dispersive

lignal; factors such as particle size, shape, geometry, scatter from the instrument, and

;o forth, confuse the already complex chemistry of the amphiboles. These have been

liscussed in many other sources and will not be discussed in detail here. One should,

lowever, be aware that such complications do occur and should interpret the spectra with

ippropriate caution.

Having settled on criteria by which one would identify the fibers, the next problem

s, "What does one wish to count or measure?" There are two philosophies which are

urrent. One is that the important factor is to determine the number and size

istribution of the fibers present as they exist in the sample. The other philosophy is

hat the mass concentration is important. We should discuss a little why these two

chools of thought have arisen. It would seem to the lay observer, that, as yet, there is

0 sound medical reason in favor of determining one or the other. There are sound

nalytical reasons for suggesting either. The most attractive feature of the fiber

umber, size distribution and shape philosophy is that as well as giving information on evels that exist in the material, it also gives the size range, which may or may not be

mportant, and much recent work has suggested that it is. It is also possible, by

actoring in a geometric factor together with a density factor, to determine the mass of

iber present. One of the major drawbacks of such a method, however, is the tendency of

ibers to overlap each other and also to overlap other material in the sample. It is

articularly common in quarry samples, for example, to find intergrowths of chrysotile

ith the related serpentine mineral antigorite. Unless a good separation between the

ntigorite and the chrysotile is obtained, it may not be possible to positively identify

he asbestos fibers and hence they will not be included in the count. Repeated over many

ibers, and bearing in mind the multiplication factors which exist by virtue of the

ifference in area examined in the microscope relative to that represented by a membrane

ilter area, this can lead to quite dramatic differences in fiber counts or mass levels

etected. In addition, the presence of one or two massive fibers can drastically skew the

ass number, again because of the multiplication factors involved.

Mass concentrations have been determined by several workers, and several methods

xist for preparation of samples to determine mass reasonably accurately. These methods,

eveloped principally by Battelle, Mt. Sinai, and Johns-Manvi 1 1 e , and ideally, applicable

nly to chrysotile asbestos, all involve the reduction of more massive fibers to the so- alled unit fibril of chrysotile. In some methods these fibrils are then individually

easured for length, and by geometric calculations the mass is determined. In the

attelle method, the intercepts of fibrils along a line are counted and compared to

imilar counts performed on a standard mass concentration sample. The advantage claimed

or such methods is that they will separate the fibrils from interfering material. One

lisadvantage is the several preparation steps which may be involved in preparing the

ample and which may lead to either cross contamination of the sample or loss of material

277
from the sample, leading to high and low readings, respectively. Additionally, such

methods may liberate fibers which would not normally be considered free fibers and

therefore presumably not hazardous. Details of these procedures have been published

previously and will not be reiterated here.

As regards methods for sample preparation for fiber counting without destroying the

identity of the fibers, one might say there are as many variations of sample preparation

methods as there are electron microscopi sts working in this field. The state of the art

does, however, seem to have boiled down to two basic direct transfer methods, one using

condensation washing and one using a wicking technique. These methods will be discussed

by Dr. Anderson, who has prepared an excellent document entitled "A Preliminary Interim

Procedure for Determining Fibrous Asbestos", which spells out the basic steps in preparing

samples and the criteria for asbestos identification. I believe this document represents

the most acceptable state of the art on asbestos determination by transmission electron

microscopy at t-he present time. Although there have been other methods proposed, these

have not received as wide favor as the direct transfer methods. These other methods

include placing a drop of the fluid suspected to contain asbestos on an electron

microscope grid with a calibrated micro pipette. Assuming that all the material from the

drop is deposited on the grid uniformly, and knowing the volume of the micro pipette, it

is possible to derive the number of fibers per unit volume of fluid. In a similar method

a calibrated micro pipette is not used, but a small drop of the liquid is placed on a grid

and the diameter of the area occupied by the deposited solids after the droplet has dried

is measured. It is assumed that the diameter of the evaporated circle represents the

diameter of the original drop and hence the volume of the drop may be calculated and again

the number of fibers per unit volume determined. One of the major drawbacks of many of

these direct drop emplacement methods is the difficulty in holding the liquid in such a manner that none of the drop is transferred off the grid to its surroundings, for example

by wicking up between the arms of a pair of tweezers or by contact with the substrate on which the grid may be supported. An additional disadvantage is the tendency for size

separation to occur within the drying drop, resulting in an uneven distribution of fibers

on the grid.

In any event, in any method involving direct transfer either from a liquid or from a filter it should be borne in mind that due to the overlapping nature of the particulate

species present, the possible ambiguities of interpretation of diffraction patterns and/or

chemistry due to such overlaps and the inability to see many of the fibers, the number of

fibers counted will, in all cases (with the exception of bad housekeeping resulting in

contamination), result in a minimal number for the total fiber loading per unit volume. A

truer estimate of the loading per unit volume may be made by applying corrections for such

overlaps or by additionally counting those ambiguous fibers which cannot be directly

identified. There is, however, no hard and fast rule as to the magnitude of such

corrections. In the case of methods reducing fibers to unit fibrils and estimating mass,

these will again be minimal numbers if the criterion used is that the fiber must be

positively identified, as, it is more difficult in general to obtain a positive

identification of a small fiber than a large one either by electron diffraction or by

chemical characterization.

Although this may paint a rather pessimistic picture in terms of establishing a standard using electron microscopy, some positive suggestions may be put forward. For

example, if it is decided that the standard should be a certain number of asbestos fibers

per unit volume, then it should be possible to set up the microscope parameters such that

the microscopist can determine all fibers in a unit area quite rapidly. This can, in

turn, be calibrated in terms of fibers per unit volume of the sample source. If none of

these fibers are asbestos and the number is still below the statutory limit, then clearly

it is not necessary to perform any identification on the fibers to determine if they are asbestos or not. Such a procedure could well be used for screening purposes. Again, a subjective opinion could be made by the microscopist as to what percentage of those fibers

are asbestos. If the total fiber content was 2 or 3 times that which is permitted by the

regulation but the asbestos content is clearly, say 10 percent, of the total fiber

content, then again there should be no major problem. This would dramatically reduce the

number of marginal cases in which the total asbestos content may be close to or exceed the

statutory limit. Only in such cases would it be necessary to perform a complete and

detailed analysis. It would be necessary, of course, to ensure valid documentation uf the

278
data in those cases where it is said that the level does not exceed the statutory limit.

A similar approach could also be applied to the mass method and indeed may be more readily

applied if one is already estimating mass on the basis of number intercepts per unit area.

In the foreseeable future it is quite conceivable that automated methods for determining asbestos in the electron microscope may come to be a reality. The application of

computer solution to the electron diffraction pattern as described by Fisher and Lee in

these proceedings could be combined with the capability for electronically recording such

diffraction patterns which is offered by the technique of scanning electron diffraction.

This could then be integrated in one instrument with an x-ray energy dispersive x-ray

system, and electron energy loss analysis system operating in the scanning transmission

mode to provide a valuable and powerful tool for automating the asbestos identification

process. It is unlikely, however, that such a tool would be applied on a routine basis,

in view of the capital cost which would be involved.

Thus, there remains the major problem of characterizing asbestos particles in the

submicroscopic size range and doing this economically. Work is currently in hand to

effect separation of asbestos from other mineral species; separation from organic material

may already be achieved by such techniques as low temperature ashing. Assuming that such

separation can be both successful and complete the analytical procedures may well be

simplified. Until such time, however, transmission electron microscopy must remain

primarily a technique applicable to the research situation and is not presently an economically viable tool for monitoring and control programs on an extensive scale.

References

In trying to put together specific references to techniques mentioned in this paper, I realized how much of my information had been absorbed through discussions both privately

and at meetings such as this — a sort of mental osmosis. The following list is therefore

not complete and should be more properly regarded as suggestions for further reading. I apologize in advance to those who may feel slighted by the omission of references to their

work.

Descriptions of the mass method can be found in the following :

Leineweber, J. P., "A Method for Determination of the Fiber Content of Water", JohnsManville Research and Engineering Center, Report No. E 404-37, August 1968.

Thompson, R. J. and Morgan, G. B. , "Determination of Asbestos in Ambient Air," Proc.

International Symposium on Identification and Measurement of Environment Pollutants,

p. 154, June 1971.

Descriptions of direct transfer methods from filters are given in :

Anderson, C. M. , "Preliminary Interim Procedure for Determining Fibrous Asbestos," July

1976. Available from Dr. C. M. Anderson. See also Dr. Anderson's paper in these

proceedings.

Overlap, loss, and similar problems :

Knight, G. , "Overlap Problems in Counting Fibers." AIHA Journal , p. 113-114, February 1975.

Beaman, D. R. and File, D. M. , "Quantitative Determination of Asbestos Fiber Concentrations,"

Anal. Chem. , 48, No. 1, p. 101-110, 1976.

Energy dispersive x-ray analysis is discussed in :

Beaman 's paper cited above and

Ruud, C. 0., Barrett, C. S. , Russell, P. A., and Clark, R. L. , "Selected Area Electron

Diffraction and Energy Dispersive X-ray Analysis for the Identification of Asbestos

Fibers, A Comparison," Micron , 7, p. 115-132, 1976.

279
Several general papers on the characterization, identification, and quantification of

asbestos also appear in the Proceedings of the First FDA Office of Science Summer Symposium

on Electron Microscopy of Microfibers, August 1976, currently in press.

Di scussion

C. ANDERSON: Ian, it strikes me that to determine mass and to determine the number

of fibers at a certain period of time are entirely incompatible for the reason that you

state-that 10 percent or even less of the fibers contribute to 90 percent of the mass.

I. STEWART: That's exactly right.

ANDERSON: Therefore, for any kind of precision of mass you must count possibly 100

large fibers.

STEWART: Or 1000 fibrils or you just look at your intercept. But I wasn't putting it

forward as being a way that we should go. You see the big problem is that you're like me,

you're an analyst too, and the medical people haven't decided what they want from us -- mass data or fiber counts and sizes. If that problem is resolved, so too will many of the

analytical problems.

ANDERSON: I wonder if you agree that determining mass and the number of fibers

in the same amount of time is almost incompatible within a certain precision?

STEWART: Yes and no. You can get a mass number out. If you're too lazy to look at the

statistics of the size distribution, the mass will give you an idea of whether you've got

a lot of big fibers there; not always, but sometimes.

Written comments by Prof. J. Zussman to Dr. Stewart's paper.

J. ZUSSMAN: Dr. Stewart mentioned that fiber counts by electron microscopy would be

expected to be in error on the low side, especially through overlapping particles. This

effect can be lessened, of course, if specimen preparation is such as to produce not too

dense a fiber population on the e/m grid. I would also like to mention that there are two

factors leading to erroneously high fiber counts - the use of the rub out technique, and

the process of ultrasounding if too vigorous.

STEWART: I agree in part. However, in the case of overlaps due to other suspended

particulates, dilution may produce too low a fiber population for the data to be statistically valid. I also agree on the comments on erroneously high fiber counts. The rub out

technique is only valid for mass data although I know that fiber counts produced by this

technique have been quoted by some people.

280
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurements Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

STATISTICS AND THE SIGNIFICANCE OF ASBESTOS FIBER ANALYSES

J. P. Leineweber

Johns-Manvi lie

Research & Development Center

Denver, Colorado

Abstract

The analysis of asbestos fibers by electron microscope methods

involves many operations, each of which can affect the final results.

Normal random fluctuations can be described by the Poisson distribution, which applies to any truly random process. Deviations from

normal statistics, sample preparation losses, identification errors,

and laboratory contamination are sources of error which are difficult

to quantify. Each, however, can cause variations which will be greater

than predicted by the Poisson distribution. The significance of each

of the sources of error are discussed together with recommendations for

experimental techniques, which should minimizethe errors.

Key Words: Analysis; asbestos; electron microscope; errors; fiber;

statistics.

Introduction

The counting of asbestos fibers by the "membrane filter" method, approved by the

National Institute of Occupational Safety and Health, has been studied in considerable

detail [1,2,3,4]^. The procedures to be followed are specified in detail, and the precision

and accuracy of the results have been analyzed by competent statisticians. The background

data are based on several controlled experiments designed to describe the variations which

can occur between operators in a given laboratory, as well as the variations which can occur

between laboratories. Although there is considerable debate over the lower limit of fiber

concentrations that can be accurately determined, the fluctuations that can occur with

standard samples have been described to a reasonable degree.

In recent years, there has been increasing emphasis on the quantitative determination

of fiber concentrations in the environment [5,6,7]. Analysis of these samples is much

more difficult because of the extremely low fiber concentrations, the very small fiber

dimensions involved, and the high concentrations of extraneous materials in the sample.

Traditional methods of analysis cannot be used, so the analyst must rely upon the electron

microscope to resolve, identify, count, and measure the fibers. This requires the introduction of several additional sample preparation techniques. Furthermore, the fraction

of the sample actually examined is extremely small and there is much more latitude for

operator interpretation.

The objective of this paper is to review the various sources of error in the counting of

asbestos fibers by electron microscope methods, discuss how they might influence the

^results, and finally, suggest steps which might be taken to minimize these errors.

^Figures in brackets indicate the literature references at the end of this paper.

281
Electron Microscopic Fiber Analysis Procedures

The techniques used to determine asbestos fiber concentrations with the electron

microscope have gone through several evolutionary changes during the past decade.

Although a "standard" procedure has yet to be agreed upon, all use most of the following

steps [8,9].

Sample collection

Deposition on Filter

Ashing and refiltration

Clearing of the filter

Scanning and counting

Each of these steps involves manipulation of the sample in the field or in the

laboratory. Errors can be introduced with each step, and, as in any sequential system,

the errors will be accumulative. The following are the principal factors which can influence the accuracy and precision of the analysis.

Normal statistical fluctuations

Deviations from normal statistics

Sample preparation losses

Identification errors Laboratory contamination

The significance of each of these sources of error will be discussed in more detail in

the following sections together with recommendations for experimental techniques designed

to minimize the errors.

Normal Statistical Fluctuations - The Poisson Distribution

In environmental systems such as air and water, it is reasonable to assume, as a first

approximation, that the fibers are distributed in a purely random manner. Furthermore, it

is also reasonable to assume that the random distribution will be maintained during the

deposition of the sample on a filter. If this is the case, the variations to be expected

can be described in terms of the Poisson distribution [10]. The distribution function can

be represented as:

X -m

f(x, m) = —^^—

where: m = the mean value of a parameter for a series of trials

X = the actual value for a specific event

e = the base for natural logarithms

f = the probability of occurrence for a specific value.

Figure 1 is a plot of the probability of occurrence for specific events for a Poisson

distribution with a mean value of 10.0.

The Poisson distribution is actually a limiting case of the more general binomia

distribution. It has the unique characteristics that:

- the variance is equal to the mean - the standard deviation is equal to the square root of the mean.

For the fiber counting problem, the most significant characteristic is that the

variance will be dependent on the total number of fibers counted-regardless of the number

of fields that were examined to obtain the results.

282
0.140 ..

31 0.130

0.120

0.110

CQO

cm

0.100

0.090 ..

0,080

0.070 ..

0.060 ..

0.050 ..

0.040

0.030

0.020

0.010

0.000

0.0

COUNT

a=4

10.0 20.0

Figure 1. Poisson distribution mean = 10.

283
The consequences of the foregoing characteristics of the Poisson distribution are best

illustrated by using the "two sigma" limits to define the range within which the results

might be expected to fall for given total fiber counts. The "two sigma" limits are chosen

on the basis of the hypothesis that about 95 percent of the results should be within two

standard deviations of the mean value.

Table 1 lists the "two sigma" limits for total counts ranging from 1 to 100. Figure 2

is a plot of the range (upper limit/lower limit) for various total counts. This plot

shows very dramatically how large the range can be for small total counts. Only when the

total fiber count is 20 or greater does the range fall to a factor close to 2. It is also

significant to note that the range decreases relatively slowly for total fiber counts in excess of 20.

Table 1. Two sigma limits for various fiber counts.

Two Sigma Limits

Total Count Lower Upper

1 0.00 3.00

2 0.00 4.83

3 0.00 6.46

4 0.00 8.00

5 0.53 9.47

10 3.68 16.32

20 11.06 28.94

30 19.05 40.95

40 27.35 52.65

50 35.86 64.14

60 44.51 75.49

70 53.27 86.73

80 62.11 97.89

90 71.03 108.97

100 80.00 120.00

284
20.0 +

18,0

0.0 20.0 40,0 60.0 80.0 100.0

TOTAL FIBER COUNT

Figure 2. Range of 2 sigma limits.

285
The final, and most important point to be made in regard to this theoretical discussion is that the Poisson distribution can only be considered to be a limiting case. It

represents the best that can be achieved under ideal circumstances. If the fibers are not

deposited in a truly random manner, the variations will be larger than predicted. As a matter of fact, all available experimental data indicates that real world samples do not

follow the Poisson distribution [11]. Although there is much more data available for

optical counting, there is no reason to believe that electron microscope samples should

be any better.

Causes for Non-Random Distribution - Experimental Results

The obvious causes for non-random distribution of fibers on a filter surface are inadequate mixing, eddy currents in the filter, and fiber clustering. With water samples,

the first two of these can probably be controlled by good experimental technique. In the case of airborne samples, the operator will have little or no influence over the initial

distribution and only some control over air currents which may influence the deposition.

Recently, an experiment was designed to test the validity of the Poisson distribution

under reasonably ideal conditions. We had available a small amount of very well characterized glass fiber, 1.5 micrometers in diameter and 30 micrometers long. A carefully

weighed quantity, calculated to contain one million fibers, was dispersed in one liter of

water. One hundred (100) mL of this dispersion was filtered on a 25 mm membrane filter.

The filter was then clarified and examined by phase contrast microscopy. Figure 3 shows a typical area near the center of the filter. The distribution appears reasonably random,

but there also appears to be too many fibers lying closely parallel to each other to say

that the distribution is completely random.

Figure 4 shows the configuration near the edge of the filter. The lower right hand corner is the region closest to the edge of the filter. Here the fibers show a tendency

to align circumferentially. Next, there is a complete ring in which very few fibers are deposited. In the next few hundred micrometers, the fibers tend to be radially oriented.

As we proceed toward the center of the filter, the distribution becomes more random, as was shown in the first photo in this series. Obviously, there are eddy currents near the

side of the filter funnel which have strong influence on the fiber distribution.

Continuing the experiment as originally designed, 1000-80 micrometer square fields were counted. The expected number of fibers per field was 2.58. The average found was

3.18. This calculates back to 1.28 million fibers per liter. An excellent correlation,

considering all the possible sources of error, including the original characterization of

the fibers.

Figure 5 shows the actual distribution of the number of fibers per field versus the

theoretical Poisson distribution for a mean of 3.18. Even in this well-controlled experiment, the distribution is significantly broader than predicted.

286
Figure 3. Glass fiber dispersion. Area near center of filter. Nominal dimensions

of the fibers are 1.5 x 30 micrometers. Phase contrast.

287
Figure 4. Glass fiber dispersion. Area near edge of filter. Nominal dimensions

of fibers are 1.5 x 30 micrometers. Phase contrast.

288
I—

21

O

0,230 ..

0,220 * 0,210

r—\

X 0,200

0.190

0,180

0.170

0.160

0,150

0.140

0.130

0,120

0,110

0.100

0,090

0,080

0.070

0.060

0,050

0.040

0.030

0.020

0.010

0.000

v/M,^////////m ACTUAL

THEORETICAL

I

0,0 10.0

COUNT

Figure 5. Actual versus theoretical fiber distribution.

289
Table 2 shows the results of actual electron microscope counts from some typical water

and air samples. The fourth water sample and the fourth air sample are of particular

interest. In the water sample, 8 grid squares were counted with a mean value of 12.13.

The probability of finding a grid square with only 2 fibers is calculated to be about 4 in

10,000. Likewise, in the water sample 20 grid squares were counted with a mean value of

2.9, the probability of finding 11 fibers in one grid square is 2 in 10,000. These are both good examples of serious deviations from the theoretical Poisson distribution which

will lead to greater than expected uncertainties.

Table 2. Typical counting results.

Grid Opening Water Samples Air Samples

1 0 2 4 15 5 0 8 1

2 0 0 1 15 6 0 3 11

3 0 2 2 10 7 0 12 2

4 0

"77 2 16 3 0 18 6

5 0 3 0 13 0 0 3 6

6 1 4 1 11 4 0 4 3

7 0 0 1 15 1 0

"77 1

8 0 1 1 2 2 1 8 1

9 0 1 3 4 1 8 3

10 0 0 1 4 0 3 3

11 0 5 0 0 2

12 0 1 0 1 0

13 0 4 0 0 3

14 0 5 0 1 2

15 0 3 0 1 0

16 0 3 4 2 0

17 0 5 1 0 3

18 0 1 2 0 1

19 0 2 0 0 3

20 0 7 1 1 6

Figure 6 is a typical clump of fibers and other material found in a water sample. One

can only speculate on whether such an agglomerate actually existed in the original sample

or is an artifact caused by sample preparation. In any event, its occurrence can have

serious consequences on the final results.

290
291
Sample Preparation Errors

After a sample has been collected on a filter surface, additional processing is

necessary prior to examination in the electron microscope. A variety of methods can be

used and each can be the source of significant errors. Perhaps the most serious of all is

the loss of a significant number of fibers during the clearing or dissolution of the

filter. The "cold finger" apparatus is commonly used to clear cellulose ester (Millipore)

membranes, and the Jaffe wick method is used for clearing Nuclepore membranes. Both depend

on dissolving the polymer in solvent vapors with the subsequent deposition of the entrapped

particles on the carbon substrate. Some particles will always be washed away as the

polymer is removed. How many and how consistently are very difficult to quantify. Beaman

et al. [8], estimate that the losses can be as high as 50 percent for amphibole fibers.

Extreme care must be exercised to avoid flooding when using the Jaffe wick method and to

control the rate of boiling when clearing by the "cold finger" method.

In many cases, a sample might be contaminated with excessive organic material which

interferes with the examination of the sample. Removal of the organic material can be

accomplished by low temperature ashing followed by redispersion and deposition on a second

membrane filter. Although this may be a necessary step, it can lead to serious clumping

of fibers. Furthermore, the redispersion can alter the size distribution of the fibers.

Chrysotile asbestos, for example, is extremely sensitive to dispersing agents such as Aerosol OT.

Another technique that is sometimes used in conjunction with low temperature ashing

is the so-called rub-out method. This is useful for reducing the size of large extraneous

particles, but does result in a radical change in the fiber dimensions. This method should

not be used if the analyst is required to report fiber counts and fiber dimensions. It can only be used to estimate the total mass of fiber present.

In general, sample preparation errors lead to an understatement of the number of

fibers present in a sample and can distort the size distribution. Some analysts multiply

the counts by a factor which was established on the basis of a few controlled experiments.

This practice could only be considered valid if the factor was determined for conditions

identical to the reported analysis. This would require the analysis of a standard sample

along with each group of unknown samples.

Fiber Identification Errors

The identification, or mis-identification, of the fiber species present can lead to

either positive or negative errors in total fiber counts. With extremely fine fibers

positive identification using electron beam techniques is very difficult. Diffraction

patterns may have only a few discernible spots and can also be quite fugative. Elemental

analyses by x-ray emission can also be erroneous due to the influence of nearby particles.

Fiber identification errors can be minimized by adequate operator training. Certainly, critical samples should be analyzed only by experienced operators.

Laboratory Contamination

Because of the extremely low levels of fibers encountered in environmental samples

and the very small sample size, contamination of the specimens can be a serious source of error. Most laboratories concerned with fiber analysis have handled bulk fibers for many

reasons. Fibers can also be present in the other media used to process the samples.

Good housekeeping practices can keep laboratory contamination to a minimum. It is

advisable to handle all samples in an isolated area. A clean air hood equipped with HEPA

Filters is most desirable. Obviously, no bulk fibers should be handled in this area. Finally, all solvents should be filtered immediately prior to use. Never rely on the fact

that distilled water or other solvents, regardless of their purity, will be fiber free.

Finally, it is advisable to run a blank sample through all of the steps of the procedure,

along with each group of samples being analyzed.

292
Work to be Done

It is obvious from the foregoing discussion that the analysis of environmental samples

for asbestos fiber is far from precise. Large errors can be the result of normal random

variations and also the manipulations required for sample preparation. It is further

obvious that additional work should be done to establish techniques which will minimize

the controllable errors.

First, and foremost, among the tasks to be accomplished is to establish an acceptable

standard procedure for fiber analysis. Work of this type is currently underway in several

laboratories. This should be pursued with vigor so that methodology can be specified as soon as possible.

Second, and concurrent with the methodology development, should be a systematic study

of filter clearing techniques. The objectives of this task would be to better describe

the losses which can occur, and to seek imporvements which might give smaller and more consistent losses.

Finally, serious consideration should be given to the preparation of a standard

dispersion which could be used for comparative studies between laboratories. Such a standard dispersion would also be useful to assist in the quantification of the errors introduced by the various analytical steps.

Reporting Results

Because of the variety of procedures currently employed and the magnitude of the

errors, it is important that as much information as possible be included with fiber

analysis reports. This information should include:

Sampling conditions

Volume filtered

Sample preparation method

Number of fibers and fields counted

Blank counts

Identification problems

Fiber dimensions

This information is absolutely essential. Too many reports are published which

show only the number of fibers found in an environmental sample without any background

information. Without this information, it is impossible to evaluate the true significance

of any and all fiber analyses.

References

[1] Beckett, S. T. and Attfield, M. D. , Inter-Laboratory Comparison of Asbestos Fibers

Samples on Membrane Filters, Ann. Occup . Hyg . J?, (1974).

[2] Curtis, P. A. and Bierbaum, P. J., Technological Feasibility of the 2 Fibers/cc

Asbestos Standard in Asbestos Textile Facilities, Amer . Ind. Hyg. Assn . J., 115-125

(February 1975).

[3] Rajhans, G. S. and Bragg, G. M. , A Statistical Analysis of Asbestos Fiber Counting in

the Laboratory and Industrial Environment, Amer. Ind. Hyg. Assn. J., 909-915

(December 1975).

[4] Walton, W. H. , Attfield, M. D. , and Beckett, S. T. , An International Comparison of

Counts of Airborne Asbestos Fibers Sampled on Membrane Filters, Ann. Occup . Hyg . 19,

215-224 (1976). ~

293
I

[5] Cunningham, H. M. and Pontrefract, R. , Asbestos Fibers in Beverages and Drinking

Water, Nature (London), 232, 332-333 (1971).

i

[6] Durham, R. W. , and Pang, T. , Asbestos Fibers in Lake Superior, Water Qual ity Parammeters , ASTM STP573, American Society for Testing and Materials, pp 5-13 (1975). ^

[7] Rohl , A. N. , Langer, A. M. , and Selikoff, I. J., Environmental Asbestos Pollution

Related to Use of Quarried Serpentine Rock, Science 196 , 1319 (June 1977).

[8] Beaman, D. R. and File, D. M. , Quantitative Determination of Asbestos Fiber Concentrations, Anal Chem . 48, 101-110 (1976).

[9] Anderson, C. H. and MacArthur Long, J. Preliminary Interim Procedure for Fibrous

Asbestos, Analytical Chemistry Branch, USEPA, Athens, Georgia (July 31, 1976).

[10] Miller, I. and Freund, J. E. , Probabi 1 ity and Statistics for Engineers , Second

Edition, pp. 77-82 (Prentiss-Hall, New Jersey, 1977).

[11] Brown, A. L. Jr., Taylor, W. F. , and Carter, R. E. , The Reliability of Measures of

Amphibole Fiber Concentration in Water, Environmental Research 12 , 150-160 (1976).

Di scussion 1

D. SARVADI: Are you familiar with the NIOSH proficiency analytical testing program,

and do you have any feel for the inter- and intra- laboratory work they are doing on asbestos counts? ^

J. LEINEWEBER: They have done a fairly credible job on making inter- and intralaboratory comparisons on standard samples, and even within one laboratory in attempting

to compare the results of a group of operators. They have come a lot farther with optical

counting than we have with EM counting. There are still problems, but I think they

have their situation under a little better control than we do.

1

294
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

SELECTION AND CHARACTERIZATION OF FIBROUS AND NONFIBROUS AMPHIBOLES FOR

ANALYTICAL METHODS DEVELOPMENT

J. C. Haartz and B. A. Lange

U.S. Department of Health, Education, and Welfare

Public Health Service, Center for Disease Control

National Institute for Occupational Safety and Health

4676 Columbia Parkway, Cincinnati, Ohio 45226

and

R. G. Draftz and R. F. Scholl

IIT Research Institute (IITRI)

10 West 35th Street

Chicago, Illinois 60616

Abstract

More than 50 mineral specimens of fibrous and prismatic

(nonfibrous) amphibole species, including tremolite, grunerite, and

cummingtonite, were collected and characterized to determine their

suitability for use as reference materials in the development of

analytical methods. These methods will be used for the detection and

measurement of hazardous materials which are found as workplace

contaminants. The specimens have been characterized using light

microscopy, x-ray diffraction (XRD), and differential thermal analysis

(DTA). Some of these specimens have been purified by appropriate

physical or chemical techniques and then ground to provide a material

with a mass median particle size of less than 10 pm (major) diameter.

The results of characterization studies of the minerals, including a comparison of the properties determined for each of the specimens, are presented. Differences in physical properties of the fibrous and

prismatic tremolite specimens are indicated by the data obtained from DTA

and XRD studies. While the prepared quantity of each mineral is quite

limited, the source of each of the specimen materials and the appropriate

methods of sample preparation have been carefully documented should

additional quantities be desired.

Key Words: Amphibole asbestos; cummingtonite; grunerite; thermal

analysis; tremolite; x-ray diffraction.

Introduction^

Under the provisions of the Federal Occupational Safety and Health Act of 1970

(PL 91-596), the National Institute for Occupational Safety and Health (NIOSH) is charged

with the responsibility for research related to occupational health, including the development and evaluation of analytical methods for the determination of hazardous workplace

contaminants. To meet this charge, the Measurements Research Branch of NIOSH has a program concerned with the development of new analytical methods as well as with the

j ^Mention of product or trace names does not constitute endorsement by the Public Health

Service.

295
evaluation and improvement of existing methods. Many mineral dusts, such as those of the

silica polymorphs, talc, and asbestos minerals, are included in the hazardous materials

for which analytical methods are needed. Earlier work in the NIOSH laboratory showed that

it was feasible to quantitatively determine by x-ray diffraction techniques (XRD) chrysotile, amosite, and crocidolite using either samples of the bulk material or of airborne

dust collected on filters [1]^. However, further work rather graphically demonstrated the

fact that specimens of a mineral originating from different deposits often exhibit significant variations in impurity content and crystal 1 inity [2], and consequently also exhibit

vast differences in their response to analytical measurement techniques. It was obvious

that reference materials were needed for the development of analytical methods, that these

materials should be from natural sources, and that they be selected on the basis of purity,

especially as to an absence of other similar minerals. Pure minerals could then be mixed

with other materials to simulate the mixtures found in samples collected from occupational

envi ronments.

For asbestos, the International Union Against Cancer (UICC) Standard Reference Samples

[3] are available as reference materials for chrysotile, amosite, anthophyl 1 ite , and

crocidolite. These samples have been well characterized with respect to overall chemical

composition (elemental weight o/o) and fiber length distribution [4]. There are also some data relating to sample response to heat treatment, and the electron and x-ray diffraction

properties [4,5]. However, since these materials were collected and prepared to provide

reference samples for inhalation and injection experiments, they were chosen not for phase

purity but to be representative of the various types of asbestos used by industry.

Further, the UICC samples do not include specimens of the prismatic (nonfibrous) forms of

the mi neral s.

Other reference materials were also needed by NIOSH for the methods development and

evaluation program. Consequently, an effort to collect and characterize at least four

representative specimens of each of eighteen minerals from different geographical

locations was initiated. Table 1 lists the minerals sought and the techniques used for

preliminary characterization of the samples. Following the preliminary evaluation and

characterization of these samples, the "best" source specimens were chosen for

benef iciation, grinding to a respirable size range, and for further characterization and

analysis for impurities. A one kilogram quantity of the ground material was established

as the final, processed amount to be prepared of each mineral. It was expected that this

amount would suffice as reference material for NIOSH analytical research; the source of

selected specimens and the appropriate methods for sample preparation were carefully

documented should additional quantities be desired.

The fonowing discussion will cover the selection, preliminary separation techniques,

benef iciation, grinding, and characterization of some of the amphibole species. Details

concerning the other minerals will be published separately.

Selection of Minerals

More than 80 sources were contacted to obtain the approximately 50 samples of mineral

specimens containing amphi boles which were received and inspected. Of these samples, 12 were discarded based on macroscopic examination; 38 were carried through the preliminary

characterization steps prior to the final selection of the eleven "best" amphibole

samples. Since the final quantity of each mineral needed was large (one kilogram), speci- mens were chosen based on (1) the least contamination by other minerals and the contrasting habit, and, (2) the amenability of the specimen to benef iciation for removal of

contaminant phases.

^Figures in brackets indicate the literature references at the end of this paper.

296
Table 1. Reference materials sought.

Mineral Characterization Techniques

Silica

-Quartz

-Cri stobal ite

-Tridymite

X-ray Diffraction

Beryl Infra-red Spectroscopy

Bunsenite (NiO) Thermal Analysis

Fl uorite (TG and DTA)

Talc

Fibrous Serpentine

-Chrysoti le

Platy Serpentine

-Anti gor ite

Fibrous Amphi boles

-Croc idol ite Macroscopic Habit

-Grunerite ("Amosite") Light Microscopy

-Anthophyl 1 ite X-ray Diffraction

-Tremolite Thermal Analysis

Prismatic Amphi boles

-Riebeckite

-Grunerite

-Cummi ngtonite

-Anthophyl 1 ite

-Tremol ite

297
After a macroscopic inspection of the specimens as received, using a hand magnifier,

portions were hand ground in an agate or diamonite mortar and pestle. The ground samples were dry sieved to pass a 325 mesh screen and were further characterized using polarized

light microscopy, qualitative x-ray diffraction (XRD), and qualitative differential

thermal analysis (DTA). The types and quantities of impurities were noted for each of the

specimens, and careful scrutiny was given to the mineral morphology, especially for the

samples needed for the fibrous and prismatic (or nonfibrous) habits.

For macroscopic specimens, the mineralogical criteria distinguishing the fibrous from

the prismatic habit are unequivocal. This is illustrated by the samples of tremolite

which are shown in figures 1 through 4. The origin of the fibrous tremolite shown in

figure 1 is Alaska, while that of figure 2 is a small sample from Italy which was collected in approximately 1890 and has since been in the collection of the Field Museum

of Natural History in Chicago, IL. It was not possible to locate a contemporary source

of fibrous tremolite in Italy. The prismatic tremolite in figure 3 is from South Dakota

and is a fairly pure sample with an acicular radiated structure which is quite evident in

the hand specimens. The sample shown in figure 4 contains interlaced prismatic tremolite,

talc and other impurities. Although the individual tremolite "needles" are colorless, the

sample has a lavender color which may be due to manganese substitutions [6].

298
Figure 3. Prismatic tremolite with calcite: South Dakota, 0.57X.

Figure 4. Prismatic tremolite

with talc and other

impurities, 0.5X.

Distinguishing between the fibrous and prismatic habits is less straightforward with

microscopic specimens. The photomicrographs of tremolite (figures 5 and 6) illustrate the

appearance of fibrous and prismatic tremolite specimens ground to a mean particle size of

3.1 \^m and 1.7 |jm respectively. Similarities in particle shape are evident, although the mean aspect ratio of the fibrous tremolite particles is greater than that of the cleavage

fragments of the prismatic material.

299
Figure 5. Fibrous tremolite:

Rajasthan State, India, 407X.

Figure 6. Prismatic tremolite:

Gouverneur, New York, 407X.

Table 2 lists the amphiboles, and their sources, which were chosen for any necessary

benef iciation and final grinding. The impurities listed are those contaminants determined

by microscopic analysis of the hand-separated portions of the desired phase. Some of the

amphiboles, including the samples of prismatic and fibrous tremolite as well as crocidolite, were obtained as nearly pure, single phase specimens. Others, such as the

prismatic grunerite, anthophyl 1 ite , and cummingtonite were intermixed with accessory

minerals. Hand specimens of the amphiboles selected for preparation as reference

materials are illustrated in figures 7-14.

300
Table 2. Amphibole sources.

Mi neral

Tremol ite

Fibrous

Prismatic

Geographical Origin

Udaipur District

Rajasthan, India

Gouverneur, N.Y.

Representative Impurities

Plant fragments

(carbonaceous) & other

minerals, <3%

Talc, Limestone,

Hematite, <2%

Cummingtonite Homestake Mine,

Lead, So. Dakota

Calcite, Quartz,

other minerals, ^-30%

Grunerite

Fibrous

("Amos ite")

Prismatic

Lydenburg District

Transvaal, South Africa

Luce #1 Mine

Newfoundl and

Magnetite & other

minerals, <11%

Quartz, Magnetite,

other minerals, -^50%

Anthophyl 1 ite

Fibrous

Prismatic

Bozeman, Montana

Bamble, Norway

Magnetite, Calcite &

other minerals, <11%

Quartz, Mica, Rutile,

Magnetite, other

minerals, "^25%

Croc idol ite South Africa Phases which are too fine

to identify, <2%

Riebeckite St. Peter's Dome

El Paso County, Colorado

Quartz, feldspar, iron

oxide, and other

minerals, ~15%

301
Figure 7. Fibrous tremolite: Rajasthan State, India, IX.
Figure 9. Fibrous grunerite ("Amosite"): Lydenburg District,

Transvaal, South Africa, 0.8X.

Figure 10. Prismatic grunerite with quartz: Luce No. 1 Mine,

Newfoundland, 0.8X.

303
Figure 11. Fibrous anthophyll ite : Bozeman, Montana, IX.
Figure 13. Crocidolite (fibrous riebeckite): South Africa, 0.57X.

Figure 14. Prismatic riebeckite (black) with quartz and feldspar:

St. Peter's Dome, El Paso County, Colorado, IX.

305
Separation and Grinding Techniques i

(ii For those samples which required benef iciation to produce the pure mineral

separation techniques were chosen which would adequately liberate the desired phases ai |' least adversely affect their purity. In order to conserve the selected mineral ' techniques were chosen which could be applied to material varying widely in size. Tl\

preliminary size reduction necessary for benef iciation and grinding of the fibro' '1 amphiboles was accomplished using a rock saw with diamond-impregnated blades. For t

nonfibrous amphiboles, a large mortar and pestle were fabricated from strongly magnet,

stainless steels so that metals abraded from the equipment during crushing could I removed from the ground material using a magnet. All benef iciation steps were done befo . the final grinding to allow efficient use of the mineral extraction methods, which a severely limited if the particle size is too small. To avoid chemical alteration of tl desired phases, benef iciation was generally limited to physical methods [7]. The fin.

grinding was designed to produce nonfibrous materials which had a mass median aerodynam

diameter between 0.5 and 5.0 pm, and a maximum size of 10 pm. For the fibrous material;

the desired median length was the range 2-10 pm, with a maximum length of 200 pm.

Benef iciation Methods

Simple, primarily physical methods of mineral extraction were employed. Three typt

of hand separation were used: (1) With a mason's hammer and chisels, the availab

specimen material was "high-graded" to obtain pieces with the greatest concentration c the desired phase; from these, the larger masses of impurities were cobbed. (2) The roc saw was used to cut cross-fiber vein materials into slabs one centimeter thick measure along the fiber length. The slabs were then chipped into small pencils of fibers fc

further benef iciation and/or preparation for milling. The saw was also used to cut wal

rock from the margins of cross-fiber vein specimens of fibrous grunerite, anthophyl 1 ite

'

and crocidolite. (3) Hand picking, or for ferromagnetic minerals a powerful hand magnet was used to remove small quantities of obvious contaminants at any stage in the siz

reduction procedure.

Only two benef iciation techniques were used in which mineral specimens were exposei

to the risk of chemical alteration. Slow dissolution of carbonate minerals from specimen'

of tremolite and actinolite was accomplished by digestion in dilute (""3 N) acetic acidi

Bromoform and tetrabromoethane were used for density separations of quartz, micas, am

other silicates from tremolite, cummingtonite and grunerite. After separation, th' samples were rinsed repeatedly, with acetone or ethanol and then distilled water, t remove residues of the organic liquids.

Grinding Techniques

Research has shown that some grinding mechanisms degrade the crystalline structure o' minerals, particularly asbestiform species, to a considerable degree. Shearing am

cutting (in the sense of pinching) actions are reported to be very destructive t( crystal 1 inity [8]. Initial attempts in this program to grind asbestos in ball mill;

equipped with lifter bars confirmed this observation. Impact between air-suspende(

particles and/or impact of elongate fragments on cutting edges accomplished size reductior

with much less reduction in crystal 1 i nity, as shown by x-ray diffraction studies.

Therefore, grinding tests were made to identify milling devices which exploit the free

impact principle and which could efficiently produce large quantities of respirable size

particles. ;

For size reductions of fibrous amphiboles, a fiber mill (Retsch Ultracentrifugal-mill

Type ZM-1) was chosen. In this device a rotor with vertical pins at the periphery spins

at_ 10,000 or 20,000 rpm impelling fibers outward against the perforated wall of the

grinding chamber (sieve ring) on which cutting edges are angled toward the oncoming

particles. The non-fibrous amphiboles were ground using a jet mill (Micron-master Jet

Pulverizer) in which tangential ly inward-directed jets of dry, filtered air (50 scfm at 90

psig) circulate the feed material in an annular grinding chamber. Size reduction is

accomplished by impact between particles; the air stream minimizes particle contact with

the walls of the grinding chamber. Additional advantages of the fiber mill and jet mill

for this work are: (1) the carrying air stream controls heat build-up in the equipment

306
thereby reducing the risk of thermal degradation of the material being milled. (2)

Virtually all particles are subjected to size reduction with each pass of material through

the mill. (3) Each mill is provided with a cyclone collector, thus providing coarse and

fine fractions. (4) The continuous processes permit efficient size reduction of kilogram

quantities of fibrous and nonfibrous amphiboles to the specified size by iterative milling

tvithout additional size classification steps. Table 3 presents particle size

distributions for fibrous and prismatic tremolite reduced to final size by the respective

milling devices.

Table 3. Particle sizes^ of "reference" tremolite samples after grinding.

Fibrous (India) Prismatic (New York)

Size Range

(pm)

Number

Percentage

Size Range

(pm)

Number

Percentage

<2 37.4 <1 28.0

2-6 35.8 1-3 47.0

6-10 15.4 3-5 18.3

10-20 6.9 5-7 5.9

20-80 3.6 7-10 0.8

80-160 0.9 >10 0.0

>160 0

3.1 pm Geometric Mean 1 . 7 pm Geometric Mean

Particle sizes determined using optical microscopy. For fibrous

tremolite, fiber length is reported; for prismatic tremolite,

Feret' s diameter.

Analytical Studies

Analytical studies have been initiated using two of the "reference" materials from

this program, the fibrous and prismatic tremolite samples. In addition to these

"reference" samples, which were processed by IITRI, and which were carefully characterized

as to identity, source, and particle size, a number of samples from the NIOSH mineral

collection were used. These samples were included in the analyses to allow comparisons of

tremolite specimens from various sources and geographical locations to determine if

general characteristics of tremolite specimens could be delineated by obtaining additional

experimental data. The NIOSH specimens were ground in a SPEX freezer mill at liquid

nitrogen temperatures, sieved through a 10 pm sieve, and sized using electron microscopy

techniques. The ground material had a mean particle length or diameter of <3.0 pm. The

following sections summarize the preliminary results obtained in the studies of tremolite.

Chemical Analyses

The relative iron, magnesium, and calcium content of several of the specimens used in

these studies was determined in order to confirm the designation of these amphiboles as tremolite. To minimize contamination which could occur from contact with metallic

surfaces during grinding, pieces of the hand specimens instead of ground material were

used for the analyses. These pieces were dissolved by heating in a mixture of HF and

concentrated HCl. Blind replicate analyses were done for each of the specimens using

307
atomic absorption spectrophotometry. The results (table 4) for the ratio (Fe + Mg : Ca

and the calculated weight percent FeO indicate that all of the samples fall within thi

empirical composition limits for tremolite [9], including a specimen previously identifiei

as prismatic actinolite. In general, the specimens of fibrous tremolite contain more iroi

than the prismatic form although the South Korean sample of fibrous tremolite was ai excepti on.

Table 4. Chemical analyses.

Atom Ratio Atom Ratio

Mmpm DO 1 e r e Mn Fe + Mg : rV L . /5 r t:U

Prismatic Tremolite

Gouverneur, N.Y.'^ 1 205 : 78 5.3 : 2. 0 0. 21

South Dakota 1 . 44 : 21 4.3 : 2. 0 1. 03

Fibrous Tremolite

Rajasthan, India^ 1 : 13 : 6 4.7 : 2. 0 2. 87

Alaska 1 : 13 : 6 4.7 : 2. 0 3 03

Korea 1 : 33 : 16 4.3 • 2 0 0 69

Italy 1 : 31 : 14 4.6 2 0 1 43

Q Prismatic Actinolite

South Dakota 1 : 15 : 7 4.6 2 0 2 63

f

Theoretical limit of ratio = 5:2.

"Reference" material, supplied by IITRI.

c Classification based on color and location of source.

X-Ray Diffraction Studies

For the x-ray powder diffraction studies of the "reference" tremolites, both bulk

powder samples (packed in cups) and thin layers on silver membrane filters were used. For

the filter studies, homogeneous suspensions of known tremolite concentration in

isopropanol were prepared using ultrasonic agitation to ensure dispersion. Aliquots of

this suspension were filtered through 25 mm, 0.45 pm pore size silver membrane filters.

The calculated weight of tremolite deposited was confirmed by weighing, using a microbalance. For both fibrous and prismatic tremolite the 310 and 110 peaks (3.14 A and

8.38 A, CuKa radiation) were step scanned to determine the integrated peak intensities.

The calibration curves (figure 15) were prepared by plotting the net normalized integrated

intensities of these peaks versus the amount of tremolite on the filters. §

The data clearly indicate that quantitation of pure samples as small as 20 pg is

feasible. However, the ratios of the reflections, l!iio):I (sio) > ^V>^ different for filter

deposits of fibrous and prismatic habits. The peak ratio (8.38 K:3.4 K) for prismatic

tremolite is approximately 1.0 while that for the fibrous tremolite is approximately 0.40.

Packed bulk samples of both tremolite habits give the same peak ratio, the value of which

is 0.20. Information in the Powder Diffraction File [10] indicates a peak ratio of 1.0

for tremolite from St. Gotthard, Switzerland. The morphology is described as "white

308 f

i
40

MICROGRAMS OF TREMOLITE

Figure 15. Calibration curves for fibrous and prismatic tremolite:

Fibrous tremolite: aS.U A; o8.38 A

o o Prismatic tremolite: •3.14 A; "8.38 A

309
radiating fine fibrous masses," but the term "radiating" suggests it may be a prismatir

form. Data obtained for specimens of tremolite from other geographical locations indicat'

that, for material deposited on filters, the samples of prismatic tremolite in genera

show a larger ratio for these peaks than do samples of fibrous tremolite (table 5). ;

Table 5. Ratio of XRD peaks observed for fibrous and prismatic tremolite.^

Amphibole

Prismatic Tremolite

Gouverneur, N.Y.'^

South Dakota

Newburyport, Mass.

No. of Replicates

7

5

10

Ratio (8.38A:3. 14A)

1.04

1.08

1.45

Fibrous Tremolite

Rajasthan, India''

Alaska

Korea

Italy

7

10

5

5

0.39

0.55

0.35

1.25

150 pg on 0.45 pm pore size silver filters.

"Reference" material, supplied by IITRI.

At this point no explanation can be advanced to account for the differences in peat

ratios, although the effects observed may be due at least in part to preferred orientatior

of the particles in some or all of the samples. Regardless of the reason, the effect is seen for a variety of samples and for a wide range of filter loadings as demonstrated b>

the calibration curves. The distinctions observed using this technique may prove useful

in analytical attempts to ascertain the type of material to which a worker is beinc

exposed.

Thermal Analysis Studies

Preliminary differential thermal analysis (DTA) studies on tremolite samples hav(

been completed. These studies included an evaluation of the feasibility of this techniqu«

for the quantitative analysis of tremolite and, while good calibration curves wen

obtained, DTA was not sensitive enough to detect microgram quantities of tremolite. Th(

samples were heated in platinum cups to a temperature of 1150 °C at a heating rate o1 10°/min in dry air flowing at 5.7 L/hr; the instrument was calibrated using SrCOs, an NBSICTA Standard Reference Material. '

In parallel with the XRD studies of the "reference" tremolite samples, difference*,

between these samples (table 6) were observed during the thermal studies of fibrous ane prismatic tremolite samples. These differences in peak position and the color of the

decomposition product were observed for samples from other geographical locations as well

as for the "reference samples." Similar differences were observed by IITRI for those

specimens considered for selection as "reference" materials. All samples displayed the

strong endotherm which is associated with the loss of structural water and the breakdown

of the amphibole structure, which subsequently recrystal 1 izes to a monoclinic pyroxene

[11]. However, the data indicate that in general the fibrous tremolite samples dehydrate

and recrystal lize at a lower temperature than do the prismatic tremolite samples. This

310
behavior is analogous to that noted for serpentine, i.e., chrysotile loses structural

water at a lower temperature than does antigorite [12]. Although it is recognized that

differences in particle size, grinding techniques and experimental conditions can affect

the position of a DTA peak [13], data obtained in both the NIOSH and IITRI laboratories

are consistent in showing that the endotherm of fibrous tremolite is lower by

approximately 50 °C than that of the prismatic tremolite. It was also observed that the

pyroxenes formed from fibrous tremolite were always brown to tan in color while the

pyroxenes formed from the prismatic tremolite were always white in color. However, XRD

scans of the pyroxenes were virtually the same regardless of color or origin of the

specimen and indicated that the final decomposition material was primarily diopside.

Table 6. Thermal analysis of tremolite.^

No. DTA^

Amphibole Samples Endotherm, °C Color of Pyroxene

Fibrous Tremolite

NIOSH*^ 4 1026 ± 27 tan

IITRI 1 1002 not determined

Prismatic Tremolite

NIOSH^ 5 1078 ± 20 white

IITRI 4 1053 ± 11 white

^ NIOSH samples included those listed in Table 5 as well as two

additional samples from the Gouverneur, N.Y. area; IITRI samples

include those screened as potential "reference" materials.

^ Geometric mean particle length <3.0 fjm. ^ Geometric mean particle maximum dimension <3.0 pm.

Summary and Conclusion

The analytical studies planned for the reference materials have been initiated

jsing the tremolite specimens. These studies have indicated that x-ray diffraction may

:urn out to be an even more useful tool than expected. The detection limits

jbtained and the differences in peak ratios observed for samples of fibrous and

)rismatic tremolite on silver filters have potential for applications to analyses

)f hazardous, workplace contaminants.

The authors gratefully acknowledge the guidance and assistance received during this

3rogram from J. V. Crable of NIOSH and B. G. Woodland of the Field Museum.

References

[1] Crable, J. V. , Am. Ind. Hyg. Assoc. J. , 27, 293 (1966).

[2] Nenadic, C. M. and Crable, J. C. , Am. Ind. Hyg. Assoc . J., 32, 539 (1971).

[3] Timbrel 1, V., Gibson, J. C. and Webster, I., Int. J. Cancer . 3, 406 (1968).

311
[4] Timbrel!, V., "Pneumonocom'osis. Proceedings Int. Conf. ," Johannesburg, 1969,,

. 28-36.

[5] Skikne, M. I. , Talbot, J. H. , and Rendall , R. E. G. , Eny. Res. , 4, 141 (1971).

[6] Deer, W. A., Howie, R. H. , and Zussman, J., "Rock-Forming Minerals, Vol. 2, Chain

Silicates," J. Wiley & Sons, N.Y. , N.Y. 1963 p. 253.

[7] Muller, L. D. , "Laboratory Methods of Mineral Separation," CH. 1, in J. Zussman, ed. , Physical Methods in Determinative Mineralogy , Academic Press, London & N.Y. , 1967.

[8] Ocella, E. and Maddalon, G. , Med. Lavoro , 54 (#10), 628 (1963).

[9] See, for example. Deer, W. A., Howie, R. A., and Zussman, J., "Rock-Forming Minerals,

Vol. 2, Chain Silicates," J. Wiley & Sons, N.Y. , N.Y. 1963, p. 251.

[10] Powder Diffraction File . Joint Committee on Powder Diffraction Standards, 1601 Park

Lane, Swarthmore, PA 19081.

[11] Deer, W. A., Howie, R. H. , and Zussman, J., "Rock-Forming Minerals, Vol. 2, Chain

Silicates," J. Wiley & Sons, N.Y., N.Y. 1963, pg. 254.

[12] Deer, W. A., Howie, R. H. , and Zussman, J., "Rock-Forming Minerals, Vol. 3, Sheet

Silicates," J. Wiley & Sons, N.Y. , N.Y. 1962, pg. 180.

[13] Martinez, E. , Am. Miner . , 46, 901 (1961).

Discussion

I. STEWART: Both DTA and x-ray diffraction are very sensitive to packing, and, of

course, this can be related to shape. Did you do any tests to determine whether packing

or repacking would change the relative ratios of peak heights or peak positions?

J. HAARTZ: No, we haven't.

STEWART: Or spinning the sample in x-ray diffraction perhaps?

HAARTZ: The relative ratios of the peaks in x-ray diffraction were the same for

the bulk samples. For the samples that were deposited on a silver filter, that is a very thin layer; we did see the differences in the peak ratios. This was the case not

only with samples of different origins, but with a great many replicas of the same material

STEWART: I see. So, it was purely the fact that it was fibrous, you think? I didn't quite catch what you meant by your bulk sample. By bulk, I was equating that

with "massive." You mean a bulk fiber sample.

HAARTZ: By a bul k sample, I mean a milligram or more, of either the massive or fibrous, showed the same diffraction pattern: identical. When these samples are deposited as a thin layer on a silver membrane filter and the pattern taken, we do see differences in the peak ratios.

312
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

ASBESTIFORM MINERALS IN INDUSTRIAL TALCS:

COMMERCIAL DEFINITIONS VERSUS INDUSTRIAL HYGIENE REALITY

John M. Dement

U.S. Department of Health, Education and Welfare

Public Health Service, Center for Disease Control

National Institute for Occupational Safety and Health

Division of Surveillance, Hazard Evaluations and Field Studies

Cincinnati, Ohio 45226

Abstract

As part of its industry-wide study of the talc industry, the

National Institute for Occupational Safety and Health (NIOSH) has

conducted Detailed industrial hygiene studies of mine and mill

operations processing talcs contaminated with asbestiform minerals. The

principal analytical method used for studies of asbestiform minerals in

talc bulk samples and airborne dust samples is analytical transmission

electron microscopy utilizing selected area electron diffraction and

microchemical analysis for fiber identification. This presentation

includes a discussion of the methods of analysis being used by NIOSH and

comparisons of results of analysis with other analytical techniques.

Also included are results of NIOSH industrial hygiene studies in

asbestiform talc operations and comparisons of airborne fiber

characteristics (fiber length, diameter, aspect ratios, etc.) in these

operations with other industrial processes using asbestos fibers.

Key Words: Amphi boles; anthophyll ite, asbestiform minerals; industrial

talc; occupational health; tremolite.

Introduction

The mineral talc is a pure hydrous magnesium silicate Mg6(Sig022)(0H)4 which has a theoretical chemical composition of 63.5 percent Si02, 21.7 percent MgO, and 4.8 percent

H2O [1,2]^. However, this ideal chemical structure is rarely found in nature due to ionic

substitution in the talc structure and due to common association with other minerals such

as tremolite, anthophyl 1 ite, calcite, magnesite, quartz, dolomite, diopside, and serpentines

(chrysotile, antigorite, and lizardite) [1,2]. Most talcs, as mined, are associated with

varying proportions of some of these minerals [1] and sold as industrial talcs. In 1974 over 1.4 million short tons of talc were produced in the United States with major uses being in ceramics, elastomers, foundry facings, insecticides, paints, paper, roofing and

toilet preparations [3].

The National Institute for Occupational Safety and Health (NIOSH) in cooperation with

the Mining Enforcement and Safety Administration has underway an industry-wide study of the

talc mining and milling industry. These studies include both epidemiological studies of

exposed worker populations to determine health effects which may be attributed to occupational exposures and detailed industrial hygiene studies to characterize the various

agents to which workers have been exposed.

Figures in brackets indicate the literature references at the end of this paper.

313
Since many talc deposits contain asbestiform amphiboles and in some cases chrysotile

(a serpentine), a large portion of the NIOSH environmental studies is directed toward

determining mineral fiber exposure patterns and characteristics. For such studies, the

primary method used is analytical transmission electron microscopy. This report includes

a description of the equipment and procedures used by NIOSH for its environmental studies

of industrial talc exposures and results of industrial hygiene studies in a talc mine and

mill producing talcs containing asbestiform amphibole minerals. Also discussed are com- mercially employed definitions of what constitutes asbestos and the relationship of these

definitions to observed industrial asbestos exposure characteristics.

