### This report contains the collective views of an international group of

experts and does not necessarily represent the decisions or the stated policy

of the United Nations Environment Programme, the International Labour

Organization or the World Health Organization.



# Environmental Health Criteria 227



# FLUORIDES

First draft prepared by Dr R. Liteplo and Ms R. Gomes, Health Canada,

Ottawa, Canada and Mr P. Howe and Mr H. Malcolm, Centre for

Ecology and Hydrology, Cambridgeshire, United Kingdom

Please note that the pagination and layout of this pdf-file

are not identical to those of the printed EHC

Published under the joint sponsorship of the United Nations

Environment Programme, the International Labour

Organization and the World Health Organization, and

produced within the framework of the Inter-Organization

Programme for the Sound Management of Chemicals.

World Health Organization

Geneva, 2002The International Programme on Chemical Safety (IPCS)

, established

i n 1980, is a joint venture of the United Nations Environment Progra mme

(UNEP )

, the International Labour Organization (ILO) and the World Health

O rganization (WHO). The overall objectives of the IPCS are to establish the

scientific basis for assessment of the risk to human health and the en vironment

from exposure to chemicals, through international peer review processes, as a

prerequisite for the promotion of chemical safety, and to provide technical

assistance in strengthening national capacities for the s ound management of

chemicals.

T he Inter-Organization Programme for the Sound Manageme nt of

Chemicals (IO MC) was established in 1995 by UNEP, ILO, the Food and

Agriculture Organization of the United Nations, WHO, the United Na tions

Industrial Development Organizat ion, the United Nations Institute for Training

and Research and the Organisation for Economic Co-operation and Development

(Participating Organizations), following recommendations made by the 1992 UN

Conference on Environment and Development to strengt hen cooperation and

increase c oordination in the field of chemical safety. The purpose of the IOMC

is to promote coordination of the policies and activities pursued by the

Participating Organiza

tions, jointly or separately, to achieve the sound management of chemicals in relation to human health and the environment.

WHO Library Cataloguing-in-Publication Data

Fluorides.

(Environmental health criteria ; 227)

1.Fluori des - adverse effects 2.Environmental exposure 3.Occupational

exposure 4.Risk assessment I.International Programme for Chemical Safety

II.Series

ISBN 92 4 157227 2 (NLM classification: QV 282)

ISSN 0250-863X

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Errors and omissions excepted, the names of proprietary products are

distinguished by initial capital letters.

The Federal Ministry for the Environment, Nature Conservation and Nuclear

Safety, Germany, provided financial support for, and undertook the printing of

this publication.

CONTENTS

ENVIRONMENTAL HEALTH CRITERIA FOR

FLUORIDES

PREAMBLE ix

ACRONYMS AND ABBREVIATIONS xxi

1. SUMMARY AND CONCLUSIONS 1

1.1 Identity, physical and chemical properties and

analytical methods 1

1.2 Sources of human and environmental exposure 1

1.3 Environmental transport, distribution and

transformation 2

1.4 Environmental levels and human exposure 3

1.5 Kinetics and metabolism in humans and laboratory animals 7

1.6 Effects on laboratory mammals and in vitro test

systems 8

1.7 Effects on humans 10

1.8 Effects on other organisms in the laboratory

and field 11

1.9 Evaluation of human health risks and effects on the environment 14

1.10 Conclusions 15

2. IDENTITY, PHYSICAL AND CHEMICAL

PROPERTIES AND ANALYTICAL METHODS 17EHC 227: Fluorides

iv 2.1 Identity and physical and chemical properties 17

2.2 Analytical methods 18

3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE 20

3.1 Natural occurrence 20

3.2 Anthropogenic sources 20

3.2.1 Production and use 20

3.2.1.1 Hydrogen fluoride 20

3.2.1.2 Calcium fluoride 21

3.2.1.3 Sodium fluoride 21

3.2.1.4 Fluorosilicic acid 21

3.2.1.5 Sodium hexafluorosilicate 22

3.2.1.6 Sulfur hexafluoride 22

3.2.1.7 Fluorapatite 22

3.2.1.8 Phosphate fertilizers 22

3.2.2 Emissions 23

4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION

AND TRANSFORMATION 24

4.1 Transport and distribution between media 24

4.1.1 Atmosphere 24

4.1.2 Water and sediment 28

4.1.3 Soil 30

4.2 Speciation and complexation 34

4.2.1 Atmosphere 34

4.2.2 Water 34

4.3 Bioaccumulation 34

5. ENVIRONMENTAL LEVELS AND HUMAN

EXPOSURE 38

5.1 Environmental levels 38

5.1.1 Surface water 38

5.1.2 Air 41

5.1.3 Soil 41

5.1.4 Biota 43

5.1.4.1 Aquatic organisms 43

5.1.4.2 Terrestrial organisms 48

5.2 General population exposure 53

5.2.1 Drinking-water 53v 5.2.2 Food 56

5.2.3 Indoor air 61

5.2.4 Consumer products 63

5.2.5 Intake estimates 63

5.3 Occupational exposure 70

6. KINETICS AND METABOLISM IN HUMANS AND

LABORATORY ANIMALS 71

6.1 Absorption 71

6.1.1 Absorption in humans 71

6.1.2 Absorption in laboratory animals 73

6.2 Distribution and retention 74

6.2.1 Fluoride in blood 74

6.2.2 Distribution in soft tissues 76

6.2.3 Distribution to calcified tissues 76

6.2.4 Transplacental transfer 78

6.2.5 Fluoride levels in human tissues and organs 78

6.3 Elimination 80

6.3.1 Renal handling of fluoride 80

6.3.2 Excretion via breast milk 80

6.3.3 Excretion via faeces, sweat and saliva 81

7. EFFECTS ON LABORATORY MAMMALS AND

IN VITRO TEST SYSTEMS 83

7.1 Single exposure 83

7.2 Short- and medium-term exposure 84

7.3 Long-term exposure and carcinogenicity 86

7.4 Mutagenicity and related end-points 92

7.4.1 In vitro genotoxicity 92

7.4.2 In vivo genotoxicity 94

7.5 Reproductive toxicity 95

7.6 Immunotoxicity 97

7.7 Mechanisms of action 97

7.8 Interaction with other substances 97

8. EFFECTS ON HUMANS 100

8.1 General population 100EHC 227: Fluorides

vi 8.1.1 Acute toxicity 100

8.1.2 Clinical studies 101

8.1.2.1 Skeletal effects 101

8.1.2.2 Haematological, hepatic or renal

effects 102

8.1.3 Epidemiological studies 102vii 8.1.3.1 Cancer 102

8.1.3.2 Skeletal fluorosis 104

8.1.3.3 Skeletal fracture 111

8.1.3.4 Reproductive effects 116

8.1.3.5 Respiratory effects 116

8.1.3.6 Neurobehavioural effects 117

8.1.3.7 Genotoxic effects 118

8.1.3.8 Dental effects 119

8.1.4 Interactions with other substances 125

8.2 Occupationally exposed workers 126

8.2.1 Case reports 126

8.2.2 Epidemiological studies 126

8.2.2.1 Cancer 126

8.2.2.2 Skeletal effects 127

8.2.2.3 Respiratory effects 128

8.2.2.4 Haematological, hepatic or renal

effects 128

8.2.2.5 Genotoxic effects 128

9. EFFECTS ON OTHER ORGANISMS IN THE LABORATORY

AND FIELD 130

9.1 Laboratory experiments 130

9.1.1 Microorganisms 130

9.1.1.1 Water 130

9.1.1.2 Soil 132

9.1.2 Aquatic organisms 132

9.1.2.1 Plants 132

9.1.2.2 Invertebrates 133

9.1.2.3 Vertebrates 138

9.1.3 Terrestrial organisms 142

9.1.3.1 Plants 142

9.1.3.2 Invertebrates 148

9.1.3.3 Vertebrates 149

9.2 Field observations 153

9.2.1 Microorganisms 153

9.2.2 Aquatic organisms 153

9.2.3 Terrestrial organisms 154

9.2.3.1 Plants 154

9.2.3.2 Invertebrates 158EHC 227: Fluorides

viii 9.2.3.3 Vertebrates 158

10. EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON

THE ENVIRONMENT 163

10.1 Evaluation of human health risks 163

10.1.1 Exposure 163

10.1.2 Hazard identification 164

10.1.3 Exposure–response analysis for adverse

effects in bone 170

10.2 Evaluation of effects on the environment 172

10.2.1 Exposure 172

10.2.2 Effects 175

10.2.3 Evaluation 176

11. CONCLUSIONS AND RECOMMENDATIONS FOR

PROTECTION OF HUMAN HEALTH AND THE

ENVIRONMENT 179

11.1 Conclusions 179

11.2 Recommendations 180

12. FURTHER RESEARCH 181

12.1 Health effects research 181

12.2 Environmental effects research 182

13. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES 184

REFERENCES 185

RESUME ET CONCLUSIONS 232

RESUMEN Y CONCLUSIONES 251ix NOTE TO READERS OF THE CRITERIA MONOGRAPHS

Every effort has been made to present information in the criteria

monographs as accurately as possible without unduly delaying their

publication. In the interest of all users of the Environmental Health Criteria

monographs, readers are requested to communicate any errors that may have

occurred to the Director of the International Programme on Chemical Safety,

World Health Organization, Geneva, Switzerland, in order that they may be

included in corrigenda.

* * *

A detailed data profile and a legal file can be ob tained from the

International Register of Potentially Toxic Chemicals, Case postale 356, 1219

Châtelaine, Geneva, Switzerland (telephone no. + 41 22 - 9799111, fax no. +

41 22 - 7973460, E-mail irptc@unep.ch).

* * *

This publication was made possible by grant number 5 U01 ES02617-15

from the National Ins titute of Environmental Health Sciences, National

Institutes of Health, USA, and by financial support from the Federal Ministry

for the Environment, Nature conservation and Nuclear Safety, Germany.x 

### Environmental Health Criteria

P R E A M B L E

Objectives

In 1973, the WHO Environmental Health Cri teria Programme was

initiated with the following objectives:

(i) to assess informati on on the relationship between exposure to

environmental pollutants and human health, and to provide guidelines for

setting exposure limits;

(ii) to identify new or potential pollutants;

(iii) to identify gaps in knowledge concerning the health effects of pollutants;

(iv) to promote the harmonization of toxicologic al and epidemiological

methods in order to have internationally comparable results.

The first Environmental Health Criteria (EHC) monograph, on mercury,

was published in 1976, and since that tim e an ever-increasing number of

assessments of chemicals and of physical effects have been produced. In

addition, many EHC monographs have been devoted to evaluating toxicological

methodology, e.g., for genetic, neurotoxic, teratogenic and nephrotoxic effects.

Other publications have been concerned with epidemiological guidelines,

evaluation of s hort-term tests for carcinogens, biomarkers, effects on the

elderly and so forth.

Since its inauguration, the EHC Programme has widened its scope, and

the importance of environmental effects, in addition to health effects, has been

increasingly emphasized in the total evaluation of chemicals.

The original impetus for the Programme came from World Health

Assembly resolutions and the recommendations of the 1972 UN Conference

on the Human Environment. Subsequently, the work became an integral part

of the International Programme on Chemical

Safety (IPCS), a cooperative programme of UNEP, ILO and WHO. In this

manner, with the strong support of the new partners, the impor t ance ofxi occupational health and environmental effects was fully recognized. The EHC

monographs have become widely established, used and recognized throughout

the world.

The recommendations of the 1992 UN Conference on Environment and

D evelopment and the subsequent establishment of the Intergovernmental

Forum on Chemical Safety with the priorities for action in the six programme

areas of Chapter 19, Agenda 21, all lend further weight to the need for EHC

assessments of the risks of chemicals.



### Scope

The criteria monographs are intended to provide critical reviews on the

effects on human health and the environment of chemicals and of combinations

of chemicals and physical and bio logical agents. As such, they include and

review studies that are of direct relevance for the evaluation. However, they

do not desc

ribe e very study carried out. Worldwide data are used and are

quoted from original studies, not from abstracts or reviews. Both published

and unpublished reports are considered, and it is incumbent on the authors to

assess all the articles cited in the references. Preference is always given to

published data. Unpublished data are used only when relevant published data

are absent or when they are pivotal to the risk assessment. A detailed policy

statement is available that describes the procedures used for unpublished

proprietary data so that this information can be used in the evaluation without

compromising its confidential nature (WHO (1999) Revised Guidelines for the

Preparation of Environmental Health Criteria Monographs. PCS/99.9, Geneva,

World Health Organization).

In the evaluation of human health risks, sound human data, whenever

available, are preferred to animal data. Animal and in vitro studies provide

support and are used mainly to supply evidence missing from human studies.

It is mandatory that research on human subjects is conducted in full accord

with ethical principles, including the provisions of the Helsinki Declaration.

The EHC monographs are intended to assist national and international

authorities in making risk assessments and subsequent risk management

decisions. They represent a thorough evaluation of risksEHC 227: Fluorides

xii and are not, in any sense, recommendations for regulation or standard setting.

These latter are the exclusive purview of national and regional governments.



### Content

The layout of EHC monographs for chemicals is outlined below.

• Summary — a review of the salient facts and the risk evaluation of the

chemical

• Identity — physical and chemical properties, analytical methods

• Sources of exposure

• Environmental transport, distribution and transformation

• Environmental levels and human exposure

• Kinetics and metabolism in laboratory animals and humans

• Effects on laboratory mammals and in vitro test systems

• Effects on humans

• Effects on other organisms in the laboratory and field

• Evaluation of human health risks and effects on the environment

• Conclusions and recommendations for protection of human health and

the environment

• Further research

• Previous evaluations by international bodies, e.g., IARC, JECFA, JMPR



### Selection of chemicals

Since the inception of the EHC Programme, t he IPCS has organized

meetings of scientists to establish lists of priority chemicals for subsequent

evaluation. Such meetings have been held in: Ispra, Italy, 1980; Oxford, United

Kingdom, 1984; Berlin, Germany, 1987; and North Carolina, USA, 1995. The

selection of chemicals has been based on the following criteria: the existence

of scientific evidence that the substance presents a hazard to human health

and/or the environment; the possible use, persistence, accumulation or degradation of the substance shows that there may be significant human or

environmental exposure; the size and nature of populations at risk (both

human and other species) and risks for the environment; international concern,

i.e., the substance is of major interest to several countries; adequate data on the

hazards are available.

If an EHC monograph is proposed for a chemical not on the priority list,

the IPCS Secretariat consults with the cooperating organizations and all thexiii Participating Institutions before embarking on the prepara tion of the

monograph.



### Procedures

The order of procedures that result in the publication of an EHC

monograph is shown in the flow chart on the next page. A designated staff

member of IPCS, responsible for the scientific quality of the document, serves

as Responsible Officer (RO). The IPCS Editor is responsible for layout and

language. The first draft, prepared by consultants or, more usually, staff from

an IPCS Participating Institution, is based initially on data provided from the

Int ernational Register of Potentially Toxic Chemicals and from reference

databases such as Medline and Toxline.

The draft document, when received by the RO, may require an initial

review by a small panel of experts to determine i ts scientific quality and

objectivity. Once the RO finds the document acceptable as a first draft, it is

distributed, in its unedited form, to well over 150 EHC contact points

throu ghout the world who are asked to comment on its completeness and

accuracy and, where necessary, provide additional material. The contact

points, usually designated by governments, may be Participating Institutions,

IPCS Focal Points or individual scientists known for their particular expertise.

Generally, some four months are allowed before the comments are considered

by the RO and author(s). A second draft incorporating comments received and

approved by the Director, IPCS, is then distributed to Task Group members,

who carry out the peer review, at least six weeks before their meeting.

The Task Group members serve as individual scientists, not as

representatives of any organization, government or industry. Their function

is to evaluate the accuracy, significance and relevance of the information in the

document and to assess the health and environmental risks from exposure to

the chemical. A summa

ry and recommendations for further research and

improved safety aspects are also required. The composition of the Task

Group is dictated by the range of expertise required for the subject of the

meeting and by the need for a balanced geographical distribution.xiv Commitment to draft EHC

Document preparation initiated

Draft sent to IPCS Responsible Officer (RO) 

### EHC PREPARATION FLOW CHART

Revision as

necessary Possible meeting

of a few experts

to resolve

controversial issues

First Draft First Draft Responsible Officer, Editor check for coherence of text and

readability (not language editing) Responsible Officer, Editor check for coherence of text and

readability (not language editing)

International circulation to Contact Points (150+)

Comments to IPCS (RO)

Review of comments, reference cross-check;

preparation of Task Group (TG) draft

Task Group meeting

Insertion of TG changes

Post-TG draft; detailed reference cross-check

Editing

Word-processing

Camera-ready copy

Final editing

Approval by Director, IPCS

WHO Publication Office

Printer Proofs Publication Graphics

Library for

CIP Data French/Spanish

translations of Summary Working group,

if required Editor

routine procedure

optional procedurexv The three cooperating organizations of the IPCS recognize the important

role played by nongovernmental organizations. Representatives from relevant

national and international associations may be invited to join the Task Group

as observers. Wh ile observers may provide a valuable contribution to the

process, they can speak only at the invitation of the Chairperson. Observers

do not participate in the final evaluation of the chemical; this is the sole

responsibility of the Task Group members. When the Task Group considers

it to be appropriate, it may meet in camera

.

All individuals who as authors, consultants or advisers participate in the

pre paration of the EHC monograph must, in addition to serving in their

personal capacity as scientists, inform the RO if at any time a conflict of

interest, whether actual or potential, could be perceived in their work. They

are required to sign a conflict of interest statement. Such a procedure ensures

the transparency and probity of the process.

When the Task Group has completed its review and the RO is satisfied

as to the scientific correctness and completen ess of the document, the

document then goes for language editing, reference checking and preparation of

camera-ready copy. After approval by the Director, IPCS, the monograph is

submitted to the WHO Office of Publications for printing. At thi s time, a

copy of the final draft is sent to the Chairperson and Rapporteur of the Task

Group to check for any errors.

It is accepted that the following criteria should initiate the updating of

an EHC monograph: new data are available that would substantially change the

evaluation; there is public concern for health or environmental effects of the

agent because of greater exposure; an appreciable time period has elapsed since

the last evaluation.

All Participating Institutions are informed, through the EHC progress

report, of the authors and institut ions proposed for the drafting of the

documents. A comprehensive file of all comments received on drafts of each

EHC monograph is maintained and is available on request. The Chairpersons

of Task Groups are briefed before each meeting on their role and responsibility

in ensuring that these rules are followed.xvi WHO TASK GROUP ON ENVIRONMENTAL HEALTH

CRITERIA FOR FLUORIDES

Members

Professor Peter Aggett, Lancashire Postgraduate School of Medicine and

Health, University of Central Lancashire, Preston, Lancashire, United

Kingdom

Dr Roberto Belmar, Environmental Health Division, Ministry of Health,

Santiago, Chile ( Chairman )

Dr John Bucher, Environmental Toxicology Program, National Institute of

Environmental Health Sciences, National Institutes of Health, Research

Triangle Park, NC, USA

Dr Julio Camargo, Ecology Department, Faculty of Science, University of

Alcalá, Madrid, Spain

Dr Jane Cauley, Department of Epidemiology, University of Pittsburgh,

Pittsburgh, PA, USA

Professor Jan Ekstrand, Department of Basic Oral Sciences, Karolinska

Institute, Stockholm, Sweden

Mr Paul Howe, Centre for Ecology and Hydrology, Monks Wood, Abbots

Ripton, Huntingdon, Cambridgeshire, United Kingdom ( CoRapporteur

)

Dr Gopalakrishnan Karthikeyan, Department of Chemistry, Gandhigram

Rural Institute, Gandhigram, Tamil Nadu, India

Dr Uwe Kierdorf, Institute of General and Systematic Zoology, JustusLiebig-University of Giessen, Giessen, Germany

Dr Päivi Kurttio, Radiation and Nuclear Safety Authority, Helsinki, Finlandxvii Dr Robert Liteplo, Existing Substances Division, Bureau of Environmental

Contaminants, Health Canada, Ottawa, Ontario, Canada ( CoRapporteur

)

Dr Akiyoshi Nishikawa, National Institute of Health Sciences, Tokyo,

Japan

Mr Daryl Stevens, Land and Water, Commonwealth Scientific and

Industrial Research Organisation, Adelaide, Australia

Professor Paolo Vineis, Department of Biomedical Science and Human

Oncology, University of Torino, Torino, Italy

Dr Jin Yinlong, Institute of Environmental Health and Engineering, Chinese

Academy of Preventive Medicine, Beijing, People’s Republic of China

Secretariat

Dr Antero Aitio, International Programme on Chemical Safety, World

Health Organization, Geneva, Switzerland ( Secretary )

Dr Bing Heng Chen, Department of Environmental Health, School of Public

Health, Shanghai Medical University, Shanghai, People’s Republic of

China

Mr John Fawell, Director, Environmental Division, Warren Associates,

Devizes, Wiltshire, United Kingdom

Ms Rose Gomes, Existing Substances Division, Bureau of Environmental

Contaminants, Health Canada, Ottawa, Ontario, Canada

Dr Philip Jenkins, International Programme on Chemical Safety, World

Health Organization, Geneva, Switzerlandxviii 

### ENVIRONMENTAL HEALTH CRITERIA FOR

FLUORIDES

A WHO Task Group on Environmental Health Criteria for Fluorides met

at the Institut e of Environmental Health and Engineering of the Chinese

Academy of Preventive Medicine in Beijing, People’s Republic of China, on

28 May – 1 June 2001. The group reviewed the draft document and the peer

review comments and revised and further updated the dra ft, including the

evaluation of the risks for human health and the environment from exposure

to fluorides.

The first and second drafts of this monograph were prepared by Dr R.

Liteplo, Health Canada, Canada, and Mr P. Howe, Centre for Ecology and

Hydrology, United Kingdom. The document was sent for peer review to the

IPCS contact points and additional experts on fluoride. The authors, in

collaboration with the IPCS Secretariat, revised the document based on the

comments received. Following an updating at the end of 2000, the document

was sent for review to the Task Group members and further revised based on

these comments.

Peer review comments were received from the following:

Dr J. Ahlers, Umwelt Bundes Amt, Germany

Dr R. Benson, Region VIII, US Environmental Protection Agency,

USA

Professor G.B. Bliss, N.N. Petrov’s Research Institute of Oncology,

Russian Federation

Dr M. Bolger, US Food and Drug Administration, USA

Dr J. Bucher, National Institute of Environmental Health Sciences,

USA

Dr J. Camargo, University of Alcalá, Spain

Dr S. Cao, Chinese Academy of Preventive Medicine, People’s

Republic of China

Dr F.M. Carpanini, European Centre for Ecotoxicology and

Toxicology of Chemicals, Belgium

Dr J. Cauley, University of Pittsburgh, USA

Dr L.K. Cohen, National Institute of Dental Research, USAxix Dr A. Conacher, Health Canada, Canada

Dr P. Dargan, National Poison Information Service, United Kingdom

Professor I. Dési, Albert Szent-Györgyi University, Hungary

Dr J. Donohue, US Environmental Protection Agency, USA

Dr J. Ekstrand, Karolinska Institute, Sweden

Dr L. Friberg, Karolinska Institute, Sweden

Dr R. Hertel, Federal Institute for Health Protection of Consumers

and Veterinary Medicine, Germany

Dr C. Hiremath, National Center for Environmental Assessment, US

Environmental Protection Agency, USA

Dr B.L. Johnson, Agency for Toxic Substances and Disease Registry,

USA

Dr G. Karthikeyan, Gandhigram Rural Institute, India

Dr U. Kierdorf, Justus-Liebig-University of Giessen, Germany

Dr J. Kriz, National Institute of Public Health, Czech Republic

Dr P. Kurttio, Radiation and Nuclear Safety Authority, Finland

Dr P. Lundberg, National Institute for Working Life, Sweden

Dr E. Ohanian, Office of Water, US Environmental Protection

Agency, USA

Dr Y.A. Rakhmanine, Sysin Research Institute of Human Ecology and

Environmental Health, Russian Federation

Dr D. Renshaw, Department of Health, United Kingdom

Dr J.M. Rice, International Agency for Research on Cancer, France

Dr T.G. Rossman, New York University School of Medicine, USA

Dr U. Schlottman, Federal Ministry for the Environment, Nature

Conservation and Nuclear Safety, Germany

Dr P.A. Schulte, National Institute for Occupational Safety and

Health, USA

Dr D. Stevens, Commonwealth Scientific and Industrial Research

Organisation, Australia

Dr G. Ungváry, National Institute of Occupational Health, Hungary

Dr P. Vineis, University of Torino, Italy

Ms J. Walter, Swedish Poisons Information Centre, Sweden

Dr G. Whitford, Medical College of Georgia, USAEHC 227: Fluorides

xx Dr A. Aitio of the IPCS central unit was responsible for the scientific

aspects o f the monograph, and Ms M. Sheffer, Ottawa, Canada, for the

technical editing.

The efforts of all who helped in the preparation and finalization of the

monograph are gratefully acknowledged.xxi 

### ACRONYMS AND ABBREVIATIONS

ATP adenosine triphosphate

ATPase adenosine triphosphatase

CAS Chemical Abstracts Service

CI confidence interval

DNA deoxyribonucleic acid

EC

50 median effective concentration

EHC Environmental Health Criteria monograph

FAO Food and Agriculture Organization of the United

Nations

HMDS hexamethyldisiloxane

IARC International Agency for Research on Cancer

ILO International Labour Organization

IPCS International Programme on Chemical Safety

IQ intelligence quotient

JECFA Joint FAO/WHO Expert Meeting on Food

Additives

JMPR Joint FAO/WHO Meeting on Pesticide Residues

LC

50 median lethal concentration

LD 50 median lethal dose

LOEC lowest-observed-effect concentration

LOEL lowest-observed-effect level

LT 50 median lethal time

MATC maximum acceptable toxicant concentration

NOEC no-observed-effect concentration

NTP National Toxicology Program (USA)

OR odds ratio

RO Responsible Officer

RR relative risk

SD standard deviation

UN United Nations

UNEP United Nations Environment Programme

WHO World Health Organization1 

### 1. SUMMARY AND CONCLUSIONS

This document focuses on environmental exposure to fl uoride

derived mostly from inorganic sources and its effects on humans, animals and other biota. Data on hydrogen fluoride, calcium fluoride,

sodium fluoride, sulfur hexafluoride and silicofluorides are covered, as

these compounds are considered to be the most relevant of the inorganic fluorides on the basis of quantities released to the environment,

environmental concentrations and toxicological effects on living organisms.



### 1.1 Identity, physical and chemical properties and

analytical methods

Hydrogen fluoride (HF) is a colourless, pungent liquid or gas that

is highly soluble in organic solvents and in water, in which it forms

hydrofluoric acid. Calcium fluoride (CaF

2 ) is a colourless solid that is

relatively insoluble in water and dilute acids and bases. Sodium fluoride (NaF) is a colourless to white solid that is moderately soluble in

water. Sulfur hexafluoride (SF

6 ) is a colourless, odourless, inert gas that

is slightly soluble in water and readily soluble in ethanol and bases.

The most common procedure used to quantify free fluoride anion

is the fluoride ion-selective electrode. Microdiffusion techniques are

considered to be the most accurate methods of sample preparation (i.e.,

liberation of free ionic fluoride from organic and inorganic complexes).



### 1.2 Sources of human and environmental exposure

Fluorides are released into the environment naturally through the

weathering and dissolution of minerals, in emissions from volcanoes

and in marine aerosols. Fluorides are also released into the environment via coal combustion and process waters and waste from various

industrial processes, including steel manufacture, primary aluminium,

copper and nickel production, phosphate ore processing, phosphate

fertilizer production and use, glass, brick and ceramic manufacturing,

and glue and adhesive production. The use of fluoride- c ontaining

pesticides as well as the controlled fluoridation of drinking-water

supplies also contribute to the release of fluoride from anthropogenicEHC 227: Fluorides

2 sources. Based on available data, phosphate ore production and use

as well as aluminium manufacture are the major industrial sources of

fluoride release into the environment.

Hydrogen fluoride is an important industrial comp ound that is

used mainly in the production of synthetic cryolite (Na

3 AlF

6 ), aluminium fluoride (AlF

3 ), motor gasoline alkylates and chlorofluorocarbons,

with an annual world consumption in excess of 1 million tonnes. It is

also used in etching semi c onductor devices, cleaning and etching

glass, cleaning brick and aluminium and tanning leather, as well as in

commercial rust removers. Calcium fluoride is used as a flux in steel,

glass and enamel production, as the raw material for the production of

hydro fluoric acid and anhydrous hydrogen fluoride, and as an

electrolyte in aluminium production. Sodium fluoride is used in the

controlled fluoridation of drinking-water, as a preservative in glues, in

glass and enamel production, as a flux in steel and aluminium

production, as an insecticide and as a wood preservative. Sulfur

hexafluoride is used extensively in various electronic components and

i n the production of magnesium and aluminium. Fluorosilici c acid

(H

2 SiF

6 ) and sodium hexafluorosilicate (Na

2 SiF

6 ) are used for t h e

fluoridation of drinking-water supplies.



### 1.3 Environmental transport, distribution and

transformation

Fluorides in the atmosphere may be in gaseous or particulate form.

Atmospheric fluorides can be transpo rted over large distances as a

result of wind or atmospheric turbulence or can be removed from the

atmosphere via wet and dry deposition or hydrolysis. Fluoride compounds, with the exception of sulfur hexafluoride, are not expected to

remain in the troposphere for long periods or to migrate to the stratosphere. Sulfur hexafluoride has an atmospheric residence time ranging

from 500 to several thousand years.

T he transport and transformation of fluoride in water are influ

enced by pH, water hardness and the presence of ion-exchange materials such as clays. Fluoride is usually transported through the water

cycle complexed with aluminium.Summary and Conclusions

3 The transport and transformation of fluoride in soil are influenced

by pH and the formation of predominantly aluminium and calcium

complexes. Adsorption to the soil solid phase is stronger at slightly

acidic pH values (5.5–6.5). Fluoride is not readily leached from soils.

The uptake of fluoride by biota is determined by the route of exposure, the bioavailability of the fluoride and the uptake/excretion

kinetics in the organism. Soluble fluorides are bioaccumulated by some

aquatic and terrestrial biota. However, no information was identified

concerning the biomagnification of fluoride in aquatic or terrestrial

food-chains.

Terrestrial plants may accumulate fluorides f o llowing airborne

deposition and uptake from soil.



### 1.4 Environmental levels and human exposure

Fluoride levels in surface waters vary according to location and

proximity to emission sources. Surface water concentrations generally

range from 0.01 to 0.3 mg/litre. Seawater contains more fluoride than

fresh water, with concentrations ranging from 1.2 to 1.5 mg/litre. Higher

levels of fluoride have been measured in areas where the natural rock

is rich in fluoride, and elevated inorganic fluoride levels are often seen

in regions where there is geothermal or volcanic activity (e.g., 25–50 mg

fluoride/litre in hot springs and geysers and as much as 2800 mg/litre

in certain East African Rift Valley lakes). Anthropogenic discharges

can also lead to increased levels of fluoride in the environment.

Airborne fluoride exists in gaseous and particulate forms, which

are emitted from both natural and anthropogenic sources. Fluoride

released as gaseous and particulate matter is deposited in the general

vicinity of an emission source, although some particulates may react

with other atmospheric constituents. The distribution and deposition

of airborne fluorid e are dependent upon emission strength,

meteorological conditions, particulate size and chemical reactivity. In

areas not in the direct vicinity of emission sources, the mean

concentrations of

fluoride in ambient air are generally less than 0.1

μg/m 3 . Levels may be slightly higher in urban than in rural locations;

h owever, even in the vicinity of emission sources, the levels of

airborne fluoride usually do not exceedEHC 227: Fluorides

4 2–3 μg/m

3

. In areas of China where fluoride-rich coal is used as a

source of fuel, reported concentrations of fluoride in ambient air have

reached 6 μg/m 3

.

Fluoride is a component of most types of soil, with total fluoride

concentrations ranging from 20 to 1000 μg/g in areas without natural

phosphate or fluoride deposits and up to several thousand micrograms

per gram in mineral soils with deposits of fluoride. Airborne gaseous

and particulate fluorides tend to accumulate within the surface layer of

soils but may be displaced throughout the root zone, even in

calcareous soils. The clay and organic carbon content as well as the

pH of soil are primarily responsible for the retention of fluoride in soils.

Fluoride in soil is primarily assoc iated with the soil colloid or clay

fraction. F or all soils, it is the soluble fluoride content that is

biologically important to plants and animals.

Fluorides can be taken up by aquatic organisms directly from the

water or to a lesser extent via food. Fluorides tend to accumulate in the

exoskeleton or bone tissue of aquatic animals. Mean fluoride concentrations of >2000 mg/kg have been measured in the exoskeleton of krill;

mean bone fluoride concentrations in aquatic mammals, such as seals

and whales, ranged from 135 to 18 600 mg/kg dry weight.

Fluoride levels in terrestrial biota are higher in areas with high

fluoride levels from natural and anthropogenic sources. Lichens have

been used extensively as biomonitors for fluorides. Mean fluoride concentrations of 150–250 mg/kg were measured in lichens growing within

2–3 km of fluoride emission sources, compared with a background level

of <1 mg fluoride/kg.

Most of the fluoride in the soil is insoluble and, therefore, less

available to plants. However, high soil fluoride concentrations or low

pH, clay and/or organic matter can increase fluoride levels in soil solution, increasing uptake via the plant root. If fluoride is taken up

through the root, its concentrations are often higher in the root than in

the shoot, due to the low mobility of fluoride in the plant. Most

fluorides enter plant tissues as gases through the stomata and

accumulate in leaves. Small amounts of airborne particulate fluoride can

enter the plant through the epidermis and cuticle. Vegetation has been

widely monitored in the vic inity of anthropogenic fluoride emission

sources. Correlations between fluoride concentrations in vegetationSummary and Conclusions

5 and annual growth increments, wind pattern, distance from fluoride

source and hydrogen fluoride concentrations in aerial emissions have

been observed.

Fluoride accumulates in the bone tissue of terrestrial vertebrates,

depending on factors such as diet and the proximi ty of fluoride

emission sources. For example, mean fluoride concentrations of 7000–

8000 mg/kg have been measured in the bones of small mammals in the

vicinity of an aluminium smelter.

Fluoride is ubiquitous in the environment; therefore, sources of

drinking-water are likely to contain at least some smal l amount of

fluoride. The amount of fluoride present naturally in non-fluoridated

drinking-wa ter (i.e., drinking-water to which fluoride has not been

intentionally added for the preventio n of dental caries) is highly

variable, being dependent upon the individual geological environment

from which the water is obtained. Levels may range up to approximately 2.0 mg/litre; however, in areas of the world in which endemic

fluorosis of the skeleton and/or teeth has been well documented, levels

of fluorid e in drinking-water supplies range from 3 to more than

20 mg/litre. In areas in which drinking-water is fluoridated (i.e., fluoride

is intentionally added for the prevention of dental caries), the

concentration of fluoride in drinking-water generally ranges from 0.7 to

1.2 mg/litre.

Virtually all foodstuffs contain at least trace amounts of fluoride.

Elevated levels are present in fish. Tea leaves are particularly rich in

fluoride; the amount of fluoride in brewed tea is dependent upon the

concentration of soluble fluoride in the tea leaves, the level of fluoride

in the water us ed in its preparation and the length of the brewing

period. The concentration of fluoride in food products is not significantly increased by the addition of superphosphate fertilizers, which

contain significant concentrations of fluoride (1–3%) as impurities, to

agricultural soil, due to the generally low transfer coefficient from soil

to plant mater

ial. However, a recent study suggests that, given the

right soil conditions and application of suff icient fluoride as an

impurity in phosphate fertilizers to soils, plant uptake of fluoride can be

increased. The use of water cont aining relatively low (<3.1 mg/litre)

levels of fluoride for crop irrigation generally does not increase fluoride

concentrations in foodstuffs. However, this is dependent on plant

species and fluoride concentrations in soil and water. The level ofEHC 227: Fluorides

6 fluoride in foods is significantly affected by the fluoride content of the

water used in preparation or processing, most notably in beverages

and dry foodstuffs

— for example, powdered baby formula — to which

water is added prior to consumption. The concentrations of fluoride in

unwashed or unpro cessed foods grown in the vicinity of industrial

sources (emissions) of fluoride may be greater than the levels in the

same foods grown in other non-industrially exposed areas. In commercially available infant formulas sold in the USA, soy-based ready-touse and liquid concentrate formulas contained higher levels of fluoride

than the equivalent milk-based products; however, no significant

difference was observed between soy- and milk-based powdered infant

formulas. Fluoride has been detected in breast milk; reported levels

range from <2 to about 100 μg/litre, with most values being between 5

and 10 μg/litre.

Available data on the concentrations of fluoride in indoor air are

limited. In the Netherlands, concentrations of gaseous fluoride ranged

from <2 to 49 μg/m 3 in the indoor air of five homes constructed with

wood treated with a preservative containing 56% fluoride. In China,

concentrations as high as 155 μg/m 3 have been reported for samples of

indoor air collected from homes where coal containing high amounts

of fluoride was burned indoors.

Dentifrice products for adults that are commercially available in

many countries generally contain fluoride at concentrations ranging

from 1000 to 1500 μg/g; some products designed for use by children

contain lower level s

, ranging from 250 to 500 μg/g. Dental products

such as toothpaste, mouthwash and fluoride supplements have been

identified as significant sources of fluoride. Mouth rinses marketed for

daily home use usually contain between 230 and 500 mg fluoride/litre,

whereas mouthwash products intended for weekly or biweekly use may

contain 900–1000 mg fluoride/litre.

A lthough individual exposure to fluoride is likely to be h ighly

variable, the inhalation of airborne fluoride general ly makes a minor

contribution to the total inta ke of this substance. For adults, the

consumption of foodstuffs and drinking-water is the principal route for

the intake of fluoride. In areas of the world in which coal rich in fluoride

is used for heating and food preparation, the inhalation of indoor air

and consumption of foodstuffs containing increased levels of fluoride

also contribute to elevated intakes. Infants fed formula receiveSummary and Conclusions

7 50– 100 times more fluoride than exclusively breast-fed infants. The

ingestion of dentifrice by young children makes a significant contribution to their total intake of fluoride. In general, estimated intakes of

fluoride in children and adolescents do not exceed approximately

2 mg/day. Although adults may have a higher absolute daily intake of

fluoride in milligrams, the daily intake of fluoride by children, expressed

on a milligram per kilogram body weight basis, ma y exceed that of

adults. I n certain areas worldwide in which the concentration of

fluoride in the surrounding environment may be exceedingly high and/

or where diets are composed of foodstuffs rich in fluoride, estimated

intakes of fluoride in adults as high as 27 mg/day have been reported,

the principal source being drinking-water obtained from groundwater

sources located in geological areas rich in fluoride.

Occupational exposure to fluoride via inhalation or dermal contact

likely occurs in individuals involved in the operation of welding equipment or in the processing of aluminium, iron ore or phosphate ore. In

relatively recent studies, reported concentrations of airborne fluoride

in the potrooms of aluminium smelters have been in the order of

1 mg/m

3

.



### 1.5 Kinetics and metabolism in humans and laboratory

animals

In humans and laborato ry animals, the absorption of ingested

fluoride into the general circulation occurs primarily in the stomach and

intestine and is dependent upon the relative aqueous solubility of the

form consumed. Soluble fluorides are almost completely absorbed from

the gastrointestinal tract; however, the e x tent of absorption may be

reduced by complex formation with aluminium, phosphorus, magnesium or calcium. There is partial to complete absorption of gaseous

and particulate fluorides from the respiratory tract, with the extent of

absorption dependent upon solubility and particle size.

Fluoride is rapidly distributed by the systemic circulation to the

intracellular and extracellular water of tissues; however, in humans and

laboratory anim als, approximately 99% of the total body burden of

fluoride is retained in bones and teeth. In teeth and skeletal tissue,

fluoride becomes incorporated into the crystal lattice.EHC 227: Fluorides

8 Fluoride crosses the placenta and is transferred from mother to

fetus. Fluoride is eliminated from the body primarily in the urine. In

infants, about 80–90% of a f luoride dose is retained; in adults, the

corresponding figure is approximately 60%. These values can be

altered by alterations in urinary flow and urinary pH.

Fluoride is present in body organs, tissues and fluids. Concentrations of fluoride in whole blo od of individuals residing in a community in the USA receiving fluoridated drinking-water ranged from 20

to 60 μg/litre. The mea n plasma level in 127 subjects with 5.03 mg

fluoride/litre in their drinking-water was 106 ± 76 (SD) μg/litre. Serum

and plasma contain virtually the same amount o f fluoride. Levels of

fluoride in calcified tissues are generally highest in bone, dentine and

enamel. The concentration of fluoride in bone varies with age, sex and

the type and specific part of bone and is believed to reflect an individual’s long-term exposure to fluoride. The concentration of fluoride

in dental enamel decreases exponentially with the distance f r om the

surface and varies with site, surface attrition, systemic exposure and

exposure to topically applied fluoride. The concentration of fluoride in

soft tissues is reflected by that in blood. Levels of fluoride in the urine

of healthy individuals are related to the intake of fluoride. Increased

levels of urinary fluoride have been measured in individuals following

occupational exposure to airborne fluoride and among those residing

in areas associated with endemic fluorosis.



### 1.6 Effects on laboratory mammals and in vitro test

systems

Effects on the skeleton, such as inhibition of bone mineralization

and formation, delayed fracture healing and reductions in bone volume

and collagen synthesis, have been observed in a variety of studies in

which rats received fluoride orally for periods of 3–5 weeks. In mediumterm exposure studies, altered bone remodelling, hepatic megalocytosis, nephrosis, mineralization of the myocardium, necrosis and/or

degeneration of the seminiferous tubules in the testis were observed

in mice adminis tered fluoride in drinking-water (>4.5 mg/kg body

weight per day) over a period of 6 months.

In a comprehensive carcinogenicity bioassay in which groups of

male and female F344/N rats and B6C3F

1 mice were administeredSummary and Conclusions

9 drinking-water containing up to 79 mg fluoride/litre as sodium fluoride

for a period of 2 years, there was no statistically significant increase in

the incidence of any tumour in any single exposed group. There was

a statistically significant trend of an increased incidence of osteosarcomas in male rats with increasing exposure to fluoride. However, the

incidence was within the range of historical controls.

Anoth er 2-year carcinogenicity bioassay involving SpragueDawley rats exposed to up to 11.3 mg/kg body weight per day in the

diet also found no statistically significant increase in the incidence of

ost eosarcoma or other tumours. Another study, which reported an

increased incidence of osteomas in mice receiving up to 11.3 mg/kg

body weight per day, is difficult to interpret, because the animals were

infected with Type C retrovirus.

In general, fluoride is not mutagenic in prokaryotic cells. Although

fluoride has be en shown to increase the frequency of mutations at

specific loci in cultured mouse lymphoma and human lymphoblastoid

cells, these mutations are likely du e to chromosomal damage rather

than point mutations. Fluoride has been shown to be clastogenic in a

variety of cell types. The mechanism o f clastogenicity has been

attrib uted to the effect of fluoride upon the synthesis of proteins

involved in DNA synthesis and/or repair, rather than direct interaction

between fluoride and DNA. In most studies in which fluoride was

administered orally to rodents, there was no effect upon sperm morphology or the frequency of c hromosomal aberrations, micronuclei,

sister chromatid exchange or DNA strand breaks. However, cytogenetic damage in bone marrow or alterations in sperm cell morphology

were reported when the substance was adm inistered to rodents by

intraperitoneal injection.

Reproductive or developmental effects were not observed in

recent studies in which laboratory animals were administered fluoride

in drinking-water. However, histopathological changes in reproductive

organs have been reported in male rabbits administered (orally) 4.5 mg

fluoride/kg body weight per day for 18–29 months, in male mice administered (orally) 

### $ 4.5 mg fluoride/kg body weight per day for 30 days

and in female rabbits injected subcutaneously with 

### $ 10 mg fluoride/kg

body weight per day for 100 days. Adverse effects on reproductive

function have been reported in female mice administered (orally) 

### $ 5.2

mg fluoride/kg body weight per day on days 6–15 after mating and inEHC 227: Fluorides

10 male rabbits administered (orally) 

### $ 9.1 mg fluoride/kg body weight per

day for 30 days.



### 1.7 Effects on humans

Epidemiological investigations on the effects of fluoride on human

health have examined occupationally exposed workers employed primarily in the aluminium smelting industry and populations consuming

fluoridated drinking-water. In a number of analytical epidemiological

studies of worke r s occupationally exposed to fluoride, an increased

incidence of lung and bladder cancer and increased mortality due to

cancer of these and other sites have been observed. In general, however, there has been no consistent pattern; in some of these epidemiological studies, the increased morbidity or mortality due to cancer can

be attributed to the workers’ exposure to substances other than fluoride.

The relationship between the cons umption of fluoridated

drinking-water and morbidity or mortality due to cancer has been

examined in a large number of epidemiological studies, performed in

many countries. There is no consistent evidence of an association

between the consumption of controlled fluoridated drinking-water and

increased morbidity or mortality due to cancer.

Fluori de has both beneficial and detrimental effects on tooth

enamel. The prevalence of dental caries is inversely related to the concentration of fluoride in drinking-water. The prevalence of dental

fluorosis is highly associated with the concentration of fluoride, with

a positive dose–response relationship.

Cases of skeletal fluorosis associated with the consumption of

drinking-water contai ning elevated levels of fluoride continue to be

reported. A number of factors, such as nutritional status and diet,

climate (related to fluid intake), conc omitant exposure to other substances and the intake of fluoride from sources other than drinkingwater, are believed to play a significant role in the development of this

disease. Skel

etal fluorosis may develop in workers occupationally

exposed to elevated levels of airborne fluoride; however, only limited

new information was identified.Summary and Conclusions

11 Evidence from several ecological studies has suggested that there

may be an association between the consumption of fluoridated water

and hip fractures. Other studies, however, including analytical epidemiological investigations, have not supported this finding. In some

cases, a protective effect of fluoride on fracture has been reported.

Two studies permit an evaluation of fracture risk across a range

of fluoride intakes. In one study, the relative risks of all fractures and

of hip fracture were elevated in groups drinking water with 

### $ 1.45 mg

fluoride/litre (total intake 

### $ 6.5 mg/day); this difference reached statistical significance for the gro up drinking water containing 

### $ 4.32 mg

fluoride/litre (total intake 14 mg/day). In the other study, an increased

incidence of fractures was observed in one age group of women

exposed to fluoride in drinking-water in a non-dose-dependent manner.

Epidemiological studies show no evidence of an association

between the consumption of fluoridated drinking-water by mothers and

increased risk of sp ontaneous abortion or congenital malformation.

Other epidemiological investigations of occupationally exposed workers have provided no reasonable evidence of genotoxic effects or systemic effects upon the respiratory, haematopoi etic, hepatic or renal

systems that may be directly attributable to fluoride exposure per se

.



### 1.8 Effects on other organisms in the laboratory and field

Fluoride did not affect growth or chemical oxygen demand degrading capacity of activated sludge at concentrations of 100 mg/litre. The

EC

50 for inhibition of bacterial nitrification was 1218 mg fluoride/litre.

Ninety-six-hou r EC

5 0 s

, based on growth, for freshwater and marine

algae were 123 and 81 mg fluoride/litre, respectively.

Forty-eight-hour LC

50 s for aquatic invertebrates range from 53 to

304 mg/litre. The most sensitive freshwater invertebrates were the fingernail clam ( Musculium transversum ), with statistically significant

mortality (50%) observed at a concentration of 2.8 mg fluoride/litre in

an 8-week flow-through experiment, and several net-spinning caddisfly

species (freshwater; family: Hydropsychidae), with “safe concentrations” (8760-h EC

0. 0 1 s) ranging from 0.2 to 1.2 mg fluoride/litre. The

brine shrimp ( Artemia salina ) was the most sensitive marine speciesEHC 227: Fluorides

12 tested. In a 12-day static renewal test, statistically significant growth

impairment occurred at 5.0 mg fluoride/litre.

Ninety-six-hour LC

50 s for freshwater fish range from 51 mg/litre

(rainbow trout, Oncorhync h us mykiss ) to 460 mg/litre (threespine

s tickleback, G asterosteus aculeatus ). All of the acute toxicity tests

(96 h) on marine fish gave results greater than 100 mg/litre. Inorganic

fluoride toxicity to freshwater fish appears to be negatively correlated

with water hardness (calcium carbonate) and positively correlated with

temperature. The symptoms of acute fluori d e intoxication include

lethargy, violent and erratic movement and death. Twenty-day LC

50 s

for rainbow trout ranged from 2.7 to 4.7 mg fluoride/litre in static

renewal tests. “Safe concentrations” (infinite hours LC

0.01 s) have been

estimated for rainbow trout and brown trout ( Salmo trutta ) at 5.1 and

7.5 mg fluoride/litre, respectively. At concentrations of 

### $ 3.2 (effluent)

or 

### $ 3.6 (sodium fluoride) mg fluoride/litre, the hatching of catla ( Catla

catla ) fish eggs was delayed by 1–2 h.

Behavioural experiments on adult Pacific salmon ( Oncorhynchus

sp.) in soft-water rivers indicate that changes in water chemistry

resulting from an increase in the fluoride concentration to 0.5 mg/litre

can adversely affect migration; migrating salmon are extremely sensitive to changes in the water chemistry of their river of origin. In laboratory studies, fluoride seems to be toxic for microbial processes at concentrations found in moderately fluoride polluted soils; similarly, in the

field, accumulation of organic matter in the v icinity of smelters has

been attributed to severe inhibition of microbial activity by fluoride.

Signs of inorganic fluoride phytotoxicity (fluorosis), such as

chlorosis, necrosis and decreased growth rates, are most likely to occur

in the young, expanding tissues of broadleaf plants and elongating

needles of conifers. The induction of fluorosis has been clearly demonstrated in laboratory, greenhouse and controlled field plot experiments.

A large number of the papers published on fluoride toxicity to plants

concern glasshouse fumigation with hydrogen fluoride. Foliar necrosis

was first observed on grapevines ( Vitis vinifera ) exposed to 0.17 and

0.27 μg/m

3 after 99 and 83 days, respectively. The lowest-observedeffect level for leaf necrosis (65% of leaves) in the snow pri n cess

gladiolus ( Gladiolus grandiflorus ) was 0.35 μg fluoride/m 3

. Airborne

fluoride can also affect plant disease development, although the typeSummary and Conclusions

13 and magnitude of

the effects are dependent on the specific plant–

pathogen combination.

Several short-term solution culture studies have identified a toxic

threshold for fluoride ion activity ranging from approximatel y 50 to

2000 μmol fluoride/litre. Toxicity is specific not only to plant species,

but also to ionic species of fluo ride; some aluminium fluoride complexes present in solution culture may be toxic at activities of 22–

357 μmol fluoride/litre, whereas hydrogen fluoride is toxic at activities

of 71–137 μmol fluoride/litre. A few studies have been carried out in

which the fluoride exposures have been via the soil. The type of soil

can greatly affect the uptake and potential toxicity of fluorides.

In birds, the 24-h LD 50 was 50 mg/kg body weight for 1-day-old

European starling ( Sturnus vulgaris ) chicks and 17 mg/kg body weight

for 16-day-old nestlings. Growth rates were significantly reduced at 13

and 17 mg fluoride/kg body weight (the highest doses at which growth

was monitored). Most of the early work on mammals was carried out on

domesticated ungulates. Fluorosis has been obse rved in cattle and

sheep. The lowest dietary level observed to cause an effect on wild

ungulates was in a controlled captive study with white-tailed deer

( Odocoileus virginianus ) in which a general mottling of the incisors

characteristic of dental fluorosis was noted in the animals at the 35

mg/kg diet dose.

Aluminium smelters, brickworks, phosphorus plants and fertilizer

and fibreglass plants have all been shown to be sources of fluoride

that are correlated with damage to local plant communities. Vegetation

in the vicin ity of a phosphorus plant revealed that the degree of

damage and fluoride levels in soil humus were inversely related to the

distance from the plant. Average levels of fluoride in vegetation ranged

from 281 mg/kg in severely damaged areas to 44 mg/kg in lightly

damaged areas; at a control site, the fluoride concentration was

7 mg/kg. Plant communities near an aluminiu m smelter showed differences in community composition and structure due partly to variations in fluoride tolerance. However, it must be noted that, in the field,

one of the main problems with the identification of fluoride effects is

the presence of confounding variables such as other atmosph eric

pollutants. Therefore, care must be taken when interpreting the many

field studies on fluoride pollution.EHC 227: Fluorides

14 The original findings of fluoride effe c ts on mammals were from

studies in the field on do mestic animals such as sheep and cattle.

Fluoride can be taken up from vegetation, soil and drinking-water.

Tolerance levels have been identified for domesticated animals, with

t he lowest values for dairy cattle at 30 mg/kg feed or 2.5 mg/litre

drinking-water. Incidents involving domesticated animals have originated both from natural fluoride sources, such as volcanic eruptions

and the underlying geology, and from anthropogenic sources, such as

mineral supplements, fluoride-emitting industries and power stations.

Symptoms of fluoride toxicity include emaciation, stiffness of jo ints

and abnormal teeth and bones. Other effects include lower ed milk

production and detrimental effects on the reproductive capacity of

animals. The lowest dietary concentration of fluoride to cause fluorosis

in wild deer was 35 mg/kg. Investigations of the effects of fluoride on

wildlife have focused on impacts on the structural integrity of teeth

and bone. In the vicinity of smelters, fluoride-induced effects, such as

lameness, dental disfigurement and tooth damage, have been found.



### 1.9 Evaluation of human health risks and effects on the

environment

Fluoride has both positive and negative effects on human health,

but there is a narrow range between intakes that are associated with

these effects. Exposure to all sources of fluoride, including drinkingwater and foodstuffs, is important.

There is little information to characterize the dose–response relationships for the different adverse effects. In particular, there are few

data on total exposure, particularly with respect to intake and fluoride

absorption.

The most serious effect is the skeletal accumulation of fluoride

from long-term excessive exposure to fluoride and its effect on nonne oplastic bone disease — specifically, skeletal fluorosis and bone

fractures. There is clear evidence from India and China t h at skeletal

fluorosis and an increased risk of bone fractures occur at total intakes

of 14 mg fluoride/day and evidence suggestive of an increased risk of

bone effects at total intakes above about 6 mg fluoride/day.Summary and Conclusions

15 In the fre shwater environment, natural fluoride concentrations are

usually lower than those expected to cause toxicity in aquatic organisms. However, aquatic organisms might be adversely affected in the

vicinity of anthropogenic discharges. Fluoride toxicity is dependent on

water hardness.

Sensitive plant species growing near anthropogenic sources of

fluoride are at risk. The release of fluoride from anthropogenic sources

is associated with damage to local terrestrial plant communities, but it

is often difficult to attribute these effects to fluoride alone, due to the

presence of other atmospheric pollutants. Fluoride is generally

strongly adsorbed b y soils. Consequently, plant uptake via this

pathway is relatively low, and leaching of fluoride through so il is

minimal.

Concentrations of fluoride in vegetation in the vicinity of fluoride

emission sources, such as aluminium smelters, can be higher than the

lowest dietary effect concentration reported for mammals in laboratory

experiments. Fluorosis in domesticated animals has been reported.

There are still some areas reporting fluorosis incidents in livestock due

to uptake of fluoride-rich mineral supplements and drinking-water.

Furthermore, there is a potential risk from fluoride-contaminated pasture and soil ingestion due to the long-term use of phosphate fertilizers

containing fluoride as an impurity. Fluoride-induced effects, such as

lameness and tooth damage, have also been reported in wild mammals

close to anthropogenic sources.



### 1.10 Conclusions

All organisms are exposed to fluoride from natural and/or anthropogenic sources. Very high intakes have been observed in areas worldwide in which the environment is rich in fluoride and where groundwater high in fluoride is con sumed by humans. Increased exposure

might occur in the vicinity of point sources. Fluoride in dental products

is an additional source for many people.

Fluoride has bot h beneficial and detrimental effects on human

health, with a narrow range between the intakes at which these occur.EHC 227: Fluorides

16 Effects on the teeth and skeleton may be observed at exposures below

those associated with the development ofother organ- or tissuespecific adverse health effects.

Effects on the bone (e.g., skeletal fluorosis and fracture) are considered the most relevant outcomes in assessing the adverse effects of

long-term exposure of humans to fluoride.

Skeletal fluorosis is a crippling disability that has a major public

health and socioeconomic impact, affectin g millions of people in

various regions of Africa, China and India.

Intake of fluoride in water and foodstuffs is the primary causative

factor for endemic skeletal fluorosis. In some regions, the indoor burning of fluoride-rich coal also serves as an important source of fluoride.

There are few data from which to estimate total exposure to and

the bioavailability of fluoride, and there are inconsistencies in reports

on the characterization of its adverse effects.

There is clear evidence from India and China that skeletal fluorosis

and an increased risk of bone fractures occur at a total intake of 14 mg

fluoride/day and evidence suggestive of an inc reased risk of bone

effects at total intakes above about 6 mg fluoride/day.

Excess exposure to bioavailable fluoride constitutes a risk to

aquatic and terrestrial biota.

Fluoride-sensitive species can be used as sentinels for the identification of fluoride hazards to the environment.

There is a need to improve knowledge on the accumulation of

fluoride in organisms and on how to monitor and control this.

The biological effects associated with fluoride exposure should be

better characterized.17 

### 2. IDENTITY, PHYSICAL AND CHEMICAL

PROPERTIES AND ANALYTICAL METHODS

This documen t focuses on environmental exposure to fluoride

derived mostly from inorganic sources and its e ffects on humans,

animals and other biota. Data on hydrogen fluoride, calcium fluoride,

sodium fluoride, sulfur hexafluoride and silicofluorides are emphasized,

as these compounds are considered the most relevant of the inorganic

fluorides on the basis of quantities r e leased to the environment,

environmental concentrations and toxicological effects on living

organisms.



### 2.1 Identity and physical and chemical properties

There is one stable isotope of fluorine (F), with an atomic mass of

18.9984. There are also several radioactive isotopes ( 17 F, 18 F, 20 F, 21 F

and 22 F), with 18 F having the longest half-life (109.7 min) (Weast, 1986).

At room temperature, hydrogen fluoride (HF) (relative molecular

mass 20.01; density 0.991 g/litre; CAS No. 7664-39-3) is a colourless,

pungent, acrid liquid or gas with a melting point of 

### ! 83 °C and a boiling point of 19.5 °C. Hydrogen fluoride is highly solu ble in many

organic solvents and in water, in which it forms hydrofluo ric acid

(Neumüller, 1981; Weast, 1986).

Calcium fluoride (CaF

2 ) (relative molecular mass 78.08; CAS No.

7789-75-5) is a colourless solid with a melting point of 1403 °C and a

boiling point of 2513 °C. It is relatively insoluble in water — approximately 3000 times less soluble in water than sodium fluoride (McIvor,

1990) — as well as in dilute acids and bases (Neumüller, 1981). Calcium

fluoride is a lso known as fluorite. Fluorspar is a mineral containing

60–97% calcium fluoride, depending on the grade.

Sodium fluoride (NaF) (relative molecular mass 41.9 9; CAS No.

7681-49-4) is a colourless to white solid with high melting (988–1012 °C)

and boiling (1695 °C) points. It is moderately solub le in water

(Neumüller, 1981).EHC 227: Fluorides

18 Fluorosilicic acid (H

2 Si F

6 ) (relative molecular mass 144.08; CAS

No. 16961-83-4), which is also known as hexafluorosilicic acid, hydrofluorosilicic acid, fluosilicic acid or fluorosilicic acid, is a colourless

solid that is highly soluble in water.

Sodium hexafl uorosilicate (Na

2 SiF

6 ) (relative molecular mass

18 8.05; CAS No. 16893-85-9), also known as disodium hexafluorosilicate or sodium silicofluoride, is a colourless solid that is moderately

soluble in water.

Sulfur hexafluoride (SF

6 ) (relative molecular mass 146.05; density

6.16 g/litre; CAS No. 2551-62-4) is a colourless, odourless, tasteless,

chemically inert and non-flammable gas. It is slightly soluble in water

but readily soluble in ethanol and bases (Weast, 1986).



### 2.2 Analytical methods

Methods employed for the quantification of fluoride in biological

samples and environmental media generally rely on the detection of

f luoride ion (F

– ). Perhaps the most widely used method of fluoride

quantification has involved potentiometry employing the fluoride ionselective el ectrode (Neumüller, 1981; Harzdorf et al., 1986; ATSDR,

1993). This method has been used for the quantification of fluoride in

biological tissues a nd fluids (e.g., urine, serum and plasma, organs,

bone, teeth), foodstuffs and environmental media (e.g., air, water, soil).

Owing to variations in the efficacy of sample preparation procedures,

detection limits using the fluoride ion-selective electrode may range

from 0.1 to 300 ng/m 3 in air, from 1 to 1000 μg/litre in water and from

0.05 to 20 mg/kg in tissues (Harzdorf et al., 1986; ATSDR, 1993). Other

approaches for the quantification of fluoride have included spectrophotometry, gas chromatography, ion chromatography, capillary electrophoresis, atomic absorption and photon activation (Neumüller, 1981;

ATSDR, 1993; Wen et al., 1996).

Appropriate sample preparation is a critical step in the accurate

quantification of fluoride, especially where only the free fluoride ion is

measured. For analyses involving biological mater ials, the most

accurate method i s the microdiffusion technique, such as the acidhexamethyldisiloxane (HMDS) diffusion method by Taves (1968), since

methods involving acid or alkali digestion may not convert all complexIdentity, Physical and Chemical Properties, Analytical Methods

19 inorganic and organic fluorides into a n ionic form that can be

conveniently measured (Venkateswarlu, 1983). Open ashing methods

may result in the loss of vo latile fluoride compounds or of fluoride

itself at temperatures in excess of 550 °C, or they may result in contamination with extraneous fluoride (Venkateswarlu, 1975; Campbell,

1987).20 

### 3. SOURCES OF HUMAN AND

ENVIRONMENTAL EXPOSURE

3.1 Natural occurrence

Fluorides are released into the environment naturally through the

weatheri ng of minerals, in emissions from volcanoes and in marine

aerosols (Symonds et al., 1988; ATSDR, 1993). Estimates of the annual

global release of hydrogen fluoride from volcanic sources through

passive degassing and eruptions range from 60 to 6000 kilotonnes, of

which approximately 10% may be introduced directly into the stratosphere (Symonds et al., 1988). Annually, approximately 20 kilotonnes

of fluoride may be released in marine aerosols (Symonds et al., 1988).

The main natural source of inorganic fluorides in soil is the parent

rock (WHO, 1 984). During weathering, some fluoride minerals (e.g.,

cryolite, or Na

3 AlF

6 ) are rapidly broken down, especially under acidic

conditions (Fuge & Andrews, 1988). Other minerals, such as fluorapatite (Ca

5 (PO

4 )

3 F) and calcium fluor i de, are dissolved more slowly

(Kabata-Pendias & Pendias, 1984). The mineral fluorophlogopite (mica;

KMg

3 (AlSi

3 O

10 )F

2 ) is stable in alkaline and calcareous soils (Elrashidi

& Lindsay, 1986). However, its solubility is affected by pH and the

activities of silicic acid (H

4 SiO

4 ) and aluminium (Al 3+ ), potassium (K + )

and magnesium (Mg 2+ ) ions.



### 3.2 Anthropogenic sources

3.2.1 Production and use

3.2.1.1 Hydrogen fluoride

Hydrogen fluoride (hydrofluoric acid) is an important industrial

compound, with an estimated annual world consumption in excess of

1 million tonnes (Greenwood & Earnshaw, 1984). Hydrogen fluoride is

manufactured from calcium fluoride and is used mainly in the

pro d uction of synthetic cryolite, aluminium fluoride (AlF

3 ), motor

gasoline alkylates and chlorofluorocarbons; however, the demand for

chlorofluorocarbons is decreasing as a result of efforts to restrict theirSources of Human and Environmental Exposure

21 use. Hydrogen fluoride is also used in the synthesis of uranium tetrafluoride (UF

4 ) and uranium hexafluoride (UF

6 ), both of which are used

in the nuclear indust

ry (Neumüller, 1981). It is also used in etching

semiconductor devices, cleaning and etching glass, cleaning brick and

aluminium and tanning leather, as well as in petrochemical manufacturing processes. Hydrogen fluoride may also be found in commercial

rust removers (Upfal & Doyle, 1990).

3.2.1.2 Calcium fluoride

Industrially, calcium fluoride is the principal fluoride-containing

mineral used (WHO, 1984). Identified production data were confined to

the USA, where the average annual production of calcium fluoride was

estimated to range from 118 000 to 225 000 tonnes during 1972–1978

(ATSDR, 1993). The consumption of calcium fluoride (as fluorspar) in

Canada in 1989 was estimated at 180 000 t onnes (Government of

Canada, 1993); in 1977, the estimated consumption of calcium fluoride

in the USA was 1 063 000 tonnes (ATSDR, 1993). Calcium fluoride is

used as a flux in steel, glass and enamel production and as the raw

material for the production of hy drofluoric acid and anhydrous

hydrogen fluoride (Neumüller, 1981). Calcium fluoride is also used as

a molten electrolyte for the separation of oxygen and alumina in

aluminium production.

3.2.1.3 Sodium fluoride

Data concerning the total annual consumption or production of

s odium fluoride worldwide were not identified. Sodium fluor ide is

usually prepared from hydrofluoric aci d and sodium carbonate or

sodium hydroxide (Neumüller, 1981); it i s used in the controlled

fluoridation of drinking-water, as a preser vative in certain glues, in

glass and enamel production, as a flux in steel and aluminium production, as an insecticide and as a wood preservative (Neumüller, 1981).

3.2.1.4 Fluorosilicic acid

Fluorosilicic acid is an aqueous solution that is most commonly

manufactur

ed as a co-product from the manufacture of phosphate

fertilizers. It is used widely for the fluoridation of dri nking-water, in

which it hydrolyses to release fluoride ions. When used for the fluoridation of drinking-water, fluorosilicic acid should meet appropriateEHC 227: Fluorides

22 standards, such as those published by the American Water Works

Association and the European Committee for Standardization or other

approved schemes for drinking-water chemicals.

3.2.1.5 Sodium hexafluorosilicate

Sodium hexafluorosilicate, like fluorosi licic acid, is used in the

fluoridation of drinking-water. It is normally completely dissolved in

water prior to dosing, when it hydrolyses to give fluoride ions. When

used for drinking-water fluoridation, it too should meet appropriate

standards of purity for drinking-water chemicals.

3.2.1.6 Sulfur hexafluoride

More than 110 tonnes of sulfur hexafluoride are imported into

Canada annually (G

overnment of Canada, 1993). This substance is

used extensively as an insulation and current interruption medium in

electrical switchgear, such as power circuit breakers, in various components in electrical substations (Government of Canada, 1993) and as a

protective inert gas over molten metals, such as magnesium and

aluminium (Neumüller, 1987). Over 90% of the total amount of sulfur

hexafluoride imported into Canada is used in the production of magnesium; the remainder is used in electrical switchgear (Government of

Canada, 1993).

3.2.1.7 Fluorapatite

Fluorapatite, an i mportant calcium- and fluoride-containing

mineral, is used as a source of phosphates in the fertilizer industry

(Neumüller, 1981).

3.2.1.8 Phosphate fertilizers

Phosphate fertilizers are the major source of fluoride contamination of

agricultural soils. They are manufactured from rock phosphates, which generally contain around 3.5% fluorine (Hart et al., 1934).

However, during the manufacture of phosphate fertilizers, part of the

fluoride is lost into the atmosphere during the acidulation process, and

the concentration of fluoride in the final fertilizer is lowered further

through dilution with sulfur (superphosph a tes) or ammonium ion

(ammoniated phosphates); the fi nal product commonly containsSources of Human and Environmental Exposure

23 between 1.3 and 3.0% fluorine (McLaughlin et al., 1996). In Australia,

an average annual addition of fluoride to soil through fertilization has

been estimated to be 1.1 kg/ha.

3.2.2 Emissions

Available quantitative infor mation concerning the release of

fluoride into the environment (air, water and so i l) from industrial

sources is limited. Fluoride is released into the environment via exhaust

fumes, process waters and waste from various industrial processes,

including steel manufacture, primary aluminium, copper and nickel

production, phosphate fertilizer production and use, glass, brick and

ceramic manufacturing, and glue and adhesive production. The use of

fluoride-containing pesticides as well as the fluoridation of drinkingwater supplies also contribute to the release of fluoride from anthropogenic sources.

The total annual amount of fluoride released to the environment

from industrial sources was estimated to be in excess of 23 500 tonnes

in Canada and 46 600 tonnes in the Nethe rlands (Sloof et al., 1989;

Government of Canada, 1993). The relative contribution of various

anthropogenic sources to total emissions of fluoride to air, water and

soil in Canada are estimated at 48% for phosphate fertilizer production,

20% for chemical production, 19% for aluminium production, 8% for

steel and oil production and 5% for co al burning (Government of

Canada, 1993). In the Netherlands, 93% of total fluoride emissions to

air, water and soil are derived from phosphate ore production and use,

with smaller amounts emitted via mineral processing (2%), the metal

industry (4%) and “other industry” (1%) (Sloof et al., 1989). The total

amounts of hydrogen fluoride released to air, surface water, underground injection and land in the USA during 1999 were 33 000, 7.7, 1800

and 64 tonnes, respectively. Total amounts of fluorine released to air,

surface water and land were 39, 24 and 500 tonnes, respectively (US

EPA, 1999).24 

### 4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION AND

TRANSFORMATION

4.1 Transport and distribution between media

The cycling of fluoride through the biogeosphere is summarize d

in Figure 1

Fig. 1. Cycling of fluoride through the biogeosphere

4.1.1 Atmosphere



### The fate of inorganic fluorides in the atmosphere is primarily influenced by vaporization, aerosol formation, wet and dry deposition an d

hydrolysis (Environment Canada, 1994). Non-volatile inorganic fluorid e

pa rticulates are removed from the atmosphere via condensation o r

nucleation processes. 

### Rivers, lakes &

groundwater

Sediments

Oceans

Rocks Volcanoes Dead organic

matter/excreta Air

Soil Anthropogenic

sources

BiotaEnvironmental Transport, Distribution and Transformation

25 

### Atmospheric fluorides emitted from both natural and anthropo

genic sources may be in gaseous or particulate form (Kirk & Lester

, 1986)

. Gaseous forms include hydrogen fluoride, silicon tetrafluorid e

(Si F ), fluorosilicic acid and sulfur hexafluoride. Particulate form s 4



### in clude sodium aluminium fluoride (cryolite), aluminium fluoride

, calci um fluoride, sodium hexafluorosilicate, lead fluoride (PbF ) an d

2



### calcium phosphate fluoride (fluorapatite). Globally, hydrogen fluoride

and i norganic fluoride particulates (sodium and calcium fluoride )

acc ount for approximately 75% and 25%, respectively, of inorgani c

fluorides present in the atmosphere (Hea lth Council of the Netherlands,

199 0). Fluorine and the silicon fluorides are hydrolysed in the atmos

phere to form hydro gen fluoride. Hydrogen fluoride may combine with

water v apour to produce an aerosol or fog of aqueous hydrofluori c

acid.

Fluorides adsorbed on particulate matter in the atmosphere ar e

generall y stable and are not readily hydrolysed, although they may b e

degraded by radiation if they persist in the atmosphere (US NAS

, 1971).

Hydrofluoric acid is approximately 5 orders of magnitude les s

solubl e than hydrochloric acid and will therefore be degassed fro m

marine aerosols more rea dily than hydrochloric acid. Hydrofluoric acid

is expected to be depleted in aged marine aerosols, and this may be a

signifi cant source of hydrogen fluoride in the troposphere (Brimble

combe & Clegg, 1988).

Schotte (1987) used a dispersion model to predict the formatio n

and behaviour of the fog formed from the release of hydrogen fluoride

to the a tmosphere. Initially, the hydrogen fluoride will cool signifi

cantly due to depolymerization. The fog will therefore stay near ground

level, since it is more dense than ambient air. As the fog mixes wit h

more air, it will begin to warm up and it may rise, depending on th e

ambient air temperature and the relative humidity.

Davison et al. (1973) re ported that between 60 and 74% of atmospheric fluoride in urban coal-burning areas in the United Kingdom was

in gaseous form. Similarly, approximately 60% of the fluorides in th e

atmos phere in the Netherlands are in the gaseous state (Sloof et al.

, 1989).EHC 227: Fluorides

26 

### Based upon available data, inorganic fluoride compounds, wit h

the e xception of sulfur hexafluoride, are not expected to remain in th e

tr oposphere for long periods or to migrate to the stratosphere. Esti

mates of the residence time of sulfur hexafluoride in the atmospher e

ra nge from 500 to several thousand years (Ramanathan et al., 1985 ;

Chu, 1991 ).

Fluo ride in aerosols can be transported over large distances b y

wi nd or as a result of atmospheric turbulence. The distance travelle d

is determined by the deposition velocity of both the gaseous hydroge n

fluorid e and the fluorides in particulate form. The transportation o f

pa rticles with a diameter greater than 10 F m is determined by th e

pa rticle falling speed, and the dispersion of such particles is generall y

limited to the immediate vicinity of the source. Smaller particles a re less

restricted by the falling speed and can be transported over large r

distances (Sloof et al., 1989).

Atmospheric fluorides may be transported to soils and surfac e

wat ers through both wet and dry deposition processes (US NAS

, 1971). Seasonal climatic conditions are expected to influence the rat e

at wh ich and mode by which atmospheric fluorides are deposited; fo r

exampl e, in the Tamar Valley, Tasmania, wet deposition dominate s

during winter (high precipitation; June to August), and dry depositio n

domi nates during summer (low precipitation; December to February )

(Low & Bloom, 1988).

Wet depo sition of fluoride may occur as washout from plume s

below c loud or rainout of particulates taken up by clouds. Th e

washout process is of particular importance for the removal of soluble

frac tions such as hydrogen fluoride aerosols at short distances fro m

the source. It is assumed that all irreversibly soluble gases such a s

hydr ogen fluoride are washed out during showers. The rainout process

is more im portant for the removal of fluorides distant from the sourc e

wh en the plume is situated at least partially in the clouds. Th e

scav enging ratio, the ratio between measured concentrations i n

rainwater and the atmos phere, was calculated to be 0.15 × 10 (Sloof et 6



### al., 19 89). For large-scale dispersion of fluorides, the annual averag e

wet deposition rate was 1.4% per hour for fluoride aerosol and 5.9% per

hou r for gaseous fluorides. These values give an atmospheri c

residence time of 12 h for gaseous fluoride and 50 h for particulates.Environmental Transport, Distribution and Transformation

27 

### The dry d eposition rate for fluoride in the Agra region of Indi a

was highest between December and June, when atmospheric fluorid e

concentrati ons were highest (Saxena et al., 1994). Seasonally averaged

dry deposition rates at the four sites ranged from 0.14 to 0.15 mg/m per 2



### day for summer (March to June), from 0.08 to 0.21 mg/m per day fo r 2



### winter (October to February) and from 0.008 to 0.03 mg/m per day for 2



### th e monsoon season (July to September). Similar patterns of dr y

deposition were rec orded by Chandrawanshi & Patel (1999) for central

India during 1995; however, higher deposition rates w ere reported, with

va lues of up to 1.1 mg/m per day being recorded during the winte r 2



### months. The overall mean fluoride flux deposited with dust an d

rainwater during 1995 in central India was 474 kg/km

. 2



### Several studies have been conducted to determine whether fluor

ide in rainwater was derived from anthropogenic emissions or natura l

sources such as sea salt cycling. Barnard & Nordstrom (1982) state d

that fluo ride should not be regarded as a cyclical sea salt, because th e

fluoride concentrations in rain from areas with no local anthropogenic

emissions were not correlated with sea salt availability (as determine d

by the sodium concentration). Mass balance considerations suggeste d

that the majority of fluorid e samples in the rainwater were of anthropogenic o rigin. Similarly, Saether et al. (1995) calculated that more tha n

90% of fluoride in precipitation samples collected in southern Ital y

were of non-marine origin.

The ra tio between total fluorine and chloride in rainwater fro m

Wa les was greater than the ratio in seawater (Neal et al., 1990). Thi s

impli ed enrichment of total fluorine relative to chloride, reflectin g

comple x fractionation processes in the transport of fluorine from th e

sea to the atmosphere and back to land as precipitation. The tota l

fluori ne/chloride ratio in streamwater was higher than it was in rain

water, su ggesting a net release of total fluorine from the catchment t o

the stream. The source of the release was uncertain, since the tota l

fluo rine concentration in baseflow waters was not significantly highe r

than stormflow values.

Mahade van et al. (1986) reported a strong correlation betwee n

fluori de and sodium concentrations in precipitation samples collecte d

from marine, coastal and inland sites in India. The authors suggeste d

that fl uoride in precipitation was derived from the cycling of sea salt

.EHC 227: Fluorides

28 

### The corre lation was not as strong in samples from urban areas, wher e

the majority of fluoride was derived from anthropogenic sources.

The dep osition of fluoride emitted from a phosphorus plant wa s

re ported to decrease with increasing distance from the source (Sidhu

, 1982). The rate of deposition at 1.4 km from the source was calculated

to be 2.61 g fluoride/ha per millimetre of rain and 3. 10 g fluoride/ha per

mil limetre of snow water. These data corresponded to an annua l

deposition rate of 3.43 kg/ha. Fluoride deposition on soil from leaf litter

also decreased with increa sing distance from the source. Fluoride input

to soil ranged from 10 to 720 g/ha per year. Input from precipitation w as

5–10 times greater than it was for leaf litter.

Davison & Blakemore (1980) determined the deposition of fluorid e

at f ield sites near areas of industrial and urban sources of fluorides

. The mean total fluoride deposited from wet and dry deposition an d

sedimentation was 38.0 F g/dm per week. Deposition of gaseous fluor- 2



### ide was 23.4 F g/dm per week. 2



### The average large-scale dep osition velocity for total soluble fluoride in the Netherlands was calculated to be 1.4 cm/s (Sloof et al., 1989).

This figu re was based upon 70% of the soluble fluoride being in a

gaseou s state and an atmospheric residence time of 14 h for gaseou s

flu orides and 12 days for aerosol fluorides. The average depositio n

velocit y calculated does not apply to the area surrounding a poin t

source. Under st able atmospheric conditions, a low deposition velocity

wi ll be accompanied by high atmospheric concentrations. The deposi

tion velocity of fluoride depends heavily on atmospheric conditions

. Th e deposition velocity for hydrogen fluoride can vary by more tha n

7 orders of magnitude; for particulate fluoride, it varies by less tha n

10%. The annual average effective deposition velocity varies wit h

height of the emission source and wa s calculated to be 1.2 and 2.5 cm/s

for low and high source heights, respectively, in the Netherlands.

4.1.2 Water and sediment



### In water, the transport and transformation of inorganic fluoride s

are influenced by pH, water hardness and the presence of ion

exchange materials such as clays (Environment Canada, 1994). Fluoride

is us ually transported through the water cycle complexed wit h

aluminium (Ares, 1990).Environmental Transport, Distribution and Transformation

29 

### In areas of extre me acidity and alkalinity, inorganic fluorides may

leach from fluoride-containing minerals into surface water or ground

water (Cuker & Shilts, 1979). Solubilization of inorganic fluorides from

minerals may also be enhanced by the presence of ion-exchang e

materials (e.g., bentonite clays and humic acid) (Pickering et al., 1988).

Onc e dissolved, inorganic fluorides remain in solution unde r

condit ions of low pH and hardness and in the presence of ion

exchange material (Cuker & Shilts, 1979; Sahu & Karim, 1989). Solubl e

inorganic fluorides m ay also form aerosols at the air–water interface or

vaporize into t he atmosphere (Brimblecombe & Clegg, 1988), whereas

und issolved species generally undergo sedimentation (Drury et al.

, 1980).