Analytical Methods \

Equipment

A number of methods are available and have been used to identify and quantitate

asbestos concentrations in environmental samples. These methods include x-ray

diffraction, differential thermal analysis, phase contrast and bright field optical

microscopy, petrographic microscopy, scanning electron microscopy, and transmission

electron microscopy. Each of these methods have certain advantages and disadvantages

[4,5]. However, many researchers today consider analytical electron microscopy to be the

method of choice for studies of occupational and environmental asbestos exposures.

For NIOSH studies of industrial talc exposures, analytical transmission electron

microscopy is employed along with other standard mineralogical techniques such as x-ray

diffraction and petrographic microscopy. The analytical system consists of a combination

transmission-scanning electron microscope with a side entry stage equipped with an energy

dispersive x-ray detector which is fitted through a port in the microscope column parallel

to the specimen holder. The specimen-to-detector distance is approximately 10 mm with the

specimen tilted 39 degrees to the electron beam for optimum x-ray collection. The energy

dispersive x-ray detector has an actual energy resolution of less than 170 electron volts,

and spatial resolutions of less than 0.5 micrometers are easily realized. This

combination of analytical instrumentation permits visual characterization of particulate

morphology such as fiber shape, length, and diameter as well as fiber identification using

both selected area electron diffraction and x-ray microchemical analysis. In addition,

surface topography may be further studied with this instrument by use of the scanning mode

of operation using secondary electron images.

Procedures

Either bulk quantities of materials of interest, such as talcs, or environmental

samples collected on membrane filters are routinely analyzed. The majority of samples

studied consists of airborne particulates collected in industrial operations for the

purpose of determining occupational exposure patterns. These samples are routinely collected on Millipore AA, 37 mm diameter membrane filters at sample rates of 1.5-2.0 liters

per minute. Sample durations may vary from 15 minutes in very dusty operations to six

hours for operations with little visible dust.

The method presently' used by NIOSH for preparation of membrane filter samples for

electron microscopic analysis is a modification of a direct clearing method first described

by Ortiz and Isom [6]. The NIOSH method has been described in detail elsewhere [4].

Briefly, this method consists of the following steps:

1. A section of the membrane filter is cut with a cork bore (8 mm diameter)

or a scalpel. This section is removed and placed sample side up on a clean

microscope slide with the edges fastened to the slide with either a gummed

binder ring or tape.

2. The slide assembly containing the sample is placed in a glass petri dish on top of four Whatman filters which have been saturated with acetone and

covered. The acetone vapors destroy the microporous structure of the filter

by slow dissolution, producing a fused, microscopically smooth surface on

314
the sample side of the membrane filter. A 10-minute fusion time has been

found to be generally acceptable for Millipore AA filters.

3. After fusion of the filter surface, the slide assembly is placed in a vacuum evaporator on a rotary stage where the sampled side of the filter receives a fairly heavy (^-200 A) carbon coat. This carbon coat aids in retaining

particles during subsequent filter dissolution and also provides for greater

thermal stability during microscopic examination.

4. The final step is dissolution of the membrane filter and deposition of the

particles onto electron microscope grids. A modified Jaffe Wick method is

used whereby four Whatman filter papers are saturated with acetone. Twohundred mesh carbon filmed grids are used and the coated filters are placed

sample side down on them. The petri dish is then covered. Complete filter

dissolution takes 8 to 16 hours. Acetone is replaced as necessary.

Using this method, many filters may be prepared as a "batch". Particle losses have

been low and estimated at less than 10 percent [6].

Samples prepared by the preceding method are analyzed using analytical transmission

electron microscopy whereby three pieces of data are gathered and used to identify each

fiber (3 to 1 aspect ratio particles) observed. These include: (1) visual identification

of single fiber electron diffraction patterns, (2) visual identification of

semiquantitative elemental analysis spectra using x-ray microchemical techniques, and (3)

observation of morphological characteristics, such as diffraction fringes, which may aid

in identification. In addition, fiber length and diameter are also recorded. For most

studies an accelerating voltage of 100 kilovolts is used with a screen magnification of

approximately 17,000X. Beam currents are usually fixed at 100 microamps (not to be

confused with specimen current).

Fiber concentrations are estimated using the average grid opening area as the calibrated counting area. To optimize statistical accuracy of the analysis while keeping

analysis time to acceptable limits, 10 grid openings or 50 fibers are analyzed for each

sample with a minimum of 5 grid openings. Analysis times range from 90 minutes to 3 hours

per sample. Using this counting criterion for a typical 90 minute sample collected at 2

liters per minute, the lower limit of detection is estimated to be less than 0.1

fibers/cc. Precision and accuracy estimates from studies of the NIOSH phase contrast

method [7] are considered generally applicable with a coefficient of variation of

approximately ±25 percent for most samples.

Environmental Studies of Talcs Containing Asbestiform Minerals

Methods

As previously mentioned, a large portion of the NIOSH industry-wide study of the talc

industry involves industrial hygiene studies of worker exposures, including exposures to

asbestiform minerals. One such operation recently studied involved a mine and mill

producing industrial talcs certified by the mining concern to be free of asbestos.

Apparently, the prime analytical methods relied upon by this company to conclude that its

products were asbestos free were gross methods such as observation with a common hand lens

or at best low power stereomicroscopy both of which were claimed to be sufficient and

proper mineralogical techniques.

In order to evaluate these claims, a detailed industrial hygiene study was conducted

at the mine and mill in question to evaluate worker exposures using best available

sampling and analytical technology. Although a number of different sampling and analysis

methods were employed, only results of the fiber samples are presented in this report.

In order to evaluate fiber exposures and exposure characteristics, personal, breathing

zone samples were collected from workers in the mine and mill using 37 mm diameter,

Millipore AA membrane filters operated at a flow rate of 1.7 liters per minute. Sample

315
filters were changed periodically throughout the work shift to prevent filter overloading.

During the study, more than 220 such samples were collected and used to determine both peak

and time-weighted-average exposures. All samples were analyzed for fiber concentrations

(>5 pm) using the standard phase contrast method recommended by NIOSH [7].

In addition, approximately 15 percent of these samples were analyzed by the electron

microscopic methods previously described.

Results

Results of the fiber concentrations in the mine and mill as determined by phase

contrast optical microscopy are shown in Table 1. Highly elevated fiber concentrations

were observed in both mine and mill operations with time-weighted-average exposures ranging

from 0.8 to 9.8 fibers >5 pm/cc in the mine and 0.2 to 15.0 fibers >5 pm/cc in the mill.

Peak exposures as high as 29.1 fibers >5 pm/cc were observed.

Table 1. Summary of fiber exposures in talc mine and mill operations as determined by

optical microscopy. ----- Fiber Concentrations (fibers >5 pm/cc) -----

Operation Time-Weighted Averages Highest Peak

Mean ± SE Median Range Cone. Observed

Mine (N=54) 4.5 ± 0.8 4.4 0.8- 9.8 18.2

Mill (N=168) 5.0 ± 0.5 4.3 0.2-16.0 29.1

N = Number of individual samples collected SE = Standard Error

Time-Weighted averages represent full shift determinations

While the above fiber concentrations, determined by phase contrast microscopy, may

include some fiber types other than asbestos (e.g., talc "fibers"), they nevertheless

represent minimum estimates of true exposures to asbestiform minerals as most asbestiform

fibers are less than 5 pm in length and, in addition, some fibers, although longer than

5 pm, may escape detection due to resolution limits of optical microscopy. These facts are demonstrated in Table 2, which show concentrations of positively identified asbestiform

mineral fibers as determined by electron microscopy. Time-weighted-average exposures were

found to range from 9.5 to 25.0 fibers/cc in the mine and 7.3 to 102.7 fibers/cc in the

mill. The highest concentration observed on a single sample was 102.7 fibers/cc.

Table 2. Summary of asbestiform mineral fiber exposures in talc mine and mill

operations as determined by electron microscopy.

- - Fiber Concentrations^ (fibers (all lengths)/cc) - -

Operation Time-Weighted Averages Highest Peak

Mean ± SE Median Range Cone. Observed

Mine (N=8) 16.4 ± 0.9 15.3 9.5- 25.0 25.0

Mill (N=19) 30.0 ±1.4 24.1 7.3-102.7 102.7

N = Number of air samples randomly chosen and analyzed by electron microscopy

SE = Standard Error

^ Concentrations reported include only those fibers positively identified as one of the asbestos minerals by analytical electron microscopy.

316
A typical electron photomicrograph of fibers in these operations is shown in figure 1 demonstrating the fibrous morphology of these particulates. The asbestiform habit of many

of these fibers is evidenced by the "fiber bundle" effect. Results of the electron diffraction and microchemical studies on these fibers clearly demonstrated the presence of

two amphibole fiber types; these being tremolite and anthophyll ite. Analytical data for

typical tremolite and anthophyl 1 ite fibers are shown in figures 2 and 3, respectively.

The anthophyl 1 ite is seen to be low in iron content.

Figure 1. Electron photomicrograph of particles in talc certified as asbestos-free.

317
blectron photoimcrographs

0 ISi e 39SEC 13e93INT

VS: see HS: 2eE V / C H

Si

Diffraction pattern X-ray spectrum

Figure 2. Analytical data for tremolite fibers in talc certified as asbestos-free.

318
Electron photomicrographs

Diffraction pattern X-ray spectrum

Figure 3. Analytical data for anthophyl 1 ite fibers in talc certified as asbestos-free.

Tabulations of results of the fiber identification studies by electron microscopy are

shown in Table 3. Of all airborne fibers (3:1 aspect ratio particles), 12-19 percent and

38-45 percent were found to be tremolite and anthophyl 1 ite, respectively, while 38-39

percent remained unidentified due to unrecognizable diffraction patterns. Tremolite fibers

were observed to be generally shorter in length than anthophyl 1 ite fibers as demonstrated

in Table 3 when only fibers longer than 5 pm were considered. Only 7 percent of the fibers

longer than 5 pm were identified as tremolite whereas 65 percent were anthophyl 1 ite. This

may also be observed in Table 4 where summary statistics of fiber length are given. While

all median fiber lengths were found to be similar and not statistically different, the

proportion of anthophyl 1 ite fibers longer than 5 pm in length was significantly (P<0.05)

greater than tremolite (8-10% for anthophyl 1 ite versus only 3% for tremolite).

319
Table 3. Summary of airborne fiber types in talc mine and mill operations

as determined by analytical electron microscopy.

Fiber Length

All Fibers

Fibers > 5 |jm

Percent of all Airborne Fibers

Not Positively

Tremolite Anthophyl 1 ite Nonasbestos Identified

12-19

7

38-45

65

1-2

3

38-39

25

Total number of fibers analyzed was approximately 1850.

Table 4. Summary of airborne fiber lengths for positive amphiboles in talc

mine and mill operations as determined by electron microscopy.

Operation and Fiber Median Length Geometric % < 5 pm

Type pm Standard Deviation in Length

Mine

Tremolite (N=83) 1.6 1.8 97

Anthophyl lite (N=164) 1.5 2.6 90-92

Mill

Tremolite (N=160) 1.5 1.9 97

Anthophyl! ite (N=687) 1.4 2.9 90

N = Number of individual fibers analyzed

Inasmuch as the NIOSH recommended phase contrast counting method defines countable

fibers only on the basis of fiber length and aspect ratio, much controversy has arisen with

various industrial and mining groups claiming that this liberal criterion would define many

mineral fragments as being asbestos. In this regard, fiber aspect ratios for positively

identified amphibole fibers in the talc mine and mill under study are shown in Table 5 for

all fiber lengths, and similar data for fibers longer than 5 pm are given in Table 6. These

tables demonstrate that anthophyl 1 ite fibers in these talcs have larger aspect ratios than

tremolite fibers and by comparison of Tables 5 and 6, aspect ratios increase with fiber

length. Of interest is the fact that less than two percent of the positively identified

amphiboles longer than 5 pm in length had aspect ratios 5 to 1 or smaller.

Table 5. Aspect ratios (length to width) for airborne amphibole fibers

(all lengths) in mine and mill operations as determined by

electron microscopy.

Fiber Type Median Ratio % < 5 to 1 % < 10 to 1

Tremolite (N=164) 7.5 23-24 70

Anthophyl lite (N=687) 9.5 15-17 70

N = Number of individual fibers identified and sized

320
Table 6. Aspect ratios (length to width) for airborne fibers

> 5 |jm in length in mine and mill operations as determined by electron microscopy.

Fiber Type % < 5 to 1 % < 10 to 1

Positively Identified

Amphi boles <2 37-38

Non-Asbestos or Unidentified Fibers 18 80

Approximately 1850 fibers analyzed

Discussion

Results of an industrial hygiene study of talc operations producing industrial talcs

certi f ied by the company under study to be asbestos free have been presented. Contrary to

claims of this company that its products do not contain asbestos, this study demonstrated

excessive exposures to airborne fibers of which more than 70 percent of the fibers >5 pm in

length could be identified as positive asbestiform amphiboles by best available analytical

techniques. Repeated requests have been made of this company to clarify analytical methods

and definitions of asbestos used to arrive at the conclusion that its products were free of

asbestiform minerals. Apparently, the analytical method used was observation of hand ore specimens with a hand lens or, at best, use of low power stereomicroscopy. The definition

of "asbestos" employed is less clear. Apparently the definition used is one which might

best be termed a "commercial definition"; that is, in order for an amphibole to be considered to be asbestos it must have commercial value due to its fibrous shape.

This same company also operates another nearby talc mine and mill producing talc

products which the company acknowledges as containing anthophyl 1 ite asbestos and labels

these products with the warning required by the Occupational Safety and Health Administration. The determination made by the company that these talcs should be labeled was again

based on macroscopic observation of hand specimens.

Having observed such elevated exposures as were presented in this report in operations

considered by this company to be "asbestos free", it would seem logical to evaluate airborne fiber characteristics in this other operation acknowledged as containing asbestos.

Such a study has been conducted using 10 airborne dust samples collected by the Mining

Enforcement and Safety Administration during a 1975 survey. These samples were analyzed

by identical electron microscopic methods which have been previously described and results

are given in Table 7 along with comparisons with the other mine and mill operations

producing products certified to be "asbestos free".

Table 7 clearly demonstrates that all airborne fiber characteristics between these

two operations are remarkably the same. In fact, the mine and mill producing "certified"

talcs were found to have a statistically (P<0.05) significantly higher proportion of

positive amphiboles based largely on a higher tremolite fiber content.

Considerations for what constitutes an "asbestos fiber" from an industrial health point

of view warrants further discussion. Many researchers continue to promote unusable definitions based on the microscopic world whereas microscopic mineral fibers are of real concern

for the health scientist. The data shown in Tables 4 and 7 demonstrate that more than 90

percent of all airborne amphibole fibers in the talc operations studied were shorter than

5 pm in length. Some individuals might argue that these fibers were mineral fragments and

not "asbestos", however, it must be pointed out that all industrial operations using or processing asbestos generate airborne fibers similar to those seen in this study. This

fact is demonstrated in Table 8 which compares airborne fiber lengths in various operations.

321
Table 7. Comparison of airborne fiber characteristics between two operations of the same company, one producing asbestos talcs and the other producing talcs

certified by the company as asbestos free.

Airborne Fiber Characteristics

Proportion Positive Amphiboles

Proportion Anthophyl 1 ite

Proportion Tremolite

Median Fiber Length

Anthophyl 1 ite

Tremol ite

Median Fiber Diameter

Anthophyl 1 ite

Tremolite

Median Fiber Aspect Ratio

Anthophyl 1 ite

Tremol ite

% of Fibers < 5 pm in Length

Anthophyl 1 i te

Tremol ite

Mine and Mill

Produci ng

Labeled Talcs

0.50

0.47

0.03

1 . 61 ^pm

0. 16^pm

9.9

92

Mine and Mill

Produci ng

Unlabeled Talcs

0.58

0.45

0. 13

1 .45 pm

1 . 55 pm

0. 13 pm

0. 19 pm

9.5

7.5

90-92

97

Stati stical

Significance

P<0.05

NS

P<0.001

NS

NS

NS

NS

Insufficient number of fibers observed for calculation of size distribution.

NS = Not significantly different at 0.05 level

Table 8. Comparison of airborne fiber length distribution in various asbestos

operations.

Operation

Textile'*

fiber preparation and carding

spinning, twisting, weaving

Friction^

mixing

finishing

Asbestos-cement pipe^

mixing

finishing

Study Talc Mine and Mill

Fiber Type

chrysotile

chrysotile

chrysotile

tremolite and

anthophyl lite

Median Length

1.4

1.0

0.9

0.8

0.9

0.7

1.4 to 1.6

% < 5 pm

4

2

2

2

2

1

3-10

Taken from reference 8.

322
Conci usions

Based on the preceding discussion, the following conclusions are drawn.

1. Commercial definitions of asbestos, whereby asbestos fibers are defined on a microscopic scale, have little or no relevance to actual airborne fiber exposures where

fibers of microscopic scale are of concern. Furthermore, those mineralogical or geological methods such as examination of ore specimens with a hand lens or low power

microscopy are of limited value for routine identification of asbestiform mineral

contamination in minerals or mineral products.

2. Users of products containing asbestos have a right to know that they have potential

for exposures to asbestos or asbestiform minerals such that proper precautions may be

taken to eliminate or reduce exposures. Producers of these products have an obligation

to provide these data based on appropriate analytical techniques. Regulatory agencies

must insist that appropriate techniques be employed and monitor results.

3. Inasmuch as considerable quantities of data are available suggesting that many

fibrous materials may be biologically active [8], consideration should be given for

establishing exposure standards for "mineral fibers" as a class of materials with

similar health effects. The lives and health of American workers, America's most

valuable resource, should not be compromised while the health scientist and the

mineralogist disagree over definitions. As Dr. Paul Kotin of the Johns-Manvi 1 1

Corporation stated so well at this conference, the body has not read the asbestos

regulations to decide which fibers should cause a biological response. Similarly,

neither has the body read a mineralogy text to determine which particles of fibrous

minerals should be considered "asbestos" or only mineral fragments.

References

[1] Rohl , A. N. and Langer, A. M. , Identification and qualitative of asbestos in talc,

Env . Health Persp . 9, 95-109 (1974).

[2] Stanley, H. D. and Norwood, R. E. , The detection and identification of asbestos and

asbestiform minerals in talc in Proceedings of the Symposi um on Talc , U.S. Bureau of

Mines, Washington, D. C. , May 8, 1973.

[3] Minerals in the U.S. Economy: Ten Year Supply - Demand Profiles for Mineral and Fuel

Commodities (1965-74), United States Department of Interior Bureau of Mines (1975).

[4] Zumwalde, R. D. and Dement, J. M. , Review and Evaluation of Analytical methods for

Environmental Studies of Fibrous Particulate Exposures, DHEW (NIOSH) Publication

No. 77-204, May (1977).

[5] Keenan, R. G. and Lynch, J. R. , Techniques for the detection, identification and

analysis of fibers, Amer. Iiid. Hy^. J. , 31, 587-597 (1970).

[6] Ortiz, L. W. and Isom, B. L. , Transfer technique for electron microscopy of membrane

filter samples, Amer. Iiid. H^. Assoc . J., 423-425 (1974).

[7] Leidel, A. L. , Bayer, S. G. , and Zumwalde, R. D. , USPHS/NIOSH Membrane Filter Method

for Evaluating Airborne Asbestos Fibers, NIOSH, November (1975).

[8] Dement, J. M. , Zumwalde, R. D. , and Wallingford, K. M. , Asbestos fiber exposures in a hard rock gold mine, Ann. N. Y. Acad, of Science, 271, 345-352 (1975).

Discussion

'^OTE: Discussion of this paper was included in the General Discussion at the end of this

session.

323

National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued (November 1978)

THE DETECTION AND IDENTIFICATION OF ASBESTOS AND ASBESTIFORM MINERALS IN TALC

Harold D. Stanley

Pfizer Inc. , MPM Division^

Easton, Pennsylvania 18042

Abstract

Concern with the health hazards associated with the presence of

chrysotile asbestos and/or the asbestiform minerals in talc has prompted

widespread investigation of methods of analysis which would be

consistent with good analytical practices. Of all the currently

available techniques examined and evaluated, the two most reliable have

been found by us to be Step Scanning X-ray Diffraction and Transmission

Electron Microscopy (TEM), with Selected Area Electron Diffraction

(SAED). The Step Scanning X-ray Diffraction technique allows

quantitative detection and identification of tremolite and the

asbestiform minerals down to 0.1 percent by weight. In the absence of

chlorite it can detect and quantitatively determine chrysotile asbestos

at the 0.5 percent level. Chlorite, however, is often associated with

talc ore bodies. When present, chlorite will mask most of the main x-ray

diffraction peaks of chrysotile. Additionally, the x-ray diffraction

technique cannot distinguish between fibrous and non-fibrous forms of

the asbestiform minerals. TEM is ideally suited to determinations of

this type because of its high resolution and magnification capabilities,

the morphological nature of the problem, and the mi neral ogical

identification capability through SAED.

Key Words: Asbestiform; asbestos; chrysotile; detection; fiber; identification; light microscopy; selected area electron diffraction; talc;

transmission electron microscopy; tremolite; x-ray diffraction.

I Introduction

The pneumoconiotic and cancer-inducing health hazards of exposure to the asbestos and

asbestiform minerals sometimes found associated with talc have been appropriately identified

by recent research, the mass media publications [1-8]^, and the papers heard earlier today.

Because of Pfizer' s position as a supplier of talc to many industries, we felt that a reliable method of detecting and identifying asbestos and asbestiform minerals possibly

present in talc had to be developed. Prior to 1970, we were looking for just such a method.

Previous investigators had addressed themselves to the problem of identifying asbestos

in bulk form or in airborne samples. We concerned ourselves with detecting and identifying

the various forms of asbestos in the bulk talc matrix. As we were to later discover, this

is indeed a hostile environment for the analyst.

^Now with Degussa Corp., Rt. 46 at Hollistor Rd. , Teterboro, N.J. 07608.

^Figures in brackets indicate the literature references at the end of this paper.

325
Our goals were:

1. Identifying the mineralogy of our products, specifically, that of our talcs.

2. The unambiguous determination of the crystal habit and crystal structure of the

mineralogical species present.

Ideally, we were looking for a technique that would be simple and direct, but above all,

it was mandatory that the technique be positive and unambiguous. The mineralogical and

chemical nature of talc and that of the amphiboles or asbestiform minerals and chrysotile

have been adequately described previously at this session. Currently available methods and

methodology for detecting asbestos, tremolite, and the asbestiform minerals in the presence

of talc were reviewed. Types of analyses which we tried included the following:

1. Infrared spectroscopy

2. Thermal analysis including TGA and DTA

3. X-ray di f fraction

4. X-ray fluorescence

5. Adsorption from solution

6. Light microscopy including phase contrast, interference contrast,

polarized light, and dispersion staining

7. Electron microscopy including transmission electron microscopy

and scanning electron microscopy

After initial investigation, the three most likely candidates were:

1. Light microscopy

2. X-ray diffraction

3. Transmission electron microscopy

In order to determine which of the above would meet all criteria for the test, we secured samples of pure talc and tremolite from various deposits owned by Pfizer. Samples

of pure and carefully characterized asbestos minerals were obtained from the International

Union Against Cancer, (UICC), Pneumoconiosis Research Unit, Llandough Hospital,

Penarth Glamorgan, United Kingdom. The talcs and asbestiform minerals were examined in

the pure or as-received state, their characteristics noted and mixtures made to determine

if detection of asbestos minerals was possible at low levels and, if so, what the minimum

detection levels might be.

Experimental

X-ray diffraction patterns were obtained for all the minerals and mixtures used in

this study employing the conventional technique of scanning at rates of 0.5 to 1.0 degrees

2 theta per minute. The samples were then subjected to scrutiny by optical and electron

microscopy. During this procedure it was discovered that certain mixtures and mineral

species shown to be free of asbestiform minerals by the conventional x-ray diffraction and

light microscopy techniques exhibited fairly large percentages (5% or more) of fibrous

tremolite and/or asbestiform minerals when viewed by transmission electron microscopy.

Delineation of the reasons for this paradox enabled us to develop reliable techniques for

detecting tremolite and the asbestiform minerals at the 0.2 percent level in most talcs by

x-ray diffraction. Even lower levels of these minerals are detectable by transmission

electron microscopy.

Light Microscopy

Techniques employing the optical microscope have been used to identify mineral speci- mens for a long time. Techniques that we have examined include polarized light

microscopy, transmission light microscopy, phase contrast, and dispersion staining. The

difficulty which we encountered in applying these techniques to the problem at hand is

that while they work well with pure samples of fairly massive fiber length (3 to 5 microns

326
and larger), observations by transmission electron microscopy have shown that naturally

3ccurring asbestiform minerals often lie below the working resolution of the light

nicroscope. While massive fiber bundles can often be observed by either light or electron

nicroscopy, the observation of individual fibers smaller than approximately 1 micrometer

long by 0.02 micrometers wide requires the high resolution capability of the transmission

electron microscope. In addition, the limit of detection is confounded by the presence of

'apparent fibers" formed when thin talc plates curl up at the edge and roll into a :ylindrical morphology. The limit of positive detection and identification of fibers is

felt by us to be too high to be of any commercial value.

I

j X-ray Diffraction

The d-spacings for talc, chlorite, tremolite, and the asbestiform minerals are seen

IIP Table 1. The values given in Table 1 are averaged for pure materials and can shift as

luch as ±0.02 to ±0.03 nanometers depending upon sample preparation, the level at which

,he constituent is found in the parent matrix, and the specimens conformity to the idealized

:hemical composition. While attempting to detect tremolite and the asbestiform minerals in

;alc at concentrations of two to five percent or below, we found that the normal scanning

ate of 0.5 to 1 degree 2 theta per minute was not satisfactory for the following reasons:

1. The noise level was too high providing a detection limit of only a few percent.

I 2. It was difficult to accurately quantify data from the high noise tracing obtained.

Table 1. Principal lattice spacings of talc and related minerals by x-ray

diffraction Cu K alpha.

- - - - Principal d-spacings in angstroms - - - -

Mineral Species 1 2 3 4 5 6

Talc 9.51 4.73

4.62

3. 14 2. 61 2.50

Chlorite 14.00 7.03 4.70 3.53 2. 82

Tremol ite 8.38 3.38

3.27

3. 12 2.2.

94

81

2.71

2.59

2.53

Chrysoti 1

7.38 4.55 3.66 2. 45 1.54

Amos ite 8.26 3.27 3.07 2. 77

Anthophyl 1 ite 9.50 8.40 4.58 3.25 3. 13 3.06

Croc idol ite 8.43 4.51 3.43 3. 11 2.72

[n order to avoid these difficulties, an automated step-scanning method was employed in

/hich the diffractometer was moved in increments of 0.05 degrees 2 theta, and the intensity

)f x-ray radiation at each step measured for a total of two minutes. An intensity versus

legrees 2 theta plot over the area of interest of 9 degrees to 11 degrees 2 theta was

lade. Figure 1 shows this step-scan method plotted for a talc which showed no evidence of

iny asbestos or asbestiform content. Calibration curves were established by integrating

^he area under the appropriate x-ray diffraction peak of mixtures of 1 to 10 percent

)f the species under investigation, the remainder being a sample of talc shown to be

:remolite and asbestiform mineral free by the method of transmission electron microscopy

:o be outlined below. Figure 2 shows this step-scan plot for the one and five percent

iddition of tremolite to the base talc matrix. Figure 3 shows the calibration curve

obtained by this technique for asbestos in talc, and figure 4 shows the same type of plot

327
2;

Hi

CO

EhD

O

U

8000

7000 i

6000 T

5000 J.

4000 J.

3000 J,

2000

11'

J 1

10.5° 10° 0.5°

Degrees 2 Theta

9°

Figure 1. Step-scan plot of intensity versus degrees 2 theta for Pfizer, Inc.

Montana Talc.

328
8000 1.

11° 10.5° 10.0° 9.5° 9.0°

Degrees 2 Theta

Figure 2. Step-scan plot of intensity versus degrees 2 theta showing the

effect of adding 1% and 5% tremolite to talc.

329
38,000

D

3

W

D

O

U

34,000

30,000

26,000

22,000

18,000

14,000

10,000

6,000

2,000

_i I I I i_ 0 123456789 10

PERCENT ASBESTOS

Figure 3. Percent asbestos as a function of intensity

of diffracted x-rays.

8,000

^ 5,000

m

CO 4,000

EHS

D

R 3,000

1 2 3 4 5

PERCENT TREMOLITE

Figure 4. Percent tremolite as a function of intensity

of diffracted x-rays.

330
for tremolite in talc. The minimum detection limit was calculated as that equivalent to

three times the square root of the background. For tremolite in talc, the minimum detection limit was found to be approximately 0.2 percent. For chrysotile and the other

asbestiform minerals, the minimum detection level obtained by this method is approximately

0.5 percent. This can only be achieved in the absence of chlorite, however. Attempts to remove chlorite by careful acid wash succeeded only in rendering the chrysotile amorphous

to the x-ray beam with the result that no x-ray spectrum was obtained in the chrysotile

region. Further experimentation revealed that the presence of tremolite at fairly low

levels tended to mask or interfere with the detection of some of the other asbestiform

minerals. It was thus clear that another technique would be required in these special cases in order to be able to achieve the unambiguous analysis originally required.

Electron Microscopy

By virtue of its ability to examine individual particles in minute detail and at very

high magnifications, the transmission electron microscope has been found by us to provide

the technique, ancillary to x-ray diffraction, that is needed to complete the unambiguous

detection and identification of asbestiform minerals in talc. The morphology of the

asbestiform minerals and tremolite is generally described as acicular or fibrous. This

immediately serves to isolate them from the platy talc matrix even in the presence of

chlorite, since the chlorite morphology closely resembles that of the talc. If the

sample, made into a specimen for the transmission electron microscope, is or can be made

homogenous, and a careful examination of approximately 100 different fields of view fails

to reveal any fibrous material, then that talc is felt by us to be free of tremolite,

chrysotile, and the other asbestiform minerals.

The lower detection limit of this technique is difficult to assess since one is often

dealing with individual crystals. Figure 5 shows a typical field of view of the fiber

free Montana talc used as a basis of comparison in this study. In order to obtain some

idea of the amount of fibrous material in a talc, we carefully counted the number of

fibers present in each of 100 fields of view of samples contaminated with 0.1, 0.5, and

1.0 percent by weight of fibrous asbestos. The average number of fibers in each field of

view is then plotted as a function of the weight percent of fibers added. A linear

relationship is seen to exist between the average number of fibers and the weight percent,

as illustrated in figure 6. Table 2 shows the results of the fiber count and the raw data

for the calibration curve construction. In the range of 0.1 to 1.0 percent, the linear

relationship shows an excellent correlation coefficient [9]. We have plotted data of

other investigators up to as high as five percent and found that this linear relationship

still holds. An interesting point to note at this time is that the standard deviation for

0.1 weight percent of fibers is more than half of the value of the average number of

fibers in the same field of view. Further investigations in our laboratories have

Table 2. Fiber count - calibration curve.

Weight % fibers Total fibers/100 FOV Avg. # fibers/FOV Std. deviation

1.0

0.5

0.1

1183

634

206

11.83

6.34

2.06

7.07

2.49

1.39

FOV = field of view.

y = mx + b

m = 10.86

b = 0.95

3V b

Correlation coefficient

= 2.92 fibers/FOV

= 0.99997

331
Figure 5. Pfizer, Inc. Platy Montana Talc. Bar is one micron.

332
333
convinced us that this linear relationship does not hold much below 0.1 percent. This is

intuitively obvious upon an examination of figure 6 which, you will remember, does not pass

through the origin. Somewhere below 0.1 weight percent of fibers in the talc, the linear

relationship no longer holds, and the line curves down through the origin. Repeated

examinations have confirmed the fact that the Montana talc used in this study is fiber

free. Below 0.1 weight percent the data must become so scattered as to be meaningless on

a statistical basis. A typical field of view of a Montana talc which was doped with 1.0

percent chrysotile fibers is seen in figure 7. A semi-qualitative estimate of the weight

percent fiber content can be easily obtained by reference back to the calibration curve.

It is mandatory, however, that the samples under investigation be prepared in exactly the same manner as the samples used in the original calibration curve construction. It is

also mandatory that one be certain of the homogeneity of the calibration samples and the
sample under investigation. Great care must be exercised in the sample preparation, or the results become totally meaningless. Figure 8 shows a commercial talc in which

approximately one percent of naturally occurring chrysotile was obscured from detection by

the method of x-ray diffraction because of the presence of chlorite.

Figure 8. Commercial talc with naturally occurring co-deposits

of chlorite and chrysotile asbestos. The asbestos

is present at approximately the 1% concentration

level. Bar is one micron.

335
Selected area electron diffraction was used in conjunction with the examination of

morphology. Using this combined method, a single crystal or particle can be selected and

analyzed. Single particles usually yielded spot patterns, but if a group or bundle of

fibers was found and would transmit electrons, a polycrystal 1 i ne ring type pattern would

result. The use of selected area electron diffraction is mandatory to prove that the

pseudo fibers of talc caused by plate-edge curling and talc plates on edge were actually

talc, and not tremolite or an asbestiform mineral. A comparison of selected area electron

diffraction patterns of these pseudo-fibers to that of the talc platelets showed that the

identical compound, talc, was the only species present.

Table 3 lists the principle electron diffraction maximum for talc, tremolite, and the

asbestiform minerals [10]. In almost all cases, many more spots or rings were observed

than are reported here. In Table 3, only the strongest lines which are the ones most

likely to be observed have been tabulated.

Table 3. Selected area minerals (in

electron diffraction

angstroms).

maxima for talc and related

Talc Tremol ite Chrysoti le Amos ite Anthophyl 1 ite

4.60 4.51 4.58 3.88 4.58

2.62 2.59 3.67 3.45 2.65

2.32 2.53 2.61 3.00 2.27

1.74 2.32 2. 14 2.64 1.75

1.59 2.27 1.70 1.74 1.55

1.53 2.04 1.55 1.61 1.33

1.33 1.86 1.34 1.55 1.28

1.28 1.69 1.29 1.32 1.23

1.65

^ The data for chrysotile, amosite, and anthophyl 1 ite were taken from

reference [11].

Concl usions

The present work has shown that properly prepared samples of talc can be examined by

x-ray diffraction to detect tremolite at levels down to 0.2 percent and chrysotile at the

0.5 percent level in the absence of chlorite. In the presence of chlorite, and at concen- tration levels lower than those stated above, the transmission electron microscope was found to provide reliable detection and identification of fibrous tremolite and the

asbestiform minerals. The transmission electron microscope is the most sensitive we have

found, and appears to be a more or less referee technique since, when morphology

observations are coupled with selected area electron diffraction studies, there are no known interferences. Light microscopy was helpful only in screening samples with large

particles and high concentrations of objectionable fibers. ^

Using the above techniques, we have been able to screen large numbers of talc specimens. We have been able to detect chrysotile and/or tremolite and the asbestiform

minerals at levels down to 0.1 weight percent of fiber. We have been able to detect the

asbestiform minerals in low concentration specifically by transmission electron microscopy

with selected area electron diffraction, when the presence of the asbestos was masked by

the presence of chlorite (which was also present at less than 5% concentration). We, therefore, feel that we have a technique that allows us to detect and identify chrysotile fibrous

tremolite, and asbestiform minerals at concentrations down to 0.1 percent by weight.

336
References

[1] Cralley, L. J., Key, M. M. , Groth, D. H. , Lainhart, W. S. , and Ligo, R. M. , Fibrous

and mineral content of cosmetic talcum products, J. Amer. Indus. Hyg. Assoc., 29, 350

(1968). ~

[2] Hogue, W. L. Jr. and Mallette, L. S. , A study of workers exposed to talc and other

dusting compounds in the rubber industry, J. Indus . Hyg . Toxical . , 31^, 359 (1949).

[3] Smith, K. W. , Plumonary disability in asbestos workers. Arch. Ind. Health , 12, 198

(1955).

[4] Schepers, G. W. H. and Durkan, T. M. , The effects of inhaled talc-mining dust on the

human lung, AMA Arch . Indus . Health, 12, 182 (1955).

[5] Brodeur, P. , The magic mineral , New Yorker Magazine , p. 12, October 1968.

[6] Merliss, R. R. , Talc-treated rice and Japanese stomach cancer. Science , 173 , 1141-

1142 (1971).

[7] Sax, N. Irving, Ed., "Talc", dangerous properties of industrial materials, Reinhold

Publishing Corp., New York, 1963, p. 1217.

[8] Sax, N. Irving, Ed., "Talc", dangerous properties of industrial materials, Reinhold

Publishing Corp. , New York, 1963, p. 469.

[9] Stanley, H. D. , The detection and identification of asbestos and asbestiform minerals

in talc, 34th Annual Proceedings of the Electron Microscopy Society of America, p. 618-619, August, 1976.

[10] Timbrell, V., Characteristics of the International Union Against Cancer Standard

Reference Samples of Asbestos, Proc. Int. Pneumoconiosis Conf . , Johannesburg, 1969.

337
Discussion

J. SCHELTZ: As the spokesman for the Cosmetic, Toiletry, and Fragrance Association,

I would like to make several comments. First: In a survey conducted recently by that

organization among its member companies, some thirty- four hundred samples of cosmetic talc

from both domestic and international sources were analyzed and not a single sample was found to contain chrysotile asbestos. We are aware that the spiking of chrysotile asbestos

into talc can be analyzed effectively by x-ray dif fractometry. These samples of talc are cosmetic which, by definition, means that they contain at least 90 percent of the actual

talc mineral species. I would also like to comment on quantitative analysis of amphibole

minerals, by x-ray di f fractometry. While x-ray di f fractometry is a good technique to

detect amphibole minerals, one needs to be very cautious in attempting to perform a quantitative analysis. I think Dr. Haartz from NIOSH just pointed out that there are major

differences based not only on compositional variations, but also morphological characteristics that make not only peak heights but also integrated peak intensity variable. So,

while x-ray di f fractometry is a good method for detection, it is not necessarily good for

quantitative analysis.

I would also like to point out that the Cosmetic, Toiletry, and Fragrance Association

is currently undertaking an extensive analysis of consumer talcum products for the traces

of amphibole minerals.

H. STANLEY: As I understand it, your first point is that x-ray diffraction is not

particularly quantitative for determination of amphiboles in talc. We haven't found that

to be the case in our laboratory, and I think there are a number of people here that I have been talking to the last several days that have had the same experience. The x-ray

diffraction is good if you want to know, for example, the total amount of tremolite present,

but if you want to know if some of that tremolite is fibrous, then as I attempted to point

out, you have to go to transmitted electron microscopy with selected area diffraction.

SCHELTZ: That's exactly my point (rest inaudible)

As to the second point, we were talking about cosmetic grade talc of at least 90 percent purity, the purity of the Montana talc is in excess of 96 percent, so I understand

your point.

338
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

MISIDENTIFICATION OF ASBESTOS IN TALC

Jerome B. Krause

Colorado School of Mines Research Institute

Golden, Colorado 80401

and

William H. Ashton

Johnson & Johnson

Raritan, New Jersey 08869

Abstract

Both optical microscopy and x-ray diffraction (XRD) are widely used

to detect minerals associated with talc. Optical microscopy can determine the morphology of a particle, but cannot always fully identify

the specific mineral. Although XRD is an excellent screening technique

for the detection of minerals associated with talc, the method can misidentify minerals due to interferences, interpretive errors, and the

inability to determine morphology.

Methods for reduction or elimination of these problems include

special techniques of sample preparation and x-ray diffraction, combined

with microscopic examination (both optical and electron).

Key Words: Amphiboles; asbestos; chlorite; electron microscopy; fiber;

morphology; optical microscopy; x-ray diffraction; talc.

Introduction

There are many ways to analyze and study any naturally occurring material. The

conclusions reached will often vary widely depending on the expertise and specific interest

of the investigator. That situation sums up the present status of "asbestos"; it is also

the status of minerals which are associated with "asbestos"; and it is becoming the status

of other minerals which can be naturally associated with talc.

Popular methods of analysis can give the wrong answer - namely that asbestos is

present when it certainly is not. That problem (misidentification) is not so much one of

limitations of the methods, but rather one of misinterpretation of data, and failure to

recognize the mi neral ogical background required to certify mineral purity, for example,

when analyzing sheet silicates for asbestos. Unfortunately, one main factor is that

asbestos has now developed variable definitions, depending on whether the point of view is

mineralogical , industrial, medical, or regulatory. The medical definition is most

concerned with whether or not the particles are biologically active; the industrial

definition is dependent upon flexibility and weavability; the mineralogical definition

upon crystallography; and the regulatory definition upon size and aspect ratio.

The word "asbestos" stems from ancient Greek and has always referred to a very

fibrous industrial mineral product . Since asbestos has historically related to a mineral

exploited as an important industrial commodity, we think a combined mineralogical and

industrial definition should take precedence [1,2]^. Other presentations during this

^Figures in brackets indicate the literature references at the end of this paper.

339
workshop have amply covered the aspects of asbestos terminology, and it is not our intent

to provide comprehensive coverage of that subject. Our primary objective is to review

some of the basic principles of analysis, and to point out problem areas where

identification of "asbestos" has been abused.

Analysis Methods and Misidentif ication of Asbestos

It is useful to categorize the various analytical methods which have been applied to

talc to highlight inherent principles which lead to mi sidenti fyi ng asbestos as being

present. We offer the following general comments on the three principle determinative

properties (chemical composition, morphology, structure).

Chemical Composition

It is well known that every mineral has a specific chemical composition, and that

each mineral has an ideal theoretical chemical formula (configuration). Unfortunately,

many investigators overlook the fundamental point that chemical composition does not

identify a specific mineral. A simple example will bring that point into focus:

A pearl, an oyster shell, a slab of marble, a piece of chalk, and the

minerals aragonite and calcite are obviously different materials, and

yet each will be identified as calcium carbonate. That is to say,

chemical analyses will identify them all as the same substance, where

everyone knows that a pearl is not a piece of chalk.

The same situation exists in certain phases of asbestos analysis. For example,

chrysotile, antigorite, lizardite, sepiolite, chlorite, and talc are all hydrous magnesium

silicates. But a Meerschaum pipe (sepiolite) is certainly not chrysotile asbestos in

spite of the fact that chemical analysis alone could lead to that misidentif ication.

Accordingly, chemistry alone does not identify a mineral, nor do those sophisticated

instrumental methods which are based on chemical principles, such as:

Wet Chemical Analysis

Classical (gravimetric, volumetric)

Instrumental (atomic absorption, flame emission)

Microprobe (electron and ion)

Emission Spectrograph

Mass Spectrograph

X-Ray Fluorescence

Morphology

Although the shape of a mineral particle is one of the key characteristics in the

identification of a mineral, shape alone cannot be the sole determinant of a specific

mineral species. There are hosts of minerals in different mineral classes whose particles

have the same shape. They exist across the spectrum of all classes of minerals and the

possibilities are beyond comprehension. Even if we limit ourselves to minerals which occur

in the true fibrous state, we would estimate there are up to 100. There have

been instances where nonasbestos particles have been misidentified as chrysotile in talc

because shape alone was the index used.

Methods based on morphology include:

Optical Microscopy

Automated Image Analyzers

Electron Microscopy (SEM and TEM)

340
structure

The configuration of atoms in the crystal lattice of a mineral does not necessarily

determine a mineral species. The atomic arrangement at the molecular level does not always

carry through to the external visible physical form. That is to say that methods based on molecular structure can misidentify a mineral. For example, chrysotile asbestos is

classified with the sheet silicates because of its crystal structure arrangement, but it

certainly does not occur in flat sheets like the micas or its sibling, antigorite.

Methods of identification which relate to molecular structure are:

Infrared Spectroscopy

Differential Thermal Analysis

X-ray Diffraction

Electron Diffraction

In general then, no single property defines a mineral, and no single method which

depends on one property can identify a specific mineral.

Conversely, methods which depend on a single factor or characteristic of a mineral

can give mis identifications.

Two Popular Methods

Optical microscopy and x-ray diffraction methods require some additional discussion

primarily because they have received widespread attention by industry and government

laboratories as possible monitoring techniques.

Although both these methods are fundamental to the science of mineralogy and are highly reliable in the hands of experts, complications arise when shortcuts are taken in

the professional procedures.

Optical Microscopy

When an experienced optical mineralogist or crystal 1 ographer identifies a mineral with

a petrographic microscope, he can come to a remarkably accurate conclusion. The reason

for high accuracy is that not one but several specific properties are determined, such as refractive indices, extinction angle, birefringence, and optical orientation. Specific

training and wide mineralogical background are required to get the right answer.

In contrast, current optical methods in federal regulatory proposals relating to

asbestos presume that asbestos is present in the first place. The analyst then merely

observes the mineral particle for size/shape. Consequently, those methods which depend

solely on aspect ratio give misidentification. They misidentify the presence of asbestos

by such simple oversights as looking at a platelet on edge and counting it as an asbestiform particle. It is not necessary to elaborate on the other shortcomings of those

methods in view of the recent NBS report on the analysis of 80 industrial talcs [3]

evaluating that methodology. The same shortcomings were also recently corroborated in a study conducted by Harvard University and NIOSH [4].

However, there are a few rare cases where abnormal crystal habit can be misleading

and subtly can lead to a misidentification. Optical microscopy is most vulnerable to this

type of misidentification. For example, talc normally occurs as micaceous plates, but

rare acicular talc does exist, and one must be very careful to avoid misidentifying the rare occurrence as asbestos. As an example, our XRD examination of an industrial acicular

talc sample has identified the presence of significant amphibole (probably tremolite).

However, when the material was subjected to thorough petrographic examination it was found

to be composed of free grains of columnar amphibole and acicular talc and composite talcamphibole. The significance is that an erroneous conclusion could be reached by

misidentifying such a rare talc variety as asbestos, if only aspect ratio and simple

optical microscopy were used.

341
Thus, simple optical microscopy can determine the morphology of a particle, but if

used alone it cannot always fully identify the specific mineral observed.

X-Ray Diffraction

Although x-ray diffraction (XRD) is a valuable technique, it cannot determine the

physical shape of a mineral particle, and for that reason it cannot determine whether or not a sample is asbestos. Furthermore, it cannot distinguish between two mineral

varieties in the same mineral class in cases such as the asbestos minerals and their

nonasbesti form analogues. It is surprising that such a basic shortcoming continues to be

overlooked by responsible investigators alleging to have identified asbestos by XRD.

One result of the inability of powder XRD to differentiate between the asbestiform

and nonasbestiform varieties of a mineral is the potential error of prejudging an XRD

detected phase to be the asbestiform variety. For example, preparing calibration

standards of mixtures of talc plus chrysotile could have the effect of causing a serpentine peak in an unknown sample to be prejudged as the asbestiform variety, i.e.,

chrysotile. A mixture of talc spiked with the serpentine mineral chrysoti 1

will give the same XRD pattern as a mixture of talc spiked with the very common platy serpentine mineral

anti gorite . It should be obvious that an unknown talc showing a serpentine peak cannot be

prejudged or branded as containing chrysotile asbestos under such circumstances.

Unfortunately, the literature has articles by responsible authors who have overlooked that error in logic [5,6,7].

For research purposes only, single crystal XRD can provide information as to whether

or not the specimen could be asbestos. However, due to the difficulty of handling minute

specimens, single crystal XRD is inadequate for particles smaller than about 20 x 5 pm,

and, of course, is also inadequate for routine monitoring procedures.

Amphi boles

Each of the five amphibole minerals, anthophyl 1 ite , cummi ngtonite-grunerite

,

riebeckite, tremolite, and actinolite has an asbestiform variety, namely anthophyl 1 ite

asbestos, amosite, crocidolite, tremolite asbestos, and actinolite asbestos, respectively.

Tremolite asbestos is quite rare, and actinolite asbestos is so rare that a recent NIOSH

project to prepare reference standard minerals has been unable to locate a source of pure

actinolite asbestos [8].

The amphiboles (named from the Greek "amphibolos ," meaning ambiguous) are characterized by similar crystal structure and wide variation in chemical composition and

appearance. All amphiboles have XRD patterns which are similaroand are characterized by

having their (110) or (210) diffraction peaks occur within ±0.2A of each other (Table 1,

Figure 1). Reliable identification of individual amphibole species is difficult in the

absence of confirming composition data.

Examination of Table 1 and Figure 1 illustrates that attempted identification of a specific amphibole on the basis of d^io^ oi^ df2io) has good potential for being in error. For example, selection of Joint Committee on Powder Diffraction Standards (JCPDS) card

13-437 as being definitive of tremolite presents serious problems. Twenty-nine additional

JCPDS amphiboles have their (110) or (210) peaks within ±O.1°20 of this tremolite (110)

peak at 10.56°2e. Identification of an amphibole as tremolite on the basis of a peak at

10.56°2e is obviously an identification with very low reliability. In other words, a peak

at that location is not necessarily the mineral tremolite since it could be one of 29

other mineral s.

342
Table 1. Amphibole JCPDS Card No's., d,^^„^ or d,^.^. peak position, and

relative intensity. ^""^ ^^'"^

PDS card # a!. 2e(Cu) I Name

23-118 8.58(1

)

10.31 100 Dri es ka i te

10-456 8.55(1) 10.35 100 richteri te

20-734 8.53(1) 10.37 70 mbozi i te

20-378 8.52(1) 10.38 100 dashkesani te

14-633 8.51(1

)

10.39 70 arfvedsoni te

21-149 8.51(1

)

10.39 55 hornbl ende

19-467 8.50(1

)

10.41 100 ferropargasite , syn

20-982 8.50(1

)

10.41 65 richteri te, syn

23-665 8.48(1

)

10.43 45 richterite, calcian, syn

23-664 8.47(1

)

10.44 35 edenite, sodian, syn

23-667 8.47(1

)

10.44 45 richterite, calcian, syn

23-663 8.46(1

)

10.46 40 eckermani te , calcian, syn

9-434 8.45(1) 10.47 50 hornblende

13-499 8.45(1

)

10.47 100 magnesi ori ebecki te

20-656 8.45(1) 10.47 100 inagnesioriebeckite

20-470 8.44(1

)

10.48 100 crossite

23-666 8.44(1) 10.48 40 tremolite, sodian, syn

20-469 8.43(1

)

10.49 100 hasti ngsi te

23-1405 8.43(1) 10.49 80 edeni te

23-1406 8.43(1

)

10.49 40 paragasite

20-1310 8.43(1

)

10.49 40 tremolite, syn

10-428 8.42(1

)

10.51 100 richterite, fluor, syn

23-603 8.42(1) 10.51 100 tirodite

10-431 8.41 (1

)

10.52 80 edenite, fluor, syn

19-1061 8.40(1

)

10. 53 100 ri ebecki te

20-481 8.40(1

)

10.53 100 hornbl ende

20-1390 8.40(1

)

10. 53 90 winch ite

23-302 8.40(1

)

10.53 100 cummingtonite, mangoan

19-1063 8.39(1

)

10.54 70 richterite

13-437 8.38(1) 10.56 100 tremol i te

17-478 8.38(1) 10.56 65 kaersutite

23-495 8.38(1) 10.56 80 eckermani te

9-330 8.37(1) 10.57 100 tremolite, fluor, syn

17-750 8.36(1

)

10.58 25 richterite, ferrian

20-386 8.35(1

)

10.59 40 eckermani te, syn

22-531 8.35(1

)

10.59 30 joesmithite

16-401 8.33(2) 10.62 70 anthophyl 1 ite , magnesi an. 17-725 8.33(1

)

10.62 100 gruneri te

17-745 8.33(1

)

10.62 100 grunerite

20-376 8.31(1) 10.65 100 crossite

17-726 8.30(1) 10.66 100 cummingtonite

20-484 8.29(1

)

10.67 100 richteri te

13-506 8.27(2) 10.70 80 gedri te

23-679 8.27(1) 10.70 90 glaucophane

9-455 8.26(2) 10.71 55 anthophyl 1 ite

20-453 8.26(1) 10.71 100 glaucophane

11-253 8.23(2) 10.75 100 ferrogedrite

23-310 8.20(1) 10.79 75 richterite, ferrian

13-401 8.11(2) 10.91 100 holmquistite

^ (110)^ or (210)^.

Maximum A20(Cu) = 10.91° - 10.31° = 0.6°

Table 1 illustrates the very close proximity of the (210) or (110) XRD peak of all

amphiboles, showing the inability to identify a specific amphibole on the basis of

^(210) ^(110)-

343
Figure 1. Amphibole d/,,^, or d/^^^x - peak positions (2e for CuK ) and relative intensity.

An additional problem further affecting the reliability of identification by XRD is

the effect of shift in peak position caused by slight mispositioning of the sample surface

in the instrument. For example, a 100 pm mispositioning of the specimen surface will

result in a shift of approximately 0.6-0.7 A in d-spacing at low 26 angles [9]. A slight

shift in the position of the peak (from a different amphibole or mispositioning of the

sample surface, for example) could go unnoticed, resulting in mi si dentifi cation of an amphibole that is not even present.

In order to conclusively identify an amphibole by XRD, it is necessary to have an essentially complete diffraction pattern. In order to obtain such an XRD pattern, the

sample must have a relatively high amphibole content and the pattern must be acquired with

a time-consuming slow scan. Acquisition and interpretation of such patterns is timeconsuming, and discourages proper application of the full procedure, especially for

routine monitoring where large numbers of samples require analysis. Shortened procedures,

such as single peak identification of amphiboles, provide good opportunity

for misidentif ication. The shortened procedure of single peak identification was apparently

used in a 1972 paper [7], where our examination of some of the same samples disagreed with

identifications of serpentine, tremol ite-actinol ite anthophyll ite , and anhydrite.

344
Chi on" te-Serpenti ne

Chlorite is one of the most common accessory minerals found associated with talcs.

The chlorite group of minerals are somewhat analogous to amphiboles in that they exhibit a wide variation in chemical composition and all have a similar crystal structure. The

diagnostic chlorite basal XRD peaks (001), (002), and (004) are characteristic, and occur

at about 14A, 7A, and 3.bK, respectively. As in the case for the amphiboles, specific

identification of a particular chlorite species by XRD is difficult. The XRD problem with

chloritfc talcs is that the serpentine first order basal peak overlaps the chlorite (002)

peak, and the corresponding serpentine second order basal peak overlaps the chlorite (004)

peak. Generally, however, the chlorite (004) and serpentine second order peaks are separate

enough to allow unambiguous determination of the presence of both phases when present in

adequate amounts to give definable peaks. Tables 2 and 3 and Figures 2, 3, and 4 are compilations of JCPDS data for the positions of the (004) basal peak for chlorites and

(002), (004), or (0012) basal peak for serpentines, respectively.

Table 2. Ch 1 nri tp

relative

JCPDS Card No's

intensity.

^(004) ^^^^ positions, and

JCPDS

card #

oA 2e(Cu) Name

10-183 3.60 24.73 100 penninite

20-671 3.60 24.73^ 90 kammereri te

16-351 3.59 24.80 70 chlorite lb

12-185 3.57 24.94 85 kotschubei te

7-160 3.58 24.87 60 kotschubeite

19-749 3.56 25.01 80 cl inochlore

7-77 3.558 25.03 50 sheridanite

16-362 3.55 25.08 80 chlorite la

19-751 3.55 25.08 65 sudoite

22-712 3.55 25.08 45 nimite

7-165 3.545 25.12 60 grochauite

7-78 3.541 25.15 60 thuringite

7-171 3.541 25.15 80 diabantite

12-242 3.54 25.16 100 leuchtenbergite

7-76 3.537 25.18 50 ripidol ite

13-29 3.53 25.23 80 thuringite

7-166 3.523 25.28 50 daphnite

12-243 3.52 25.30 92 aphrosiderite

21-1227 3.52 25.30 100 thuringite

3-67 3.49 25.52 100 thuringite

^(115)-

Table 2 illustrates variation in position of the chlorite d^^Q^^ XRD peak.

Table 2 should be compared with Table 3 to see that the chlorite and

serpentine XRD peaks overlap and interfere with each other. Identification

and quantification of serpentine in the presence of chlorite is extremely

difficult at best.

345
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346
Table 3. Serpentine, Kaolinite, Halloysite, and Dickite JCPDS Card Nos.,

peak position, miller index (hkl), and relative intensity.

JCPDS o Card # A 29(Cu)

18-779 3.67 24.25 80

9-444 3.66 24.32 100

21-543 3.65 24.39 70

7-417 3.63 24.52 300

11-386 3.62 24.59 60

21-963 3.61 24.66 80

12-583 3.56 25.01 80

13-4 3.56 25.01 70

7-339 3.55 25.08 100

11-388 3.55 25.08 100

7-315 3.52 25.30 100

9-493 3.52 25.30 100

6-221 3.58 24.87 1004

14-164 3.579 24.88 80

12-447 3.56 25.01 50

9-453 3.63 24.52 90

10-446 3.58 24.87 100+

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Table 3 illustrates variation in position of

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(hkl ) Serpentines

(002) lizardite, IM

(0012) antigorite, 60

(004) chrysotile, 2M

(102) antigorite, 6M

(002) lizardite, 10^, aluminian

(002) antigorite, 6M

(0012) antigorite, 60^, aluminian

(0012) antigorite, 60^, aluminian

(002) berthierine

(0012) antigorite, 60, syn

(002) berthierine

(004) amesite

Kaol inites

(002) kaolinite, IMd

(002) kaolinite, IT

(002) kaolinite, IT

Hal loysite

(002) halloysite, dehydrated

Dickite

(004) dickite 2Mi

24.73 - 25.52

XRD peaks of serpentine, kaolinite,

these minerals interfere with each

347
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Three essential features are demonstrated in Tables 2 and 3, and Figures 2, 3, and 4:

1. The diagnostic peaks show considerable variation in the position in

which they occur (A2e=0.79° for chlorites and 1.05° for serpentines).