Kudo et al. (1987) calculated the fluoride mass balance for th e

onc e severely polluted Maurienne Valley in the French Alps. Fluorid e

emi ssion into the valley from aluminium production plants wa s

500 tonnes per year in 1980. Fluoride output by th e river was calculated

to be 680 tonnes per year, of which 665 tonnes were due to water flow

and 15 tonnes to sediment movements.

Chamblee et al. (1984) analysed approximately 100 estuarine wate r

sampl es and reported that 10.5% of fluoride originated from fluorid e

complexes with trivalent cations such as Fe and Al

. The proportion 3+ 3+



### of fluoride in the form of magnesium fluoride (MgF ) ranged from 0.4

2



### to 33.7%. Fluoride concentrations were reported to increase wit h

salinity (within a salinity range of 0.1–16‰ ).

Flu oride in seawater is divided between the following fraction s

(Stumm & Morgan, 1981):

Fraction Proportion (%) Concentration (mol/litre)

F 51 4.1 × 10

– –5



### MgF 47 3.7 × 10 + –5



### CaF 2 1.6 × 10 + –6



### In seawater, flu orides are removed by the formation of complexes

with c alcium compounds, principally carbonate and phosphate (Car

pent er, 1969). Undissolved fluoride is generally removed from th e

aquati c phase by sedimentation (US EPA, 1980). Carpenter (1969 )EHC 227: Fluorides

30 

### calc ulated a residence time for fluoride in ocean sediment to be 2

– 3 million years.

Fluoro silicic acid and hydrofluoric acid in high aquatic concen

trations such as may be found in industrial waste ponds may volatilize,

rel easing silicon tetrafluoride and hydrogen fluoride into the atmos

phere (US NAS, 1971).

4.1.3 Soil



### Factors that influence the mobility of inorganic fluorides in soi l

ar e pH and the formation of aluminium and calcium complexe s

(Pickering, 1985; Environment Canada, 1994).

In more acidic soils, concentrations of inorganic fluoride wer e

consi derably higher in the deeper horizons. The low affinity of fluor

ides for organic material results in leaching from the more acidic surfac e

horizon and increased retention by clay minerals and silts in the mor e

alkali ne, deeper horizons (Davison, 1983; Kabata-Pendias & Pendias

, 1984). This distribution profile is not observed in either alkaline o r

saline soils (Gilpin & Johnson, 1980; Davison, 1983). The fate o f

inorganic f

luorides released to soil also depends on the chemical form,

rate of deposition, soil chemistry and climate (Davison, 1983).

Fluori de in soil is mainly bound in complexes. The maximu m

adsorption of fluoride to soil was reported to occur at pH 5.5 (Barro w

& Ellis, 1986). In acidic soils with pH below 6, most of the fluoride is i n

complexes with either aluminium or iron (e.g., AlF , AlF , AlF , AlF

, 2+ + 0

–

2 3 4



### FeF

, FeF , FeF ) (Perrott et al., 1976 ; Murray, 1984b; Elrashidi & 2+ + 0

2 3 

### Lindsay, 1986). Fluoride in alkali ne soils at pH 6.5 and above is almost

com pletely fixed in soils as calcium fluoride, if sufficient calciu m

carbonate is available (Brewer, 1966).

Fluo ride binds to clay by displacing hydroxide from the surfac e

of the c lay (Huang & Jackson, 1965; Bower & Hatcher, 1967 ;

Meeu ssen et al., 1996). The adsorption follows Langmuir adsorptio n

equations and is strongly dependent upon pH and fluoride concen

tra tion. It is most significant at pH 3–4, and it decreases above pH 6.5.

Pickering et al. (1988) determined changes in free fluoride ions an d

to tal fluoride levels following equilibration of either poorly solubl eEnvironmental Transport, Distribution and Transformation

31 

### fluori de species, such as calcium fluoride and aluminium fluoride, o r

wast es from aluminium smelters. The experiments were carried out on

materials that had different cation-exchange capacities, such a s

synthetic resins, clay minerals, manganese oxide and a humic acid

. Increased amounts of fluoride were released from fluoride salts an d

fluori de-rich wastes when solids capable of exchanging cations wer e

present. The effect was greatest when there were more exchange site s

av ailable and when the fluoride compound cation had greater affinit y

for the exchange material. In a few cases, soluble complex ions wer e

formed when the released fluoride attacked the substrate, such as illite

or alumina wastes.

Fluoride is extremely immobile in soil , as determined by lysimeter

experiments. MacIntire et al. (1955 ) reported that 75.8–99.6% of added

fluoride w as retained by loam soil for 4 years. Fluoride retention wa s

corr elated with the soil aluminium content. The leaching of fluorid e

occu rred simultaneously with the leaching of aluminium, iron an d

or ganic material from soil (Polomski et al., 1982). Soil phosphate may

cont ribute to the mobility of inorganic fluoride (Kabata-Pendias &

Pend ias, 1984). Oelschläger (1971) reported that approximately 0.5

–

6. 0% of the annual addition of fluoride (atmospheric pollution an d

artif icial fertilizers) to a forest and agricultural areas was leached from

the s urface to lower soil horizons. Arnesen & Krogstad (1998) foun d

that fl uoride (added as sodium fluoride) accumulation was high in th e

upper 0– 10 cm of soil columns, where 50–90% of the accumulate d

fluoride was found. The B-horizons sorbed considerably more fluoride

than the Ah-horizons, due to higher content of aluminium oxides /

hy droxides. A study by McLaughlin et al. (2001) involving long-ter m

application of phosphate fertilizers has shown a large portion of fluoride applied as impurities in the fertilizer to remain in the 0- to 10-c m

depth of the soil profile.

In sandy ac idic soils, fluoride tends to be present in water-soluble

forms ( Shacklette et al., 1974). Street & Elwali (1983) determined th e

activ ity of the fluoride ion in acid sandy soils that had been limed

. Fluorite was shown to be the solid phase controlling fluoride ion activity in soils between pH 5.5 and 7.0. At pH values below 5.0, the fl uoride

ion activity indicated supersaturation with respect to fluorite. Thes e

data i ndicate that liming of acid soils may precipitate fluorite, with a

sub sequent reduction in the concentration of fluoride ion in solution

.EHC 227: Fluorides

32 

### Murr ay (1984b) reported that low amounts of fluoride wer e

leached from a highly disturbed sandy podzol soil of no distinct structure. Even at high fluoride application rates (3.2–80 g per soil colum n

of diameter 0.1 m with a depth of 2 m), only 2.6–4.6% of the fluorid e

appl ied was leached in the water-soluble form. The pH of the eluat e

increased with increasing fluoride application, and this was probabl y

due to adsorption of fluoride, releasing hydroxide ions from the soi l

metal hydroxides. Over time, the concentration of water-soluble fluoride decreased due to increased adsorption on soil particles.

Mean soil concentrations in Pennsylvania, USA, were 377, 0.3 8

an d 21.7 mg/kg for total fluoride, water-soluble fluoride and resin

exchangeable fluoride, respectively. The authors suggested that fluor

ide is relatively immobile in soil, since most of the fluoride was no t

readily soluble or exchangeable (Gilpin & Johnson, 1980).

The w ater-soluble fluoride in sodic surface soil treated with gyp

sum increased with increasing exchangeable sodium per cent (Chhabra

et al., 1979). The increase in e xchangeable sodium per cent also caused

an inc rease in soil pH, which in turn caused an increase in water

soluble fluoride. Incubation st udies revealed that a major portion of the

add ed fluoride was adsorbed to soil within the first 8 days. Adsorption

to so il followed Langmuir isotherms up to an equilibrium solubl e

fluoride concentr ation (11.4 mg/litre), with precipitation at higher concentrations.

Calciumfluoride was formed in soils irrigated with fluoride solutions. Calcium fluoride is formed when the fluoride adsorption capacity

is exceed ed and the fluoride and calcium ion activities exceed the io n

ac tivity product of calcium fluoride (Tracy et al., 1984). Less than 2 %

of applied fluoride was measured in the leachate, and between 15 an d

20% of added fluoride was precipitated as calcium fluoride. Fluorid e

was p recipitated in the upper profile, although the authors expecte d

that o nce the adsorption mechanisms were exceeded, soluble fluorid e

would leach deeper into the soil with continued irrigation.

A lar ge fraction of the fluoride in topsoil sampled at a distance of

0.5–1.0 km from an aluminium smelter was reported to be in water

solu ble form (Polomski et al., 1982). The authors concluded that th e

fluoride was present as calcium fluoride.Environmental Transport, Distribution and Transformation

33 

### Breimer et al. (1989) determined the vertical distribution of fluorid e

in the so il profiles sampled near an industrial region. In calcareou s

soi ls, fluoride (as extractable with hydrochloric acid) was restricted t o

the top 40–50 cm, probably due to the precipitation of calcium fluoride

in the presence of lime. A slight leaching of fluoride into the Bt and C

horizons was reported i n non-calcareous soils. Water-extractable fluoride showed an increase with depth in the A horizons and subsequently

decreased to base levels in the lower subsoil.

The adsorption of fluoride fr om the water phase may be an important transport characteristic in calcareous soils at low flow rates, bu t

thi s exchange may be rate-limited at high flow rates (Flühler et al.

, 19 82). Dissolved fluoride concentrations may be high around the roo t

zone in soils with a high fluoride input such as from atmospheri c

depo sition. The high concentrations exist only for a limited time unti l

th e fluoride is withdrawn from the solution. The adsorption isother m

was reported to be non-linear between initial concentrations of 10 and

50 mg fluoride/litre. Retention of fluoride in uncontaminated calcareous

soil was higher than retention in calcareous soil from areas wit h

fluoride contamination. The adsorption and desorption of fluoride i n

acidic soil were not related to previous fluoride contamination.

Fluoride-containing solutions increased the mobilization an d

leaching of aluminium from soils. Lea ching of aluminium was reported

to be gr eater from soil contaminated from an aluminium smelter tha n

from uncontaminated soil (Haidouti, 1995 ). In the uncontaminated soil,

losses of alumin ium from the acid soil were higher than those from the

calcareous soil. Arnesen (1998) also found that fluoride can solubilize

aluminium, ir on and organic material and can increase soil pH through

exchange with hydroxide ions.

Unlike other soluble salts, fl uoride was not leached from naturally

saliniz ed salt-affected soil. It was redistributed within the soil profil e

(Lavado et al., 1983). The adsorpti on of fluoride to soils increased with

decreasing pH within the pH range 8.5–6. Retention of fluoride in th e

soil was p ositively correlated with ammonium acetate extractable iron.EHC 227: Fluorides

34 

### 4.2 Speciation and complexation

4.2.1 Atmosphere



### Mole cular fluorine hydrolyses to form hydrogen fluoride, th e

most stable form of fluorine in the at mosphere (ATSDR, 1993). Silicon

tetrafluoride reacts with moisture in the atmosphere, forming hydrated

silica and fluorosilicic acid. Uranium hexafluoride, which is used i n

nuclear power applications, is hydrolysed to hydrogen fluoride an d

uranyl fluoride (UO F ), which are removed from the atmosphere b y 2 2 

### condensation or nucleation processes.

4.2.2 Water



### In dilu te solutions at neutral pH, dissolved fluorides are predominantly p resent as the fluoride ion (Bell et al., 1970). As the p H

decreases below pH 5.5, the proportion of fluoride ions decreases, and

th e proportion of non-dissociated hydrogen fluoride increases. How

ever, if sufficient aluminium is p resent in solution, aluminium–fluoride

complexes (AlF , AlF and AlF ) generally dominate below pH 5. 5 2+ +

2 3



### until pH 1, where hydrogen fluoride begins to dominate as p H

decreases further (Parker et al., 1995). Aluminium solubility is lo w

be tween pH 5.2 and pH 8.8, whereas at higher pH values, aluminiu m

solubilizes as the aluminate ion (Al(OH) ).

4 –



### 4.3 Bioaccumulation

So luble fluorides are bioaccumulated by some aquatic and terrestrial biota. However, no information was identified concerning th e

biom agnification of fluoride in aquatic or terrestrial food-chain s

(Heme ns & Warwick, 1972 ; Barbaro et al., 1981; ATSDR, 1993)

. Inorganic fluorides tend to accumul ate preferentially in the skeletal and

dental hard tissues of vertebrates, exoskeletons of invertebrates an d

cell walls of plants (Hemens & Warwick, 1972; Davison, 1983; Michel

et al., 1984; Kierdorf et al., 1997; Sands et al., 1998).

Biocon centration factors greater than 10 (expressed on a we t

we ight basis) were reported in both aquatic plants and animals following expos ure to solutions of up to 50 mg fluoride/litre (Sloof et al.

, 1989 ). Twenty-four hours after sodium fluoride (22 mg fluoride/litre )

was r eleased into an experimental pond, the concentration of fluorid eEnvironmental Transport, Distribution and Transformation

35 

### in aqua tic vascular plants was increased 35-fold, and uptake was als o

increased in algae (14-fold), mol luscs (12-fold) and fish (7-fold) (Kudo

& Garrec, 1983).

The water hyacinth ( Eichhornia crissipes ) has been reported t o

ta ke up fluoride from water. Plants were exposed to fluoride solution s

of 6–26 mg/litre for 4 weeks, and fluoride uptake was related to expo

sure, ranging from 0.8 to 5 mg/kg (Rao et al., 1973).

The fl uoride concentration in Sydney rock oyster ( Saccostre a

com mercialis ) sprat increased with increasing fluoride exposure. Th e

spr at were exposed to 0.7–30.7 mg fluoride/litre for 3 weeks and ha d

whol e-body concentrations ranging from 45 to 204 mg/kg dry weigh t

(Nell & Livanos, 1988).

Follow ing exposure to inorganic fluoride levels of 52 mg/litre for

72 days, prawn ( Penaeus indicus ), crab ( Tylodiplax blephariskios )

, shrimp ( Palaemon pacificus ) and mullet ( Mugil cephalus ) had whole

animal (a sh) concentrations of 3248, 1414, 3116 and 7743 mg fluor

id e/kg, respectively (Hemens & Warwick, 1972). The fluoride wa s

accumulated from the water and not via ingested plant food. No differences in total-body fluoride levels were reported in the same specie s

when exposed to 5.7 or 5.9 mg/litre for either 68 or 113 days (Hemens

et al., 19 75). Fluoride was accumulated mainly in the calcified skeletal

structures of fish and crustaceans, with higher accumulation rate s

repo rted during the early stages of growth in fish and during period s

of deposition of new skeletal material (ecdysis) in crustaceans.

Wright (1977) exposed brown trout ( Sa lmo trutta ) fry to inorganic

flu oride (5, 10 or 20 mg/litre) for 200 h (12 E C; pH 6.8; hardnes s

73 mg/litre). Fry accumulate d 10, 18 and 30 mg fluoride/kg at the three

fluoride concentrations, respectively.

Terr estrial plants may accumulate inorganic fluorides followin g

airborne deposition and uptake from the soil (Davison, 1983). Sloof et

al. (1989) reported that the main route of uptake of fluoride by plants is

from aerial deposition on the plant surface. Plant uptake from soil i s

gen erally low (except for accumulators) unless the fluoride has bee n

added suddenly, such as following amendment with sludge or phos

phat e fertilizer. The availability to plants tends to decrease with tim e

following appli cation of fluoride. The degree of accumulation dependsEHC 227: Fluorides

36 

### on seve ral factors, including soil type and, most prominently, pH. A t

acidic pH (below pH 5.5), fluoride becomes more phytoavailabl e

through complexation with soluble aluminium fluoride species, which

are th emselves taken up by plants or increase the potential for th e

flu oride ion to be taken up by the plant (Stevens et al., 1997). Plan t

upta ke of fluoride from solution culture is dependent on plant specie s

and pos itively related to the ionic strength of the growth solution

. Once a th reshold fluoride ion activity in nutrient solutions is reached

, fluoride concentrations in plants increase rapidly (Stevens et al.

, 1998a).

The up take of fluoride by ryegrass ( Lolium multiflorum ) grow n

in s oil amended with a fluoride-rich sludge increased with increasin g

fluo ride application (84–672 kg/ha) (Davis, 1980). Fluoride concen

trations in the plant tissue exceeded the 30 mg/kg dry matter threshold

of toxic ity to cattle in the first cuts of grass exposed to 300 kg sludge /

ha or greater. Concentrations in the second cut of grass exceeded th e

threshold value at 672 kg sludge/ha, and the third cut of grass wa s

below the threshold at all concentrations tested.

The amount of fl uoride taken up from soil by sunflower seedlings

( Helia nthus annuus ) was proportional to the fluoride concentration o f

th e solution added to the soil (10–100 F g/ml). Highest concentration s

were found in the roots, with reduced concentrations in successive leaf

ranks (Cooke et al., 1978). Similarly, concentrations of fluoride wer e

high in roots a nd low in shoots in tomatoes ( Lycopersicon esculentum )

and oa ts ( Avena sativa ) grown on fluoride-enriched media (Stevens e t

al., 2000).

Reynolds & Laurence (1990) found that exposure of kidney bea n

( Pha seolus vulgaris ) plants to intermittent high levels of atmospheri c

hydroge n fluoride (3 F g fluoride/m for 5 consecutive days or 5 F g 3



### fluorid e/m for 3 consecutive days) caused higher accumulation i n

3



### leave s than did exposure to a continuous dose at a lower level (1 F g

fluoride/m for 15 consecutive days), even though the plants receive d

3



### the same total dose. They also noted that the rate of uptake from th e

air over a 15-day period, particularly for the highest dose (5 F g fluor

ide/m ), was most significant at first exposure and declined durin g

3



### subsequent exposures.Environmental Transport, Distribution and Transformation

37 

### Wa lton (1987a) demonstrated that untreated earthworms ( Lum

bri cus terrestris ) from which gut soil had been removed (depurated )

contained onl y 6% of the amount of fluoride reported in whole worms.

Worms kept in soil were expo sed to a sodium fluoride concentration of

1000 mg/l itre for 30 days. The fluoride content of the worms wa s

establi shed either at the end of exposure or following an 8-day starva

ti on period. The fluoride concentration in treated worms with their gut

conten ts washed out was more than 6 times greater than the fluorid e

concentration of untreated worms. Even after an 8-day starvatio n

perio d, the concentration in exposed worms was 4 times greater tha n

the concentration in the unexposed worms. The fluoride concentration

in the worms was always lower than the concentration in the soil.

Th e deposition of fluoride in the bones of white leghorn ( Gallu s

gallus ) c hicks exposed to 252 mg fluoride/kg in the diet from hatching

for 3–10 weeks was 3–7 times greater than for birds fed a basal diet

. Fluoride was deposited in the bones of exposed females followin g

sexu al maturity and was shown to be associated with physiologica l

fact ors associated with egg production, since birds with restricte d

ov ulation had fluoride levels similar to those of males (Michel et al.

, 1984).

The bi oavailability of fluoride to sheep ( Ovis aries ) from plant s

such as sea aster (

Aster tripolium ), sand couch ( Elymus pycnanthus )

, fes cue ( Festuca rubra ) and common salt-marsh grass ( Puccinelli a

maritima ) grown in an industrial area was calculated to range from 6 5

to 90% (Baars et al., 1987).

Dai ry calves ( Bos sp.) were fed on continuous (1.5 mg/kg bod y

weight), periodic (1.5 mg/kg bo dy weight for 6 months; control diet for

6 months) and alternate (3 mg/kg body weight for 4 months; 0. 75 mg/kg

body weight for 8 months) diets for 6 years. Vertebral fluoride level s

were 550 mg/kg ash weight for controls and 15 000, 7700 and 14 00 0

mg/kg for the three treatment groups, respectively (Suttie, 1983).

Suttie et al. (1985) maintained white-tailed deer ( Odocoileu s

virginianus ) on diets containi ng fluoride at 25 and 50 mg/kg for 1 year.

Fluo ride levels in antlers ranged from 3000 to 5800 mg/kg ash weigh t

and in vertebrae from 4200 to 7400 mg/kg.38 

### 5. ENVIRONMENTAL LEVELS AND

HUMAN EXPOSURE

5.1 Environmental levels

5.1.1 Surface water

Fluoride levels in surface waters vary according to geographical

location and proximity to emission sources. Surface water concentrations generally range from 0.01 to 0.3 mg/litre (ATSDR, 1993). Ambient

surfac e water fluoride levels are summarized in Table 1. Seawater

contains more fluoride than fresh water, with concentrations ranging

from 1.2 to 1.5 mg/litre.

Higher levels of fluoride have been measured in areas where the

natural rock is rich in fluoride and near industrial outfalls. Skjelkvåle

(1994a) measured fluoride in Norwegian lakes and found concentrat ions ranging from <0.005 to 0.56 mg/litre, with a mean value of

0.037 mg/litre. Fluoride content in the bedrock was the most important

factor determining fluoride levels in lake waters. Elevated fluoride concentrations were found in acidified areas compared with other regions

with similar geology (Skjelkvåle, 1994a). Similarly, Hirayama et al. (1996)

reported increased levels of fluoride (up to 1 mg/litre) in some rivers

flowing into Lake Biwa, Japan, because of the local geology.

Elevated inorganic fluoride levels in surface water are often seen

in regions where there is geothermal or volcanic activity, at the foot of

high mountains and in areas with geological deposits of marine origin.

Thus, hot springs and geysers in Yellowstone Natio nal Park, USA,

contain 25–50 mg fluoride/litre (Neuhold & Sigler, 1960), whereas the

Firehole and Madison rivers, also in Yellowstone National Park, contain 1–14 mg fluoride /litre. Walker and Pyramid lakes, in Nevada, USA,

contain levels as high as 13 mg fluoride /litre (Sigler & Neuhold, 1972).

The mo st well documented area of high-fluoride surface water

associated with volcanic activity follows the East African Rift Valley

system from the Jordan Valley down through Sudan, Ethiopia, Uganda,

Kenya and Tanzania. Many of the lakes of the Rift Valley system have

extremely high fluoride concentrations — for example, 1640 mg/litreEnvironmental Levels and Human Exposure

39 Table 1. Concentrations of fluoride in unpolluted water

Location Fluoride

concentration

(mg/litre) a Reference

Areas with low natural fluoride

Canada 0.05 Environment Canada

(1994)

USA 0.035–0.052 b

(<0.001–0.59) Overton et al. (1986)

USA (Cache la Poudre

River) (0.3–0.5) Camargo et al. (1992)

Belgium (River

Meuse) 0.13–0.2 Van Craenenbroeck &

Marivoet (1987)

France (rivers) 0.08–0.25 Martin & Salvadori

(1983)

Norway (lakes) 0.037 (<0.005–0.56) Skjelkvåle (1994a)

Spain (Duratón River) 0.1 Camargo (1996a)

United Kingdom

(rivers) <0.05–0.4 Fuge & Andrews (1988)

Wales, United

Kingdom (streams) 0.02–0.22 Neal (1989)

Nigeria (River Niger) 0.1–0.12 Nriagu (1986)

India (rivers) 0.2–0.25 Zingde & Mandalia

(1988)

India (rivers) 0.038–0.21 Datta et al. (2000)

Tibet, China (rivers) 0.04 Cao et al. (2000)

Areas with high natural fluoride

Hot springs and

geysers, Yellowstone

National Park, USA (25–50) Neuhold & Sigler

(1960)

Firehole and Madison

rivers, USA (1–14) Neuhold & Sigler

(1960)

Walker and Pyramid

lakes, Nevada, USA (up to 13) Sigler & Neuhold

(1972)

Kenya (lakes) (up to 2800) Nair et al. (1984)EHC 227: Fluorides

40 a Mean and range of fluoride concentrations, unless otherwise stated.

b Range of means from four different regions of the eastern USA.

and 2800 mg/litre, respectively, in the Kenyan lake s Elmentaita and

Nakura (Nair et al., 1984).

Anthropogenic sources can also lead to increased local levels of

fluoride. Harbo et al. (1974) found increased concentrations of fluoride

in the surface waters of Kitimat Harbour, Canada, in the vicinity of a

large smelter. Fluoride concentrations in the River Meuse, Belgium,

increased from a maximum of 0.2 mg/litre upriver to a mean value of 0.65

mg/litre near the outfall of a phosphate fertilizer plant (Van

Craenenbroeck & Marivoet, 1987). Zingde & Mandalia (1988) found

that fluoride levels were below 0.3 mg/litre in unpolluted surface

waters; however, levels were higher c lose to a plant manufacturing

fluoride chemicals in India. Surface water concentrations ranged from

0.8 to 2.8 mg fluoride/litre, with a mean value of 1.6 mg fluoride/litre.

Similarly, Somashekar & Ramaswamy (1983) reported a mean level of

2.97 mg fluoride/litre (range 0.34–5.12 mg/litre) in the River Cauvery,

India, near discharges from both fertilizer and paper factories. Mean

fluoride levels had declined to 0.64 mg /litre 8 km downstream of the

factory discharges. Fluoride concentrations in the Uppanar Estuary,

South India, ranged from 0.2 to 23.2 mg/litre in the vicinity of a factory

producing fluoride compounds (Karunagaran & Subramanian, 1992).

Camargo (1996a) monitored the Duratón River, Spain, downstream from

an effluent discharge point. The mean fluoride concentration in the

effluent was 25.3 mg /litre; fluoride concentrations at 0.1, 2.2 and 7.3 km

downstream were 6.8, 2.7 and 1.3 mg /litre, respectively.

Skjelkvåle (1994b) found that streams close to Norwegian aluminium smelters contained 10 times more fluoride than natural background

levels due to 40 years of fluoride emissions. The levels had decreased

to background within 5 km. The author pointed out that despite the

higher levels near the smelters, the fluoride concentrations are still

w ithin the general range of concentrations for Norwegian su rface

waters. Similar results were reported by Roy et al. (2000) for an aluminium smelter on the Saguenay River, Quebec, Canada. Mean fluoride

concentrations 300 m downstream of the smelter outfalls ranged from

0.2 to 0.28 mg /litre. Camargo et al. (1992) analysed the fluoride

concentration in the Cache la Poudre River, USA, downstream from a

wastewater treatment plant. The mean fluoride concentration downstream was 1.17 mg/litre, about 4 times the mean fluoride concentration

upstream.Environmental Levels and Human Exposure

41 5.1.2 Air

Airborne fluoride exists in gaseous and particulate forms emitted

from both natural and anthropogenic sources. The gaseous fluorides

include hydrogen fluoride, carbon tetrafluoride (CF

4 ), hexafluoroethane

(C

2 F

6 ) and silicon tetrafluoride. Particulate fluorides include cryolite,

chiolite (Na

5 A l

3 F

14 ), calcium fluoride, aluminium fluoride and sodium

fluoride. Fluoride released as gaseous and particulate matter is deposited in the general vicinity of an emission source (Sidhu, 1979; Low &

Bloom, 1988), although some particulates may react with other atmospheric constituents. The distribution and deposition of airborne

fluoride are dependent upon emi ssion strength, meteorological

conditions, particulate size and chemical reactivity (Low & Blo o m,

1988).

Levels of gaseous and particulate fluoride in ambient air and in air

near industrial sources are summarized in Tables 2 and 3, respectively.

In areas not in the di rect vicinity of emission sources, the mean

concentrations of fluoride in ambient air are generally less th an 0.1

μg/m 3

. Levels may be slightly higher in urban than in rural locations;

however, even in the vicinity of emission sources, the levels of

airborne fluoride usually do not exceed 2–3 μg/m 3

. In Canada, mean

concentrations of fluoride in samples of outdoor air collected between

1980 and 1991 in the vicinity of industrial emission sources ranged up

to 0.85 μg/m

3 (Health Canada, 1993). In the Netherlands (Groningen,

Sloe and Sas van Gent), mean concentrations of fluoride in samples of

outdoor air collected during 1985 and 1986 in the vicinity of various

industrial emission sources (brickworks, aluminium plant and a glass

fibre factory) ranged from 0.25 to 0.4 μg/m 3 (Sloof et al., 1989). Median

concentrations of fluoride in the air surrounding a Norwegian alumini um smelter in the spring and summer of 1994 ranged from 1.3 to

3.8 μg/m

3 (Søyseth et al., 1996). In areas of China where fluoride-rich

coal is used as a source of fuel, concentrations of fluoride in ambient

air have reached 6 μg/m 3 (Liu, 1995).

5.1.3 Soil

Data on the levels of total and water-soluble fluoride in soil are

presented in Table 4. Fluoride is a component of most types of soil,

with total concentrations ranging from 20 to 1000 μg/g in areas without

n atural phosphate or fluoride deposits and up to several thousand

micrograms per gram in mineral soils with deposits of fluorideEHC 227: Fluorides

42 Table 2. Concentration of fluoride in ambient air

Location Detection

limit

(mg/m 3 ) Number

of

samples Concentration a

(mg/m 3 ) Reference

Arctic, Canada 0.001–0.00

4 na b 0.002–0.007 c Barrie &

Hoff (1985)

0.001–0.00

4 na 0.006–0.008 c Barrie &

Hoff (1985)

Toronto,

Ontario,

Canada na na 0.03

(0.01–0.05) Health

Canada

(1993)

147 nonindustrial

urban

locations, USA 0.05 3687 <0.05

(nd d –1.65) Thompson

et al.

(1971)

29 rural

locations, USA 0.05 724 <0.05 (nd) Thompson

et al.

(1971)

1 nonindustrial

urban

location,

United

Kingdom 0.1 na <0.1

(<0.1–0.17) Bennett &

Barratt

(1980)

4 nonindustrial

urban

locations, The

Netherlands na na 0.07

(0.05–0.08) Sloof et al.

(1989)

a Mean and range of concentrations of total (gaseous and particulate) fluoride

in ambient air, unless otherwise stated.

b na = not available.

c Range of means.

d nd = not detectable.

(Daviso n

, 1983). Airborne gaseous and particulate fluorides tend to

accumulate within the surface layer of soils but may be displaced

throughout the root zone , even in calcareous soils (Polomski et al.,

1982). The clay and organic carbon content as well as the pH of soil are

primarily responsible for the origin and/or retention of fluoride in soils.

Fluoride in soil is primarily associated wi th the soil colloid or clay

(Omueti & Jones, 1977). For all soils, it is the soluble fluoride content

that is biologically important to plants and animals. It has also been

reported that in saline soils, the bioavailability of fluoride to plants is

related to the water-soluble component of the fluoride present

(Davison, 1983).Environmental Levels and Human Exposure

43 Table 3. Concentration of fluoride in outdoor air near industrial sources

Location Distance from

source (km) Concentration a

(μg/m 3 ) Reference

Cornwall Island,

Ontario, Canada 1.65 0.79–0.85

(nd b –5.54) Environment

Canada

(1989)

4.0 0.43

(nd–23.08)

Brampton, Ontario,

Canada <1.0 0.73

(0.28–2.01) Health

Canada

(1993)

Trail, British

Columbia, Canada # 5.0 0.59

(0.51–0.61) Environment

Canada

(1994)

Various locations,

Quebec, Canada 0.5–2.0 0.1–0.67

(0.03–2.16) Environment

Canada

(1994)

South African

Highveld Various 0.08–0.14 c

2.9 (maximum) Scheifinger &

Held (1997)

Norway 1.3–3.8 Søyseth et al.

(1996)

Groningen, The

Netherlands 1.3 0.4 Sloof et al.

(1989)

Zeeland (Sloe area),

The Netherlands 6.0 0.25 Sloof et al.

(1989)

China 2–6 Liu (1995)

a Mean and range of fluoride concentrations, unless otherwise stated.

b nd = not detectable.

c Range of means.

5.1.4 Biota

Inorganic fluorides have been measure d in a wide variety of

organisms; therefore, the data summarized here will be only a representative sample of the available literature.

5.1.4.1 Aquatic organisms

Fluorides can be taken up by aquatic organisms directly from the

water or, to a lesser extent, via food. Uptake of fluorides by biota will

very much depend on the proximity of anthropogenic sources, the local

geology and the physicochemical conditions, which will determine the

bioavailability of fluorides to any given organism.Table 4. Concentration of fluoride in soil

.

Location Soil description Soil depth

(cm) Total fluoride

(mg/kg) a Water-soluble

fluoride (mg/kg) a Reference

Canada 3 reference soil samples from the

Canadian Soil Survey Committee 0–15 160 (90–247) na b Schuppli (1985)

Canada 23 reference soil samples from the

Canadian Soil Survey Committee 0–130 309 (63–1003) na Schuppli (1985)

Newfoundland, Canada forest soil na 6 2 (na) Sidhu (1982)

soil humus from various forests 0–3 (6–11) na (0.95–2.72) Sidhu (1979)

0.7 km north-east of an elemental

phosphorus plant 0–3 1138–1915 9.7–60.2 Sidhu (1979)

18.7 km north-east of an elemental

phosphorus plant 0–3 18.7–26.1 0.93–1.9 Sidhu (1979)

Pennsylvania, USA 55 samples of silt and clay 0–10 377 (136–990) 0.38 (<0.05–1.5) Gilpin & Johnson (1980)

Illinois, USA 201 surface soil samples from various

locations na 271 (70–618) na Omueti & Jones (1977)

Montana, USA forest soil samples from an area exposed to

atmospheric fluoride emissions from an

aluminium smelter na 330–1747 15.6–704 Polomski et al. (1982)

Ohio, USA silt loam (0–5 cm) collected from 7 sites

located in the vicinity of an aluminium

plant 0.5–4 353–371 na McClenahen (1976)Table 4 (contd).

Location Soil description Soil depth

(cm) Total fluoride

(mg/kg) a Water-soluble

fluoride (mg/kg) a Reference

Oklahoma, USA reference site 0–2 121 (117–124) 0.2 Schroder et al. (1999)

petrochemical waste site 0–2 1954

(38.1–5871) 4.8 (1.2–12.6)

Greece 0–4 km from an aluminium plant 0–5 823 (729–910) na Tsiros et al. (1998)

5–15 km from an aluminium plant 0–5 570 (509–658) na

8–15 km from an aluminium plant 0–5 339 (258–480) na

Austria 0.5 km from an aluminium smelter 0–10

– 84–124 c Tscherko & Kandeler

(1997)

1 km from an aluminium smelter 0–10

– 48–54 c

4 km from an aluminium smelter 0–10

– 21–33 c

15 km from an aluminium smelter 0–10

– 9.8–10 c

The Netherlands 72 samples of agricultural soil na na (39–679) na (0.5–13) Sloof et al. (1989)

Guangdong Province,

China 19 samples of cultivated, acidic soil (pH

3.8–4.5) 0–20 186–387 c 0.76–2.71 c Fung et al. (1999)

Tibet 40 samples of agricultural, forest and

urban soils na

– 0.45 Cao et al. (2000)

a Mean and range of fluoride concentrations, unless otherwise stated.

b na = not available.

c Range of means.EHC 227: Fluorides

46 Hocking et al. (1980) indicated that although there was some

accumulation of inorganic fluoride in marine vegetation, the rate of

accumulation was far lower than that of airborne inorganic fluoride by

terrestrial plants. In the vicinity of an aluminium smelter, samples of

seaweed were analysed for their inorganic fluoride concentrations. For

the seaweeds Fucu s distichus and Ectocarpus sp., inorganic fluoride

concentrations were determined for both low- and mid-tide sites at 150

and 500 m from the outfall. A t the low-tide sites

, F. distichus had

values of 62 and 48 mg fluoride/kg at 150 and 500 m, respectively.

Ectocarpus sp. had a level of 143 mg fluoride/kg at 500 m from the

outfall. A t the mid-tide sites at 150 and 500 m, E ctocarpus sp. had

levels of 317 and 1 40 mg fluoride/kg, respectively, while F

. distichus

had a level of 18 mg fluoride/kg at 500 m from the outfall.

Four species of sea grass, a marine higher plant, were sampled in

the Antikyra Gulf, Greece, near an aluminium factory. Mean fluoride

concentrations ranged from 23.4 to 34.4 mg/kg dry weight (Malea,

1995).

Aquatic invertebrates and fish tend to accumulate fluoride in the

exoskeleton and in bone, respectively. Adelung et al. (1987) sampled

two krill species, Euphaus ia superba and Meganyctiphanes

norvegi ca , and found mean whole-body fluoride concentrations of

1058 and 2153 mg/kg dry weight, respectively. Most of the fluoride was

concentrated in the exoskeleton, with levels of <6 mg/kg being found

in soft tissues. Similar whole-body and exoskeleton values were found

by Boone & Manthey (1983) and Christians & Leinemann (1980); however, they found highe r levels in soft tissues, which Adelung et al.

(1987) suggested was due to contamination from the exoskeleton during analysis. Sands et al. (1998) monitored a range of Antarctic crustaceans and found that euphausiids accumulated the highest fluoride

concentrations, with levels up to 5477 mg/kg in the exoskeleton of

Euphausia crystallorophias. T he mouthparts of E. superba contai ned

almost 13 000 mg fluoride/kg dry weight. Copepods containe d the

lowest fluoride levels (0.87 mg fluoride/kg whole body).

Wright & Davison (1975) studied the accumulation of fluoride in

a number of marine and intertidal animals found close to an aluminium

smelter at Lynemouth, United Kingdom. The seawater was found to

contain approximately 3.4 mg fluoride /litre (1.9 mg fluoride /litre

above background levels). The skeletal tissue of both vertebrates and

invertebrates was found to contain elevated fluoride levels. The meanEnvironmental Levels and Human Exposure

47 exo skeleton fluoride concentrations for the swimming crab P ortunus

d epurator , the shrimp C rangon vulgaris and the prawn Leander

serratus were 11.6, 11.5 and 11.3 mg/kg, respectively. Tissue accumulation of fluoride in the Atlantic co d ( G adus morhua ) was highest in

the skin (mean 29.6 mg fluoride / kg); in haddock ( G. aeglefin us ) and

dabs ( Ple uronectes limanda )

, the mean tissue values were highest in

the axial skeleton, 49.3 and 99.7 mg fluoride /kg, respectively.

Fish, predominantly mullet ( Mugil auratus

, M ugil cephalus and

Mugil labrosus ), caught in Gabes Bay, South Tunisia, where fluoriderich effluents were discharged (inorganic fluoride levels in water were

about 2–3 mg/litre), were found to have tissue fluoride levels 4–5 times

higher than fish obtained from the Tunis Bay, which is remote fr o m

point sources (fluoride levels in water were about 1.4 mg/litre) (Milhaud

et al., 1981). The mullet caught in Gabes Bay had mean inorganic

fluoride values of 320, 9.6 and 14.6 mg/kg wet weight for bone, muscle

and muscle/skin, respectively. Comparatively, the mean levels of fluoride in control fish were 73, 1.8 and 3.8 mg/kg wet weight, respectively.

Similar values to those found in polluted environments were reported

by Gikunju (1992) for fish inhabiting Lake Naivasha, Kenya (water

fluoride concentrations ranged from 2.4 to 2.6 mg/litre). Tilapia ( Oreochromis leucostictus ) contained fluoride concentrations of 1.97, 4.96,

143.1 and 210.6 mg/kg wet weight for muscle, skin, gills and bone,

respectively.

Adelung et al. (1985) analysed bone and soft tissue from Antarctic

s eals (Weddel seal, L eptochynotus weddelli

, and crabeater seal,

Lobodon carcinophagus ). Mean bone fluoride concentrations ranged

from 135 to 6380 mg/kg dry weight; soft tissues contained mean concentrations ranging from 2.3 (kidney) to 9.1 (brain) mg fluoride/kg.

Bone samples taken from fin whales ( B alaenoptera physalus ) in the

North Atlantic contained fluoride concentrations ranging from 4300 to

18 600 mg/kg (Landy et al., 1991); fluoride concentrations were positively correlated with age. Mikaelian et al. (1999) found mean bone

fluoride levels of 10 365 mg /kg in beluga whales ( D elphinapterus

leucas ) from Hudson Bay, Canada, compared with mean levels of

4539 mg fluoride /kg in whales from the St. Lawrence estuary, Canada;

fluoride l evels were positively correlated with age only in the latter

population.EHC 227: Fluorides

48 5.1.4.2 Terrestrial organisms

Fluoride levels in terrestrial biota tend to be increased in areas

with high fluor

ide levels due to both natural and anthropogenic

sources.

Lichens have been used extensively as biomonitors for fluorides.

Davies & Notcutt (1988) sampled lichens from the slopes of the Mount

Etna volcano in 1985 and 1987 and found fluoride levels ranging from

2 to 141 mg/kg (lichen from control sites contained <2 mg fluoride/kg).

Similarly, Davies & Notcutt (1989) found that lichens growing in the

Canary Islands accumulated fluorides from minor volcanic eruptions.

Fluoride levels of up to 23 mg / kg were measured, compared with a

background level of <1 mg /kg. Lichens have also been used to monitor

anthropogenic outputs of fluorides from both brickfields (Davies, 1982,

1986) and an aluminium smelter (Perkins et al., 1980; Perkins & Millar,

1987). Levels of fluoride were found t o be related to site emissions,

prevailing winds and distance from source. Mean fluoride

concentrations of 150–250 mg/kg were measured in lichens growing

within 2–3 km of the pollution source.

Most of the inorganic fluoride in the soil is insoluble and therefore

less available to plants. The capacity for a plant to absorb inorganic

fluoride from the soil will also depend on the species of plant and, to

some extent, the ionic species of fluoride present in solution (Stevens

et al., 1997, 1998a, 1998b) (see section 4.2). For example, some genera

(e.g., Dichapetalum

, Thea

, Camellia

, Oxylobium

, Acacia and

Palicoure ) accumulate f

l uoride and show none of the symptoms of

fluoride toxicity, with fluoride concentrations up to 4000 μg/g dry

weight (Jacobson et al., 1966; Weinstein & Alscher-Herman, 1982). In

samples obtained near a reclaimed fluorspar mining site, the levels of

inorganic fluorides in pl ants were higher than those in samples

obtained from a control site (Andrews et al., 1982). High total soil

fluoride ( 1 0 000 mg/kg) has been measured in the metalliferous

fluorspar tailings and is reflected by elevated concentrations in

vegetation (300–1000 mg/kg) (Andrews et al., 1989). Other genera are

non-accumulators of fluoride and have shown signs of fluoride toxicity

at much lower fluoride concentrations in their tissues. For example,

gladiolus ( Gladiolus sp.) plants may become necrotic with 20 μg

fluoride/g dry weight (Jacobson et al., 1966). Normal concentrations ofEnvironmental Levels and Human Exposure

49 fluoride in plant leaves usually range from 0.1 to 15 μg/g (Cholak, 1959;

Cooke et al., 1976; Hara et al., 1977).

Several plant species have the ability to convert soluble fluorides

taken up from soi l into carbon–fluoride compounds, such as monofluoroacetic acid, monofluoro-oleic acid, monofluoropalmitic acid and

monofluoromyristi c acid (Marais, 1944; Ward et al., 1964). Two well

known Aust ralian species that synthesize monofluoroacetates are

Gas trolobium spp. (Aplin, 1968) and Georgina gidgee ( Acacia

georginae F.M. Bailey) (Oelrichs & McEwan, 1961); other species

include Oxylobium spp. (Australia), Dichapetalum spp. (Africa) and

Palicourea marcgravii (reviewed by Weinstein, 1977). The function

of monofluoroacetate in the plant is unknown. The assumption that its

synthesis by the plant is a response to high concentra tions of

available inorganic fluoride in soil or water (Preuss et al., 1970) is not

supported by the finding that some plants containing

monofluoroacetate grow in soils with low fluoride concentrations (Hall,

1972).

Most fluorides enter plant tissues as gases through the stomata

and accumulate in leaves. Small am ounts of airborne particulate

fluoride can enter the plant through the epidermis and cuticle

(Weinstein, 1977). Vegetation has been widely monitored in the vicinity

of anthropogenic emission sources of fluoride. Rice et al. (1984)

obtained background flu oride concentrations for 17 plant species

indigenous to the Northern Great Plains in the USA. Mean fluoride

concentrations ranged from 1. 5 to 3.3 mg / kg. Nine of these species

were al so monitored in polluted areas, and mean fluoride

concentrations ranged from 2.8 to 11.3 mg/kg, with Rocky Mountain

juniper ( Ju niperus scopulorum ) accumulating the highest amounts of

fluoride.

Leece et al. (1986) found increased le vels of fluoride in basal

leaves of grapevines ( V itus vinifera )

, 9–25 km downwind of an

aluminium smelter in New South Wales, Australia. Inorganic fluoride

concentrations of 4–42 mg /kg were recorded, with the highest levels

9–11 km from the smelter. Bowen (1988) monitored vegetation around

two aluminium smelters in Hunter Valley, Australia. Foliar concentrations were greater than background levels at distances of up to 3 km

from one smelter and up to 1 km from the other. Close to the smelters,

tree species accumulated more foliar fluoride than shrub species, which

in turn accumulated more foliar fluoride than herb species.EHC 227: Fluorides

50 Fluoride levels in trees near an alumi nium smelter in Kitimat,

British Columbia, Canada, have been measured since 1954. From 1954

to 1973, western hemlock ( Tsuga het erophylla ) tree foliage from the

vicinity of the smelter contained a mean fluoride concentr ation of

271 mg /kg; the surrounding area had mean levels of 104 mg/kg. For the

5-year period 1974–1979, during which time there was a 64% decline in

smelter emissions, foliage from the inner, outer and surrounding zones

contained mean inorganic fluoride levels of 87, 29 and 22 mg / kg,

respectively (Bunce, 1985). Similarly, Amundson et al. (1990) found

significantly higher levels of foliar fluoride in pine species ( Pinus sp.)

growing within 0.8 km of a smelter than in those growing at a distance

of 1.8 km. Mean fluoride levels in vegetation in the vicinity of a phosphorus plant ranged from 44 mg /kg in lightly damaged ar eas to

281 mg /kg in severely damaged areas (Thompson et al., 1979). Horntvedt (1995) monitored pine and spruce ( Picea sp .) needles for 15–

25 years on permanen t plots around eight aluminium smelters and

found a high correlation between needle fluoride levels and smelter

emissions.

Taylor & Basabe (1984) established correlations between fluoride

concentrations in needles of Douglas-fir ( Pseu dotsuga menziesii ) and

annual growth increments, wind pattern, distance from fluoride source

(aluminium smelter) and hydrogen f l uoride concentrations in aerial

effluents. Mean fluoride concentrations in needles ranged from 27.6 to

60.9 mg/kg dry weight for the period 1972–1975, with an overall range

of 2–590 mg /kg. Needles collected from a control site contained mean

fluoride concentrations ranging from 3.2 to 5.8 mg /kg.

Several invertebrate species have been sampled in the vicinity of

fluoride sources such as aluminium smelters. Walton (1986) analysed

earthworms collected at different distances from an aluminium smelter.

The mean whole-body fluori de concentration was 112 mg / kg within

1 km of the plant and ranged from 19 to 48 mg/kg at a distance of 3–

15 km. Breimer et al. (1989) found a highly significant correlation

between total fluoride in earthworms ( Lumbricus sp.) and hydrochloric

acid-extractabl

e fluoride in topsoil. Worm tissue (without gut) contained 6–14 mg/kg at control sites and up to 135 mg/kg at contaminated

sites (topsoil contained >200 mg fluoride /kg). Vogel & Ottow (1991)

sampled a variety of earthworm species in the vicinity of a chemical

factory. They found a significant difference in fluoride accumulation

between species. Lumbricus terrestris showed the lowestEnvironmental Levels and Human Exposure

51 accumulation; the authors pointed out that this species tends to

migrate to deeper, less contaminated mineral horizons. Those species

that remain in the upper soil horizons tended to accumulate larger

amounts of fluoride.

Buse (1986) monitored a range of invertebrates near an aluminium

smelter and found that scavengers, such as millipedes and woodlice,

accumulated the highest concentrations (mean 1100 mg fluoride/kg).

Predatory spiders (Arachnida: Araneae), harvestmen (Arachnida: Opiliones), slugs and snails (Gastropoda: Pulmonata), earthworms (Oligochaeta), beetles (Insecta: Coleoptera) an d centipedes (Chilopoda)

contained mean fluoride concentrations of 393, 258, 190, 148, 50 and 48

mg/kg, respectivel y

. The lowest mean fluoride value was found in

grasshoppers, at 20 mg/kg.

Fluoride has been measured in the femurs of 12 species of predatory birds in the British Isles. Mean fluo ride concentrations ranged

from 112 mg/kg (common barn-owl, Tyto alba ) to 2690 mg/kg (merlin,

Falco columbarius ). Raptors that feed predominantly on small birds

ac cumulated the highest fluoride concentrations (Seel & Thomson,

1984). Henny & Burke (1990) measured fluoride in femurs of blackcrowned night-herons ( Nycticorax nycticorax ) near a phosphateprocessing complex. Fluoride concentrations ranged from 540 to 11 000

mg/kg and increased with age. Vikøren & Stuve (1996a) found that the

mean eggshell fluoride concentration was signif icantly increased in

mew gull ( Larus canus ) and herring gull ( Larus a rgentatus ) eggs

collected near aluminium smelters (120–212 mg fluoride/kg ash weight)

compared with a control site (83–143 mg fluoride/kg).

Several authors have monitored bone fluoride concentrations in

small mammals (voles, mice and shrews) in the vicinity of anthropogenic sources of fluoride (Walton, 1988). A t a heavily polluted site near

an a luminium smelter in the United Kingdom, field voles ( M icrotus

agrestis ) contained bone fluoride concentrations ranging from 910 to

11 000 mg /kg (mean 71 48 mg/kg), and wood mice ( A podemus

sylvaticus ) contained bone fluoride concentrations ranging from 1800

to 17 200 mg /kg (mean 8430 mg/kg) (Walton, 1987b). Small mammals

(fie l d vole, M. agrestis

, and common shrew, Sorex araneus ) sampled

from metalliferous fluorspar tailings contained mean fluoride concentrations ranging from 120 to 360 mg /kg. Individuals collected from aEHC 227: Fluorides

52 control site contained mean fluoride concentrations ranging from 11 to

85 mg /kg (Andrews et al., 1989).

Thomson (1987) studied the bone fluoride in the prey of common

barn-owls ( T. alba ), field voles ( M. agrestis ) and common shr ews ( S

.

araneus ). Specimens were collected from owl pellets 0.9 km from an

aluminium smelter and another site 22 km from the plant. Voles were

also trapped at two locations, and shrews were trapped at six sites. A

negative correlation was found between distance from the smelter and

inorganic fluoride levels in the vole, and inorganic fluoride levels did

not widely differ between trapped specimens and owl pellet specimens.

Fluoride concentrations in bones of the trapped voles ranged from

1581 to 2318 mg /kg at the plant site and from 111 to 257 mg /kg at the

control site. Walton (1985) found a downward trend in bone fluoride

concentrations in mice and voles at increasing distances from the

smelter. Walton (1986) analysed bones from common shr ews ( S

.

araneus ) and moles ( Talpa europaea ) collected at d ifferent distances

from the emission source. Fluoride concentrations in shrews decreased

with distance from the smelter. Mean fluoride concentrations in shrews

were 2093 mg /kg close to the plant and ranged from 770 to 1705 mg/kg

at a distance of 4–15 km. Moles from within 1 km of the plant had a

mean bone fluoride content of 7740 mg/kg; however, moles collected

at distances from 3 to 15 km showed no significant relationship with

distance, with mean concentrations ranging from 935 to 1853 mg

fluoride /kg. Shore (1995) established that it was possible to predict the

bone fluoride content of field voles ( M. agrestis ), common shrews ( S.

araneus ) or wood mice ( A. sylvaticus ) at a particular site based on data

from any one of the other species.

Walton (1984) monitored red foxes ( Vulpes vulpes ) in the United

Kingdom and found mean bone fluoride concentrations ranging from

283 mg /kg at an unpolluted site to 1650 mg/kg near a smelter. There

was a positive correlation between bone fluoride content and age.

Larger mammals have also been extensively monitored for bone

fluoride accumulation. Kierdorf et al. (1989) found mandibular fluoride

in roe deer ( Capreolus capreolus ) to be positively correlated with age,

the increase in concentrati on being higher in younger animals and

declining in older deer. Similarly, positive correlations between age and

bone fluoride content in the same species (Walton & Ackroyd, 1988),

in red deer ( Cervus elaphus ) (Dabkowska & Machoy, 1989) and inEnvironmental Levels and Human Exposure

53 European e lk (

A lces alces ) (Machoy et al., 1995) have been found.

Sever al studies have found that bone fluoride is increased in larger

mammals in the vicinity of fluoride emission sources. Newman & Yu

(1976) found that the bones of deer from an area ne a r an aluminium

plant in northwest Washington, US A, contained 10–35 times more

fluoride than bones of control deer. The ribs of control deer contained

157 and 465 mg fluoride/kg, whereas the ribs of exposed deer contained

2820 and 6809 mg fluoride/kg. H. Kierdorf & Kierdorf (1999) found a

significant reduction in the bone fluoride content of roe deer ( C.

capreolus ) near a coal-f ired power plant (Germany) when comparing

deer monitored between 1973 and 1986 (mean 1529 mg fluoride/kg dry

weight) with animals monitored between 1987 and 1998 (mean 452 mg

fluoride /kg). Kierdorf & Kierdorf (2000) carried out a historical

biomonitoring study on red deer ( C. elaphus ) antlers. Antlers collected

prior to 1860 contained fluoride levels ranging from 28 to 79 mg/kg ash

weight. The highest fluoride concentrations (up to 1392 mg /kg) were

found d uring the 1970s, with a pronounced decline during the late

1980s and 19 90s to fluoride concentrations ranging from 159 to 367

mg /kg.



### 5.2 General population exposure

5.2.1 Drinking-water

Fluoride is ubiquitous in the environment, and, therefore, sources

of drinking-water are likely to contain at least some small amount of

fluoride. The amount of fluoride present naturally in non-controlled

fluoridated drinking-water (i.e., drinking-water to which fluoride has not

been intentionally added for the prevention of dental caries) is highly

variable, being dependent upon the individual geological environment

from which the water is obtained. Available data from national surveys

conducted in a number of countries are summarized in Table 5.

In 1986, a pproximately 40% of the population of Canada was

served with controlled fluoridated dr inking-water (Droste, 1987).

Throughout Canada, there are a number of communities where sources

of d rinking-water contain elevated levels of fluoride (as high as

4.3 mg/litre) from natural sources; however, those identified communities represent only a very small proportion (0.8%) of the total population (Droste, 1987). Approximately 62% of the US population thatEHC 227: Fluorides

54 Table 5. National surveys of fluoride in drinking-water

Location Fluoride

concentration

(mg/litre) Comment References

Canada 0.05–0.21 Range of mean concentrations in

non-fluoridated a

samples

collected between 1984 and 1989

from 67 communities in 5

provinces Health

Canada

(1993)

0.73–1.25 Range of mean concentrations in

fluoridated b

samples collected

between 1986 and 1989 from 320

communities in 8 provinces Health

Canada

(1993)

Czech

Republic 0.05–3.0 Range of concentrations in more

than 4000 samples of drinkingwater collected between 1994 and

1996 from 36 districts within the

Czech Republic NIPH (1996)

Finland <0.1–3.0 Range of concentrations in 5900

groundwater samples Lahermo et

al. (1990)

<0.1–5.8 Range of concentrations in 1421

well-water samples KorkkaNiemi et al.

(1993)

<0.1–6.0 Range of concentrations in

groundwater database of

Geological Survey of Finland,

7229 shallow wells Lahermo &

Backman

(2000)

<0.1–9.3 Range of concentrations in

groundwater database of

Geological Survey of Finland,

571 drilled wells Lahermo &

Backman

(2000)

Germany 0.02–0.17 Range of concentrations of

drinking-water collected from

various facilities in Germany

between 1975 and 1986 Bergmann

(1995)

The

Netherlands 0.04–0.23 Public drinking-water samples

collected in 1985 from water

treatment plants in 12 provinces Sloof et al.

(1989)

Poland 0.02–3.0 Range of mean concentrations in

samples of drinking-water

collected from 94 localities in

central and northern Poland

between 1993 and 1995 Czarnowski

et al. (1996)Environmental Levels and Human Exposure

55 Table 5 (contd).

Location Fluoride

concentration

(mg/litre) Comment References

USA <0.1–1.0 Fluoride levels in drinkingwater of approximately 62%

of the US population served

by public supplies range from

<0.1 to 1.2 mg/litre; levels of

fluoride in drinking-water of

approximately 14% of the US

population served by public

supplies range from 1 to 2

mg/litre US EPA

(1985); US

DHHS

(1991)

a Drinking-water in which inorganic fluoride was not intentionally added for the

prevention of dental caries.

b Drinking-water in which inorganic fluoride was intentionally added for the prevention of dental caries.

is served by public water sys tems is supplied with drinking-water

containing fluoride at concentrations at or below 1.2 mg/litre (US EPA,

1985; US DHHS, 1991). Approximately 0.4% of the population in the

USA is supplied with drinking-water (from groundwater sources) containing natural fluoride that exceeds a concentration of 2.0 mg/litre (US

EPA, 1985; US DHHS , 1991). In other countries, such as Poland,

Finland and the Czech Republic, levels of fluoride in drinking-water as

high as 3 mg/litre have also been reported (Lahermo et al., 1990; Bergmann, 1995; Czarnowski et al., 1996; NIPH, 1996).

In areas of the world in which endemic fluorosis of the skeleton

and/or teeth has been well documented, levels of fluoride in groundwater s upplies have been reported to range from 3 to more than

20 mg/litre (WHO, 1984; Krishnamachari, 1987; Kaminsky et al., 1990;

US DHHS, 1991). In Tanzania, 30% of waters used for drinking-water

contained fluoride at concentrations above 1.5 mg/litre, levels in the

Rift Valley being up to 45 mg/litre (Latham & Gretch , 1967).

Mean concentrations of fluoride ranged from 0.19 to 0.33 mg/litre

in more t h an 24 varieties of domestic and imported bottled waters

purchased in the USA in 1989 (Nowak & Nowak, 1989; Stannard et al.,

1990). In a study of 52 varieties of bottled water purchased in the

vicinity of Houston, Texas, USA, between 1989 and 1991, the levels of

fluoride ranged from <0.1 to 0.72 mg/litre (Tate & Chan, 1994). Similar

findings were reported in a study of bottled water sold in Cleveland,

Ohio, USA (Lalumandier & Ayers, 2000). The concentration of fluoride

in 24 samples of mineral water collected in Germany between 1984 and

1989 ranged from 0.017 to 2.70 mg/litre (Bergmann, 1995).EHC 227: Fluorides

56 5.2.2 Food

Since publication of the first EHC document on fluoride (WHO,

1984), additional information on the levels of fluoride in foodstuffs has

become available. Virtually all foodstuffs contain at least trace amounts

of fluoride. A summary of various studies in which the levels of fluoride in foods have been assessed is presented in Table 6.

Table 6. Levels of fluoride in foodstuffs

Table 6 (contd).

Food Fluoride

concentration

(mg/kg) a Comment References

Milk and

milk

products 0.01–0.8 Range of concentrations

in 12 varieties of dairy

products in Canada Dabeka &

McKenzie

(1995)

0.045–0.51 Range of mean

concentrations in 13

varieties of dairy products

in Hungary Schamschula

et al. (1988a)

0.019–0.16 Range of concentrations

in milk and milk products

sampled between 1981

and 1989 in Germany Bergmann

(1995)

Meat and

poultry 0.04–1.2 Range of concentrations

in 17 varieties of (cooked

and raw) meat and poultry

in Canada Dabeka &

McKenzie

(1995)

0.01–1.7 Range of mean

concentrations in 7

varieties of meat and

poultry in Hungary Schamschula

et al. (1988a)

0.29 Mean concentration in

canned meat and sausage

sampled between 1981

and 1989 in Germany Bergmann

(1995)

Fish 0.21–4.57 Range of concentrations

in 4 varieties of fish

available in Canada Dabeka &

McKenzie

(1995)Environmental Levels and Human Exposure

Table 6 (contd).

Food Fluoride

concentration

(mg/kg) a Comment References

57 Fish

(contd). 0.06–1.7 Range of concentrations

in 6 varieties of fish

available in the USA Whitford

(1996)

Soups 0.41–0.84 Range of concentrations

in 4 varieties of soup

available in Canada Dabeka &

McKenzie

(1995)

0.42–0.94 Range of mean

concentrations in 7

varieties of soup available

in Hungary Schamschula

et al. (1988a)

Baked

goods and

cereals 0.04–1.02 Range of concentrations

in 24 varieties of baked

goods and cereals

available in Canada Dabeka &

McKenzie

(1995)

1.27–1.85 Range of mean

concentrations in rice

consumed in three

villages in China Chen et al.

(1996)

0.06–0.49 Range of mean

concentrations in 13

varieties of baked goods

and cereals available in

Hungary Schamschula

et al. (1988a)

0.05–0.39 Range of concentrations

in bread and grains

sampled between 1981

and 1989 in Germany Bergmann

(1995)

Vegetable

s 0.01– 0.68 Range of concentrations

in 38 varieties of raw,

cooked and canned

vegetables in Canada Dabeka &

McKenzie

(1995)

0.28–1.34 Range of mean

concentrations in three

staple vegetables

consumed in three

villages in China Chen et al.

(1996)

0.01–0.86 Range of mean

concentrations in 24

varieties of vegetables

available in Hungary Schamschula

et al. (1988a)

0.023 Mean concentration in

some vegetables sampled

between 1981 and 1989

in Germany Bergmann

(1995)EHC 227: Fluorides

Table 6 (contd).

Food Fluoride

concentration

(mg/kg) a Comment References

58 Fruits and

fruit juices 0.01–0.58 Range of concentrations

in 25 varieties of fruit and

fruit juices available in

Canada Dabeka &

McKenzie

(1995)

0.03–0.19 Range of mean

concentrations in 16

varieties of fruits and fruit

juices available in

Hungary Schamschula

et al. (1988a)

0.02–2.8 Range of concentrations

in 532 varieties of fruit

juice and juice-flavoured

beverages in the USA Kiritsy et al.

(1996)

0.027 Mean concentration in

some fruits sampled

between 1981 and 1989

in Germany Bergmann

(1995)

0.014–0.35 Range of concentrations

in some fruit juices

sampled between 1984

and 1989 in Germany Bergmann

(1995)

Fats and

oils 0.05–0.13 Range of concentrations

in 3 varieties of fats and

oils available in Canada Dabeka &

McKenzie

(1995)

Sugars

and

candies 0.01–0.28 Range of concentrations

in 7 varieties of sugarcontaining products available in Canada Dabeka &

McKenzie

(1995)

0.01–0.31 Range of mean

concentrations in 12

varieties of sugarcontaining foods

available in Hungary Schamschula

et al. (1988a)

Beverages 0.21–0.96 Range of concentrations

in 6 varieties of beer,

wines, coffee and soft

drinks available in

Canada Dabeka &

McKenzie

(1995)

0.19–0.78 Range of mean

concentrations in 3

varieties of coffee and soft

drinks available in

Hungary Schamschula

et al. (1988a)

0.003–0.39 Range of concentrations

in some soft drinks

sampled between 1984

and 1989 in Germany Bergmann

(1995)Environmental Levels and Human Exposure

Table 6 (contd).

Food Fluoride

concentration

(mg/kg) a Comment References

59 Beverages

(contd). 0.02–1.28 Range of concentrations

in 332 samples of soft

drinks sold in Iowa, USA,

between 1995 and 1997 Heilman et

al. (1999)

Tea 4.97 Concentration in tea

available in Canada Dabeka &

McKenzie

(1995)

90.94–287.9 Range of mean

concentrations of tea

consumed in 3 villages in

China Chen et al.

(1996)

243.7 Mean concentration in 4

samples of tea leaves

used in Hungary Schamschula

et al. (1988a)

82–371 Range of concentrations

in samples of 32 tea

leaves purchased in Hong

Kong Wei et al.

(1989)

0.005–0.174 Range of concentrations

in herbal and children’s

teas sampled between

1984 and 1989 in

Germany Bergmann

(1995)

0.37–2.07 Range of concentrations

in black tea sampled

between 1984 and 1989

in Germany Bergmann

(1995)

a For liquid items, concentrations are in mg/litre.

Tea leaves are particularly rich in fluoride (see Table 6). The conc entration of fluoride in brewed tea is dependent upon the concen

tration of soluble fluoride in the tea leaves, the level of fluoride in the

water used in its preparation an d the length of the brewing period

(Smid & Kruger, 1985). Chan & Koh (1996) reported that the mean

concentration of fluoride in 21 brands of caffeinated tea, 11 brands of

decaffeinated tea and 12 brands of herbal tea purchased in the USA

and brewed (with water containing <0.02 mg fluoride/litre) for 5–120

min was approximately 1.5–2.4, 3.2–4.2 and 0.05–0.1 mg/litre, respectively. The levels of fluoride in 40 brands of brewed and instant coffee

purchased in the USA ranged from 0.1 to 0.58 mg/litre, with no significant difference between caffeinated and decaffeinated coffees (Warren

et al., 1996).EHC 227: Fluorides

60 The concentration of fluoride in food products is usually not signific antly increased by the addition of superphosphate fertilizers to

agricultural soil (Oelschläger, 1971), due to the generally low transfer

coefficient from soil to plant material. However, a recent study by

McLaughlin et al. (2001) found significant increases in fluoride concentrations in herbage harve sted from plots fertilized with phosphate

fertilizers (537 kg total phosphorus added over 59 years) over a long

period (22 mg fluoride/kg) compared with concentrations in herbage

harvested from u nfertilized plots (11 mg fluoride/kg). These data

suggest that, given the right soil condit ions and application of

sufficient fluoride as an impurity in phosphate fertilizers to soils, plant

uptake of fluoride can be increased. The use of water containing relatively low (<3.1 mg/litre) levels of fluoride for crop irrigation generally

does not increase foodstuff fluoride concentrations (Schamschula et

al., 1988a). However, this is dependent on plant species and fluoride

concentrations in soil and water. For example, Kabasakalis & Tsolaki

(1994) showed that fluoride concentrations in vegetables irrigated with

water containing 10 mg fluoride/litre were increased compared with

fluoride concentrations in vegetables grown with irrigation water containing low fluoride concentrations (0.15 mg/litre). They also comme n ted that fluoride has a tendency to accumulate in the vegetable

leaves rather than in the fruits.

Levels of fluoride in foods are significantly affected by the fluoride content of the water u sed in preparation or processing, most

notably in beverages and dry foodstuffs to which water is added prior

to consumption (Kumpulainen & Koivistoinen, 1977; Schamschula et

al., 1988a). In a study conducted in a rural area of China, immersion of

vegetables in hot spring water containing elevated levels of fluoride

(approximately 20.3 mg/litre) reportedly led to a significant increase in

the fluoride content of the food product (Xu et al., 1995). The concentration of fluoride in water used to parboil rice influenced the level

in the final product (Anasuya & Paranjape, 1996). The concentrations

of fluoride in unwashed or unprocessed foods grown in the vicinity of

industrial sources (emissions) of fluoride in Japan (Sakurai et al., 1983;

Tsunoda & Tsunoda, 1986; Muramoto et al., 1 991) and the United

Kingdom (Jones et al., 1971) have been up to 100-fold greater than the

levels in the same foods grown in other non-industrially exposed areas.

In commercially available infant formulas sold in the USA, soybased ready-to-use and liquid concentrate formulas contained higherEnvironmental Levels and Human Exposure

61 levels of fluoride than the equivalent milk-based products; however, no

significant difference was observed between soy- and milk-based powdered infant formulas (McKnight-Han es et al., 1988) (Table 7). The

mean concentrations of fluoride in liquid milk- and soy-based concentrated formulas diluted with water containing 1 mg fluoride/litre were

0.62 and 0.74 mg/litre, respectively. The mean concentrations in powdered milk- and soy-based formulas diluted with water containing 1 mg

fluoride/litre were 0.83 and 0.85 mg/litre, respectively (McKnight-Hanes

et al., 1988). For infant formula s available in Australia, the average

concentrations of fluoride in powdered milk- and soy-based formulas

diluted with water cont aining 1 mg fluoride/litre were 1.2 and 1.34

mg/litre, respectively (Silva & Reynolds, 1996). Studies of fluoride

levels i n infant foods available in Germany revealed mean concentrations gener ally of 0.02–0.3 mg/litre (Bergmann, 1995). In other

studies (see Table 7), levels of fluoride in infant formulas have ranged

fr om 100 to 1600 μg/litre (Fomon & Ekstrand, 1993). A study of a

variety of infant food products available in the USA indicated concentrations of fluoride ranging from 0.01 to 8.38 μg/g; the highest concentrations were in products containing chicken (Heilman et al., 1997). In

other infant food and beverage products (see Table 7), fluoride levels

ranged from 10 to 6000 μg/litre (Fomon & Ekstrand, 1993). Reported

levels of fluoride in breast milk have ranged from <2 to 100 μg/litre, with

most values being between 5 and 10 μg/litre (Ekstrand, 1981; Esala et

al., 1982; Dabeka et al., 1986; Bergmann, 1995).

5.2.3 Indoor air

Available data on the concentrations of fluoride in indoor air are

limited. In the Netherlands, concentrations of gaseous fluoride ranged

from <2 to 49 μg/m 3 in the indoor air of five homes constructed with

wood treated with a preservative containing 56% fluoride (Sloof et al.,

1989). Gu et al. (1990) reported a mean concentration of fluoride of

approximately 60 μg/m 3 for samples of indoor air collected from homes

in China where coal containing high amounts of fluoride was burned

indoors. In other studies conducted in China, the levels of fluoride in

th e indoor air of homes where fluoride-rich coal was burned have

ranged from 2.1 to 46.1 μg/m 3 (Liu, 1995) and from 15 to 155 μg/m 3

(Zhang & Cao, 1996). (See section 5.1.2 for concentrations of fluoride

in outdoor air.)EHC 227: Fluorides

62 Table 7. Concentrations of fluoride in infant foods a

Food item Fluoride

concentration

(μg/litre) b Reference

Human milk 5–10 Esala et al. (1982);

Spak et al. (1983);

Ekstrand et al. (1984)

Cow’s milk 30–60 J. Ekstrand

(unpublished data)

Formula Johnson & Bawden

(1987); McKnightHanes et al. (1988) Ready to feed 100–300

Concentrated

liquid

Milk-based 100–300

Isolated

soybean-based 100–400

Powdered

Milk-based 400–1000

Isolated

soybean-based 1000–1600

Most products other than

dry cereals 100–300 Singer & Ophaug

(1979); Dabeka et al.

(1982)

Fruit juices Singer & Ophaug

(1979); Dabeka et al.

(1982) Produced with

non-fluoridated

water 10–200

Produced with

fluoridated water 100–1700

Dry cereals Singer & Ophaug

(1979); Dabeka et al.

(1982) Produced with

non-fluoridated

water 90–200

Produced with

fluoridated water 4000–6000

Wet-pack cereal fruit

products 2000–3000 Singer & Ophaug

(1979); Dabeka et al.

(1982)

Poultry-containing

products 100–5000 Singer & Ophaug

(1979); Dabeka et al.

(1982)

a From Fomon & Ekstrand (1993); Fomon et al. (2000).

b Concentration ranges have been rounded off. Most reported values fall within

the ranges listed in the table.Environmental Levels and Human Exposure

63 5.2.4 Consumer products

Dentifrice products for adults that are commercially available in

many countries generally contain fluoride at concentrations ranging

from 1000 to 1500 μg/g (Whitford, 1987; Sloof et al., 1989; Newbrun,

1992). Some dent ifrices designed for use by children contain lower

levels of fluoride, ranging from 250 to 500 μg/g (Newbrun, 1992). Dental

products such as toothpaste, mouthwash and fluoride supplements

have been identified as significant sources of fluoride (Ekstrand, 1987;

Drummond et al., 1990). Topical mouth rinses marketed for daily home

use may contain between 230 and 500 mg fluoride/litre, while

mouthwash products intended for weekly or biweekly use may contain

900–1000 mg fluoride/litre (Sloof et al., 1989; Grad, 1990; Whitford,

1996).

5.2.5 Intake estimates

Published estimates for the intake of fluoride have been summarized in Table 8. Although individual exposure to fluoride is likely to be

highly variable, the inhalation of airborne fluoride in most cases makes

a minor contribution to t he total intake of this element. Infants may

receive small quantities of fl uoride from breast milk. For adults, the

consumption of foodstuffs and drinking-water is the principal route for

the intake of fluoride. The ingestion of dentifrice by young children

makes a significant contribution to their total intake of fluoride. Studies

have indicated that children between 2 and 5 years of age may ingest

between 0.11 and 0.39 g of dentifrice per brushing (Bruun & Thylstrup,

1988; Simard et al., 1989; Naccache et al., 1990, 1992). In general,

estimated intakes of fluoride in children and adolescents do not exceed

approximately 2 mg/day.

Although adults may have a higher absolute daily intake of fluoride in milligrams, the daily intake of fluoride by children on a milligram

per kilogram body weight basis may exceed that of adults. In certain

areas of the world in which the concentration of fluoride in the

surrounding envir o nment (mainly groundwater) may be exceedingly

high and/or diets are composed of foo ds rich in fluoride, estimated

intakes of fluoride in adults as high as 27 mg/day have been reported

(Liu, 199 5 ; Anasuya et al., 1996; Cao et al., 1996; Karthikeyan et al.,

1996). In certain areas of China in which coal rich in fluoride is used for

heating and food preparation (e.g., cooking, food drying), theTable 8. Estimated intakes of fluoride

Sources of fluoride

exposure Age group Estimated fluoride

intake, mg/day (mg/kg

body weight per day) a Comment References

Foodstuffs Adults 0.6 Intakes based upon levels of fluoride and

consumption of major foodstuffs Varo &

Koivistoinen

(1980)

Foodstuffs and

drinking-water in four

regions of the USA infants (6 months):

(drinking-water <0.3 mg fluoride/litre)

(drinking-water >0.7 mg fluoride/litre)

children (2 years old):

(drinking-water <0.3 mg fluoride/litre)

(drinking-water >0.7 mg fluoride/litre) 0.226 (0.028)

0.418 (0.052)

0.207 (0.017)

0.621 (0.05) Intakes based on fluoride levels in market

basket survey of foods and drinking-water

and estimated consumption Ophaug et

al. (1985)

Foodstuffs (including

infant formulas) and

beverages,

fluoridated or nonfluoridated drinkingwater in North

America children (up to 6 years of age) 0.05–1.23 (0.01–0.16) Summary of 8 studies published between

1943 and 1988 on the estimated intakes of

fluoride from food and beverages by North

American children Levy (1994)Table 8 (contd).

Sources of fluoride

exposure Age group Estimated fluoride

intake, mg/day (mg/kg

body weight per day) a Comment References

Ambient air,

foodstuffs (including

infant formula or

breast-fed),

fluoridated or nonfluoridated drinkingwater, soil, dentifrice

in Canada infants (up to 6 months of age)

children (7 months to 4 years)

adolescents (5–11 years)

adults (20+ years) <0.01–0.65

(<0.001–0.09)

0.6–2.1 (0.05–0.16)

0.7–2.1 (0.03–0.08)

2.2–4.1 (0.03–0.06) Estimated total intakes by multimedia

exposure analysis based upon ranges of

mean concentrations of fluoride in

ambient air, fluoridated or non-fluoridated

drinking-water and soil; levels of fluoride in

survey of 109 foodstuffs in Canada, breast

milk, infant formula and average level of

fluoride in dentifrice available in Canada,

as well as assigned reference values for

body weight, inhalation of air, and

consumption of water, soil and foodstuffs,

by various age groups of the population of

Canada Government

of Canada

(1993)

(Infant formula or

breast-fed), cereal,

juices, fluoridated or

non-fluoridated

drinking-water,

dentifrice, fluoride

supplements in the

USA infants (6 months of age)

children (1 year of age)

children (2–3 years of age) 0.4–1.4 (0.05–0.19)

0.32–0.73 (0.03–0.08)

0.76–1.23 (0.06–0.09) Estimated intakes based upon

concentrations of fluoride in breast milk or

various infant formulas reconstituted with

fluoridated or non-fluoridated drinkingwater, levels in juices and cereals, as well

as estimated intakes from dentifrice and

fluoride supplements by children in the

USA Levy et al.

(1995)Table 8 (contd).

Sources of fluoride

exposure Age group Estimated fluoride

intake, mg/day (mg/kg

body weight per day) a Comment References

Various infant

formulas

reconstituted with

fluoridated or nonfluoridated drinkingwater in Australia infants (6 months of age)

infants (1 year of age) 0.13–1.35 (0.02–0.17)

0.14–1.65 (0.02–0.17) Estimated intakes based upon levels of

fluoride in various infant formulas

available in Australia reconstituted with

either fluoridated or non-fluoridated

drinking-water Silva &

Reynolds

(1996)

Ambient air,

drinking-water and

limited variety of

foodstuffs in China adolescents (7–15 years)

adults (16+ years) 1.16–4.57

1.61–7.51 Estimated intakes based upon levels of

fluoride in ambient air, local supplies of

drinking-water and levels in a limited

variety of locally grown foodstuffs in an

area of China with known elevated levels

of fluoride in local water supplies Liu (1995)

Ambient air,

drinking-water and

limited variety of

foodstuffs in China adolescents (8–15 years)

adults (16+ years) 1.51–10.6

1.79–17.0 Estimated intakes based upon levels of

fluoride in ambient air, indoor air, local

supplies of drinking-water and levels of

fluoride in a limited variety of locally

grown foodstuffs in four areas of China

where fluoride-containing coal is burned

for heating and cooking Liu (1995)Table 8 (contd).

Sources of fluoride

exposure Age group Estimated fluoride

intake, mg/day (mg/kg

body weight per day) a Comment References

Principal foods

consumed by

Tibetan and Han

peoples residing in

Sichuan province in

China (levels of

fluoride in drinkingwater were low [0.1

mg/litre]) Tibetan

(8–15 years)

(>15 years)

Han

(8–15 years)

(>15 years) 5.49

10.43

1.44

2.54 Increased intake of fluoride by Tibetans

based upon their consumption of a local

type of prepared barley and brick tea;

foodstuffs not consumed by Han residing in

this area; prevalence of dental and

skeletal fluorosis greater among Tibetans

than among Han Cao et al.

(1996)

Ambient air,

beverages, food and

drinking-water in

Hungary children with a mean age of 3.9 years

adolescents with a mean age of 14

years 0.22–1.11

0.3–1.49 Estimated intakes based upon levels in

available foodstuffs, beverages, air and

drinking-water containing levels of fluoride

ranging from 0.06 to 3.1 mg/litre Schamschula

et al. (1988b)

Drinking-water and

food in India children (age not specified) 1.5–20 Estimated range of mean intakes based

upon levels in foodstuffs and local supplies

of drinking-water that ranged in

concentration from 0.32 to 9.6 mg/litre Karthikeyan

et al. (1996)Table 8 (contd).

Sources of fluoride

exposure Age group Estimated fluoride

intake, mg/day (mg/kg

body weight per day) a Comment References

Drinking-water and

food in normal or

fluorotic villages in

India adults (age not specified) 0.84–4.69 (normal)

3.40–27.1 (fluorotic) Range of intakes based upon consumed

foodstuffs and local supplies of drinkingwater from rural areas in India considered

either normal or fluorotic, based upon the

absence or occurrence of endemic skeletal

fluorosis in these areas, respectively Anasuya et

al. (1996)

Diet, beverages and

toothpaste in New

Zealand children (3–4 years of age) 0.17–1.31 (0.01–0.07) Range of intakes based on duplicate-diet

survey of foodstuffs and beverages (nonfluoridated or fluoridated) consumed as

well as calculated intake from toothpaste,

in a study of 66 children GuhaChowdhury et

al. (1996)

Commercially

available foods and

drinking-water in

Germany infants 1–12 months of age 0.099–0.205 Estimated intake based upon consumption

of commercially available food and

drinking-water containing 0.13 mg

fluoride/litre Bergmann

(1995);

Bergmann &

Bergmann

(1995)

Breast milk and

homemade food in

Germany infants 1–12 months of age 0.002–0.075

(0.0005–0.007) Estimated intakes by infants receiving

breast milk as well as homemade foodsTable 8 (contd).