2. The chlorites and serpentines overlap and interfere with each other.

3. Basal peaks of the clay minerals kaolinite, halloysite, and dickite

overlap the positions of the chlorite and serpentine peaks, and will

interfere when present.

The significance of the chl ori te-serpenti ne interference is increased by the fact

that chlorite is a very common accessory mineral associated with talcs, whereas serpentine

is much less commonly associated.

In spite of the chlorite-serpentine problem, numerous investigators have performed

XRD identification and/or quantification of serpentine in chloritic talcs. It is obvious

to us that they have misidentif ied asbestos as being present by overlooking the

chlorite/serpentine interference and by misconcluding that a chlorite peak was serpentine.

Other Methods

Infrared Spectroscopy (IR)

The infrared absorption spectrum of a material results from vibrational and bending

frequencies of various atomic bonds within the structure. For example, Si-0 stretching

frequencies produce similar IR peaks for all silicate minerals. As a result, IR spectra

are not particularly useful for identifying the minerals present in a mixture, and the

method certainly is not capable of determining whether or not a detected mineral is the

asbestiform variety.

Differential Thermal Analysis (DTA)

The rearrangement or decomposition of mineral crystal structures due to thermal

heating is a characteristic and reproducible reaction. It follows that DTA can identify

specific minerals in a mixture but the method is not capable of determining morphology.

Therefore, any DTA data which might point to the presence of a serpentine mineral could

lead to misidenfying chrysotile asbestos in a talc when the mineral could well be a normally occurring platy antigorite having the same DTA pattern.

Electron Microscopy

Electron microscopic techniques of identification of asbestos have been amply covered

in other presentations during this workshop. We do not intend to cover that subject

again, but rather to point out some areas where asbestos can be mi sidenti f ied.

The high magnification attainable with electron microscopy is, in itself, inadequate

as the sole index of mineral identity. For example, chrysotile is often identified by the

presence of a hollow central core and streaked electron diffraction spots. But the clay

mineral halloysite also crystallizes in that form and will produce a similar electron

diffraction pattern. Therefore, in the absence of exact chemical composition, halloysite

can be misidentified as asbestos. Similar care must be exercised to avoid misidentifying

other fibrous clay minerals as asbestos, e.g., attapulgite and alpha sepiolite. In

addition, talc ribbons can be mistaken to be asbestos, especially when some talcs have

particles which roll up into spiral tubes giving the appearance of a chrysotile particle.

Selected area electron diffraction is routinely used to identify a mineral particle

as amphibole. Many investigators simply observe the electron diffraction pattern in the

microscope and decide on the basis of general pattern geometry whether or not the particle

is an amphibole. This can lead to misidentif ication, since numerous other minerals can give electron diffraction patterns with amphibole pattern geometry [10,11]. Careful

measurement of an electron diffraction pattern is required in order to identify the type

350
of mineral which produced the pattern. Chemical composition is further required in order

to have a chance at identifying the particular species when the mineral is a member of a complex group such as the amphiboles. Otherwise, misidentif ication will result.

Cosmetic Talc Free from Asbestos

In the United States, we have a self-regulating association known as the Cosmetic

Toiletry and Fragrance Association. In certifying the purity of the talcs which they use,

they are aware that no single method can identify asbestos and their most recent specification for cosmetic talc [12] combines two methods (XRD and optical microscopy) for

monitoring their types of talc.

The rationale is that a talc is first examined by XRD, and if even the smallest

amount of amphibole is indicated, then the test proceeds into optical microscopy using a dispersion staining technique to determine whether or not the material contains

asbestiform particles in the amphibole group.

Summary

This paper has categorized the main methods which have been used for detection of

asbestos in talcs. The basic principles of the various methods were categorized to explain

how asbestos has been and can be misidentif ied in talc. Generally, misidentif ications

arise by jumping to a conclusion from a single mineral characteristic, when, in fact, many

characteristics are required to fully identify a mineral species and/or its variety.

Both optical microscopy and XRD required a more detailed review than other methods

since they have received the most attention from a monitoring point of view.

This review is presented with the hope that our guidelines will enable analysts to

avoid the misidentif ication of asbestos in talcs.

References

[1] Ampian, S. C. , Asbestos minerals and their nonasbestos analogs. Mineral Fibers

Session, Electron Microscopy of Microfibers Symposium, Penn State Univ. , August, 1976.

[2] Thompson, C. S. , Discussion of the mineralogy of industrial talcs. U.S. Bureau of

Mines Information Circular 8639, Proceedings of the Symposium on Talc, Washington,

D.C. , May 8, 1973.

[3] National Bureau of Standards Staff, A report on the fiber content of eighty industrial

talc samples obtained from, and using the procedures of, the Occupational Safety and

Health Administration, 51 pp. (1977).

[4] Bowndy, M. G. , Gold, K. , Burgers, W. A., and Dement, J. M. , Exposure to industrial

talc in Vermont talc mines and mills: AIHA Conference presentation, May 1977.

[5] Rohl , A. N. , Langer, A. M. , Selikoff, I. J., Tordini, A., Klimentidis, R. , Bowes, D. R. , and Skinner, D. L. , Consumer talcums and powders: mineral and chemical characterization. Jour, of Toxicology and Environmental Health, 2, 255-284 (1976).

[6] Rohl, A. N. and Langer, A. M. , Identification and quantification of asbestos in

talc, Environmental Health Perspectives, 9, 95-109 (1974).

[7] Snider, D. W. , Pfeiffer, D. E. , and Mancuso, J. J. , Asbestos form impurities in

commercial talcum powders, Compass of Sigma Gamma Epsilon, 49, 65-67 (1972).

[8] Scholl, R. and Drafts, R. , 1977, XRD characterization of asbestiform reference

minerals. Symposium on Electron Microscopy and X-Ray Applications to Environmental

and Occupational Heal th Analyses , April 1977.

351
[9] Jenkins, R. , A review of x-ray diffraction procedures as related to the quantitative

analysis of air particulates. Symposium on Electron Microscopy and X-Ray Applications

to Environmental and Occupational Health Analyses, April 1977.

[10] Zoltai, T. and Stout, J. H. , Comments on asbestiform and fibrous mineral fragments,

relative to Reserve Mining Company taconite deposits: Report to Minnesota Pollution

Control Agency, 89 pp. (1976).

[11] Lee, R. , Electron optical identification of particulates: Symposium on Electron

Microscopy and X-Ray Applications to Environmental and Occupational Health Analyses,

April 1977.

[12] CTFA Specification - COSMETIC TALC Issued 10/7/76, The Cosmetic, Toiletry and

Fragrance Association, Inc.

Discussion

A. WILEY: You said that instantaneous recognition of SAD patterns is difficult. Could

you give some examples as to what kind of confusions could exist in this? Can you confuse

amphibole with serpentine or amphibole with talc, or is that kind of a gross mistake

possible?

J. KRAUSE: Those kinds of mistakes probably would not generally happen if you are looking at pyroxenes or olivine. Electron diffraction is not one of my areas of real

expertise, but I think that you could possibly get feldspars that would give confusing

patterns, depending upon their orientation in the microscope.

L. MADSEN: We are using all the methods that have been talked about today for identification for asbestos materials and do not in any way limit ourselves to fiber length and

aspect ratios.

J. WAGMAN: I would like to comment that it is possible by x-ray diffraction and

through a special technique to identify and measure the presence of asbestos fibers even when they are in the presence of their non-fibrous counterparts. About two years ago this was demonstrated in a study which we supported at the Naval Research Laboratory in which

samples were pre-treated so that fibers were first aligned and then the x-ray diffraction

intensities measured at two different orientations with respect to the x-ray beam and in

this way the intensity due to the non-fibrous counterparts could be subtracted from the

total diffraction intensities.

KRAUSE: You were putting the fibers in some specific preferred orientation in the

sample and then looking for those orientations by XRD.

WAGMAN: That is correct, and this had the advantage of not only making possible

corrections, that is correcting for the non-fibrous material present, but also it greatly

enhances the detectabi 1 ity for the fibers themselves.

KRAUSE: Is this method being currently used?

WAGMAN: This is a method whose feasibility was demonstrated and there are two publications on this in the literature. Actually our objective was to apply this method to

airborne samples, which is a much more difficult application incidently, I should think

than in the case of talc. The problem here is a preparative problem in that an air sample

usually has a lot of organic material, sticky material present which interferes with the

ability to orient the fibers. This is a preparative problem which will have to be overcome. But I should think that in the case of talc samples you probably would not have that

problem.

352
K. HEINRICH: Would the talc plates interfere just as well with the orientation of

the fibers?

WAGMAN: The orientation of the fibers is accomplished in an electric field, and the

platy material does not preferentially orient itself.

HEINRICH: I mean, just in the sense of a passive restraint to the movement of the

fibers.

WAGMAN: This of course would have to be tested experimentally.

A. LANGER: We heard today from a representative of one of the member organizations

of the Cosmetic, Fragrance, and Toiletry Associations, that of 3800 consumer talcs

examined none contained chrysotile. Today you presented some interesting information on the identification of crocidolite in talc. Have you seen crocidolite in many talcs you

have examined?

KRAUSE: No I have not seen it, nor did I say that I have.

LANGER: It does not occur in consumer talcs, or is it industrial talc. I just do

not see why the crocidolite issue was raised; have you seen it?

KRAUSE: Just because I have not seen it certainly does not mean that it could not

conceivably exist. All I was trying to do was point out that choosing a specific

amphibole peak as being representative and definitive for giving a good identification of

a particular amphibole species has great potential for error. There are many, many other

minerals that could fall within that same two theta region.

LANGER: I would agree with you that even though talcs occur in nature and they have

great mineralogical variability they are still bound by the physical and chemical laws

involving calcium-silicate rock systems. A mineral phase such as you described would not occur normal ly.

353

National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

AMBIENT AIR MONITORING FOR CHRYSOTILE IN THE UNITED STATES

Richard J. Thompson

Analytical Chemistry Branch

Environmental Monitoring Support Laboratory

Environmental Protection Agency

Research Triangle Park, North Carolina 27711

Abstract

The only continuing national air monitoring has been conducted by

the National Air Surveillance Network. The objective is long term trend

assessment of air quality. The information has proven of value in

setting standards, in consideration of health effects, in estimation of

economic effects, and in showing patterns of pollutant distribution in

both urban and non-urban areas.

In order to provide samples which could be analyzed for constituents

not determinable in particulate matter samples collected with glassfiber filters, a membrane sampling network was instituted. The only

analyses of the samples conducted thus far has been for airborne asbestos

using in part a method developed under contract which provides for the

determination of the mass of chrysotile in the particulate samples.

A viewpoint will be presented on the method needed for air

monitoring and an assessment of the mass method as the most suitable for

this purpose. Data obtained will be examined which will include

information on inter- and intra- laboratory replication.

Key Words: Air monitoring; airborne particulate; asbestos; chrysotile;

fi Iters.

National air monitoring had its inception in a Public Health Service survey of protein

in airborne particulate matter conducted at seventeen sites in 1953-54. Sufficient amounts

of material were collected using glass fiber filters to permit chemical analyses as well

as the determination of total suspended particulate matter. In 1955 the Federal Air

Pollution Research and Technical Assistance Act, Public Law 159, 84th Congress, was passed.

The Network was expanded to 66 stations nationwide for every year sampling and 110 urban

and 51 non-urban stations for an intermittent sampling and all the then 48 states and

Alaska, Hawaii, and the Commonwealth of Puerto Rico. Currently some 270 stations collect

particular matter in the National Air Surveillance Network (NASN).

Certain constituents of the particulate matter collected could not be determined when

glass fiber filters were used. As a result, a membrane sampling network was instituted

within the NASN in 1969. Until recently 51 stations were maintained, but currently only

some two dozen are operated. Samples collected on the cellulose acetate membrane filters

can be analyzed for constituents of glass such as boron and silica. The only analyses of

the samples conducted thus far, however, have been for the mass of chrysotile in the

particulate samples using the method developed by EPA under contract, or a variation of

this method.

Ambient air samples collected by EPA had been analyzed by contract [1]^ in 1966 by

both ordinary light field techniques and with dispersion staining with the optical

^Figures in brackets indicate the literature references at the end of this paper.

355
microscope and by scanning electron microscopy using magnifications up to 18,500 X. Fibers were noted which were believed to be chrysotile. Because chrysotile comprises

approximately 95 percent of the total asbestos used in the U.S., chrysotile was the form

of asbestos for which a monitoring method was desired. It was also decided that a mass method would be more appropriate for a survey tool than the fiber count method

traditionally used in health effects studies. Although adverse health effects of asbestos

on man is the reason for the interest in asbestos in air (airborne asbestos having no known adverse economic effect of significance), the optical method did not seem to be

appropriate for analysis of ambient air monitoring samples, albeit effective in the work

room where asbestos fibers of optically detectable size were known to prevail. An

electron microscopic method would obviously be desired since submi croscopi c particles were

demonstrated. Chemical analyses obviously would not be an appropriate survey tool, unless

sufficiently high concentrations of chrysotile would be found to permit x-ray diffraction

as a possible tool for application. Using brake lining consumption figures and assuming

that all of the asbestos remains airborne, it was estimated that the chrysotile content of

air could under these conditions be in the nanograms per cubic meter range.

j

The objective of monitoring using the mass method would be to determine the quantity

of chrysotile asbestos in ambient air. Thus the objective did not include a need for a knowledge of fiber length, fiber size distribution, and other factors that could be

obtainable if the asbestos fibers per se as collected were to be examined. Since a known

standard of asbestos in air was perceived a philosophical nightmare, the problem of a quantitative recovery of fibers from air without diminution or destruction, and a quantitative estimation of fiber size and length was considered to be unobtainable for

routine application for monitoring chrysotile levels in ambient air.

One problem in particular was the problem of what is to be counted if one is to count

that material which is taken from air directly without alteration and if particle

recognition, using the morphology of chrysotile was to be employed as a working tool

(chrysotile fibrils are cylindrical tubules). One would be posed with the problem of

fibrils of chrysotile in ambient air samples of some 30 nm in diameter being present and

fibers of chrysotile composed of hundreds of thousands of fibrils being also possibly

present in the same sample (if taken at an urban sight where construction/demolition might

be ensuing). How would one then handle the problem of counting a fiber and counting an artifact fibril from that fiber? Would they both be counted as fibers (assuming they met

aspect ratio criteria)? Fibrils might be produced by one handling technique which might

not be produced by what was thought to be the identical technique in the hands of another

operator. Furthermore, the non-homogeneity of such a sample would make the counting

statistics very unfavorable toward application at a reasonable level. Reasonable in this case is defined as being of the accustomed precision expected by analytical techniques

that are more objective and less subjective than particle recognition based on morphology.

The method developed for monitoring of chrysotile in ambient air for EPA under

contract [2] has been described in detail elsewhere [2,3]. The method was discussed in

detail in a conference held at the Research Triangle Park, North Carolina, by EPA in July

1970 attended by representatives of all U.S. laboratories then known to be working on asbestos estimation from air samples and included representation of the United Kingdom.

A method similar to the EPA method in some details was developed independently [4].

The method developed for EPA differed slightly from other mass methods employed at

that time. The method in use at Johns-Manville used a gold labeling technique to achieve

quantitation of chrysotile; a watch glass was used to grind a sample suspended in amyl

acetate on a microscope slide. Gold 198 was added prior to ashing and the efficiencies of

recovery was estimated by radioactivity measurements of the gold, the chrysotile was assumed to behave as did the gold standard [5]. The method then employed by Mount Sinai

Laboratories involved grinding with a glass and spiking the samples with known weights of

chrysotile from which a recovery factor was derived and used in calculation [6].

The method developed for EPA for the determination of the mass of chrysotile in^

ambient samples involves starting with a portion of a particulate matter sample taken on a cellulose acetate filter, ashing at low temperature, suspending in water with the aid of a surfactant, and grinding to fibrils by ultrasonicating at high energy. The now homogenous

samples containing shattered fibrils is filtered on a membrane filter coated with a 20 nm

356
layer of carbon, sectioned, the filter substrate removed with acetone, and the carbon film

placed on a 200 mesh copper electron microscope support grid. The sample is examined at

20,000 X with a transmitting electron microscope (TEM), and the chrysotile fibers

(fibrils) determined by counting grid openings to obtain a count of 100, or a minimum of 5 grid openings if a count of 100 is not obtained. The mass equivalent of the count is

obtained from a working curve constructed from data derived by counting samples containing

known amounts of added chrysotile.

Synthetic standards were made by addition of known quantities of pulverized sea sand,

particulate matter collected from air, (ignited to 800 °C to destroy chrysotile) fly ash,

and water. The samples so prepared were subjected to the procedure described. It was established that the curve obtained by plotting count versus mass of known chrysotile

added may be derived satisfactorily by adding weighed known chrysotile to water alone.

Asbestos obtained from commercial supplies of mineralogical samples included

chrysotile, amosite (which constitutes almost all of the non-chrysotile asbestos used in

the U.S. commercially), and crocidolite. The chrysotile used in the developmental work

was a "respirable pure" white chrysotile obtained from Johns Manville.

Advantages to be noted by this procedure are that if the ultrasonif ication is

complete, there should be a uniform distribution of fibrils of a spectrum of lengths which

is related to the energy of ultrasonification applied and that the uniformity of the

sample and the (comparatively) tremendous number of fibrils of chrysotile to be determined

enhances the statistical possibility of replication, at a reasonable level, using

simplified counting techniques. There is of course the possibility of a recognition

problem of any material in air which would behave as does chrysotile and appear as does

chrysotile in the carbon replica which contains fibrils. The diameters of chrysotile

fibrils from diverse geographical origins are said to be within a very narrow size

distribution approximating 30 nm [4]. Conf irmational data such as SAED and atom ratios by

probe can be obtained.

The method was applied to samples taken from ambient air in urban areas where

asbestos might be expected to be found on the basis of industrial activity and to samples

taken from a remote location. Representative data are given in Table 1. The remote

location was chosen as being as far from road traffic as could be found in one day's

commuting from the laboratory and at a site where power existed. The replication at low

levels was surprisingly good; triplicate samples gave mean values of approximately 0.1

nanograms per cubic meter with a replication within 10 percent of the value measured.

Even at the level of 0.03 nanograms per cubic meter the spread of measured values was

within 10 percent of the value measured. For samples which contain tens of nanograms per

cubic meter, replication was achieved within 50 percent of the average value noted. The

method was checked by a phenomenol ogical ly different approach wherein samples of asbestos,

activated by neutron irradiation, were blown into a chamber and recollected. As shown in

Table 2, radioassays and the TEM estimates agreed within 30 percent of the average value

of the two readings recorded by the different methods. The replication found within the

method in the limited comparison between methods lead one to believe that the two

phenomenological ly independent methods gave comparable results and that the electron

microscopy method gave replication in the vicinity of 50 percent. It may also be noted

that the Stokes diameter was checked at sites downwind from a point source at distances of

1 and 2 miles, the predominant diameter distribution in terms of the mass seemed to be in

the fraction of asbestos particles which were in the 8 to 16 micrometers diameter stage of

the collection device.

357
Table 1. Replication filter section determination (TEM).

3 Site Location ng Chrysoti 1 e/m air Average

A Near use site ( 1 970) 280, 260 270

A Near use site (1971

)

no, 86 98

AA Near use site (1971

)

7900, 7200, 9700 8200

na Near use site ( 1 970) 28, 40 34

B Near use site (1971) 130, 117 124

A

1^ Remote site 0.112, 0.102, 0.147 0. 12

A 1^ Remote site 0.094, 0.119, 0.106 0. 10

A 2 Remote site 0.028, 0.024 0.026 0. 03

Two samples taken concurrently.

Table 2. Method comparison check.

Sample Radio assay TEM Difference %

1 8.3 11.0 29

2 34.0 40.0 15

3 17.6 20.8 15

4 4.7 4.0 18

Quarterly composites constructed from the 51 network sites were analyzed for

chrysotile. The average of the analyses of some 521 of these composites samples is 2.6

nanograms of chrysotile per cubic meter of air sampled. The samples analyzed were quarterly composites of those samples collected through the second quarter of 1973. In

Table 3 the data replicate slices of quarterly composites are given; these samples were provided to the contract laboratory on a blind basis for the purpose of an external audit.

The percent of absolute deviation from the average of 22 individual sample sets was 40

percent. In Table 4 the internal QC replication of a different laboratory is given; note

that in the analyses of 16 sets of replicate sections from samples, the percent absolute

deviation from the average is 43. In Table 5 the data are shown obtained from a sample

split program between the two laboratories conducted on a blind basis to the participating

laboratories. Note that some of these data are common to Tables 3 and 4 also. It is of

interest that in 24 sample sets of samples analyzed by each laboratory in some cases the

data shown are averages of replicates within one of the laboratories. The percent

absolute deviation from the average is 59 percent. From an examination of these data one

gets the impression that the average percent deviations are roughly the same between

laboratories and within laboratories. It is also of interest that in the inter- laboratory

358
Table 3. Intra-lab replicate analyses for chrysotile, (high cities, blinds

external audit).

Lab A

3 Site Sample period (ng/m ) Average % absolute

location 1971 (quarter) 1st 2nd Mean deviation from mean

A 1 1 . 7 1 . 2 1 .

33

4 2.1.8 2.0 8

B 1 4.0 6.7 5.2 25

4 7.4 7.2 7.3 3

C 1 4.0 3.7 3.9 4

4 5.3 1.5 3.4 56

D 1 9.4 4.4 6.9 39

4 11.0 3.

7. 0

"7 b/

E 1 8.4 8.0 8.2 3

4 3.0 4.6 3.8 23

1972 (quarter)

A 1 1 c

\ . D OC "7 OOQQ

2 3.7 2.8 3.2 34

B 1 0. 1 o oo

/I K 4. 0

7'?

2 6.6 1.4 4.0 53

3 9.6 1.6 5.6 71

Z 2 0.4 11.1 14.

97

c 1 4.2 2.5 3.4 25

2 0.7 1.2 1.0 25

D 1 6.8 2.0 4.4 50

2 0.8 2.8 1.8 56

E 1 18.8 11.8 15.3 23

2 3.1 1.6 2.3 31

Average 40

359
Site

location

Table 4. Intra-lab replicates for chrysotile, internal Q.C.

Lab B

Sample period

quarter-year 1st

(ng/m ) 2nd MeanAverage % absolute

deviation from mean

F 1-70 0. 8 0.4 0. 6 33

G 4-69 20. 3 12.6 16. 5 23

A 3-69 110 80 95 16

H 3-69 25. 3 13.5 4.5 14. 4 48

I 3-69 5 4 3.3 4. 4 23

J 2-70 1 1 0.1 0. 6 83

B 3-69 5 2 3.1 4. 2 24

C 4-69 62 3 17.7 40 56

D 4-69 1 3 0.0 0. 7 85

Z 3-69 50 27 38 31

K 2-70 5 2 1.0 3 1 68

L 2-69 1 7 1.1 1 4 21

L 1-70 6 3 2.4 4 4 44

M 2-69 5 3 2.1 3 7 43

N 2-69 25 5.3 1.3 10 2 95

0 3-69 19 3 16.6 18 7

Average 43

data given in Table 5 one may note that of the 5 value sets (of the 24 given) which are

not within a factor of 10 of each other, findings above 10 nanograms per cubic meter

(which is twice the average value for the set including the high values) are involved, and

that three of the high values were reported by one lab, and two by the other. It is

possible that the samples of high value (for which the agreement is the poorest) have

large particles of asbestos and are thus more inhomogenous than are the samples with lower

asbestos contents. It is also of interest that in a comparison of mass by the sample

count versus standard count method with a mass computed from fiber volume from direct

fiber counts of replicates, a bias of the mass method toward higher readings is noted in

Table 6.

360
Table 5. Replicate analysis for airborne chrysotile between laboratories (in ng/m ).

City Quarter Lab B Lab A Mean

Average % absolute

deviation from mean

(Samples collected in 1969)

2

3

4

2

3

4

2

3

4

2

3

4

23

4

2

3

4

0.4

95

0.7

3.9

4.2

8.0

0.4

1.2

38

1.3

1.5

40.0

1.1

11.8

0.7

4.4

0.7

2.1

1.8

3.9

15.6

5.3

6.7

3.5

0.5

0.5

0.4

n.i

0.7

0.5

0.4

0.5

0.5

1.0

1.1

0.6

1.1

49

8.2

4.6

5.5

5.8

0.5

0.9

19.2

6.2

1.1

20.3

0.8

6.2

0.6

2.7

0.9

1.4

63

202

182

15

22

39

11

41

98

80

36

98

47

92

17

63

22

56

(Samples collected in 1970)

A

B

Z

C

D

E

1.0

6.5

1.2

2.2

1.5

4.6

1.4

1.3

0.9

0.6

0.8

1.5

1.2

3.9

1.1

1.4

1.2

3.1

17

67

14

57

30

51

Average 59

Table 6. Mass methods comparisons, count vs. volume (in ng/m ),

Mass by

Sample fibril count (C)

Mass computed from Ratio

"fiber" volume-density (V) C/V

1

2

3

21

216

1 ,674

141

476

5.1

1.5

3.5

361
The consideration of the health effects of asbestos fibers, fibrils, fiber size,

etc., will be considered elsewhere in this symposium. For the problem of monitoring for

the definition of air quality on a long-term basis which conceivably could be used for

regulatory purposes for citing standards and for control measures and possibly for

interpretations with respect to human health, in my judgment the mass method outlined in

this paper is a superior method. It may avoid two very significant problems in the

estimation of the chrysotile content of air as measured in collected particulate matter.

One is the problem of homogeneity which is a problem with every sample that one obtains

from the air. For example, asbestos fibers may be put into the air by construction/demolition. The other is the problem of what constitutes a fiber? This is in a sense another aspect of the same problem. If one had a uniform distribution of fibrils over a sample, the fibrilar estimation would probably be comparable by both methods. If however,

one obtains a fiber or two, here and there, obviously then the sample is automatically

inhomogenous since fibers could conceivably consist of 10^ fibrils. In the method where

the fibers and free fibrils are ground ultrasonical ly , the resulting particle size

distribution should be a function of the energy put in. The procedure described should

then yield a homogenous mixture. It is not suggested that this approach is the final answer for all monitoring problems, or that it addresses anything at all concerning fiber

length in real air samples of any form of asbestos, or fiber size distribution. It is

patently apparent that information of this nature cannot be obtained reliably using a method wherein the material has been subjected to diminution.

References I

[1] Walter C. McCrone Associates, Inc. reports to E. C. Tabor, EPA, 1966. ^

[2] Henry, W. M. et al . , Development of a Rapid Survey Method of Sampling and Analysis

for Asbestos in Ambient Air, Battelle Columbus Report, Contract No. CPA 22-69-110

(February 1972).

[3] Thompson, R. J. and Morgan, G. B. , Determination of Asbestos in Ambient Air. Pr-o- ceedings, International Symposium on Identification and Measurement of Environmental

Pollutants, 154-157 (June 1971).

[4] Rickards, Anthony L. , Estimation of Submicrogram Quantities of Chrysotile Asbestos by

Electron Microscopy. Anal . Chem. , 45, 809-811 (1973).

[5] Spiel, S. and Fenner, E. , personal communication.

[6] Nicholson, W.J. et. al . , Measurement of asbestos in Ambient Air, Mount Sinai School

of Medicine, Contract CPA 70-92 (1971).

1

362 I
Discussion

0. MENIS: Are you familiar with the work of Spurny et al. on the Nuclepore and

embrane filter retention and would you like to comment on it, because there appears to be ome loss, 20 percent internal loss. Also, the question of prefiltering a lot of junk

eforehand seems to be attractive.

THOMPSON: Let me tell you why I don't like prefiltering. When you use a filter that

s composed of a bunch of fibers matted together as are our glass fiber filters and the

embrane filters we use (that's not so with Nuclepore, obviously; they drill holes in

heir's) then you are dealing with a brush pile of fibers, and as you put that particular

atter on there I am convinced you go from a surface of the fiber to a particulate laden

urface. After your first few minutes of sampling on a 24 hour basis, it's my belief

hat what you are dealing with is particulate matter filtration, and not filter filtration

nymore. The particulate matter itself is now your filter, and to support that I will

ell you of a two-week sampling shot I made to collect massive quantities of materials for

etailed chemical analysis. I wanted the total elemental composition of particulate

atter so I would know what I was up against analytically. Nobody had ever done that,

ou are filtering with particulate matter and here is why I think that.

You start off with a high volume sampler at about 60 cfm, and if you run about 10 days

ou find that the flow is down to a constant of about 30 cfm. You put in 8x10 cellulose

cetate filter on the same type of device, calibrate it to draw what it should be, 60 cfm

ith the glass fiber filter, and you sample about 35 cfm through that membrane filter,

fter about 10 days you will be filtering about the rate of about 30 cfm. If you throw

nother kind of filter substrate on there you see the same thing. That loading, I think,

s your terminal loading of particulate matter that affects flow, but I am convinced you

re filtering with particulate matter. I do not like pref i Itration for that reason. You

re going to get stuff hung on there; you are going to lose material, and that filter is

ot smart enough to open up and let whatever it is you want through quantitatively. It

ust won't do it. We tried it and I have had notable lack of success with that approach,

t sounds nice, that you could screen out the lumps, but in practice it doesn't work that

ay. I don't think it feasible, and I have never been able to accumulate data that were

ery satisfying.

363

National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

ENVIRONMENTAL PROTECTION AGENCY INTERIM METHOD

FOR DETERMINING ASBESTOS IN WATER

Charles H. Anderson

Environmental Research Laboratory

U.S. Environmental Protection Agency

Athens, Georgia 30601

Abstract

The discovery of asbestos and asbestiform minerals in water

supplies and drinking water has resulted in the requirement for a reliable analytical method. In order to meet this requirement, an interim method, based upon the state-of-the-art in asbestos analytical

methodology, has been prepared. In this paper, the broad elements of the

method are set forth and discussed.

Key Words: Analytical Chemistry; asbestos; environmental pollutants;

water.

Introduction

Environmental concern following the discovery of asbestos and asbestiform minerals in

Water supplies and drinking water has resulted in a broad range of activities within the

Environmental Protection Agency to improve detection sensitivity and to delineate human

sxposure and subsequent health effects. An important initial step is the development of a reliable analytical method for determining asbestos in water. Based upon the premise that

a method should reflect the state-of-the-art of asbestos analytical methodology, an interim

Drocedure has been written. As such, it is a working document subject to subsequent revision and validation. The method relies on previously published work [1-5]^ together with

the work that has been carried out at the Environmental Protection Agency's laboratories at

Duluth, MN, Athens, GA, and Cincinnati, OH.

I In this paper, the broad elements of the method and a discussion of the rationale for

some of the decisions that were made when choosing between alternatives is presented. The

basic features of the method are summarized in Table 1; the complete, detailed method is

available upon request from the author.

Figures in brackets indicate the literature references at the end of this paper.

365
Table 1. Summary of EPA interim method for asbestos in water.

Definition;

Instrumentation :

Sample :

Sample Preparation :

TEM Examination:

Chrysotile - A magnesium silicate, the fibrous form of serpentine,

possessing a layered, helical cylindrical structure.

Amphibole —A silicate mineral whose basic structural unit is a double silica chain, of variable composition, and

layered structure.

Fiber — A particle in the micron size range possessing

parallel sides and a length/width ratio of greater

than or equal to 3:1

Transmission Electron Microscope capable of selected area diffraction.

One 1 iter of water.

Filter sample through .1 pm Nuclepore or .22 ym Millipore using

sample volume 50-500 mL. Maximum of 20 yg/cm^ total particulate.

High organic requires low temperature ashing and resuspension by

mild ul trasonification.

Portion of Millipore placed on TEM grid, dissolve by condensation

washing or, carbon coat Nuclepore, dissolve by Jaffe Wick in

chloroform.

At 10,000-20,000 magnification. Count 100 fibers or 20 grid

squares. Use field of view method if greater than 50 fibers/grid

square.

IdentificationChrysotile on the basis of morphology and SAED,

the basis of morphology and SAED.

Amphibole on

Reporting : Confirmed chrysotile and amphibole fibers in MFL (million

fibers/1 iter)

Mass/1 iter

Distribution by length, width, and aspect ratio

Definition of Asbestos

Before any quantitative analytical procedure could be outlined, it was obvious that

the term asbestos required a definition in terms of measurable chemical and physical

parameters. Of the two broad classes of asbestos, chrysotile is readily defined on the

basis of its unique morphology, crystalline structure, and elemental composition.

Amphibole' s characterization, on the other hand, is not so straightforward. The broad

class of amphiboles can be defined as silicate minerals whose basic structural unit is a double silica chain, a fibrous morphology, and elemental composition corresponding to the

recognized amphibole asbestos types. In the EPA method, amphibole asbestos determination

is based on crystal structure, amphibole morphology, and a fiber aspect ratio of 3:1 or greater. The basis for this fiber aspect ratio is conservative and reflects the state-ofthe-art in asbestos analytical methods. Although this aspect ratio is lower than that

proposed by Ampian [6], it would seem that the ultimate test, insofar as environmental

samples are concerned, lies in the health effects of mineral fibers of different size and

aspect ratio. Although health effects data will prove difficult to obtain, it seemed

prudent to use this more conservative approach.

366
The Environmental Sample

As the EPA interim method would be applied to a variety of pollution sources and used

for a variety of purposes, no attempt was made to furnish specific sampling instructions,

[nstead, only guidelines and precautions were included in the method. Asbestos is, in

Pact, a special type of particulate matter exhibiting a range of particle sizes, and a /ertical distribution of asbestos concentrations may be present in a water supply. For

;xample. Cook [7] has documented the variability of amphibole fiber concentrations in Lake

superior at the Duluth water supply intake and demonstrated that the amphibole fiber

:oncentrations were dependent on the presence or absence of an ice cover on the lake, the

jirection and velocity of winds, and the depth of the thermocline. It is important,

:herefore, to plan a sampling program for a particular purpose and to use the results only

in context of the sampling procedure.

Another analysis issue was whether the sample taken in the field should be filtered

i/ith the filter and its deposited particulates sent to the laboratory; or, whether the

;ntire water sample should be collected and furnished to the analytical laboratory.

\lthough each approach has advantages, it was considered that the possibility of

:ontamination, the potential for loss from the filter paper, and the general lack of

:ontrol of the filtration step were overriding disadvantages of filtration in the field.

Collection of a sample of the water itself was therefore suggested as the better

ilternative.

The Analytical Approach

:hoice of Instrumentation

In broad terms, the approach to the determination of asbestos in water uses ireconcentration by filtration followed by direct microscopic identification and

leasurement of the asbestos fibers.

Because asbestos fiber diameters are below the range of optical microscopy

techniques, electron microscopic methods must be employed. Although scanning electron

licroscopy (SEM) has been suggested to be applicable [8], those laboratories that have

;ompared transmission electron microscopy (TEM) with SEM have concluded that TEM is the

superior tool [1,4,9]. TEM allows examination at low ('^'200x) and high ('^20,000x)

magnification and gives excellent brightness and contrast. Furthermore, most modern TEM

instruments readily allow selected area electron diffraction (SAED) to be carried out on

individual fibers; such capability allows a positive identification of the characteristic

:rystalline structure of chrysotile and amphiboles. An energy dispersive x-ray (EDX)

ietector is adaptable to the newer TEM's and can furnish additional information on the

jlemental composition of individual fibers that are under examination, but its use was not

"equired in the EPA-proposed method.

^reparation of Samples

The analytical sample, as received by a laboratory, will consist of a 1-liter polyethylene bottle containing a representative sample from the environmental source. The

ibjective of preparing the subsample and subsequent microscopic sample is to transfer the

isbestos particles from the environmental source to the TEM with a minimum loss. At the

ame time the particle size, shape, and size distribution in the original sample should be

laintained. Furthermore, the TEM sample must allow the examination of single asbestos

ibers with no overlapping or obscuration by extraneous material.

The initial step in the sample preparation is the filtration of a known volume of the

'ater sample containing the suspended particles of asbestos onto a membrane filter. This

iltering is a critical step whose function is not only to separate, but also to uniformly

istribute the particulate matter with minimum of overlap. Some precautions are therefore

ecessary in this procedure. The liquid sample is agitated in a low-power ultrasonic bath

rior to filtration to ensure homogeneity. A fixed volume, ranging from 50-500 mL, is

dded to a vacuum filtration apparatus containing a 0.1-pm Nuclepore or a 0.22-pm

.illipore filter. The volume is determined by the amount of particulate matter present,

367
and the maximum loading that can be tolerated is 20 (jg/cm, or about 200 |jg on a 47-mm

filter. The applied vacuum should be sufficient for filtration but gentle enough to avoid

the formation of a vortex. Once the filtration has been initiated, no additional water

should be added nor should the sides of the funnel be rinsed.

If the sample contains a substantial amount of organic material, a preliminary,

ashing step is required, followed by resuspension and filtration. Low- temperature ashing

in an oxygen plasma with resuspension in a fixed volume of water followed by mild

ultrasonification has been found to be satisfactory.

Preparation of TEM Specimen

The transfer of a part of the filter on which the particulates have been deposited on the TEM grid and the subsequent elimination (by dissolution) of the filter material so that a TEM examination can be accomplished is probably the most critical step in the

analysis procedure. As the examination in the TEM and subsequent calculations assumes a random orientation and little or no loss of particles, it is essential that the transfer

be carried out not only without losing particles, but also with a minimum of movement.

This goal becomes very difficult to achieve, largely because the asbestos fibers are in

the colloidal size range; movement apparently can take place very easily.

Two approaches acceptable for TEM sample preparation are:

a. The condensation washer method, which is used when a Millipore filter is

empl oyed.

b. The Jaffe Wick method, which is used with a Nuclepore filter.

In the condensation washing technique [1,3], acetone vapors are condensed in a special reflux condenser at the position just below the TEM grids. Successful operation

requires the delicate introduction of sufficient vapor to dissolve the filter in a reasonable time but not enough to cause pooling, movement, or wash-off of the deposited

fibers. As a result, close control of bath temperature, cooling water temperature, and

flow is required. McCrone [1] and Lishka, et al . [3] claim successful results with this

procedure. Beaman [4] in a detailed study of the condensation washing technique, found,

under his experimental conditions, amphibole fiber losses ranging from 37 to 60 percent.

Chrysotile fibers apparently are less mobile, for Beaman found losses ranging from 0 to 21 percent. In spite of the criticisms of the condensation washer, the fact that at least

two laboratories obtained successful results dictated the inclusion of the method as an alternative preparation step in the EPA procedure.

In the Nuclepore-Jaffe Wick technique, the Nuclepore filter is carbon-coated in a vacuum evaporator (after filtration) before attempting to dissolve the filter material

from the grid. Fixed by the carbon coating, the particles are thereby rendered immobile

and less susceptible to loss. The filter material is dissolved away by a simple wicking

action that can be obtained from several layers of filter paper in a covered Petri dish

containing chloroform. The dissolving time, although longer than that for the

condensation washer, can usually be accomplished overnight. The Nuclepore filter is well

adapted to carbon coating because it has a flat surface and no disturbing, replicated

structure is found in the grid film. In contrast, the Millipore filter contains a fibrous-like structure that, when replicated, interferes with the TEM examination. Cook

[5] at the Duluth Environmental Research Laboratory, Nicholson [2] at Mt. Sinai, Glass

[10] at Ontario Research Foundation, and chemists at our laboratory have all obtained

excellent results with the Jaffe Wick preparation method. An advantage of this method is

that if a fiber is lost during the dissolving step a replica of the fiber remains; thus, an internal check on the procedure is preserved. The fact that such fiber replicas are rarely if ever observed gives substance to the conclusion that no significant loss or movement takes place during the preparation process.

Counting of Fibers

The prepared TEM grid holding the asbestos fibers and other particulate matter is

initially examined at low magnification (300x-1000x) in order to determine whether the

368
grid preparation has been prepared satisfactorily. If the grid is too heavily loaded

(>300 fibers/grid square), if the distribution is noticeably uneven, or if a majority of

the grid squares have broken carbon films, a new preparation is required. For those

natural waters that contain sufficient organic matter to obscure other particulates, the

filtered material must be subjected to low temperature ashing, resuspension, and

f i Itration.

The analytical procedure employs standard counting techniques at 1 0 ,000-20 ,000x in

determining the number, dimensions, and type of asbestos fibers that are present in the

area that is examined. Two general approaches-random search or systematic search-were

suggested for the EPA method depending on the number of fibers present.

If an 80 pm x 80 pm grid square contains more than about 50-100 fibers, it is convenient to use the field of view method. Beaman [4] and chemists at the Athens Laboratory

have found this jnethod satisfactory for these situations. In this method, several grid

squares are selected and random fields of view examined. The area of the field is known

from the magnification of the microscope and the area of the projected image. The total

fibers counted in the known number of fields of the known area can be then converted to

million of fibers per liter (MFL) through a simple conversion factor that is dependent on

the original filter diameter and the amount filtered.

If only a few fibers are found in each grid square, it is more convenient to systematically search up to ten whole grid squares and count the fibers lying within these

areas. As the area of individual grid squares may vary by ~10 percent, the dimensions of

each grid square examined should be recorded.

Ideally, 100 fibers are examined for each sample, 50 each from two grid preparations.

In practice, however, some samples may contain so few fibers that considerations of time

become important. In the EPA method, ten grid squares on two grid preparations are examined, and the number of fibers in this fixed area are counted when the fiber

concentrations are quite low.

Identification of Fibers

Each fiber that is found should be subjected to further examination to determine

whether it is asbestos and classified as chrysotile or an amphibole type. Chrysotile's

unique tubular structure and its tendency to form bundles of single fibers makes it

readily identifiable. For an unequivocal identification, however, a selected area

electron diffraction (SAED) pattern of chrysotile gives a unique pattern exhibiting

prominent streaks on the first layer line and a triple set of double spots on the second

layer line. UICC standard asbestos fiber material is available to furnish standard

comparison diffraction patterns.

Amphibole fibers are identified on the basis of lath-like morphology, aspect ratio,

and an SAED pattern. Although it would be desirable to identify the different amphibole

asbestos types, their diffraction patterns are almost identical and their differentiation

by SAED is almost impossible and clearly impractical. Amphibole identification is more

difficult than chrysotile because the amphibole SAED does not have the unique characteristics of the chrysotile pattern and requires some judgement in interpreting the SAED

pattern. Some amphibole fibers show only partial patterns that are not sufficiently

complete to allow positive identification; these are classified as "probably" amphiboles.

As Beaman [4] and Millette [11] have indicated, it is useful to determine the

elemental composition of a fiber as an aid to identification. This is particularly true

if a fiber fails to give an identifiable electron diffraction pattern and additional

information is required for identification. Because the fiber width and thickness is less

than that excited by the electron beam, the elemental x-ray intensities are a function of

width. This variation with particle size can be partially overcome, however, by

determining x-ray intensity ratios. But these ratios, because of differential absorption,

are also a function of particle size. Because of the difficulty of specifying

quantitative procedures based upon x-ray intensities, the EPA method suggests the use of

energy dispersive x-ray analysis as a useful tool but does not require its use. As Ruud

[[12] has pointed out, even though a good quantitative analysis could be obtained from EDX,

it should not be considered a definitive identification without an SAED pattern.

369
The length and width of each fiber positively identified, as well as the "probables",

are recorded.

Precision of Analysis

The analysis precision obtained within an individual laboratory is dependent upon the

number of fibers counted. If 100 fibers are counted and the loading is at least 3.5

fibers/grid square, computer modeling of the counting errors shows that a relative

standard deviation of only about 10 percent can be expected. In actual practice, some degradation from this precision will be observed but should not exceed ±20 percent if

several grids are prepared from the same filtered sample.

The relative standard deviation of analyses of the same water sample in the same laboratory will increase because of sample preparation errors, and a relative standard

deviation of about ±20-30 percent can be expected. Table 2 shows the results obtained on five sets of samples of asbestos and indicates that this range can be achieved. As the

number of fibers counted decreases, the precision will also decrease approximately proportional to N'^ where N is the number of fibers counted.

Table 2. Precision of C-coated Nuclepore method.

Type

asbestos

No.

samples

Ave. cone. (MFL)

Standard

deviation

Coefficient

of variation

Chrysotile

Croc idol ite

Crocidol ite

"Taconite"

"Taconite"

10

9

10

10

10

23

13

16

21

28

4.7

1.7

2.8

5.0

3.4

23%

13%

17%

24%

12%

Average 18%

Although there have been a number of interlaboratory testing programs, few of these

have been carried out using the same procedure. Those that have been done indicate that

agreement within a factor of two is achieved if 100 fibers can be counted. Results

obtained among three laboratories at different locations within the Environmental

Protection Agency are given in Table 3. Although these data are insufficient for

statistical purposes, they indicate the analysis capability obtainable at the present;

time.

370
Table 3. Comparison of resuHs-NucI epore method (except as noted)

positively identified fibers (MFL).

Sample Asbestos type Lab A Lab B Lab C

1 Amphibol137 150

2 Amphibole 86 92

a 70

3 Amphibol130 220 140

13

a 120

4 Amphibole 44 58 58

17^ 48^

5 Chrysoti 1

29 14

17^

6 Chrysotile 66 58 60

56^ 50^

Condensation Washer.

Summary

The Environmental Protection Agency has written an analytical method for asbestos in

water, based on what was considered to represent the state-of-the-art asbestos analytical

methodology. In its present form, the method should be considered as an interim method

having no official status. When the results of future research efforts and cooperative

testing are available, it is expected to be proposed as a referee method for asbestos.

References

[1] McCrone, W. C. and Stewart, I. M. , Asbestos, Amer . Lab . 6(4), 10-18 (1974).

j [2] Nicholson, W. J., Analysis of amphibole asbestiform fibers in municipal water

supplies, Env. Health Perspectives 9, 1965-172 (1974).

I [3] Lishka, R. G. , Millette, J. R. , and McFarren, E. F. , Asbestos Analysis by Electron

Microscope in Proc . AWWA Water Qua! ity Tech. Conf . American Water Works Assoc .

,

Denver, CO, XIV-1 - XIV-12 (1975).

; [4] Beaman, D. R. and File, D. M. , Quantitative determination of asbestos fiber concen-

! trations. Anal . Chem. 48, 101-110 (1976).

j[5] Cook, P. M. , Rubin, I. B. , Maggiore, C. J., and Nicholson, W. J., X-ray Diffraction

i and Electron Beam Analysis of Asbestiform Minerals in Lake Superior Waters in Proc.

Inter . Conf . on Environ . Sensing and Assessment 34, Las Vegas, NV, 1-9 (1976).

[6] Ampian, S. , Asbestos Minerals and Their Nonasbestos Analogs, paper presented at

Electron Microscopy of Microfibers Symposium, Pennsylvania State University,

University Park, PA, August 23-25, 1976.

i [7] Cook, P. M. , Glass, G. E. , and Tucker, J. H. , Asbestiform amphibole minerals:

detection and measurement of high concentrations in municipal water supplies, Science

! 185, 853-855 (1974).

371
[8] Pattnaik, A. and Meakin, J. D. , Development of an Instrumental Monitoring Method for

Measurement of Asbestos Concentrations i n or Near Sources , (U.S. Environmental

Protection Agency, Washington, DC, EPA 650/2-73-016, 1973).

[9] Flickinger, J. and Standridge, J., Identification of fibrous material in two public

water supplies, Envi ron . Sci . and Tech . 10 , 1028-32 (1976).

[10] Glass, R. W. , Improved Methodology for Determination of Asbestos as a Water

Pollutant, Ontario Research Foundation Report, April 30, 1976, Mississauga, Ontario,

Canada.

[11] Millette, J. R. and McFarren, E. F. , Eds of waterborne asbestos fibers in TEM, SEM,

and STEM, Scanning Electron Microscopy/1976 (Part III) 451-460 (1976).

[12] Ruud, C. 0., Barrett, C. S. , Russell, P. A., and Clark, R. L. , Selected area electron

diffraction and energy dispersive X-Ray analysis for the identification of asbestos

fibers, a comparison. Micron 7, 115-132 (1976).

Discussion

R. LEE: I noticed in your description of the method that you rely on chrysotile

which has a selected area diffraction, and has morphology. For amphiboles you rely on morphology plus selected area diffraction or chemistry. If you accept that as your

definition of an asbestos particle, I think it is very important to know whether or not

what you are telling me is that now I have to treat any cleavage fragment, any massive

hand specimen which I grind down, in which there should be a more morphological and orientation difference, as an asbestos particle. Secondly I'd like to say that, before you

answer, that we're going to show some preliminary data that suggest that we can give you

a very close diagnostic method for distinguishing between them.

C. ANDERSON: This is not my idea of what should be done or should' nt be done, this

is our concept of the consensus of the state of the art of analytical methodology in

asbestos as it existed when we wrote the method. The state of the analytical methodology

for amphiboles is just very, very muddy. We certainly are willing to listen to your

suggestions as to how we can do this better.

LEE: Is there any reason to assume that all amphibole cleavage fragments are identical to amosite asbestos?

ANDERSON: I think that the critical issue is what are the health effects of one versus the other.

LEE: The only data we have seen on that to date was shown yesterday, indicating that

grunerite had no cellular activity.

ANDERSON: I saw some slides showing almost any particle has some in vitro effects.

LEE: In this particular case grunerite (the non-fibrous variety) did not show any

activity.

ANDERSON: What were the particle characteristics of the grunerite?

i A. WILEY: I suggest that you change your title. Rather than identifying asbestos,

say that you are identifying chrysotile and amphibole. Since you can't say that it is

asbestos, why not say just amphibole, period.

v. WOLKODOFF: I notice in your paper, for five fibers, you would say statistically

significant, and anything less than that would be not statistically significant. Do you

still hold to that?

372
ANDERSON: The five-fiber criterion was considered to be the state of the art, and I was happy to see Dr. Leineweber point out that at five fibers the statistics show you the

range is between .48 and 10. It seems to me that five fibers is statistically significant

to indicate asbestos is present.

WOLKODOFF: If you go by the Poisson distribution. But there are cases where less

than five fibers is extremely important in the interpretation of particular problems to

us, providing our background is zero.

; ANDERSON: You apply the statistics to your problems in the context of what you are

' worrying about. What we did was, if you find less than five in the water samples you

: really can't say with much confidence how much is there.

! WOLKODOFF: I'm glad to hear you say that and really it's a big help then. On this

t business of hornblende, is this your offical stance or posture that these are not to be

' counted?

ANDERSON: I can't take any official stance. I claim in the method you will misidentify hornblende as an amphibole asbestos. If the mineralogists want to take issue

with me, let me know. We will take that out.

WOLKODOFF: Have you gone into this as a subject?

ANDERSON: You mean as far as differentiating various types?

WOLKODOFF: Of the various types, yes.

ANDERSON: No.

WOLKODOFF: As far as you are concerned then, a hornblende is a hornblende. I mean,

an amphibole is an amphibole.

ANDERSON: Right.

WOLKODOFF: Your people, like Milette and Cook and yourself, can you actually

differentiate amphiboles by selected area electron diffraction? Have you gone into this

subject?

ANDERSON: As differentiate types, no.

WOLKODOFF: As far as you are concerned, an amphibole is an amphibole.

ANDERSON: Right.

WOLKODOFF: I thought then perhaps that when you say that EDS is not absolutely

necessary, that maybe there was a matter of cost reduction, but you are saying that for

technical reasons, very much like Don Beaman pointed out.

ANDERSON: Look at this from my point of view. Suppose I say, Valdimir write a method

that everybody agrees with and put it down specifically enough so that people can follow

it. How do you do this with an EDS system? I don't know. I don't know that much; I strongly recommend using it, but I was not really very comfortable in just saying use the

EDS like the manufacturer said to use it.

WOLKODOFF: For many of our problems it would be of great benefit.

ANDERSON: And, of course, there is a cost consideration involved here too.

WOLKODOFF: I must commend and compliment you on your paper. We felt it was very

well done, and I think with some additions and so forth it will

ANDERSON: Thank you.

373
BEAMAN: I'd like to mention the EDS,. Charles, again I think there have been

presented at this meeting and last year's some very serious challenges to the use of

selected area electron diffraction identification and classification of amphiboles. I've

heard people say it was almost impossible to classify cleavage fragments as an amphibole

looking at the selected area electron diffraction pattern on the screen of the TEM. You

may be able to classify by taking a photograph and indexing it, but I think that in

conjunction with the energy dispersive spectrometry you are on much firmer ground.

ANDERSON: I agree, but I think what you have to remember is also the purpose of the

method that we wrote. We wrote it from the point of view of not giving a complete

characterization of the particulate matter that was in a water source. We consider that

to be a little bit beyond the scope of an analytical method. There is a fine distinction

between a very quick and dirty method and a research method in which you are characterizing the whole source and an analytical method that the broad analytical laboratory

might want to use.

BEAMAN: If you were going to use just the SAED, then you have to put some confidence

limits on it. The numbers that you present in an interlaboratory comparison, for

example, you would have to put a range on there and say that those 60 or 150 could be as low as 5 or 10 if you were to make a positive identification.

J. MCALEAR: NBS Associates, I'm going to have to speak in behalf of some of the scores of laboratories who have been doing some scanning electron microscope analysis for

asbestos for some years to make the point that the actual application in this area is

fairly extensive using the SEM, and I think it is growing. I'm not going to take time now

to make a detailed comparison here. It has been done at many places, but I think it is a very poor mistake to rule out scanning electron microscopy in a general, even interim'

method when such things have a tendency in fact to become regulations; become standards.

I think that this needs to be objectively reviewed. ,

i ANDERSON: Let me respond to that. I came into this program having little experience

in transmission electron microscopy. My major experience was with scanning electron

microscopes, wavelength electron probes, and energy dispersive x-ray detectors. I too

thought that the people using TEM were crazy. As a matter of fact I tried hard to see if an SEM wouldn't do the job. I will be the last to make the broad statement that SEM's are

no good; I know better than that. There are higher brightness sources, the LaBe source

gives you an increased electron density, not too many people have been working with

asbestos with better electron sources or field emission source; this can give you an increased yield of x-rays I am trying to be objective, but you look at what people!

have done and compared SEM with TEM and they all come up with the same conclusion about

the superiority of the TEM.

MCALEAR: We have many customers who use both TEM and SEM and I don't believe the

votes are in on this as yet by a long shot.

ANDERSON: The whole difference is the size range that we are considering. We are considering asbestos in water and the asbestos fibers are very small-about 250A wide.

I. STEWART: There was a comment about the statistical significance of results and,, as I understand it, your phi is basically an attempt to be realistic and say that there

will be backgrounds. Now, the gentleman from Johns Manville surprised me by mentioning

there is zero background. We have done a lot of blanks with nothing in them but we do not

call them zero background, which I think is totally unrealistic with asbestos. The

values that have been published in the literature range from 30 fibers per grid square,

reported by Tony Richards of Turner Bros., down to this claim for zero or near zero. Now

if you take your 20 grid squares, that means you have six hundred fibers, at which point

you are really talking about noise- to-signal ratio.

J. KRAMER: I'd like to address the question of SAED confirmation or chrysotile and

the amphiboles. I think you ought to be complimented on the details of your general

method of preparation, which I think all people need, and they can go through step by step

and determine whether this works in their lab or not. But in the literature and here in

terms of electron diffraction confirmation we have seen two different wall paper patterns.,

374
I think Don Beaman came the closest to suggesting what specifically about these patterns

should be used as a method of confirmation. Furthermore, we have always seen a pattern of

an amphibole, generally one of the asbestos mineral species and chrysotile. I would like

to point out particularly with water and environmental samples that there are probably two

to three hundred other fibrous minerals by your definition, all having electron diffraction patterns. Dr. Zussman brought up the point yesterday, you need a three-dimensional

orientation to know precisely what you are going to get, and that does not get into other

problems of defects and so on. What bothers me is, nowhere have I seen anything but

pictures in saying that this is different than that and I think, and maybe you have done

this, we need a step-by-step procedure for confirmation of the amphibole group or the

chrysotile group or something along this line. Then mineralogists can take these and they

can say generally you'll get this or you won't get this. Watch out, these mineral species

will do the same thing. I have not seen this anywhere and it is rather frustrating to say

you need electron diffraction confirmation when you don't know what the step-by-step

procedure is to the same degree you have so eloquently done with the sample preparation.

ANDERSON: We certainly recognize you have to balance the realities of the analysis

in how much time can you really spend in analyzing an electron diffraction pattern from a single fiber. As Sumudra pointed out last spring, if you use a very small camera length

you get a large percentage of fibers giving an electron diffraction pattern. They are reasonably characteristic, the amphibole pattern is reasonable, and certainly the

chrysotile stands out. The amphiboles are certainly all very similar; they are all

characteristic and there is certainly a judgmental factor involved, although we have

compared our judgments on the Duluth amphiboles versus what Beaman published and we get

almost the same curve. Our judgment was about the same as Seaman's and I guess that is

all you can come up with, and I think that other people will find somewhat the same thing.

KRAMER: Let me repeat, because in these cases the amphiboles and the chrysotile have

been worked with. There are many other minerals in the environment, such as chain

silicates; I'm not saying there is a unique method, but I think we need to know as an interim method, if you want to call it that, the procedure by which these are to be

confirmed. Then we can go ahead to the next step.

ANDERSON: Confirmed as far as identified?

KRAMER: As identified by SAED in your lab. Then we can go ahead to the next step.

ANDERSON: I don't care to confirm halite as halite; I don't care about some other

minerals, all I care about is asbestos minerals.

P. McGRATH: What I contended, although I can appreciate the problem I have with the

development on an interim method, I think we have to begin to realize that all of the

analysts who are going to be doing this over the next few years are not going to be an

Eric Chatfied or Jim Millette. I think that the EPA and other groups that are going to do

an awful lot of this testing, and in all probability will end up setting the standards for

the rest of the country, should look into other methods, and I agree with Jim McAlear that

we have abused scanning electron microscopy and it's not going to be a panacea or an

answer for all these things, but I know from my own experience and the experience in other

laboratories that you can get reasonable counts and reasonable chemical information from

the scanning electron microscopy, and in all probability quicker and at much reduced cost

than you can with your method. You mentioned somewhere that this is a sort of a quick and

lirty method; it is not a quick or dirty method.

ANDERSON: It is not a quick or dirty method.

McGRATH: It's a long and involved tedious thing, and the operator has to be an

iJxcellent operator to get the kind of results that you got, with Jim Millette and Phil

|:ook.

I ANDERSON: Well I think the whole crux of the matter is whether the SEM with the

':onventional , lanthanum hexaboride, or field emission source can indeed detect two hundred

ingstrom wide fibers and also give sufficient x-ray data to identify that fiber as an

I'lmphibole or chrysotile.

1

375
NOTE: The following was a note sent following the meeting and was not part of the verbal

discussion at the end of this paper.

D. JACKSON: Dr. Anderson could you comment on the areas which may prove problematic

and the areas requiring particular attention in using your proposed Analytical Methodology

for determining asbestos in water.

ANDERSON: The following areas appear to me to be the major problems to be overcome

in determining asbestos in water.

1) Assuring that you have a representative sample.

2) Contamination, both during the sampling process and in the laboratory.

3) Filtering the sample in such a manner that the particulates deposit in a near- random distribution and without over-loading the filter.

4) The presence of a large amount of extraneous particulate matter in relationship

to the amount of asbestos.

5) Dissolving the filter material without loss or movement of the asbestos fibers.

6) The identification of amphibole asbestos fibers.

376
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

INTER- LABORATORY MEASUREMENTS OF AMPHIBOLE AND CHRYSGTILE FIBER CONCENTRATION IN WATER

K. S. Chopra

Union Carbide Corporation - Metals Division

Niagara Falls, New York 14302

Abstract

ASTM Committee E-4 has been experimentally evaluating high

magnification microscopic techniques being used for the analysis of

fiber contamination in water. This paper will describe the procedures

and present status of this technique evaluation.

Key Words: Amphibole; ASTM; asbestos; amphibole; chrysotile; fiber;

transmission electron microscope; water.

Introduction

Great interest in the identification, characterization, and concentration determination of mineral fibers in environmental samples has been generated in recent years due to

the fibers' potential carcinogenic effect for humans. The variety of sample preparation

techniques, instrumentation, identification methods, technical definitions, and levels of

analyst experience have often produced scattered and inconsistent results for related or shared samples.

A Task Group was formed under the ASTM E-4 Committee to study the reasons for this

inter- laboratory divergence and to establish a recommended standard method for determining

fiber concentrations in water. The Task Group is composed of 17 experts in fine particle

analysis from government, industry, and commercial service laboratories in the United States

and Canada.

Members of the Task Group agreed on the necessity of using a transmission electron

microscope (TEM) for the determination of concentratoions of very small fibers, such as asbestos fibers, which have diameters as small as 200 A. The (TEM) technique will serve as

a reliable method of calibration for other more rapid and less expensive techniques which,

hopefully, can be developed. The scanning electron microscope (SEM) was not selected for

use because:

1. The SEM lacks the selected area electron diffraction capability for

identification of fiber mineral type (e.g. , amphibole or chrysotile).

2. The SEM has inferior imaging capability because the image is distorted by

sample movement, and the brightness and contrast are less than in the TEM

at 20,000X.

3. Some distinctive fiber morphologies, such as the hollow core of single

chrysotile fibrils (200-400 K) , cannot be observed by SEM.

o

4. Searching sample areas at magnifications of 10,000 to 25,000 A for

fibers is more fatiguing with the SEM. Analyst fatigue contributes

significantly to a loss of precision.

5. These observations are meant to define the current limitations of

the instruments.

377
The Task Group analyzed four Duluth, Minnesota, tap water samples containing amphibole

fibers and two samples of filtered water with a chrysotile standard added. The laboratories were supplied with filtered samples on Nuclepore and/or Millipore filters.

Analytical Methods

Techniques for the preparation of samples and TEM counting of fibers have been

published by Task Group members [1,2,3,4,5,6,7]^. In almost every case, water is filtered

onto Millipore or Nuclepore filters. Sections are cut from the filters and placed on TEM

grids. The process, whereby the filter is dissolved in a solvent to leave the sample on or in a carbon film on the grid, is a direct transfer method. The filter dissolution step

can be done in several different ways and is a key difference between many methods of

sample preparation.

Most Nuclepore filter preparations are carbon-coated prior to the filter piece dissolution step so that the resulting grid has the fibers held in the carbon film on the

grid. The inclusion of the fibers in the carbon film is made possible by the very flat

surface of the Nuclepore filter and is intended to prevent loss of fibers during filter

extraction in a Jaffe washer.

Millipore filter preparations usually involve the acetone dissolution of filter pieces

on a carbon-coated grid in a condensation washer or a Jaffe washer. The condensation washer

employs the careful regulation of the level of acetone condensation near a point in a condenser at or just below the position of the grid, so that only acetone vapor is present

to dissolve the filter.

Fiber identification is often based on the morphology and selected area electron

diffraction (SAED) characteristics of the fiber. Many laboratories also rely on energydispersive spectrometry (EDS) to classify fibers by elemental intensity ratio. The

observation of morphology at high magnification in the TEM is particularly useful for

identifying chrysotile fibrils because of the hollow core or tubular appearance frequently

observable. SAED patterns are used to distinguish amphibole and chrysotile fibers from

each other and other fibers which have different crystal structures or are amorphous.

High-voltage TEM allows the analysis of SAED patterns from fibers too thick for SAED at

the normal TEM operating voltages of 60-125 kV. The voltages available on most TEM's do

not allow the identification of all mineral fibers, particularly if they are very thin or thick. Considerable controversy exists as to the adequacy of SAED for the positive

identification of single chrysotile fibrils (200-400 K diameter). Some analysts rely on the observation of the chrysotile magnesium/silicon intensity ratio in the energy-dispersive

spectrum instead of a positive SAED pattern.

There are some cases when EDS spectra from different minerals are similar. Consequently, an identification based on a combination of morphology, SAED pattern, and EDS

spectrum is considered most reliable, particularly for samples which are collected from

previously uncharacterized systems. The members of the Task Group used the combinations

TEM-SAED or TEM-SAED-EDS for characterization and identification.

Figure 1 shows the inter- laboratory reproducibility for the group analyses and is

plotted chronologically. It must be stressed that the inter- laboratory reproducibility is a measure of precision and not accuracy. The Task Group is presently characterizing a sample containing a known chrysotile mass. It is apparent that improvement has occurred;

in a year and that reproducibility of ±50 percent is possible for fiber concentrations'

above 70 MFL. The reproducibility at lower concentrations was not this good. The data

imply that when all aspects of the analysis are under rigid control, the inter- laboratory

reproducibility achievable with the existing TEM technique could be about ±25 percent for

relatively clean samples of the type studied herein. Considering the fact that these

analyses correspond to the measurement of 50 ppb of amphibole fibers in environmental

samples, reproducibility in the range of 25-50 percent is respectable.

^Figures in brackets indicate the literature references at the end of this paper.

378
180

L 0

11/18/75 5/3/76 8/23/76 12/6/76 8/23/76 12/6/76

DATE

Figure 1. Plot of chronological inter-laboratory reproducibility for the group analysis,

379
Summary

These methods offer a feasible means of measuring relatively low levels of fiber

contamination in environmental water samples. Other bulk-type methods lack the needed

sensitivity and selectivity. The transmission electron microscope is the best basic

instrument for performing analysis, particularly when equipped with selected area electron

diffraction and energy-dispersive spectroscopy capabilities. The mean fiber concentration

by different groups agree within a factor of two. The inter- laboratory reproducibility of

50 percent can be expected in relatively clean water samples unless the concentration is

low. In samples with high concentration of interfering solids, the precision will not be

as good. Inter-laboratory reproducibility of 25 percent is as good as the method can provide. When applied on a broad scale, there are variable (0-84%) and significant

(mean = 30%) losses associated with the condensation washing of samples containing

amphibole. The losses are low (mean = 14%) and less variable when using condensation

washing to prepare samples containing chrysotile.

References

[1] Cook, P. M. , Rubin, I. B. , Maggiore, C. J., and Nicholson, W. J., X-ray diffraction

and electron beam analysis of asbestisform minerals in Lake Superior waters. Proc . Int . Conf . on Environmental Sensing and Assessment , 34(2) , 1-9 (1976).

[2] Millette, J. R. and McFarren, E. F. , EDS of waterborne asbestos fibers in TEM, SEM,

STEM scanning electron microscopy/1976 (Part III) 451-460 (1976).

[3] Beaman, D. R. and File, D. M. , Quantitative determination of asbestos fiber concentrations, Aiial. Chem . 48(1) , 101-110 (1976).

[4] Anderson, C. H. and Long, J. M. , Preliminary interim procedure for fibrous asbestos,

U. S. Environmental Protection Agency, Athens, Ga. (1977).

[5] Chatfield, E. J. and Glass, R. , Improved methodology for determination of asbestos as a water pollutant. Report ORE, Mississauga, Ontario, Canada, Center for Inland Waters

(1976).

[6] Dement, J., Zumwalde, R. , and Wallingford, K. M. , Asbestos fiber exposure in Hard Rock

Gold Mine, Annals of New York Academy of Sciences , 271 , 341-352 (1976).

[7] FDA Symposium on Electron Microscopy of Microfibers, August 19, 1976, Penn State

University, State College, Pa. (in press).

[8] Lee, R. J. , Debray, D. R. , and Szirmae, A. , Sample preparation and measurement of

losses in electron optical analyses of particulates in air and water samples. Thirtyfourth Annual Emsa Proceedings, Miami Beach, Fl., Aug. 1976, pp. 556-557.

This paper will be published in its entirety in the July 1978 issue of Testing and Evaluation published by ASTM.

Discussion

NOTE: Discussion of this paper was included in the General Discussion at the end of this

session.

380
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

THE STANDARD FOR OCCUPATIONAL EXPOSURE TO ASBESTOS BEING CONSIDERED BY

ASTM COMMITTEE E-34

M. Cossette

Director, Centre for Technology of the Environment

University of Sherbrooke, Canada

and

A. A. Winer

CANMET

Industrial Minerals Laboratory

Ottawa, Canada

Abstract

This presentation reviews the consensus reached by the Task Group on Naturally Occurring Inorganic Fibers of ASTM Committee E-34.

Significant differences with the OSHA regulation are pointed out on the

following topics: Definitions, exposure limits, record keeping,

monitoring, and the counting method. The reasons for these differences

are outlined and a rationale in support of a dual standard is presented.

This Task Group document is now under study according to official ASTM

procedures.

Key Words: Asbestos; ASTM; consensus; definitions; exposure limits;

monitoring; occupational exposure; record keeping.

Introduction

ASTM Committee E-34 is presently considering a standard for occupational exposure to

asbestos. This standard differs from others in one very significant respect, in that it

is a consensus document. There is input from both the regulators and the regulated, and

this situation makes it a unique document.

Scope

This ASTM standard is applicable for all occupational exposures including mining and

-milling, as well as manufacturing and end- use industries. It is intended for use both in

; the USA, and in other countries where ASTM standards are in current usage.

Excluded from the scope of application are situations where the airborne fibrous

particulates can be proven to be pathologically inert [1,2]^. Recent epidemiological

studies by Ahlmark at the University of Sweden, and by P. Radovan on two asbestos cement

factories in Yugoslavia, in addition to a major study by Greg and Weiner at Battelle Pacific

! Northwest, are said to indicate that the biological activity of asbestos fibers is altered

by the autoclave process of producing asbestos cement.

^Figures in brackets indicate the literature references at the end of this paper.

381
This standard is flexible in application

only respirators for occasional work that may

be the case where asbestos lagging must be

chemical plant.

to the extent of recommending the use of

involve intermittent exposure. This would

removed from a valve, occasionally, in a

Definitions

The ASTM document presents the following mineralogical definitions:

asbesti form - mineral structured in the form of asbestos.

asbestos - generic term for naturally occurring, inorganic hydrated silicates that when

crushed and processed separate into flexible fibers made up of fibrils [3,4].

Minerals defined as asbestos are the asbestiform varieties of the following: serpentine (chrysoti le) , riebeckite (crocidol ite) , cummi ngtonite (amosite), anthophyll i te

,

tremolite, and actinolite [5-8].

fiber - for the purpose of this standard, fiber means naturally occurring inorganic fibers.

f ibri

- a single crystal in the form of a fiber [9].

fibrous particulate - for the purpose of this standard, fibrous particulate designates

fibers, fiber fragments, and fiber agglomerates.

naturally occurring inorganic fiber - form of mineral characterized by properties of

flexibility and length-to-width ratio in the order of 100, composed of definite

crystal unit cells oriented with respect to a specific axis [4].

Note 1 - The designated 100:1 aspect ratio is considered to represent a reasonable lower

limit for naturally occurring inorganic fibers. Fibers of these dimensions [10] can

be broken into parts of fibers that may maintain their same surface properties and

activities. Therefore fiber fragments may have to be evaluated for atmospheric

monitoring purposes. However, attempting to define a fiber by its aspect ratio alone

is inadequate since it is obvious that particles of non-fibrous material do not

become fibers as their aspect ratio increases through comminution.

Other non-mineralogical definitions include:

aspect ratio - ratio of the length of a fibrous particulate to its equivalent diameter [11].

monitored particulate - fibrous particulate with an aspect ratio of at least 5:1, a minimum

length of 5 pm, a maximum diameter of 3 pm, and the appearance of a fascine (bundle

of sticks effect). Only particulates that fit these requirements are counted in the

monitoring method [12-16].

peak sample - for the purpose of this standard, a sample taken over a short interval (not

exceeding 15 min) to evaluate brief excursions in the airborne fibrous particulate

concentration level [17].

Definitions applicable to monitoring include:

personal sample - sample collected on a membrane filter that is attached near to the operator or employee's breathing zone.

Geographical samples -

static sample - sample collected on a membrane filter at a fixed station.

dynamic sample - sample collected on a membrane filter transported over a fixed route at

a specific speed.

382
Permissible Exposure Levels

The exposure level being considered for mines and mills is 5 fibers/cm^ (same as the

present MESA regulation.)

The exposure level being considered for manufacturing and end use industries is

2 fibers/cm^ (same as the present OSHA regulation).

The bases considered in reaching a consensus on a dual standard were the following:

Gibbs and Hwang [18] have shown that the particulate size distributions of airborne

fibrous particulates differ for different types of asbestos, and for different occupations.

For example the percentage of countable fibers (diameter smaller than 0.5 pm and length

greater than 5 pm) was found to be 18.3 percent at one site where amosite insulation was installed, compared against 1.0 percent in a bagging area of a chrysotile mill. This

implies that 18.3 percent of the airborne fibrous particulates would be invisible in the

optical microscope in one case versus only one percent in the other case. In general, it

appears that with each successive step in milling, and manufacturing, the fibers become

more finely divided, and more of them become invisible in the optical microscope. On the

other hand, the hazard may increase with finer fibers because more of them are likely to

reach the lower airways.

It has also been demonstrated rigorously [19] that the likelihood of counting a fiber

is a function of fiber length. A fiber 40 pm long has about a 10 percent higher probability

of being counted than a 5 pm fiber. An 80 pm fiber has about 50 percent more probability of

being counted than a 5 pm fiber. Now the manufacturing and end-use industries generally

shorten the fibers. For example Gibbs and Hwang [12] have shown that the median length of

airborne fibrous particulates in the bagging area of a mill (the last milling operation) was

1.00 pm versus 1.35 pm for the same type of asbestos in the carding area of a textile plant.

The International Labor Organization has established [20] that the highest risks are found in the insulation trade (an end-use industry). On the other hand "in chrysotile

mining and milling, despite very heavy dust concentrations in the past, the incidence of severe asbestosis, asbestos cancers, and especially mesotheliomas has been low."

McDonald [21] has found that the mesothel ioma-inducing potential was greater in

asbestos manufacture and application than in mining and milling, and he stated: "This may

be related to fiber size but also possibly to co-carcinogens in the industrial environment"

"mining environments may well be free from co-carcinogens of the kind found in

factories, ports and industrial cities."

The sedimentation velocity of airborne fibrous particulates has been shown to be a function of diameter [22]. Gibbs and Hwang [18] have shown that for a given type of

asbestos the proportion of fibers finer than 0.5 pm was 67 percent in the ore drying area

(beginning of milling process), 82 percent in the bagging area (end of milling) and 88

percent in the carding area (manufacturing). There is no question that fewer of the

airborne fibrous particulates are respirable in mining and milling, than in manufacturing

and end use industries. In addition fibers in mines and mills show a notably greater

propensity to flocculate together, thus reducing their respirabi 1 ity while increasing

their countability [23].

The formula for the calculation of the 8-hour time weighted average that has been

Rationale for a Dual Standard

Time Weighted Average

adopted is:

8 h TWA = I Ni Ti / 1 Ti

1

where Ni

and Ti

Number of fibrous particulates in the ith sample,

Time period over which the ith sample was collected.

383
Medical Surveillance

A preplacement medical examination is mandatory. Enforcement of annual examination

is recommended where legal to do so.

The question of starting medical surveillance at one-half the permissible exposur

limits versus the full limit is still unresolved.

An interesting document on the diagnosis of asbestosis is annexed to the standard.

Medical Records

These are to be available to government agencies, and upon written request, t employees, or former employees. Records are to be kept 50 years. This is in recognitio

of the long latent period necessary for the manifestation of asbestos related diseases.

Labeling (Posting)

Materials containing asbestos, bound or reacted in such a way as to give off emanation

of dust that can be demonstrated to be non-toxic, when produced by foreseeable activities

are exempt from labeling.

Monitoring

The emphasis is placed upon personal samplers. Static geographical sampling is alsi

called for. Areas above the permissible limits must be monitored every six months. Twi to twelve samples per worker per shift are recommended [17]. Monitoring records are alsi

to be kept 50 years.

The midget impinger may be used to obtain correlation data since it was the basis fo

the most reliable epidemiological data, but may not be used for referee testing.

Analytical Method

The method is based upon the use of a 37 mm diameter membrane with a pore size o 0.8 pm, and personal sampling pumps operating at 2 dm^/min for periods of 15 min to 4h a concentrations of 1 to 20 fibrous particulates per cubic centimeter. Only fibrous particu

lates with a length greater than 5 pm, a maximum diameter of 3 pm, and an aspect ratio o at least 5 to 1 are counted.

The 5 to 1 aspect ratio was adopted when it was ascertained that the 3 to 1 rati

originally adopted by the British was strictly arbitrary [15], and when it was determine

that the higher ratio could exclude many acicular rock slivers while making no appreciabl

difference with true fibrous particulates.

For referee purposes, it must be established that the items counted are indee

asbestos, as defined.

Typically, 4 to 7 samples per shift are demanded for 8-h TWA.

The details of pump calibration, microscope adjustment, and counting rules are lik

those presented in the NIOSH method, issued 30 Mar 77.

In view of the very low precision and accuracy obtained, we are not satisfied with £ method of analysis based on counting. A gravimetric method based upon the collection ot only the respirable fraction of fibrous particulates, and coupled with the quantitative

analysis of asbestos present, would be preferred, and appears feasible. X-ray diffractior

of fiber arrays, and acid titration at constant pH [24] appear promising for this purpose.

384
Concl usion

In conclusion, it should be emphasized that in spite of its shortcomings (it is the

product of a committee) the ASTM document has the single advantage of being a consensus

document, reflecting the views of both the regulators and the regulated.

References

[1] Kogan, F. M. , Gerasimenko, A. A., Bunimovic, G. I., Kler, 0. V., Karacarova, V. N.

,

Olsvang, R. A., Hygienic characteristics of the asbestos-cement dust, Collection of

papers on silicosis. The Book Publishing Institution of Middle-Ural, Sverdlovsk,

p. 173-85, 1966. English translation available from the same source as reference 23.

[2] Rhodes, H,, Detection of chrysotile asbestos in airborne dust from thermoset resin

grinding, 3rd Int Conf Chem Phys Asbestos Min, Quebec 20 Aug 1975. (Same source as

23).

[3] Federal Register, Vol. 38, No. 188 - Friday 28, 1973, page 27076 (Food and Drug

Administration).

[4] Ann. N.Y. Acad. Sci 132, 23-30, 1965.

[5] Asbestos Fundamentals, Berger, H. and Oesper, R. E. , Chemical Publishing Company

Inc., New York, 1963, p. 1-3.

[6] Federal Register, Vol. 39, No. 127 - Monday, 1 Jul. 1974, p. 24316. (U.S. Bureau

of Mines).

[7] Rutley's Elements of Mineralogy, 25th Ed. H. H. Read, Thomas Murry & Co, London.

[8] Thompson, C. S. , Proceedings of the Symposium on Talc, p. 22-42, Washington, D.C. 8

May, 1973. (Same source as 23).

[9] ASTM Glossary of Terms, p. 585. D2946-71T.

[10] Prasad, N. A. and Pooley, F. D. , Characteristics of amphibole asbestos dust surfaces

in aqueous media with reference to quartz, J. Appl . Chem . Bi otechnol . , 23, 675-87

(1973).

[11] Federal Register, Vol. 9, No. 87, 3 May 1974, p. 15396.

[12] Holmes, S. , The measurement of airborne asbestos dust by the membrane filter method,

Technical note #1, Asbestos Research Council, Box 40, Rochdale, Lancashire, England,

1971.

[13] Timbrel, V., The inhalation of fibrous dusts, Proc. Conf . Biol . Effects Asbestos,

N.Y. Acad. Sci. 1964.

[14] Field Information Memorandum #74-92, OSHA, 21 Nov. 1974.

£15] Holmes, S. , The definition of an asbestos fiber, Asbestosis Research Council, P.O.

Box 40, Rochdale, Lancashire, England 0L12 7EQ.

)'

[16] Health Division Instruction Memorandum #8-Def inition of asbestos fiber for tremolite

occurring in talc, MESA, 13 Dec. 1974.

!17] Leidel, N. A., Optimum sampling times for airborne asbestos fibers, NIOSH, 1014

Broadway, Cincinnati, OH 45202, Nov. 1972.

18] Gibbs, G. W. and Hwang, C. Y. , Physical Parameters of Airborne Asbestos Fibers in

Various Work Environments - Preliminary Findings, American Industrial Hygiene

Association Journal, June 1975, pp. 459-466.

385
[19] Comments of Johns-Manvi 1 1 e Corp. with respect to notice of Proposed Rulemaking

Occupational Exposure to Asbestos (Fed. Register, Oct. 9, 1975) to O.S.H.A.

,

U.S. Dept. of Labor, April 1976.

[20] International Labour Organization, Meeting of Experts on the Safe Use of Asbestos,

Geneva, 11-18 Dec. 1973, Draft Report, p. 1-32.

[21] McDonald, A. and McDonald, C, Epidemiology of Mesothelioma from Estimates of Incidence., 18th Int'l Congress on Occupational Health, Brighton, Sept. 16, 1975, p. 7-8.

[22] Timbrell, V., The Inhalation of Fibrous Dust, Ann. N. Y. Acad. Sci^. , 1_32, 255-273

(1965).

[23] Draft standard for occupational exposure to asbestos. Rationale supporting the selection of a dual ASTM standard. Second draft ASTM Committee E-34, 25 April 1977.

[24] Barbeau, C. , Roy, J. C. , and Dupuis, M. , Reactivity of magnesium silicates in acid

solutions. Means of distinguishing between antigorite and chrysotile, 3rd Int. Conf.

on the Physics and Chemistry of Asbestos Minerals, Laval U. 17-21 Aug. 1977.

Discussion

NOTE: Discussion of this paper was included in the General Discussion at the end of this

session.

386
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

IDENTIFICATION AND COUNTING OF MINERAL FRAGMENTS

R. J. Lee, J. S. Lally, and R. M. Fisher

U. S. Steel Corp. , Research Laboratory

Monroeville, Pennsylvania 15146

Abstract

Positive identification of submicrometer-diameter mineral

fragments, especially amphiboles, requires both chemical and

crystal lographic analysis. At present, only electron optical methods

can be used for this purpose, and considerable care must be taken to ensure that (1) the x-ray spectra and diffraction patterns pertain only

to the particle in question (that is, spatial-resolution limitations

must be recognized); (2) x-ray data are compared with well characterized

reference standards; (3) overlapping chemical composition and/or similar

crystal structures of mineral series are recognized; (4) crystal

fragments are tilted into zone-axis orientation before recording the

electron-diffraction pattern; and (5) appropriate statistical criteria

are used to evaluate the significance of the results.

The required procedures are time consuming (and costly), but less

rigorous methods are subject to considerable uncertainty, which limits

the validity of the data and its usefulness in any assessment of

biological effects. Adoption of a definition of mineral fibers based on

an aspect ratio of 10:1 and parallel edges would eliminate most non- asbestos mineral fragments from consideration, and reduce the analytical

problems to more manageable proportions.

Analysis of the face orientations of amosite fibers (commercial

amphibole asbestos) and grunerite fragments (nonasbestiform amphibole)

reveals pronounced distinctions which originate in their different

crystal growth or cleavage characteristics.

Key Words: Amosite; amphibole; asbestos; electron diffraction; fibrous;

grunerite; mineral identification; non-fibrous.

Introduction

I The organization in 1977 of a workshop devoted to identifying points of agreement and

disagreement on definitions and measurement methods for asbestos was a most welcome and

logical initiative on the part of the National Bureau of Standards (NBS) and the Occupai tional Safety and Health Administration (OSHA). Changes in meaning of the term "asbestos

I fiber," which have occurred with the advent of concern about very fine particles (only

observable in the electron microscope), have been discussed and deplored by Tibor Zoltai

[1,2]^. Such loosening of the definition of asbestos results in the inclusion of

varieties of sheet silicates, chain silicates, and even non-silicates. Malcolm Ross [3]

ij has pointed out that serpentine, amphibole, clay, mica, chlorite, and alumina-silicates

I are prime examples of widely occurring minerals that could be erroneously classified with

i "asbestos." As a further consequence, the term "emission sources" becomes broadened to

include extended, naturally occurring geological formations.

^Figures in brackets indicate the literature references at the end of this paper.

Three digit bracketed numbers, e.g., [113] refer to reciprocol space vectors.

387
The use of vague terminology coupled with limited biological research data has

blurred the distinction between scientific fact and speculation regarding the health

hazard resulting from exposure to low concentrations of silicate dust particles. The

correct identification of micrometer-size mineral particles and the accurate measurement

of their concentration in air or water samples is not easy. Unfortunately, reported

observations of mineral varieties in samples collected at locations where these minerals

should not occur, coupled with differences of many orders of magnitude in the particulate

concentrations reported by various laboratories, confuse those with the political or administrative responsibility for reacting to public concern about environmental quality.

Hopefully, publication and distribution of the proceedings of the NBS/OSHA workshop will

help repair the damage to the credibility of analysts and their procedures that public

controversy has engendered.

United States Steel has expended a great deal of effort in developing reliable

methods for identifying and counting particles. The details have been published elsewhere

[4,5]. The purpose of the present report is to emphasize the precautions that must be

taken to avoid errors and illustrate the results that can be obtained if appropriate

methods are used. Fiber characteristics pertinent to the definition of "asbestos" are also discussed at the end of this report.

Particle Identification

It is necessary to use electron microscopy, either scanning (SEM) or transmission

(TEM), to examine particles with dimensions of a few micrometers or less. Transmission

electron microscopes can be adjusted to obtain electron-diffraction (ED) patterns from

single particles which provide cyrstal lographic information. Scanning electron

microscopes are usually equipped with facilities for x-ray emission spectroscopy which

provide elemental information about single particles (if properly dispersed). Some hybrid

instruments combine SEM, TEM, ED, and x-ray functions.

Characteristic Diffraction Patterns . The term "characteristic pattern" has come into common use in connection with the identification of particles of minerals by transmission

electron microscopy as if such characteristics (diagnostic patterns) could be ascribed to

each mineral. As a general rule this is incorrect. Many minerals have very similar diffraction patterns, as illustrated in figures 1 and 2, and it is impossible to distinguish

between them by visual inspection. If they are measured and interpreted (indexed as in

figures 1 and 2), they can be used as references for other identical (not similar) patV«5A

Chrysotile

*/ 7l10

4 * £ ^ ^

<' J ^1

.••".•*, .itf^

G runerite :

11121

Figure 1. Selected area electron diffraction patterns of mineral

particles which all show a d-spacing of about 5 A.

388
Figure 2. Indexed electron diffraction patterns of representative amphiboles

and non-amphiboles showing essentially similar appearance.

terns. These are good patterns obtained by carefully tilting into a "zone axis" orientation. If this is not done, the patterns are diffuse, irregular, and useless. Because of

its tubular shape and helical structure, the diffraction pattern of chrysotile is not

strongly dependent on orientation and is recognized more readily.

Another factor affecting electron-diffraction analysis, as illustrated in Figure 2

for actinolite, is that every mineral has several different "zone axis" patterns, which

depend on the orientation of the particle with respect to the electron beam. This is also

illustrated in figure 3 for the amphibole mineral grunerite. However, the presence of

extensive twinning, as in figure 3 for grunerite, or fine-scale exsolution in the

pyroxenes (as in augite in figure 2), can give rise to closely spaced spots in a diffraction pattern. This may lead the unsuspecting microscopist to conclude that he is

; observing a large d-spacing when, in fact, the pattern contains "extra" spots due to

Irreciprocal lattice spikes, multiple zone-axis orientations, or satellite spots.

o The 5.3 A d-spacing of the c-axis is frequently taken as definitive of the

amphiboles. Yet, of the eight diffraction patterns shown in figures 1 and 2, six have d-

; spacings ~5 K, although only two of these are from amphibole particles. In general, as .discussed by Zoltai [1], many minerals fragment into acicular particles and have

|;d-spacings ~5 A. Because of differences in fragmentation characteristics, the broad faces

of the two mineral varieties, amosite and grunerite, occur along different

crystal lographic planes, so the patterns are usually different.

i

389
The characteristic growth habit of amosite asbestos gives rise to a fiber with the

largest face on (100) planes, which will then lie flat on electron-microscope grids [6].

As a result, the nearest reciprocal lattice section will contain b'^xLlOS]*, as pointed out

by Nord [7]. A typical pattern from amosite, shown in figure 4(a), contains b*x[113]*,

the basic vectors for zone axis perpendicular to the [100]* direction in reciprocal space.

In contrast, a cleavage fragment should lie near a (110) face, and the expected zone-axis

diffraction patterns nearly perpendicular to [110]* would not contain b*. While the

cleavage _fragments are more randomly oriented, the diffractjon pattern in figure 4(b),

[021]*x[221]*, and the pattern containing the twin spots [1 30]*x[l 1 1 ]* in figure 3, are both within about 15° of [110]*. Thus, the predominant face of the particle can be

determined if the pattern is indexed on the assumption that the fiber axis c in real space,

[103]* in reciprocal space, is perpendicular to the beam.

390
Figure 4. Electron micrographs and diffraction patterns of amosite

and grunerite particles which indicate that the asbestos

and non-asbestos varieties can be distinguished if the

diffraction patterns are interpreted properly.

Preliminary results of a study of the typical orientations of a Penge amosite, and a grunerite from Presque Isle, Michigan, are shown in table 1. In this comparison, 75

percent of the amosite particles had b* vectors within 10° of the normal to the electron

beam, thus indicating they were lying on (100). Only 18 percent of the grunerite

particles had this orientation. The remaining 75 percent were more than 30° away from

[100]* on the [010]* side of the [110]* direction in reciprocal space. The cleavage

fragments are not as tightly clustered about [110]* as the amosite particles are about

[100]*. These data suggest that it may be possible to distinguish amosite fibers from

grunerite cleavage fragments by looking for b* reflections. Very recent SEM observations

of crystal -growth habits of amosite and grunerite have revealed that these distinctions

between fiber formation by "delamination" and fragment formation by cleavage are also

evident in bulk samples, figure 5.

Table 1. Face orientations of Amosite and

Grunerite fibers.

Face Amosite Grunerite

(100) 17 (74%) 7

(010) 1 2

(110)^ 5 30 (77%)

^ Cleavage plane.

391
10,000X

Figure 5. Cross-sections of grunerite and amosite looking down the c-axis.

(a) Exsolution lamellae, cleavage traces and TOO parting are all evident in grunerite.

O (b) The delamination of thin lamellae produced by fine-scale twinning {^50 A) along (100]

is shown. This leads to the development of amosite particles with large 100 faces.

X-ray Analysis . As mentioned, the development of energy-dispersive spectroscopy as an adjunct to scanning or transmission microscopy has made it possible to obtain

information about the elemental composition of small particles. It is tempting to assume

that the x-ray spectra are diagnostic, but in many cases this is not true. Unless

precautions are taken, near-by particles can contribute to the x-ray spectra. Absorption

and fluorescence effects depend on particle size and orientation, so their x-ray spectra

may differ from those of reference standards. These effects are not great; but for many

minerals, differences in composition are also not large, (as shown in figure 6 with x-ray

spectra from amphiboles, serpentines, and non-amphiboles).

Grunerite

. MgSi Fe

' Pigeonite Minnesotaite

1

K

MgAlSi Ca 1 MgSi Fe

Figure 6. X-ray spectra of representative amphiboles, serpentines, and non-amphiboles

showing essentially similar appearance illustrating difficulty of identifying

silicate minerals by non-quantitative x-ray spectroscopy.

392
Improved Identification Techniques . These difficulties with identification, although

formidable, have been overcome with effort and better understanding of electron-diffraction

and x-ray spectroscopy. Key features of the method are (1) tilting of particle into one

or two zone axis orientations; (2) obtaining an x-ray spectrum from the same particle;

(3) comparison of diffraction and x-ray data by computer with a complete library of all

minerals that could be present. Figure 7(a,b) [4,5] shows block diagrams for the program

DIFFPAT, which simulates zone-axis diffraction patterns for any crystal with known unitcell parameters and space-group symmetry, and SEARCH, which compares measured parameters

obtained from zone-axis diffraction patterns with the simulated patterns generated by

DIFFPAT. The minerals included in the computer library are listed in table 2. Prior

consideration of chemical information eliminates many of these minerals and reduces

computer time considerably.

Table 2. Silicate minerals used in programs "DIFFPAT" and "SEARCH".^

PYROXENES AMPHIBOLES SERPENTINES TALCS CHLORITES

Augite Act i no! ite Amos ite Minnesotaite CI inochlore

Diopside Anthophyl 1 ite Antigorite Pyrophyl 1 ite Penninite

Enstatite Arfvedsonite Berthierite Talc Prochlorite

Hedenbergite Barkevikite Chamosite Talc-Chlorite

Hypers tene Cummingtonite Chrysotile

Jadeite Eckermanite Cronstedtite MICAS

Johannsenite Eden ite Greenal ite CLAYS

Pigeonite Ferrogedrite Lizard ite Biotite

Spodumene Gedrite CI intonite Apophyl 1 ite

Glaucophane Glauconite Illite

Grunerite KAOLINS Lepidol ite Montmorillonite

PYROXINOIDS Hastingsite Margarite Prehnite

Holmquistite Die kite Muscovite Vermicul ite

Pectol ite Hornblende Donbassite Paragonite

Rhodonite Kaesutite Halloysite Phlogopite

Wo 11 as ton ite Katophorite Kaol inite Sti 1 pnomelane

Pargasite Nacrite Xanthophyllite

Richterite Zinnwaldite

Riebeckite

Tremol ite

Tschermakite

' ® Obtained from Ref. 1

i 393
< 1

BEAD A. B. C. Q a. y READ LATTICE TYPE, CODES FOR SYMMETRY CONDITIONS

CALL SMAT

(PAGE A 21

SMAT - CALCULATED

Sit. S12, .

CALL DCALC

DCALC - CALCULATED D SPACINGS. ORDERS

BY SIZE, AND SEPARATES INTO ALLOWABLE AND FORBIDDEN VECTORS

PICKS A ZONE AXIS, FINDS THE LARGEST ALLOWED D SPACING BELONGING TO IT - THEN CHECKS FOR DOUBLE DIFFRACTION

FINALLY COMPUTES THE ANGLE BETWEEN

THE VECTORS TO SIMULATE THE DIFFRACTION PATTERN

CATALOG TAPE CONTAINING SIMULATED PATTERNS

Figure 7. (a) Summary flow chart for computer program DIFFPAT which

calculates reciprocal lattice diffraction patterns.

Enter Di,

Figure 7. (b) Block diagram of the program SEARCH which compares

measured parameters obtained from zone-axis diffraction

patterns with simulated patterns generated by DIFFPAT.

394
In many cases, a well characterized x-ray spectrum and one good low-order diffraction

pattern are sufficient for a positive identification. If the x-ray spectra are not

available, or if there is more than one mineral matching the selected-area diffraction

pattern, two patterns must be measured and indexed for positive identification. These two

approaches to positive identification are illustrated in figure 8. These methods,

although very reliable, are very time consuming. A much simpler method based on grouping

particles into "classes" is described in the subsequent section, "More Rapid Electron

. II

-Solution #1

-Solution #2-

Mg Ai Si Ca

Figure 8. Schematic illustration of particle- identification criteria.

Sample Preparation and Particle Counting

Even when all necessary precautions are taken with particle identification, a number

of factors can affect their apparent concentration. Very large variability between

laboratories has been reported [8], in part due to problems with sample preparation

methods, particulate losses, contamination, casual identifications, subjective definition

of 3:1 aspect ratio, and inherent statistical limitations. Particularly large variations

can occur for conditions of relatively high dust loadings. In this case the air sample

volume is very small and the corresponding scale factor will be very large. The particle

density on the electron-microscope specimen is still likely to be rather high, with the

result that observation and positive identification of mineral fragments will be much more difficult than for low-particle-density samples of ambient air.

Improved Sample-Preparation Procedure . The block diagram of our well proven

procedure [4] is shown in figure 9. The first step in sample preparation is to ash the

filter and its contents. This low- temperature ashing is an important aspect of the sample

preparation since it eliminates organic debris. Next, the sample is agitated

ultrasonical ly to break up agglomerates. If friable material is present, this may result

in some modification of the original size distribution. The alternatives to this

procedure are "direct" examination or "rubout" procedures. In the first case, the sample

may contain extensive debris; and in the second case, modification of the size

distribution may occur.

395
Pump Filter

Low

Temp

Ashing

Ultrasonic

Vibration

Filtering

Spec &

Control

Carbon

Coating

Punch

3 mm Disk

Spec & Cont

Dissolve

Filter

TEM

Grid

Gold

Coat.

Figure 9. Block diagram of steps in sample preparation procedure.

The material is now collected on a second filter paper by suspending the sample in

distilled water and pulling the water through a vacuum aspirator. Dilution may be used to

control the amount of material deposited on the filter. In addition, the particle distribution will be much more uniform than that on the original filter. This second filter is

carbon-coated. The carbon film serves to entrain the particles and provide a support

material that is transparent to the electron beam. A 3-mm disk is punched from the

laboratory filter; the filter material is then dissolved in acetone, leaving the carbon

film and entrained particulates. The film is picked up on the lettered grid, which

permits determination of the exact position of a particle. This technique is rapid, and

does not differ in any substantive manner from any method in which a carbon film is

deposited on the filter to entrain the particulates.

Finally, a thin film of gold is deposited on the replica, which serves as a calibration material for the diffraction work; failure to include this calibration precludes

measurement of SAD patterns with sufficient accuracy to allow differentiation between the

complex crystal structures of the minerals under consideration.

Particle Losses . In any sample preparation technique, particulate losses may be an important source of error and some method must be developed for quantifying any loss. To

check on this, the same carbon-coated filter material was examined before and after

dissolution. As illustrated in figure 10, the losses are negligible, confined only to

those particles in the body of the filter that are not entrained in the carbon. Since

filters with 0. 2-micron-diameter pores are used, these losses are minimal. Other laboratories report losses as high as 40 to 80 percent of the particulate matter deposited on the filter.

A -Particles on Fii-ief^^^^B B- Particles in Carbon Film

Figure 10. Comparison of samples before and after dissolving filter.

(a) Particles on filter after carbon coating.

(b) Identical particles entrained in carbon film after

dissolution of the filter material.

396
Electron-Microscope Examination . Specimens are examined in the scanning electron

microscope and the million-volt electron microscope, and micrographs are made of random

areas until 35 to 50 particles with a 3:1 aspect ratio or larger are located. Visual

examination, although obviously much quicker, is liable to large subjective errors in

recognizing 3:1 "fibers" and in measurement of particle size. Permanent records are important in case of subsequent need for rechecking or confirmation by others. The total

grid area photographed can be related to the original volume of air samples through the

series of dilution and scale factors involved. Typically, one full grid opening cor- responds to about 10 liters of clean ambient air and to about 10 mL of very dusty air or stack samples. In most cases, "average" concentrations of 2 to 10 particles per grid

opening are about right. Smaller values lead to prolonged searching to obtain adequate

statistics, and higher particle concentrations give difficulties with identification

procedures.

Statistical Factor and Mis identification

Examination of a large number of samples has clearly demonstrated that the concentration (per unit area) of particles follows a Poisson distribution where the variance is

about equal to the mean. The corresponding distribution of particles between grid

openings is illustrated schematically in figure 11. The mean concentration is 2.5

particles per square. Obviously, differences of nearly an order of magnitude could result

by chance if only the left-central or right-central four openings were examined with means

of 0.5 and 3.3, respectively. This distribution effect can be minimized by continuing to

search and record micrographs until enough data are obtained to be valid at a predetermined confidence level.

Figure 11. Schematic illustration of Poisson distribution

of particles between grid squares.

397
Random Misidentif ication . Another source of error that is not so easily circumvented

is the misidenti f ication of mineral fragments if only electron diffraction is employed.

This can occur by chance even when every care is taken to tilt the particle properly, the

pattern is measured accurately, and comparison is made with an appropriate suite of

minerals. This error is particularly serious in view of the growing tendency to equate

"amphibole" with "asbestos".

The frequency of chance computer matches of diffraction patterns of randomly oriented

mineral particles is shown in table 3. The chance of misidentif ication of a particle as an amphibole when minnesotaite and magnetite are both present ranges from 9 to 18 percent.

The misidentif ication probability is reduced when lattice- symmetry effects are introduced

into the calculation. An illustration of the effects of chance misidentif ication is shown

in table 4. It was assumed that 35 particles of a non-amphibole mineral were counted and

7 misidentif ied as amphibole. If amphiboles could have been present, it is only possible

to say that the concentration was less than 10^/m^. Because of the larger scale factor

for dusty air, or if only a few grid squares were scanned, an even larger apparent

concentration would be reported (as has already occurred) [9].

Table 3. Computer matches of randomly generated diffraction patterns.^

- - - - Randomly Generated Patterns From - - - - Computer Indexed

Sol utions Minnesotaite Actinol ite Magnetite

Minnesotaite 100 24 12

Actinol ite 9 100

Magnetite 0 0 100

Grunerite 11 li 11

^ Accidental matches are underlined.

Table 4 . False identification as amphiboles. probability '\'0.2.

Apparent

Scale Factor Concentration Actual

Ambient Air 10^ 'v5 x lO'^/mS 0^ - <103'^

Dusty Air 5 x

10'^ ^1 x lO^/m^ 0 - <105

^ (Cubic meter per grid opening)"^.

^ When none could be present.

Maximum if occurrence possible.

More Rapid Electron-Microscope Methods

The identification and counting procedures described in previous sections are very

time consuming and expensive. Costs per individual air sample are in the range of $300

to $1500, depending on the methods used and the degree of reliability that the analytical

laboratory is willing to certify. Deployment of more than 1000 air monitoring stations

around the United States might easily be deemed necessary. The financial and manpower resources are just not available for electron-microscope analysis on this scale.

398
A more simplified method, currently under development, is to group particles observed

in the microscope into classes based on their appearance and their x-ray emission spectra,

that is, their approximate composition, using automatic image-analysis techniques for

measurements and recording. Complete electron-diffraction identification is then carried

out on randomly selected particles from each class. This cuts the time required by a factor of five or more, admittedly at some loss in certainty. However, the improved

statistics appear to overcome this deficiency.

In some cases of particular interest, simpler methods may be developed to achieve

reasonably reliable identification. For example, the development of different crystal

faces by amosite and grunerite affect their orientation on the electron-microscope grid

and the diffraction patterns most commonly observed. This could be used to screen

samples for amosite and grunerite with a reasonable degree of accuracy on a quality-control

basis. Other specific analysis problems might be solved in similar fashion. However,

this method will not work on ambient-air samples, which could contain a large number of

minerals or chemical compounds. Finally, automatic image-analysis facilities to process

scanning electron-microscope images are coming into use. Effective methods of utilizing

these devices are being developed to expedite analysis of air and water samples by

eliminating manual data logging and particle counting and measurement.

Physical Characteristics of Mineral Fragments

Aside from questions of errors in identifying and counting amphibole and other mineral

fragments, the very pronounced distinctions between their physical characteristics and

those of asbestos must be recognized. In addition to obvious differences in particle size

and shape, more subtle features such as crystal structure, face orientation, surface

chemistry, associated impurities, lattice imperfections, and concentration could well be

important in the biological response to small particles. These factors cannot be over- looked when attempting to generalize from health-effects studies with a particular mineral

variety.

Scanning-electron-microscope micrographs in figure 12 demonstrate the difference in

appearance of crocidolite fibers and several cleavage fragments of hornblende with a 5:1

aspect ratio. The difference in character between the two types of particles is quite

apparent, yet there has been a growing tendency to equate them.

CROCIDOLITE HORNBLENDE

Figure 12. Scanning electron micrographs of crocidolite fiber

and fragments of hornblende.

399
The cumulative distribution of particle aspect ratios of amosite fibers is shown in

figure 13 with a similar plot for comminuted actinolite particles. Differences in the

distribution of the aspect ratio of particles are marked. Very few actinolite cleavage

fragments have an aspect ratio greater than 10:1, whereas very few amosite particles are

less than 10:1.

Figure 13. Plot of measured aspect ratio of amosite fiber

and ground actinolite.

Studies of more basic structural differences are just beginning in a number of

laboratories. Differences in cleavage properties and growth characteristics between

amosite and grunerite that are reflected in particle morphology and surfaces were discussed in the Section, "Characteristic Diffraction Patterns." Planar lattice defects,

responsible for extensive streaking in certain electron-diffraction patterns, can be seen

by high-resolution electron microscopy [11]. When present, these grown-in faults may

promote a tendency to split into long narrow fibers. Several years ago,

electron-microscope studies revealed that chrysotile fibers are actually hollow tubes

[12]. Recently, high-resolution studies of cross-sections of crocidolite have shown the

presence of somewhat similar micropores between the fibers [13].

Summary

Identification of mineral fragments and determination of their concentration in air

and water samples with a satisfactory degree of accuracy can be achieved using electron

optical methods if the procedures reviewed in this report are followed. The most

important precautions are:

1. Loss of particles or changes in their dimensions during specimen preparation

must be avoided.

2. Crystal fragments must be tilted into a zone-axis orientation before selectedarea electron-diffraction patterns are recorded.

3. Spot spacings and angles must be measured accurately and compared with

computed patterns for any minerals that could occur in the sample.

400
4. X-ray emission spectral data from overlapping or closely adjacent particles

must be discarded, effects of particle size on line intensities must be

recognized, and data must be compared with well characterized reference

standards.

5. Appropriate statistical criteria must be used to interpret the significance of

apparent particle concentrations.

In our view, a definition of a fiber, incorporating the following points, would

resolve most analytical difficulties and remain compatible with all known facts concerning

health effects.

1. Aspect ratio greater than 10:1.

2. Paral lei edges.

It is also necessary to establish a lower limit on particle size in keeping with

capabilities of analytical procedures to ensure consistency in count between various

laboratories. In the absence of any conclusive evidence for adverse biological effects

due to very small particles, the current >5 pm length standard should be maintained.

A recent Bureau of Mines Information Circular [14] contains discussion and documentation of many of the foregoing points including: (1) Detailed discussion of definitions

relating to asbestos and the importance of eliminating loose terminology from the

scientific and popular literature. (2) Discussion of the differing growth and cleavage

origins of fibers and fragments as emphasized in this report. (3) Criticism of the 3 to 1 aspect-ratio criterion for mineral fibers on the basis that fibers from asbestiform

minerals always average more than 10 to 1 and often go up to 200 to 1 or more, whereas the

usual ratio for cleavage fragments is less than 10 to 1.

References

[1] Zoltai, T. and Stout, J. H. , "Comments on Asbestiform and Fibrous Mineral Fragments,

Relative to Reserve Mining Company Taconite Deposits," Contract report to Minnesota

Pollution Control Agency, March 1976.

[2] Zoltai, T. , "History of Asbestos-Related Mi neral ogi cal Terminology," Proceedings,

Workshop on Asbestos: Definitions and Measurement Methods, National Bureau of

. Standards, Gaithersburg, Md. , July 18 to 20, 1977.

[3] Ross, M. , "Minerals Commonly Occurring in the Earth's Crust That Might be Defined as Asbestos by Various Regulatory Agencies," Proceedings, Workshop on Asbestos: Definitions and Measurement Methods, National Bureau of Standards, Gaithersburg, Md. , July

18 to 20, 1977.

[4] Lee, R. J., "Electron Optical Identification of Particulates," Proceedings of

Symposium on Electron Microscopy of Microfibers, Pennsylvania State University,

August 23 to 25, 1976, in press (1977).

[5] Lally, J. S. and Lee, R. J., "Computer Indexing of Electron Diffraction Patterns

Including the Effects of Lattice Symmetry," Proceedings of Electron Microscopy

Society of America Annual Meeting, Boston, August 22 to 26, 1977.

[6] Champness, P. E. , Cliff, G. , and Lorimer, G. W. , "The Identification of Asbestos,"

Journal of Microscopy , 108 , Pt. 3, 231-249 (1976).

[7] Nord, G. L. , Jr. , "State-of-the-Art of the Analytical Transmission Electron Microscope," Symposium on Electron Microscopy and X-ray Diffraction in Environmental and

Occupational Health, in press (1977).

401
[8] Brown, A. L. , Jr., Taylor, W. F. , and Carter, R. E. , "The Reliability of Measures of

Amphibole Fiber Concentration in Water," Environmental Research , 12 , 000-000 (1976).

[9] Nichelson, W. J., "Analysis of Mesabi Iron Range Samples," Environmental Sciences

Laboratory, Mount Sinai School of Medicine, Contract report to Minnesota Pollution

Control Agency, July 1975.

[10] Chadfield, E. , Ontario Research Foundation, private communication (1976).

[11] Irusteta, M. C. and Whittaker, E. J. W. , High-Resolution Electron Microscopy and

Diffraction Studies of Fibrous Amphiboles, Acta Cryst . A31 , 794 (1975).

[12] Yada, K. , High Resolution Electron Microscopy of Chrysotile, Acta Cryst . 23, 704

(1967).

[13] Franco, M. A., Hutchison, J. L. , Jefferson, D. A., and Thomas, J. M. , "Structural

Imperfection and Morphology of Crocidolite (blue asbestos)," Nature , 266 , 7 (1977).

[14] Bureau of Mines Information Circular (IC8751), "Selected Silicate Minerals and Their

Asbestiform Varities: Mineralogical Definitions and Identification-Characterization,"

U. S. Dept. of the Interior, 1977.

Discussion

NOTE: Discussion of this paper was included in the General Discussion at the end of this

session.

402
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

NOTE: This manuscript was not presented at the Workshop but was submitted for inclusion in

the Proceedings.

PRACTICAL ASPECTS OF TALC AND ASBESTOS

C. J. Parmentier and G. J. Gill

Cyprus Industrial Minerals Company

Talc Division

Los Angeles, California 90071

Abstract

The present day controversy and misunderstanding regarding talc and

asbestos has existed for many years. This paper reviews some of the reasons for the widespread public misconception that all talcs contain

asbestos.

The experiences of a major talc producer are discussed in relation

to occurrences of talc and asbestos, and the analytical techniques

required to substantiate a talc-asbestos relationship are reviewed.

Key Words: Asbestos; scanning electron microscopy; talc; transmission

electron microscopy.

Introduction

Numerous environmental, occupational safety, and health agencies have recognized the

medical hazards associated with asbestos minerals and have issued regulations for their

use. However, during the past five years an increasing amount of controversy has been

encountered regarding terms, definitions, and measurement methods.

Due to the ambiguities in these criteria and various misconceptions regarding the

mineralogy of talc, disagreements also exist between industry, medical researchers, state

and federal regulatory agencies concerning talc and asbestos.

This controversy affects a variety of industries, ranging from the talc producers

themselves to the industrial consumers, their insurance carriers, and even the household

consumer of the numerous products containing talc.

This presentation will highlight some observations and experiences of a major talc

producer, in relation to occurrences of talc and asbestos. Analytical techniques used for

identification of asbestos minerals and fibers in a talc matrix are also discussed.

Definitions

Asbestos :

As used in this presentation, the term "asbestos" pertains to fibrous forms of actinolite, tremolite, anthophyl 1 ite, and chrysotile. All of the six recognized asbestos minerals

are not included in this review as the above mineral types are the only asbestos minerals

this laboratory has found to occur in talcs to date.

403
The terms acicular, lath, bladed, cleavage fragments, rods, needle, and columnar are often used as synonyms for the term fiber or asbestiform. It is the term "fiber" which

appears in need of a uniform definition. As used in this presentation, a fiber is described

as a particle with a length to width ratio of 10:1 or greater. The present OSHA definition

[1]^ allows a length to width ratio of 5 or more to 1, with a maximum diameter of 3 pm.

Figure 1 illustrates and compares the simulated appearance of particles with the aforemenntioned ratios. The 5:1 length to width ratio allows blocky particles to be classified as fibers, illustrating the need for more realistic definitions and size criteria of a fiber.

ASPECT RATIOS

3:1

5:1

10:1

Figure 1. Illustrated by the above drawing are the geometric shapes which have been defined

as fibers. The Asbestos Regulation CFR 1910. lOOL stipulates that a particle with

an aspect ratio of 2:1 or greater is a fiber. However, these criteria were further modified by OSHA field information memorandum #74-92, November 21, 1974.

The OSHA modification changed the criteria for a fiber from a 3:1 aspect ratio

to a 5:1 length-to-width ratio with a maximum diameter of 3 pm.

The 10:1 aspect ratio is used at the Cyprus Industrial Minerals laboratory.

Talc

The term "talc" has also been misused in published studies and requires definition.

Talc refers to a specific mineral with a hydrated magnesium silicate composition of laminar

or sheet structure. The natural platelet diameter of a talc varies, depending on deposit

location and geological condition. Both the size and orientation of the laminar plates,

with respect to each other, determine the characteristic form of the talc, e.g., massive or steatite talc versus foliated or micaceous talc. It is this characteristic talc structure

which most often determines end use applications. The large micaceous or foliated talcs are ideal for cosmetic applications; while the finer particle size, massive or steatite

type talcs are most often used in filler and extender applications. The purity and locations of the talc deposit, in addition to the degree of benefication, also have a significant effect upon the end use application.

^Figures in brackets indicate the literature references at the end of this paper.

404
Talc and Asbestos

Many misconceptions and misunderstandings of talc have existed due to improper use of

terms such as tremolite talc, asbestiform talc, and fibrous talc. The majority of these

improper terms were used to describe talc from the New York State talc district. In many

earlier medical studies, which indicated a high incidence of talcosis, pneumoconiosis and

mesothelioma among talc miners and millers from St. Lawrence County, New York, the supposition is made that talc dust was the cause. Kleinfeld and workers in 1967 [2] compared the

mortality among talc miners and millers in New York State to findings among asbestos

workers and noted similar pathological findings, to quote, "Rather characteristic was the

presence of elongated, terminally clubbed bodies indistinguishable from asbestos bodies as seen in asbestosis." The talc dust exposure consisted predominantly of talc admixed with

other silicates such as serpentine and tremolite, carbonates and a small amount of free

silica, according to Dr. Kleinfeld. Additionally, Dr. Kleinfeld cites numerous other

oublications in which medical studies were performed on workers engaged in the milling or

nining of the "fibrous variety of talc" [3-6]. However, none of these studies have differentiated between the mineral talc and the asbestiform variety of tremolite.