Sources of fluoride

exposure Age group Estimated fluoride

intake, mg/day (mg/kg

body weight per day) a Comment References

Food, beverages and

drinking-water in

Germany children 1–15 years of age 0.112–0.264 Estimated intake based upon consumed

foodstuffs, beverages and drinking-water Bergmann

(1995);

Bergmann &

Bergmann

(1995) Foods, beverages

and drinking-water in

Germany adolescents (15–18 years of age) 0.523 (males) (0.008)

0.470 (females) (0.009) Estimated intake based upon consumed

foodstuffs, beverages and drinking-water

Foods, beverages

and drinking-water in

Germany Adults 0.560 (males) (0.007)

0.442 (females) (0.007) Estimated intake based upon consumed

foodstuffs, beverages and drinking-water

16- to 40-month-old children

consuming drinking-water containing

0.3 mg fluoride/litre 0.965 (0.073) Estimated intake based upon consumed

foodstuffs, beverages and drinking-water

Foods, beverages

and dentifrice in the

USA 16- to 40-month-old children

consuming drinking-water containing

0.8–1.2 mg fluoride/litre 0.965 (0.07) Estimated intake based upon consumed

foods, beverages and dentifrice RojasSanchez et

al. (1999)

a Data in parentheses are the estimated intakes of fluoride, expressed as mg/kg body weight per day, when presented in the reference cited.EHC 227: Fluorides

70 inhalation of ind o or air and consumption of foodstuffs containing

increased levels of fluoride also contribute to elevated intakes (Zhang

& Cao, 1996; Liang et al., 1997).



### 5.3 Occupational exposure

The informati o n presented in this section focuses on data that

have become available since the last EHC document on fluoride was

pub lished (WHO, 1984). Occupational exposure to fluoride via

inhalation or dermal contact likely occurs for individuals involved in

the operation of welding equipment or in the processing of aluminium,

iron ore or phosphate ore (Sloof et al., 1989). In the Netherlands,

concentrations of fluoride in the workroom air of seven machine shops

and shipyards where welding operations were conducted ranged from

30 to 16 500 μg/m 3 ; levels were highest in areas where welding

activities were conducted in small enclosed spaces (Sloof et al., 1989).

The mean concentration of fluoride in the workroom air of an aluminium

plant in Sweden was 900 μg/m 3 , with 34% of the fluoride present in the

gaseous form (Sloof et al., 1989). The concentration of total airborne

fluoride in the potroom of an aluminium smelter in British Columbia,

Canada, was approximately 0. 48 mg/m 3 (Chan-Yeung et al., 1983a).

Søyseth et al. (1995) reported that between 1986 and 1988, the average

concentration of total fluoride in the potroom of an aluminium smelter

in western Norway was app roximately 0.5 mg/m 3

. Rønneberg (1995)

indicated that, based upon monitoring studies conducted at a Norwegian aluminium smelter in 1962, time-weighted-average concentrations

of airborne fluoride ranged from 1.5 to 2.7 mg/m 3 . The time-weightedaverage concentrations of either dust-borne fluoride or hydrogen fluoride at two aluminium production facilities in the Netherlands operating

since the mid-1960s were reported to be approximately 0.5 mg/m 3 (Sorgdrager et al., 1995). The mean level of total a irborne fluoride in the

potroom of an Iranian aluminium smelter was reportedly 0.93 mg/m 3

(Akbar-Khanzadeh, 1995). During 1987–1988 and 1990–1994, the mean

levels of gaseous fluoride in the air of a hydrofluoric acid production

facility loca ted in Mexico were reportedly 1.78 and 0.21 mg/m 3

, respectively (Calderon et al., 1995). Mean levels of hydrogen fluoride

up to 3 mg/m

3 were reported for some areas of a phosphate fertilizer

production facility in Poland (Czarnowski & Krechniak, 1990).71 

### 6. KINETICS AND METABOLISM IN HUMANS AND

LABORATORY ANIMALS

6.1 Absorption

6.1.1 Absorption in humans

In humans, the dominating route of fluoride absorption is via the

gastrointestinal tract. Airborne fluoride may also be inhaled.

Fluoride ions are released from readily soluble fluoride compounds, such as sodium fluoride, hydrogen fluoride, fluorosilicic acid

and sodium monofluorophosphate (Na

2 PO

3 F), and almost completely

absorbed (Ekstrand et al., 1978; Spak et al., 1982). Fluoride compounds

with low solubility, on the other hand, including c alcium fluoride,

magnesium fluoride and aluminium fluoride, are poorly absorbed.

After intake of sodium fluoride as tablets or a solution, fluoride is

rapidly absorbed. Only a few minutes after intake, there is a rise in the

plasma fluoride conce ntration, and the plasma peak usually occurs

within 30 min . The height of the plasma peak is proportional to the

fluoride dose ingested (Ekstrand et al., 1977b).

The absorptive process occurs by passive diffusion, and fluoride

is absorbed principally from both the stomach and the intestine. There

is no convincing evidence that active transport processes are

involved. The mechanism and the rate of gastric absorption of fluoride

are related to gastric acidity.

Fluoride is mainly absorbed in the form of hydrogen fluoride,

which has a p K

a of 3.45. That is, when ionic fluoride enters the acidic

environment of the stomach lumen, it is largely converted into hydrogen fluoride (Whitford & Pashley, 1984). Most of the fluoride that is

not absorbed from the stomach will be rapidly absorbed from the small

intestine.

In a bioavailability study in which young volunteers were given

4 mg fluoride as calcium fluoride (a poorly soluble fluoride compound)

and plasma fluoride was followed fo r 6 h, no increase in the plasmaEHC 227: Fluorides

72 flu oride concentration was detected following intake, indicating no

fluoride absorption (Afseth et al., 1987).

Fluoride compounds that occur naturally or are added to drinkingwater yield fluoride ions, which are almost completely absorbed from

the gastrointestinal tract. Thus, fluoride in drinking-water is generally

bioavailable.

There is only limited information on the bioavailability of fluoride

from fluoride-containing diets. In a balance study in infants, it was

found that the bioavailability of the fluoride in the infants’ diet was

about 90% (Ekstrand et al., 1994).

The ingestion of fluoride with food retards its absorption and

reduces its bioavailability. When fluoride was ingested as sodium

fluoride tablets on a fasting stomach, the bioavailability of fluoride was

almost 100%. When the same dose was taken together with a glass of

milk, the bioavailability decreased to 70%; when it was taken together

with a calcium-rich breakfast, the bioavailability was further reduced to

60% (Ekstrand & Ehrnebo, 1979; Trautner & Einwag, 1989; Shulman &

Vallejo, 1990). The decrease in absorption associated with the

ingestion of milk or food is probably due to binding of fluoride with

certain food constitue nts, including calcium and other divalent and

trivalent cations. When this occurs, the faecal excretion of fluoride will

increase. The timing of fluoride ingestion in relation to a meal is critical

with respect to fluoride bioavailability. When a few grams of a fluoride

dentifrice are swallowed on a fasting stomach , the plasma peak is

recorded within 30 min; however, when the dentifrice is swallowed 15

min after a meal, the peak does not occur until after 1 h. The fluoride

from most dental products int ended for oral application is almost

completely absorbed when swallowed (Ekstrand, 1987).

There is partial to complete absorption of gaseous and particulate

fluorides from the respiratory tract (McIvor, 1990), with the extent of

absorption dep e ndent upon solubility and particle size. Particulate

fluorides deposited in the bronchioles and nasopharynx may be swallowed (via ciliary clearance and/or coughing) and reach the gastroi ntestinal tract, where they are absorbed; relatively insol uble

particulate fluorides deposited deep within the lungs may be absorbed

gradually over time.Kinetics and Metabolism in Humans and Laboratory Animals

73 Available information on the absorption of fluoride through the

skin is limited to cases of acute dermal exposure to hydrofluoric acid.

Although hydrofluoric acid appears to be rapidly absorbed following

dermal ex

posure, in view of the extremely corrosive nature of this

compound, absorption into the general circulation could also be a

consequence of damage to the vascular system.

6.1.2 Absorption in laboratory animals

Experimental studies performed in vivo with rats (Sato et al., 1986)

and in vitro with isolated segments of dog jejunum (Me sser et al.,

1989 ) have indicated that fluoride (as sodium fluoride) is rapidly

absorbed from the stomach and intestinal tract in animals. The rate at

which fluoride is absorbed from the stomach is inversely related to the

pH of the stomach contents (Whitford, 1990; Messer & Ophaug, 1993).

Although most of the fluoride ingested by laboratory animals is

absorbed through the gastrointestinal tract, small amounts may also be

absorbed from the oral cavity. In female Fischer F-344 rats intubated

endotracheally (with oesophageal ligation) with 200 μl of a solution of

sodium fluoride (Na 18 F), approximately 7% of the administered material

was absorbed from the oral cavity within 2.5 h (Patten et al., 1978). The

absorption of

fluoride (as sodium fluoride in solution) from the oral

cavity of Syrian hamsters increased with decreasing pH of the solution

(Whitford et al., 1982).

In laboratory animals, the presence of food (Rao, 1984) and fluoride-binding ions (i.e., aluminium, calcium, magnesium) in the gastrointestinal tract (Spencer et al., 1981) significantly reduces the amount

of fluoride absorbed into the general circulation. The absorption of

ingested fluoride by female Wistar rats was reduced from 76 to 47%

when the level of calcium in their diet was increased from 0.5 to 2%

(Harrison et al., 1984 ). In male albino rabbits administered drinkingwater containing 25 or 250 mg fluoride/litre (as sodium fluoride) for 4

weeks, the levels of fluoride in the serum ( and femoral bone) were

approximat e ly 2-fold higher in animals administered a diet low in

calcium (0.4%) than in controls administered a diet containin g 1.6%

calcium (Tsuchida et al., 1992).

Other than the observation by Morris & Smith (1982) that gaseous

hydrogen fluoride was almost completely absorbed from the upperEHC 227: Fluorides

74 respiratory tract following the exposure of rats to concentrations ranging from 30 to 176 mg fluoride/m 3

, no additional quantitative data on

the absorption of fluorides following inhalation exposure were identified.

Quantitative information on the dermal absorption of fluorides in

animals was not identified.



### 6.2 Distribution and retention

6.2.1 Fluoride in blood

Fluoride is rapidly distributed by the systemic circulation to the

intracellular and extracellular water of tissues; however, the ion normally accumulates only in calcified tissues, such as bone and teeth.

Fluoride is not bound to any plasma proteins (Taves, 1968; Ekstrand

et al., 1977a). In the blood, the ion is asymmetrically dist ributed

between plasma and the blood cells, so that the plasma concentration

is approximately twice as high as that associated with the cells (Whitford, 1996).

There is no homeostatic regulation of the fluoride concentration

in the blood. In a short-term human pharmacokinetic study, fluoride

doses ranging from 3 to 10 mg were given orally in the form of tablets.

The data were interpreted using an open three-compartment model, and

the plasma half-l ife was determined from the final terminal phase,

ranging from 3 to 10 h. The plasma level rose and fell during each dosage interv al. That is, the fluctuation of the plasma fluoride concentration depended on the fluoride dose ingested, dose frequency and

the plasma half-life of fluoride (Ekstrand et al., 1977b).

The literature contains a wide range (0.4–2.4 μmol/litre) for “normal” plasma f

luoride concentrations. Some of the results may have

been due to the use of fasting individuals in some studies and nonfasting in others. It is virtually certain also that problems with the analysis of fluoride have been contributory. This is especially the case

when only the fluoride electrode is used for the analysis of samples

with low concentrations. The use of preparative methods that concentrate the fluoride in small volumes, suc h as the acid-HMDS

microdiffusion method, is necessary when such low levels of fluoride

are to be measured.Kinetics and Metabolism in Humans and Laboratory Animals

75 Under steady conditions of exposure via drinking-water, the concentration of fluor

ide in plasma collected from fasting subjects is

directly related to the concentration in the drinking-water consumed

(Guy et al., 1976; Ekstrand, 1978). The mean concentration of fluoride

in the blood plasma of 30 residents of communities in the USA served

by drinking-water contain ing low concentrations of fluoride (i.e.,

<0.1 mg/litre) was 0.4 μmol/litre, while the mean concentration in plasma

from individuals consuming drinking-water containing higher amounts

of fluoride (i.e., 0.9–1.0 mg/litre) was reportedly 1 μmol/litre (Guy et al.,

1976). Serum and plasma contain virtually the same amount of fluoride

(Guy et al., 1976; Kono et al., 1986). There is a considerable variation

during the day in plasma fluoride levels in subjects living in an area

with a high fluoride concentration in the drinking-water, particularly in

adults (Ekstrand, 1978).

In addition to recent fluoride intake and the level of chronic fluoride intake, plasma fluoride levels are influenced by the relative rates of

bone accretion and dissolution and by the renal clearance rate of

fluoride (Waterhouse et al., 1980). In the long term, there is a positive

relationship between the concentration of fluoride in plasma and bone.

Also, a positive relationship between plasma fluoride and age has been

reported (Parkins et al., 1974).

The levels of fluoride in plasma, serum and urine have been considered useful biomarkers for fluoride exposure (Ekstrand & Ehrnebo,

1983; Ekstrand et al., 1983; Ehrnebo & Ekstrand, 1986; Whitford, 1996;

WHO, 1996a; Lund et al., 1997). The concentra tions of fluoride in

parotid saliva have also been used to assess plasma levels of fluoride

(Ekstrand, 1977; Whitford et al., 1999a). There are, however, ethical and

technical limitations of the use of these fluids for large-scale monitoring of the body burden of fluoride i n humans. It has been

suggested that the fluoride concentration in nails and hair can be used

as a marker of fluoride exposure (Czarnowski & Krechniak, 1990; Kono

et al., 1990; Whitford et al., 1999b) . However, there is only limited

information on the reliability of these methods and the risks of

contamination during exposure in field conditions. Informati on on

appropriate preparation methods as well as analytical techniques needs

to be further evaluated before these methods can be used on a largescale basis.EHC 227: Fluorides

76 6.2.2 Distribution in soft tissues

Fluoride is distributed from the plasma to all tissues and organs.

The rates of delivery are generally determined by the blood flow to the

t issues in question. Consequentl y, steady-state fluoride

concentrations are achieved more rapidly between plasma and well

perfused tissues, such as the heart, lun gs and liver, than between

plasma and less well perfused tissues, such as resting skeletal muscle,

skin a nd adipose tissue. In general, steady-state tissue-to-plasma

fluoride concentration ratios fall between 0.4 and 0.9, regardless of the

rates at wh ich the steady-state levels are achieved (Whitford et al.,

1979). Exceptions to this range include the kidney, pineal gland, brain

and adipose tissue. Fluoride is concentrated to high levels within the

kidney tubules, so this organ has a higher concentration than plasma.

Most information on the levels of fluorid e in soft tissues of

humans is derived from a report published by Taves et al. (1983), in

which the amounts in a number of tissues (from autopsies of 13 cases

of sudden death in the USA) were quantified (see Table 9 in section

6.2.5 below).

6.2.3 Distribution to calcified tissues

The rate of clearance of fluoride from plasma by bone is higher

than that of calcium. In humans and laboratory animals, approximately

99% of the total body burden of fluoride is retained in bones and teeth

(Kaminsky et al., 1990; Hamilton, 1992), with the remainder distributed

in highly vascularized soft tissues and the blood (McIvor, 1990). The

degree to which fluoride is stored in the skeletal tissue is related to the

turnov e r rate of skeletal components and the level of previous

exposure (Caraccio et al., 1983). Levels of fluoride in calcified tissues

are generally highest in bone, dentine and enamel. The concentration

of fluoride in bone varies with age, sex and the type and specific part

of bone and is believed to reflect an individual’s long-term exposure to

fluoride.

During the growth phase of the skeleton, a relatively high portion

of an ing ested fluoride dose will be deposited in the skeleton. In

infants and children with skeletal growth or individuals not consuming

fluoridated drinking-water, up to 75% of the daily amount of fluoride

that is absorbed may be incorporated into skeletal tissue (US DHHS,

1991). When a fluoride dose (e.g., a fluoride tablet or an infant formulaKinetics and Metabolism in Humans and Laboratory Animals

77 diluted with fluoridated drinking-water) is given to infants, the retention will be strongly correlated with the absorbed fluoride dose per

kilogram body weight: the higher the fluor ide dose, the higher the

fluoride retention. Retention of fluoride following intake of a fluoride

supplement of 0.25 mg given to infants was shown to be as high as

80–90%. In a study with adults (aged 23–27 years) in which fluoride

was given as a single intravenous injection, about 60% of the injected

dose (3 mg fluoride as sodium fluoride) was retained (Ekstrand et al.,

1978).

The selective affinity of fluoride for mineralized tissues is, in the

short term, due to uptake on the surf a ce of bone crystallites by the

processes of isoionic and heteroionic exchange. In the long run, fluoride is incorporated into the crystal lattice structure of teeth and skeletal

tiss ue by replacing some hydroxyl ions within the unit cells of

hydroxyapatite, produci n g partially fluoridated hydroxyapatite (i.e.,

fluorapatite or fluorhydroxyapatite) (WHO, 1994).

Fluoride is not irreversibly bound to bone. This has been demonstrated in persons who had lived in an area with a high fluoride

concentration in the drinking-water and then moved to an area with a

low water fluoride level. The urinary fluoride conc e ntration in these

individuals fell slowly for long periods, indicating tha t fluoride was

being mobilized continu ously from the skeleton and subsequently

excreted (Hodge et al., 1970). Similar findings have been noted among

workers with chronic occupational exposure to fluoride who were

subsequently employed elsewhere (Boillat et al., 1979). Their plasma

fluoride levels reflected their bone fluoride concentrations (based upon

iliac crest biopsies) for long periods (2–3 years) after the industrial

fluoride exposure had stopped.

The “balance” of fluoride in the body (i.e., the difference between

the amount of fluoride ingested and the amount of fluoride excreted in

the urine and the faeces) can be positive or negative. When the

fluoride is derived from human milk or cow’s milk, biological fluids with

a low fluoride content, urinary excretion generally exceeds intake (i.e.,

there is a negative fluoride balance). In infants, when fluoride intakes

are low, sufficient fluoride is released from bone to extracellular fluid to

result in urinary excretion being higher than intake (Ekstrand et al.,

1994).EHC 227: Fluorides

78 Hence, the plasma concentrations and the urinary excretions

mirro r a physiological balance that is determined by earlier fluoride

exposure, the degree of accumulation of the ion in bone, the mobilization rate from bone and the efficiency of the kidneys in excreting

fluoride.

6.2.4 Transplacental transfer

Human studies have shown that the placenta is not in any sense

a barrier to the passage of fluoride to the fetus. There is a direct relationship between the serum fluoride concentration of the mother and

that of the fetus; the cord serum concentration is 75% that of the

maternal fluoride concentration. From the fetal blood, fluoride is readily

taken up by the calcifying fetal bones and teeth (Shen & Taves, 1974).

6.2.5 Fluoride levels in human tissues and organs

Information on the levels of fluoride in the tissues and organs of

individuals is summarized in Table 9. The concentration of fluoride in

the plasma of healthy individuals may range from 7.6 to 28.5 μg/litre

(Guy, 1979). The mean plasma level i n 127 subjects with 5.03 mg

fluoride/litre in drinking-water was 106 ± 76 (SD) μg/litre (Li et al., 1995).

A study of 250 healthy individuals residing in Spain revealed levels of

fluoride in serum ranging from 1 to 47 μg/litre (Torra et al., 1998).

Table 9. Concentration of fluoride in human tissues and organs

Tissue/organ Number of

samples a Concentration b

(mean [range]) Reference

Whole blood na c na (20–60) μg/litre Kissa (1987)

Serum 1088 14.4 (na) μg/litre Kono et al. (1986)

Serum 250 17.4 (1–47)

μg/litre Torra et al. (1998)

Plasma 72 14.3 (2.7–79.8)

μg/litre Guy et al. (1976)

Urine na 780 (na) μg/litre Kono et al. (1986)

Saliva 98 8.74 (na) ng/g Schamschula et al.

(1985)

Tooth

enamel d na na (740 000–

2 100 000) ng/g Berndt & Stearns

(1979)Kinetics and Metabolism in Humans and Laboratory Animals

79 Table 9 (contd).

Tissue/organ Number of

samples

a Concentration b

(mean [range]) Reference

Iliac crest e 78 720 500

(106 000–

2 360 000) ng/g Alhava et al. (1980)

Iliac crest f 10 1 500 000 (na)

ng/g Zipkin et al. (1960)

Rib f 9 1 600 000 (na)

ng/g Zipkin et al. (1960)

Vertebrae f 10 2 200 000 (na)

ng/g Zipkin et al. (1960)

Hair 53 2505 (na) ng/g Tagaki et al. (1986)

Brain g 7 31.2 (na) ng/g Taves et al. (1983)

Body fat g 5 28.5 (na) ng/g Taves et al. (1983)

Liver g 5 19.6 (na) ng/g Taves et al. (1983)

Muscle g 9 40.3 (na) ng/g Taves et al. (1983)

Lung g 9 71.4 (na) ng/g Taves et al. (1983)

Thymus g 4 9005.2 (na) ng/g Taves et al. (1983)

Aorta g 8 4331.6 (na) ng/g Taves et al. (1983)

Kidney g 9 159.2 (na) ng/g Taves et al. (1983)

Fingernails 22 8800 (na) ng/g Czarnowski &

Krechniak (1990)

Fingernails 6–9 na (1590–7570)

ng/g Whitford et al.

(1999b)

a Total number of tissue samples analysed.

b Mea n and range of concentrations of fluoride in the tissues and organs of

individuals.

c na = not available.

d Samples of surface tooth enamel from adults 20 years of age. Samples were

taken from individuals consuming drinking-water containing up to 1 mg

fluoride/litre.

e Samples of iliac crest bone from adults (mean age 60 years). Samples were

taken from individuals consuming drinking-wat e r containing up to 0.97 mg

fluoride/litre over a period of 14–18 years.

f Samples of bone from adults 26–90 years of age. Samples were taken from

individuals consuming drinking-water containing up to 1 mg fluoride/litre over

a period of 10–87 years.

g Tissues (analysed on a wet weight basis) were obtained from autopsies of cases

of sudden death in the USA (mean age 29 years). Some tissue samples may

have been prepared with water containing 0.9–1 mg fluoride/litre.

Levels of fluoride in calcified tissues are generally highest in

bone, dentine and enamel, although they are highly variable, owing, atEHC 227: Fluorides

80 least in part, to the methods of analysis used (Weidmann &

Weatherell, 1970).

The concentration of fluoride in dental enamel decreases exponentially with the distance from the surface and varies with site, age,

surface attrition, systemic exposure and exposure to topically applied

fluoride (Weatherell et al., 1977; Schamschula et al., 1982). The average

concentration of fluoride in dentine is approximately 2- to 3-fold higher

than that in enamel and, like enamel, is higher in surface regions,

increases with age and is related to the levels of fluoride in the

drinking-water consumed (Weidmann & Weatherell, 1970; US NAS,

1971).



### 6.3 Elimination

Whitfor d et al. (1991) examined a number of pharmacokinetic

parameters (i.e., plasma, renal and extra renal clearances) in mongrel

dogs, Sprague-Dawley rats, cats, rabbits and hamsters intravenously

administered a single dose (0.5 mg fluoride/kg body weight) of sodium

fluoride and concluded that dogs most resembled humans with respect

to their elimination of fl u oride; plasma clearance rates were approximately 2-fold higher in rats than in dogs.

6.3.1 Renal handling of fluoride

The major route for the removal of fluoride from the body is by the

kidneys.

The renal clearance of fluoride in the adult typically ranges from

30 to 50 ml/min, whereas clearance rates of the other halogens (chloride, iodide and bromide) are usually less than 1.0 ml/min. The percentage of the filtered fluoride reabsorbed from the renal tubules can range

from about 10 to 90%. The degree of reabsorption depends largely on

the pH of the tubular fluid, urinary flow and renal function (Ekstrand et

al., 1980, 1982; Whitford, 1996). The excretion of fluoride in urine is

reduced in indiv iduals with impaired renal function (Schiffl & Binswanger, 1980; Spak et al., 1985; Kono et al., 1986).

6.3.2 Excretion via breast milk

The literature contains a wide range (0.1–5 μmol/litre) for fluoride

levels in breast milk. It is probable that problems with the analysis of

fluoride have been contributory. The conce ntration of fluoride in

colostrum and mature breast milk is reported to be the same — aboutKinetics and Metabolism in Humans and Laboratory Animals

81 0.4 μmol/litre (Spak et al., 1983). The same investigators found no

significant difference in fluoride concentrations of milk from mothers

living in areas with fluoride concentrations in drinking-water of 1 or 0.2

mg/litre , even though their plasma concentrations reflected this

difference. Further, they found no diurnal variation in the fluoride concentration (Spak et al., 1983). Studies of lactating mothers have shown

t hat there is a limited transfer of fluoride from plasma to breast milk

(Ekstrand et al., 1981). Dabeka et al. (1986), on the other hand, reported

that the concentration of fluoride in breast milk was rel ated to the

fluoride content of the drinking-water consumed by the women; the

mean concentration of fluoride in breast milk obtained from 32 women

consuming drinking- water containing <0.16 mg fluoride/litre was

0.23 μmol/litre , whereas breast milk obtained from 112 women consuming drinking-water containing 1 mg fluoride/litre reportedly contained 0.48 μmol fluoride/litre. Concentrations of fluoride in samples of

breast milk collected in Finland (Esala et al., 1982) ranged from 0.1 to 2.7

μmol/litre. In the Finnish study, the fluoride in the milk (both ionic and

total flu oride) was measured after ashing the samples. Taves (1983)

showed no difference between inorganic (microdi ffusion) and total

(ashing) fluoride in cow’s milk. Obviously, there is some uncer-tainty

as to whether there really is a non-ionic fraction of fluoride in milk or

whether the discrepancy is due to an analytical overestimation.

The fluoride content of human breast milk represents the natural

daily fluoride intake during the first 6 months of life. This is especially

important when comparing the daily fluoride intake by formula-fed and

breast-fed infants.

6.3.3 Excretion via faeces, sweat and saliva

It is generally accepted that most of the fluoride in the faeces is

not absorbed. Faecal fluoride usually accounts for less than 10% of the

amount ingested each day (Ekstrand et al., 1984).

The quantitative role of sweating in fluoride balance studies has

not been explored using modern analytical methods in controlled studies. Based on some preliminary data from Hens chler et al. (1975) on

predicted losses in workers whose urinary fluoride levels are about

5 mg/litre and who lose 6 litres of sweat containing 0.2–0.3 mg fluoride

during a shift, the sweat could account for approximately 5% of the

fluoride excreted. In tropical climates, during periods of prolonged andEHC 227: Fluorides

82 heavy exercise or in occupational exposure to elevated temperatures,

the fluid loss from the body via sweat may approach as much as 4–6

litres a day.

The concentration of fluoride in saliva is about two-thirds of the

plasma fluoride concentration and seems to be independent of flow

rate, in contrast to the situation for most electrolytes (Ekstrand, 1977;

Oliveby et al., 1989; Whitford et al., 1999a). A diurnal fluctuation in the

saliva fluoride concentration is also seen in an area with fluoridated

drinking-water containing 1 mg fluoride/litre (Oliveby et al., 1990). The

levels of fluoride in saliva are important, because this potentially

provides further topical exposure of the teeth to fluoride.83 

### 7. EFFECTS ON LABORATORY MAMMALS AND

IN VITRO TEST SYSTEMS

7.1 Single exposure

LD 50 s for the oral administration of sodium fluoride, sodium monofluorophosphate and stannous fluoride (SnF

2 ) to rats include values of

3 1–101 mg fluoride/kg body weight, 75–102 mg fluoride/kg bod y

weight and 45.7 mg fluoride/kg body weight, respectively (IARC, 1982;

Whitford, 1987, 1990; ATSDR, 1993). LD

50 s for the oral administration

of sodium

fluoride, sodium monofluorophosphate and stannous

fluoride to mi ce include values of 44.3 and 58 mg fluoride/kg body

weight, 54 and 94 mg fluoride/kg body weight and 25.5 and 31.2 mg

fluoride/kg body weight, respectively (IARC, 1982; Whitford, 1990).

The acute oral exposure of laboratory animals to fluoride produces

salivation, lacrimation, vomiting and diarrhoea, as well as respiratory

arrest and cardiac depression (WHO, 1984).

Nephrotoxic effects pr oduced in laboratory animals following

acute oral exposure to fluoride have been reviewed (WHO, 1984). Subsequent studies have indicated that the severity of the acute renal

toxicity of sodium fluoride in rats appears to be related to the age of the

animal. In a study in which single doses of sodium fluoride (13.6 or 21.8

mg fluoride/kg body weight) were injected intraperitoneally into 1-, 8-,

15- or 29-day-old male and female Sprague-Dawley rats, proximal

tubular necrosis and marked ch anges in kidney weight, urine

osmolarity and pH, and chloride excretion were observed in the 29-dayold animals; effects in the younger animals were considered mild and

less severe (Daston et al., 1985).

In laboratory animals, adverse effects within the gastrointestinal

tract have been reported following the ingestion of acutely toxic doses

of fluoride. In a study in which solutions of 1, 10 and 50 mmol fluoride/litre (as sodium fluoride dissolved in 0.1 N HCl) were introduced

into the stomachs of anaesthetized female Wistar rats,

histopathological effects on the gastric mucosa (i.e., desquamation of

surface epithelial cells, cell loss and damage) were observed in animalsEHC 227: Fluorides

84 administered 10 and 50 mmol/litre within 30 min of exposure (Easmann

et al., 1984). Subsequently, Easmann et al. (1985) reported that

following intubation of Holtzman rats with 1.5 ml of 100 mmol sodium

fluoride/litre ( approximately 17.8 mg fluoride/kg body weight),

histopathological effects (i.e., haemorrhage, disruption of epithelial

integrity and glandular structure, lysis and loss of epithelial cells)

within the gastric mucosa were observed. After 48 h, there was

recovery of gastric mucosal integrity.

Hydrogen fluoride is acutely toxic when administered via inhalation. LC

50 s ranging from 4065 to 14 400 mg fluo ride/m 3 have been

reported for the 5-min exposure of rats to hydrogen fluoride (WHO,

1984; ATSDR, 1993). An LC

50 of approximately 1084 mg fluoride/m 3 has

been reported for the 60-min exposure of rats to hydrogen fluoride

(Rosenholtz et al., 1963). LC

50 s of approximate ly 5000 and 280 mg

fluoride/m

3 have been reported for the 5- or 60-min exposure of mice to

hydrogen fluoride, respectively (WHO, 1984; ATSDR, 1993).

The inhalation exposure of laboratory animals to levels of hydrogen fluoride near the LC

50 produces severe ocular and nasal irritation,

pulmonary congestion, oedema, respiratory distress and erythema of

the exposed skin (ATSDR, 1993).

Direct exposure of the skin to hydrofluoric acid produced severe

burns and tissue damage, with the severity of these effects dependent

upon the length of the exposure and concentration (Derelanko et al.,

1985). The direct application of sodium fluoride (0.5 and 1.0% in

distilled water) to the abraded skin of rats produced effects ranging

from superficial necrosis to oedema and inflammation (Essman et al.,

1981).

Application of an aqueous solution of 2% sodium fluoride to the

eyes of rabbits caused corneal epithelial defects and necrosis in the

conjunctiva (Grant & Schuman, 1993).



### 7.2 Short- and medium-term exposure

In short-term s tudies, survival was reduced in male and female

F344/N rats and in male, but not female, B6C3 F

1 mice administeredEffects on Laboratory Mammals and In Vitro Test Systems

85 drinking-water containing 363.2 mg fluoride/litre for a period of 14 days

(NTP, 1990). In other investigations, fluoride-induced effects on the

skeleton included inhibition of trabecular bone mineralization in female

Wistar rats administered drinking-water containing 113.5 or 136.2 mg

fluoride/litre for a period of 5 weeks (Harrison et al., 1984); inhibition of

endosteal bone formation and a reduction in cancellous bone volume

in male Holtzman rats administered drinking-water containing 85.5 mg

fluoride/litre for a period of 21 days (Turner et al., 1989); delayed

fracture healing and a reduction in collagen synthesis in male albino

rats receiving 14 mg fluoride/kg body weight per day for 30 days (Uslu,

1983); an increase in dermatan sulfate and chondroitin-6-sulfate in the

tibia of male Sprague-Dawley rats receiving 17.5 mg fluoride/kg body

weight per day for a period of 1–2 months (Prince & Navia, 1983); and

a 20% increase in bone matrix formation in male C57BL/6 mice receiving

0.8 mg fluoride/kg body weight per day for 4 weeks (Marie & Mott,

1986). Ultrastructural changes were observed in skeletal muscle of male

Wistar rats administered drinking-water containing 100 mg fluoride/litre

(as sodium fluoride) for 8 weeks (Pang et al., 1996).

Although male Swiss mice administered (orally) 5.2 mg fluoride/kg

body weight per day over a period of 35 days reportedly had reduced

red blood cell counts and numbers of lymphocytes (39%) and

increased numbers of monocytes, eosinophils and basophils compared

with controls (Pillai et al., 1988), the levels of red blood cells, lymphocytes, neutro p hils, monocytes and eosinophils in male B6C3F

1 mice

receiving 8.1 mg fluoride/kg body weight per day (from drinking-water

for 24 weeks) were similar to those in controls receiving 0.6 mg

fluoride/kg body weight per day (NTP, 1990).

In medium-term exposure studies, femoral bone bending strength

was increased (approximately 38%) or decreased (approximately 20%)

in adult rats administered drinking-water containing 16 mg fluoride/litre

or 64–128 mg fluoride/litre, respec tively, over a period of 16 weeks

(Turner et al., 1992). Vertebral bone quality (compression resistance

normalized for ash content) was reportedly reduced in female Wistar

rats administered drinking-water containing 100 or 150 mg fluoride/litre

for a period of 90 days (Søgaard et al., 1995). Altered bone remodelling,

based on thickening of the osteoid seams in the tibia and femur, was

observed in male and female B6C3F

1 mice administered drinking-water

containing 

### $ 22.7 and 45.4 mg fluoride/litre, respectively, over a period

of 6 months (NTP, 1990).EHC 227: Fluorides

86 Compared with unexposed controls, other effects observed in

animals administered drinking-water containing added fluoride for

6 months included hyperplasia of the stomach and pathological effects

(i.e., lymphocyt ic infiltration, hyperplasia, necrosis) in the glandular

stomach o f F344/N rats administered drinking-water containing 45.4

and 136 mg fluoride/litre, respectively (NTP, 1990); and reduced survival (82% and 44% in female and male B6C3F

1 mice , respectively),

hepatic megalocytosis, renal nephrosis, mineralization of the myocardium, necrosis and/or degeneration of the seminiferous tubules in the

testis of B6C3F

1 mice r eceiving drinking-water containing 272.4 mg

fluoride/litre (NTP, 1990).

The daily intragastric administration of 22.7 mg fluoride/kg body

weight per day (as sodium fluoride) to rabbits for 136 days interfered

with the maturation and metabolism of collagen (Sharma, 1982a).



### 7.3 Long-term exposure and carcinogenicity

In early carcinogenicity bioassays conducted by Tannenbaum &

Silverstone (1949), Taylor (1954) and Kanisawa & Schroeder (1969), the

incidence of tumours in mice administered sodium fluoride (in either

their diet or drinking-water) was, in general, not markedly greater than

that observed in the unexposed controls. However, the documentation

and protocols of these studies were inadequate. Deficiencies in design

included small groups of ani mals of single sexes or various ages

exposed to single dose levels for short periods of time with inadequate

examination of possible target tissues.

In a comprehensive study of the carcinogenicity of sodium fluoride in laboratory animals (NTP, 1990), group s of male and female

F344/N rats were administered drinking-water containing 0, 25, 100 or

175 mg sodium fluoride/litre (0, 11, 45 and 79 mg fluoride/litre) for a

period of 2 ye ars. There were 100 rats in each of the control and

175 mg/litre groups, while 70 rats per group were administered drinkingwater containing 25 or 100 mg sodium fluoride/litre. Groups of 10 rats

of each sex at each level of exposure were sacrificed after 27 and 66

weeks. In the high-dose group, 42 males and 54 females survived until

terminal sacrifice. The estimated total intakes of fluoride from food and

drinking-water by the male and female F344/N rats administered

drinking-water containing 0 (control), 25, 100 or 175 mg sodiumEffects on Laboratory Mammals and In Vitro Test Systems

87 fluoride/litre were approximately 0.2, 0.8, 2.5 and 4.1 mg/kg body weight

per day and 0.2, 0.8, 2.7 and 4.5 mg/kg body weight per day,

respectively. A t the end of the 2-year study, the levels of fluoride in

the humeral bone of the control, low-, mid- and high-dose male and

female rats were approximately 0.44, 0.98, 3.65 and 5.26 μg/mg bone ash

and 0.55, 1.34, 3.72 and 5.55 μg/mg bone ash, respectively (NTP, 1990).

In male F344/N rats receiving 0.2, 0.8, 2.5 or 4.1 mg fluoride/kg

body weight per day, the incidence of osteosarcomas (three tumours

in the vertebra and one in the humerus) was 0/80, 0/51, 1/50 and 3/80,

respectively (NTP, 1990). A pairwise comparison of the incidence in the

high-dose group versus controls was not statistically significant ( P =

0.099); if an extraskeletal osteosarcoma, located in the subcutis of the

flank of one high-dose male rat , was included in the total tumour

incidence in this group of animals, the pairwise comparison with the

control group remained statistically insignificant ( P

= 0.057). However,

the osteosarcomas occurred with a statistically significant ( P = 0.027,

by logistic regressi

on) dose–response trend (NTP, 1990). The incidence of osteosarcoma at any site was within the range of historical

controls; however, the amount of fluoride in the die t s in previous

National Toxicology Progra m (NTP) studies of other chemicals was

uncont rolled and was estimated to be approximately 3.5- to 5.9-fold

higher than in the NTP sodium fluoride study ( NTP, 1990). In male

F344/N rats receiving 0.2, 0.8, 2.5 or 4.1 mg fluoride/kg body weight per

day, the inci dence of oral cavity lesions (squamous papillomas or

squamous cell carcinomas) was 0/80, 1/51, 2/50 and 3/80, respectively;

the incidence in the fluoride-exposed groups was not significantly

different from the controls and was not considered to be compoundrelated. The incidence of (thyroid gland) follicular cell tumours (adenomas and carcinomas) was 1/80, 1/51, 1/50 and 4/80 in the control, low-,

medium- and high-dose males, respectively; the incidence in the highdose group was not significantly different from controls and was not

considered to be compound-related. There w as no increase in the

incidence of osteosarcomas in female F344/N rats receiving fluoride;

the incidence of oral cavity neoplasms (squamous papillomas or squamous cell carcinomas) was 1/80, 1/50, 1/50 and 3/81 in female F344/N

rats receiving 0.2, 0.8, 2.7 and 4.5 mg/kg body weight per day, respectively; the incidence in the high-dose group was not significantly

different from the controls (NTP, 1990).EHC 227: Fluorides

88 In the NTP carcinogenicity bioassay with male and female F344/N

rats, no significant compound-rel ated effects upon survival, body

weight or weights of major internal organs were observed, compared

with controls (NTP, 1990); however, the incidence of osteosclerosis in

female rats administered drinking-water containing 175 mg sodium

fluoride/litre (18/81) was significantly ( P

= 0.04) increased, compared

with controls (6/80) (NTP, 1990). It was concluded (NTP, 1990) that the

osteosarcoma finding was “equivocal evidence of carcinogenic

activity” in male rats, and that there was “no evidence of carcinogenic

activity” in the female rats exposed to fluoride under these conditions.

In a carcinogenicity bioassay conducted with Sprague-Dawley

rats, groups of 70 animals of each sex were administered diets supplemented with various amounts of sodium fluoride for a period of 95–

99 weeks (Maurer et al., 1990). The estimated total intake of fluoride by

these groups of animals was 0.1, 1.8, 4.5 or 11.3 mg/kg body weight per

day, respectively. After 26 weeks on study, as many as 10 animals of

each sex per group were sacrificed, and after 53 weeks, 10 animals of

eac h sex per group were sacrificed (Maurer et al., 1990). At terminal

sacrifice (i.e., after 95 and 99 weeks on study for males and females,

respectively), there were 26 males and 12 females remaining in the highdose groups. A t study termination, the concentration of fluoride in the

bone (radius and ulna) of the males and females receiving 0.1, 1.8, 4.5

or 11.3 mg fluoride/kg body weight per day was 0.5, 5.0, 8.8 and 16.7

μg/mg bone ash and 0.5, 4.5, 8.3 and 14.4 μg/mg bone ash, respectively.

In this study, the incidence of bone tumours was 0/70, 0/58, 2/70

(one chordoma and one ch ondroma) and 1/70 (fibroblastic sarcoma

with areas o f osteoid formation) in male rats and 0/70, 2/52 (one

osteosarcoma and one cho ndroma), 0/70 and 0/70 in female rats

rec eiving 0.1, 1.8, 4.5 and 11.3 mg fluoride/kg body weight per day,

respectively (Maurer et al., 1990). However, detailed information on the

incidence of

tumours in tissues or organs other than the bone and

stomach were not presented, and histological examination of bone from

both mid-dose groups was limited. The craniu m, femur, premaxilla,

maxilla, mandible, cervical vertebra, sto mach, liver, kidney, incisors,

adrenals, brain, heart, lungs, ovaries, uterus, pancreas, pituitary, prostate, seminal vesicles, spleen, bladder, testes, epididymides, thyroids

and parathyroids obtained at the interim and terminal sacrifices from all

animals receiving 0.1 or 11.3 mg fluoride/kg body weight per day wereEffects on Laboratory Mammals and In Vitro Test Systems

89 examined microscopically. The stomach, bones and teeth from animals

receiving 4.5 mg fluoride/kg body weight per day and sacrificed after

26 weeks and from animals receiving 1.8 or 4.5 mg fluoride/kg body

weight per day a nd sacrificed after 53 weeks were also examined

microscopically. Not all of the bones (i.e., cranium, femur, premaxilla,

maxilla, mandible, cervical vertebra) from each of the remaining animals

(i.e., those alive after the interim sacrifices) receiving 1.8 or 4.5 mg

fluoride/kg body weight per day were examined microscopically;

however, tissues with gross lesions obtained from dead and moribund

animals were evaluated.

Sprague-Dawley rats receiving 11.3 mg fluoride/kg body weight

per day (administered in the diet) over a period of 95–99 weeks had

reduced weight gain; animals receiving 4.5 or 11.3 mg fluoride/kg body

weight per day had an increased incidence of su bperiosteal hyperostosis in the skull and hyperkeratosis and acanthosis in the stomach,

compared with controls receiving 0.1 mg/kg body weight per day

(Maurer et al., 1990).

In the NTP (1990) carcinogenicity bioassay, male and female

B6C3F

1 mice were also administered drinking-water containing 0, 25,

100 or 175 mg sodium fluoride/litre (0, 11, 45 and 79 mg fluoride/litre) for

2 years. There were 100 animals in each of the control and 175 mg/litre

groups, and 70 mice per group were a dministered drinking-water

c ontaining 25 or 100 mg sodium fluoride/litre; the total intake of

flu oride from water and the diet for the males and females in these

groups was estimated to be approximately 0.6, 1.7, 4.9 and 8.1 mg/kg

body weight per day and 0.6, 1.9, 5.7 and 9.1 mg/kg body weight per

day, respectively. A t the end of the 2-year study (groups of 10 animals

of each sex at each level of exposure were sacrificed after 24 and

66 weeks), the levels of fluoride in the humeral bone of the control, low-

, mid- and high-dose male and female mice were approximately 0.72,

1.61, 3.58 and 5.69 μg/mg bone ash and 0.92, 1.52, 4.37 and 6.24 μg/mg

bone ash, respectively (NTP, 1990).

In male B6C3F

1 mice receiving 0.6, 1.7, 4.9 or 8.1 mg fluoride/kg

body weight per day, the incidence of hepatoblastoma was 0/79, 1/50,

1/51 and 3/80, respectively (NTP, 1990). The overall incidence of

hepatic neoplasms (adenoma, carcinoma, hepatoblastoma) was similar

among all groups, and the incidence of live r tumours in all groups

(control and exposed) of male mice (73–78%) was higher than observedEHC 227: Fluorides

90 (16–58%) in previous NTP carcinogenicity bioassays (NTP, 1990). In

female B6C3F

1 mice receiving 0.6, 1.9, 5.7 or 9.1 mg fluoride/kg body

weight per day, the incidence of hepatoblastoma was 0/80, 1/52, 0/50

and 2/80, respectively. The overall incidence of hepatic n eoplasms

(adenoma, carcinoma, hepatoblastoma) was similar among all groups,

and the incidence of liver tumours in all groups (control and exposed)

of female mice (52–69%) was higher than observed (3–20%) in previous

NTP carcinogenicity bioassays (NTP, 1990). The incidence of

malignant lymphoma was 11 /80, 5/52, 11/50 and 19/80 ( P

= 0.051),

respectively. The incidence of malignant lymphoma in the control and

low-dose groups was less than the lowest incidence observed in nine

other investigations conducted at the study laboratory. In addition, the

incidence in the high-dose group was less than the average incidence

observed in historical controls (35%) and within the range of incidence

observed in historical controls (10–74%) (NTP, 1990).

The administration of drinking-water containing 25, 100 or 175 mg

sodium fluoride/litre to male or female B6C3F

1 mice over a period of 2

years had no signi ficant compound-related adverse effects upon

survival, body weight or weights of major internal organs, compared

with controls (NTP, 1990). It was concluded (NTP, 1990) that there was

“no evidence of carcinogenic activity” in male and female mice exposed

to fluoride under these conditions.

In a carcinogenicity bioassay in which sodium fluoride was administered in the diet to groups of 60 male and 60 female CD-1 mice over a

period of 95 and 97 weeks, respectively (10 mice of each sex per group

were sacrificed after 40 weeks), the incidence of osteomas in male and

female controls and mice receiving 1.8, 4.5 or 11.3 mg fluoride/kg body

weight per day was 1/50, 0/42, 2/44 and 13/50 and 2/50, 4/42, 2/44 and

13/50, respectively (no statistical analysis provided) (Maurer et al.,

1993). The incidence of this type of tumour was increased in the highdose groups compared with the controls. These animals were infected

with a Type C retrovirus, and the rol e of fluoride in the etiology of

these tumours is not clear (Maurer et al., 1993). Moreover, there is

some contro versy concerning whether they should be classified as

neoplasms (US NRC, 1993). The concentration of fluoride in the bone

(radius or ulna) of male controls and mice receiving 1.8, 4.5 or 11.3 mg

fluoride/kg body weight per day was approximately 1.5, 4.4, 7.2 and 13.2

μg/mg bone ash, respectively; the concentration of fluoride in the

(radius or ulna) bone of female controls and mice receiving 1.8, 4.5 orEffects on Laboratory Mammals and In Vitro Test Systems

91 11.3 mg fluoride/kg body weight per day was approximately 1.0, 3.4, 6.2

and 10.6 μg/mg bone ash, respectively.

In studies on non-neoplastic effects associated with the chronic

toxicity of fluoride, bone mineralization (based on mi c roscopic analysis) was inhibited in male and female rats administered drinking-water

containing 22.7 a nd 36.3 mg fluoride/litre (as sodium fluoride) for a

period of

250 days (Qiu et al., 1987). Femoral bone strength was

reduced in male Sprague-Dawley rats administered drinking-water containing 50 mg fluoride/litre for 18 months (Turner et al. , 1995). Compared with controls, the oral administration of a single dose of 4.5 mg

fluoride/kg body weight per day (as sodium flu oride) to rabbits for

perio ds ranging from 6 to 24 months produced slight alterations in

ATPase (sodium and potassium) activity within eryth rocytes, the

activity of serum acid and alkaline phosphatase (Jain & Susheela,

1 987a), the levels of dermatan sulfate, chondroitin-4-sulfate a n d

chondroitin-6-sulfate in cancellous bone (Sharma & Susheela, 1988a),

the number of haematopoietic cells in the blood (Susheela & Jain, 1983)

and the disaccharide content of glycosaminoglycans isolated from

cancellous bone (Sharma & Susheela, 1988b).

Evidence of mineralization of the aorta (Susheela & Kharb, 1990),

morphological changes within the duodenum (Susheela & Das, 1988)

and renal glomerulus (Bhatnagar & Susheela, 1998), and alterations in

skin collagen metabolism (Sharma, 1982b) have also been observed in

rabbits administered 4.5 mg fluoride/kg body weight per day for periods ranging from 6 to 24 months. Other effects produced following the

long-term exposure of rabbits to this dose of fluoride included alterations in the proportion of erythrocytes with abnormal morphology

(Susheela & Jain, 1986), the level of cortisol and corticosterone in the

plasma (Das & Susheela, 1991), the level of sialic acid and glycosaminoglycans in the serum (Jha et al., 1982) and the amount of

hydroxyproline present in collagen derived from tendons and cortical

bone (Susheela & Sharma, 1982).

Alterations in bone remodelling (based on histomorphometric

analysis) have been observed in pigs (Mosekilde et al., 1987;

Kragstrup et al., 1989) administered (orally) 2 mg fluoride/kg body

weight per day (as sodium flu oride) and dogs (Snow & Anderson,

1986) receiving 0.32 mg fluoride/kg body weight per day (from drinkingwater containing sodium fluoride) over a period of 6 months.EHC 227: Fluorides

92 

### 7.4 Mutagenicity and related end-points

7.4.1 In vitro genotoxicity

The genotoxicity of fluoride has been examined in a large number

of in vitro and in vivo assays, in which a wide range of end-points has

been assessed. Since publication of the first EHC document on fluoride

(WHO, 1984), the results from a number of studies have confirmed that,

in general, fluoride is not mutagenic in prokaryotic cells (Li et al., 1987a;

Tong et al., 1988; NTP, 1990; Zeiger et al., 1993); however, Ahn &

Jeffery (1994) reported no significant uptake of fluoride into S

. typhimurium TA98 cells.

Fluoride has been shown to increase the frequency of mutations

at the thymidine kinase locus in cultured mouse lymphoma and human

lymphoblastoid cells (Cole et al., 1986; Caspary et al., 1987, 1988; Crespi

et al., 1990). In the studies by Cole et al. ( 1986) and Caspary et al.

(1987), exposure to sodium fluoride produced a preferential increase in

the frequen cy of “small mutant colonies,” a phenomenon generally

associated with chromosomal damage rather than poin t mutations

(Moore et al., 1985). Indeed, the failure of sodium fluoride to increase

the frequency of cells resistant to ouabain (which is produced only by

a specific point mutation within the Na +

, K + -ATPase gene locus) (Cole

et al., 1986) is consistent wit h this result. In human lymphoblastoid

cells, the mutagenic response at the thymidine kinase locus following

a 20-day exposure to sodium fluoride was non-linear and lower than

predicted from extrapolation of the 28-h exposure data, a result

suggested to be indicative of a threshold for the mutagenicity of

(sodium) fluoride at concentrations above 50 mg/litre (Crespi et al.,

1990). Sodium fluoride did not increase the frequency of mutations at

the hypoxanthine–guanine phosphoribosyl transferase locus in rat

liver epithelial cells (Tong et al., 1988), Chinese hamster ovary cells

(Oberly et al., 1990) or Chin ese hamster lung cells exposed under

neutral (Slamen ova et al., 1992) or acidic (Slamenova et al., 1996)

conditions.

Sodium fluorid e was clastogenic in many, but not all, i n vitro

cytogenetic assays. The frequency of chromosomal aberrations was

increased (compared with unexposed controls) following exposure of

Chinese hamster lung (Don) cells (Bale & Mathew, 1987), Chinese

hamster ovary cells (Aardema et al., 1989a; NTP, 1990), Syrian hamsterEffects on Laboratory Mammals and In Vitro Test Systems

93 embryo cells (Tsutsui et al., 1984a), rat vertebral body-derived cells

(Mihashi & Tsutsui, 1996), rat bone marrow cells (Khalil, 1995), human

leukocytes (Jachimczak & Skotarczak, 1978), human peripheral blood

lymphocytes (Kishi & Tonomura, 1984; Albanese, 1987), human

fibroblasts (Tsutsui et al., 1984b; Scott, 1986; Scott & Roberts, 1987;

Suzuki & Tsutsui, 1989), human amnion (F1) cells (Aliev et al., 1988),

human and c himpanzee lymphoid cells (Kishi & Ishida, 1993) and

human oral keratinocytes (Tsutsui et al., 1991) to sodium fluoride. The

chromosomal aber

r ations induced by sodium fluoride consisted primarily of breaks/deletions and gaps, with very few exchanges. No

sig nificant increase in chromosomal aberrations was observed in

human fibroblasts, Chinese hamster ovary cells or human diploid lung

cells exposed to sodium fluoride at concentra tions at or below

10 mg/litre (Scott, 1986; Scott & Roberts, 1987; Aardema et al., 1989a;

Oguro et al., 1995; Tsutsui et al., 1995) or in Chinese hamster lung cells

at concentrations at or below 500 mg/litre (Ishidate, 1987).

Although no increa se in the frequency of chromosomal

aberrations was observed in human lymphocytes exposed to fluoride

(Gebhart et al., 1984; Thomson et al., 1985; Gadhia & Joseph, 1997),

these results are likely attributable to a number of variables related to

the methodology used to assess clastogenic activity (i.e., the method

of classifying chromosomal aberrations, phase of the cell cycle during

which the cells were exposed and the concentration of fluoride). The

pattern of induced chromosomal aberrations, the increased formation

of endoreduplicated cells (Aardema et al., 1989a, 1989b), the increased

delay in the cell cycle and the increased sensitivity of cells in the G

2 phase to sodium fluoride are all consistent with a mechanism of

clastogenicity involving an inhibition of DNA synthesis and/or repair,

and it has been suggested tha t the effect of fluoride is upon the

synthesis of proteins involved in DNA synthesis and/or repair rather

than involving direct interaction between fluoride and DNA.

Although no increase in sister chromatid exchange was reported

following the exposure of human peripheral blood lymphocytes (Kishi

& Tonomura, 1984; Thomson et al., 1985; Tong et al., 1988; Gadhia &

Joseph, 1997) and Chinese hamster ovary cells (Li et al., 1987b; Tong

et al., 1988) or rat bone marrow cells (Khalil and Da’dara, 1994) to

sodium fluoride, increased sister chromatid exchange was observed in

Syrian hamster embryo cells (Tsutsui et al., 1984a) and Chinese hamster

ovary cells (NTP, 1990) exposed to sodium fluoride. Differences in

harvest times used to accommodate cell cycle delay may be, at least inEHC 227: Fluorides

94 part, responsible for the inconsistency in the results observed for the

induction of sister chromatid exchange by fluoride.

Although the results of some studies have indicated that (sodium)

fluoride increases unscheduled DNA synthe sis in Syrian hamster

embryo cells, human foreskin fibroblasts and human keratinocytes

(Tsutsui et al., 1984a, 1984b, 1984c), Skare et al. (1986a) suggested that

these results might be an artefact, possi bly due to the formation of

precipitable complexes of magnesiu m, fluoride and [ 3 H]thymidine

triphosphate.

Sodium fluoride has been reported to induce the morphological

transformation of Syrian hamster embryo cells (Tsutsui et al., 1984a;

Jones et al., 1988a, 1988b; Lasne et al., 1988), but not murine BALB/3T3

embryo cells (Lasne et al., 1988).

With sodium monofluorophosphate, both negative and positive

results on cytogenetic change ( mostly chromosomal aberrations) in

human lymphocytes and leukocytes have been reported, without a

clear explanation for

why some studies were negative and others

positive (Zeiger et al., 1993).

Fluoride induces chromosomal aberrations in several plant

species, including onions ( Allium spp.), broadbean ( Vicia faba ) and

barley ( Hordeum vulgare ) (Zeiger et al., 1993).

7.4.2 In vivo genotoxicity

Sodium fluoride was reported to induce recessive lethal mutations

in the germ cells of male fruitfly ( Drosophila melanogaster ) (Dominok

& Miller, 1990). The results of studies on the genotoxic potential of

fluoride following its in vivo administration to laboratory animals have

varied, principally depending upon the route of administration.

Sodium fluoride induced cytogenetic damage in bone marrow or

sperm cells (i.e., chromosomal aberrations, micronuclei, alterations in

sperm morphology) when administered to rodents by intraperitoneal

injection (Ma et al., 1986; Pati & Bhunya, 1987); negative results have,

however, also been reported (Hayashi et al., 1988). While some positive

results have been reported (Akhundow et al., 1981; Aliev & Babaev,

1981; Mohammed & Chandler, 1982; M a et al., 1986; Pati & Bhunya,

1987), i n most studies in which (sodium) fluoride was administeredEffects on Laboratory Mammals and In Vitro Test Systems

95 orally (either acutely or chronically) to rodents, t here was no effect

upon sperm morphology or the frequency of chromosomal aberrations,

micronuclei, sister chromatid exchange or DNA strand breaks (Martin

et al., 1979; Skare et al., 1986b; Albanese, 1987; Li et al., 1987b, 1987c,

1987d, 1989; Pillai et al. , 1988; Dunipace et al., 1989, 1998; Lu et al.,

1989; Zeiger et al., 1994).

After administration of sodium monofluorophosphate,

cytogenetic studies have also mostly given negative results

(Voroshilin et al., 1973; Gocke et al., 1 981; Albanese, 1987; Li et al.,

1987b, 1989; Hayashi et al., 1988).



### 7.5 Reproductive toxicity

No evidence of pregnancy or implantation of embryos within the

uterus was observed in female mice administered (orally) 

### $ 5.2 mg

fluoride/kg body weight per day on days 6–15 after mating (Pillai et al.,

1989), although few experimental details were provided. Reductions in

fertility have been observed in male rabbits administered (orally) 

### $ 9.1

mg fluoride/ kg body weight per day and in male mice given 4.5 mg

fluoride/kg body weight per day for 30 days (Chinoy et al., 1991;

Chinoy & Sharma, 1998). Histopathological changes within the organs

of the reproductive system have been observed in the testes of male

rabbits administered (orally) 4.5 mg fluoride/kg body weight per day for

18–29 months (Susheela & Kumar, 1991), in the ovaries of female

rabbits injected subcutaneously with 

### $ 10 mg fluoride/kg body weight

per day for 100 days (Shashi, 1990 ) and in the testes of male mice

administered (orally) 

### $ 4.5 mg fluoride/kg body weight per day for 30

days (Chinoy & Sequeira, 1989a, 1989b). Sperm motility and viability

were reduced in rats and mice administered 4.5 mg fluoride/kg body

weight per day (as sodium fluoride) orally for 30 days (Chinoy et al.,

1995; Chinoy & Sharma, 1998). A single injection of sodium fluoride

(0.05 ml of a solution containing 250 mg sod ium fluoride/litre;

equivalent to an injection of approximately 5.6 μg fluoride) directly into

the testes of male Sprague-Dawley rats reportedly had no significant

effect upon the morphology of this organ (Sprando et al., 1996).

Sprando et al. (19 97) also reported that spermatogenic effects (e.g.,

sperm count, testes weight, histopathology) and endocrine effects

(serum testosterone, luteinizing hormone and follicle stimulatingEHC 227: Fluorides

96hormone) were not observed in rats administered drinking-water containing 0, 25, 100, 175 or 200 mg sodium fluoride/litre for 14 weeks or in

their F

1 offspring exposed in utero and after parturition to fluoride. In

a follow-up study, morphometric analysis revealed no changes in the

testes of F

1 rats exposed in utero and a f ter birth to similar levels of

fluoride in drinking-water (Sprando et al., 1998).

In an older multigeneration study conducted with female SwissWebster mice administered a low-fluoride diet and drinking-water

containing 0, 50, 100 or 200 mg fluoride/litre, reproductive function

appeared normal in the group receiving drinking-water supplemented

with 50 mg fluoride/litre, based on litter production, infertility proportions, a ge at delivery of first litter, time interval between litters and

frequency of postpartum conception; maternal toxicity and impaired

reproduction were observed at higher doses (Messer et al., 1973). Tao

& Suttie (1976) reported that various parameters of reproductive

function (i.e., reproduction rate, litter size and weight) were not significantly different in female Webster mice administered diets containing

either <0.5 or

approximately 2 or 100 mg fluoride/kg for up to three

generations. In an investigation in which rats were fed dog food containing high fluoride levels (56 or 460 mg fluoride/kg), no adverse

reproductive effects were observed; however, there was uncertainty

about the precise dose of fluoride due to a lack of data on the intake

and bioavailability of fluoride in the diet (Marks et al., 1984). Although

significant bone resorptio n was observed in breeding female rats

exposed to drinking-water containing 150 mg fluoride/litre (as sodium

fluoride) prior to breeding, during pregnancy and during lactation, no

effects were observed in the bones of weanling pups from these

females (Ream et al., 1983a, 1983b).

Adverse eff

ects on fetal development were not observed in a

study conducted with Charles River rats, in which dams received up to

approximately 25 mg fluoride/kg body weight per day from drinkingwater on days 0–20 of gesta tion (Collins et al., 1995). Fetal

development was similar in a study in which pregnant CD rats and New

Zealand White rabbits were administered drinking-water conta ining

sodium fluoride on days 6 through 15 and 6 through 19 of gestation,

respectively, at concentrations up to 300 and 400 mg/litre, respectively

(Heindel et al., 1996). In this study, the total intake of fluoride from feed

and drinking-water (and intake of fluoride from feed alone) for the ratsEffects on Laboratory Mammals and In Vitro Test Systems

97 and rabbits in the highest exposure groups was approximately 13.2 (1.0)

and 13.7 (0.7) mg/kg body weight per day, respectively.



### 7.6 Immunotoxicity

Compared with controls, T-cell mitogenesis was significantly

increased (84%) while B-cell activity (antibody production) was significantly reduced (10%) in female C57BL/6N mice administered (intragastrically) 13.6 mg fluoride/kg bod y weight per day (as sodium

fluoride dissolved in distilled water) for 10 weeks (Sein, 1988). Antibody production was also inhibited in female rabbi t s administered

(orally) 4.5 mg fluoride/kg body weight per day over a 6- to 9-month

period (Jain & Susheela, 1987b). Evidence of fluoride’s activity as a gut

and systemic adjuvant w as presented by Butler et al. (1990), based

upon the results of a study i n which rats were administered (intragastrically) 5 ml of a 100 mmol/litre solution of sodium fluoride twice a

week for 2–3 weeks and given an antigen (ovalbumin) in their drinkingwater.



### 7.7 Mechanisms of action

Tissue- or organ-specific effects linked with repeated exposure to

fluorides may involve metabolic pathways associated with lipid, carbohydrate, bone and energy metabolism, as well as signal transduction

pathways (Kaminsk

y et al., 1990). Fluoride influences a number of

enzymatic activities. The results of studies carried out in vitro have

indicated that fluoride inhibits the synthesis of DNA and protein,

inhibits cell proliferation and is cytotoxic in sufficient ly high doses

(Gilman, 1987; Elsair & Khelfat, 1988; Godfrey & Watson, 1988;

Kaminsky et al., 1990). Effects produced by the exposure of laboratory

animals and humans to fluoride may be attributable to one or more of

these metabolic and biochemical effects. The stimul atory effect of

fluoride on osteoblast proliferation may proceed, at least in part,

through the inhibition of phosp hotyrosyl protein phosphatases

(Thomas et al., 1996; Lau & Baylink, 1998).



### 7.8 Interaction with other substances

In a study designed to assess the effects of fluoride on aluminium

distribution and toxicity, Stevens et al. (1987) reported that while theEHC 227: Fluorides

98 concurrent administration of 1 mg fluoride/day (as sodium fluoride) to

male Sprague-Dawley rats receiving 0.5 mg aluminium/day (as aluminium chloride) (both compounds administered by subcutaneous injection) ov e r a period of 30 days increased the amount of aluminium

deposited in the liver (3.7-fold, P < 0.005), spleen (2-fold, P < 0.005) and

adrenal glands (1 .6-fold, P < 0.05) compared with animals receiving

aluminium alone, the co-administration of fluoride had no effect upon

the amount of aluminium deposited in the brain. Deficits in some tests

of open field behaviour as well as reductions in body weight gain were

greater in animals co-administer ed fluoride and aluminium than in

animals administered either alone.

In a study conducted by Ahn et al. (1995) in which groups of male

New Zealand rabbits were administered drinking-water containing 0–50

mg fluoride/litre (as sodium fluoride), 0–500 mg aluminium/litre (as

aluminium chloride) or both combined for a period of 10 weeks, the

accumulation of aluminium in the liver was not significantly affected by

the concurrent consumption of fluoride. However, the accumulation of

aluminium in the tibia (w hich was not influenced by the addition of

aluminium to the drinking-water) was increased when the drinkingwater contained 50 mg fluoride/litre. The accumulation of fluoride in the

teeth and bone (tibia) was reduced with the concurrent consumption

of aluminium. The aluminium content of the sterna of high-dose and

control ra ts from the NTP (1990) sodium fluoride study described

above (see sections 7.2 and 7.3) was also measured and found to be

approximately 8-fold higher in rats receiving 79 mg fluoride/litre in

drinking-water than in controls receiving deionized water (Ahn et al.,

1995).

The level of aluminium in the brains of male Long-Evans rats

given laboratory chow and distilled water or distilled water containing

2.1 mg sodium fluoride/litre or 0 .5 mg aluminium fluoride/litre for

52 weeks was reported to be approximately 2-fold higher in the sodium

fluoride group and about 2.5 higher in the aluminium fluoride group

than in animals given the same feed and distilled water for drinking.

There was significant mortality in the aluminium fluoride group. In the

kidney, there was no increased aluminium in the sodium fluoride group

but about twice as much in the aluminium fluoride group. Levels in the

liver were not different between the three groups. Pathology studies of

the brain revealed increased neuronal abnormalities in both fluorideexposed groups in parts of the right and left hemispheres, alterationsEffects on Laboratory Mammals and In Vitro Test Systems

99 in the neuronal density in the left hemisphere and alterations of 

### $

-

amyloid, amyloid A and IgM in various parts of the brain (Varner et al.,

1998). In an earlier study, the authors reported greater mortality and

effects at the dose of aluminium fluoride used in this study than at 10-

and 100-fold greater levels of aluminum fluoride. No dose–response in

changes in the brain was apparent (Varner et al., 1993).

In a study on the neurotoxicity of sodium fluoride in rats (Mullenix

et al., 1995), changes in behaviou r were monitored in groups of

Sprague-Dawley rats after exposure to fluoride at three different experimental stages. A number of behavioural patterns were examined, and

pairs of control and experimental animals were observed at the same

time. Some of the statistical methods were not fully described. In the

f irst group, dams were administered subcutaneous injections o f

0.13 mg sodium fluoride/kg on gestation days 14–18 or 17–19, 2–

3 times daily. Nine weeks after delivery, they were examined, and

measures o f time–structure changes were depressed in exposed

animals compared with controls. The second group was exposed to 0,

75, 100, 125 or 175 mg fluoride/litre in their drinking-water for 6 or 20

weeks immediately afte r weaning. The top group was discontinued

because of mortality and dehydration, and the seco nd top group

showed significant deficits in body weight. Plasma flu oride was

elevated over controls in all groups, and low-level behavioural effects

from noise were correlated with plasma fluoride levels but not dose.

Some specific behavioural changes compared with controls were

reported for 100 and 125 mg/litre females and 125 mg/litre males, but

there was considera ble variation in the controls, and data for some

dose groups were not reported. Plasma fluoride did n ot show a

dose–response trend. The third group was given 0 or 100 mg

fluoride/litre in drinking-water for 5–6 weeks. Testing after 10 weeks

was reported to show a depression in low-level behavioural effects in

females but not males. It is difficult to interpret the results of this study

without more detailed analysis of the data, some of which are not

presented; consequently, the significance of these data remains

uncertain.1 Gastrointestinal effects linked to longer-term exposure to fluoride

have been reported in some older studies of occupationally exposed

workers (effects included gastritis, duodenal ulcers, abdominal

distention, nausea) (see US DHHS, 1991; ATSDR, 1993) and observed

100 

### 8. EFFECTS ON HUMANS

8.1 General population

8.1.1 Acute toxicity

Acute oral exposure to fluoride may produ ce effects including

nausea, vomiting, abd ominal pain, diarrhoea, fatigue, drowsiness,

coma, convulsions, cardiac arrest and death (Kaminsky et al., 1990;

Whitford, 1990; Augenstein et al., 1991; ATSDR, 1993). Severe tissue

damage, respiratory effec ts, cardiac arrest and deaths have been noted

in case reports of indi viduals exposed accidentally to hydrofluoric acid

throu g h dermal contact (Buckingham, 1988; Upfal & Doyle, 1990;

Bordelon et al., 1993).

The lethal dose of sodium fluor ide to the average adult has been

estimated to be bet ween 5 and 10 g (32–64 mg fluoride/kg body

weight); an acute d o se of 5 mg fluoride/kg body weight has been considered to be the minimum that might lead to a dverse health effects

(Whitford, 1996). Gessner et al. (1994) reported the case of a death due

to acute fluoride poisoning resulting from improperly fluoridated

drinking-water; the individual was estimated to have ingestedapproximately 17.9 mg fluoride/kg body weight prior to death.

The toxicity of fluoride is depende nt upon the type or species of

the compound ingested. Generally, the more soluble salts of inorganic

fluorides (e .g., sodium fluoride) are more toxic that those that are either

weakly soluble or insoluble (e.g., calcium fluoride) (WHO, 1984).

Gastrointestinal effects produced following the acute ingestion of

toxic amounts of fluoride likely arise from the corrosive action of

hydrofluoric acid, which i s produced within the acidic environment of

the stomach (Spak

et al., 1990; Whitford, 1990; Augenstein et al.,

1991). 1 Damage to the gastric mucosa (e.g., haemorrhage, loss ofEffects on Humans

in some individuals residing in areas of endemic skeletal fluorosis

(effects included dyspepsia, abnormal surface morphology of

gastrointestinal mucosa ) (Gupta et al., 1992; Dasarathy et al., 1996) or

in some patients receiving fluoride for the treat ment of osteoporosis

(effects included pain, nausea, vomiting, diarrhoea, histological

changes in gastrointestinal mucosa) (Laroche & Mazières, 1991; Das

et al., 1994).

101 epi thelium) has also been observed in human volunteers administered

acidulated phosphate fluoride gels (Spak et al., 1 990) or sodium fluoride

solutions (Spak et al., 1989). Some individuals may be u nusually

hypersensitive to stannous fluoride, as mani fested by ulcerations in

the oral cavity after topical treatment (Razak & Latifah, 1988).

Cardiac arr est following accidental exposure to high levels of

fluoride has been attributed to the development of hypocalcaemia

and/or hyperkala emia (Cummings & McIvor, 1988; Augenstein et al.,

1991; ATSDR, 1993). The acute effects of fluoride upon the central

nervous system may be due to fluoride-induced hypocalcaemia and the

inhibition of cellular enzymes (Augenstein et al., 1991).

R espiratory effects (e.g., haemorrhage, pulmonary oedema, tra

c heobronchitis, shortness of breath) have been observed in

individuals following inhalation of hydrogen fluoride (Dayal et al.,

1992; ATSDR, 1993).

8.1.2 Clinical studies

8.1.2.1 Skeletal effects

Since the 1960s, fluoride (usually as sodium fluoride or sodium

m onofluorophosphate, in combination with added calcium and, sometimes, vitamin D) has been used for the treatment of age-dependent

osteoporosis at high dose levels (approximately 20–30 mg fluoride /day). While i t seems apparent that such treatment increases the

trabecular bone density, it apparently has no similar beneficial effect on

cortical bone. Although such treatment may be protective against vertebral fractures, data on other fractures, including femoral bone, are

very controversia l. The assessment of the efficacy of fluoride therapies

for osteoporosis is outside the scope of this document. The most often

encountered side-effects of high-dose fluoride therapy includeEHC 227: Fluorides

102 gastrointestinal pains and painful stres s microfractures of feet (Bayley

et al., 1990; Delmas et al., 1990; Gutteridg e et al., 1990; Murray et al.,

1990; Orcel et al., 1990; Riggs et al., 19 90; Schnitzler et al., 1990; Riggs,

1991; Pak et al., 1994; Rizzoli et al., 1995; Meunier et al., 1998; Reginster

et al., 1998; Alexandersen et al., 1999). Exposure to fluoride during

treatment for osteoporosis may lead to calcium deficienc y, owing to the

stimulation of bone growth, even in cases where patients are given

supplemental calcium as part of the therapeutic protocol (Dure-Smith

et al., 1996).

8.1.2.2 Haematological, hepatic or renal effects

No evidence of significantly adver se haematological, hepatic or

renal effects was reported in a study of osteoporotic patie nts administere d approximately 60 mg sodium fluoride/day (equivalent to a dose

of 389 μg fluoride/kg

body weight per day in an adult weighing 70 kg)

over a p eriod of 5 years (Hasling et al., 1987). In a study with elderly

postmenopausal osteoporotic females receiving 23 mg elemental flu oride/day for a mean period of 4.2 years (ranging fro m 1.4 to 12.6 years)

(equivalent to an intake of 470 μg/kg body weight per day in an individual weighing 58 kg), no clinically adverse alterations in blood and

urine chemistries or in the frequency of sister ch romatid exchange in

peripheral blood lymphocytes were observed in the fluoride-exposed

patients ( n = 25) compared with controls not admi n istered fluoride

(Jackson et al., 1994).

8.1.3 Epidemiological studies

8.1.3.1 Cancer

The relationship between the consumption of fluoridated

drinking

- water and morbidity or mortality due to cancer has been

examined in a large number of epidemiological studies, performed in

many count ries. These studies were largely prompted by a report by

Yiamouyiannis & Burk (1977) that found an increase in overall ca ncer

mortality in two of several broad age groups in 10 U S cities following

the implement ation of drinking-water fluoridation. Although dismissed

based on a variety of methodological flaws ( see Doll & Kinlen, 1977;

Smith, 1 9 80; Kinlen & Doll, 1981; Chilvers, 1982; IARC, 1982, 1987;

Knox, 1985), the Yiamouyiannis & Burk (1977) study stimulated a large

number of other ecological studies, performed in Australia, Canada,Effects on Humans

103 China and the Pro vince of Taiwan, England and Wales, New Zealand,

Norway and the USA (Hoover et al., 1976; IARC, 1982, 1987; Knox,

1985; Hrudey et al., 1990; M ahoney et al., 1991; Cohn, 1992; Freni &

Gaylor, 1992; Yang et al., 2000), that found no consistent relationship

between deaths due to any type of cancer and the consumption of

fluoride-containing (fluoridated or with naturally high fluoride content)

dr i nking-water. Although some age- and sex-related increases in

tumour incidence over time for cancer of the bones and joints and

osteosarcomas were observed in one study (US DHHS, 1991), these

increases were not related to the length of time that the water had been

“fluoridated.” Another report of an age- and sex-related increase in the

rate of osteosarcoma in areas of New Jersey, USA, served with fluoridated drinking-water was based on only 10 and 7 cases in the fluoridated and non-fluoridated areas, respectively (Cohn, 1992).

Although there has been no consistent evidence of an

association bet ween the consumption of fluoridated drinking-water

and increased morbidity or mort ality due to cancer, most of these

epidem iological studies were primarily geographic or ecological

correlational investigations. Such studies are characterized by the use

of aggregate units of observation, such as counties, states or

provinces, rather than individuals, and usually involve the comparison

of mortality or morbid ity rates between exposed and unexposed areas

or among areas with varying degrees of exposure. Generally, studies of

t his nature are limited, since the movement of individuals in and out of

the exposed and non-exposed groups and other variable fact ors (e.g.,

industrialization, personal habits, et c.) that have an influence on the

developme nt of adverse health effects are not taken into account, and

the statistical power may be insufficient to reveal small differences in

health-related effects (e.g., increases in the inci dence of rare tumours).

Moreover, in such ecological stu dies, the intake of fluoride from other

sources such as food and d e ntal care products is not taken into

account. Notably, the total intake of fluoride by individuals co n suming

fluoridated or non-fluoridat ed drinking-water may not be markedly

different, due to the intake of significant amounts of fluoride from food

and dental care products (US DHHS, 1991; Burt, 1992).

However, in a case–control study conducted in New York State

(but excluding New York City), USA, information on the intake of

f luoride from drinking-water and dental care products (e.g., flu oride

tablets, mouth rinses, toothpaste and dental treatments), but notEHC 227: Fluorides

104 foodstuffs, was obtained for ma les and females 

### # 24 years of age

having been diagnosed with osteosarcoma between 1978 and 1988

(Gelberg et al., 1995). The analyse s were based on 130 cases and as

many controls (matched by years of birth and gender ). Interviews on

exposure patterns were made with the subjects themselves and/ o r with

their par ents. No significant risks were observed for any individual

fluoride exposure group, using either the parents’ or the children’s

exposure assessments. Nor was any significant trend observed when

using the p arents’ exposure assessments. However, using the

subjects’ exposure estimates, there was a monotonous increase in the

odds ratios (ORs) for osteosarcoma with inc reasing exposure

e stimates: 1, 1.16 (95% confidence interval [CI] = 0.44–3.04), 1.72 (95%

CI

= 0.55–5.39) and 1.88 (95% CI

= 0.64–5.55) for the exposure

categories of 0–1250, 1251–2338 , 2339–3987 and 3988–9291 mg total

fluoride.

In a case–control study, M oss et al. (1995) found no evidence of

a significantly increased risk of osteosarcoma among mal es or females

(or both genders combined) residing in Wisconsi n, USA, associated

with the consumption of fluoridated drinking-water. Cases of osteosarcoma (and brain and digestive system cancers) and their controls

were studied in relation to their consum p tion of fluoridated drinkingwater (i.e., containing >0.7 mg fluoride/litre) between 1979 and 1989.

Controls (approximately four per case) were matche d to cases based

upon age, sex

and race. Odds ratios (also adjusted by conditional

logistic regression fo r likely natural exposure to waterborne radiation

and population size) for risk of osteosarcoma with consumption of

fluoridated drinking-water were 1.0 (95% CI

= 0. 6–1.5; 110 exposed

cases), 0.9 (95% CI

= 0.5–1.6; 56 exposed cases) and 1.1 (95% CI

=

0.6–1.9; 54 exposed cases) fo r both genders combined, females and

males, respectively.

In a further hospital-based case–control study on osteosa rcoma

(22 cases and 22 matched co ntrols), the odds ratio for “high”

(>0.7 mg/litre) average lifetime or childhood drinkin g-water fluoride

concentration was 0.33 (McGuire et al., 1991).

8.1.3.2 Skeletal fluorosis

Skeletal fluorosis is a pathological condition that may arise following long-term exposure (ei ther by inhalation or by ingestion) to

elevated levels of fluoride. Although the incorpor ation of fluoride intoEffects on Humans

105 bone may increase the stability of the crystal lattice and render the

bone less soluble, bone mineralization is delayed or inh ibited (Grynpas,

1990), and con sequently the bones may become brittle and their tensile

strength may be reduced. The severity of the effects associated with

skeletal fluorosis is rela t ed to the amount of fluoride incorporated into

b one. In a preclinical phase, the fluorotic patient may be relatively

a symptomatic, with only a slight increase in bone mass, detected radiographically. Sporadic pain and stiffness of the joints, chro nic joint pain,

osteosclerosis of cancellous bone and calcification of li gaments are

associated with the first and second clin ical stages of skeletal

fluorosis. Crippling skeletal fluorosis (clinical phase III) may be

associated with limited move m ent of the joints, skeletal deformities,

intense calcification of ligaments, muscle wasting and neurolo gical

deficits (Krishnamachari, 1987; Kaminsky et al., 19 90; US DHHS, 1991).

A consi stent finding in cases of chronically elevated fluoride uptake

is an increase in mi neralization lag time of bone, which can be

demonstrated by dynamic histomorphome try (Boivin et al., 1989).