In a later publication [7], studies of New York State talc deposits and their asbestos

:ontents were carried out. Mineralogical analyses of these materials indicated that all

samples were predominantly asbestos.

The amount of asbestos impurities encountered in commercial talc ranges from <0.1

Dercent to over 50 percent. The majority of commercial talc samples analyzed have asbestos

:ontents ranging from <0.2 percent to a maximum of 2 percent. Commercial production talc

samples from New York State show a range of 20 percent to over 50 percent asbestos. A few

additional commercial talcs have an asbestos content of 5 to 15 percent.

Figures 2 and 3 illustrate the asbestos contents of typical New York commercial talcs.

Figure 2. Talc-Fiber No. 1 from International Talc Co. Analyzed

as asbestiform tremolite with minor talc content.

405
Figure 3. New York talc product used in the paint industry. Actual talc content is less

than 40 percent. Majority of fibers are asbestos- tremol ite , identified by

TEM/SAED.

Cyprus Industrial Minerals Co. is one of the largest talc producers in the world. We

have a continuing exploration program and over the past ten years have characterized talc

deposits worldwide, in addition to analyzing numerous commercial talc samples. With this

background and experience we feel justified in stating that not all talcs contain, or are associated with, asbestos. We also feel confident in stating that our ultra-fine grind

Montana talc is the standard of talc purity throughout the world. Although high-purity

talc deposits such as the Montana talcs are rare, asbestos-free talcs are not uncommon.

Based on our experience and bank of analytical data, we are aware that some talcs on the market do contain varying amounts of asbestos minerals. The most commonly encountered

asbestos impurities in talc are tremol ite and anthophyl 1 ite. There have been occurrences

in which chrysotile asbestos has been found in selected talc samples. However, these

occurrences are considered unusual but not unlikely.

Analytical Techniques

The methodology used for the analysis of asbestos fibers in talcs is a subject of

considerable controversy. Following is a summarized description of the techniques used by

the Cyprus laboratory and the reasons for their use.

Illustrated in Table 1 is the typical test procedure used to analyze talc for possible

asbestos contamination. Although x-ray diffraction is shown as the initial method of

analysis, it must be remembered that the primary function of the Cyprus Industrial Minerals

laboratory is the characterization of talcs. If we were concerned with analyzing talcs

for the presence of asbestos only, we would consider scanning electron microscopy as the

most applicable technique to initiate analyses by screening samples for the presence of

fibers.

406
Table 1. Analytical procedure flow sheet

XRD

ASBESTOS FREE. "° ^'^^^^

SEN

^'^^''^

TEM/SAED

Scanning Electron Microscopy (SEM) has two very unique advantages compared to optical

microscopy techniques. First is the capability to accurately identify a fiber by tilting

the specimen, thus viewing a particle from various angles. Additionally, the added depth

of focus characteristic of SEM allows the complete particle to be studied at the same

time. Figure 4 is included to illustrate this advantage, and shows the typical curled

edge of a talc platelet. If a similar talc platelet was observed by optical microscopy,

the limiting depth of focus would dictate that only the curled edge was in focus and would

appear as a fiber, or the plate would be in focus and appear as a separate particle.

Figure 4. This micrograph illustrates the morphology of a typical curved talc platelet.

The problems associated with attempting to define a fibrous structure by optical

microscopy and it limited depth of focus can be seen. The optical microscope

would make the above particle appear to be two separate particles, one of which

would appear as a fiber and the other as a platelet.

407
The second advantage of SEM is the easily varied magnification capabilities with

sufficient resolution to distinguish the presence of very fine fibers. In contrast,

optical microscopy techniques can allow a large number of very fine fibers such as chrysotile to go undetected. Langer, Selikoff, et al., state "Many particles found in lung

tissue are submicroscopic, measuring as little as 200 K (0.02 microns) in diameter, therefore requiring electron microscopy" [1]). Suzuki and Churg also stated the preponderance

of submicroscopic asbestos fibers observed in the successive steps in the development of

the asbestos body were less than 1 |jm in length, necessitating the use of the electron

microscope [14].

Figures 5 and 6 are included to illustrate the SEM capabilities by revealing numerous chrysotile fibers present in a talc sample spiked with 1.5 percent chrysotile. Many of

these fibers can be observed in figure 6 with sizes approaching single fiber diameters of

'^'20 nm (200 ^), well below the theoretical resolution limit of optical microscopy.

Sum

Figure 5. CTFA spiked talc by

SEM. 1.5% chrysotile,

0.5% tremolite x 2800

at 40°.

L|lfr\

Figure 6. Spiked talc by SEM.

1 .5% chrysotile

X 13,5000 at 35°.

408
Scanning electron microscopy for initial sample screening also has advantages compared

to transmission electron microscopy methods. The sample preparation is considered easier

and less time-consuming than TEM, which requires preparation of filmed specimen grids for

sample mounting. Additionally, and most significant is the fact that by SEM screening of

talc samples for fiber presence, the amount of sample examined is approximately an order

of magnitude greater than TEM methods (0.1 mg vs. <0.01 mg). This difference becomes a major factor when investigating talc samples for trace fiber content (<1000 ppm.).

Transmission Electron Microscopy and Selected-Area Electron Diffraction

This powerful analytical technique is capable of furnishing a combination of morphological and crystal structure data of small single fibers which can result in very

conclusive identification. However, this method requires a good deal of operator expertise

and accuracy of data. We feel that fiber analysis via electron diffraction, supplemented

with morphological data, provides a positive identification. We have observed, however,

many cases where workers have identified minerals through using only partial diffraction

patterns; that is to say, only the high angle reflections (low numerical spacings). These

spacings are very similar between silicate minerals making absolute identification

impossible without the more conclusive low angle reflections (high numerical spacings).

Additionally, due to the unique possibilities of unusual mineral occurrences, which are more the expected than the unexpected in mineralogy, the morphology of a fiber does not,

and should not indicate asbestos.

Along these lines, some examples of unexpected trace mineral fibers which have been

encountered and subsequently identified in specific talc samples or deposits are: zeolite

fibers (mordenite), clay mineral fibers (attapulgite-polygorskite) , and a rare fibrous

variety of antigorite-serpenti ne known as picrolite [12,15]. These materials are not

asbestos by definition.

All of the indicated fibers have similar d-spacings in the high angle reflections

(numerically lower than -^-5.00 K) , indicating the necessity for using only the numerically

high, low angle spacings for positive identification.

Although SAED allows positive and undisputed identification of mineral fibers, only

under specific conditions are SAED patterns considered positive identification. The

following criteria must be met before an SAED pattern is considered accurate:

1. The camera constant must be determined on the same grid and same sample area as the SAED pattern, using a known standard. Preferred

accuracy is obtained by shadowing the specimen preparation with a gold or aluminum metal which allows the camera constant to be

calculated directly on the SAED pattern and acts as an internal camera constant.

2. The indexed d-spacings should include the most intense low angle

spacings. Any pattern without d-spacings numerically higher than

^'5.00 8 (low angle) should be questionable, as many silicate

minerals have similar d-spacings in the higher reflection angles.

3. Where applicable, unit cell parameters should also be used to

supplement fiber identification.

X-Ray Diffraction

X-ray diffraction (XRD) is a standard mineralogical technique. Within levels of

detectabi 1 ity and lack of interfering reflections, it allows the identification and quantitation of asbestos minerals in talc. The major limitations of XRD are the lack of

morphological data and the lower levels of sensitivity can allow a large number of asbestos

fibers to go undetected.

The information derived from XRD is invaluable for the characterization of a talc,

and is of considerable help in the understanding of the mineralogical processes of forma409
tion and the possible impurities present. The background information of mineral phases

present aids and expedites the TEM-SAED interpretation of unknown fibers.

Optical Microscopy

Optical microscopic techniques are considered of minimal value in the analyses of

fine-grained complex silicate mineral mixtures, and often result in ambiguous data of

questionable value. As previously mentioned, optical microscopy techniques can allow a large number of very fine fibers such as chrysotile to go undetected [7,13]. Due to

these findings and the health and economic considerations involved, optical microscopy is

not used at the Cyprus laboratory for asbestos in talc analyses or airborne asbestos fiber

analyses.

Conclusions

This presentation has reviewed the misunderstandings and widespread misconceptions

that all talcs contain, or are associated with, asbestos. Some of the reasons for these

misconceptions were shown to be the lack of mineral background in the use of terms and

definitions. However, the use of inadequate analytical methods has been shown to be a major cause. The use of ambiguous analytical techniques such as optical microscopy for reasons of expense, lack of experience, or ease of analysis has far-reaching economic and

health implications. Only TEM-SAED techniques supplemented by SEM appear to give the

necessary degree of accuracy needed for positive results.

The existence of large deposits of high-purity, asbestos-free talc are well documented, and it is hoped that future references to talc will be more clearly defined as to

proper mineral content.

In view of the evidence presented from both the medical and mineralogical science

fields, it is evident that state and federal regulatory agencies need to redefine terms,

definitions, and analytical methods for the assessment of asbestos and talc. This applies

to both airborne exposure and bulk samples containing asbestos.

References

[1] Tremolite and Talc, U.S. Department of Labor, OSHA Field Information Memorandum

#74-92, November 21 , 1974.

[2] Kleinfeld, M. , Messite, J., Kooyman, 0., et al., Mortality among Talc Miners and

Millers in New York State, Arch. Environ . Health , 14, 663-667 (1967).

[3] Kleinfeld, M. , Messite, J., and Tabershaw, I. R. , Talc Pneumoconiosis, Arch . Indus - trial Health , 12, 66-72 (July 1955).

[4] Kleinfeld, M. , et al.. Lung Function in Talc Workers: A Comparative Physiologic

Study of Workers Exposed to Fibrous and Granular Talc Dusts, Arch. Environ . Health , 9, 559-566 (Nov. 1964).

[5] Messite, J., Redding, G. , and Kleinfeld, M. , Pulmonary Talcosis, A Clinical and

Environmental Study, Ind. Health Perspect . , 20, 408-413 (1959).

[6] Siegal, W. , Smith, A. R. , and Greenburg, L. , The Dust Hazard in Tremolite Talc

Mining, Including Roentgenological Findings in Talc Workers, Amer. J. Roentgen .

49, 11-29 (Jan. 1943).

[7] Kleinfeld, M. , Messite, J., and Langer, A., A Study of Workers Exposed to Asbestiform

Minerals in Commercial Talc Manufacture, Environ . Res. , 6, 132 (1973).

[8] Rohl , A. N. and Langer, A. M. , Identification and Quantitation of Asbestos in Talc,

Environ . Health Perspec . , 9, 95-109 (1974).

[9] Rohl , A. N. , Asbestos in Talc, Environ . Health Perspec . , 9, 129-132 (1974).

410
[10] Rohl , A. N. , Langer, A. M. , and Selikoff, I. J., Environmental Asbestos Pollution

Related to Use of Quarried Serpentine Rocks, Science , 196 , 1319-1322 (June 1977).

[11] Mumpton, F. A., Characterization of Chrysotile Asbestos and Other Members of the

Serpentine Group of Minerals, Siemens Review XLI (1974).

[12] Zussman, J., Brindley, G. W. , and Comer, J. J., Electron Diffraction Studies of

Serpentine Minerals, Amer. Minerals , 42, 133-153 (1957).

[13] Ehrenreich, T. , Mackler, A. D. , Langer, A. M. , Selikoff, I. J., Identification and

Characterization of Pulmonary Dust Burden in Pneumoconiosis, Annalof CI inical

Laboratory Science , 3, No. 2, 118-131 (1973).

[14] Suzuki , Y. and Churg, J. , American J. Path. , 55, 79 (1969).

[15] Deer, W. A., Howie, R. A., and Zussman, J., Rock-Forming Minerals, Vol. 3, Sheet

Silicate 173-174.

411
ll

I
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

GENERAL DISCUSSION OF ANALYTICAL METHODS

M. ROSS: I first would like to congratulate the U. S. Steel group. That was a beautiful presentation. I think that they have shown a method to use electron diffraction in a quantitative way, which is very important. Also, I like to mention that my own colleague at

the U. S. Geological Survey, Gordon L. Nord, is also working in this area from a slightly

different point of view, developing a method of indexing electron diffraction patterns.

His and U. S. Steel's methods, I think, will have a great use in making electron diffraction

really useful and quantitative and much simpler than it has been in the past. Next, I would like to address myself to the

R. LEE: Malcolm, may I interrupt? We'd like to acknowledge the fact that without

Gordon Nord there's an awful lot of twin patterns around my lab that wouldn't have been

indexed.

ROSS: Gordon Nord will have a paper on the subject of indexing electron diffraction

patterns coming out in a volume concerned with identification of microparticles based on a conference held earlier this year in Denver ("State-of-the-Art" of the analytical

transmission electron microscope, in Proc. Symp . on Elec . Microscopy and X-Ray

Appl i cations to Environmental and Occupational Health Analysis , Ann Arbor Sci. Publ., in

press (1978)). The next thing I'd like to bring up now is more of an observation. I'd

like to quote a paragraph from my paper for this conference. "The crushing and milling of

any rock will usually produce mineral particles that are within the size range specified

in the OSHA rules. Thus, these regulations present a formidable problem to those

analyzing for 'asbestos' minerals in the multitude of materials and products in which they

may be found in some amount, for not only must the size and shape of the 'asbestos'

particles be determined, but also an exact mineral identification must be made." Now as far as Dr. Anderson's presentation of an amphibole analysis in water samples, with his

method you will find asbestos in every mine and mill effluent in the country, unless you

make strict rules of identification and characterization of asbestos. To go back to my

discussion the first day when I showed the maps of the U. S. , you will be affecting every

hard rock mining and quarrying operation in the United States unless you can get an identification and a definition of asbestos that does not include every amphibole,

pyroxene, zeolite, and gosh knows what else that's in the crust of the earth.

C. RUUD: Listening to what Malcolm Ross says I can't help but agree, but I think if

you read the Federal regulations with respect to water, you will find the word asbestos

and then several mineral names following. Until it can be demonstrated that a chain

silicate is distinguishable from an asbestos chain silicate on a single fiber basis in the

microscope, then Chuck Anderson and the rest of us are stuck with the situation that

Malcolm points out, that is to say that the whole world is dangerous.

LEE: Clay, I think our point here is that if you look at the electron diffraction

pattern from amosite particles, at least 70 percent lie on a 100 face. If they lie on a

100 face, they have to have a b* component, which is the 18 K d-spacing, perpendicular to

that face; therefore, it has to be very close to the normal to the electron beam. Hence,

vithin a couple of degrees - we were using about five on this study - of the 00 tilt in

/our microscope, you should find a strong 9 ^ row through the center of your diffraction

pattern. We would say, on the basis of these data, that particular pattern is, as far as

ve are concerned, close to being diagnostic. Now you also have diffraction patterns from

:leavage fragments which tend to lie between 110 and 010, and those patterns can give you

the standard kind of pattern that people are using for identification of amphi boles and

:leavage fragments in lake water.

RUUD: Rich, you and I have discussed this and I think you have an excellent point

id we both agree that it has to be demonstrated. If we can do that, and if our microropists are able to recognize what you are saying at a glance in the microscope, I think

413
it will be an important step. I'd like to make one more comment with respect to what

Jim Kramer mentioned this morning. Jim was asking Chuck Anderson why he did not outline

the method for recognition of an SAED pattern. Well, first of all it takes a highly

experienced technician to do good transmission electron microscopy. On top of that it

takes a much better technician to do SAED. To train that man to recognize patterns is

probably one of the easiest things.

S. COHEN: My question is directed to Dr. Cossette. You mentioned recommending a secondary sampling method using a mini-impinger. I was wondering if you could expand on that and, if any studies have been done, comparing that to the membrane filter.

M. COSSETTE: Yes, some studies have been done. We found better reproducibility, but

not that much better. We think it should be used if somebody wants to get correlation

data to compare against the epidemiological data that we have. The large epidemiological

studies are all based on midget impinger and you cannot translate midget impinger counts

to fiber counts, not directly, not right across the board.

I. STEWART: I had a comment which is really diametrically opposed to Clay Ruud's

comment. It's my feeling really that everything that we've seen on these requires someone with the knowledge of diffraction. If you're looking for somebody to drive your

microscope, this should be a first requirement, a knowledge of the mineralogy of these

materials and a knowledge of their diffraction patterns. You can teach any monkey to push

the right buttons. I've done it over the phone. This is no respect really to the

biologist. I'd like to make this comment, that this is in the health effects field; that

a lot of people in the health effects field are biologists. They're damned good electron

microscopists; they have never had to do any diffraction in the past; they have never been

exposed to diffraction theory, and they are going to have a problem because they have to

learn first of all the technique of getting the pattern and then what it all means. Now

Rick has mentioned the fact that he had problems with some of the twin materials. There

is probably more diffraction done in his field, in metallurgy, particularly in high

voltage electron metallography, than there is in any of the other material sciences, and I think this highlights the problem that you need someone who is highly skilled in the

interpretation of the diffraction patterns (first requirement); secondly, the knowledge of

the variations that you get in mineral structures, the variations you can get in the

natural mineral within a single crystal, and then you can say I have a man who is worth

training on the electron microscope.

R. FISHER: Perhaps the solution to this - we recognize the difficulties - would be

to establish a central facility with a big computer, with an automatic digitizing device,

and where people send in their diffraction plates and these are processed in a routine

way. The people processing would have no idea what the sample is, they wouldn't have any

leanings, whether they want, or do not want, to find amphi boles, and the cost of doing

this could be I think reduced considerably over every individual becoming an expert

diffractionist, and then measuring them by hand and calculating by hand unless he has a computer and the computer library of data available. This is one possibility of an interim solution I think to set up one facility; the plates are mailed in and they are analyzed and identified on a more routine basis.

K. CHOPRA: I think there will be another problem with respect to giving you the camera constant and operator's judgment on how he got the camera constant, and if you

don't have that right you might as well not do an analysis on it.

LEE: I'd like to respond to Dr. Chopra. Let's say you have two minerals that you're

interested in identifying and you want to reject any other mineral. In that case I can take the angle between the rows and the ratio of the d-spacings; they are the only two

things which are independent of the camera constant and pretty much independent of the

operator - from those I think you have a very high certainty of a correct identification

or a rejection. There will be cases when you can't accept the identification because

there is not enough information available.

J. ZUSSMAN: I'd like to join the others in complementing Dr. Fisher and his group on his very fine presentation of what has obviously been a very careful, painstaking piece of

work. After making that comment, I'd like to say that the kind of approach to analytical

414
echniques used for a given problem depends very much upon that problem. If there is a ompletely open new situation where very little or nothing is known about the sample, then

'm quite sure that the approach which Dr. Fisher and his group have explained is the only

afe one to adopt, because it's the only way of being sure of your identifications of not

nly what you think is likely to be there but what you may not expect to be there. But it

s obviously a lengthy procedure. I agree fully with what others have said. Ian Stewart

alked about the need to have really well-trained people to execute these techniques, and

0 understand diffraction above all because you need to understand diffraction to

nterpret not only diffraction patterns but to interpret the electron micrograph as well,

hey aren't just pretty pictures and shadowgraphs; there's more to it than that,

iffraction comes into it. Not everybody can employ highly trained crystal lographers to

0 lengthy procedures for long periods of time and it isn't always necessary. There may

ome a stage in a situation where you do know quite a lot of the background of the problem

nd you don't have to worry too much about unexpected things coming up. In this case you

an take shortcuts once you get to know the kind of field you are in. But one should

Iways bear in mind, and there will be enough critics to keep an eye on you I'm sure, that

ou may have overlooked something unexpected. For example, the question of using in addiion to electron microscopy, energy-dispersive, analytical methods has been mentioned, and

think this is a very useful technique to adopt. It can give you clues as to what mineral

ight or might not be present. If an ambiguity exists in an electron diffraction pattern

hich doesn't allow you to resolve this, or if you don't have an electron diffraction

attern, the energy-dispersive analysis can narrow down the possibilities. It is done

uch more rapidly, and less expertise is required perhaps than for the interpretation of

lectron diffraction patterns. So I do think that perhaps the most powerful, the ultimate

echnique is the combination of all - electron micrographs, energy-dispersive analysis,

nd electron diffraction pattern analysis in full. A good approximation can be gotten

erhaps in certain circumstances using the x-ray spectrometric analyses to guide you.

hat's one general point that I wanted to make.

Another point: Dr. Anderson has expressed his worry about not being able to

istinguish between what is asbestos and what is not asbestos. We've heard again with

reat interest the promising signs which seem to show us that it may be possible, even

hen you have started out with a true asbestos on the one hand, or you have started out

ith a clearly non-asbestos material on the other, and you grind the hell out of both of

hem, to recognize one from the other. I think there are promising signs that you can.

ut, faced with the situation that you're not convinced by this, there's a way out: you

ust don't commit yourself. Why call something asbestos if you don't know or, in some ircumstances , when you know darned well that it started out as being non-asbestos and yet

t's listed at the head of table "Content of Asbestos Particles." Why not use a nomenclature in a more sensible way, depending upon the amount of information you have about the

pecimen? If all you know is that it's crystalline and you say it's a fiber, define the

iber how you like, as long as you tell us, 3 to 1 , 5 to 1 , but specify what it is you

lave in mind. Say it's a crystalline fiber and that's all you know, perhaps. At the next

tage of knowledge you might say it's a mineral fiber or an inorganic fiber. At the next

tage you might say you know it's an amphibole fiber but you don't know which amphibole.

hat's O.K., say amphibole fiber. You might then have identified it as tremolite: say

t's a tremolite fiber. If you know that it's asbestos because it has come from an

isbestos deposit, say tremolite asbestos, but if you don't, say tremolite fiber, numbers

if fibers, numbers of amphibole fibers, not numbers of asbestos fibers. Those are my

leneral comments.

I'd still like to make two very small points. On technique, I agree with the

;xperience of my colleague in Manchester, Dr. Champness. Our work has been done with the

:arbon coating method; and we agree that there doesn't seem to be any great percentage

OSS in carbon coating. Secondly, I wondered if anyone else has this experience: she

-ells me also that she uses dimethyl sulfoxide as a solvent for getting rid of the

luclepore filter. I haven't heard it mentioned here at all. There's been chloroform and

icetone, but Dr. Champness swears by dimethyl sulfoxide as being a solvent which dissolves

:he plastic more slowly and therefore causes less disruption to the carbon film. Also,

t's a more pleasant material to work with. It isn't as volatile and so it has less

inpleasant fumes and there are other factors which she thinks favor the use of that

ol vent.

415
K. HEINRICH: Would you agree that probably x-ray spectrometry would be more useful

in that area if one could determine, for instance, the magnesium-silica ratio with better

accuracy than one can presently?

ZUSSMAN: You mean using energy-dispersive methods?

HEINRICH: Yes.

ZUSSMAN: Certainly. The greater accuracy you can get the more satisfactory it will

be. But I think with proper use of the energy-dispersive method, and with intelligent

application of it to the right kinds of specimens, specimens of the right thickness, that

is, you can get very good accuracy which enables you to distinguish nearly all of these

various magnesium silicates, but not all. There may be an occasional overlap, but 90

percent of them can be done within the present state of the art for accuracy, I believe.

HEINRICH: Thank you. Prof. Zussman. Would you have any comments as to Prof.

Zussman' s points?

CHOPRA: I think he's brought up very good points. I think this combination of two

which is using EDS/SAED in morphology combination and just calling them fibers is the way

to go at it.

A. SUNDARAM: I have to congratulate Dr. Fisher for his braveness in suggesting 10 to

1 ratio and 2 micrometer length. If we accept your definition of asbestos, we having the

regulatory responsibility are faced with at least two major problems. Number one, if you

insist on a 10 to 1 ratio and have the length as 2 micrometers, that means we've got to

have the diameter of the fiber as .2 micrometer. Then immediately the use of optical

microscopy for monitoring purposes is ruled out. If we take your method of detecting

fibers of only 2 micrometers in diameter (should be, length? [90]), I just would like to

know how feasible it is for a routine monitoring basis. Also, as a standard reference

method, I'd like you to find out on that; that's number one. Number two, we have another

responsibility now to show that fibers below 2 micrometer are not hazardous, so we are faced with that problem as well. Number three, I would like you to comment on the use of

the i_n vivo studies as well as vr\ vitro studies and the use of those to prove that 2 micrometer length is a safe length of choice.

FISHER: Well, working backwards, I can try to comment on the proper testing. What I had in mind is to say, let's divide these particles into domains that can be clearly

identified and there's no question that 10 to 1 does that. There's very little overlap

between the fragments produced by grinding and the fibers produced by the fibril growth

habit that occurs in what is well known as asbestos. When you take 5 to 1 , now you kind

of get into that middle ground again. When you get down to 3 to 1, why it's just hopeless

to run any tests and decide that there's any distinction in the biological activity above

and below 3 to 1 . You couldn't prepare the samples. There's already a problem with some

small fraction of long fibers occurring in the so-called short-fiber specimens and this

completely, I think, affects the results. Now your point about at the limit of the 10 to

1 and the smallest fibers getting down to pushing the analytical techniques, that is a good one, that would indicate that some of those would be lost from the analysis.

F. CHUNG: We routinely use x-ray diffraction, x-ray emission and microscopy for

material characterization including asbestos. We actually analyzed many hundreds of

asbestos samples either on membrane filters or as bulk powder. Based on our experience, I would like to make some comments:

(1) Identification : The term "asbestos fiber" combines two different features: the

work "asbestos" indicates chemical composition and crystal structure; the word "fiber"

indicates morphology, i. e. , external shape and size. The OSHA phase-contrast

microscopical method is adequate to count the number of fibers, but not the ASBESTOS

fibers. As to the methodology of identification of asbestos (chemical composition and

crystal structure) we have to make a distinction between a single fiber and components in a mixture. For components identification, x-ray diffraction is about the only choice; for

single fiber identification, combined results of electron diffraction, and x-ray emission

416
(Mg/Si, Mg/Si/Fe, Mg/Si/Ca ratios) are most convincing. Dispersion staining and

polarizing microscopy can give only supplementary information.

(2) Bui k Material

: For asbestos analysis we have to differentiate between membrane

filter sample and bulk sample. The OSHA phase-contrast microscopical method cannot be

used to obtain a fiber count for bulk samples. A reasonable indicator of asbestos content

in bulk samples would be its weight percent, be it amosite, tremolite, or others. X-ray

diffraction analysis can provide this weight percent with a precision of about ±10 percent

relative.

(3) Monitoring Methods : An official monitoring method ought to be practical and not

too expensive. An optical microscope costs $1 ,000'^'$2 ,000. An x-ray diffraction unit

costs $20,000^'$30,000. An electron microscope costs $100,000'v$200,000. In order to be

"practical and not too expensive," I believe the current phase-contrast microscopical

method is good enough for fiber counting and the x-ray diffraction method is adequate for

identification and/or quantification. Note that if no fiber is observed under a microscope, identification by x-ray diffraction is not necessary. When the combined

results of microscopy and x-ray diffraction are doubtful or challenged, then electron

diffraction, x-ray emission, dispersion staining, and polarizing microscopy can be called

upon for further confirmation.

(4) Definition of Fiber : An important feature of a fiber under a microscope is a pair of sides parallel lengthwise. This feature combined with a high aspect ratio, say 20

to 1, would exclude all the "cleavage fragments" which are non-fibrous and should not be

regulated.

FISHER: I think on this identification question the problem has now been defined and

recognized and I'm sure methods, reasonably satisfactory methods, will be developed in the

near future. Also, on the counting, there are automatic image analysis facilities

becoming available on microscopes. So I think the main point is to recognize that the

problem is difficult, and the approaches that must be followed to get an absolutely

positive identification; there are approaches that will give you a fairly high degree of

reliability and I think that the next step now is to really document what these are.

RUUD: I'd like to cast my vote with Dr. Zussman that I think it's high time that we

come up with a nomenclature that is clear with respect to what we are trying to describe.

Perhaps, Kurt Heinrich and the NBS will have that task. With respect to sending off

electron diffraction patterns to a central source: we have been working in our laboratory

with metallic substrates for transmission electron microscope samples and have settled

upon a fine-grain alloy that gives us some very sharp Debye rings that could well be used

to determine the camera constant.

T. ODGEN: I've got a question for Dr. Cossette. Did I understand you to say that

you would prefer to use size-selective sampling and then to determine the mass of

asbestos? This is the same as giving weight to the larger fibers in the respirable range,

isn't it? Have you any medical evidence for this, epidemiological evidence, or is it that

you just feel it would be a more accurate thing to determine?

COSSETTE: You're right in your assumption that we would like to classify fibers

before we collect them on the filter, eliminate the oversized ones and the undersized

ones. We've examined the literature on short fibers and we find generally two situations.

In some cases there has been no biological activity, or little activity. In other cases

they have shown some biological activity, but in those cases the short fiber invariably

contained a significant percentage of long fiber; and this, in our view, faults the

results.

J. SAUNDERS: I just have a comment to reply to Dr. Zussman' s comment. Asbestos

isn't the only thing in the world that has teeth. If I were going to play with dimethyl

sulfoxide I'd be very careful to look up and see what it does. It seems to me a number of

years ago there was some research done on how it caused other materials to penetrate the

skin. So, before I work with DMSO, or other solvents for that matter, I'd be careful.

417
D. BEAMAN: I'd like to ask Dr. Fisher: is your computer program available and can

it be used on anything other than your instrumentation?

LEE: In answer to your second question, as part of this ASTM round robin, I've

recently analyzed some diffraction patterns from several labs. There are some labs who

properly record the diffraction pattern. I have no problem indexing and interpreting

their diffraction patterns, taken on either 100 kV microscopes or 80 kV. I found that

other labs weren't as careful with their patterns, and I had difficulty with the measurements. So the answer is: yes, our methods can be used if you get a zone axis. If you

get a very incomplete pattern, our methods are unusable. However, our preliminary data,

and we want to emphasize it's preliminary data, suggest that the characteristic amphibole

pattern that is recognized by people with experience is that of the amphibole cleavage

fragment and thus they wouldn't recognize the typical pattern from a single crystal

amosite, asbestos particle.

FISHER: You really asked about the availability of the program and I see no difficulty with that, making copies available.

D. GIOIELLO: Question to Dr. Cossette. What TWA is the committee recommending for

the two industrial groups that you split up, what excursion or fifteen minute exposure

limit, and what is your medical justification for it?

COSSETTE: This is not completely settled and that is why I didn't mention any

specific figures. The numbers that we are considering presently for the mines and mills

are the same as the MESA regulation, which is five fibers, and for manufacturing and end

use industries are the same as the OSHA regulation, which is two fibers, but this is not

yet resolved. The justification for it is a review of the literature where we considered

all the significant information published, particularly epidemiological data. We were not

as strongly concerned with animal experimentation, but with the health effects on humans.

T. PANG: I would like to ask Dr. Fisher to comment on the identification of

chrysotile fibers.

LEE: In the quantitative identification of chrysotile fibers, I have very limited

experience. We have been working primarily on the identification of amphiboles. I have

not obtained chrysotile patterns which I have indexed. I use a reference pattern which

looks a lot like that which anyone else would use, as the pattern is diagnostic of

rotational symmetry. I think a problem occurs only if you don't have some indication of

the chemistry or no SAD pattern, for then you could be talking about a very acicular clay

mineral or anything else.

HEINRICH: Would anybody else want to comment on the identification?

ZUSSMAN: The least one can say about chrysotile is that if you are looking at the

electron diffraction pattern, now I'm talking about chrysotile asbestos, then the diffraction pattern is simpler to interpret because you don't have a rotation problem. A single

fiber has already produced a rotation effect, because it is cylindrical, and no matter how

much you turn it about the fiber axis it won't affect the pattern. So you are up against

less of a problem than in the amphiboles, of the kind we have heard about. I would have

thought that on the whole, if it is true chrysotile asbestos you are interested in, well,

^ rather than with other forms of serpentine (some of which may have greater or less 1 similarities), the problem is very easy because the morphology is also relatively easy to ] see, the length-to-width ratios are usually extremely high, the diameters are extremely

'

low, and you can often see the central void channel in a number of the fibrils you look

at. Other forms of fibrous serpentine, though not asbestiform, not silky, not things \ which would have on the macro scale the properties of silky asbestos, let's say, give ' diffraction patterns somewhat similar, similar enough I think to put you on the right

track, but not identical to asbestos.

418
You can index quite a number of the reflexions, quite a number of the spots, but some

f the spots are not spots, they are streaks. You can do some sort of approximation to

ndexing those, but it is not as easy, but again there are fewer of them, and there are

ot many spots and streaks to index because the structure is rather randomized and not

erywell crystallized.

ROSS: I would like to make a comment again, concerning health aspects of asbestos,

erhaps we are now beginning to understand which shapes and sizes of certain minerals

ause ill health, but it comes down to what actually causes cancer. What are the chemical

roperties of silicate minerals which relate to cancer development? High health risk is nown only for four commercial forms of asbestos. I don't know of any health studies that

elate to other types of minerals that may or may not be asbestos, but have never actually

een commercial. So I'd like to repeat that we need epidemiological studies in areas

ther than true asbestos mining, milling, and in the asbestos trades. The Homestake Mine

s one. If the miners there can be proven not to have health problems due to amphibole,

hen there is a very high probability we can quit worrying about the grunerites, cummingonites, and hornblende and our common rocks. We should also look at the hard rock iron

re miners who are also exposed to these same minerals. I am not impressed with rat and

nimal studies. A great many solid state materials have been injected into the pleura of

nimals. Fiberglass may or may not cause disease. I saw one study where actinolite did

ot cause disease, one study where tremolite did, and so forth. I think it's got to boil own to the health of the people involved in the operations other than strict commercial

sbestos mining. If we can find that there is not a health hazard in general mining

ommunities, we can quit worrying about a great deal of country rock and concentrate on

rue asbestos. I think the mineralogists have shown that there are some very interesting

ineralogical properties in what we consider true asbestos that may have something to do

ith cancer.

R. THOMPSON: Everybody has danced around the issue, but nobody has addressed it. If ou are going to set up a method for monitoring, and ultimately that is what you are oming to, you are going to have to have some kind of objective, and your objective is

oing to determine what method you use. I would contend for the objective I was given;

've got a method that works for chrysotile in ambient air samples. It would not be

ppli cable to anything else, nor do I think that some of the mineralogical work we have

one in depth would be possible or necessary on air samples when you are dealing with one

art of asbestos in ten to the fourth of the total particulate matter. Then we are going

0 have everybody talking about a method as though you are going to have one to do everyhing with, and that is complete balderdash, so we are going to have lots of methods to

etermine lots of things and ultimately it's going to go back to health effects as has

een mentioned. And maybe when the threshold response that was brought up yesterday is

nswered the main method we've got may prove to be of practical value there, who knows.

QUESTION: Would you comment on the role, if any, of the optical microscope?

THOMPSON: I say, for ambient air samples, optical microscopy is an impractical tool,

proposed in 1970 to do a fence to background study of the distribution of chrysotile by

iber length, to get a fiber length distribution. I believe you will find that if you do

his you will be able to establish (up to a point) a ratio between the asbestos by the

ass method and the optical count, and that might prove to be a survey tool. If your

sbestos count is high enough, x-ray diffraction is very elegant and sophisticated, for

urvey work it depends on your loading again. Part of our primary concern is particulate

atter in ambient air where asbestos is approximately one out of 10*, again, one out of

en thousand parts by mass. There you are stuck, you have no choice; your flexibility has

een removed. But, if you tell me the context then I think we, or anybody, is going to ome up with a set of survey techniques that would be applicable. The ultimate objective

f course is cost effectiveness, which I didn't go into this morning and should have, ecause I think I've got a winner on that basis.

D. WALIA: I would like to commend the U. S. Steel researchers on employing interpreation of electron diffraction patterns for distinguishing fibrous and non-fibrous mineral

articles. My optical microscopic observations of known fibrous and non-fibrous amphibole

mineralogical criteria) minerals seem to support that, that the fibrous particle

asbestos forming) tend to sit on 100 plane, and their counterpart non-fibrous particles

419
sit on 110 plane. This can be easily distinguished by measuring extinction angles. Of'

course, this is not the case with orthorhombic anthophyl 1 ite. I think this methodologyi!

should be looked into more, so it can be applied even on optical microscopic^

determinations.

LEE: Thank you. I think that the only thing we are trying to suggest is that there,

is not a mystical transition between a massive cleavage fragment that is visible in theii optical microscope and a cleavage fragment, at least at a range we are able to work, in' the transmission microscope. That was one of them.

H. RHODES: I am speaking for the Asbestos Information Association, which is a group

of about 40 companies who produce and use asbestos. The question of the validity of the

optical method has been touched on here only briefly and the conference seems to have:j

focused on whether it is SEM or TEM that should be used. We in the industry, and I thinki

the government would agree to this, have generated a lot of useful knowledge and field!

experience with the membrane filter method. We feel that with chrysotile asbestos and thei

volume of monitoring that is mandated by regulations, the method has a great deal of\

utility. It has shortcomings, but as long as you recognize these there are very many!

situations where this method is quite effective and we would hate to see a move to even! scanning electron microscopy mandated as a primary compliance monitoring procedure.

420
ational Bureau of Standards Special Publication 506. Proceedings of the Workshop on sbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

977. (Issued November 1978)

INTRODUCTION

John Martonick, OSHA - Chairman

I would like to make brief comments to put the aspect of regulatory

agencies into perspective. First, I think that if we reflect on the

information that has been presented over the last 2-1/2 days, we could

conclude that there is a considerable amount that we do know about asbestos,

with which we can all agree. From this information which we do know about

asbestos, the regulatory agencies must constructively formulate their

regulatory postures. Their interpretation of this information must be

practical in the sense that the job has to be performed and it has to be

performed now in many cases. The regulatory agencies don't necessarily have

time to reflect on which path they might take, or which path might be better to

take. The uncertainties in measurement and health effect that have been

discussed thus far must be put into perspective and this perspective must

reflect the goals and objectives that a particular agency has.

My second point is: How does an agency determine its goals? Each agency

has a defined rule, defined by Congress when they mandated that the agency

take certain action. In order to assure that the intent of Congress is being

met, the Congress has the General Accounting Office periodically investigate

regulatory agencies to see whether or not they are performing as Congress

intended. In addition, the public has a great deal of influence on the

regulatory agencies. They influence us in all aspects; they influence the

Congress, they influence the President, and they have direct influence on the

regulatory agencies; through meetings like this, through public hearings, and

through general day-to-day interactions. Finally, the courts make decisions

which direct the agencies and their activities. If agencies get out of line

and assume too much authority, the courts will hopefully bring them into

perspective.

These are the introductory comments I wanted to make. If you listen to

the papers presented today, you will see that action has taken place, and that

certain types of consideration are being made to everyone involved. It would

be unfortunate if some of the individuals being regulated feel that the

regulatory agencies are insensitive.

i 421

National Bureau of Standards Special Publication 506. Proceedings of the Workshop on

Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

THE MINING ENFORCEMENT AND SAFETY ADMINISTRATION - REGULATIONS AND METHODS

Aurel Goodwin

MESA - Metal and Nonmetal

4015 Wilson Blvd.

Arlington, VA 22203

Abstract

MESA regulations for exposure to asbestos require that no employee

be exposed to airborne concentrations greater than 5 fibers/mL (soon to

be reduced to 2 fibers/mL) greater than 5 micrometers in length on a time-weighted average basis. We are proceeding with public meetings

to obtain necessary data to reduce this permissible exposure even

further. We use the membrane filter method for sampling and phase

contrast microscopy for counting. Our regulations specify that the

term asbestos refers to chrysotile, amosite, crocidolite, anthophyllite asbestos, tremolite asbestos, and actinolite asbestos. In order

to analyze for specific minerals we have contracted with Dr. Ruud at

the University of Denver.

Keywords: Asbestos; dust; fiber; metal and nonmetal mines; optical

microscopy; phase contrast.

The Mining Enforcement and Safety Administration (MESA) is responsible for administering two laws for occupational health and safety, The Federal Metal and Nonmetal! ic Mine

Safety Act which was passed in 1966 and the Federal Coal Mine Health and Safety Act of

1969. Regulations for occupational exposure to asbestos have been promulgated under both

Acts. The standard for coal mines which is found in Title 30 Code of Federal Regulations

(30 CFR) Part 71.202 states:

71.202 Asbestos dust standard; measurement.

(a) The 8-hour average airborne concentration of asbestos dust to

which miners are exposed shall not exceed two fibers per cubic centimeter

of air. Exposure to a concentration greater than two fibers per cubic

centimeter of air, but not to exceed 10 fibers per cubic centimeter of

I air, may be permitted for a total of 1 hour each 8-hour day. As used in

this subpart, the term asbestos means chrysotile, amosite, crocidolite,

anthophyllite asbestos, tremolite asbestos, and actinolite asbestos, but

does not include nonfibrous or non-asbesti form minerals.

(b) The determination of fiber concentration shall be made by

counting all fibers longer than 5 micrometers in length and with a length-to-width ratio of at least 3 to 1 in at least 20 randomly selected

fields using phase contrast microscopy at 400-450 magnification.

The standard for metal and nonmetal mines which is found in 30 CFR Part 55.5-l(b),

;56.5-l(b), and 57.5-l(b) states:

(b) The 8-hour time-weighted average airborne concentration of

asbestos dust to which employees are exposed shall not exceed 5 fibers per

milliliter greater than 5 microns in length, as determined by the membrane

filter method at 400-450 magnification (4 millimeter objective) phase

contrast illumination. No employee shall be exposed at any time to airborne

423
concentrations of asbestos fibers in excess of 10 fibers longer than 5

micrometers, per milliliter of air, as determined by the membrane filter

method over a minimum sampling time of 15 minutes. "Asbestos" is a generic

term for a member of hydrated silicates that, when crushed or processed,

separate into flexible fibers made up of fibrils.

Although there are many asbestos minerals, the term "asbestos" as used herein is

limited to the following minerals: chrysotile, amosite, crocidolite, anthophyl 1 i te

asbestos, tremolite asbestos, and actinolite asbestos.

MESA has proposed a reduction for metal and nonmetal mines to provide the same exposure level as for coal mines, i.e., 2 fibers/mL for an 8-hour time-weighted average.

This proposed change was published in the Federal Register on July 7, 1977.

MESA uses the accepted industrial hygiene method of phase contrast microscopy for

counting and the membrane filter method for sampling fibers. A detailed description of

the method is given in the NIOSH Analytical Method P & CAM 239.

There are several practical problems with this method for determining exposure. One

of the more serious of these is the time and cost required for sampling and counting. Ir order to measure a worker's exposure, a sampling pump and filter are worn by the worker.

Because a heavy accumulation of dust on the filter can hinder or prohibit sample counting,

it is usually necessary to change the filter several times during a shift. Anywhere froir

2 to 15 filters may be required to determine one person's exposure. Usually 5 to £ filters are used. It costs a minimum of $10 to count each filter; thus the cost tc determine one person's exposure for one shift ranges from $20 to $150. In addition, the

cost of analyzing each sample for "asbestos" content increases this cost substantially.

We do not have conclusive information on the cost of such analyses on a routine basis, but

at present the cost for a single sample may be as high as $300 for electron microscopic

analysis. Besides these counting and analyses costs, the industrial hygienist collecting

the samples can, under average conditions, obtain reliable samples for only about five

employees in one day. This may go to as high as ten employees under good circumstances,

but in other mining situations it may be possible to cover only one or two employees.

This will add another $10 to $20 for each sample. The total cost for determining timeweighted average exposure is therefore $400 - $500 if a single filter is sufficient for ar electron microscope analysis, and could be as high as $3000 if ten filters are analyzed.

In any event, the major contribution to cost is the mineralogical analysis by electron

microscopy. The MESA Denver Technical Support Center is currently developing an innovative sampling pump which operates intermittently to obtain a time-weighted average

exposure on a single filter. The sampling rate now being experimented with is one minute

out of every six minutes. That is, the pump is on for one minute and off for 5 minutes.

The total "on time" of the pump is accumulated in a memory cell. This avoids the

necessity for the industrial hygienist to precisely determine the on/off time of the pump.

We will be testing this concept along with a conventional sampling- method, such as changing filters during the shift, in the next few weeks. If this is successful then the

cost per time-weighted exposure will be reduced to only slightly over the cost of the

electron microscopic analysis. Since a single filter would be sufficient to measure the

total time-weighted exposure, only a single count and electron microscopic analysis woulc

be needed for each full -shift, time-weighted average exposure.

You might ask, "since it is necessary to use an electron microscope for analysis, why

not also use it for counting?" Other than the fact that our current regulations specify

the use of phase contrast microscopy, the added cost of electron microscopy for counting,

and the correlation of such counts with disease prevalence or with the existing phasecontrast method, are factors which must be considered. However, there are no known

technical problems with this approach.

There are several other practical problems with sampling and counting asbestos using

the membrane filter method and phase contrast microscopy. One of these is the

non-uniformity in the deposition of dust on a filter, which occurs for a number of reasons. One of these reasons is non-uniformity in the filter manufacture. Figure 1 illustrates a pattern of deposition on some filter samples which were collected at a mining operation. The pattern is visible because the air in the workplace contained dark

material (probably diesel smoke) which stands out when collected on the white filter.

424
-im^ tlili'i'lBtlMlltf'

Figure 1. Photograph showing

uniform particulate

density on filter.

Usually such patterns are not visible because, when collecting fiber samples, only a light

loading is desired and the collected material is often white. However, such patterns,

when they do occur, can cause variations in counts between different counters and may be one cause for the non-uniformity discussed in P & CAM 239. Unfortunately, we have no quantitative data on the occurrence of such patterns or on their effect on counting

preci sion.

Another practical problem is that occasionally a filter, after being mounted, will

show what are described by our microscopists as radial aggregates. Figure 2 illustrates

this condition in an extreme case. Obviously, such samples cannot be counted and would be

rejected. Other "artifacts" which may be mistaken for fibers have been observed

occasionally in some samples. However, they are usually distributed throughout the depth

|of the filter material and not on the surface, as is usual for filtered fibrous dust.

These artifacts are similar to those obtained in the filters distributed by NIOSH in Round

40 of the PAT program.

425
Figure 2. Microphotograph

showing radial

aggregates that

form in clearing

filters for

phase contrast

microscopy.

MESA participates in the NIOSH PAT program. We began the program with round 15 and

have submitted acceptable results since that time on all subsequent PAT rounds. Although

not without problems, the PAT program is worthwhile. One of the problems, however, for

mine samples at least, is that the background of non-fibrous particles, as well as the

kind of fibrous particles, differ greatly from those found on samples taken in work

environments. Figure 3 is an example of a sample collected at a mine not expected to have

asbestos. Figure 4 is an example of a PAT sample. It would be extremely difficult to

detect fibers in the presence of dust, such as shown in figure 3, particularly if the

level is less than current regulations permit.

426
»

Figure 4. Microphotograph showing typical PAT sample for asbestos counting.

427
Here I would like to comment on one feature of optical microscopy which has led to some confusion among those persons responsible for counting fibers but who are not experts

in optics. This is the concept of "resolution." To some people, "resolution" implies the

minimum-sized object which can be seen. "Resolution" refers to the minimum distance

between two objects which still allows them to be distinguished as separate. Particles

smaller than the "resolution" distance can be seen as a diffraction pattern and hence,

fibers as small as 0.1 micrometer (and perhaps smaller) can be reliably counted.

Resolution will restrict the size of particles which can be analyzed by some optical

microscope techniques. Hence, mineral identification by optical microscope will only be

applicable in general to particles with dimensions greater than the microscope resolution.

At present we do not do any mineral analyses using optical microscopic techniques. Most

of the analyses that we have required have been done by Dr. Clay Ruud who discussed his

methods earlier during this conference.

Thus far, I have discussed some methodological and technical considerations inherent

in mesa's enforcement of its asbestos fiber standard. Now I would like to address what I believe to be a more fundamental issue, namely, the merits of the standard itself.

The Mining Enforcement and Safety Administration's current and proposed (revised)

asbestos standard covers six minerals. At least four of these have definitely been

associated with increased cancer incidence in humans. These are crocidolite, chrysotile,

amosite, and anthophyl 1 ite asbestos. We also know that these four minerals produce tumors

in experimental animals. Furthermore, we know that other mineral fibers, whatever their

mineralogical nature, produce similar tumors in experimental animals, as reported in this

conference by Dr. Mearl Stanton. As a result of these data, MESA proposed to its advisory

committee that the asbestos standard be revised to cover all insoluble mineral fibers. In so doing we proposed to continue to use the existing phase contrast, membrane filter

method for evaluation.

Using the animal experiments to extrapolate from known human carcinogens to other

substances in a similar class seems to me the prudent thing to do. This course of action

would not only further reduce human risks, but also eliminate the need for an expensive

electron microscopic or petrographic analysis to determine the mineral species of fibers.

There is great concern among mine operators that such a general mineral fiber

standard would impact upon every mining operation. All minerals are likely to have

fragments that meet the criteria of 3 to 1 aspect ratio for particles longer than five

micrometers in length and less than 5 micrometers in diameter. Obviously the impact of

such a regulation would also depend on the permissible fiber concentration. If we believe

the animal data is valid for extrapolating to humans for cancer induction, should we also

not believe the animal data for setting fiber dimension? If so, a minimum length of eight

micrometers and a maximum diameter of 0.25 micrometers would be indicated by Dr. Stanton's

work. These two parameters (length and diameter) would seem to be a more appropriate

specification than an aspect ratio and minimum length. These seem to be the two critical

parameters in animal studies for induction of tumors. In a "true" asbestos mining and

milling operation, reasonable variation in these parameters will not greatly affect the

fiber count. However, in an iron mine or a stone quarry, variations in these parameters

could make a great deal of difference in the "fiber" count. If a particle is carcinogenic

because of its size and shape, it should be counted; otherwise, it should be considered in

another dust category, such as respirable silica or nuisance dust. I would ask the

medical-biological researchers to review the information on fiber dimension and arrive at

a consensus on the appropriate fiber specifications and also whether the carcinogenic

properties are due to chemical or physical properties. This is a crucial issue with the

mining industry and is the cause for their great concern that the "asbestos" regulations

will affect all mining operations.

Finally, we need an estimate of risk vs exposure from the medical and biological

researchers. It is impossible to set a rational standard without this information. To

simply set all carcinogens to their lowest detectable limit does not make sense. It is

easy to imagine two carcinogens, one very potent and the other weakly carcinogenic. It

may be possible to measure the weak one at very low levels and the potent one only at

relatively high levels. We should not spend our resources on controlling the weak one with low benefit while the other substance would be relatively uncontrolled. A rational

428
and equitable standard cannot be set, except perhaps a total ban on exposure to all

carcinogens, without knowing the risks and benefits for any man-year's exposure. A total

ban is not practical nor necessary for all carcinogens in our modern society.

Discussion

W. SMITH: Dr. Goodwin and others before him here have called upon the medical and

biological people to comment on things that might give some clues about the estimate of

risk. I am a physican and my patients are mice, hamsters, rats, and so forth, and I have

some things to say that the hamsters have been telling us that would be pertinent to this

question. We have used six different preparations of crysotile and we put these in the

chest cavity, in the pleura space, of the hamsters. In our experiments with intrapleural

injection of hamsters, we got many mesotheliomas in response to preparations of commercial

asbestos that contained many fibers that I could see with 400X optical (phase) microscopy.

We did not get mesotheliomas with three preparations of chrysotile that contained relatively

few fibers that I could see with 400X (phase) microscopy. Our experience says that optical

microscopy is a more pertinent method than electron microscopy for monitoring dusts for

fibers. As I sat here this morning and saw the electron micrographs of these tiny fibers

I feel that from what our hamsters are telling us those are not really the problem.

Dr. Goodwin, does that give you any comfort in your using phase microscopy?

A. GOODWIN: Well, yes, I believe what you have said is very helpful with our current

regulation. However, I am also looking for future revisions to our regulations, both the

exposure levels and, more importantly, are we looking at the correct minerals and the

correct particles? For those materials that are generally agreed to be asbestos there

isn't a great deal of problem, but if we need to look at other minerals as well, is the

current definition of fiber too broad?

E. HOOVER: You said we are going to see the mineral fiber standard again in the

mining industry, and I missed a point. Are we going to be looking at a 3 to 1 aspect

ratio? I thought I heard some reference to the numbers changing a bit; particles over 5 microns long and not wider than 5 microns? Or are we going to look at some other kind of

criteria for the fiber standard?

GOODWIN: No, I didn't say that we are necessarily going to have another standard in

the mining industry. This is a long process, and advisory committees, public hearings,

all these things precede any changes in our regulations. We had proposed to the advisory

committee last year that the standard be revised to refer to mineral fibers rather than

asbestos; and in that proposal we retained the current phase contrast microscopy technique

for counting these fibers, i.e., fibers which have an aspect ratio of 3 to 1 and are greater than 5 microns in length. I am asking the biological and medical people if this

is the correct interpretation of the information from animal and human studies. In other

words, should we consider all mineral fibers that have a certain physical characteristic,

and is this physical characteristic the one we are using now or should it be changed?

HOOVER: I think in view of what you have said I wouldn't want that standard

presented again until we can get the medical evidence to support it. I think you are aware

of what we have heard here the last three days. Such a standard could wreak havoc on the

mining industry in America. It is a serious problem when you define a mineral fiber to

include everything, because as your records will indicate, many limestones can be interpreted as being fibrous. I personally feel that this is a problem that will require

additional medical studies before proposing a standard. One then has to try to live with

it and see how many mining companies would be left after these standards are imposed. If

you are thinking about this type of standard, certainly the threshold limit values would

have to be adjusted upwards, I would think, because we would have a real problem going to

the half of fiber per milliliter or 1/10 of a fiber per milliliter just based on what I have

seen so far. Those are my comments, and I am very much concerned about the proposed

standard; I have a feeling, I guess a fear that we are going to see it again.

GOODWIN: Well, I can't say what will occur, but much of what I have given you is my

opinion, but MESA has no plans to reintroduce a mineral fiber standard at the present time.

When we proposed revising our regulation to reduce the standard we have now from 5 fibers

429
per milliliter to 2 fibers per milliliter we stated that we intend to consider further

reductions in light of the OSHA proposal and in light of the NIOSH recommendations to

OSHA. We will be conducting some informal meetings with the mining community in different

areas of the country to discuss this reduction, however, before any such reductions are proposed. In these discussions we will be considering the NIOSH recommendations and the

OSHA proposal which retains the current definition of asbestos and methods for analysis.

HOOVER: One final question: I know with the new Secretary coming to the Interior;

Dept. that there was some comment about avoiding the use of the Advisory Committees since;

they, in effect, bottleneck the enforcement of the regulations. My concern is that if we

go to a similar situation as we have in coal where we don't have an Advisory Committee to

filter proposed standards, this would be a real problem. I would hope that the Advisory

Committee will be able to be effective, as they were in September of 1976.

GOODWIN: Well, I don't know what you are referring to about avoiding consulting with

the Advisory Committee. Our current law requires that we consult with an Advisory Committee. When I talk about having meetings and discussions with the mining community, this'

wasn't to circumvent that requirement. It was to get data that would be presented to the

Advisory Committee, if we decided that the proposal to reduce the standard further would

be prudent.

W. CAMPBELL: If you change the 3 to 1 aspect ratio to 10 to 1, you will eliminate a lot of problems for all of us. I think we all agree that the cleavage fragments would not

go beyond 10 to 1 or 15 to 1. So all this semantics of whether one has fibers or fragments

could be fairly easy satisfied by going to 10 to 1 or a little higher aspect ratio. The

3 to 1 is really the basic problem, I think.

430
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gai thersburg , MD , July 18-20,

1977. (Issued November 1978)

OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION METHODS

Willard C. Dixon

Occupational Safety and Health Administration

Salt Lake City, Utah 84117

Abstract

Occupational Safety and Health Administration (OSHA) uses the

membrane filter method at 400 - 450X magnification (4 mm objective)

with phase contrast illumination for the analysis of asbestos in

air. This method is substantially the same as is used by NIOSH.

In an atmosphere known to contain asbestos, all particulates with a length to diameter ratio of 3:1 or greater and a length greater than 5

micrometers are, in the absence of other information, considered to be

asbestos fibers and counted as such.

The equipment for optical analysis of asbestos in use at the OSHA

Salt Lake City Laboratory includes Zeiss microscopes having 40X objectives and lOX eyepieces, rotating stages, phase contrast illumination,

polarized light, and retardation plates. The transmission electron

microscope equipment in use by OSHA at the Salt Lake Laboratory is a Jeol model JEM lOOC with a side entry goniometer and ASID-45 Model

EM-15 SPS-2 scanning image display unit. We also have an Ortec-Delphi

x-ray energy dispersive system.

X-ray diffraction, atomic absorption, and other instrumentation

are also available.

The techniques used for the identification of asbestos include

sight recognition based on morphology, and optical tests including

polarized light, index of refraction, angle of extinction, dispersion

staining, and retardation. Electron microscopy tests include morphology, selected area diffraction, and a determination of elemental

composition by x-ray energy dispersive analysis.

A plan is presented for distinguishing between asbestos and other

fibers which may be mistaken for asbestos. A system for differentiating

between the various kinds of asbestos fibers is also presented.

Key Words: Airborne fiber; asbestos; bulk samples; dispersion staining;

; membrane filter; optical microscope; phase contrast.

i. OSHA performs all routine determinations of airborne concentrations of asbestos

fibers by the membrane filter method at 400 to 450X magnification (4 millimeter objective)

'^^ith phase contrast illumination.

The optical microscopes in use at the Salt Lake City OSHA Laboratory are Zeiss phase

contrast microscopes which are also equipped with a polarizer, analyzer, retardation

plates, and rotating stage with degree markings at the edge. The objectives are 4QX and

the eyepieces are lOX. We also have Wild Stereo microscopes equipped with a polarizer,

analyzer, retardation plates, and rotating stage.

431
The primary emphasis in identification of asbestos fibers is optical microscopy.

Back-up methods include electron microscopy, x-ray diffraction, atomic absorption, and wet

chemistry. Other instrumentation or methods are available if needed.

The Salt Lake City OSHA Laboratory has a Jeol transmission electron microscope, JEM

lOOC, with a side entry goniometer and ASID-4S model EM-15 SPS-2 scanning image display

unit. The system includes an Ortec-Delphi x-ray energy dispersive unit with a PDP 11/05

computer and Digital Decwriter II teletype with AED 3100 P dual drive for floppy disks.

The JEM lOOC is basically a transmission microscope, but is equipped to function as a scanner. We can obtain selected area diffraction patterns, or determine which elements

are present in particles or fibers, provided that the atomic number is eleven or greater.

The OSHA Salt Lake City Laboratory uses Philips Norelco XRG-3000 x-ray

diffractometers. This Lab has eleven goniometers.

Analysis of Bulk Samples

Bulk samples are examined on a reflected light stereo microscope for the presence of

fibers. Fibers can be isolated from the matrix at this time for identification by optical

methods, x-ray diffraction or electron microscopy, or further analysis can be performed

with fibers still in the matrix.

Small fibers not easily identified by optical techniques, samples subject to litigation,

or samples which are not positively identified by other means are the most likely candidates

for electron microscopy.

Slides are prepared and examined with a Wild transmitted light stereomicroscope

having crossed polars and a first order red retardation plate.

Asbestos fibers and bundles are recognized by their appearance. Oftentimes plant

fibers will curve a little at the edge. The slides are examined at 6X, then at higher

magnifications up to SOX on the stereomicroscope. This is followed by optical examinations

at various magnifications, including 400X with a phase contrast microscope. At this point,

it would be known whether asbestos is present and in approximately what concentration. If

organic materials interfere too greatly, the sample is ashed at 550 °C and re-examined.

The percent ash places an upper limit on the possible concentration of asbestos.

X-ray diffraction scans are run between 6° and 60° 20. X-ray diffraction can determine

the concentration of a mineral but not how fibrous the mineral is. Tremolite may be

present in high concentration in a talc sample, for example, but an actual fiber count may

show the tremolite asbestos concentration is much lower. For this reason, OSHA does not

place its entire reliance on the results of x-ray diffraction without optically confirming

the concentration of fibers present.

The percent by number of asbestos in talc samples is determined by particle counting.

If a scan of two slides shows no fibers present, the analyst will report no asbestos

detected without counting the slide.

If a preliminary scan shows the presence of asbestos fibers, 100 fields or 100 asbestos

fibers will be counted with a minimum count of 20 fields.

In order to randomize possible differences between slides, the counts will be divided

between four slides taken from different parts of the bulk sample.

432
Analysis of Membrane Samples

A fiber which has the correct size and aspect ratio for counting is not counted if

other information is obtained which proves that the fiber is not asbestos. This information may be obtained by any scientifically valid method, including either optical or electron microscopy, x-ray diffraction, or wet chemical tests. In outlining some procedures

which have been found useful at the Salt Lake City OSHA Laboratory, it is not intended to

imply that other procedures cannot be used.

Many textbooks on mineralogy will include identification tables and systematic

outlines for mineral identification. "Optical Mineralogy" by Paul F. Kerr [1]^ will be

useful for the beginning analyst. "The Microscopic Determination of the Non-Opaque

Minerals," Geological Survey Bulletin 848 [2] has extensive tables. "Gemstone and Mineral

Data Book" by John Sinkankas [3] has specific gravity and other tables for mineral

identification.

The optical tests for asbestos or other fibers are divisible into two categories: A,

those tests which can be performed while the fiber is still on the membrane, and B, those

tests which are performed after fibers have been removed from the membrane.

A - Fibers on the Membrane

In making the distinction between asbestos and non-asbestos fibers, it is highly

desirable for the analyst to be familiar with the morphology of asbestos fibers and those

fibers which are likely to be confused with asbestos. Thickness, pattern, and morphology

will often be a clue that a fiber is fiberglass, fur, hair, plant fiber, or other non- asbestos fiber. If a fiber bundle is more than one or two micrometers thick, striations

may be seen or fibrils may be splitting off in a way that is characteristic of asbestos.

If long fibrils are seen and no bundles can be seen, the possible presence of fiberglass

should indicate a need for further testing. With experience, the analyst will be able to

distinguish between chrysotile asbestos, amphibole asbestos, and most non-asbestos fibers

by recognizing the morphology as characteristic of one or the other. The fibers of

chrysotile have a fine silky appearance. Sometimes a wavy pattern is seen in the bundles.

When an interference is expected, the industrial hygienist collecting the sample

should also collect bulk samples of potentially interfering substances so that these can

be studied separately and methods found to differentiate between asbestos and the

interference. The analyst may have to delay his report until bulk samples are obtained

for study in some circumstances. As bulk samples are received for analysis, there will be

an opportunity to collect a small library of reference samples. Wards Natural Science

Establishment, Inc. [4] sells mineral specimens, including asbestos. The International

Union Against Cancer (UICC) asbestos standards can be obtained free from Pneumoconiosis

Research Unit [5].

Polarized Light and Retardation Color Patterns

Minerals having directional qualities yielding double refraction are anisotropic.

Minerals lacking directional qualities yielding double refraction are dark between crossed

polars and are isotropic. By crossing the polarizer and the analyzer, it is possible to

determine whether fibers are isotropic or anisotropic. An isotropic fiber has only one index of refraction. Isotropic substances include minerals of the isometric system and

amorphous substances, such as glass. By viewing fibers with crossed polars and noting

that they remain at extinction (non-visible) at all positions of rotation, it is possible

to eliminate interference from fiberglass, perlite veins, or diatomaceous earth. The

latter substance may be crystalline, but since the difference between the high and low

index of refraction is only 0.003 for Cristobal ite, this will not present a problem in

small diameter particles.

If crocidolite asbestos is present, the crossed polar test must be applied cautiously

since crocidolite fibers may not be seen with crossed polars. This is due to the dark

^Figures in brackets indicate the literature references at the end of this paper.

433
blue color of crocidolite and its birefringence, which may be as low as 0.004. However,

the blue color of crocidolite is itself a clue that crocidolite asbestos may be present.

If crocidolite has been heated above 200 °C, the fiber may be brown.

An anisotropic substance has more than one index of refraction, and can include plant

and other fibers as well as asbestos fibers. The tetragonal and hexagonal mineral classes

have two indexes of refraction, omega and epsilon. The orthorhombic , monoclinic, and

triclinic minerals have three indexes of refraction; alpha, beta, and gamma. If an anisotropic fiber is examined with crossed polars, it will have four positions in which it

goes to extinction, and four positions in which brightness will be a maximum as the stage

is rotated. The positions of extinction will be 90° apart. If a first order red

retardation plate is now added to the optical path, a retardation color can be added (or

subtracted) to produce a second order blue or first order yellow color in asbestos fibers,

depending upon the orientation of the fast or slow rays of the fibers with respect to the

slow ray of the retardation plate. The quadrants can be numbered as follows: Upper left

and lower right, one and three respectively; upper right and lower left, two and four

respectively. Fibers can be described as aligned with quadrants one and three, or aligned

with quadrants two and four if the fibers are at maximum brightness. Most asbestos fibers

will be yellow if aligned with quadrants one and three, or blue if aligned with quadrants

two and four. The exception is crocidolite, which sometimes gives a yellow to greenish

color if the fibers are aligned with quadrants two and four, and a blue color if the

fibers are aligned with quadrants one and three.

If amorphous (isotropic) fiberglass is present, the first order red plate will make

the fibers clearly visible, but they will have the red color of the background and will

not change their color as the stage is rotated. Small asbestos fibers, less than about

1.5 micrometers in diameter, may appear as dark lines in which the yellow color is so faint that it is not recognized. It is characteristic of asbestos that the yellow or blue

color developed in this way will be pure. A pure color is a single color or shade along

the length of the fiber as long as the fiber does not bend or change orientation. Talc

fibers may show a variation of color with blue shading slightly toward orange as the fiber

varies slightly in thickness. This may be due to the high birefringence of talc, 0.030 to

0.050.

Plant fibers will have a mottled appearance with a recognizable color pattern showing

the complicated structure of the fibers. In rare cases, plant fibers will have pure

colors like asbestos, and in such cases it will be necessary to pay close attention to the

morphology, particularly the thickness of the fibers, the bluntness of the ends, and the

way in which fibrils separate from the bundle. In such cases, it is possible to see structures which would not otherwise be visible by looking at the fibers at the extinction

position without retardation plates. If morphology and color patterns provide insufficient

clues to distinguish plant fibers, it will be necessary to ash the fibers at 500 to 550 °C

and re-examine the sample after ashing.

Birefringence has already been mentioned. Birefringence is n2-ni, the difference

between the high index of refraction and the low index of refraction of a particle. The

higher the birefringence or the thicker the particle, the higher the order of color seen when particles are examined with crossed polars. By the use of a Michel-Levy color chart,

it is possible to determine the birefringence of particles if their thickness is known.

This will help to limit the number of minerals which must be considered in determining

what is present.

434
The following table shows the birefringence of several minerals [6]:

croc idol ite 0. 004

chrysotile 0. Oil to 0. 014

anLnopny i i i it; n U 1 u n 0?5 U L_

tremol ite-actinol ite 0. 022 to 0. 027

amosite

(cummingtonite) 0 025 to 0 029

(grunerite) 0 042 to 0 054

gypsum 0 009

WO 1 1 db Lull 1 Lc n 014

anhydrite 0 044

talc 0 .030 to 0 .050

Angle of Extinction

Many minerals extinguish between crossed nicols when cleavages or crystal boundaries

lie at oblique angles to the planes of vibration of the two nicols. These are said to

have inclined extinction.

By measurement of the angle of extinction, anthophyl 1 ite and chrysotile can be

distinguished from other asbestos minerals. Anthophyl 1 ite has parallel extinction: that

is, the angle of extinction is zero degrees. The extinction of chrysotile will be close

to zero degrees. The angle of extinction of other asbestos minerals is as follows [7]:

tremol ite 15-20°

actinolite 10-15°

amosite 10-20°

crocidolite 80-90°

Wollastonite will have parallel or very nearly parallel extinction. If a mineral is

known to be either anthophyl 1 ite or tremolite by dispersion staining tests, the angle of

extinction can then be used to distinguish between the two. Caution: it is possible for

a mineral which usually has inclined extinction to have a few fibers with parallel or

close to parallel extinction, depending upon orientation.

Measurement of the angle of extinction can be performed as follows: Line up the

cross hairs (if the eyepiece does not have a cross hair, it is possible to use the lines

of a Patterson Globe and Circle Reticle or a Porton Reticle) with a natrolite particle or

fibers of an anthophyl 1 ite asbestos standard which is at extinction when the polars are

crossed. The fiber should be parallel to the cross hair and displaced slightly to the

side so as to be visible in bright field. Tape the eyepiece so that it is immobilized in

this position. Check the alignment with several other fibers to be sure that it is exact.

Line up an unknown fiber with the same cross hair line. Take a reading of the position of

the stage. With the polars crossed, move the fiber by rotation to its position of maximum

extinction. Take a reading of the position of the stage again. Repeat the measurement to

be sure that it is accurate. If the difference between the two readings is close to zero,

the fiber has parallel extinction. If the extinction angle is 15° to 20° and the index of

refraction matches tremolite, it is probable that the fiber is tremolite.

435
In making measurement of angles of extinction, measure the highest angle of

extinction obtainable by rotating the fiber around its long axis.

A binocular microscope which is adjustable for various interpupillary distances

should always be used on the same interpupillary setting as was used for alignment of the cross hairs for zero extinction.

Determination of the position of maximum extinction of some dark fibers may be

difficult. The fibers may appear to be dark over a wide range of rotation of the stage.

In such cases, it may be possible to locate the position of maximum brightness. If the

position of maximum brightness is 45° from the cross hair, the angle of extinction is zero.

Cleavage

Some minerals which have lathlike cleavage, such as gypsum, may be confused with

asbestos by inexperienced analysts. Such particles may have aspect ratios of five to one

or greater. Gypsum will often have the appearance of small rectangles. The blocky

appearance of gypsum is usually sufficient to make a distinction. The low indexes of

refraction of gypsum (alpha = 1.520, gamma = 1.529) can be used to make a distinction if

the analyst needs additional clues.

Although wollastonite is similar to tremolite, careful attention to fine details of

the cleavage patterns can make distinction between the two minerals. The cleavage lines

of tremolite tend to be straight; the cleavage lines of wollastonite tend to curve

slightly. The cleavage planes of tremolite tend to be uniform in thickness; wollastonite

cleavage planes tend to feather to thin edges. Sides of tremolite particles will be

straight or palisaded; wollastonite edges may be serrated. The ends of tremolite are square; wollastonite will be more smoothly rounded. If some fibers are still not

recognized, other tests can be applied after removal of the fibers from the membrane.

B - Removal of Fibers from the Membrane

Removal of fibers has the disadvantage that the count of fibers is difficult to

relate to a known area and therefore to the concentration of fibers in air. However, it

is possible to mark the position of fibers on the membrane and remove selected fibers for

further analysis. This particle picking technique is described in "The Particle Atlas"

[8].

When asbestos is in a mixture with other fibers, it is possible to bracket the

asbestos concentration by determining the percent of asbestos fibers in the mixture

removed from the membrane and applying this percentage to the total fiber count on the

membrane.

Ashing a Millipore membrane is difficult due to the tendency of the membrane to flash

when it is heated. Low temperature ashing is a solution to this problem but low

temperature ashing equipment will not be available in every laboratory. A Millipore

membrane can be ashed by folding the membrane, sample side in, moistening with alcohol,

then igniting the alcohol with a small flame.

Instead of ashing, it is possible to dissolve the membrane in acetone and separate

fibers and particles by centrifuging, followed by removal of excess acetone. After the

third treatment, an aliquot can then be placed on a slide, and after evaporation of the

acetone the particles can be blended into an index of refraction medium selected for

identification of the particles present.

A quick and simple separation procedure is to place one drop of the same index of

refraction medium on each of three slides, then cut a small segment of the membrane and,

holding it with fine tipped tweezers, dip the membrane sample side down successively into

each drop of index of refraction medium. After placing a cover slip over the medium, the

slides are ready for study.

436
Dispersion Staining

Dispersion staining is a convenient technique for determining the identity of fibers

and particles. If the analyst is unfamiliar with this technique, McCrone Research

Institute, Chicago, Illinois, teaches courses in dispersion staining. This training may

also be obtained from a university if it has a department of geology or materials science.

"The Microscope" [9] has an article entitled "Identification of Asbestos Fibers by

Microscopical Dispersion Staining." Other articles on dispersion staining are in "The

Microscope," and the techniques are also described in "The Particle Atlas" [10].

The Zeiss microscopes in use at Salt Lake City produce the equivalent of a central

stop (dark field) dispersion stain by using a phase 2 16X phase contrast objective with

the phase 3 ring in place. Leitz manufactures a phase contrast microscope which produces

central stop dispersion colors at 400X. If the microscopes in use at other labs do not

produce a central stop dispersion stain in this way, a "dispersion stainer" can be

purchased from Walter C. McCrone Associates [11].

For dispersion staining analysis, it is necessary to have quality high dispersion

liquids. These are available from R.P. Cargille Laboratories, Inc. [12].

The Appendix of this paper gives directions for the dispersion staining

identification of asbestos minerals and wol 1 astonite , a common interference.

In distinguishing between fibers, as many clues as necessary to make the distinction

should be used. In most cases, morphology, color patterns with crossed polars and

retardation plates, angles of extinction, or central stop dispersion staining colors,

especially if tests are made at more than one index of refraction, will give sufficient

clues to identify fibers.

Some fibers may remain unidentified after this type of screening. A sample analyzed

at the Salt Lake City OSHA Laboratory contained fibers very similar to asbestos. Optical

tests, however, indicated that they were not asbestos. X-ray energy dispersive analysis

showed a high concentration of silicon in the fibers. It was then suspected that the

fibers might be one of the polymorphs of SiOg. The fibers were separated from other

particles by treating the sample for twelve minutes with hot phosphoric acid. Central

stop dispersion staining and x-ray diffraction showed that the fibers were quartz.

Quartz fibers have been reported in the literature. However, it was unexpected to find

quartz fibers in a sample taken from a vacuum cleaner bag.

References

[1] Kerr, Paul F., Optical Mineralogy . Third Edition (1959), McGraw Hill Co., NY.

[2] Geological Survey Bulletin 848, 1934.

[3] Sinkankas, John, Gemstone and Mineral Data Book , Collier Books, New York, N.Y.

[4] Wards Natural Science Establishment, Inc., Rochester, N.Y.

[5] Pneumoconiosis Research Unit, Penarth, Glamorgan, Wales. UICC standards can be

purchased from McCrone Accessories and Components, 2820 South Michigan Avenue, Chicago,

IL 60616.

[6] ibid. Reference 1.

[7] Berkley, C. , Langer, A. , and Baden, V. , Instrumental Analysis of Inspi red Fibrous

Pulmonary Particulates , Transactions, New York Academy of Sciences, pp. 333-350,

Dec. 1967.

[8] The Particle Atlas, Edition Two, Vol. I, pp. 233-258, Ann Arbor Science Publishers.

437
[9] The Microscope, Vol. 18, No. 1, pp. 1-18, January-April 1970, Microscope Publications,

2820 South Michigan Avenue. , Chicago, IL 60616.

[10] The Particle Atlas, Ann Arbor Science Publishers.

[11] Walter C. McCrone Associates, 2820 South Michigan Ave., Chicago, IL 60616.

[12] R. P. Cargille Laboratories, Inc., 55 Commerce Road, Cedar Grove, NJ 07009.

Appendix

If chrysotile is mounted in 1.546 high dispersion medium, and viewed by a central

stop dispersion staining technique with the polarizer in and analyzer out, the colors will

be yellow to orange if the fibers are oriented parallel to the polarizer, and orange red

to red blue if the fibers are oriented perpendicular to the polarizer, depending upon the

index of refraction of the fibers. (In all asbestos fibers except crocidolite, the high

or gamma index of refraction will be seen when the fibers are oriented parallel to the

pol ari zer.

)

If chrysotile is mounted in 1.560 high dispersion medium, the central stop color will

be blue if the fibers are oriented parallel to the polarizer and blue white if the fibers

are oriented perpendicular to the polarizer. Amphibole asbestos minerals will not give

dispersion colors in 1.560 high dispersion medium, or the color will be straw yellow and

easily distinguishable from the colors given by chrysotile asbestos.

It is possible for fiberglass to have the same index as one of the indexes of

chrysotile or other asbestos minerals. Fiberglass and other amorphous substances have

only one index of refraction. By rotating the stage, this type of interference can easily

be detected since fibers oriented parallel or perpendicular to the polarizer will have the same central stop dispersion color. Synthetic polymers may show birefringence, which is

due to the orientation of molecules in the drawing process. These fibers will generally

be too thick to be confused with asbestos.

Talc fibers can be very similar to anthophyl 1 ite asbestos in appearance. Intermediate forms may occur which are between talc and anthophyl! ite in physical and optical

characteri sties.

In 1.550 high dispersion medium, talc fibers which are oriented parallel to the

polarizer will be yellow, indicating that the index of refraction is higher than 1.550

(gamma and beta). Talc fibers oriented perpendicular to the polarizer will be blue,

indicating an alpha index of about 1.550.

In 1.585 high dispersion medium, talc fibers which are oriented parallel to the

polarizer will have a blue central stop dispersion color, indicating a gamma index of

about 1.585. Fibers which are oriented perpendicular to the polarizer will have a blue

white central stop dispersion color, indicating an alpha index less than 1.585.

In 1.585 high dispersion medium, the central stop dispersion colors for tremolite or anthophyl 1 ite fibers will be yellow if the fibers are oriented parallel to the polarizer,

and orange yellow if the fibers are oriented perpendicular to the polarizer.

In 1.585 high dispersion medium, the central stop dispersion colors for chrysotile

will be similar to talc fibers. In 1.550 medium, however, the orange red color of

chrysotile fibers oriented parallel to the polarizer compared to a yellow color of talc

fibers similarly oriented will serve to make a distinction.

In 1.620 high dispersion medium, actinolite will be yellow if the fibers are oriented

parallel to the polarizer and the central stop color for fibers oriented perpendicular

will be orange yellow. Large particles will have a natural greenish color which may

influence the central stop dispersion color.

438
In 1.620 high dispersion medium, the central stop dispersion color for anthophyl 1 i te

,

tremolite, and wollastonite will be yellow orange to orange if the fibers are oriented

parallel to the polarizer. If the fibers are oriented perpendicular to the polarizer, the

colors will range from yellow orange to blue depending upon how the fiber is lying. By

rotating the fiber around its own long axis, the fiber can be brought to a position in

which it will be blue. Tremolite may be blue green.

The fibers can be caused to rotate about their long axis by gently tapping the

coverslip with a dissection needle.

Amosite asbestos can be expected in samples of insulation from steam lines and

boilers, especially from ships. If amosite is mounted in 1.670 high dispersion medium,

the central stop dispersion color will be yellow if the fibers are oriented parallel to

the polarizer, and red violet if the fibers are oriented perpendicular to the polarizer.

Other asbestos minerals, except crocidolite, have an index of refraction far enough from

amosite that no dispersion color will be developed in 1.670 medium. The central stop

dispersion color for crocidolite will be yellow orange if the fibers are oriented parallel

to the polarizer, and yellow if the fibers are oriented perpendicular to the polarizer.

Crocidolite will show the low (alpha) index parallel to the polarizer.

If the dispersion staining tests or cleavage patterns show that wollastonite may

be present and a test other than cleavage or the angle of extinction is needed to

distinguish between wollastonite and tremolite, the following method may be useful.

This method can be used in the absence of chrysotile asbestos to distinguish between

fairly acid resistant amphibole minerals and wollastonite.

Wash the fibers into a drop of concentrated hydrochloric acid on a slide by dipping

a membrane segment sample side down as previously described. Place a coverslip over the

drop of hydrochloric acid and heat the slide on a hot plate which is warm to the touch

but not hot enough to be uncomfortable. The slides will be dry in one hour. The

coverslip will tend to prevent the particles from migrating as the acid evaporates.

Let the slide cool, and add a drop of 1.620 high dispersion medium at the edge of the

coverslip. Capillary action will immerse the particles in the medium. When the slide

is examined, tremolite or anthophyl 1 ite will still show central stop dispersion colors;

wollastonite will not. Wollastonite will have been decomposed by the hydrochloric

acid or partially decomposed with separation of silica, but without formation of a jelly.

The wollastonite fibers will still have their original shape, but larger fibers will

show a crosshatchi ng pattern, and the anisotropy of the fibers will be greatly reduced.

Fibers which were not previously present in the sample will result from the treatment of wollastonite with hydrochloric acid, followed by evaporation of the acid. These

fibers will be needlelike and often form radiating patterns. The highest concentration

of these fibers will be in areas in which the hydrochloric acid evaporated last.

In 1.620 high dispersion medium, these artifact fibers will not give a central stop

color like that obtained from wollastonite, tremolite, or anthophyl 1 ite, and are distinguishable from the fibers which were originally present.

439
Discussion

W. ROFF: On your Zeiss microscope, maybe I misunderstood, you have the combination

phase as well as the optical mineralogy incorporated in one microscope?

W. DIXON: Yes.

ROFF: You do?

DIXON: We have a Zeiss universal; with this microscope we can make the switch back

and forth between the two techniques (phase contrast or polarized light) very quickly

because of its fingertip control.

ROFF: You mention something about ashing between 500 and 550 °C; well for chrysotile,

you have to be very, very careful

DIXON: Right, at 650 °C its going to be converted to forsterite.

ROFF: And possibly a little enstatite will keep its fiber form. We really have to

do it at a much lower temperature for a longer period of time.

DIXON: What temperature do you use, may I ask?

ROFF: We use 400 °C overnight, or a plasma asher. With respect to the nitric acid

for wetting your Millipore, we would rather fold the Millipores carefully and then wick

with alcohol and ignite and then put that into the furnace; I think you would find it

quite successful. Incidentally, I think your paper was very well done and I think should

be commended. There are many people here from the various mining companies, especially

from the western part of the U.S. that are concerning themselves with zeolite fibers, and

may I suggest that perhaps in your final text you might incorporate a sentence or two on zeolites; how to differentiate the zeolite fibers from the other fibers you are talking

about.

DIXON: I can't answer that question at the moment. What I would have to do would be

to look up the index of refractions of the zeolites and I would probably find a dispersion

staining technique from that which would help me to make a distinction between the two.

440
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

FDA PROJECTS AND METHODS

J. A. Wenninger, I. M. Asher, and P. McGrath

Food and Drug Administration

200 "C" Street, S.W.

Washington, D. C. 20204

Abstract

An overview of FDA projects related to asbestos detection and

quantitation is presented. The results of a recent FDA symposium on the

availability of suitable techniques are included. We then review the

technical and regulatory issues in the food and cosmetics area with

regard to asbestos contamination with emphasis on the analysis of

parenteral drugs and cosmetic talc. For the present, SEM using Nuclepore

filters as a substrate and EDXA for chemical analysis appears to be a reasonable, cost effective method for routine detection of asbestos in

foods, drugs, and biologicals, although quantitation and reduction in

the number of ambiguous fibers is still a problem.

Key Words: Asbestos; cosmetic talc; EDXA; fibers; food; parenteral

drugs; SEM.

Part I: An Overview

(I. M. Asher)

Since the Food and Drug Administration (FDA) programs related to asbestos are spread

i throughout several Bureaus, my colleagues have asked me to give an overview of FDA research

i efforts and interests. As you know, asbestos contamination of air and water is largely

: the domain of the EPA, while contamination of the workplace is of direct importance to

(j OSHA, and products for home use are the responsibility of CPSC. Thus, FDA interest has

centered on the asbestos contamination of food, cosmetic talcs, and parenteral drugs. A

major problem is developing rapid, reliable methods for the monitoring of asbestos in such

Ij products. An FDA symposium to evaluate the current state of electron microscopic methods

i for microfiber detection and analysis was held last August at Penn State University, with

; many of the current participants present. Naturally enough, the speakers tended to point

|j( out the promise of their methods and the weaknesses of alternate methods, but the consensus

was that a single method, simple and accurate enough for embodiment in FDA standards and

regulations, has yet to be perfected. (Copies of the Proceedings are available, free of

I. charge, from the FDA Office of Science.)

In the interim , the FDA has published a regulation banning the use of asbestos filters

and other filters releasing mineral contaminants with aspect ratios of >3:l-in the final

stages of manufacture of injectable products, unless followed by a membrane filter (40 FR

11865). It is hoped that this interim regulation can be replaced by appropriate standards,

and Phil McGrath' s group in the Bureau of Biologies has been trying to perfect and validate

an appropriate i nterim SRM method. An FDA Asbestos Work Group (chaired by Dr. Armand Casola,

Bureau of Drugs) meets regularly to discuss these and other issues.

The Bureau of Biologies has its own scanning and transmission electron microscope

facilities to detect and identify particulate contaminants in biological products and

parenteral drugs. The Bureau of Drugs has also initiated additional studies to identify

particulate contaminants in commercial samples of parenteral drugs, under contract at the

441
University of Kentucky. The Bureau of Foods has an ongoing program of analyzing cosmetic

talcs for tremolite and anthophyllite contamination (by contract).

The most ambitious FDA project in this area is an animal study of the carcinogenic

effects of subacute, intraveneous injection of chrysotile asbestos in Charles River CD

rats and CD-I mice of both sexes. The project is being conducted by the Bureau of Drugs,

under contract at the International Research and Development Corporation, Mattawan,

Michigan. There are three negative control groups: saline/single injection, saline/4

weekly injections, and kaolin/10 weekly injections ("inert" particulates)-for each

species/sex group of animals. There are also positive control groups receiving

methyl nitrosourethane once weekly throughout the lifetime of the animal. There are six

different asbestos dosages-single or four weekly injections of 0.2, 0.4, 0.8 mg/kg-for

each species/sex group. This gives a total of 10 dosages groups for each species/sex

group and amounts to 3480 animals in all. The FDA chronic study utilizes 18 grams of

asbestos sample, prepared to mimic typical releases of pharmaceutical-grade asbestoscellulose filters. These are typically short and very narrow. The mean fiber length in

the sample was 2.34 pm (ranging from <1 pm to 70 pm), and the mean diameter was 0.056 pm

(ranging from <0.01 pm to 0.25 pm). So far, at 16 months, too little data is available to

report definitive results; however, the incidence of lung tumors at necropsy in the male

CD-I mouse group at the highest asbestos dosage currently exceeds that for the saline

controls (i.e., 9/39 compared 2/23 and 3/24). The co-project officers of this study are Jules Lamar and Stephen Crop of the FDA Bureau of Drugs.

Part II: Food and Cosmetics - An FDA Update on the Asbestos Question

(J. A. Wenninger)

My discussion will focus on FDA's activities to prevent the contamination of cosmetics

and food by asbestos particles. I have been involved only with the problem of asbestos in

cosmetics, but I will extend my discussion to cover food. Cosmetics and food share similar

regulatory and physical-science characteristics, but there the similarity ends; to a large

degree, the problem with food centers on the ingested fibers, whereas with cosmetics it

centers more on inhalation of such fibers.

No regulations for either food or cosmetics have yet been established which either

prohibit the use of asbestos-containing filters in food processing or limit the amount

of asbestos fiber in talc used as a component of food or cosmetics. A proposal for certain

restrictions on food only was published in the Federal Register (38 FR 27076-81),

September 28, 1973. However, this regulation has not been published as a final order and

is still pending. The comments received in response to this proposal clearly indicated

that no regulation for food and food processing was warranted until more reliable data

could be obtained on methodology for the determination of asbestos and on a more complete

evaluation of the health hazard associated with ingested asbestos fibers. FDA's reply to

these comments were published in the Federal Register (40 FR 11865-70), March 14, 1975. It should be emphasized that on the basis of information received the agency did conclude that

the asbestos content of talc used in the manufacture of food - or drug - contact paper

packaging does not represent a potential contaminant of packaged food or drugs as assessed

by current methodology.

With regard to cosmetics it is unlikely that we will be in a position in the near'

future to propose a limitation on the asbestos fiber content of talc used for cosmetic

talcum powders. However, we do have a modest surveillance program under which we monitor

the asbestos fiber content of retail units of cosmetic talcum powder products. To date we have not found any grossly contaminated cosmetic talcum powder products on the market.

Although this is somewhat reassuring, our sampling of products was small; for example, we looked at only 28 samples by x-ray powder diffraction during 1975 and 1976. Of these,, one sample was found to contain 0.7 percent tremolite and three samples contained traces

of tremolite (approximately 0.1%) and anthophyllite.

In our laboratories we are now using three basic methods for the evaluation of

asbestos contamination of cosmetic talcs. We estimate our limits of detection as follows:

442
X-Ray

Diffraction

Optical

Microscopy

Differential

Thermal

Analysis

CHRYSOTILE 2%^ 0.5%^

TREMOLITE 0.1% 0.1%

ANTHOPHYLLITE 1%

a In the absence of interference from chlorite.

The Cosmetic, Toiletry and Fragrance Association, Inc. (CTFA) has continued to

cooperate with FDA's Division of Cosmetics Technology in developing reliable methodology

for the determination of asbestos in cosmetic talc. Results from a testing program set

up by the CTFA to establish the reliability of analytical methodology are expected to

be available in the near future. The CTFA has been active in establishing appropriate

specifications for cosmetic talc and developing analytical methodology for industry.

An article on cosmetic talc powder which appeared in Lancet (Volume 1, pp. 1348-9,

June 25, 1977) concluded: . . . "there is no reason to believe that normal consumer

exposure to cosmetic talc in the past led to either cancer at any site or to measurable

loss of lung function. It seems unlikely that future exposure to cosmetic talc of the

specifications now agreed to by major manufacturers will present a health hazard."

We do not know if this assessment is correct. However, it is the responsibility of

all of us to assure that appropriate steps are taken to prevent the use of talc unsuitable

for use in food and cosmetics. It now appears that several years may be required to fully

clarify some of the scientific questions on this subject. In the meantime it may be

prudent to establish by regulation a standard for all to follow. No doubt this approach

will be questioned in the absence of widespread contamination. However, we know that

efficient enforcement of any specification is very difficult without the assistance of

regulation.

Part III: Scanning Electron Microscopy for the Detection of Asbestos in Foods,

Drugs, and Biological

For the past two days we have heard of the many problems associated with detection,

identification, and quantification of asbestos and asbestiform minerals in the environment. We have experienced many of these same problems in an attempt to design methods

which could be used for routine electron microscopic analysis to detect asbestos con- taminants in products regulated by the United States Food and Drug Administration. For

routine analysis of these products we feel that scanning electron microscopy (SEM) using

energy dispersive x-ray analysis (EDXA) is the most cost effective method.

The rationale for choosing SEM-EDXA over Transmission Electron Microscopy, selected

area electron diffraction (TEM-SAED) technique is based on many factors. Since most of

the products examined contain very low levels of asbestos, the size limitation imposed by

an E.M. grid would interfere with detection of these small numbers of fibers. Most

samples are prepared for TEM examination through some type of filtration and the filter

must be destroyed by chemical or thermal means to allow examination in the TEM. Filter

residue left on the E.M. grid consistently interferes with the analysis and production of

diffraction patterns. Many fibers do not produce measurable diffraction patterns or are

lost during the preparation of the sample [1,2]^. Even those fibers which do produce

diffraction patterns must be indexed to identify the fibers. To index these patterns is

time consuming and requires sophisticated methods such as that developed by Lee at U.S.

Steel [3,4].

^Figures in brackets indicate the literature references at the end of this paper.

(P. P. McGrath and J. B. Ewell)

443
For analysis in the SEM, the filter surface itself is examined. If one compares a 47 mm or 13 mm diameter filter with a 3.05 mm diameter electron microscope grid, the

difference in the area available for examination is obvious, as for example figure 1. Further, less than 70 percent of the surface area of an E.M. grid is available for TEM

examination because of the grid bars which are not penetrated by the electron beam as shown in figure 2.

Figure 1. Comparison of 47 mm and

13 mm diameter filters

with 3.05 mm diameter

E.M. grid.

Figure 2. Electron microscope grid

illustrating surface area of grid bars.

Arguments against using SEM for this type of analysis cite the limits of resolution

in the SEM, the lack of diffraction capabilities; or that the chemical profiles developed

by energy dispersive x-ray analysis are not definitive criteria for classification of these

asbestos minerals [5,6]. These arguments in our estimation are not valid. The resolution

of the majority of scanning electron microscopes is near or below 10 nanometers and most

of the newer models guarantee 3 nanometers resolution. The lack of diffraction capabilities

is not a major factor because in the TEM a very large percentage of the asbestos fibers do

not yield usable diffraction patterns. X-ray analysis of fibers does produce sufficient

chemical information to classify fibrous asbestos minerals [7].

One method depends on preparing a clean sample on a Nuclepore filter, enabling the

operator to identify the particle of interest in a reasonable length of time [8]. We use Nuclepore filters in preference to Millipore filters because the surface of the Millipore

filter interferes with the detection of small fibers as shown in figure 3.

444
Figure 3. Asbestos fibers partially

obscured by configuration

of Millipore filter

surface.

The filters are first examined in the SEM at low magnification to determine if the

preparation is usable and to look for large particulates or product residue which might

obscure the small asbestos fibers. If the sample is suitable for examination, representative micrographs are taken of fibers found on the filter surface. Fibers or fiber bundles

resembling asbestos are subjected to energy dispersive x-ray analysis for 100 to 400

seconds (machine count time) depending on the spectra developed.

Identification of chrysotile asbestos is based on the morphology of the fibers or

'iber bundles, the x-ray counts for magnesium and silicon, and the absence of any

appreciable iron or other elemental peaks. We have not established x-ray criteria for

imphibole asbestos, but would only record them as a mineral fiber with the chemical

)rof i 1 e recorded.

At the present time we are able to routinely identify chrysotile asbestos fibers less

:han 70 nanometers in diameter on the filter surface using EXDA, but only after long count

:imes, up to 400 seconds. Larger fiber bundles, 1/2 micrometer and above, produce peaks

i/hich can be read on the analyzer display CRT in less than a minute, reducing the count

:ime and enabling the operator to go to the next fiber of interest.

To quantitate the number of fibers, we can estimate their size by comparison with a nicron marker on the display CRT or by comparing them to the pores in the Nuclepore

Filter as shown in figure 4. For more accurate counts, SEM micrographs at 5000X or

greater are taken and the fiber measured with a ruler and map reader. This is a slow and

:ime-consumi ng task. We still have problems with uneven filter surfaces and product

^esidue interfering with the analysis, but this is less a problem than it would be in the

FEM because the surface examined is so much greater.

Figure 4. Small asbestos fiber

traversing pores of

a Nuclepore filter.

445
In the future we plan to incorporate an automated image analysis system similar to

that developed at Penn State University [9]. We also are attempting to develop our own x-ray data reduction system based partially on the work done by Friedman et al . , for

analysis of neutron activitation spectra here at NBS for the Bureau of Foods, FDA [10]. We

feel that the SEM-EDXA, automated image analysis system will enhance our ability to do

routine analysis for asbestos and other particulate contaminants.

References

[1] Seaman, D. R. , NBS Workshop on Asbestos , July 18-20, 1977.

[2] Beaman, D. R. , Difficulties encountered in the identification of asbestos fibers by

analytical transmission electron microscopy in El ectron Mi croscopy of Microf ibers -

Proceedi ngs of the Fi rst FDA Of f i ce of Science Summer Symposi um , Penn State

University. August 23-25, 1975.

[3] Fisher, R. M. and Lee, R. J., NBS Workshop on Asbestos , July 18-20, 1977.

[4] Lee, R. J., Computerized SAED and the electron optical identification of particulates

in El ectron Mi croscopy of Microf ibers - Proceedi ngs of the Fi rst FDA Office of Science

Summer Symposi um , Penn State University, August 23-25, 1976.

[5] Stewart, I., Selected thoughts on asbestos quantitation in El ectron Microscopy of

Microf ibers - Proceedi ngs of the Fi rst FDA Office of Science Summer Symposi um , Penn

State University, August 23-25, 1976.

[6] Ruud, C. 0., Characteristics of silicate mineral fibers as seen by TEM-SAED and

SEM-EDXA in El ectron Microscopy of Microf ibers - Proceedi ngs of the Fi rst FDA Office

of Science Summer Symposi um , Penn State University, August 23-25, 1976.

[7] Pooley, F. D. , The identification of asbestos dust with an electron microscope

microprobe analyzer, Norel co Reporter , 23, No. 2 (October, 1976).

[8] McGrath, P. P. and Ewell, J. B. , Application of electron microscopy to the problem of

particulate contaminants in food, drugs, and biologicals in Proceedi ngs of El ectron

Microscopy , IIT Research Institute , Chicago, Illinois, Part III, 1976.

[9] Johnson, G. G. , Image Analysis Techniques in El ectron Microscopy of Microf ibers -

Proceedi ngs of the Fi rst FDA Office of Science Summer Symposi um , Penn State

University, August 23-25, 1976.

[10] Friedman, M. H. and Tanner, J. T. , A computer language for reducing activation

analysis data, submitted to the Journal of Radioanalytical Chemistry, May, 1977.

Discussion

H. RHODE: I have a question for Phil McGrath. We are very much interested in the

use of the scanning electron microscope for commercial asbestos samples and the problem

you illustrated beautifully there with the Millipore is like looking for a needle in a large haystack, except that the NIOSH procedure requires that Nuclepore not be used for

J collecting air samples. Thus we are kind of on the horns of a dilemma. Have you done

anything in the way of trying to mask the structure of the Millipore?

I P. McGRATH: No, but Dave Manolin of Millipore told me that the reverse side of a • Millipore filter is smooth. You might reverse the filter. I have not done it. Or, you : could ash the Millipore filter, suspend the ash in water, and run it through a Nuclepore

j filter.

RHODE: We tried controlled exposure to acetone vapor with some promising results,

but we are not ready to be sure that we've got it yet. I was hoping that someone else had some ideas about collapsing it rather than dissolving it, but that has some problems too.

446
J. LEINEWEBER: Our company seems to be the favorite stopping place for everybody who

has developed gadgetry of one sort or another to help in the counting of asbestos fiber. We

have encouraged this because we would like to see what is happening in this field, and

among the things we have done is to follow the methods of automated analysis and everytime

we get into the laboratory with some asbestos fiber samples the fiber sizes are too fine,

the samples are too complex; we just have not gotten off the ground in that direction.

It's an interesting concept.

McGRATH: It is an interesting concept. I have talked to Jerry Johnson of Penn

State about the use of image analysis. They probably have the hardware but need to develop

programs for fiber analysis. I believe the group at Penn State would be willing to

develop the programs if someone would supply the monies.

LEINEWEBER: Another comment on the Millipore texture problem and carbon coating

Millipore filters for TEM work-many times you carry this texture along and it kind of

interferes in the TEM work; we have found that collapsing with acetone vapor prior to

coating with carbon does give a much smoother surface and a lot less interference.

McGRATH: Sometimes we sputter coat the Nuclepore filters with gold-palladium before

we use them. This reduces the pore size slightly but also reduces charging.

A. LANGER: The only drama associated with any presentation on asbestos was the drama

of Irv Selikoff and myself in 1968 at the Food and Drug Administration, presenting a seminar on the "Contributions of Fibers from Talc to Human Lung Burden." We have given

FDA nine years, and I am delighted to hear that you are taking some action.

J. WENNINGER: Let me set the matter straight for the public record of this meeting.

The FDA has not taken any action in regard to the possible contamination of cosmetic

talc by asbestiform minerals.

LANGER: I won't be quite as dramatic, but this study in Lancet, is that the study

of the Italian deposits?

WENNINGER: I don't think it was. It was a general review article summarizing a meeting held in England sometime ago.

LANGER: I think this is based on the study of the Italian talcs, the pure talcs.

That's the five nought variety that has very, very little mineral contamination, and

I think that your assurances are directed to the users in the United Kingdom and not the

users of consumer talcums here in the States.

WENNINGER: That could be correct, however that was not my understanding.

NOTE: The following was a note sent following the meeting and was not part of the verbal

discussion at the end of this paper.

G. LEE: In his presentation of the FDA regulatory status with respect to cosmetic

talc, Mr. Wenninger quoted from an editorial "Cosmetic Talc Powder" which appeared in the

June 25, 1977 issue of The Lancet.

During the ensuing discussion period. Dr. A. H. Langer speculated that conclusions of

the safety of cosmetic talc may have been drawn solely from data restricted to the Val

Chisone Italian talc and would therefore bear no relevance to American talc products.

To answer this apprehension and to set the records straight, I am including a copy of

this precise editorial, which explicitly references data, human and animal, covering

cosmetic talcs which are used both in the United Kingdom and the United States.

This editorial conclusion clearly applies to American cosmetic talcs as well.

447
The following editorial was photographed from The LANCET, Volume 1 for 1977,

No. 8026, dated Saturday, 25 June 1977, pages

1348 and 1349. This editorial has been

reproduced here by permission of

Mr. Ian Munro, Editor, The LANCET.

COSMETIC TALC POWDER

From time immemorial man, like his evolutionary

predecessors, has been exposed to airborne dusts. Such

exposure is a corollary of living and survival. Not unexpectedly, therefore, the lungs have efficient means of

clearing themselves of inhaled particles and a functional

reserve such that the accumulation of uncleared dust mav be considerable before there is any obvious loss of

work-capacity. However, it has long been recognised

that heavy exposure to dusts, such as quartz and

asbestos, may lead to loss of function and, in the case of

asbestos, to cancer of the pleura and of the lung itself. The observation that even casual exposure to asbestos

may be associated with increased risk of mesothelioma, now occurring at the rate of nearly 200 new cases a year

in the United Kingdom,' has brought into question the

safety of other common dusts such as cosmetic talc. There are two main concerns. Firstly, will inhalation of

a dust cause loss of function through fibrosis or emphysema? And, secondly, will it predispose to cancer?

Although talc can cause granulomas when introduced

into the tissues or body cavities,^ exposure to cosmetic

talc has been widely assumed not to predispose to pulmonary fibrosis. However, the fact that no association

has been seen between the use of talc and loss of lung

function might simply reflect the lack of methods sensitive enough to detect losses of function that are small

compared with those due, for example, to smoking and

to heterogeneity in a,-antritypsin status. For similar rea- sons any effect of talc exposure on cancer incidence

would probably escape notice unless deliberately sought.

Until lately facilities for studying the long-term effects of

inhalation of dusts in laboratory animals have been

scarce, and even now the predictive value of animal

models is questionable. Thus, even in the case of tobacco

smoke, where the cancer hazard to man is indisputable,

duplication of the effect, by the inhalation route, in laboratory animals has proved difficult or impossible,'

although inhaled asbestos dust has given positive results

in animals.'' The possibility that talc causes cancer dramatically

hit the headlines of the daily Press when workers in Cardiff reported finding talc particles in cancers of the

ovary and uterine cervix. The report was greeted with

scepticism because the particles were not positively identified as talc, because their presence did not prove causation, and because they might have found their way onto

the sections as a result of contamination of tissues after removal from the body. Subsequent mineral analysis

failed to confirm that the particles were talc* and the

passage of six years without publication of confirmatory

evidence suggests that the early scepticism was well- founded. A meeting of talc-powder manufacturers and

independent scientists took place at Cardiff during May,

1976, under the chairmanship of Dr J. C. Gilson, direc- tor of the Medical Research Council Pneumoconiosis

Unit. At that meeting the toxicology of talc was

reviewed and the need for further information discussed.

Assessment of toxicity necessarily starts with a consideration of the physical and chemical specifications of the

test material, and this, unfortunately, is also where

much of the assessment ends in the case of cosmetic talc because most of the published reports—epidemiological,

clinical, and experimental—concern exposure either to industrial talcs that are variously contaminated with

minerals known to be hazardous or to talc of undefined

physical and chemical characteristics.

The long thin fibrous shape of asbestos particles

enables them to be carried more deeply into the lungs

than spherical particles of similar mass. The fact that the normally effective clearance mechanisms have

difficulty in coping with large, long thin particles de- posited deeply in the lungs is an important determinant

of the hazards from asbestos dust. Geologically, talc (which is nominally a hydrated magnesium silicate) and

certain amphiboles—tremolite, actinolite, and anthophyllite—may occur in juxtaposition and consequently

talc may be contaminated with these minerals. Apart

2. HluL-mel, (",

, I'i/a, I-., /ischka-Konorsa, Vf. Wien. kim. VC'schr. 1962, 74, 12.

3. navi'i, H. R., W hiiehcad, J. K., Gill, M. E., l.cc, P. N., Bulterwonh, A. D., Roe, 1-, ] (..Br.J.Caticer. 1975,31,469.

4. Warner, I. c;., Ikrrv, G., Skidmore, J. Vi ., Timbrell, V. thid. 1974, 29, 252.

5. IlL-ndcrson, W. .1., joslin, C. A. F., Turnbull, A. C, Griffiths, K J Ohsiei.

(i\ iiici\ Hr. Commoiiu: 1971, 78, 266.

l.<.rcciihcr«, l.lovd Oavies, 1. A. Rr. J. ind. Med. 1974, 31, 91 6, Hildick-Smilh, G. V. flr.J mJ. Mi-d, 1976,33, 217.

448
from this, talc may contain chlorite, quartz, carbonates

(such as calcite, dolomite, and magnesite), and occasionally other minerals in lesser amounts. During the

past few years, major cosmetic manufacturers in the

United Kingdom and the United States of America, as represented by the Toilet Preparations Federation and

the Cosmetic, Toiletry and Fragrance Association, have

drawn up specifications for cosmetic talc which ensure

the virtual absence of fibrous amphiboles.^ '" At present

there is no direct statutory control of the quality of cos- metic talc in any country and it is questionable whether

such control is necessary to bring minor manufacturers

into line with the standards now adopted by the major

firms. The presence of fibrous particles in talc reduces its free flow and lubricity, thereby rendering it less cosmetically desirable. Such contamination is thus self-limited. More important, however, is the fact that the fibrous

materials most likely to contaminate talcs which do

not comply with the specifications—namely, tremolite,

anthophyllite, and actinolite—are not those most clearly

associated with carcinogenic hazard (crocidolite,

amosite, and chrysotile). Furthermore, it would be sensible to consider what controls, if any, are necessary for

talc as used in medicines, before introducing legislation

specifically in relation to cosmetic talc. If the inhalation of particles of amphibole and silica contaminated talc dust were found to be harmless, one might reasonably assume that talc free from these

materials is safe. Kleinfeld and his colleagues have stu- died the incidence of cancer and respiratory diseases in

talc miners and millers in New York State. The talc concerned, which is heavily contaminated with both amphiboles and free silica, was initially reported to be associ- ated with an increased mortality from mesothelioma and

cor pulmonale." Later the same workers reported that men employed in the mine after dust levels had been

reduced had death-rates from malignant diseases that were similar to those for White males in the U.S.A.

generally.'^ Also in the U.S.A., Fine and his colleagues"

have reported a higher prevalence of productive cough

and chronic obstructive lung disease among rubber

workers exposed to a non-fibrous industrial-grade talc than among control workers. From their data they cal- culated that a safe exposure level would be provided by

a threshold limit value of 0-25 mg/m^ mass-respirable

particulate talc. In Italy, Rubino and his colleagues'*

compared the spectra of causes of death among talc miners, talc millers, and agricultural workers. The talc miners were exposed to dusts containing 5% silica at

levels far in excess of threshold limit value. Significantly more of them than of the controls died from respiratory

disease, but death-rates from all forms of cancer, including lung cancer, were significantly lower among the

7. Toilet Preparations Federation Ltd., specification no. 12: Cosmetic laic. 1977.

8. C.T.F.A. Specification; Talc, Cosmetic. Cosmetic, Toiletry and Fragrance

Association, Inc., issue 10-7. 1976.

9. Toilet Preparations Federation Ltd., analytical method 77: Cosmetic Talc

1977.

10. Hamer, D. H., Rolle, F. R., Schelz, J. P. Am. ind. Hyg. Ass. J. 1976, 37, 296.

11. Kleinfeld, M., Messite, J., Kooyman, O., Zaki, M. H. Archs envir. Htlh,

1967, 14, 663.

12. Kleinfeld, M., Messite, J., Zaki, M. H.J. occup. Med. 1974, 16, 345.

13. Fine, L. J., Peters, J. M., Burgess, W. A., Di Beradinis, L. J. Archs envir. HUh, 1976,31, 195.

14. Rubino, G., Scansetti, G., Piolatto, G., Romano, C.J. occup. Med. 1976, 18, 186.

miners than among the controls. By contrast, among the

talc millers, exposed to dusts containing 0-05% silica; but no detectable asbestos, at concentrations of 20 million particles per cubic foot (27 litres), there was no

excess of deaths from pulmonary disease or cancer of any site compared with the control group. The deficit of lung cancer among the talc miners is plausible in so far

as a similar deficit of lung cancer among coal miners seems to be real." A continuing study of over 3200 persons, mainly women, at a factory in Britain where cos- metic talc has been made and packed for over fifty years, has so far revealed no evidence of health hazard,'* but

follow-up would need to be extended for at least a further decade before one could be confident of a negative result. Other less informative epidemiological studies are reviewed by Hildick-Smith.*

In most of the work in animals the quality of the talc has not been specified. An exception is a report by

Wehner and others" who studied the effects in hamsters

of repeated exposure to aerosols of cosmetic talc up to

total doses of respirable particles equal to nearly 2000

times those received by humans using cosmetic talc during baby care. Exposure had no adverse effect on bodyweight, survival, incidence of pathological changes in the respiratory tract, or incidence of neoplasia at any

site. Another exception is the report by Wagner and his colleagues," who saw no mesotheliomas in 48 rats after intrapleural administration of cosmetic talc whereas 18 out of 48 rats similarly exposed to chrysotile asbestos

acquired such tumours. The same workers exposed rats

to cosmetic talc by the inhalation route on five days a week for up to a year. At the highest level of exposure —about three times that studied by Wehner and his col- leagues'^—there was slightly more pulmonary fibrosis than in controls, but no substantial excess of pulmonary

neoplasms. A number of less relevant animal studies, all of which gave negative results for carcinogenicity, are reviewed by Hildick-Smith.* In summary, there is no

reason to believe that normal consumer exposure to cos- metic talc has in the past led either to cancer at any site or to measurable loss of lung function. It seems unlikely

that future exposure to cosmetic talc of the specifications now agreed to by major manufacturers will present a health hazard.

15. Goldman, K. P. Br. J. ind. Med. 1967,22, 72. 16 Newhouse, M. L., Miller, B. F., Moore, W. K. S. Paper given at seminar on

Biology of Talc Used in Health Products, Cardiff, May, 1976.

17. VCehner, A. P., Zwickei, G. M., Cannon, W. C, Watson, C. R., Carlton,

\X'. W. FdCosmct. Tax. 1977, 15, 121.

IS. Wagner, J. C, Berry, G., Cooke, T. J., Hill, R. J., Skidmore, J. W. in Pro- ceedings of Fourth International Symposium on Inhaled Particles and

\apour. Oxford, 1977.

449
f
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

CPSC REGULATION OF NON-OCCUPATIONAL EXPOSURE TO ASBESTOS IN CONSUMER PRODUCTS

Robert M. Hehir, Steven P. Bayard, and June Thompson

Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, Maryland 20207

Abstract

The Consumer Product Safety Commission (CPSC) has found that

exposure to respirable free-form asbestos in two consumer products

poses an unreasonable health risk. The Commission has recently

voted to propose bans on the use of free-form asbestos in consumer

patching compounds and in artificial fireplace ash or emberizing

materials under Section 8 of the Consumer Product Safety Act. The

broad regulatory provisions under CPSA, as well as those under the

Federal Hazardous Substances Act (FHSA) are discussed.

Data on consumer exposure to asbestos are very limited. One study

of airborne asbestos resulting from use of consumer spackling/patching

compounds has reported levels of airborne asbestos fibers exceeding

the occupational exposure levels.

Direct evidence exists of asbestos inhalation in non-occupational ly

exposed individuals from autopsy findings of asbestos fibers in lung

tissue and indirect evidence of asbestos-related cancers in non- occupational ly exposed individuals from epidemiological studies.

A risk assessment has been made of the potential increase of lung cancer deaths resulting from consumer exposure to asbestos containing

patching compounds.

Key Words: Artificial fireplace ash; consumer exposure; Consumer

Product Safety Act (CPSA); Consumer Product Safety Commission

(CPSC); emberizing material; free-form asbestos; patching compounds;

risk assessment.

Introduction

The Consumer Product Safety Commission (CPSC) has broad regulatory authorities under

several Acts to help it marshal its resources to reduce unreasonable risk of injury

associated with consumer products.

When risks of injury resulting from reasonable or reasonably foreseeable use of consumer products are brought to the Commission's attention, either through petitions or through findings from in-house or externally-sponsored studies, the regulatory mechanism

which can most appropriately remedy or prevent an identified hazard is utilized. Thus,

in a recent decision, the CPSC Commissioners voted to regulate respirable, free-form

asbestos in two consumer products (consumer patching compounds and artificial fireplace

ashes) under Section 8 of the Consumer Product Safety Act (CPSA) [16]^.

It is the sequence of this regulatory process which I will discuss today.

^Figures in brackets indicate the literature references at the end of this paper.

451
Prior to promulgating a safety rule under the CPSA, the Commission must first propose

a rule for public comment. In issuing a final rule, it must make special findings under

sec. (9) subsection (c) of the CPSA. Such findings include:

(a) the degree and nature of the risk of injury the rule is designed to

eliminate or reduce;

(b) the approximate number of consumer products, types or classes that will

be subject to the rule;

(c) the need of the public for the product and probable effect of such rule

upon the utility, cost, or availability of such products to meet such

needs; and

(d) any means of achieving the objective of the order while minimizing

adverse effects on competition or disruption or dislocation of

manufacturi ng. . . etc. , consistent with the public health and safety.

In addition, the Commission must consider other things as well:

(a) Which Act will be used in promulgating the rule. (Sec. 30 CPSA).

(b) Jurisdiction under Section 3(a) and Section 31 CPSA.