Osteomalacia may be observed in fluorotic individuals with a reduced

or suboptimal intake of calcium; sec ondary hyperparathyroidism may

also be observed in a subset of patients (Krishnamac hari, 1987; US

DHHS, 1991). Apparently in combinat ion with nutritional deficiencies,

high intakes of fluoride and the subsequent osteomalacia may also lead

in chil dren to bone deformities such as genu valgum, originally

described as Kenhardt bone disease (Jackson, 1962; Krishnamachari

& Krishnaswamy, 1973; Krishnamachari, 1976 ; Chakma et al., 2000). In

osteoporotic patients, fluoride can stimulate bone formation to such an

extent that, despite calcium supplementation, calcium deficiency,

secondary hyperparathyroidism and osteomalacia occur (Dure-Smith

et al., 1996).

The concentration of fluoride in the bone of individuals in the preclinical or crippling stages of skeletal fluorosis may be bet ween 3500

and 5500 mg/kg bone or greater than 8400 mg/kg bone, respective ly,

compared with the reference values of 500–1000 mg/kg bone ash

weight (US DHHS, 1991).

A number of factors, such as ag e, nutritional status, renal function

an d calcium intake, in addition to the extent and duration of exposure,

can influence the amount of fluoride deposited in bone and, consequently, the development of skeletal fluorosis (US DHHS, 1991).

Individuals with impaired renal function, such as those with diabetes,

may be more prone to developing fluoride-related toxicological effectsEHC 227: Fluorides

106 (i.e., fluorosis) due to their dim i nished excretion of fluoride (Kaminsky

et al ., 1990; US DHHS, 1991). Skeletal fluorosis may be reversible to

some degree in a manner that is dependent upon the extent of bone

remodelling (Grandjean & Thomsen, 1983).

Felsenfeld & Roberts (1991) reported the case of a 54-yea r-old

woman who, after having consumed drinking

- water containing approximately 8 mg fluoride/litre over a period of 7 years, had osteosclerosis

and stiffness in her knees and hips. Five cases o f crippling skeletal

fluorosis in t he USA have been reported over the past 40 years; the

total intake of fluor ide by some of these individuals over a 20-year

period was estimate

d to be approximately 15–20 mg/day (US DHHS,

1991) (equivalent to a daily intake of 230–310 μg fluoride/kg body

weight per day in an adult weighing 64 kg). There have been no systematic studies of the prevalence of this disease in the USA.

The occurrence of endemic skeletal fluorosis has been well documented in case reports and surveys of individuals residi ng in certain

areas of the world (e.g., India, China, northern, eastern, central and

southern Africa), where the intake of fluoride may be inordinately high

as a result o f the often significant consumption of drinking-water containing substantial amounts o f naturally occurring fluoride, the indoor

burning of fluoride-rich coal for heating and cooking, t he preparation

of foodstuffs in water con taining increased fluoride and/or the consumpti on of specific foodstuffs naturally rich in fluoride (Haimanot et

al., 1987; Krishnamachari, 1987; Pettifor et al., 1989; Kaminsky et al.,

1990; Tobayiwa et al., 1991; Mithal et al., 1993; Wang et al., 1994;

Abdenn ebi et al., 1995; Liu, 1995; Michael et al., 1996; Zhao et al., 1996;

Teotia et al., 1998). Large numbers of individuals residing in India and

China are afflic ted with skeletal fluorosis, which in some cases may be

severely crippling. In addition to an increased intake of fluoride from

foodstuffs and drinking-water with high levels of fluoride, other

factors, such as nutritional status as well as clim ate and other factors

influencing fluid intake, may possibly play a significant role in the

development of endemic skeletal fluorosis (Krishnamachari, 1987;

Haimanot, 1990; Zang et al., 1996). These issues make it difficult to

c h aracterize the exposure–response relationship in studies of skeletal

fluorosis, such as those outlined below.

In China, endemic fluorosis associated with coal burning ha s been

identified in epidemiological investigations. Local residents absorbEffects on Humans

107 high doses of fluoride through inhalation and/ or ingestion, as a consequence of the indoor use of high-fluoride coal in cooking, heating and

drying of food (the average concent rations of fluoride in coal were

200–1500 mg/kg, with th e highest up to 3000 mg/kg). In those areas, the

intakes of fluoride via drinking-water were relatively low (range from 0.1

to 0.52 mg/day pe r person) (Table 10). The number of cases of coalburning-type skeletal flu o rosis has been estimated to be 1.5 million

( Hou, 1997; Liang et al., 1997).

Table 10. Daily fluoride intake in different endemic areas in China using

high-fluoride coal for cooking and drying foodstuffs indoors

Endemic area Coal type Daily intake (mg/person)

Food Drinkingwater Air Total

Sichuan Soft coal 8.86 0.1 0.67 9.63

Hubei Anthracite 4.12 0.45 0.55 6.12

Jiangxi Anthracite 2.54 0.5 0.24 3.28

Hunan Anthracite 1.81 0.52 0.31 2.64

Hubei Anthracite 1.86 0.42 0.15 2.43

Jiangxi

(control) Firewood 1.14 0.24 0.11 1.49

In a short communication with few deta ils, the relationship

between air, well-water and dietary fluoride and skeletal fluorosis (no

information on diagnostic cr iteria provided) was studied among

6792 individuals in Inner Mo ngolia (Xu et al., 1997) (Table 11). The

concentrations of fluoride in air and di et were low, and that in drinkingwater sh owed a correlation of 0.87 with the prevalence of fluorosis. The

skeletal fluorosis prevalence was 

### # 0.21% for fluoride concentrations

of 0.65 mg/litre or lower and reached 19.9% for fluori de concentrations

of 6.9 mg/litre.

The relationship between fluoride concentrations in drinkingwater and the prevalence of skeletal fluorosis was also reported in

another Chinese study (Liang et al., 1997) (Table 12).

A ccording to an early estimate, the number of persons at risk of

developing skeletal fluorosis was 5 million in Punjab and more in

Andhra Pradesh and Madras, India (Siddiqui, 1970).EHC 227: Fluorides

108 Table 11. Prevalence of skeletal fluorosis in villages in Inner Mongolia,

China a

Fluoride content of

drinking-water Skeletal fluorosis

Cases %

0.4 0 0

0.65 2 0.21

1.4 93 7.72

1.6 109 12.3

3.2 101 12.7

3.4 132 15.2

4.7 42 19.6

6.9 166 19.9

a From Xu et al. (1997).

Table 12. Prevalence of skeletal fluorosis in China as a function of drinkingwater fluoride concentration a

Fluoride concentration

in drinking-water

(mg/litre) Prevalence of

skeletal fluorosis (%)

among individuals

with normal

nutrition b Prevalence of skeletal

fluorosis (%) among

individuals with deficient

nutrition c

<0.3 0 0

0.6–1.0 0 0

>4.0 43.8 69.2

a From Liang et al. (1997).

b Normal nutrition

= protein >75 g/d ay, high-quality protein >20% of total

protein, calcium >600 mg/day.

c Deficient nutrition

= protein <20 g/day, high-quality protein <10% of total

protein, calcium <400 mg/day.

The frequency of skeletal fluorosis (as identified by the clinical

picture ) among children 3–10 years of age was 39% (18/46) in a village

in India, where the fluoride concentrations in the three wells were 0.6,

4.0 and 1.34 mg/litre (Shivashankara et al., 2000). It was not possible to

discern, fr om the information available, the contribution of each well to

the drinking-water of the residents.

In a clinical survey for fluoros is in a random sample of residents

i n five areas in Tamil Nadu, South India, the drinking-water fluor ideEffects on Humans

109 concentration was directly related to th e prevalence of dental fluorosis

i n children (8–15 years of age) and adults. Among children, no skeletal

fluorosi s (no information on diagnostic criteria provided) was

observed; among adults, the pr evalence of fluorosis was 34% (157 individuals surveyed) in the area with the highest drinking-water fluoride

concentration (summer month average 6.8 mg/litre, non-summer month

average 5.6 mg/litre) (estimated total daily fluori de intake 20 mg), while

no skeletal fluorosis was observe d in the other areas, where the mean

fluoride concentrations were 2.2 (summer months) and 1.8 (non-summer

months) mg/litre or lower, with estimated total daily flu oride intakes

less than 10 mg (Karthikeyan et al., 1996).

A correlation between average water fluoride concentration and

p revalence of skeletal fluorosis (assessed by X-ray) was found among

adults in 15 villages in Dungapur district in Raj asthan, India (Choubisa

et al., 1997) (Table 13). The pre valence ranged from 4.4% at a water

fluoride level of 1.4 mg/litre to 63.0% at the level of 6.0 mg/litre.

Crippling fluorosis was consistently observed in villages with fluoride

concentrations of 

### $ 3 mg/litre.

In four villages in the Faridabad district, No rth India, the percentage of people wit h skeletal fluorosis (assessed by the clinical appearance of impaired mobility) was 57, 43, 18 and 17, while the respective

me ans (ranges) of the water fluoride contents were 3.2 (0.25–8.0), 3.7

(0.3–7.0), 2.5 (0.3–5.4) and 1.0 (0.7–1.6) mg/litre (Susheela et al., 1993).

A cross-sectional study in Punjab also reported the relati o nship

between water fluoride and the prevalence of skeletal fluorosis (J o lly

et al., 1968). Skeletal fluorosis was rare (assessed by X- ray) (2.4%) in

a village where the average w e ll-water fluoride concentration was

1.4 mg/litre, but its incidence was 71% in the village with the highest

water fluoride concentration, 9.7 mg/litre. In five villages where the

water fluoride concentratio n was 3–4 mg/litre, the prevalence of

skeletal fluorosis was 10–42%. It was suggested that lower calcium

c oncentrations in some water sources were associated with h igher

skeletal fluorosis prevalence.

The dependence of skeletal fluorosis on duration of exposure and

age was studied in a village in Andhra Pradesh, India, where theEHC 227: Fluorides

110 Table 13. Relationship between drinking-water fluoride concentration and

skeletal fluorosis in Rajasthan, India a

Village Fluoride

concentration

(mg/litre) Prevalence

of fluorosis % Crippling

fluorosis

Mean Range

Amaliya

Fala 1.4 0.5–1.8 4/92 4.3 No

Doja 2 1.2–2.0 10/102 9.8 No

Selaj 2 1.5–2.5 4/85 4.7 No

Anturi 2.3 0.3–3.5 16/180 8.9 No

Batikada 2.4 1.3–3.1 16/120 13.3 No

Devsomnath 2.5 0.0–3.1 14/188 7.4 No

Masania 2.6 1.0–2.6 28/176 15.9 No

Dora 3 1.2–3.9 22/96 22.9 Yes

Dolwaniya

Ka Oda 3 2.5–3.5 14/78 17.9 Yes

Palvasi 3.4 2.3–4.2 38/114 33.3 Yes

Jogiwara 3.4 1.0–4.3 27/106 25.5 Yes

Kolkhanda 4.5 4.2–4.7 52/106 49.1 Yes

Banda

Ghanti 5.7 3.8–6.7 61/115 53.0 Yes

Hadmatiya 6 3.9–8.3 118/205 57.6 Yes

Pantali 6 2.4–10.

8 121/192 63.0 Yes

a From Choubisa et al. (1997).

d rinking-water was derived from five wells, in which the fluoride c oncentrations were between 7.2 and 10.7 mg/lit re (average 9.0 mg/litre); it

was estimated that the daily water consumption was 4.6 li tres, which

would lead to a d aily dose of 36–54 mg fluoride (Saralakumari &

Ramakrishna Rao, 1993). Skeletal fluorosis started to appear after

10 years of residence in the village and reached 100% after 20 years.

In a cross-sectional study of 50 randomly selected adults who had

be en residents of one of two villages for all their lives in Senegal,

kyphosis was used as an indicator of skeletal fluorosis (and was

radiologically confirmed to be fluorosis in three cases) (Brouwer et al.,

1988). The prevalence of severe kyphosis was 4 out of 55 (7%) inEffects on Humans

111 Guinguineo, where the well-water fluoride concentrat ion was 3.9 mg/litre, and 11 out of 42 (26%) in Darou Rahmarie Fall, where the fluoride

concentration was 7.4 mg/litre.

8.1.3.3 Skeletal fracture

Several ecological

and cross-sectional studies have been performed to investigate the relationship b etween fluoride in drinkingwater (from natural sources or f rom fluoridation) and bone fractures or

bone density (McClure, 1944; Gog gin et al., 1965; Bernstein et al., 1966;

Korns, 1969 ; Madans et al., 1983; Simonen & Laitinen, 1985; Arnala et

al., 1986; Avorn & Nielssen, 1986; Sowers et al., 1986; Danielson et al.,

1992; Jacobsen et al., 19 92, 1993; Suarez-Almazor et al., 1993; Kröger

et al., 1994; Jacqmin-G adda et al., 1995; Lan et al., 1995; Czarnowski et

al., 1999; Fabiani et al., 1999). Limitations in exposure assessment and

study design preclude firm conclusions from being dr awn from these

studies.

Based on an ecolo gical study of the rates of skeletal fracture

among men and women between 65 and 90 years of age in the USA, the

r a tes of hip fracture were not significantly increased among those

residing in fluoridated areas (i.e., 

### $ 0.7 mg fluoride/litre) compared with

rates in those residing in non-fluoridated areas (i.e., 

### # 0.3 mg

fluoride/litre); however, among males, the relati ve rates of fracture of

the p roximal humerus and distal forearm were significantly increased by

approximately 23% and 16%, respectively (Karagas et al., 1996).

Other stu dies have reported either no increase or a reduced risk

of hip (or skeletal) frac t ure associated with the consumption of

fluoridated drinking-water (Madans et al., 1983; Simon en & Laitinen,

1985; Arnala et al ., 1986; Jacobsen et al., 1993; Suarez-Almazor et al.,

1993; Lehmann et al., 1998; Fabiani et al., 1999).

The relative risk of hip, wrist or spinal fracture was 2.2 (95% CI =

1.07–4.69) in women 55–80 years of age residing in an “elevated

fluoride community” (with drinking-water containing 4 mg/litre)

compared with those in a control community, with drinking-water containing 1 mg flu o ride/litre (Sowers et al., 1986, 1991). The estimated

mean intake of fluoride (f rom water-based beverages only) by women

in the “el evated-fluoride community” was approximately 72 μg/kg body

weight per day.EHC 227: Fluorides

112 In a retrospective cohor t study of 144 627 persons who had lived

at least dur ing 1967–1980 in a Finnish village outside the municipal

water system, the relationship between hip fracture in 1981–1994 (from

hospital discharge records) an d drinking-water fluoride concentration,

as estimated from a nationwide groundwater survey of 8927 wel ls, was

s tudied (Kurttio et al., 1999). The fluoride levels in the wells were

estimated from a national database and were approximately 1.4 times

higher than the actually measured fluoride levels. The median fluoride

concentration in the well-water was 0.1 mg/litre; the maximum value

was 2.4 mg/lit re. No association was observed between hip fractures

in either men or women and the well-water fluoride concentration, when

all age groups were considered. Howev er, in women 50–65 years old at

the start of follow-up, age- and area-adjusted relative risks (RR) for hip

fracture increased with increasing well-water concentration in the

categories 0.11–0.3, 0.3–0.5, 0.5–1.0, 1.1–1.5 and >1.5 mg/litre (RR

=

1.16, 95% CI = 0.93–1.43; RR = 1.31, 95% CI

= 0.86–1.99; RR = 1.53 [ P <

0.05], 95% CI = 1.08–2.16; RR = 1.24, 95% CI = 0.77–2.01; RR

= 2.09 [ P

< 0.05], 95% CI

= 1.16–3.76), in compa rison with a fluoride

concentration of 

### # 0.1 mg/litre.

In a case–control study, Feskanich et al. (1998) assessed the risk

of forearm and hip fracture among a group of female US nurses in

relation to their long-term exposure to fluor ide, assessed on the basis

of the levels of fluoride in toenails. Women in the three highest quartiles of fluoride exposure (i.e., levels of fluoride in toenails of 2.00–3.35,

3.36–5.50 and >5.50 mg/kg) had increased and reduced ri sks (not

st atistically significant) of forearm and hip fracture, respectively, compared with women in the lowest quartile of fluoride exposure (i.e., <2.00

mg/kg).

Bone mineral density was investigated in a random strat ified

s ample of 3222 perimenopausal women in eastern Finland (Kröge r et al.,

1994). Of these women, 969 had used artificially fluoridated drinkingwater (1. 0–1.2 mg/litre) for more than 10 years, 2024 had never used it

(drinking-water fluoride concentration <0.3 mg/litre) and 229 had used

fluoridated water for less than 10 years. The re was no significant

difference in the 10-year incidence of self-re ported bone fractures

between the first group and the second and third groups combined.

Bone mineral densities of the spi ne and femoral neck, measured by dual

X-ray densitometry and adju sted for age, weight, menopausal status,

calcium intake, physical activity c l ass, deliveries, alcohol consumptionEffects on Humans

113 and oestrogen use, were statistically significantly (approximately 1%)

higher among women who had used f luoridated drinking-water longer

than 10 years than among the rest.

In a 5 -year follow-up study (Jacqmin-Gadda et al., 1998) of

3216 men and women aged 65 years or more, risk factors of fractures of

the hip o r elsewhere were studied. The fluoride exposure was estimated

from analyses of fluoride in water in 78 areas and by weighting the

concentrations b y duration of water supply use during the last 10

years and the relative contributions of different water s ources in the

drinking-water. Fract ure rates were assessed from questionnaires and

verified by the doctor of each patient reporting a fracture, when the site

or multiplicity of the fracture was question able. Logistic regression

analysis was used to assess the influence of different variables on the

fracture risk; the analysis considered age, sex, body mass index, smoking status, alcohol consumption , use of psychotropic drugs and

fluoride exposure. No rela tionship was observed between fluoride

exposure and fra ctures other than at the hip. For hip fractures, participants in the two highest drinking-water fluorid e quartiles (0.11–

0.25 mg/litre and >0.25 mg/litre) were at a higher risk (OR

= 3.25, 95% CI

= 1.66–6.38; and OR = 2.43, 95% CI = 1.11–5.33, respectively) than

those below these levels. Howe ver, participants at drinking-water

fluoride levels >0.7 mg/litre were not at a higher risk than those below

this level (OR = 0.77, 95% CI = 0.37–1.62). When divided at the 1

mg/litre level, no increased risk appeared either.

In a multicentre prospective study on the risk factors of osteoporosis in postmenopau sal women ( n = 7129) (Phipps et al., 2000) (in

which the earlier study, Cauley et al., 1995, is subsumed), the relationship between drinking-water fluoride exposure during th e years 1950–

1994 and density of lumbar spine , proximal femur, radius and calcaneus,

plus incident fractures of vertebrae, hip, wrist and humerus in

1971–1990, was investigated. In a mult ivariate analysis, the results were

adjusted fo r age, weight, education, muscle strength, surgical

menopause, calcium intake, dr inks per week, current oestrogen use,

current thiazide use, non-insulin-dependent diabetes, current thyroid

hormone use, walking for exercise and smokingstatus. The bone density was 2% higher among women continuously exposed to fluoride in

drinking-water for 20 years in lumbar spine and proximal femur but

lower in distal and proximal radius; for calcaneu s

, the difference was

not statistically significant. Risk of incident fracture of the hip (RR =EHC 227: Fluorides

114 0.69, 95% CI = 0.50–0.99) and spine (RR = 0.73, 95% CI = 0.55–0.97) was

signi ficantly lower among those continuously exposed to fluoride than

among the non-exposed; for fracture s of the humerus, the difference

was not s i gnificant (RR

= 0.85, 95% CI

= 0.58–1.23), and for fractures of

the wrist, the risk among those exposed to fluoride was eleva ted (RR

= 1.32, 95% CI = 1.00–1.71).

In a population-based case–control study on t he relationship

between naturally occurring fluor ide in drinking-water and fractures of

the hip, lifetime drinking-water fluoride concentration w as determined

from residential history and data from water suppliers on 514 cas e s and

5 27 sex- and age-matched controls in the United Kingdom (Hillier et al.,

2000) . After adjustment for sex and age, body mass index, physical

activity, age at menopause, cur rent alcohol consumption, smoking,

current treatment with oral corticosteroids and dietary calcium, the

odds ratio for lifetime drinking-water containing 

### $ 0.9 mg fluorid e /litre

was 1.0 (95% CI

= 0.7–1.5) in comparison with lifetime drinking-water

containing lower fluoride concentrat ions. No effect of fluoride concentration early or late in life on hip fracture risk w a s observed either.

However, based on estimated total fluoride intakes in the United Kingdom, the contribution of fluoride in drinking- water was rather small

(probably less than one-third).

The relationship between drinking-wa t er fluoride concentration

and hip fracture, as well as all bone fractu res since the age of 20 years,

was st udied among 8266 Chinese men and women, residents of six

vi llages with different drinking-water fluoride concentrations (Li et al.,

2001). The studied per sons had lived in the same village for no less

than 25 years, most for th eir whole lives, and were no less than

50 years of age at the time of the study. Altogether, 531 subjects

rep orted one or more fractures, and for 526 of them the fracture was

confi rmed by X-ray; the number of hip fractures was 56. In a multiple

logistic regression analysis, adjusted for age an d gender, the odds

ratio for any fracture was 1.50, 1.25, 1.00, 1.17, 1.18 and 1.47 for

drinking-wa

ter fluoride concentrations of 0.25–0.34, 0.58–0.73,

1.00–1.06, 1.45–2.19, 2.62–3.56 and 4.32–7.97 mg/litre, respectively

(Table 14). From analysis of the fluoride concentrations in tea and air

and anamnestic information on the use of fluoride-containing

toothpastes or mouth rinses, it was concluded th at drinking-water was

the only significant source of fluoride exposure, and the estimated

daily fluoride intake from drinking-water was estimated to be 0.73, 1.62,

3.37, 6.54,Effects on Humans

115 Table 14. Water fluoride concentration and risk of skeletal fracture a

Water fluoride

concentration

(mg/litre) Total fluoride

intake

(mg/day) Odds ratio for all

fractures

( P value) Odds ratio for

hip fracture

( P value)

0.25–0.34 0.73 1.50 (0.01) 0.99 (0.99)

0.58–0.73 1.62 1.25 (0.17) 1.12 (0.85)

1.00–1.06 3.37 1.00 1.00

1.45–2.19 6.54 1.17 (0.33) 2.13 (0.15)

2.62–3.56 7.85 1.18 (0.35) 1.73 (0.34)

4.32–7.97 14.13 1.47 (0.01) 3.26 (0.02)

a From Li et al. (2001).

7.85 and 14.13 mg in the six expos ure categories. The difference

between the group with the lowest odds ratio was significant ( P < 0.01)

for the lowest and highest exposure group. The observation remained

qualitatively similar when only fr actures after the age of 50 years were

considered, but reached statistical significance o nly for the high exposure group. For hip fractures, the prevalence was similar for the three

lowest exposure groups, but elevat ed for the three high exposure

groups (OR

= 2. 13, 1.73 and 3.26); the difference was significant for the

high exposure group.

In a meta-ana lysis (Jones et al., 1999) of ecological, crosssectional and cohort studies on water fluoridation and bone fractures

published in 1966–1997, wate r fluoridation was not observed to have

a n effect on fracture incidence (RR

= 1.02, 95% CI

= 0.96–1.09) . Out of

26 studies (published in English), 18 contained information that could

be used in the meta-analysis and were included. The meta-analysis

correctly assi

gned a qualitative score to the different studies (by which

the studies were weighted) and considered sources of bias such as

publication bias. Although overall no relationship between fluoridation

and fracture risk was observed, there was considerable hete rogeneity

between the studies. Four of the studies also repor ted on the

relationship between wat er fluoridation and bone mass. A significant

incr ease in lumbar spine bone mass was observed; for femoral neck,

the change was positive, but statistical ly not significant, and for distal

radius, it was negative and statistically not significant.EHC 227: Fluorides

116 8.1.3.4 Reproductive effects

In case–c ontrol studies, no evidence of an association between

the consumption of fluoridated drinking-w ater by mothers and

increased risk of spontaneous abortion (Aschengrau et al., 1989), late

adverse pregnancy outcome (Aschen grau et al., 1993) or congenital

cardiac disease in children (Zierler et al., 1988) was identified. These

findings confirm previous observations of no apparent rel ationship

between the rate s of Down syndrome or congenital malformation and

the consumption of fluoridated drinking-water (see Berry, 1962;

Needleman et al., 1974; Erickson et al., 1976; Berglund et al., 1980;

Erickson, 1980; all cited previously in WHO, 1984).

Freni (1994) reported evidence suggesting that exposure to fluoride in d rinking-water may be associated with reduced fertility rates,

based upon the results of an ecological study that evaluated the “total

fertility rate” (i.e., total age-specific births per 1000 women) between

19 70 and 1988 for white women, 10–49 years of age, residing in

30 regions in nine US states. However, this study was base d upon

population means, rather than individual data.

8.1.3.5 Respiratory effects

Ernst et al. (1986) exami ned respiratory function in a group of male

and female adolescents with “ high” or “low” exposure to the emissions

fr om an aluminium plant located near Cornwall, Ontario, Canada, and

reported evidence of respiratory abno rmalities (i.e., a 49% increase [ P

= 0.05] in the ratio of the closing volume/vital capacity) in males, but

not females, in the “high” exposure group, compared with those with

“low” exposure. Individuals were considered to have “h igh” and “low”

exposure if they resided more than 60% of their lives within

approximately 4 and 17 km of the plant, respectively.

Lung X-ray f

indings were reported in 45 cases with skeletal fluorosis in an area of China contaminated by co al combustion. Chronic

b ronchitis with diffuse interstitial fibrosis and pulmonary emphysem a

were reported to occur (Liu, 1996).

Since the residents in both studies were likely exposed to other

airborne contamina nts and particulates, it is difficult to attribute the

effects on respiratory function solely to fluorides per se

.Effects on Humans

117 8.1.3.6 Neurobehavioural effects

Two studies in two different regions of China have considered the

potential effects of fluoride from drinking-water on children’s intelligence.

Th e first study (Li et al., 1995) was conducted on 907 children

(ages 8–13) of the Guizhou provin ce. Intelligence was measured by the

China Rui Wen’s Scaler for Rural Areas. Children lived in four areas

with different degrees of fluorosis prevalence (urinary fluoride ranging

from 1.02 to 2.69 mg/litre). The average IQ was 8 9.9 in the non-fluorosis

area and 80.3 in the high prevalence area. The trend among the four

areas was statistically significant ( P < 0.01).

The second study was carried out in Sh anxi (Zhao et al., 1996) and

involved 160 children (ages 7–14) randomly selected from each of two

villages, one with a high leve l of fluoride contamination of the water

(4.12 mg/litre, with 86% of the population having signs of dental

fluorosis), and one with low contamination (0.9 1 mg/litre and 14%

dental fluorosis). The “official intelligence quotient (IQ)” was measured. The av erage IQ in the first village was 97.69, and in the second

it was 105.21 ( P < 0.01). (Th e much higher IQ in comparison with the Li

et al. (1995 ) study is noteworthy, but it is probably justified by the use

of a different scale [Zhao et al., 1996].)

These two studies deserve similar comments:



### C T here is no reference to the reliability of IQ measurement in the

context of rural China.



### C There is no evidence that the measurements were blind; in fact,

they were probably not, being conducted in different villages.



### C There is no information on the tr aining of the professional figures

who performed the tests.



### C In the second study, an attempt was made to adjust for confounding by only the edu cational level of the parents, and the

difference between differently contaminated areas persisted.

The significance of these studies remains uncertain, but in a study

of 197 children between the ages of 7 and 11 yea rs in which childhood

behavioural problems were assessed in relation to different levels ofEHC 227: Fluorides

118dental fluorosis, there was no association between behavioural problems and dental fluorosis (Morgan et al., 1998).

8.1.3.7 Genotoxic effects

Based on an analysis of the frequency of sister chromatid

exchanges in peripheral blood lymphocytes obtained from groups of

approximately 100 male and female Chinese adults consuming drinkingwater containing from 0.11 to 5.03 mg flu o ride/litre, Li et al. (1995)

concluded that fluoride was not genotoxic at these levels of exposure.

The average estimated daily intake of fluoride, based upon levels in

food, wat er and average body weight, ranged from about 20 to 280

μg/kg body weight per day . The plasma fluoride level in the 5.03

mg/litre area was 5.56 μmol/litre.

Although Jackson et al. (1997) observed a slight (7–15%)

although s tatistically significant ( P < 0.001) increase in the frequency

of sister chromatid exchange in peripheral blo od lymphocytes collected

from individuals in the USA ( n = 68, males and females) residi ng in an

area ser ved with drinking-water containing 4.0 mg fluoride/litre (compared with tha t from individuals in other areas served with water

containing 0.2 and 1.0 mg fluoride/litre [ n = 64 and 59, respectively] ), a

subsequent comparison among indiv iduals residing in the highfluoride area having consumed either city water (4 mg/litre; n = 30) or

w ell-water (<0.3 mg/litre; n = 28) revealed no significant differe nce in

the frequency of sister chromatid exchange in blood lym phocytes

(Jackson et al., 1997).

In a report w i th scanty details on the selection of persons to be

s tudied, an increased peripheral lymphocyte micronucleus and sister

chromatid exchange frequency wa s observed among fluorosis patients

( n = 53), compared with healthy referents ( n = 20) from a fluorosisendemic area

and non-fluoride exposed referents ( n = 30) in Inner

Mongolia, China (Wu & Wu, 1995). In another study with limited

reporting, an increased sister chromatid exchange frequency was

reported among residents of a fluorosis-endemic area in North Gujarat,

India ( n = 100), in comparison with referents from a non-endemic area

in Ahmedabad (

n = 20) (Sheth et al., 1994). In a further similar study,

sister chro matid exchange frequencies were elevated among residents

of one out of three fluorosis-endemic villages, and chromosomal aberrations were elevated

in all three villages, compared with referents fromEffects on Humans

1 This section was based pri marily on a review prepared by WHO

(1994).

119 a nearby township in south Gujarat, India (Joseph & Gadhia, 2000). In

all these studies, the interpretation is complicated by the limited details

provided on subject selection and by possible confounding variables.

However, no effect on chromosomal aberrations or micronuclei in

lymphocytes was observed in a randomized double-blind study on

seven non-smoking female osteoporosis patients treated with sodium

fluoride or sodium monofluorophosphate (av erage dose 29 mg fluoride/

day) for an average of 29 months, in comparison with seven matched

non-treated controls (van Asten et al., 1998).

8.1.3.8 Dental effects 1

It has been recognized for over five decades that fluoride may

have both beneficial and potentially harmful effects on dental health.

While the prevalence of dental caries is inversely related to a ra n ge of

concentrations of fluoride in drinking-w ater consumed, the prevalence

of dental fluorosis has been shown t o be positively related to fluoride

intake from many sources (Fejerskov et al., 1988, 1996). Publi c health

programmes seeking to maximize the beneficial effects of fluoride on

dental health through the introduction of fluo ridated drinking-water

have, a t the same time, strived to minimize its adverse fluorotic effects

on teeth. Based upon the studies conducted by Dean and colleagues

five decades ago, the “optimum” level of fluoride in drinking-water,

associated wi

th the maximum level of dental caries protection and

minimum level of dental fluorosis, was conside r ed to be approximately

1 mg/litre. The effects of fluoride on dental health were examined by a

WHO Expert Committee (WHO, 1994).

1) Dental caries

Since the first reports b y Dean and colleagues published in the

1930s, oral fluoride is still considered an effective means of reducing

dental caries. Historically, populations consuming fluoridated dri nkingwater had a much lower prevalence of dental caries than did those

consuming non-fluoridated drinking-water. Over time, t h e difference inEHC 227: Fluorides

120 caries prevalence among those consuming fluoridated and nonfluoridated dr inking-water has narrowed significantly. This apparent

diminution in the cariostatic effectiveness of fluoridated drinking-water

is likely attributable to a “dif fusion” in which individuals consuming

non-fluoridated drinking-water may consume significant amounts of

beverages prepared in other locales with fluoridated drin king-water, as

well as ex

posure to fluoride through the use of dental care products —

m ainly fluoridated toothpaste. It has been estimated that whereas

approximately 210 million individuals throughout the world consume

drinki ng-water containing levels of fluoride considered adequate for

the preventio n of dental caries, approximately 500 million people use

fluoridated toothpastes (WHO, 1994).

Historically , it was believed that fluoride needed to become incorporated into the crystal lattice of enamel in order to effectively prevent

the development of dental caries. F luoride was considered to improve

lattice stability and render the enamel less soluble to acid demineralization. Since the incorp oration of fluoride into enamel, as partially

fluoridated hydroxyapatite, was believed to be essential for its action,

fluoride was thought best ingested. There is now, however, an increasing body of evidence to suggest that a substantial part of the

cariostatic activity of fluoride is due to its effe cts on erupted teeth, and

that the continual presence of fluoride in the saliva and in the fluid

phase of dental plaque is critical to it s mechanism of action. There is a

g rowing consensus that through its interaction with the surface of

enamel, fluoride in saliva and dental plaque inhibits the

demineralization and promotes the remineralization t aking place at the

surface of the tooth.

Since the introduction of controlled fluorid ated drinking-water,

efforts to reduce dental caries have been extended to include the use

of fluoridated tooth

paste, mouth rinses and topically applied dental

treatments (e.g., gels, varnishes, solu tions), as well as through the use

o f fluoride supplements, fluoridated milk and fluoridated salt. Th e

effectiveness and factors affecting the implementation of these various

exposure regimens have been reviewed in detail by WHO (1994), and

therefore only a brief summary is presented here.

The controlled fluoridation of community drinki ng-water to an

optimum level is one of the most cost-effective means of deliveringEffects on Humans

121 fluoride to large numbers of individuals. This method of fluoride delivery req uires a suitable community-wide drinking-water delivery system

al ong with a reasonable level of technological development (e.g., infrastructure, equipment and appropriately trained support personnel).

Depending upon the annual average maximum daily air temperature,

r ecommended levels of fluoride in drinking-water considered usef ul for

the prevention of dental caries have ranged from 0.5 to 1.2 mg/litre.

Some countries have introduced cont rolled fluoridated salt as a

means of reducing the prevalence of dental caries among their respective populations. Unlike controlled fluo ridated drinking-water and

toothpastes, there is little quantitative information on the cariostatic

action of fluorida ted salt, although it is considered to act in a manner

like that of fluoridated drinking-water. The optimum concentr ation of

fluoride in salt needed to reduce the incidence of dental caries must

take into account the level of salt intake an d the concentration of

fluoride in drinking-water in individual geographical areas; however,

200 mg fluoride/kg salt has been suggested to be a minimum value

(WHO, 1994).

Formerly, the administratio n of fluoridated milk to children was

consider ed to be a suitable means of increasing their intake of fluoride;

however, little quantitative inform a tion is available on the efficacy of

this delivery system in the prevention of dental ca ries. To be effective

a s a means of delivering fluoride to children, implementation of a

fluoridated milk programme requires close cooperation with the dairy

industry as well as a widespread system of distribution.

It has been estimated that, worldwide, almost twice as many

people are expos ed to fluoride for the prevention of dental caries

thro ugh the use of toothpastes as from the consumption of controlled

fluoridated drinking-water. In many countries, fl uoridated toothpastes,

which usually contain approximately 1000 mg fluoride/kg, represent

more than 95% of total dentifrice sold. The use of t hese products is

considered to be one of the major factors responsible for the gradual

decline in the prevalence of dental caries in most industrialized

countries. In are as where the prevention of dental caries through the

widespread use of fluoridated dri nking-water, salt or milk may not be

feasible, the use o f fluoridated toothpastes remains an effective means

of improving dental health.EHC 227: Fluorides

122 Fluoride supplements, in the form of tablets, liquid drops or

lozenges, are intended to provide a systemic source of fluoride when

fluoridated drinking-wa

ter is not available. Problems associated with

the widespread use of such supplements include poor compliance

among socially and economically disadvantaged groups and the

potentially inappropriate use of these products by those already

consuming drinking-water containing optimal amounts of flu oride.

Moreover, the results of studies suggest that fluoride is most effective

when continually present at low levels in saliva and plaque fluid. In a

number of jurisdictions, the reco mmended daily dosage of fluoride

supplements is linked to the level of fluoride in the drinking-wat er as

well as the age of the child. Although fluoride suppleme nts may be

appropriate for use in certain areas where the prevalence of de n tal

caries is high, available data on the efficacy of this fluoride delivery

system in preventing dental caries are equivocal, and there appears to

be a growing consensus that fluoride supplements have a limited

public health role in improving dental health.

The use of fluorida ted mouth rinses has achieved a significant

level of po pularity among publicly based health care programmes,

particularly t hose involving school-aged children. The levels of fluoride in these mouth rinses (0.05 or 0.2%) are related to whether they are

recommended for daily or weekly use. The efficacy of fluoridated

mouth rinses in the prevention of dental caries is related to the frequency of use, the level of compliance and exposure to other sources

of f luoride, most notably in drinking-water. The use of fluoridated

mouth rinses may be recommended for individuals with an elevated risk

of dental caries, although the mouth rinses may not be appropriate for

u se by children younger than 6 years of age, due to their propensity to

swallow significant amounts of such material, thereby increasing their

risk of developing dental fluorosis.

Solutions, gels or varnishes usually applied infrequently over the

course of a year by dental care profes sionals may be most efficacious

in individuals with an elevated risk of dental caries. Owing to the level

of fluoride in these materials (e.g., up to 22 300 mg/kg), health care

professionals mus t follow protocols that reduce inadvertent ingestion

o f significant amounts of these products by younger children, w hich

could cause acute toxic effects.Effects on Humans

123 2) Dental fluorosis

Since t he publication of the WHO (1994) assessment on the

quantitative relationship between dental fluorosis and fluoride intake,

a large number of further studies have been published on the matter.

A recent meta-analysis (McDonagh et al., 2000) of such studies is presented in Figures 2 and 3.Proportion of population withfluorosis

Fluoride level – mg/L (log scale) 0.1 0.2 0.4 1.0 2.0 4.0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1

Note: Fluoride level plotted on the log scale because there was an approximately linear association between this

and the log (odds) of fluorosis.

Fig. 2. Proportion of the population with dental fluorosis by water fluoride

level together with the 95% upper and lower confidence limits for the

proportion

[Reproduced with permission from Br Med J (2000) 321 : 855–859]

Dental fluorosis is a condition t h at results from the intake of

excess levels of fluo ride during the period of tooth development,

usually fro m birth to approximately 6–8 years of age. It has been termed

a hypoplasia or hypomineralization of dental enamel and dentine and

is associated with the excessive incorporation of fluoride into these

structures. The severity of this condition, generally characterized as

ranging from very mild to sever e, is related to the extent of fluoride

exposure during the period of tooth development . Mild dental fluorosis

is usually typified by the appearance of small white areas in the

enamel; individuals with severe dental fluorosis have teeth that are

stained an d pitted (“mottled”) in appearance. In human fluorotic teeth,

the most prominent feature is a hypomineralization of the enamel. In

contrast to many animal species, flu o ride-induced enamel hypoplasia

(indicating severe fluoride disturba nce of enamel matrix production)

seems to be rare in fluorosed human enamel. The stai ning and pittingEHC 227: Fluorides

124Proportion with fluorosis of aesthetic concern

Fluoride level

– mg/L 0 .4 .8 1.2 1.6 2 2.5 3 3.5 4 4.5 .1 .2 .3 .4 .5 .6 .7 .8 .9 1

Note: Fluoride level plotted on the untransformed scale because there was an approximately linear association

between this and the log (odds) of “aesthetic fluorosis.”

Fig. 3. Proportion of the population with fluorosis of aesthetic concern by

water fluoride level [Reproduced with permission from Br Med J (2000) 321 :

855–859]

of fluorosed dental e namel are both posteruptive phenomena (i.e.,

acquired after tooth eruption and occur as a consequence of the

enamel hypomineralization). The incorporation of excessive amounts

of fluoride into e namel is believed to interfere with its normal

ma turation, as a result of alterations in the rheologic structure of the

enamel matrix and/or effects o n cellular metabolic processes associated

wi th normal enamel development (WHO, 1994; Aoba, 1997; Whitford,

1997). Experimental animal studies suggest that this hypomineralization

results from fluoride disturbance of the process of enamel maturation

(Richards et al., 1986).