(c) Under CPSA, if the Commission preliminarily determines that a product

presents an unreasonable risk of injury, it could commence proceedings to

develop a mandatory safety standard addressed to that risk. If it

appears that no feasible standard can adequately protect the public, the

Commission could declare that it is a banned hazardous product (Sec. 8

CPSA). Where the Commission concludes that a product presents an imminent and unreasonable risk of death, serious illness, or severe

personal injury, the Commission may file in a U.S. district court an action for a court declaration that a product is an imminent hazard (Sec.

12 CPSA).

In the case of asbestos exposure, the injury would not be immediate but may be

impending because of the long latency period. In fact, this chronic hazard area is one that is receiving new emphasis in the Commission. By themselves, our methods of emphasizing the acute injuries and toxicities by national surveys of emergency room injuries

appear inadequate for chronic hazard evaluation and regulation. Chronic hazard information

most frequently comes from retrospective epidemiological occupational studies, case reports, and animal studies. Chronic hazards are the most silent type of hazards because

the consumer is unknowingly exposed to chemical products which have hitherto been assumed

safe. A partial list of chronic hazards on which the Commission has taken action to

regulate or propose to regulate includes:

Lead (in paint)

Vinyl Chloride (as an aerosol propellant)

TRIS (flame retardant)

CFC's Chlorof 1 uorocarbons (as aerosol propellants)

Asbestos (fireplace embers, patching compounds)

Petitions

One other factor is important in describing the sequence of events in CPSC's regulatory

process. Interested persons may petition the Commission to commence proceedings for the

issuance, amendment, or revocation of a rule under any Act administered by the Commission.

It was through the petition process that the Commission's regulatory sequence began for

asbestos-containing products.

The Commission has considered three petitions [11,15,18] requesting it to ban consumer patching compounds and artificial embers and ash containing respirable, free-form asbestos.

The request on artificial embers and ash, received in November 1975, was initially treated

452
as a consumer complaint, and the staff conducted follow-up investigation on the complaint.

Subsequently, in July 1976 and March 1977, two petitions were received seeking bans of

free-form asbestos-containing consumer patching compounds.

The Commission then proceeded to investigate:

(a) what hazard was actually associated with these products,

(b) how the hazard could be reduced with maximum compliance and minimum

disruption, and in addition, to evaluate

(c) what future protective rules should be made for public safety.

Non-Occupational Exposure

The first step was to decide whether consumers could be exposed to asbestos. Direct

and indirect evidence exists that individuals, other than those working directly with

asbestos minerals, are being exposed to asbestos. For example, asbestos fibers have been

demonstrated at autopsy in the lungs of persons who were not occupational ly exposed

[6,7,14,23]. Substantial evidence also exists that human lungs may harbor thousands of

fibers, some of which are chrysotile. However, the number of asbestiform fibers found in

non-occupational ly exposed individuals is relatively small compared with the numbers in

occupational ly exposed individuals [19].

The next step was to decide if there was any risk of injury to exposed consumers. Since the reports from emergency rooms were not suitable for our needs, other data were

sought.

Indirect evidence of asbestos-caused adverse health effects was provided by

epidemiological studies which showed malignant mesotheliomas, rare in the general

population, to be associated with individuals with no occupational exposure to asbestos,

but who lived in the vicinity of the asbestos fields or mines [2,12,24].

Another investigation of the extent of asbestos exposure associated with 42 diagnosed

mesothelioma cases was conducted in southeastern Pennsylvania. Of these, 8 were

neighborhood exposures and 10 had questionable exposure. Among this group was a 14 year

old boy who alledgedly helped his father replace plasterboard during extensive home

remodel ing [8].

A short exposure (according to the report) of mixing and applying asbestos cement

insulation to a boiler in a consumer's home has also alledgedly caused mesothelioma [8].

It has also been suggested that inhalation of small numbers of asbestos fibers over a long period of time could result in focal concentrations at the lung bases, possibly

reaching fibrogenic or carcinogenic concentrations [23].

Next, we had to decide just what type of products had asbestos available for respiration, i.e., free vs. bound fiber. In numerous products the fibers are tightly bound to

the matrix or are encapsulated. A potential health risk occurs when asbestos fibers

become airborne, such as by mixing, sanding, or cleanup operations when using asbestoscontaining patching compounds. However, in terms of risk to the public health, a single

individual engaged in such a process may inadvertently expose other individuals in the

vicinity. The importance to such "bystander" exposure has been emphasized in several

reports [1,9,17,20] and we had to consider this also.

Risk Assessment

Another big question: how much risk of injury is associated with the product? A model

for lifetime risk assessment of death from respiratory cancer due to consumer use of

asbestos-containing wall-taping compounds was prepared by one of the authors (S.B.). In

order to compute such a risk assessment for the use of asbestos-containing wall-joint

I compounds, many assumptions had to be made. The model selected for analysis was that

jdeveloped by Enterline and Henderson [4], which in turn was derived from data on amosite

453
asbestos factory workers and asbestos insulation workers [20]. Measurements of asbestos

fibers longer than 5 microns from work with wall -taping compounds were taken from data

provided by Rohl , Langer, Selikoff, and Nicholson, [17]. Projections of consumer use and

exposure were determined and age central death rates from respiratory cancer based on the

1970-71 vital statistics of the United States were utilized.

The assumptions used in the risk assessment model are presented below:

(a) The dose-response relationship between asbestos and lung cancer is

linear [4]. This hypothesis assumes no threshold.

(b) Time to tumor is dependent on dose and can be described by a log normal

distribution with median time to tumor t:

where D = 8-hour time weighted average dose in fibers/cc and a log

standard deviation of 1.5. (Enterline and Henderson, 1976, [4] based on Jones and Grindon, 1975 [5]).

(c) Competing risks of death for the first 40 years following exposure are considered to be normal.

(d) Risk of asbestos caused death after the first 40 years following exposure

is considered to be zero.

(e) Effect of dose is cumulative and is assumed to have the same effect as if

that dose had been accumulated in the first year of exposure.

(f) Intermittent exposure with occasional high peaks has the same cumulative

effect as continuous exposure at double the dose [3,4].

While the assumptions (a through f) may seem at first unclear, the total effect is to

present a cumulative dose-response curve of the form log dose-log response. This is shown

in figure 1. Explanation of how these figures were derived is given below. It is

emphasized, however, that this model is to be used for low exposure estimates. It is not

designed to fit data for high or long-term exposure data.

1/3

454
oo

o

o

+-> Q

SOlo

c

(_) (JCO >, cn

s- o

O I—

+-> — CO

s-

•r—

to d:

(D

II >-

100,000

10,000

1 ,000

100

10

"log Y = 2.081+2.513 log X

r = .992

16

X = Average Daily Dose f/cc (log scale)

Figure 1. Response vs. dose for low level asbestos.

Exposure: Asbestos induced respiratory cancer deaths

per million lifetime vs. daily exposure (f/cc) for

1 year. Estimates based on the model.

Derivation of Total Cases Caused by Asbestos Exposure

Besides the assumptions above, the major data used to estimate the total cancer

deaths attributable to dose were the Selikoff data on 294 factory workers who had been

exposed to asbestos for 3-11 months during the years 1941-45 [20]. Estimates of the

concentration of asbestos dust during this period averaged 30 f/cc. Since the average

exposure was only 5/8 year, the equivalent concentration was figured at 18.75 f/cc/day on

a 1-year basis. By assumption (b), the median time to death from respiratory cancer is

37.1 years. Also, by assumption (b) the log normal distribution shows that for the 28

years of follow-up used in the Selikoff paper only 24.4 percent of these deaths would have

occurred. Since the adjusted relative risk of these workers was 2.95 [4], and the age

central death rate from respiratory cancer (ages 35+) was 850/minion, the number of

respiratory deaths which could have been caused by the asbestos exposure was the solution

to:

28(. 000850 + .244 X)

28(. 000850)

or X = .190205 or 190,205 deaths/million. But, since only 40 years of exposure are considered (assumptions c and d), assumption (b) allows only 57.3 percent or 109,000

lifetime cancer respiratory deaths per million exposed.

By assumption (a), the number of potential cases by dose can then be calculated and

risk estimates can be derived from these. This is shown in Table 1, along with the

calculated relative risks. Here it can be seen that excess deaths and relative risks do

not increase linearly with increasing dose but in a geometric manner.

455
Table 1. Lifetime (40 years) risk estimates of respiratory cancer deaths by dose for a 1-year equivalent exposure. Median latent periods and relative risks are

incl uded.

(1)

8-hour Avg.

Daily Expo- sure Level D f/cc

.5

1

2

4

8

16

18.75

(2)

Latent

Periods

Years , t=98. 65(^)1/3

124.3

98.6

78.3

62.

49.3

39.

37.

(3)

Potential

Cases/

Mi n ion

(see text)

5,072

10,145

20,290

40,578

81 ,155

162,310

190,205

(4)

Proportion

Developed

in 40 years

(log normal)

0026

0130

,0488

1488

,3030

,4776

,5727

(5)

Asbestos

Induced

Respi r. Cancer

Deaths/

(3)x(4)

13

132

990

6,038

24,590

77,519

109,000

(6)

Relative

Risk

(5)+850x40

850x40

1.00038

1 . 00388

1.02912

1.17759

1 . 72324

3.27997

4.20588

Estimates of Exposure Level

of Consumer Users of Wal 1 Taping Compounds

Rohl [17] measured peak fiber concentrations of ten drywall taping compounds during

sanding, dry mixing, and floor sweeping. The average peaks were as high as 47 f/cc with

the highest individual peak of 59 f/cc. Based on these peaks the 8-hour time weighted

average was estimated as 10 f/cc. Taken with assumption (f) that high intermittent

exposure was estimated to have doubled the effect of continuous exposure, this estimate

was increased to 20 f/cc. If there are four uses projected per year, the estimate of

yearly equivalent is:

20 f/cc/day x 4 days ^ f/cc/dav for 1 vear

200 days/year T/cc/day tor I year

Thus, based on the results of the model. Table 1, it is estimated that 4 heavy

exposures by consumers in one year will cause an additional 10 lifetime respiratory cancer death/million. Continued use for five years will, by assumption (e), raise that estimate

to 990 deaths per million (see Table 1).

No quantitative risk assessment was made for asbestos exposure from the artificial

embers and ash since there are no known measurements of the airborne fiber content. It can be assumed, however, that whatever air concentrations are present, they expose the

home occupant to a continuous inhalation of free fibers vs. only intermittent exposure for

the wall -taping compounds. The risk from these embers and ashes, therefore, may be

considered at least as high as that from the wall-taping compounds. In our opinion the

greatest period of risk for embers, ashes, and patching compounds is both during the

application and removal processes.

Regulatory Decision

Since we considered this risk of injury too high, a safety rule was obviously called

for. Because of possible cumulative effects of exposure to respirable asbestos, we felt

that total exposure should be kept as low as possible and it was, therefore, decided to

issue a regulation.

456
The options available to the Commission were:

(a) under the Federal Hazardous Substances Act (FHSA) as "banned hazardous

substances"

(b) under Section 8, CPSA, a proposal to ban manufacture, sale, and distribution.

The Commission decided to issue a ban under Section 8 of CPSA.

CPSA Ban

The Commission decided that it was in the public interest to propose the ban of consumer patching compounds and emberizing materials containing respirable free-form

asbestos under the CPSA (Sec. 30(d), CPSA), although the petitions were submitted under

FHSA and the risk of injury could be eliminated or reduced to a sufficient extent under

the FHSA. The Commission believes that the rulemaking proceedings under the FHSA are likely to be lengthy and resource consuming and that those proceedings could make it more difficult for interested persons to participate.

On the other hand. Section 8 of the CPSA, under which a CPSA banning rule would be

issued, provides for a period wherein all persons affected by the proposed banning action

can submit written comments. An opportunity for oral presentation of data, views, or arguments, is also provided. During this period, any additional information or data that

night better define the nature or degree of the hazard associated with the affected

products may be brought to the Commission's attention for consideration prior to the

promulgation of a final rule.

Removal and Pi sposal

While the banning rule is considered, the removal and disposal problems associated

/ith artificial asbestos ash/embers will also have to be addressed.

The disposal of the material in the homes of consumers poses a difficult problem.

The Commission has been requested to declare fireplace emberizing materials

rontaining asbestos "to be imminently hazardous consumer products," and to direct

lanufacturers of such products to remove them from the homes of consumers. -

The Commission solicited the advice of experts as to whether consumers could safely

emove the asbestos "ashes" from their own fireplaces. While the consensus is that,

xercising caution in accordance with available expert advice, they could. However, there

'as some contradiction among the experts as to how it should be done. The Commission,

herefore, will consider various removal procedures before issuing advice to the public.

Guidelines on safe removal may mention di sposal instructions for unused patching

impounds. The Commission's staff believes that their removal may pose no hazard since,

nlike the "ashes", this material is not loosely scattered. The asbestos patching

aterial on the walls is assumed to have already been suitably covered and should not

reate an unacceptable risk.

uture Commission Actions on Asbestos

Asbestos in consumer products has been established as the Commission's highest

riority project for FY 78.

This project will assess the potential hazard of other consumer products containing

sbestos. The asbestos content of a given product is not necessarily the sole criterion

f that product's relative health risk. A potential hazard occurs when asbestos fibers

jBcome airborne and can be inhaled. Thus, the Commission's concern is to determine what

ther consumer products contain asbestos fibers which can readily become airborne under

prmal use conditions.

i The Commission will then decide if additional rulemaking is required for the

"otection of the consumer.

I 457
References

[1] Anderson, H. A., Lisis, R. , Daum, S. M. , Fischbein, A. S. and Sel i kof f , I. J., HouseholdContact Asbestos Neoplastic Risk, Ann. N. Y. Acad . Sci . , 272, 311-323 (1976).

[2] Barow, M. A., Conston, L. L. , Livornes, L. L. , Schalet, N. , Mesothelioma and its

Association with Asbestosis, J. A.M. A. , 201(8) , 93-97 (1967).

[3] Enterline, P. E. , DeCoufle, P., Henderson, V., Mortality in Relation to National

Exposure in the Asbestos Industry, JOM, 14(12), 897-903 (Dec. 1972).

[4] Enterline, P., Henderson, V., A Model for Extrapolating to Low Levels of Asbestos

Exposure. Presented at Conference on Problems of Extrapolating the Results of

Laboratory Animal Data to Man and Extrapolating the Results from High Dose Level

Experiments to Low Dose Level Exposure, Pinehurst, NC (March 11, 1976).

[5] Jones, H. B. , Grindon, A., Environmental Factors in the Origin of Cancer and Estimation of the Possible Hazard to Man, Food , Cosmet . Toxicol . , ]8^, 251-268 (1975).

[6] Langer, A. M. , Ashely, R. , Baden, V., Berkley, C. , Hammond, E. C. , Mackler, A. D.

,

Maggiore, C. J., Nicholson, W. J., Rohl , A. N. , Rubin, I. B. , Sastre, A., and

Selikoff, I. J., Identification of Asbestos in Human Tissues, vL_ Occup . Med . , 15(3),

287-295 (March 1973).

[7] Langer, A. M. , Selikoff, I. J., and Sastre, A., Chrysotile Asbestos in the Lungs of

Persons in New York City, Arch. Environ . Health , 14, 559-563 (April 1967).

[8] Lieben, J., and Pistawka, H. , Mesothelioma and Asbestos Exposure, Arch. Envi ron . Health , 22, 559-563 (April 1967).

[9] Lillington, G. A., Conjugal Malignant Mesothelioma, New Engl . J. Med., 291(11), 583-

584 (September 1974).

[10] McDonald, J. C. , McDonald, A. D. , Gibbs, G. W. , The Health of Chrysotile Asbestos

Mine and Mill Workers of Quebec, Arch Environ . Health , 28 , 61 (1974).

[11] Natural Resources Defense Council (NRDC) Petition, HP 76-18, Consumer Patching

Compounds Containing Respirable Asbestos (July 15, 1976).

[12] Newhouse, M. L. and Thompson, H. , Mesothelioma of Pleura and Peritoneum Following

Exposure to Asbestos in the London Area, Brit. J. of Indust . Med. , 22, 261-269 (1965).

[13] Nicholson, W. J.,: Case Study 1: Asbestos--The TLV Approach. Occupational

Carcinogenesis, Annal

of the New York Academy of Sciences , Vol . 271 , 152-169 (May

1976) .

[14] Pooley, F. D. , Oldham, P. D. , Dm, C. H. , and Wagner, J. C. , The Detection of Asbestos

in Tissues, Pneumoconiosi s Proceedi ngs of the International Conference , 1 969 , Cape Town : H. A. Shapiro, Ed., Oxford Univ. Press, 108-116 (1970).

[15] Public Citizens Health Research Group (HRG) Petition, HP 77-9, Patching Compounds

with Tremolitic Talc Containing Asbestos Fibers (Asbestiform Tremolite) (February 9,

1977) .

[16] Public Law 92-573; 15 U.S.C. 2051, 92nd Congress, S. 3419, October 27, 1972. Consumer

Product Safety Act.

[17] Rohl, A. N. , Langer, A. M. , Selikoff, I. J. and Nicholson, W. J., Exposure to Asbestos

in the Use of Consumer Spackling, Patching, and Taping Compounds, Science , 189 , 551-

553 (1975).

[18] Scott, Ms. Rachel, joined by Environmental Defense Fund (EDF), HP 77-11, Artificial

Fireplace Ash Containing Respirable Free-Form Asbestos (April 15, 1977).

458
[19] Selikoff, I. J. and Hammond, E. C. , Asbestos Bodies in the N.Y. Population in Two

Periods of Time, Pneumoconiosis Proceedings of the International Conference , 1969 , Cape Town , H. A. Shapiro, Ed., 99-105 (1970).

[20] Selikoff, I. J., Hammond, E. C. , Seidman, H: Cancer Risk of Insulation Workers in

the United States. lARC , Biological Effects of Asbestos , Lyon, France, (1973).

[21] Selikoff, I. J. and Hammond, E. C. , III. Community Effects of Nonoccupational

Environmental Asbestos Exposure, A. J. P. H. , 58(9), 1658-1666 (September 1968).

[22] Selikoff, I. J., Bader, R. A., Bader, M. E. , Churg, J., and Hammond, E. C. , Editorial:

Asbestosis and Neoplasia; The Amer. J. of Medicine , 42(4), 487-496 (April 1967).

[23] Thomson, J. G. , Asbestos and the Urban Dweller, Ann . N.Y. Academy of Sci . , 123 , 196-214 (1965).

[24] Wagner, J. C. , Sleggs, C. A., and Marchand, P., Diffuse Pleural Mesothelioma and

Asbestos Exposure in the Northwestern Cape Province, Brit . J. Indust . Med. 17 , 260-

271 (1960).

Discussion

J. LEINEWEBER: I'd like to make the statement that some of the applications of

asbestos fiber that you are discussing here are considered among those of us in the

asbestos industry as applications that are not necessary and can be eliminated from the

workplace and from the environment. I wasn't able to follow several of the arguments you

were giving in terms of your risk assessment, and I think for the purposes of bringing a discussion like this to a reasonable conclusion, I for one will appreciate seeing some of

this and maybe having an opportunity to rebut it before the final publications of these

proceedings are out-is that possible?

R. HEHIR: It certainly is. All the information that we have on risk assessment and

all the briefing packages are in the Office of the Secretary of the Commission. They are located at 1111 18th Street, and Mr. Richard Rapp or Miss Sadie Dunn would be very happy

to provide all the pertinent information I've discussed here, and any of the additional

materials which are submitted should go to that particular office so it can be considered

in the rulemaking process.

C. COOPER: I thought that the presentation of the risk assessment was a fascinating

exercise, and I too would like to see the details by which these numbers were attained. I thought I heard the figure of an average exposure for a year of 0.4 fibers per cc arising

out of four applications.

HEHIR: Yes.

COOPER: That seems to be an extraordinarily high number to arrive at from four

applications when compared with the exposures that we observed in insulating workers, for

example, who work with insulating materials around the clock. We found average exposures

of maybe ten times that for men who work with asbestos year around. It seems to me that

your number is an unusually high average concentration for a year, but I am not questioning

I it but I would like to see some figures from which it was derived.

|; HEHIR: Dr. Cooper, I'm sure you'll have an opportunity to see the figures. As a batter of fact we received additional information from other people. As I have told you

'initially, the material on patching compounds was from the publication by Rohl , Langer,

Nicholson, and Selikoff, and that was our jumping off point. For example, that was the data

iwe utilized and we came up with the figure based on six assumptions. I'm sorry I was not

'able to have a slide of the table and the figure and some other mathematical calculations

to show you how they are derived; however, the paper will be published and the information

is readily available at this point.

459
COOPER: I do think that this is an interesting approach to this problem and I'm very

anxious to see how it was reached.

M. BROWNSTEIN: Two things: you have not mentioned anything about the time table for

this proposed ban. I wonder if you could go into that at all. The other area is, how is

it planned to differentiate between the products that are intended for the home handy man, or will be used by the home handy man, and those which are used by the construction

industry?

HEHIR: Well, we regulate products that come into the home that are sold to the consumer. We don't regulate anything that might be considered an occupational hazard. As

far as the risk assessment, and the deliberations on time tables, that is in the hands of

the general council. I can't tell you how long it will take; a prudent man could contemplate a year. A person dealing with government knows that the wheels of progress in this

particular regulatory forum move ever so slowly; probably in a few years. Since these are my own expressed opinions, I don't feel compelled to tell you that the Commission may have

a different view.

BROWNSTEIN: Just to continue on that restriction that you only deal with consumer

products, my question was more on how are you planning to differentiate between what is a consumer product? Let's say a building supply store, this sort of thing where you find

both groups going to get products from the same outfit.

HEHIR: I find it difficult for similar regulatory agency representatives to ask a question like that. The Act spells out very clearly we handle consumer products which are

not food, drugs, cosmetics, or economic poisons; now the interpretation really centers on what constitutes a consumer product. If you can buy it in a hardware store, then we consider it a consumer product. If, however, the manufacturer regulates from point of

sale to distribution and can so demonstrate such regulations and such control then, quite

frankly, we might not have jurisdiction.

ROSS: Do you have any data on the health of professional plasterers and also

professionals in other similar areas, like cement workers?

HEHIR: Dr. Ross - I personally don't, but I'm sure by the end of our rulemaking

procedures we will have that kind of information.

460
National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

IMPACT OF ASBESTOS REGULATIONS ON THE MINING INDUSTRY

C. S. Thompson

R. T. Vanderbilt Company, Inc.

Norwalk, Connecticut 06855

Abstract

No one in the mining industry objects to proper regulation of toxic

substances. No one in the mining industry has any objection to the rea- sonable control of asbestos as long as the regulations apply to the

truly asbestiform varieties of specific minerals. Unfortunately, the

regulators have ignored basic mi neralogical data and have included

numerous minerals which bear no resemblance to the asbestos upon which

essentially all health data have been obtained. This gross extrapolation of the known health hazards of excessive exposures to true asbestos,

to the non-asbesti form varieties of common rock-forming minerals is

totally unwarranted.

The full assessment of the economic impact of asbestos regulations,

as with other restrictive legislation, will undoubtedly take many years.

The impact is also greatly dependent upon the outcome and recommendations resulting from this workshop. As of today, if the regulatory

agencies apply their present rules and definitions regarding "asbestos",

the entire mining industry and those dependent on it face an adverse

economic impact unparalleled in its history. Furthermore, proposed

regulations, based on the same erroneous definitions and extrapolations,

are so restrictive they threaten the existence of major segments in a wide variety of areas within the mining industry. The continued

promulgation and enforcement of mineral legislation based on errors and

misconceptions will have severe economic effects on the total U.S.

economy and on the individual taxpayer.

Keywords: Amphibole; copper; crushed stone; fiber; iron; minerals;

mining; quarrying; solid waste.

First of all I would like to state that I am not a medical doctor and, therefore,

will not attempt to evaluate the problems of real or imagined health hazards involved with

exposure to minerals. I am a mineralogist and I am here today representing the American

Mining Congress to do five things, as follows:

1. Remind everyone of the value of the mining industry to the overall

U.S. economy;

2. Point out the widespread geographic distribution of the various

segments of our industry;

3. Describe briefly the almost universal occurrence of certain

minerals of interest in essentially all mineral deposits;

4. Discuss the confusion resulting from the erroneous and unwarranted

expansion of the term "asbestos" to include many non-asbestiform

minerals; and

5. Illustrate the inevitable economic disaster the enforcement of the

present and/or proposed regulations will have on mineral related

industries.

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With regard to Item 1, it is probably unnecessary to spend much time pointing out to

this audience the value of mineral products to the U.S. economy, but at times all of us forget how important these products are to our everyday life, and most of us are unaware

of the quantities we consume in our various work and leisure activities. Figure 1,

prepared by the Bureau of Mines, U.S. Department of the Interior, illustrates rather

graphically our dependence on materials derived from the mining and related industries.

Without detailing the extreme diversity of uses of the basic commodities, it is obvious

that the mining and mineral based industries are the very backbone of the economy of this

country.

At a time when our nation has finally become aware of the serious problems it faces

in the general overall economic situation and in the specific areas of energy and raw material supply, it seems very strange and unfortunate that a small but very vocal segment

of our population would insist on legislation that would directly increase the already

great burden on the industry responsible for both. This is particularly unfortunate since

the intent of the original and subsequent legislation regarding asbestos was to protect

workers from excessive exposures in industrial environments where these exposures have

been shown to pose a health hazard. No similar hazard has been shown to exist with

exposures to the mineral dusts associated with normal mining and mineral handling

industries now threatened. Secondly, the widespread geographic distribution of the various

segments of our industry has been adequately discussed by several previous speakers - Drs.

Zoltai, Ross, and Campbell in particular. To my knowledge, no state is without some form

of mining operation, although the type and concentration of mining activities vary greatly.

To illustrate the economic contribution, both in product value and jobs, and the distribution of activities, I have chosen three of the many critical segments of our industry -

iron mining (Table 1), copper mining (Table 2), and stone quarrying (Table 3). All the data

presented were obtained from U.S. Department of the Interior documents, principally the

Commodity Data Summaries 1977 [1]^.

Table 1. Iron mining industry (1976 estimate).

Mine Production - Ore 78 Mi 1 1 ion Tons

Value - Ore 1.8 Billion Dollars

No. of Major Companies

Major Mines

Concentration Plants

Pel leti zing Plants

86

60

44

20

Employment - Mine/Mill 20,500

Geographic Distribution

Minn., Mich., Calif., Utah, Wy. , Mo., Penn. , N.Y., Tex., Wise.

^Figures in brackets indicate the literature references at the end of this paper.

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ABOUT 40,000 POUNDS OF NEW MINERAL

MATERIALS ARE REQUIRED ANNUALLY

FOR EACH U.S, CITIZEN

8000 LBS

SANO AND CiRAVt L

660 LBS 450 LBS 430 LBS 1400 LBS

CtMENT CLAVS SALT OTHER

NONMETALS

1000 LBS

IRON AND STEEL

46 kBS

ALUMINUM

16 LBS

COPPER

14 LBS

/INC

11 LBS

LEAD

31 LBS OTHER

METALS

PLUS

7650 LBS 5200 LBS COAL 4200 LBS 1/7 LB URANIUM

PFTROLEUM NATURAL GAS

TO GENERATE:

ENERGY EQUIVALENT TO 30Q PERSONS WORKING AROUND THE CLOCK FOR EACH U S CITIZEN

U.S. TOTAL USE OF NEW MINERAL SUPPLIES IN 1975 WAS ABOUT

4 BILLION TONS i

BUREAU OF MINES

US DEPARTMENT OF THl INTERIOR

Figure 1. Mineral use in the USA.

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Table 2. Copper mining industry (1976 estimate).

Mine Production 1.6 Million Tons

Value 2.25 Billion Dollars

No. of Major Companies 15

No. of Major Mines 25

Employment - Mine/Mill 34,000

Geographic Distribution

Ariz., Utah, New Mexico, Mont., Mich., Nev. , Mo., Tenn.

Table 3. Stone quarrying industry (1976 estimate).

Crushed Stone

Production 888 Million Tons

Value 2.02 Billion Dollars

2000 Companies - 5400 Quarries - 49 States

Dimension Stone

Production 1.5 Million Tons

Value 104 Million Dollars

300 Companies - 460 Quarries - 43 States

Total Employment - Quarry/Mill 54,000

It should be emphasized that all data presented are for the mining and milling industries only and do not include the value added by the subsequent benef iciation and ultimate

fabrication and use of these materials. This added value, the number of dependent

industries with the required employment, and then geographic distribution dwarf the numbers

listed in these tables. For example, while the iron mining industry produced ore valued

at 1.8 billion dollars in 1976 and employed slightly over 20 thousand workers, the iron,

steel, and foundry industries had a combined output valued at an estimated 42 billion

dollars and employed nearly three quarters of a million workers.

Several previous speakers have thoroughly discussed the third point on my list, that

of the almost universal occurrence of those mineral groups of particular interest to this

workshop - the chain silicates (amphiboles and pyroxenes) and serpentines. These minerals

are present in varying but significant amounts in all three of the mining industry segments mentioned above, as they are in essentially every other mining operation in the

United States, and for that matter the world. I would estimate that the chain silicates

and serpentines make up about 15 percent of the earth's crust.

All of the geoscientists , and several others who have addressed this audience, have

made it very clear that the mineral species under discussion may occur in nature in both

non-asbestiform and asbestiform morphologies. They have also pointed out that the

asbestiform varieties are very rare relative to their normal non-asbestiform counterparts.

464
and in some cases, such as with tremolite and actinolite, the asbestiform varieties are

not available commercially and probably exist only in specimen quantities. The lack of

understanding of this fact has led to the confusion surrounding the use and misuse of the

term "asbestos." As I pointed out in an earlier article [2] the majority of the

regulatory agencies developed standards without making use of readily available

mineralogical expertise. With the publication of the OSHA Asbestos Standard in July 1972

[3], which listed six (6) minerals as being "asbestos" regardless of their morphology,

using the single criterion of aspect ratio (>3:1 length: width) for classification as "fibers" or "non-fibers," the die was cast for all these intervening years. OSHA wrote

its own mineralogical dictionary and most other agencies merely followed suit.

Professor Zoltai, speaking earlier in this workshop, most elegantly stated the need

"for an unambiguous, interdisciplinary language" in order that medical researchers,

regulatory personnel, analysts, and geoscientists can speak together and understand each

other. Drs. Zussman, Ross, and Campbell emphatically supported this need. It is my

opinion that it is absolutely necessary that the materials being investigated, whether

commercial, industrial, or environmental, be correctly defined and thoroughly characterized by geoscientists in order that medical researchers will know what they are testing

and evaluating. It is only then that we will know the nature of the mineral particulates

which constitute health hazards and be able to delineate the type and degree of such

hazards. It does make a difference!

The last and key* topic of my presentation is to shed some light on the economic

disaster in store for the mining industry if the present, let alone proposed, "asbestos"

regulations are enforced.

First of all, who is involved? Not just asbestos miners and millers, not just the

small operators (although they would undoubtedly be the first to be hurt), but essentially

every mining/milling operation, every taxpayer, every citizen.

At present, OSHA, EPA, and, in practice, MESA consider all mineral particles three

times longer than they are wide (3:1 aspect ratio) as "fibers" regardless of whether they

grew as fibers or were broken into cleavage or fracture fragments. They list six (6) minerals as being asbestos; chrysotile (a truly fibrous serpentine polymorph) and five

amphi boles: crocidolite, "Amosite," anthophyl 1 i te , tremol ite , and actinol ite . Of the

agencies mentioned, only MESA states in its regulation that the last three names (underlined) are used for both non-fibrous and fibrous forms and must be qualified by the

addition of the term asbestos; i.e., anthophyl 1 ite asbestos, etc. The others appear to

believe that all forms of these three are asbestos, the only difference being that when

they are not long silky fibers, but short stubby cleavage fragments, they become "noncommercial asbestos" [4], another term of convenience created by government bureaucrats.

These regulations, as pointed out by the chairman of this session, were proposed and

promulgated under intense public and political pressure in a panic situation without, I'm

sure, any intent or realization of the scope of the problems created by the inclusion of

mineralogical errors. The mining industry has been faulted because they failed to speak

to the issue at the time of the OSHA asbestos hearings in early 1972. Only the asbestos

segment of the industry was represented. The fact is that the rest of the mining industry

had no need for input at that time because they did not have asbestos in their ores or

products. It was only after an erroneous definition was promulgated that the industry

gradually became aware that what they knew to be common rock- forming minerals present in

essentially all mining operations had suddenly become "Government Asbestos .

Reaction to this problem has been slow in coming, basically because of the great

immediate pressure to pour vast amounts of time and money into complying with other

government regulations regarding air and water effluents, changes in equipment and

material handling procedures, etc. Another reason for a slow reaction, however, has been

the general belief that the regulatory agencies, once informed of their error, would

immediately seek proper mineralogical information and make the necessary corrections to

limit their regulations to deal with the known hazards of true asbestos. This action not

only hasn't taken place, but the agencies have continued to propose and/or promulgate

regulations aimed at both lowering the permissible level of "government asbestos" and

465
including more and more mineral particles which bear no resemblance to true asbestos, but

which meet the sole criteria for a fiber (three times longer than they are wide).

In the five years since the issuance of the OSHA Asbestos Standard we have seen the

permissible levels decrease from 5 fibers/cm^ to 2 fibers/cm^ to a proposed 0.5 fibers/cm^

and a recommended (NIOSH) 0.1 fibers/cm^. Philosophies on measurements are shifting from

expression as fiber numbers to weight of total fiber in nanograms/m^. This latter ex- pression could allow for over 90 percent of the total fiber weight to be accounted for by one "fiber". No company or industry can develop a program to improve working conditions

when faced with such constantly changing requirements. The zero level or lowest detectable

amount philosophy is totally impractical and impossible to achieve.

One clear and very disturbing fact stands out. A huge effort in time, energy, and

money has been expended in medical research, development of analytical equipment and

techniques, legislative efforts and interminable court battles, all before the material to

be studied, detected, quantified, and regulated has even been properly defined or characterized. The cart has been placed before the horse. This situation must be reversed

before an additional, and in many cases unbearable, burden is placed upon the backbone

industry of the U.S. economy.

My company, R. T. Vanderbilt Company, Inc., has experienced the results of this

confusion in "asbestos" definition and characterization. We are obviously not alone, but we have been directly or indirectly involved in two cases where "asbestos" citations were

issued by OSHA on preliminary findings. These citations were contested, and in both cases

all allegations regarding "asbestos" were dropped before trial when subsequent analytical

data failed to show sufficient evidence of a violation of the asbestos standard.

The overall economic impact of enforcement of the present asbestos regulations using

the present "asbestos" definitions covers such a broad range of mining/milling activities

that it would be impossible to even mention them all in the time or space allotted. I have chosen to illustrate the problem with the discussion of only one factor, which affects

the majority of all mining operations, the disposal of waste materials. All metal and

many non-metal mines are confronted with this task. In those cases of industrial mineral

operations where there are no tailings, since the total material mined becomes the product,

the impact of asbestos regulations becomes more complex and acute. In these instances

the mining companies and their customers often must comply with the requirements of OSHA,

FDA, CPSC, etc. , in addition to meeting the regulations of MESA and EPA.

In Table 4, I have selected a typical porphyry copper mining operation and only one of the many "asbestos" regulations governing it. This type of ore body is associated with

varying but significant quantities ('^'2-6%) of amphiboles, present as the normal non-fibrous

variety. Assuming a daily ore production of 60,000 tons containing 3 percent amphibole,

approximately 58,000 tons of waste containing 1800 tons/day of "government asbestos" would

be dumped as waste, most of it meeting the 3:1 aspect ratio, and therefore asbestos. Such

a mining operation normally has a 2:1 stripping ratio, thus 120,000 tons of overburden

containing (^-5 percent) 6000 tons of "government asbestos" is also blasted, moved, and

dumped every day, making a total of 7800 tons/day to be dealt with. The one regulation I referred to is the EPA regulation requiring all active mine dumps containing over one percent "asbestos" be covered by at least six inches of compacted non-asbestos containing

material at least once every 24 hours [5]. Assuming that it was possible to find soil,

pulverized rock, etc. which was free of "government asbestos," and assuming that the farmers

or environmentalist groups, etc. would allow it to be moved, it takes little imagination to

visualize the costs involved with digging, transporting, spreading, and compacting some 18,000 tons/day of this material. This is the estimated amount of cover needed for a waste

dump of 180,000 tons of tailings six feet deep covering 15 acres.

The hypothetical case presented in Table 4 for a copper mining operation will hold

true for most other metal and some non-metal mining activities by substitution of the

proper numbers. Remember that this case discusses only one factor in any mining operation

and only one regulation. The added costs of this one item alone would be prohibitive in

most cases, opening the door for our country's dependence on foreign sources for more and more of our raw materials.

466
Table 4. Copper mining - typical operation.

Material Handled

Ore Mined

2- 5% Amphiboles

Tailings Dumped

3- 6% Amphiboles

Overburden Moved

5% Amphiboles

60,000 Tons/Day

1 ,800 Tons/Day

58,000 Tons/Day

1 ,800 Tons/Day

120,000 Tons/Day

6,000 Tons/Day

TOTAL AMPHIBOLES 7,800 Tons/Day

Area of Dump (6' Depth)

Tai 1 i ngs

Overburden

5 Acres/Day

10 Acres/Day

TOTAL DUMP AREA 15 Acres/Day

Amount of Cover Required - "Asbestos" Free (6" Depth)

Tailings 5,000 Tons/Day

Overburden 10,000 Tons/Day

TOTAL COVER 15,000 Tons/Day

In order to remain viable and serve in its proper place in the U.S. economy, t

mining industry needs the following conditions with regard to "asbestos":

1. Correct mineral definitions developed by geoscienti sts

2. Adequate analytical methods and qualified analysts for thorough

characterizations and quantification of mineral particulates;

3. Medical data on the health effects of such well characterized

materials; and

4. Realistic exclusion levels for those materials which will afford

acceptable risk.

References

[1] Commodity Data Summaries - 1977, Bureau of Mines, U. S. Department of the Interior.

[2] Thompson, C. S. , Asbestos In Your Future, Mining Congress Journal , 62 , (12) (Decemb

1976).

[3] Federal Register 37 F.R. 11320-11322 July 7, 1972.

[4] Federal Register 40 F.R. 47652-47665 October 9, 1975.

[5] Federal Register 40 F.R. 48292-48302 October 14, 1975.

Discussion

NOTE: Discussion of this paper was included in the General Discussion at the end of this

session.

467

National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20,

1977. (Issued November 1978)

GENERAL DISCUSSION OF REGULATORY ASPECTS

A. WYLIE: I had some comments on the use of the petrographic microscope for distinguishing asbestos. Mr. Dixon gave an eloguent presentation on the many different tests

that could be made to describe mineral particles, but no reference was made to the unigue

optical properties that asbestos has. I've examined many samples of different kinds of

asbestos from many localities and they have a characteristic parallel extinction. This is

not found in the textbook by Kerr on Optical Properties of Minerals; it is alluded to in

Deer, Howie, and.Zussman for crocidolite; it is not well described in the literature, but

true asbestos, true amphibole asbestos has parallel extinction and, in its optical

properties in large size samples (I don't mean air samples or water samples, but samples

you can get a little data on) it does not resemble ordinary amphiboles. This criteria

has never been mentioned and I think people who are involved in amphibole characterization

should be aware of it. I am not referring to anthophyl 1 ite asbestos. I am referring to

the monoclinic amphiboles that have characteristic parallel extinctions in all

orientations. It is not an orientation problem. You can take these fibers, tap them

over, they roll around; you can see that the parallel extinction is maintained. This is

not just my observation. You'll find it scattered in the literature, and I've spoken to

several other optical microscopists here who have done similar work and I think that you

should be aware of this in your characterization.

W. DIXON: Crysotile also has the nearly parallel extinction.

WILEY: Yes, but I am talking about the monoclinic amphiboles, crocidolite, amosite

(which, by the way, is really both grunerite and actinolite as it is commercially mined),

actinolite asbestos, and some forms of tremolite asbestos. These are monoclinic

amphiboles which, according to the textbooks, should have inclined extinction, but do not

when they have a true asbestiform habit.

DIXON: What would happen then is that a mineral which is thought to be anthophyl 1 ite

might actually be tremolite in that kind of an error situation.

L. SWENT: I'd like to comment a bit on a factor that was mentioned at the beginning

of this Workshop, but has not received much discussion since, although Aurel Goodwin may

have been referring to it without naming it.

In the study of biologic effects we must at all times remember the additive effects

of asbestos fibers and tobacco smoke on the individuals being studied.

Virtually all studies in which smoking habits have been taken into account show that

the biologic effect of asbestos fibers on non-smoking individuals is markedly less than on smokers, and that the elevation of health risk for the non-smokers is small.

Regulatory agencies are faced with a choice between two philosophies in generating

regulations and permissible limits of exposure to fibers. These two philosophies are:

1. Set the permissible levels of exposure to fibers so that such exposure is

safe for non-smokers.

2. Set the permissible levels of exposure to fibers so that such exposure is

safe for smokers.

The first philosophy is a much easier one to regulate and administer, and the

individual is left to decide whether not to take on the risks of smoking.

The second philosophy presents many complex problems. It in essence reguires the

regulators and industry to take responsibl i 1 ity for most of the problems and risks arising

from smoking. The cost of doing this, in the long run, will be passed on to the public.

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This cost will be very great and will be very inflationary, especially if non-asbestos

fibers are regulated.

I urge the regulatory agencies to consider seriously the merits, demerits, and equity

of each of these two philosophies and to choose the philosophy of basing permissible

exposures on the biologic effects in non-smokers.

Educational campaigns, health risk notices, anti-smoking campaigns, etc., should be

the tools used to combat the effects of smoking.

I. STEWART: Phil McGrath made some comments about the scanning electron microscope

and some of the conclusions that were derived at the Penn State meeting. Proceedings of

this meeting are available, and I suggest that if you were not present you should get this

and perhaps get a more objective feeling of what the consensus of the participants was.

In connection with the size of the fibers on the SEM and TEM, the large fiber he showed

was, based on his pore size of 0.4 pm, approximately 0.1 to 0.2 pm wide, which would have

made it maybe 50 to 100 pm long. Dr. Asher referred to the materials shed from filters

showing a maximum diameter of 0.25 pm and maximum length of about 70 pm, and these

measurements were obtained with the transmission electron microscope. Yes, it (i.e. the

TEM) can handle large material.

P. McGRATH: This was also confirmed using the scanning electron microscope.

STEWART: I don't know what work you did, I'm sorry..

McGRATH: One of these fibers measured 70 nanometers in diameter. This is an evolutionary process; for example, at the Penn State Conference last year, Don Beaman felt more

sure of his ability to identify chrysotile asbestos fibers than he reported at this

conference the other day.

STEWART: At this time I think you should be fair and say that there has been a decrease in confidence as well in the energy dispersive systems...! think...

McGRATH: I think the resolution of the SEM-EDXA system is increasing. I don't

believe any system in operation today will give us all the information we need and it is

necessary to develop the SEM-EDXA system - not just stay with TEM-SAED, which is

essentially the same system we have been using for ten years. I think that many

transmission electron microscopists who don't routinely do scanning electron microscopy

have a tendency to ignore the dramatic changes in scanning electron microscopy. We

routinely identify particulates, including asbestos. Although we can't always completely

characterize them, we realize enough information to make decisions relative to these

products.

STEWART: You have run nicely into my next comment which was on the nationwide survey

on water, which we did. The feature which was evident in asbestos from natural sources was that this tended to be unit fibers, approximately 300 ^ in diameter. This was also

the sort of size range that we are seeing in ambient air. I'm not talking about material

from point sources now. Three to four miles down stream from a point source it is already

breaking up to the two or three unit fibril level, and the identification of this, I think, cannot be confidently handled with an energy dispersive system. Now I don't want

to go into the whole argument, but you and I do this on a friendly basis every year as you

say (at least I hope it is still friendly).

But I would refer people to the review paper that was done by Clay Ruud, which

appeared in Micron and was very similar to what he gave at Penn State. Also the work that

Rick Lee presented at Penn State on the energy dispersive systems and on the possibilities

of error, purely and simply, on the complex chemistry of these materials.

McGRATH: We have to be pragmatic about this. Using TEM-SAED you cannot routinely do

any kind of regulatory or survey work because of the cost and problems of sample

preparation. Don Beaman said it cost about $1200 per sample to do a complete analysis.

He also said he could only do about five samples per week in his laboratory.

d7n
STEWART: Well that figure on his TEM is substantially higher than we charge, and it

is also twice the price of some work done on a SEM I heard someone quote, which is again

substantially higher than the figure we charge. I am not going to be commercial and say

the figure we charge, but I don't think that that $1200 figure is realistic.

McGRATH: There is a recent EPA report by the Aerospace Corporation comparing TEM and

SEM analysis of commercial asbestos fibers. They reported both methods were essentially

equal in surveying a population of fibers but that the SEM costs were much less than the

cost per TEM analysis.

STEWART: If you were to use the commercial asbestos fibers so you have a standard

where you know what you are dealing with, or if you can come up with a technique which

will indeed separate the asbestos and ensure that you have only asbestos mineral fibers

there, then I will grant you that the SEM could be used as a screening tool. It could

indicate fibers that could be asbestos, but I do not think you can positively identify

them on the SEM.

McGRATH: We also heard Fisher and Lee report to this conference using a beautiful

method to index SAED patterns, but that is a research tool, not a method for routine

analysis.

D. SARVATTI: I have one comment in relation to the occupational health standard.

Those of you mineralogists and analysts who have been insisting that hygienists and

medical people like myself should change our approach in evaluating occupational exposures

on the basis of this aspect ratio, I should caution you with one very important point:

That analytical technique which we currently use is related to the incidence of disease.

If you change the parameters of analysis you may change that relationship and find yourselves with a lower standard. So think about that before you decide on a 10 to 1 or a 5 to 1 or 100 to 1 or a 1 to 1 aspect ratio. It doesn't matter what that aspect ratio is,

just so that everybody is using the same one and that there is some relationship to the

disease incidence we are trying to prevent. Question for anyone from the Bureau of

Standards: I've heard no comments these three days about the NBS report that was requested by OSHA and published in April of this year, and I would like someone from NBS

to tell me why they did that study the way they did, especially in light of all the

information that we have had here these last three days?

K. HEINRICH: In the first place it would have been difficult for us to put in the

report the information we have gotten in the last three days. On the other side I don't

know quite what you are referring to with respect to this report, but this was a report

an agency asked us to do, and we did it the way we understood the request.

C. GRAVATT: If I may clarify that a bit, the request asked us to perform an analysis

according to the procedures and methods specified in the Federal Register. Whether we

liked it, or you liked it or not, that locked us into phase contrast microscopy, by legal

regulation. If NBS had been asked to measure the eighty samples by anyway it wanted to, we probably would have never done it completely by phase contrast microscopy. However,

NBS had to do it that way to respond to the request. The NBS report did not imply that

OSHA only uses that one method and technique. They use a number of techniques as specified in the presentation here today by Dixon, which provide them with further

information. However, by just the nature of the request, we had to do it the way we did.

SARVATTI: The report, as it stands today, now causes OSHA at least to consider

encompassing a number of other minerals under the definition of asbestos, and this is what

is so disturbing to those of us who have to deal with this kind of mixture of compounds,

and mixture of minerals in the industrial setting. My impression of what Dr. Corn

requested the National Bureau of Standards to do (I read that entire report from cover to cover about seven times and I still don't understand it) was to determine whether or not

certain industrial talcs currently in use today contain commercial asbestos, one of the

six minerals that are defined in the Federal Register. Now it seems to me to do that you

have to follow some of the procedures that Mr. Dixon described before you do any kind of

fiber count. One of the things that get lost in this whole discussion was brought out by

Mr. Dixon. If an industrial hygienist goes out to take an air sample, the sampling method

that you use depends on what is there in the factory to begin with. You don't go out and

471
sample mica using the asbestos sampling technique. Before you go out and take an air

sample you determine whether or not one of the six minerals that is included in the

asbestos regulation is present and then you take an air sample and you make the assumption

that whatever is present in the air is asbestos, and make the particle count accordingly,

and then set up your control parameters. But it's just disturbing to me to find reports

of fibrous material in a variety of minerals, which people here have been telling us, well

yes, maybe it's present, maybe it's not. It's all in how you define a fiber to tell

whether or not it is present.

DIXON: We specify in our writeup of the method that any fiber which is known to occur in the environment in which asbestos is used is considered to be asbestos in the

absence of other information. The method or technique of getting this other information

is left as an open question for people to use the best scientific method they can find to

find out what those other fibers are.

A. LANGER: Mr. Chairman, I agree with the thrust of Dr. Thompson's presentation. I think that he is quite correct in suggesting that we may be dealing with different

substances which may have different biological activities. This concept is more than just

recognized in the United Kingdom where they have two different asbestos standards: One is

for crocidolite, which is 0.2 fiber per mL; and one for the other asbestos fibers at 2.0

fibers per ml. So there are workers who support the position that fibers possess a range

of properties and subsequent biological potential.

Mr. Swents remarked that smokers have much greater lung cancer risk. That is

absolutely correct. There is a synergism between cigarette smoking and asbestos fiber

inhalation, now well documented in a number of studies, demonstrating the potency of such

combinations in inducing lung cancer. Perhaps the mining industry itself could contribute

to the health and protection of their workers if they were to insist that they don't

smoke. That would mean that even if these particles were as potent as asbestos you would

decrease the associated excess cancer risks by almost one half.

M. BROWNSTEIN: For users of the refractive index (RI) oils who aren't totally aware of

their composition, a word of caution is in order. In the past they certainly have been

formulated using PCB's (polychlorinatedbiphenols). From various studies it has been

observed that these materials are carcinogenic in animals; they cause birth defects in

animals, and further that they are absorbable through the skin. Now in time, as the

products are reformulated and PCB RI oils disappear from your stock and your shelves, this

problem will go away. In the meantime a caution for those who aren't aware of this;

caution should be exercised in handling these materials, and also in disposal. In time,

with the prohibitions that are coming in on PCB use, say for example in Canada (I'm not

familiar with the American regulations), this problem is going to go away. But for now if

you have oils and are using them, you should watch how you are doing it.

DIXON: Would you care to comment on the volatility of these dispersion oils, how

much is getting into the air?

BROWNSTEIN: I'm not familiar with this aspect, but I presume they have quite low

volatility. One of the greater problems would presumably be handling, if you get it on your hands. A year or two ago, this would have been a much greater problem in that some of the microscope immersion oils were formulated with PCB's, which would be used by lab

tech's in large scale. I know in Canada this type of usage of PCB's has been banded. I believe most of the manufacturers are reformulating or have reformulated so it shouldn't

be a problem in the future. It is a question of getting it on your hands and absorbing it

through the skin.

J. MARTONIK: Is there a trace of vinylchloride monomer in the PCB?

BROWNSTEIN: No polychlorinatedbiphenols themselves. Depending on which refractive

index you have, some of them have been up to 100 percent PCB. It isn't a trace

contaminant.

472
J. MACLEAR: I'd like to add a little bit to the discussion of methodology for

asbestos analysis and to ask that people from EPA (Dr. Anderson) and at OSHA (Mr. Dixon)

and the FDA consider the possibility that it might be best to keep the options open as far

as techniques are concerned rather than adopting a standard technique for the following

reasons. I understand that Chuck Wright at Penn State, at our laboratory, and Dr. Fisher

of U. S. Steel, are all in the process of developing automated methods which could lead to

asbestos analysis using an image analysis computer system which also detects the x-ray

information at the same time and uses this information to distinguish particles not only

by size and shape but by chemical composition as well. Whereas this hasn't been applied

yet extensively to asbestos, there are several groups that I know of who are working

toward this. It is not a matter of hardware but a matter of software now, getting the

right programs in and getting them working right. To eliminate the scanning electron

microscope, for example from the EPA, regulation would eliminate basically the application

of a technology which may promise to gather data about a thousand times more efficiently

than we can presently do it. I think this could make an enormous contribution both to the

accuracy and to the surveying capability of a very complex analytical problem.

N. TATE: I'd like to comment on the reference to LANCET article on talc. That

article says that, with the specification now agreed, talc will present no health hazard

in the future. I would like to say that this is the British way of handling these things:

introduce measures to deal with a hazard, while denying that the hazard ever existed.

Following the DONIACH study published in 1975 which showed asbestos bodies in the

lungs of women dying of breast cancer, we have been asking questions about talc.

There undoubtedly have been fibers in talc in the UK during the last year. I am delighted to hear that they are now saying in the future we will be protected by the use of this specification.

I would like to make a few other comments. Firstly, one of our biggest

pharmaceutical companies is now producing a non-asbestos filter for home brewing, which

should set people's minds at rest on the use of filters. After all, if you are worried,

it is better to use something that you feel is safe.

Secondly, when you have made your regulation, will you look at enforcement, because

this has been our biggest problem area at home. At the recent public evidence hearings

held by our Government Advisory Committee on asbestos, our biggest company, Turner and

Newall , presented data which showed that for only 58 out of a work force of 2000 could

they guarantee that exposure had been to only the official limit of 2 fibers a cubic

centimeter. For the rest of their workers they could not claim that they had kept within

the regulations.

Other companies are not using asbestos now. Our CEGB won't use it; the Post Office

won't use it; British Rail won't use it. When they are dealing with existing asbestos,

workers are demanding and getting, in those industries, a better level. For existing

asbestos, the Post Office works to 0.2 fibers a cubic centimeter; British Rail, when

stripping blue asbestos from our passenger carriages, is working to 0.05 fibers cc. If

they can do it, so can other people.

However, the biggest step we are taking is to train safety representatives amongst

workers. I even heard recently that the Post Office, which put out delagging work to

contract and is bound to take the lowest estimate, found that two men with little hammers

went to do the work, without any protective equipment. It was only a Post Office worker,

on that site, who recognized the danger and was able to save his colleagues from exposure.

Now, if we are going to train safety representatives, then please give us monitoring

equipment that they can use. You have produced the technology to get us to the moon; find

us simple monitoring equipment which will give men peace of mind when they are using

asbestos.

Many of them don't want to cause unemployment by banning it, but they want to know

that they are not taking a cancer risk home to their families if they use it.

473
E. NORTON: I'm a reporter for the Syracuse Post Standard, but I've been here for

these three days on vacation as an observer because I need to learn as much as I possibly

can as a reporter in the area where talc is mined and has been under question. I am responsible for trying to explain to the miners and to the people of my area, which is

very economically depressed, why one of our finest, most modern industries, employing the

latest dust pollution controls is losing its competitive position on the American market,

because of OSHA regulations of it. I'm trying to explain why it is subjected to a barrage

of press attacks based on quotes from government officials in Washington; why this talc

product and this talc only has been singled out by OSHA and other environmental health

agencies at the federal level for regulating rules that were designed to protect us from

asbestos. Our miners know that their mining product is not sold at asbestos prices. I found no mineralogist or geologists in the universities in my area or at this gathering

who would include non-asbesti form tremolite, actinolite, or anthophyl 1 ite under a list of

asbestos minerals headed by chrysotile. But OSHA has done it for five years and has based

regulations and industrial enforcement on that definition and on the size and shape

definition. Mr. John Dement of NIOSH characterized that size and shape 3 to 1 aspect

ratio as an arbitrary figure yesterday. I heard an expert from the Colorado School of

Mines and others say that asbestos tremolite is a rarity and asbestos actinolite is almost

nonexistent. On the other hand, I heard John Dement say yesterday that five percent of

the talc in the United States is contaminated with asbestos. I've heard numerous references to a study of chrysotile and the other three asbestos minerals, but apparently

there are none except a Klinefelt study on these three non-asbestos minerals. Klinefelt

has been used on both sides to prove whatever anybody seems to want to prove. So I find

it inclusive. A question from the representative of the Department of Labor yesterday

asked for the toxic quality of talc and there was no one who answered him. Pneumoconiosis

has been a problem in northern New York mines, and our talc mines for 100 years. We have

three doctors in the area who feel that cancer is not a problem and never has been a problem, who have noticed the phenomena that no new cases of pneumoconiosis are being seen coming out of employees who are employed only in our Governor Talc Mine and have never

been employed in the older ones of the area. This is a phenomena; maybe it's not based on studies. Because of all of these contradictions and for the sake of the 180 miners who

work in my area and who read my writing, for the economic health of our community which

receives annually an estimated six million dollars through this company in salaries and

goods purchased, and also gives us a great deal of money for our tax base to help educate

our childern and for the survival of this industry, I feel that the National Bureau of

Standards should be commended for this effort to bring some intellectual integrity into

the situation. I ask that those present support the National Bureau of Standards in its

efforts to make a two year study to really get into this business of identification, and I ask that until this study is completed or until the definitive medical studies show the

hazard of tremolite talc, specifically, that there be a moratorium on what they are doing

to our talc mines.

MARTONIK: Are there any comments on that statement?

NORTON: I'd appreciate any comments.

MARTONIK: Thank you, I don't know if Ray McClure of the Health Compliance Programming

is in the audience; he might want to make a comment.

R. McCLURE: I don't know what comment I can make to the last participant. I would

like to say something quickly though about medical examinations for asbestos. That is a part of our regulations and other people have asked questions about that. Our present

policy is under review by the Assistant Secretary. The present policy is that a medical exam starts at a tenth of fiber per cc. Another way of stating a tenth of fiber per cc is

a hundred thousand fibers per cubic meter, the fibers being longer than 5 pm as checked by

phase contrast microscopy. These are fibers generated or released at the work place, of

greater than 3 to 1 length to width ratio. In a recent District Court case (GAF Company

versus the Occupational Safety and Health Review Commission), the court upheld the Review

Commission decision of any exposure as a beginning point for medical exams. I do not know

if GAF has or will appeal this case. In my opinion, background asbestos levels not

released, or generated, due to the work place should be subtracted from sampling data.

This opinion is not accepted by all those concerned in OSHA. There may be a background

problem due to outdoor ambient air levels of asbestos, in some cases. In my opinion,

474
periodic chest x-rays of exposed workers does not constitute an unnecessary risk to the

worker.

MARTONIK: I want to add one more thing. Since I have been employed by OSHA for the

last 18 months, the Agency has in no way gone out to seek a certain company, to single out

that particular company, and enforce its regulatory authority. The agency does seek high

risk industries in general, and perhaps may exert some effort out of the ordinary where it

is deemed that this industry is associated with high risks. But we have not gone into any

one of those industries for the last 18 months and chosen a particular company or companies that should be inspected or would be inspected.

P. DeNEE: I have a comment and a question. A comment on Phil McGrath's paper: You

mentioned that asbestos and other fibers are more difficult to "see" in the SEM if they

are on membrane filters such as those made by Millipore or Gelman and that they should be

put on Nuclepore-type filters in order to be seen. I disagree with that conclusion. In

the paper that I presented yesterday, I showed how to "see" asbestos fibers on a fibrous

type filter in the SEM by using the Backscattered Electron Imaging. The only requirement

is that the sample be carbon coated rather than heavy metal coated to prevent specimen

charging. (See Philip B. DeNee, "The use of Backscattered Electron Imaging in the Scanning

Electron Microscope for the Detection of Microfibers in Airborne Dust Samples and

Biological Tissue," published in Proceedings of the First FDA Office of Science Summer

Symposium, the Symposium on Electron Microscopy of Microfibers, Penn State University, Aug.

23-25, 1976, U. S. Govt. Printing Office, Washington, D. C. , Stock No. - 01701200244-7.

Presented at NBS Workshop but not reported in these Proceedings.)

There seems to be some confusion on backscattered electron imaging. Up to a year or

so ago, backscattered electron detectors were not really that available for scanning

electron microscopes, but they are now available as an accessory. They are at the same state-of-the-art as energy dispersive x-ray detectors were a few years ago since they are just beginning to be put on scanning microscopes. There is one company that I know of,

ORTEC, which is making them commercially, and I think they will be available from other

companies in the future. Professor White at Penn State, and Dr. Rich Lee of U. S. Steel

have also used backscattered electron detectors for detecting particles. Backscattered

Electron Imaging is an important way of "seeing" the fibers against a background; a nice

way to pick them out.

The question I have is for S. Thompson and Dr. A. Goodwin. Are there engineering

methods available for reducing the number of asbestos fibers seen in the mining and

processing industry? Since the Coal Mining Industry has been able to reduce their dust

levels, there should be technology applicable to the non-coal mining and processing

industries as wel 1

S. THOMPSON: There is no question that there are dust collectors and many mechanisms

to reduce the dust under any conditions or circumstances. Many of them are in fact used

in all mines and used to a great extent. I'm pointing out that the economics of this can,

in order to get to the dust levels that have been suggested by many people who are following the continued zero type level approach, make it really impractical and

impossible to engineer toward them. The mining industry is constantly working on the dust

problem and I know that MESA reports are constantly coming out on reductions in dust

control, and the improvements that have been made under their jurisdictions and their

guidance. I think the mining industry is continually trying to do a better job on it. It

gets a little difficult when you try and translate or transfer realistic occupational

levels, from the controllable indoor processing plant, to the great outdoors. The mills

are somewhat easier than the great open pits, where you are at the mercy of nature. But

we are trying, and we spray and wet drill , so this is good.

GOODWIN: I really don't have much to add to what he says. We have not had real

difficulty with mine operators, and commerical asbestos producers getting in compliance

with fine fiber regulation which we have today. Many of them, probably most of them,

actually are anticipating reduction to two fibers and are already to date on that level.

As Slim indicated in his presentation, these asbestos producers are not nearly as large as the copper mine operations. If you want to talk about feasibility to handle asbestos at

very low levels, you can get things like glove boxes and that sort of stuff, and you start

475
escalating the cost of the material. I can't imagine how to operate a copper mine of

sixty thousand tons a day or anything like that where you can bring a railroad car full of ore and dump it; how do you put a dust collector on that? Now there are things you can

do; you can isolate the individual who might have to be there and air condition his

cubical or whatever, that sort of thing, and that's done. The feasibility of getting

whatever level you want depends upon the level.

P. TAYLOR: I'd like to direct my question to Willard Dixon. Would you care to

comment on something in the light field optical method? Would you comment on the very

poor background or very poor clearing properties of the Millipore filter?

DIXON: The Millipore membranes lately have been a lot poorer in quality than they were several years ago. The Millipore Corporation is aware of this problem, and OSHA has

taken the step of reviewing batches of membranes which are going to be purchased before

purchase. I might make the additional comment that the Gelman Corporation has developed a membrane which clarifies just as well as the Millipore membrane does, with, I think, very

few fibers in it, and we are in the process of evaluating the Gelman membrane for use in

addition to the Millipore membrane. The best thing that you can do when you get a membrane that has this kind of background is to look at the membrane structures very

carefully to make sure that you are not counting membrane structures rather than fibers in

this type of situation. When we encounter this we inform the industrial hygienist that

this has occurred and warn them not to use that particular batch of membranes another

time. I've sent out a field memorandum requesting that all membranes coming in for

analysis in the future shall have the lot number of the membrane with the analysis sheet

so we can identify those bad batches of membranes which are in circulation.

TAYLOR: We have done extensive studies on the filters themselves and we have found

that even that within the same lot number you will have bad filters and good filters. I have sent quite a few samples back to Millipore showing them blown up pictures of these,

and actually sent along the samples of the filters themselves and we have gotten no comment back from the company. I will say that we have looked at the Gelman' s and they

are not any better.

DIXON: What I am hoping is that by getting a competition going between the two

companies, that we can get some benefit from the competition. Hopefully one of them is

going to be able to produce a superior quality membrane to what we have been getting in

the recent past.

TAYLOR: My feeling is that if you are going to go exclusively to the optical system

that you are talking about, you are going to have to have very experienced people looking

at these and counting these fibers. If you take a small company that might be doing this

and using a person that doesn't count frequently, they will not be able to distinguish a fiber from what we call a ghost fading in and out of this filter background. I think you

will have all kinds of serious problems. We are very unhappy with the method.

DIXON: This not only can happen, I've seen it happen with inexperienced counters

just starting out to count asbestos fibers. When they get this kind of a membrane, they

may be counting membrane structures rather than counting fibers, so it's a situation that

has to be watched very closely.

STEWART: May I just ask one quick question on the same thing? There was a Dr. Torem

of Millipore technical services at this meeting earlier. Is he here to comment on this?

R. THOMPSON: Mr. Smyrloglou is here from Millipore too. I have spent eight years

getting a competitive situation with glass fiber filters. Lots of luck.

J. WARREN: The results of these three days and our firm's recent completion of a study of asbestos in the construction industry leads me to make the suggestion that this

conference is the first step. We really need some type of interagency committee on asbestos, however you want to define "asbestos," let's use the term asbestos. Asbestos

needs more than just a microscopic approach, you need a wholistic approach; when I use the

term macroscopic, you can't just look at the simple approach.

476
The way this can be done is by agencies getting together. You can talk to people in

industry, and this is one of the things usually brought up. This agency says one thing and

OSHA comes in and says this: Well, we have to deal with MESA over here and then low and

behold the FTC is looking at our product on the shelf. This is why I think some type of

interagency approach might be needed with asbestos and I would suggest very quickly that

it: 1) come up with some type of formal definitions that everyone can agree on (we have

talked around this, but we have not resolved this in these three days); 2) standardize

methodology for different material, whether it is in food, cosmetic talc, or ambient air,

for water, or occupational exposure; and 3) review the current state of research, particularly vis-a-vis health effects. These are very difficult studies that Art Langer could

tell us about. They require an enormous amount of money. They are not something you can

run off in 6 months, tell me what the incidence of cancer was, and what people were exposed

to a certain type of asbestos. It is not that easy, and I think that this type of interagency group could come up with some kind of a protocol list of priorities where we need

further research. To my knowledge this has not been done, and we looked for this kind of

thing when we got into business and it was not there.

I would think that the research should focus on particularly epidemiological evidence

of mesothelioma. I think this is really the clincher. This is what I feel like is

pushing NIOSH to lower and lower limits. We come up with the data of this very insidious

cancer; it appears to occur in people who have very low non-occupational exposure and it scares people. For better or worse they are scared; and Rockville, Maryland is a good

example of this. Whether it's rational or not they get scared and they get very

emotional. I think this is something that's got to be dealt with. You cannot say: well,

those are people; they do not know what they are talking about; that's just the public.

You have to deal with them. It's political whether you want it that way or not; it is a fact of life.

I think the interagency group should suggest where we need research, the gentlemen on the stage and other people have suggested areas, but let's get this down in black and

white. Here are the fifteen key things we need to do in asbestos and here is why we need

to do them, and who is going to pay for it and why.

Finally, I think this group could also put in a good plug for the needed cooperation

between these agencies. Gentlemen, it has not been said, but this has not occurred in the

past. That is just the long and short of it, and if we are ignoring it we are not facing

reality. There has not been cooperation particularly between the regulatory agencies

arrayed here, OSHA, MESA, EPA, FDA, CPSC. Then you have NIEHS and NIOSH, and sometimes

the left hand does not know what the right hand is doing and we are talking about

something that kills people. So I am making a very strong plea for an interagency task

force, and I think we have got the people in this room that could put it together.

Thank you.

J. LEINEWEBER: I would like to comment on the remarks that were just made. There

are selected industry groups that have addressed themselves to the needs for research and

other work in these areas. For example, the Asbestos Cement Pipe Industry has had

workshops very similar to this (perhaps on a smaller scale) to consider the needs of their

particular industry associated with asbestos fiber and water. The Thermal Insulation

Manufacturer's Association is conducting studies on so called man-made mineral fibers and

their biological effects. Industry itself is doing this. If there are government

agencies that wish to do this, these agencies should also include industry in these types

of studies. I would suggest that in studying problems of this type we forget the word

asbestos for a while. Let's talk about biologically active fibers. Let's move away from

"Is this asbestos or is it not?" Let's ask "Is it a biologically active fiber?"

BROWNSTEIN: Dragging Art Langer back into this, I would like to second the comment

he made a bit earlier. I am surprised that no one has really taken this up during the

conference, well, not surprised a lot, regarding smoking and the allowance of smoking by

workers. It has been agreed here that it seems that asbestos is a disease that is doseresponse related and we are looking at lower and lower standards to increase the protection.

Equally, a greater protection, it seems, could be achieved by the controlling of smoking.

For example, a total ban of smoking within the parimeter of the work environment, in the

477
plant perhaps; in the mine site. I am surprised that this is not taken up and looked on

as an alternative for the very large capital cost that the industry is so concerned about.

They can achieve similar degrees of protection by other means.

NOTE: The following was a note sent following the meeting and was not part of the verbal

discussions at the end of the session.

ZUSSMAN: Although a lot has been said about the difference between real asbestos and

the non-asbestos varieties of amphibole and serpentine, I would like to make two further

points on this theme, because I was amazed at the continued lack of distinction between the

two kinds of material shown in some of this afternoon's papers, both in the use of the

word asbestos and in the proposed regulatory procedures.

It has been shown that commercial asbestos can have serious biological effects, but

there is little or no evidence that the non-asbestos varieties of amphiboles and serpentines

have the same effects. Dr. Goodwin of MESA indicated that in order to know what limits to

set for occupational and non-occupational exposure to commercial asbestos you need to know

the risk factor. Surely the same applies to the non-asbestos forms of amphibole and

serpentine. Do we know the risk factor for these? Should it be assumed the same and the

limits the same as for asbestos, with our present knowledge?

One speaker from the floor mentioned the general public's acute concern about asbestos

and the fact that it was a highly emotional subject. In view of this, it seems unwise, to

say the least, to use the word asbestos and an ore deposit indiscriminately, and perhaps

only three years later to say, well - the material isn't really asbestos after all. If it were just a matter of semantics it would not matter so much, but it is precisely because

of the now heavy emotional content of the word asbestos that I think much more discrimination should be exercised in its use.

478
LIST OF ATTENDEES

Frederick R. Allen

N.C. Aggregates Association

P. 0. Box 30603

Raleigh, NC 27612

Francis M. Alpiser

Environmental Protection Agency

Region III

Curtis Building, 6th & Walnut

Philadelphia, PA 19106

William Anderl

Minnesota Pollution Control Agency

Division of Water Quality

Roseville, MN 55113

Charles H. Anderson

Athens ERL

Environmental Protection Agency

College Station Road

Athens, GA 30601

Sandra Anderson

Battel le, Columbus Laboratories

505 King Avenue

Columbus, OH 43201

Irvin Asher

Office of Science

Food and Drug Administration

8800 Rockville Pike

Bethesda, MD 20014

William H. Ashton

Johnson & Johnson

U.S. Rt. 202

Raritan, NJ 08869

Steven Aust

Bureau of Air Quality

201 W. Preston Street

O'Conor Building

Baltimore, MD 21201

Russell W. Ayres

Read, Smith, Shaw and McClay

747 Union Trust Building

Pittsburgh, PA 15230

James H. Baird

W. R. Grace & Company

7379 Route 32

Columbia, MD 21044

William G. Banfield

National Cancer Institute

9000 Rockville Pike

Building 10, Rm. 8B19

Bethesda, MD 20014

Walter Bank

Mining Enforcement & Safety Admin.

Denver Technical Support Center

P. 0. Box 25367, DFC

Denver, CO 80225

Virgil J. Barczak

Kerr-McGee Corporation

Technical Center

P. 0. Box 25861

Oklahoma City, OK 73125

Kenneth Barry

BNA - Occupational Safety and

Health Reporter

1231 - 25th St., NW

Washington, DC 20037

Ian Bartky

Institute for Materials Research

National Bureau of Standards

Washington, DC 20234

D. R. Beaman

Dow Chemical Company

574 Building

Midland, MI 48640

William E. Bell

Division of Resource Protection

Montgomery County Department of

Environmental Protection

6110 Executive Boulevard, Room 340

Rockville, MD 20852

Ed Berg

EMSL

Quality Assurance Branch

Cincinnati, OH 45268

Roy Bernard

MESA

309 Shadeswood Drive

Birmingham, AL 35226

J. Bignon

Universite Paris - Val de Marne

Centre Hospital ier Intercommunal

40 Avenue de Verdun

94010 Creteil

FRANCE

Kyle Bishop

Minnesota Department of Health

717 Deleware Street SE

Minneapolis, MN 55440

479
Rolland L. Blake

U.S. Bureau of Mines

Metallurgy Research Center

Twin Cities, MN 55111

R. L. Bleifuss

U.S. Steel Corporation

Research Laboratory

Coleraine, MN 55722

Hal Bohmer

PPG Industries, Inc.

P. 0. Box 31

Barberton, OH 44203

Krell Bosler

Spartek Inc.

1375 Raff Road, SW

Canton, OH 44711

Fred M. Bowers

FMC Corp.

P. 0. Box 8

Princeton, NJ 08540

Kenneth W. Boyer

HFF-147

Food & Drug Administration

200 C Street, SW

Washington, DC 20204

Joseph Breen

Environmental Protection Agency

Office of Toxic Substances

401 M Street, SW

Washington, DC 20460

John A. Breslin

U.S. Bureau of Mines

2401 E Street, NW

Washington, DC 20241

Philip D. Brick

Pickands Mather & Company

811 Sellwood Building

Duluth, MN 55803

Alan T. Broderick

Inland Steel Mining Company

1701 North Ninth Avenue

Virginia, MN 55792

Harlan Browning

Alpha Portland Cement Company

Alpha Building

Easton, PA 18042

Morley Brownstein

Consumer & Corporate Affairs

Product Safety Branch

Ottawa, Ontario KIA 0C9

CANADA

Leonard Bruckman

Department of Environmental Protection

Air Compliance

State Office Building

165 Capitol Avenue

Hartford, CT 06115

Merle Bundy

U.S. Steel Corporation

600 Grant St.

Pittsburgh, PA 15230

Edmund M. Buras, Jr.

| Harris Research Laboratories ij Gillette Research Institute \

1413 Research Boulevard

Rockville, MD 20850

M. Raymond Buyce

N. Y. Geological Survey

Education Building Annex

Albany, NY 12186

Peter Buynok

Naval Facilities Engineering

Command

Alexandria, VA 22332

Daniel Cacchione

Portland Cement Association

5420 Old Orchard Road

Skokie, IL 60076

William J. Campbell

U. S. Bureau of Mines

College Park Metallurgy Research Center

College Park, MD 20740

Melvin C. Cannon, Jr.

Texas A & M University

109 Parkway

Bryan, TX 77801

Armand R. Casola

Food & Drug Administration

Bureau of Drugs

5600 Fishers Lane

Rockville. MD 20857

William A. Cawley

Environmental Protection Agency

Mail Code RD680

401 M Street, SW

Washington, DC 20460

James H. Chapman

Consad Research Corporation

121 North Holland Avenue

Pittsburgh, PA 15206

480
Eric J. Chatfield

Ontario Research Foundation

Sheridan Park Research Community

Mississauga, Ontario L5K 1B3

CANADA

Chi a Ting Chen

OSHA - U.S. Dept. of Labor

Room 602

400 First Street, NW

Washington, DC 20215

Lauren Choate

Interpace Corporation

Mountain View Drive

Willsboro, NY 12996

K. S. Chopra

Union Carbide

4625 Royal Avenue

Niagara Falls, NY 14302

James M. Christie

Vulcan Materials Company

One Metroplex Drive

Box 7497

Birmingham, AL 35223

Frank H. Chung

Sherwin-Williams Company

10909 Cottage Grove Avenue

Chicago, IL 60628

Harold Clements

EMSL

Quality Assurance Branch

Cincinnati, OH 45268

Robert A. Clifton

U.S. Bureau of Mines

2401 E Street, NW

Washington, DC 20241

Jay Coffman

Luck Quarriers, Inc.

P. 0. Box 4682

Richmond, VA 23229

Stuart Cohen

Environmental Protection Agency

Pesticides & Toxic Substances

Enforcement

Mail Code EN-342

401 M Street, SW.

Washington, DC 20460

Richard R. Cole

Harry T. Campbell Sons' Company

100 W. Pennsylvania Avenue

Towson, MD 21204

Benjiman Collins

North American Exploration, Inc.

P. 0. Box 7584

Charlottesville, VA 22906

Philip M. Cook

U.S. Environmental Protection Agency

Environmental Research Laboratory

6201 Congdon Blvd.

Duluth, MN 55804

W. Clark Cooper

Equitable Environmental Health, Inc.

2020 Mil via Street

Berkeley, CA 94704

Joseph R. Copeland

Interpace Corporation

260 Cherry Hill Road

Parsippany, NJ 07054

R. E. Corcoran

U.S. Bureau of Mines

2401 E Street, NW

Washington, DC 20241

James D. Cornell

U.S. Gypsum Company

101 S. Wacker Drive

Chicago, IL 60606

Marcel Cossette

Centre for Technology of the

Environment

University of Sherbrooke

Sherbrooke, P.Q. JIK 2R1

CANADA

Edwin Cox

Commonwealth Labs, Inc.

P. 0. Box 8025

Richmond, VA 23223

Edward Crandall

Maryland State Health Dept.

Division of Employee Health Programs

201 W. Preston St.

Baltimore, MD 21201

Bill Crowley

Maryland Geological Survey

Johns Hopkins University

Baltimore, MD 21218

Alan Davidson

0. M. Scott

Research Building

Marysville, OH 43040

Richard L. Davis

Koppers Co. , Inc.

1177 Pinewood Drive

Pittsburgh, PA 15243

481
E. K. Davison

National Sand and Gravel Association

900 Spring Street

Silver Spring, MD 20910

Peter DeBruyn

Office of the Director

National Bureau of Standards

Washington, DC 20234

John G. Delly

McCrone Associates

2820 S. Michigan Avenue

Chicago, IL 60616

John M. Dement

National Institute for Occupational

Safety and Health

4676 Columbia Parkway

Cincinnati, OH 45226

Phillip B. DeNee

NIOSH-ALOSH

944 Chestnut Ridge Road

Morgantown, WV 26505

Catherine Dentan

Carborundum Corp.

Res. and Dev. Division

P. 0. Box 1054

Niagara Falls, NY 14302

Lois Dicker

Occupational Safety & Health Admin.

Division of Occupational Health

Programming

DOL Rm N3119

200 Constitution Avenue

Washington, DC 20210

Robert H. Dickey

MESA

4800 Forbes Avenue

Pittsburgh, PA 15213

Willard C. Dixon

U.S. Department of Labor

Occupational Safety & Health Admin.

390 Wakara Way

Salt Lake City, UT 84117

Ken Doolan

U.S. Coast Guard

400 - 7th Street, SW

Washington, DC 20590

M. J. Doyle

The Hanna Mining Company

100 Erieview Plaza

Cleveland, OH 44114

Ronald G. Draftz

IIT Research Institute

10 West 35th Street

Chicago, IL 60616

Guy F. Driver, Jr.

P. 0. Drawer 84

Winston-Salem, NC 27102

James R. Dunn

Dunn Geoscience Corporation

Mountain View Drive

Averill Park, NY 12018

Frank Echelberger

Hooker Chem. & Plastics

P. 0. Box 344

Niagara Falls, NY 14302

Richard D. Edsell

U.S. Department of Labor

OSHA, Rm. N-3657

200 Constitution Avenue, NW

Washington, DC 20210

William V. Eisenberg

U.S. Food & Drug Administration

Washington, DC 20234

Michael H. Eisner

U.S. Department of the Interior

Bureau of Mines

College Park Metallurgy Research Center

College Park, MD 20740

Samuel El kin

Temple University

3307 N. Broad Street

Philadelphia, PA 19116

William Ellis

Maryland Occupational Safety and

Health Service

203 East Baltimore Street

Baltimore, MD 21202

John T. Enwright

NL Industries, Inc.

P. 0. Box 700

Hightstown, NJ 08520

Edwin S. Erickson, Jr.

Bethlehem Steel Company

Homer Research Laboratories

Bethlehem, PA 18016

Lidia Farmer

Gillette Research Institute

1413 Research Boulevard

Rockville, MD 20850

482
William Fassuliotis

GAF Corporation

1361 Alps Road

Wayne, NJ 07470

Donald R. Ferry

Charles Mathieu, Inc.

18-22 Bank Street

P.O. Box A.M.

Summit, NJ 07901

R. M. Fisher

U.S. Steel Research Laboratory

Monroeville, PA 15146

Jean J. Fitzpatrick

Colorado School of Mines

Research Institute

P. 0. Box 112

Golden, CO . 80401

A. McM. Foster

Hollingsworth & Vose Company

112 Washington Street

East Walpole, MA 02032

Douglas P. Fowler

Stanford Research Institute

333 Ravenswood Avenue

Menlo Park, CA 94025

James E. Fox

Virginia Aggregates Assn.

2317 Westwood Avenue

Richmond, VA 23230

Kenneth S. Freeman

U.S. Gypsum Company

1000 East Northwest Highway

Des Plaines, IL 60016

Melvin H. Friedman

Food & Drug Administration

HFF 147

200 C Street, SW

Washington, DC 20204

Norman E. Fritsche

Environmental Protection Agency

Annapolis Field Office

Annapolis Science Center

Annapolis, MD 21401

Robert M. Furlong

W.W. Box 13527

Boxley Building

Jefferson Street

Roanoke, VA 24035

Arthur E. Gass

Office of Training and Education

OSHA

200 Constitution Avenue, NW

Washington, DC 20101

Lois L. Gerchman

Stanford Research Institute International

333 Ravenswood Avenue

Menlo Park, CA 94025

John C. Gifford

Asarco, Inc.

Oak Tree Road & Park Avenue

S. Plainfield, NJ 07080

Philip Giles

Bethlehem Steel Corp.

Homer Research Labs.

Bethlehem, PA 18016

Gordon J. Gill

Cyprus Industrial Minerals Company

555 S. Flower Street

32nd Floor

Los Angeles, CA 90071

J. K. Gilmore

Vermont Asbestos Group, Inc.

P. 0. Box 70

Hyde Park, VT 05655

David M. Gioiello

National Aeronautics & Space Admin.

Goddard Space Flight Center

Health Unit, Bldg. 5

Greenbelt, MD 20771

Samuel Goldberg

MESA

4800 Forbes Avenue

Pittsburgh, PA 15213

David Goldheim

Martin Marietta Corporation

1450 S. Rolling Road

Baltimore, MD 21227

Aurel Goodwin

MESA

4015 Wilson Blvd.

Arlington, VA 22203

Gary Gravatt

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234

David Gray

Minnesota Department of Health

717 Deleware Street SE

Minneapolis, MN 55440
Leven B. Gray

Goddard Space Flight Center

Greenbelt, MD 20771

Alice L. Greife

NIOSH/ALOSH

944 Chestnut Ridge Road

Morgantown, WV 26505

Joseph R. Gross

Jones & Laugh! in Steel Corp.

504 North 1st Street

Virginia, MN 55792

Paul Gross

Industrial Health Foundation

5231 Centre Avenue

Pittsburgh, PA 15232

Richard Gruenbaum

0. M. Scott

Research Building

Marysville, OH 43040

Fred I. Grunder

Bethlehem Steel Corporation

Homer Research Laboratories

Bethlehem, PA 18016

Richard Gullickson

International Minerals & Chemical Corp.

501 E. Lange

Mundelein, IL 60060

Joe A. Gutierrez

Vulcan Materials Company

P. 0. Box 4195

Winston-Salem, NC 27105

Robert A. Haagensen

ASARCO, Inc.

Central Research Department

901 Oak Tree Road

South Plainfield, NJ 07080

Janet C. Haartz

NIOSH-MRB

4676 Colorado Pkwy,

Cincinnati, OH 45226

C. Y. Haas

Minerals & Chemicals Division

Engelhard Minerals & Chemicals Corp.

Menlo Park

Edison, NJ 08817

George Haecker

Plastic Engineering Company

Sheboygun, WI 53081

Wi 1 1 iam Harri

Martin Marietta Corporation

1450 S. Rolling Road

Baltimore, MD 21227

Allan M. Harvey

R. T. Vanderbilt Co., Inc.

30 Winfield Street

Norwalk, CT 06855

Robert Hehir

Consumer Products Safety Commission

Westwood Towers Building, Rm. 712

4501 Westbard Avenue

Bethesda, MD 20207

James Heil

Certain-Teed Corporation

Pipe & Plastics Group

P. 0. Box 860

Valley Forge, PA 19482

Kurt F. Heinrich

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234

Clarence A. Herbst, Sr.

Resinoid Engineering Corporation

3445 Howard Street

Skokie, IL 60076

John Heter

Interpace Corporation

2901 Los Feliz Blvd.

Los Angeles, CA 90039

John L. S. Hickey

Research Triangle Institute

Research Triangle Park, NC 27709

Gavin Hi 1 dick-Smith

Johnson & Johnson

501 George Street

New Brunswick, NJ 08903

William B. Hillegass

0. M. Scott

Research Building

Marysville, OH 43040

J. A. Hodgeson

Office of Air & Water Measurement

National Bureau of Standards

Washington, DC 20234

John D. Hoffman

Institute for Materials Research

National Bureau of Standards

Washington, DC 20234

484
Liselotte Hochholzer

Armed Forces Institute of Pathology

Washington, DC 20306

Pat Honchar

Preventable Diseases Division

Connecticut State Department of

Health

79 Elm Street

Hartford, CT 06115

Earl G. Hoover

National Crushed Stone Association

1415 Elliot Place, NW

Washington, DC 20007

Emanuel Horowitz

Institute for Materials Research

National Bureau of Standards

Washington, DC 20234

Arthur J. Huetteman

Personal Products Company

Van Liew Avenue

Mi 11 town, NJ 08850

Charles W. Huggins

U.S. Department of the Interior

Bureau of Mines

College Park Metallurgy Research Ctr.

College Park, MD 20740

Ruth Hughes

Western Health Services Research

1213 Varsity Estates Road

Calgary, Alberta T3B 2X1

CANADA

Robert Huntington

Martin Marietta Corporation

1450 S. Rolling Road

Baltimore, MD 21227

Daniel W. Hurley

NL Industries, Inc.

P. 0. Box 700

Hightstown, NJ 08520

C. Y. Hwang

McGill University

3775 University Street

Montreal , Quebec

CANADA

Robert Hylan

GAP Corporation

1361 Alps Road

Wayne, NJ 07470

Donald A. Jackson

State of Maryland

Department of Natural Resources

Water Resources Administration

Tawes State Office Bldg.

580 Taylor Avenue

Annapolis, MD 21401

Joseph C. Jackson

A/C Pipe Producers Association

1600 Wilson Boulevard

Suite 1308

Arlington, VA 22209

Harry E. Jaworski

OSHA - Chicago Regional Office

290 South Dearborn St.-Rm. 3263

Chicago, IL 60604

Dale Johnson

GAP Corporation

1361 Alps Road

Wayne, NJ 07470

Frank Johnson

Armed Forces Institute of Pathology

Washington, DC 20306

H. Bradley Johnson

American Mining Congress

1100 Ring Building

Washington, DC 20036

Patricia C. Johnson

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234

Ronald B. Johnson

Institute for Materials Research

National Bureau of Standards

Washington, DC 20234

David R. Jones

I. I. T. Research Institute

10 West 35th Street

Chicago, IL 60616

Robert D. Joyce

Bethlehem Steel Corporation

Martin Tower, B-252

Bethlehem, PA 18016

Elizabeth Kaegi

Western Health Services Research Ltd.

1213 Varsity Estates Rd., NW

Calgary, Alberta T3B 2X5

CANADA

Eila Kairinen

Gillette Company Research Institute

1413 Research Blvd.

Rockville, MD 20850

485
David A. Kandel

Kaiser Steel Corporation

P. 0. Box 217

Fontana, CA 92335

Mark D. Kaufman

Sutherland, Asbill & Brennen

3100 First National Bank Tower

Atlanta, GA 30303

Martin G. Kemplin

Nicolet, Inc.

Maple Street

Ambler, PA 19002

Charles B. Kenahan

U.S. Department of the Interior

Bureau of Mines

College Park Metallurgy Research Ctr.

College Park, MD 20740

Robert J. Kilgour

Armstrong Cork Company

Liberty and Charlotte Streets

Lancaster, PA 17604

William B. King

Armstrong Cork Company

Suite 205

1666 K Street, NW

Washington, DC 20006

William H. Kirchhoff

Office of Air & Water Measurement

National Bureau of Standards

Washington, DC 20234

Diana M. Kirkpatrick

Consumer Product Safety Commission

200 C Street, SW

Washington, DC 20204

Owen H. Kittilstad

CertainTeed Corporation

P. 0. Box 860

Valley Forge, PA 19482

Partricia B. Klinger

Kennecott Research Center

P. 0. Box 11299

1515 Mineral Square

Salt Lake City, UT 84147

Carl E. Kollmar, Jr.

J. M. Huber Corporation

Route 4, Huber

Macon, GA 31201

C. Kommineni

NIOSH

DBBS Pathology Section

4676 Columbia Parkway

Cincinnati, OH 45226

Paul Kotin

Johns-Manvi lie Corporation

Ken-Caryl Ranch

Denver, CO 80217

George J. Krafcisin

Kemper/NATLSCO

Long Grove, IL 60049

Sidney Krakauer

Pall Biomedical Products Corporation

30 Sea Cliff Avenue

Glen Cove, NY 11542

James R. Kramer

Department of Geology

McMaster University

Hamilton, Ontario L85 4MI

CANADA

Jerry Krause

Colorado School of Mines

Research Institute

P. 0. Box 112

Golden, CO 80401

Stephen Krop

Food and Drug Administration

Bureau of Drugs

200 C Street, SW

Washington, DC 20204

Edward Kuchar

01 in Corporation

New Haven, CT 06527

Philip D. La Fleur

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234

Jule K. Lamar

Food and Drug Administration

Bureau of Drugs

5600 Fishers Lane

Room 18-B-31

Rockville, MD 20857

Helen W. Lang

U.S. Bureau of Mines

4800 Forbes Avenue

Pittsburgh, PA 15213

Arthur Langer

Environmental Sciences Laboratory

Mt. Sinai Hospital

New York, NY 10029

Maxwell W. Layard

National Cancer Institute

Landow Building, Rm C318

Bethesda, MD 20014

486
A. Philip Leber

Battelle - Columbus Laboratories

505 King Avenue

Columbus, OH 43201

George Lee

Applied Research

Johnson & Johnson Baby Products Co.

Route 202

Raritan, NJ 08869

R. J. Lee

U.S. Steel Research Laboratory

Monroeville, PA 15146

Robert Lee

Rogers Corporation

Rogers, CT 06263

James Leineweber

R&D Center

Johns-Manvi 1 le Corporation

Denver, Colorado 80229

Robert S. Lemire

Reserve Mining Company

Silver Bay, MN 55614

Jacques Lepoutre

Eternit S.A.

2920 Kapelle-op-den-Bos

BELGIUM

Archie Liao

Prince Georges County Health Dept.

10210 Greenbelt Road

Seabrook, MD 20801

Charles Lichtenwalner

Bell Laboratories

Murray Hill , NJ 07974

Jeff Limoge

Vermont Asbestos Group

P. 0. Box 70

Hyde Park, VT 05655

Burt Linck

The Arundel Corporation

110 West Road

Baltimore, MD 21204

C. M. Llewellyn, Jr.

Lone Star Industries, Inc.

P. 0. Box 1-J

3011 Dock Street

Richmond, VA 23201

Harold L. Lloyd

Pennsylvania Glass Sand Corp. (ITT)

Berkeley Springs, WV 25411

Thomas Loch

Clayton Environmental Consultants

25711 Southfield

Southfield, MI 48075

Robert H. Locke

W. R. Grace & Company

62 Whittemore Avenue

Cambridge, MA 02140

Howard R. Ludwig

National Institute for Occupational

Safety & Health

Taft Laboratories

4676 Columbia Pkwy

Cincinnati, OH 45226

Bernard S. Mac Cabe

Carborundum Co.

NAO-Water Management Division

P. 0. Box 1054

Niagara Falls, NY 14302

John Maciejczyic

Rockwell International

600 Grant Street

Pittsburgh, PA 15219

Joseph Mackey

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234

Joseph A. Macko, Jr.

Army Environmental Hygiene Agency

Aberdeen Proving Ground

Edgewood, MD 21010

Lloyd A. Madsen

Occupational Safety & Health Admin.

Analytical Laboratory

390 Wakara Way

Salt Lake City, UT 84108

Ralph E. Magnuson, Jr.

The Cleveland-Cliffs Iron Company

1460 Union Commerce Building

Cleveland, OH 44115

S. E. Malovrh

The Hanna Mining Company

100 Erieview Plaza

Cleveland, OH 44114

Roland E. Manger

Harry T. Campbell Sons' Company

100 W. Pennsylvania Ave.

Towson, MD 21204

487
Gregory J. Manning

Diamond Shamrock Corporation

T. R. Evans Research Center

P. 0. Box 348

Painesville, OH 44077

Thomas J. Manthey

Pickands Mather & Company

1 100 Superior Avenue

Cleveland, OH 44114

John Marsh

Raybestos Manhatten Inc.

100 Oakview Drive

Trumbull, CT 06611

Eugene Martin

EDAX International, Inc.

157 Colique Avenue

New Rochelle, NY 10801

Robert F. Martin

Institute for Materials Research

National Bureau of Standards

Washington, DC 20234

John F. Martonik

U.S. Department of Labor

Occupational Safety & Health

Administration

200 Constitution Avenue, NW

Washington, DC 20210

Brian Mason

Mineral Sciences

Smithsonian Institution

Washington, DC 20560

Woodrow W. Massad

Continental Oil Company

Box 1267

Ponca, OK 74601

Darrell K. Mattheis

Occupational Safety and Health Agency

Room N 3603

200 Constitution Avenue

Washington, DC 20210

John Matwey

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234

Arthur J. McLaughlin

MESA

9 Mayfair Drive

Slingerlands, NY 12159

Lottie McClendon

Institute for Materials Research

National Bureau of Standards

Washington, DC 20234

Ray McClure

Division of Occupational Health

U.S. Department of Labor

Occupational Safety & Health Admin.

200 Constitution Avenue, NW

Washington, DC 20210

Brian McCoy

The Arundel Corporation

110 West Road

Baltimore, MD 21204

Ronald McCullen

Travelers Insurance Co.

248 CP Lab

1 Tower Sq.

Hartford, CT 06115

Philip P. McGrath

Bureau of Biologies

Food and Drug Administration

8800 Rockville Pike

Bethesda, MD 20014

Douglas McLean

Stauffer Chemical Co.

Eastern Research Center

Dobbs Ferry, NY 10522

James F. McVeigh

American Can Company

U.S. Highway 22

Union, NJ 07083

Carl W. Melton

Battelle, Columbus Laboratories

505 King Avenue

Columbus, OH 43201

Eric S. Mendelsohn

Air Pollution & Noise Control

Department of Environmental Protection

of Montgomery County

Room 340

6110 Executive Building

Rockville, MD 20852

Oscar Menis

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234

J. C. Meranger

Environmental Health Center

Health & Welfare

Ottawa, Ontario KIA 0L2

CANADA

Dennis Michalski

International Minerals & Chem. Corp

IMC Plaza

Libertyville, IL 60048

488
A. P. Middleton

Institute of Occupational Medicine

Roxburgh Place

Edinburgh, EH8 9SU

SCOTLAND

W. J. Miles

Industrial Mineral Ventures, Inc.

5920 Mclntyre Street

Golden, CO 80401

Roger N. Miller

Windsor Minerals, Inc.

P. 0. Box 680

Windsor, VT 05089

James R. Millette

Environmental Protection Agency

HERL

26 West St. Clair Street

Cincinnati, OH 45268

Robert J. Moolenaar

Dow Chemical Company

1702 Building

Midland, MI 48640

John A. Moore

National Insitute of Environmental

Health Sciences

P. 0. Box 12233

Research Triangle Park, NC 27709

Sanders Moore

01 in Corporation

P. 0. Box 248

Charleston, TN 37311

Robert E. Morgan

Virginia Division of Mines

and Quarries

908 Branchwater Street

Fredericksburg, VA 22401

Bruce Morrissey

Office of the Director

National Bureau of Standards

Washington, DC 20234

J. Eraser Morton

Congoleum Corporation

2700 Emory Road

Finksburg, MD 21048

Wolfgang Mueller

Newmont Exploration Limited

44 Briar Ridge Road

Danbury, CT 06810

Frederick A. Mumpton

State University College

Department of the Earth Sciences

Brockport, NY 14420

Ronald A. Munson

Bureau of Mines

2401 E Street, NW

Washington, DC 20241

Jack C. Murchio

School of Public Health

University of California - Berkeley

Earl Warren Hall

Berkeley, CA 94720

Charles T. Myers

U.S. Steel Corporation

Room 6044

600 Grant Street

Pittsburgh, PA 15230

Andrew J. Nawa

Mining Enforcement & Safety Admin.

4800 Forbes Avenue

Pittsburgh, PA 15213

Harry Nay lor

Moore & Munger

140 Sherman Street

Fairfield, CT 06430

Dale Newberry

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234

Marvin W. Nichols, Jr.

MESA

130 North Arlington St.

Salisbury, NC 28144

W. Nicholson

Environmental Sciences Laboratory

Mt. Sinai Hospital

New York, NY 10029

Clifford W. Niemi

U.S. Steel Corporation

Minnesota Ore Operations

P. 0. Box 417

Mountain Iron, MN 55768

Gordon L. Nord, Jr.

U.S. Geological Survey

959 National Center

Reston, VA 22092

Robert E. Norwood

Pfizer, Inc.

640 N. 13th Street

P. 0. Box 548

Easton, PA 18042

489
Andrew F. Oberta

A.F. Oberta Consulting Services

1200 Quince Orchard Boulevard

Gaithersburg, MD 20760

John 0' Conner

PPG Industries, Inc.

1 Gateway Center

Pittsburgh, PA 10522

Trevor L. Ogden

Health and Safety Executive

403 Edgware Road

London, NW2 6LN

ENGLAND

David McNeil Olds

Read, Smith, Shaw & McClay

747 Union Trust Bldg.

Pittsburgh, PA 15230

Lawrence W. Ortiz

Los Alamos Scientific Laboratory

P. 0. Box 1663

Los Alamos, NM 87544

Donald G. Oss

Hanna Mining Company

2125 Second Avenue, East

Box 218

Hibbing, MN 55746

T. Dixon Oulton

Engelhard Minerals & Chemicals Corp.

Menlo Park

Edison, NJ 08817

Lalita D. Palekar

Northrop Services, Inc.

P. 0. Box 12313

Research Triangle Park, NC 27709

Thomas Pang

Ministry of Environment

Laboratory Services Branch

French Resource Road

Islington, Rexdale, Ontario

CANADA

Ed Parkison

Martin Marietta Corporation

1450 S. Rolling Road

Baltimore, MD 21227

C. J. Parmentier

Cyprus Industrial Minerals Company

555 S. Flower Street

32nd Floor

Los Angeles, CA 90071

Deran Pashayan

Environmental Protection Agency

401 M St. , SW

Washington, DC 20460

Premysl V. Pelnar

Institute of Occupational and

Environmental Health

Suite 603, 3 Place Ville Matie

Montreal , Quebec H3B 2E3

CANADA

Edward T. Peters

Arthur D. Little, Inc.

15 Acorn Park

Cambridge, MA 02140

Daryl E. Peterson

Occupational Safety & Health Admin.

Analytical Laboratory

390 Wakara Way

Salt Lake City, UT 84108

Terry Philippi

IITRI

10 West 35th Street

Chicago, IL 60616

John A. Pickrell

Inhalation Toxicology Research Inst.

Lovelace Biomedical & Environmental

Research Institute

P. 0. Box 5890

Albuquerque, NM 87116

Bob J. Pigg

Asbestos Information Association

1835 K Street, NW

Suite 402

Washington, DC 20006

F. D. Pooley

Johnson & Johnson

501 George Street

New Brunswick, NJ 08903

Warren Porter

Consumer Product Safety Comm.

Fed. Bldg. 8, Rm 5844

200 C Street, SW

Washington, DC 20204

Gene Proctor

National Aeronautics & Space

Administration

600 Independence Avenue

Code QG

Washington, DC 20546

David Pytynia

Nalco Chemical Company

6216 West 66th Place

Chicago, IL 60638

490
Don Quilici

Hanford Environmental Health Foundation

P. 0. Box 100

Richmond, WA 99352

Pamela P. Quinn

U.S. Environmental Protection Agency

4th and M Streets, SW

Waterside Mall

Washington, DC 20460

Paul Radauskas

City of Rockvil le

111 Maryland Avenue

Rockville, MD 20850

Lewis Raymond

MESA

4800 Forbes Avenue

Pittsburgh, PA 15213

Curt W. Reimann

Institute for Materials Research

National Bureau of Standards

Washington, DC 20234

Harrison B. Rhodes

Union Carbide Corporation

Metals Division

P. 0. Box 579

4625 Royal Avenue

Niagara Falls, NY 14302

Richard W. Richards

Pennsylvania Glass Sand Corp.

SR 522, North

Berkeley Springs, WV 25411

Roger Riley

Interpace Corporation

3502 Breakwater Court

Hayward, CA 94545

Malcolm L. Roberts

Trudeau Institute, Inc.

Box 59

Saranac Lake, NY 12983

K. Robock

Wirtschaftsverband Asbestzement e.V.

Arbetis- und Umweltschutz

Koelner Str. 102

D - 4040 Neuss

Germany

Fred J. Rogers

Gypsum Association

1603 Orrington Avenue

Evanston, IL 60201

F. Robert Rolle

Johnson & Johnson

501 George Street

New Brunswick, NJ 08903

Harry L. Rook

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234

Richard H. Rosenberg

Borg Warner Research Center

Wolf & Algonquin Road

Des Plaines, IL 60091

Joan R. Rosenblatt

National Bureau of Standards

Washington, DC 20234

Malcolm Ross

U.S. Geological Survey

National Center 959

Reston, VA 22092

Robert G. Rucker

Congoleum Corporation

2700 Emory Road

Finksburg, MD 21048

Clyde L. Russell

Kerr-McGee Corporation

P. 0. Box 25861

Oklahoma City, OK 73125

Clayton 0. Ruud

Denver Research Institute

University of Denver

Denver, CO 80208

A. H. Samuel

Reserve Mining Company

Silver Bay, MN 55614

Joseph K. Samuels

Republic Steel Corporation

6801 Brecksville Road

Independence, OH 44131

David G. Sarvadi

Sherwin-Williams Company

101 Prospect Avenue, NW

Cleveland, OH 44115

James A. Saunders

Bureau of Toxic Substance Info.

Virginia Dept. of Health

109 Gov. Street

Richmond, VA 23219

Jim W. Scales

J. M. Huber Corporation

Route 4 Huber

Macon, GA 31201

491
Mary Lee Schaefer

Employers Insurance of Wausau

2000 Westwood Drive

Wausau, WI 54401

John P. Schelz

Johnson & Johnson

501 George Street

New Brunswick, NJ 08903

Wayne L. Schiffelbein

U.S. Consumer Product Safety

Commission

111 - 18th Street, NW

Washington, DC 20207

Marvin Schneiderman

National Cancer Institute

National Institutes of Health

Landow Building

Rm. C403

Bethesda, MD 20014

Richard F. Scholl

Fine Particles Research Section

IIT Research Institute

10 West 35th Street

Chicago, IL 60616

George Schwartzman

Food & Drug Administration

Code HFD 402

501 First Street, SE

Washington, DC 20204

J. M. Shackelford

Environmental Protection Agency

401 M Street

Mail Code RD680

Washington, DC 20460

Peter Shaffer

Carborundum Company

P. 0. Box 1054

Niagara Falls, NY 14302

Raymond Shapiro

NIEHS

P. 0. Box 12233

Research Triangle Park, NC 27709

George Sharpe

Medical Office

National Bureau of Standards

Washington, DC 20234

Lawrence E. Shirley

U.S. Bureau of Mines

Liaison Office

P. 0. Box 2828

Raleigh, NC 27602

George R. Simon

Health Effects Div. (RD 683)

U.S. Environmental Protection Agency

401 M. Street, SW

Washington, DC 20460

S. B. Singer

State Department of Health

& Environmental Control

Air Bureau

2600 Bull Street

Columbia, SC 29201

Fred J. Sisson

GSA - Accident & Fire Prevention

Branch (3P0A)

7th & D Streets, SW

Room 7712

Washington, DC 20407

Henry J. Smahlik

Dresser Industries, Inc.

Oilfield Products Group

601 Jefferson

Houston, TX 77002

John A. Small

Analytical Chemistry Division

National Bureau of Standards

Washington, DC 20234

William E. Smith

Health Research Institute

Fairleigh Dickinson University

Madison, NJ 07940

Eli Smyrloglou

Millipore Corporation

Ash by Road

Bedford, MA 01730

Vernon R. Snyder

The General Crushed Stone Company

P. 0. Box 231

Easton, PA 18042

James A. Soles

Canada Center for Mineral

& Energy Technology (CANMET)

405 Rochester Street

Ottawa, Ontario KIA OGl

CANADA

Harold Stanley

Pfizer, Inc.

M.P.M. Division

P. 0. Box 548

Easton, PA 18042

492
Mearl F. Stanton

National Cancer Institute

National Institutes of Health

Laboratory of Pathology

Bethesda, MD 20014

David N. Staples

Industrial Hygiene Section

Office of Chief of Naval

Operations

Occupational Safety & Health Div.

(OP-45)

The Pentagon

Washington, DC 20350

John T. Stasny

Structure Probe, Inc.

535 East Gay Street

West Chester, PA 19380

Eric B. Steel

U.S. Department of the Interior

Bureau of Mines

College Park Metallurgy Research Center

College Park, MD 20740

John Steelnack

U.S. Department of Labor

OSHA/Rm. N-3657

200 Constitution Avenue, NW

Washington, DC 20210

Arland Stein

747 Union Trust Building

Pittsburgh, PA 15230

Robert J. Stevenson

Department of Geology & Geophysics

University of Minnesota

Minneapolis, MN 55414

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Walter C. McCrone Assoc., Inc.

2820 S. Michigan Avenue

Chicago, IL 60616

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Standard Oil Research Center

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Mail Station B-3

Naperville, IL 60540

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Washington, DC 20241

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Environmental Protection Agency

401 M St. , SW

Washington, DC 20460

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Hanft, Fride, O'Brien & Haines

1200 Alworth Bldg.

Duluth MN 55802

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Homestake Mining Company

650 California Street

9th Floor

San Francisco, CA 94108

Reginald Sykes

Asbestos Research Council

TBA Industrial Products, Ltd.

P. 0. Box 40

Rochdale, Lanes. 0L12 7EQ

ENGLAND

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Churchill Fellow

38 Drapers Road

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National Bureau of Standards

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Food and Drug Administration

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General Motors Corporation

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MESA

Denver Technical Support Center

P. 0. Box 25367

Denver Federal Center

Denver, CO 80225

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R. T. Vanderbilt Co., Inc.

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Norwalk, CT 06855

E. June Thompson

Consumer Product Safety Commission

Rm. 700, 5401 Westbard Avenue

Bethesda, MD 20207

493
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DHEW/PHS/FDA/BF

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Washington, DC 20204

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U.S. Environmental Protection Agency

Research Triangle Park, NC 27711

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Rockville Crushed Stone, Inc.

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13900 Piney Meeting House Road

Rockville, MD 20850

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Ash by Road

Bedford, MA 01730

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U.S. Geological Survey

959 National Center

Reston, VA 22092

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Environmental Protection Agency

{WH550)

401 M Street

Washington, DC 20460

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MESA

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Pittsburgh, PA 15213

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Engelhard Minerals & Chemicals Corp,

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1501 Euclid Avenue

514 Bulkley Building

Cleveland, OH 44115

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Warren Brothers Co.

675 Massachusetts Ave.

Cambridge, MA 02139

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Department of Labor

OSHA/Rm. N3657

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Washington, DC 20210

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Federal Railroad Administration

2100 - 2nd Street, SW

Washington, DC 20590

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DeSoto, Inc.

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Des Plaines, IL 60018

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Thorp, Reed & Armstrong

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Pittsburgh, PA 15219

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Occupational Health & Safety Div.

Government of Alberta

9820 - 106 Street

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Department of Consumer &

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Standards Laboratory Building

Tunney's Pasture

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Robert L. Virta

U.S. Department of the Interior

Bureau of Mines

College Park Metallurgy Res. Ctr.

College Park, MD 20740

Joseph Volk

Gold Bond Building Products Div.

National Gypsum Company

1650 Military Road

Buffalo, NY 14217

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Eagle-Picher Industries, Inc.

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U.S. Environmental Protection Agency

Research Triangle Park, NC 27711

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Plastic Engineering Company

Sheboygun, WI 53081

Daman S. Walia

IIT Research Institute

10 W 35th Street

Chicago, IL 60616

John L. Warren

Research Triangle Institute

Cornwall is Road

Research Triangle Park, NC 27709

494
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Occupational Safety & Health Admin.

Room N3660

200 Constitution Avenue, I^W Washington, DC 20210

James R. Weber

The Bendix Corporation

Executive Offices, Bendix Center

Soutlrfield, MI 48076

Richard J. Wedlund

Minnesota Pollution Control Agency

Division of Air Quality

1935 W. Co. Road, B-2

Roseville, MN 55113

John M. Wehrung

EMV Associates, Inc.

15825 Shady Grove Road

Rockville, MD 20850

S. Weiss

The Flintkote Company

365 West Passaic Street

Rochelle Park, NJ 07062

John F. Welch

A/C Pipe Producers Association

1600 Wilson Boulevard

Suite 1308

Arlington, VA 22209

John Wenniger

Bureau of Biologies

Food and Drug Administration

8800 Rockville Pike

Bethesda, MD 20014

Lewis F. Wheatley

Virginia Division of Mines

Drawer V

Big Stone Gap, VA 24219

Judith A. Whelan

Air Pollution & Noise Control

Department of Environmental Protection

of Montgomery County

Room 340

6110 Executive Boulevard

Rockville, MD 20852

Benjamin D. White

Assistant Secretary for Health

Department of Health and Mental

Hygiene

201 West Preston Street

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Lowell D. White

ASARCO Incorporated

3422 South 700 West

Salt Lake City, UT 84119

James Whitney

Environmental Protection Agency

401 M Street, SW

Mail Code RD680

Washington, DC 20460

Diane Whittier

University of Pittsburgh

G.S.P.H.

130 DeSoto Street

Pittsburgh, PA 15261

John R. Whyte

The Anaconda Company

P. 0. Box 27007

Tucson, AZ 85726

Peter C. Wight

Environmental Quality Control Div.

B-252MT

Ind. Relations Department

Bethlehem Steel Corporation

Bethlehem, PA 18016

Allen Winer

Naval Ship Engineering Center

Crystal City NC-2 (6101E)

Washington, DC 20360

Steven Winzer

Martin Marietta Corporation

1450 S. Rolling Road

Baltimore, MD 21227

George J. Wolfe

JEOL (USA), Inc.

101 Colonial Drive

Irwin, PA 15642

Vladimir E. Wolkodoff

Johns-Manvi 1 le Corporation

Research and Development Center

Denver, CO 80217

Gilbert H. Wood

Environmental Protection Agency

OAQPS, ESED, ISB, SSS (MD-13)

Research Triangle Park, NC 27711

Sandra Worblewski

Kemper/NATLSCO

Long Grove, IL 60049

George W. Wright

460 S. Marion Parkway

Denver, CO 80209

Gale D. Wyer

Consumer Product Safety Comm.

Directorate for Eng. and Science

200 C Street, SW

Room 5844

Washington, DC 20204

495
Ann G. Wylie

Department of Geology

University of Maryland

H.J. Patterson Hall

College Park, MD 20740

Julie C. Yang

W. R. Grace & Company

62 Whittemore Avenue

Cambridge, MA 02140

Brian Yawney

Ontario Research Foundation

Sheraton Park

Mississauga, Ontario L5K 1B3

CANADA

J. E. Zatek

Mine Safety Appliances

600 Penn Center Blvd.

Pittsburgh, PA 15235

Carolyn Zelek

Ford Motor Company

Rotundo Blvd., Building 5 Dearborn, MI 48121

F. H. Zimmerman

National Gypsum Company

4100 First International Building

Dalles, TX 75270

Tibor Zoltai

Department of Geology and

Geophysics

University of Minnesota

Minneapolis, MN 55455

Richard M. Zomnir

Thorp, Reed & Armstrong

2900 Grant Building

Pittsburgh, PA 15219

Jack Zussman

Department of Geology

University of Manchester

Manchester M13 9PL

ENGLAND

496
4BS-114A (REV. 7-73)

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR RICPORT NO.

NBS SP 506

2, Gov't Accession

No.

3. Recipient's Accession No.

i. TITLE AND SUBTITLE

Proceedings of Workshop on Asbestos: Definitions and

Measurement Methods

5. Publication Date November 1978

6. Performing Organization Code

7. AUJHOR(S)_

C.C. Gravatt, Phillip D. LaFleur, and Kurt F.J, Heinrich

8. Performing Organ. Report No.

1. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

2. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

OSHA

Department of Labor

200 Constitution Avenue, NW

Washington, DC 20210

13. Type of Report & Period

Covered

14. Sponsoring Agency Code

5. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number 78-600109

6. ABSTRACT (A 200-word or less factual summary of most sigrxificant information. If document includes a significant

bibliography or literature survey, mention it here.)

This document contains invited papers which were given at a workshop

on "Asbestos: Definitions and Measuranent Methods" which was jointly

sponsored by the National Bureau of Standards of the U. S, Department of

Commerce and the Occupational Safety and Health Administration of the

U. S. Department of Labor. The discussion portions of the Workshop

also have been included as has written material appropriate to the topics

under consideration which \;as submitted to the editors at a later date.

The Workshop covered four major topics: Mineralogical Aspects, the

Relationship Between Chemical and Physical Properties and Health

Effects, Analytical Methods, and Regulatory Positions and Criteria.

Also included in these Proceedings is a summary of each of these topics.

These summaries serve to define those factors for which there was

general agreement at the Workshop, identify remaining points of controversy,

and, in some cases, describe additional research required to resolve

remaining problems.

7. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Amphibole, asbestos, fibers, light microscopy, mineralogical terminology,

scanning electron microscopy, serpentine, talc, transmission electron

microscopy.

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