Unlike skeletal fl u orosis, which is considered to be a marker of

long -term exposure to fluoride (due to the ongoing process of bone

remodelling), dental fluorosis is considered to be indicative of the level

of exposure to fluori de only during the period of enamel formation.

Exposure to excess ive levels of fluoride after tooth development

appears to have little influence on the extent of fluorosis. Re-evaluation

of classica l fluorosis data (Dean et al., 1941, 1942; Richards et al., 1967;

But ler et al., 1985) has shown that even at low fluoride intake from

water, a certain level of dental fluorosis will be found (Fejerskov et al.,

1996). A dose–response relationship was also demons trated. The data

demonstrated an increase of the fluorosis community index by 0.2 for

every dose increase of 0.01 mg fluoride/kg body weight.Effects on Humans

125 Over the past 30–40 years, there has been an increase in the

prevalence of dental fluorosis amon g populations consuming either

fluoridated or non-fluoridated drinking-water. Although greater numbers of individuals are n ow being served by fluoridated drinking-water,

for the most part this increased p revalence in dental fluorosis has been

attributed to the widespread intake of fluoride from sour ces other than

dr inking-water, especially in areas served by non-fluoridated drinkingwater. Unlike the situation in the 1930s, when the primary sources of

exposure to fluoride were limited to drinking-water and foodstuffs, now

there is potential exposure to fluoride from a variety of additional

sources, such as tooth

pastes, mouth rinses, fluoride supplements and

topically applied dental gels, solutions and va rnishes. Exposure to

fluoride may also result from the ingestion of fluoridated salt or fluoridated milk.

The prevalence of dental fluorosis is also elevated in certain areas

of the world where th e intake of fluoride may be inordinately high, due

in large part to the elevated fl uoride content of the surrounding

geological environment. In China, large numbers of people exhibit

dental fl uorosis (Liu, 1995). In addition to the actual consumption of

often large amounts of drinking-water containing naturally occurring

elevated levels of fluoride, the indoor burning of coal rich in fluoride,

the prepara tion of foodstuffs in water containing increased fluoride

levels and the consumption of specific foodstuffs naturally rich in

fluoride, such as tea, are believed to contribute to the elevated intake

of fluoride , with the resultant development of dental fluorosis (Chen et

al., 1993, 1996; Grimaldo et al., 1995; Han et al., 1995; Liu, 1995; Xu et al.,

1995).

8.1.4 Interactions with other substances

In a cross-over study, sixvolunteers were exposed to drinkingwater with high fluoride (2.3 mg/litre), high arsen i c (0.47 mg/litre) or

high fluoride and high arsenic (4.05 mg fluoride/litre and 0.58 mg

arsenic/litre). All volunteers followed one of these three regimes for

5 days, drank distilled water for 3 days and then were exposed to

another regime. Exposure to this level of arsenic did not influence the

rate of urinary excretion of fl uoride of the volunteers (Wu et al., 1998).EHC 227: Fluorides

126 In the area

of Kuitun, Xinjiang, in China, it was found that among

619 wells investigated, 102 wells contained high levels of arsenic and

fluoride. It was found that arsenic dermatos is manifested when the

water arsenic level was at or ab ove 0.12 mg/litre, with no association

with the fluoride level in the water; dental fluorosis developed when

the water fluoride level was at or above 3 mg/litre, regardless of the

water arsenic level (Wang et al., 1997).



### 8.2 Occupationally exposed workers

The he alth of workers occupationally exposed to fluorides, particularly those employed in the aluminium smelting industry, has been

examined in a vari ety of epidemiological studies. Workers in this

indu strial setting are also exposed to a number of other substances,

such as ammonia, carbon monoxide, sulfur dioxide, distillatio n products

of tar, pitch and coal, alu m inium oxide (alumina), cyanides, dust and

metals such as nic kel, chromium and vanadium (IARC, 1984; Søyseth

& Kongerud, 1992).

8.2.1 Case reports

Severe tissue damag

e

, respiratory effects, cardiac arrest and

deaths ha ve often been noted in case reports of workers exposed

accidentally to hydrofluoric acid through dermal contact (Mayer &

Gross, 1985; Chan et al., 1987; Mullet et al., 1987; Greco et al., 1988;

Upfal & Doyle, 1990; Gubbay & Fitzpatrick, 1997). Following the

exposure of two male workers to breakdown produ cts (sulfur tetrafluoride, thionyl fl uoride, hydrogen fluoride) of sulfur hexafluoride, the

men became semicomatose a nd developed cyanosis and pulmonary

oedema (Pilling &Jones, 1988). Eye and throat irritation, chest tightness, nausea, vomiting, headache and fatigue have also been observed

in electrical workers exposed to the breakdown products of sulfur

hexafluoride (Kraut & Lilis, 1990).

8.2.2 Epidemiological studies

8.2.2.1 Cancer

In a number

of analytical epidemiological studies, an increased

incidence of lung and bladd er cancer and increased mortality due to

cancer of the lung, liver, bladder, stomach, oesophagus, pancreas,Effects on Humans

127 lymp hatic–haematopoietic system, prostate or brain (central nervous

system) have been observed in fluoride-exposed workers employed in

the aluminium smelting industry (Giovanazzi & D’Andrea, 1981; Andersen et al., 1982; Rockette & Arena, 1983; Theriault et al., 1984; Gibbs,

1985; Armstrong et al., 1986, 1994; Mur et al., 1987; Siemiatycki et al.,

1991; Spinelli et al., 1991; Rønneberg & Andersen, 1995; Romundstad

et al., 2000). However, in general, there has been no consi stent pattern,

and bone cancer was not usually assessed. Although increases in lung

cancer were observed in se veral studies, it is not possible to attribute

these increases to fluoride exposure p er se due to concomita n t

expo sure to other substances. Indeed, in some of these epidemiological

studies, the increas ed morbidity or mortality due to cancer was

attributed to the workers’ exposure to aromatic hydrocarbons.

In a cohort study of cryolite mill workers in Denmark, Grandjean

et al. (1992) indicated that a portion of the inc rease in the incidence of

bladder cancer (17 observed versus 9.2 expected cases) among the

workers may have been attributable to occupational exposu re to fluoride; however, the workers were also exposed to other substances, such

as quartz, siderite and small amounts o f metal sulfides (Grandjean et al.,

1985).

8.2.2.2 Skeletal effects

Generally, most data on the occurrence of skeletal fluorosis in

occupationally e xposed workers have come from older studies. Based

upon a review of older studies involving aluminium smelter workers in

which the n u mber of workers examined was usually small and quantitative data on exposure to airborne fluoride were not alw ays provided,

Hodge & Smith (1977) concluded that the “in cidence of detectable

osteosclerosis was often high” when the levels of fluoride in the air

exceeded 2.5 mg/m 3 and/or levels of fluoride in the urine of these

workers were greater than 9 mg/litre; at airborne concentrations below

2.5 mg/m

3 (and levels in the urine of below 5 mg/litre ), “ years of exposure in potrooms did not produce osteosclero s is.” The development

of skeletal fluorosis in cryolite workers in Copenhagen was attributed

to the intake (from occupational exposure) of between 20 and 80 mg

fluoride/da y (Grandjean, 1982). Chan-Yeung et al. (1983a) reported

finding no definitive signs of skeletal fluorosis in potroom wo rkers

employed in an aluminium smelter and exposed to 0.48 mg fluoride/m 3

.EHC 227: Fluorides

128 In a more recent study in which skeletal changes in 2258 workers

employed at an aluminium plant in Poland were assessed (clinically and

radiologically), the occurrence of fluorosis (multiple joint p ain, initial

ossification, osteosclerosis) wa s reported to increase with increasing

duration of employment (Czerwinski et al., 1988). The occurrence of

these skeletal changes was related not to quantitative data on the

concentration of airborne fluoride per se

, but to a qualita tive “exposure

index,” calculated on the basis of the years of employment and the

ex tent to which the concentration of fluoride in the air in different areas

of the plant exceeded the highest permitted level of 0.5 mg hydrogen

fluo ride/m 3

. The prevalence of skeletal fluorosis reportedly increased

with this “index of exposure-years,” the more severe eff ects being

observed in older workers.

8.2.2.3 Respiratory effects

Since publication of the first EHC on fluorides (WHO, 1984),

additiona l studies have reported adverse effects on the respiratory

system (e.g., reduced lung capac ity, irritation of the respiratory tract,

asthma, cough, bronchitis, shortness of b reath and/or emphysema) in

wo rkers, predominantly those employed in aluminium smelters, occupation ally exposed to airborne fluorides (Chan-Yeung et al., 1983b;

Larsson et al., 1989; Søyseth & Kongerud, 1992; Rønneberg, 1995;

Søyseth et al., 1995; Radon et al., 19 99; Romundstad et al., 2000).

Owing to the exposure of these workers to other airborne contaminants

and particulates, it may not be possible to attribute the effects on respiratory function solely to fluoride per se.

8.2.2.4 Haematological, hepatic or renal effects

No eviden ce of haematopoietic, hepatic or renal dysfunction was

observed i n potroom workers employed at an aluminium smelter and

exposed to 0.48 mg fluoride/m 3 (Chan-Yeung et al., 1983a).

8.2.2.5 Genotoxic effects

The mean fre q uency of sister chromatid exchange in peripheral

blood lymphocytes obtained from 40 Chines e fertilizer production

workers was significantly ( P < 0.01) increased by approximate l y 50%,

compared with that in a similarly sized group of controls matc h ed for

age, sex a

n d smoking habits (Meng et al., 1995). During the period ofEffects on Humans

129 anal ysis, workers were exposed to levels of fluoride (mostly hydrofluoric acid and silicon tetrafluoride) ranging from 0.5 to 0.8 mg/m 3

, as

we ll as to phosphate fog, ammonia and sulfur dioxide. Among the

workers, the avera ge frequency of sister chromatid exchange was

ap proximately 27% higher ( P < 0.01) in smokers than in non-smokers.

Information on the total intake of fluoride was not presented.

In a further study, an increased frequency of both chromosomal

aberrations and micronuclei in circulating blood l ymphocytes was also

observed among the fertilizer plant worker s ( n = 40), in comparison with

40 c o ntrols working and studying in Shanxi University, situated in the

same city as the factory, matched for sex, age and smoking habits

(Meng & Zhang, 1997); the microscopi c analysis was performed on

coded slides.130 

### 9. EFFECTS ON OTHER ORGANISMS IN THE

LABORATORY AND FIELD

9.1 Laboratory experiments

9.1.1 Microorganisms

9.1.1.1 Water

Fluoride (100 mg/litre) did not affect growth or the chemical

oxygen demand degrading capacity of activated sludge when added

either as a pulse or continuously. Sludge settleability did not change

following a pulse addition of fluoride; however, continuous addition

of fluoride resulted in poor settling, indicated by 100–200% increases

in settled sludge volume. The authors concluded that the poor settling

was probably due to enhanced growth of filamentous organisms

(Singh & Kar, 1989). Beg (1982) found the EC

50 f o r inhibition of

bacterial nitrification to be 1218 mg fluoride/litre.

McNulty & Lords (1960) exposed the green alga C hlorella

pyrenoidos a to hydrogen fluoride in 110-min tests. Significant

increases in oxygen consumption and total phosph orylated

nucleotides were observed at fluoride concentrations of 2, 20 and 200

mg/litre (0.105, 1.05 and 10.5 mmol/litre). The authors concluded that,

based on measurements of gas exchange at several pH values, the

stimulation was probably due to the undissociated hydrogen fluoride

i n the medium. Smith & Woodson (1965) found that fluoride

concentrations greater than 19 mg/litre (1 mmol/litre) caused growth

inhibition in the same species. However, Nichol et al. (1987) found no

effect of fluoride at concentrations ranging from 5 to 150 mg/litre at a

variety of pH levels (5.9–8.0).

LeBlanc (1984) calculated 96-h EC

50 s, based on growth, to be 123

and 81 mg fluoride/litre for the fr e shwater green alga Selenastrum

capricornutum and the marine alga Skeletonema costatum

, respectively.

Ra i et al. (1998) calculated 15-day LC

5 0 s for the alga Chlorella

vulgaris to be 380 and 266 mg fluoride/litre (14 and 20 mmol/litre) at pHEffects on Other Organisms in the Laboratory and Field

131 6.8 and pH 6.0, respectively; at pH 4.5, the 3-day LC

5 0 was 133 mg

fluoride/litre (7 mmol/litre). Non-inhibitory concentrations w e re 66.5,

28.5 and 9.5 mg fluoride/litre (3.5, 1.5 and 0.5 mmol/litre) at pH 6.8, 6.0

and 4.5, respectively.

Antia & Klut (1981) exposed five euryhaline phytoplankton species to fluoride concentrations ranging from 50 to 200 mg/litre (14–15‰

salinity). The growth rate and maximum growth density of the

chlorophyte Duniella tertiolecta and the diatom Thalassio sira weissflogi i w ere unaffected at all exposure concentrations. The growth of

the diatom Chaetoceros gracilis appeared to be stimulated by the

presence of fluorid e. The haptophyte P avlova lutheri was 35–50%

inhibited at fluoride concentrations of 

### $ 150 mg/litre. The dinoflagellate

Amphidinium carteri was 20–25% inhibited at 150 mg/litre and more

than 90% inhibite d at 200 mg/litre. Hekman et al. (1984) studied the

effect of dissolved fluoride concentrations of up to 150 mg/litre on six

phytoplankton species. Growth and photosynthetic oxygen evolution

were unaffected at fluoride concentrations up to 50 mg/litre in all algae

except Synecho coccus leopoliensis. S. leopoliensis g rowth ceased for

a period followed by growth at a reduced rate at 50 mg fluoride/litre;

the threshold for growth effects and inhibition of photosynthesis in

this species was 25 mg/litre. Nichol et al. (1987) found that fluoride concentrations of 

### $ 100 mg/litre (5.2 mmol/litre) caused a growth lag in S.

leopoliensis at neutral pH. The effect of fluoride on the growth lag was

pH-dependent, with the growth lag increasing with decreasing pH. At

pH 5.9, there was a measurabl e growth lag at 5 mg fluoride/litre.

Fluoride resistance was induced by prior growth in the medium at noninhibitory levels of sodium fluoride. It was suggested that fluorideresistant cells retain less fluoride (taken up as undissociated hydrogen

fluoride) by developing increased permeability to the fluoride anion.

No effect on growth of 12 species of marine phytoplankton was

observed at fluoride concentrations ranging from 10 to 50 mg/litre. At

the highest

concentration (100 mg/litre), no effect on growth was

observed in 9 of the 12 species tested; however, 25–30% inhibition of

growth was found in a diatom ( Nitzschia angularis affinis ), a dinoflagellate ( A. carteri ) and a haptophyte ( P. lutheri ) (Oliveira et al., 1978).

Joy & Balakrishnan (1990) studied the effect of fluoride on the

diatoms Nitzschia palea (fres hwater) and A mphora coffeaeformis

(brackish water) during 96-h exposures. Sig nificant enhancement of

growth, compared with controls (no added fluoride), was observed atEHC 227: Fluorides

132 fluoride concentrations ranging from 30 to 110 mg/litre with N. palea

and at a concentration of 70 mg/litre in A

. coffeaeformis

. A. coffea e

formis did not show significant gro wth differences from controls at

fluoride concentrations of 90 and 110 mg/litre.

The marine dinoflagellate Amphidinium carteri was unable to

grow in nutrient-enriched seawater containing 200 mg fluoride/litre.

However, the organism could be adapted to grow under these conditions after repeatedly being cultured with stepwise increases in subinhibitory fluoride concentrations. Electron microscopic investigation

of the adapt ed dinoflagellate cells revealed abnormal ultrastructural

features in the chloroplast, mitochondria and nucleus. Fluoride adaptation seemed to confer a prolamellar-like configuration on the thylakoids

(extensive membrane s ystem containing the components of

photosynthesis) in the centre of the pyrenoid (protein structure associated with formation and storage of starch); in organisms that had not

been adapted, fluoride caused extreme disorganization of thylakoid

formation (Klut et al., 1981).

9.1.1.2 Soil

Van Wensem & Adema (1991) studied the effect of potassium

fluoride (32.3–3230 mg fluoride/kg [1.7–170 μmol fluoride /g]) on

C arolina poplar (

P opulus canadensis ) litter. After 4 weeks, total respiration was increased and the phosphate conc entration was

decreased at th e highest fluoride concentration. Ammonium, nitrate

and pho sphate concentrations were decreased by fluoride after 9

weeks. No-observed-effect concentrations (NOECs) for the effect of

fluoride on net mineralization of ammonium, nitrate and phosphate were

323, 100.7 and 1007 mg/kg dry weight (17, 5.3 and 53 μmol/g), respectively. The authors concluded that fluoride seems to be toxic for microbial processes at concentrations found in moderately fluoride polluted

areas.

9.1.2 Aquatic organisms

9.1.2.1 Plants

Wang (1986) expo sed the common duckweed ( L emna minor ) to

fluoride and calculated an EC

50 , based on a reduction in frond growth,

to be >60 mg fluoride/litre.Effects on Other Organisms in the Laboratory and Field

133 9.1.2.2 Invertebrates

The acute toxicity of fluoride to aquatic invertebrates is summarized i n Table 15. Forty-eight-hour LC

5 0 s/EC

50 s range from 53 to

304 mg/litre.

Hemens & Warwick (1972) found that fluoride concentrations of

up to 100 mg/litre caused no mortality in prawns exposed for 96 h.

However, the brown mussel ( Perna perna ) showed up to 30% mortality

at an initial fluoride concentration of 7.2 mg/litre during a 5-day test

(the background fluoride concentration was 1 mg/litre).

LeBlanc (1980) found a 48-h NOEC for Daphnia magna of 50 mg

fluoride/litre, whereas Kühn et al. (1989) reported a no-effect

concentration of 231 mg fluoride/litre (24 h). Camargo & La Point (1995)

calculated “safe conce n trations” (8760-h EC

0.01 s) for the last-instar

larvae of several net-spinning caddisfly species. “Safe concentrations”

ranged from 0.39 mg fluoride/litre ( Hydropsyche pellucidula ) to 1

. 18

( Hydropsyche lobata ) and 1.79 mg fluoride/litre ( Chimarra marginata ).

Further “safe concentrations” were calculated for the caddisfly species

Hydropsyche bronta

, at 0.2 mg fluo ride/litre, and H

. occidentalis and

Cheumatopsyche pettiti , at 0.7 mg fluoride/litre (Camargo, 1996b).

Pankhurst et al. (1980) performed toxicity tests on the blue mussel

( Mytilus edulis ) (160 h), the anemone Anthopleura a ureoradiata

(144 h) and the red krill ( M unida gregaria ) (259 h) using seawater

dilutions of both fluoride-loaded effluent and sodium fluoride. Effluent

solutions of 50 and 100 mg fluoride/litre produ ced high mortality,

whereas sodium fluoride at concentrations up to 100 mg fluoride/litre

caused negligible mortality.

Nell & Liv anos (1988) found that weight gains in Sydney rock

oysters ( Saccostrea commercialis ) decreased linearly ( P < 0.01) with

increasing fluoride additions from 0 to 30 mg/litre, and there was a 20%

growth depression at the highest fluoride concentration. T h e

b ackground level of fluoride in this study was 0.7 mg/litre. Fluorid e

concentrations of up to 11 mg/litre had no significant effect on growth

of prawns ( Penaeus indicus ) over a 20-day exposure period (McClurg,

1984). Fluoride (5.88 mg/litre) had no effect on the survival of mud

crabs ( Tylodiplax blephariskios ) or the survival and growth ofTable 15. Acute toxicity of sodium fluoride to aquatic invertebrates a

Organism Size/age Temperatur

e ( o C) Hardness

(mg/litre) b pH Salinit

y (‰) Parameter c Concentration

(mg

fluoride/litre) d Reference

Water flea

( Daphnia magna ) Neonates 20 24-h EC 50 205 n Dave (1984)

<24 h 20 8 24-h EC 50 352 n Kühn et al. (1989)

<24 h 173 8 24-h LC 50 308 n LeBlanc (1980)

<24 h 173 8 48-h LC 50 154 n LeBlanc (1980)

Neonates 20 48-h EC 50 98 n Dave (1984)

<24 h 15 169.3 8.14 48-h LC 50 304 m Fieser et al. (1986)

<24 h 20 169.3 8.14 48-h LC 50 251 m Fieser et al. (1986)

<24 h 25 169.3 8.14 48-h LC 50 200 m Fieser et al. (1986)

Caddisfly

( Chimarra

marginata ) Last instar 15.2 15.6 7.5 48-h LC 50 120 m Camargo (1991)

Last instar 15.2 15.6 7.5 72-h LC 50 79.7 m Camargo (1991)

Last instar 15.2 15.6 7.5 96-h LC 50 44.9 m Camargo &

Tarazona (1990)

Caddisfly

( Hydropsyche

bulbifera ) Last instar 15.2 15.6 7.5 48-h LC 50 79.2 m Camargo (1991)

Last instar 15.2 15.6 7.5 72-h LC 50 44.9 m Camargo (1991)

Last instar 15.2 15.6 7.5 96-h LC 50 26.3 m Camargo &

Tarazona (1990)Table 15 (contd).

Organism Size/age Temperatur

e ( o C) Hardness

(mg/litre) b pH Salinit

y (‰) Parameter c Concentration

(mg

fluoride/litre) d Reference

Caddisfly

( Hydropsyche

exocellata ) Last instar 15.2 15.6 7.5 48-h LC 50 86.6 m Camargo (1991)

Last instar 15.2 15.6 7.5 72-h LC 50 43.7 m Camargo (1991)

Last instar 15.2 15.6 7.5 96-h LC 50 26.5 m Camargo &

Tarazona (1990)

Caddisfly

( Hydropsyche

lobata ) Last instar 15.2 15.6 7.5 72-h LC 50 78.2 m Camargo (1991)

Last instar 15.2 15.6 7.5 96-h LC 50 48.2 m Camargo &

Tarazona (1990)

Caddisfly

( Hydropsyche

pellucidula ) Last instar 15.2 15.6 7.5 48-h LC 50 112 m Camargo (1991)

Last instar 15.2 15.6 7.5 72-h LC 50 59.1 m Camargo (1991)

Last instar 15.2 15.6 7.5 96-h LC 50 38.5 m Camargo &

Tarazona (1990)

Caddisfly

( Hydropsyche

bronta ) Last instar 18 40.2 7.8 48-h LC 50 52.6 m Camargo et al.

(1992)

Last instar 18 40.2 7.8 72-h LC 50 25.8 m Camargo et al.

(1992)

Last instar 18 40.2 7.8 96-h LC 50 17 m Camargo et al.

(1992)Table 15 (contd).

Organism Size/age Temperatur

e ( o C) Hardness

(mg/litre) b pH Salinit

y (‰) Parameter c Concentration

(mg

fluoride/litre) d Reference

Caddisfly

( Hydropsyche

occidentalis

) Last instar 18 40.2 7.8 48-h LC 50 102 m Camargo et al.

(1992)

Last instar 18 40.2 7.8 72-h LC 50 53.5 m Camargo et al.

(1992)

Last instar 18 40.2 7.8 96-h LC 50 34.7 m Camargo et al.

(1992)

Caddisfly

( Cheumatopsyche

pettiti ) Last instar 18 40.2 7.8 48-h LC 50 128 m Camargo et al.

(1992)

Camargo (1996b) Last instar 18 40.2 7.8 72-h LC 50 73.2 m

Last instar 18 40.2 7.8 96-h LC 50 42.5 m

Prawn ( Penaeus

indicus ) 35 96-h LC 50 1118 n e McClurg (1984)

Mysid shrimp

( Mysidopsis

bahia ) 96-h LC 50 10.5 n LeBlanc (1984)

a All tests were conducted under static conditions (water unchanged for duration of test).

b Hardness expressed as mg calcium carbonate/litre.

c EC 50 s based on immobilization.

d n = based on nominal concentrations; m = based on measured concentrations.

e Since seawater (35‰) was used in this test, it must be assumed that only approximately 100 mg fluoride/litre was, in fact, dissolved.Effects on Other Organisms in the Laboratory and Field

137 penaeid shrimps ( Penaeus indicus ) duri ng 68-day exposures when

compared with contr ols (0.89 mg fluoride/litre). In a 113-day test,

shrimps gained significantly more weight during exposure to fluoride

(5.5 mg/litre) than did controls. The authors attributed this to variations

in the food source within the tanks (Hemens et al., 1975).

The fingernail clam

( Musculium transversum ) appears to be one

of the most sensitive freshwater species tested. Sparks et al. (1983)

conduct ed an 8-week flow-through experiment in which statistically

significant mortality (50%) was observed at a concentration of 2.8 mg

fluoride/litre. The brine shrimp ( Artemia salina ) was the most sensitive

marine species tested. In a 12-day static renewal test using brine

shrimp larvae, statistically significant growth impairment (measured as

body lengt h increase relative to controls) occurred at 5.0 mg

fluoride/litre (Pankhurst et al., 1980). In a flow-through 90-day life cycle

test, the amphipods G randidierella lutosa and G. lignorum showed

maximum population increase at a mean fluoride concentration of 2.6

mg/litre (background seawater levels ranged from 1.3 to 1.7 mg

fluoride/litre). Population performance was comparable to controls at

5 mg fluor

ide/litre. A maximum acceptable toxicant concentration

(MATC) was set at between 5.0 and 6.2 mg fluoride/litre. However,

female fecundity appeared to be the most sensitive parameter, and a

mean MATC based on this parameter was 4.2 mg fluoride/litre (Connell

& Airey, 1982).

In a 3-week exposure test, survival and reproduction of Daphnia

magna were studied (Fieser et al., 1986). Impairment of reproduction

was observed at fluoride concentrat ions greater than 26 mg/litre. A

concentration of 35 mg fluoride/litre reduced the neonate production

to 44% of controls. The average number of live young drop ped by

more than 98% at 49 mg fluoride/litre. However, no statistics were

performed i n the study. Dave (1984) calculated that the NOEC for

growth in Daphnia magna after 7 and 21 day s was between 3.7 and

7.4 mg fluoride/litre. Similarly, for parthenogenic reproduction, the 21-

day NOEC was between 3.7 an d 7.4 mg fluoride/litre. The “safe”

concentration, equivalent to the geometric mean of the NOEC or

MATC in har d water, was 4.4 mg fluoride/litre. Kühn et al. (1989)

reported a 21-day NOEC of 14 mg fluoride/litre for Daphnia magna ; the

most sensitive parameter was reproduction rate.EHC 227: Fluorides

138 9.1.2.3 Vertebrates

The acute toxicity of fluoride to fish is summarized in Table 16.

Ninety-six-hour LC

50 s for freshwater fish range from 51 mg fluoride/litre

(rainbow trout, Oncorhynchus mykiss ) to 460 mg f luoride/litre

(threespine stickleback, Gasterosteus aculeatus ). All o f the acute toxicity tests (96 h) on marine fish gave r esults greater than 100 mg

fluoride/litre.

Inorganic fluoride toxicity to freshwater fish appears to be negatively correlated with water hardness (due to t he complexation of

fluoride ions with calcium) and positively correlated with temperature

(Angelovic et al., 1961; Pimentel & Bulkley, 1983; Smith et al., 1985).

The 96-h LC

50 for ra inbow trout exposed to sodium fluoride in soft

wat er (17 mg calcium carbonate/litre) was 51 mg fluoride/litre.

Increasing the water hardness to 49 mg calcium carbonate/litre doubled

the LC

50 to 128 mg fluoride/litre; a further increase in water hardness to

182 mg calcium carbonate/litre led to an LC

50 of 140 mg fluoride/litre

(Pimentel & Bulkl ey, 1983). Angelovic et al. (1961) found that

increasing temperature significantly increased the toxicity of fluoride

to rainbow trout at temperatures ranging from 7.2 to 23.9 °C.

Camargo & Tarazona (1991) exposed rainbow trout ( O

. mykiss )

and brown trout ( Salmo trutta ) to fluoride in soft water (22 mg calcium

carbonate/litre) during short-term toxicity tests. For rainbow trout, 120-,

144-, 168- and 192-h LC

50 s were 9 2.4, 85.1, 73.4 and 64.1 mg

fluoride/litre, respectively; for brown trout, they were 135.6, 118.5, 105.1

and 97.5 mg fluoride/litre, respectively. The addition of chloride ions

(sodium chloride) decreases the toxicity of fluoride. LC

50 s (120 h) for

rainbow trout were 6 mg fluoride/litre in the absence of chloride ions

and 22 mg fluoride/litre at a chloride ion concentration of 34 mg/litre

(Neuhold & Sigler, 1962). LT

5 0 values for brown trout exposed to

fluoride at a water hardness of 73 mg calcium carbonate/litre have been

calculated. LT

50 values ranged from ~12 h at 60 mg fluoride/litre to ~80

h at 20 mg/litre; at concentrations of 

### # 15 mg/litre, LT 5 0 values were

>240 h (Wright, 1977).

Neuhold & Sigler (1960) reported that 20-day LC

50 s for rainbow

trout ( O. mykiss ) (10–20 cm) ranged from 2.7 to 4.7 mg fluoride/litre in

static renewal tests at 13 °C under soft-water conditions (<3 mg calcium

carbonate/litre). The authors noted that there was no furtherTable 16. Acute toxicity of fluoride to fish a

Organism Size/age Temperatur

e (°C) Hardness

(mg/litre) b pH Salinit

y (‰) Parameter Concentration

(mg fluoride/

litre) c Reference

Rainbow trout

( Oncorhynchus

mykiss ) <3 g 15 23–62 7.4–8.0 96-h LC 50 200 n Smith et al. (1985)

1.8 g 12 17 7.2 96-h LC 50 51 m Pimentel & Bulkley (1983)

1.8 g 12 49 8.3 96-h LC 50 128 m Pimentel & Bulkley (1983)

1.8 g 12 182 8.3 96-h LC 50 140 m Pimentel & Bulkley (1983)

1.8 g 12 385 8.7 96-h LC 50 193 m Pimentel & Bulkley (1983)

fry 15.1–15.5 20.6–24.2 7.5–7.8 96-h LC 50 107.5 m Camargo & Tarazona

(1991)

Brown trout ( Salmo

trutta ) fry 15.1–15.5 20.6–24.2 7.5–7.8 96-h LC 50 164.5 m Camargo & Tarazona

(1991)

Fathead minnow

( Pimephales

promelas ) <1 g 15–19 10–44 7.5–8.0 96-h LC 50 315 n Smith et al. (1985)

Threespine

stickleback

( Gasterosteus

aculeatus ) <1 g 20 78 7.4–7.9 96-h LC 50 340 n Smith et al. (1985)

<1 g 20 146 7.4–7.9 96-h LC 50 380 n Smith et al. (1985)

<1 g 20 300 7.4–7.9 96-h LC 50 460 n Smith et al. (1985)

Bluegill ( Lepomis

macrochirus ) 96-h LC 50 >240 n LeBlanc (1984)Table 16 (contd).

Organism Size/age Temperatur

e (°C) Hardness

(mg/litre) b pH Salinit

y (‰) Parameter Concentration

(mg fluoride/

litre) c Reference

Sheepshead minnow

( Cyprinodon

variegatus ) 8–15 mm 25–31 10–31 96-h LC 50 >225 n Heitmuller et al. (1981)

Ambassid (

Ambassis

safgha ) adult 20–21 10–28 96-h LC 50 >100 n Hemens & Warwick (1972)

Crescent perch

( Therapon

jarbua ) adult 20–21 10–28 96-h LC 50 >100 n Hemens & Warwick (1972)

Mullet ( Mugil

cephalus ) juvenile 20–21 10–28 96-h LC 50 >100 n Hemens & Warwick (1972)

a All tests were conducted under static conditions (water unchanged for duration of test).

b Hardness expressed as mg calcium carbonate/litre.

c n = based on nominal concentrations; m = based on measured concentrations.Effects on Other Organisms in the Laboratory and Field

141 mortality after 10 days. The symptoms of acute fluoride intoxication

included lethargy, violent and erratic movement and de ath. The

authors postulated that the variation in the response of fish to fluoride

could be due to a chloride–fluoride excretion mechanism over the

epithelial tissues (Sigler & Neuhold, 1972). Camargo (1996a) calculated

“safe con centrations” (infinite hours LC

0 .01 s) for rainbow trout and

brown trout at fluoride concentrations of 5.1 and 7.5 mg fluoride/litre,

respectively.

Hemens et al. (1975) found that fluoride (5.9 or 5.5 mg/litre) had no

effect on survival of mullet ( Mugil cephalus ) during 68- or 113-day

exposures when compared with controls (0.9 mg fluoride/litre). Fluoride

had no significant effect on the growth of larger mullet (50–55 mm);

however, smaller mullet (16–18 mm) showed a significant decrease in

growth during the 68-day test.

The eggs of the freshwater catla ( Catla catla ) w ere exposed to

fluoride concentrati ons ranging from 1.9 to >16 mg/litre from both

effluent and sodium fluoride dilutions. Hatching occurred after 6 h in

both controls and those exposed to 1.9 mg fluoride/litre. A t concentrations of 

### $ 3.2 mg fluoride/litre for effluent dilutions and 

### $ 3.6 mg

fluoride/litre for sodium fluoride dilutions, hatch i ng was delayed by

1–2 h. The authors stated that the low pH (4.1) of the effluent may have

contributed to its toxicity. The weigh t of eggs exposed to fluoride

decreased with increasing fluoride concentration and exposure time.

Significant decreases in egg protein were observed at fluoride concentrations causing delayed hatching. The toxicity of fluoride to eggs was

more related to the availability of fluoride ions than to total fluoride in

the media (Pillai & Mane, 1984).

Kaplan et al. (1964) found litt le external evidence of toxicity in

adult leopard frogs ( Rana pipiens ) exposed to fluoride concentrations

ranging from 5 to 50 mg/litre for 30 days. Total red and white cell

counts were reduced at all fluoride exposure concentrations; however,

no statistical analysis was carried out. A t fluoride concentrations ranging from 50 to 300 mg/litre, the survival time decreased with increasing

exposure concentration. All frogs died within 30 days at both 250 and

300 mg fluo ride/litre. Kuusisto & Telkkä (1961) exposed frog ( R ana

temporaria ) larvae to sodium fluoride concentrations of 1, 2 and 10 mg/

litre. All fluoride concentrations caused a delay in metamorphosis andEHC 227: Fluorides

142 reduced the activity of the thyroids revealed by histological

examination. No statistical analysis of the results was carried out.

9.1.3 Terrestrial organisms

9.1.3.1 Plants

Fluoride toxicity to terrestrial plants has been studied extensively

(Weinstein, 1977). Signs of inorganic fluoride phytotoxicity (fluorosis),

such as chlorosis, necrosis and decreased growth rates, are most likely

to occur in the young, expanding tissues of broadleaf p lants and

elongating needles of conifers (Pushnik & Miller, 1990). The induction

of fluorosis has been clearly demonstrated in laboratory, greenhouse

and controlled field plot experiments (Weinstein, 1977; Hill & Pack,

1983; Staniforth & Sidhu, 1984; Doley, 1986, 1989; McCune et al., 1991).

Weinstein & Alscher-Herman (1982) reviewed the phys iological

responses of plants to fluoride. They concluded that calcium and

magnesium play a central role in the response of plants to fluoride. A

detoxification mechanism appears to consist of the sequestration and

insolubilization of fluoride by reaction with calcium. The effects of

atmospheric fluoride on a wide variety of terrestrial plant species have

been extensively reviewed (VDI, 1989); the studies that follow have

been cho sen to reflect the lowest adverse effect levels cited in the

literature.

A la rge number of the papers published on fluoride toxicity to

plants concern greenhouse fumigation with hydrog en fluoride.

Wolting (1975) observed leaf necrosis on freesia ( Freesia sp.) cultivars

during continuous fumigation at 0.5 μg fluoride/m 3 for 5 months and

during intermittent fumigation with 0.3 μg fluoride/m 3 (6 h/day,

3–4 times/week) for 18 weeks. Leaf tip necrosis was identified in a

variety of tulip ( Tulipa sp.) cultivars exposed to fluoride for 6 h/day for

3 days at concentrations ranging from 0.15 to 0.67 μg fluoride/m 3

(Wolting, 1978). Hitchcock et al. (1962) reported necrotic leaf tips in

gladiolus ( Gladiolus sp.) cultivars e xposed to 0.17 μg fluoride/m 3 for

9 days. In 40-day exposures of gladiolus cultivars to 0.76 μg/m 3 , Hill et

al. (1959) found 46% necrosis and a significant increase in respiration

(39%). Long

- term greenhouse experiments (2–10 growing seasons)

were conducted to determine the effects (necrosis, photosynthesis and

growth) of hydrogen fluoride on 16 varieties of flower, fruit, vegetable

and forage crops (Hill & Pack, 1983). Three identical greenhouses wereEffects on Other Organisms in the Laboratory and Field

143 used to represent a cont rol (filtered ambient air; mean hydrogen

fluoride level was 0.03 μg fluoride/m 3 ), a hydrogen fluoride treatment

(filtered ambient air; mean hydrogen fluoride levels ranged from 0.3 to

1.9 μg fluoride/m 3

, depending on the exposure duration for gladioli) and

an industrial treatment (unfiltered ambient air; located 1.6 km downwind

of a steel plant; mean hydrogen fluoride levels ranged from 0.2 to 1.9

μg fluoride/m

3 ). The most sen sitive species tested (based on

measurement of necrosis over two growing seasons, following

117 days of hydrogen fluoride exposure) was the snow princess

gladi o lus ( Gladiolus grandiflorus ). The lowest-observed-effect level

(LOEL) for leaf necrosis (65% of leaves ) in this plant was 0.35 μg

fluoride/m

3

. The extent of necrosis was positively corr elated with

increased hydrogen fluoride concentration and increased exposure

duration. Less severe necrosis (2%) occurred in the industrial greenhouse chamber. The results from other test species included reduced

growth or necrosis at hydrogen fluoride exposure concentrations of

0.44, 0.54 and 21.3 μg fluorid e/m 3 for apples ( Malis domestica borkh ),

pole beans ( Phaseolus vulgaris ) and forage (red clover, T rifolium

pratense , and alfalfa, Medicago sativa ), respectively.

Murray (1984a) exposed grapevines ( Vitis vinifera ) to hydrogen

fluoride concentrations of 0.07 (control), 0.17 and 0.27 μg fluoride/m 3

for 189 days. Foliar necrosis was first observed on vines exposed to

0.17 and 0.27 μg fluoride/m 3 after 99 and 83 days, respectively. Fluoride

had no significant effect on bunch weight, number of bunches, grape

yield, grape water or potential alcohol content, leaf chlorophyll b or leaf

protein concentration. Both chlorophyll a and total chlorophyll were

significantly reduced by fluoride exposure. Doley (1986) fumigated

three varieties of grapevine with hydrogen fluoride for four successive

growing seasons (the duration of exposure varied from 54 to 159 days

for each season). Leaf size during the first growth of the season was

not affected by fluoride concentrations of up to 1.5 μg/m 3 . However,

leaf size was significantly reduced during the middle and latter portion

of the fourth season of fumigation in two of the varieties at 0.64 μg

fluoride/m

3

.

Suture red spot is a serious physiological disorder of the peach

( Prunus persica ) fruit. In open- top field chambers, hydrogen fluoride

levels causing an induction of this disorder were 0.3 μg fluoride/m 3 in

continuous exposures of 80 days and 1.0 μg fluoride/m 3 in intermittentEHC 227: Fluorides

144 exposures for three 6-h periods each week for 9 weeks (MacLean et al.,

1984b).

Wheat ( Triticum aestivum ) and barl ey ( H ordeum vulgare )

exposed to hydrogen fluoride (0.38 μg/m 3 ) for 90 days showed no

effect of treatment on yield. There was, however, a significant increase

in the grain protein conc entration of fluoride-exposed barley plants

(Murray & Wilson, 1988c). MacLean & Schneider (1981) found a

significant reduction (20%) in the mean dry mass of wheat plants ( T.

aestivum ) exposed to 0. 9 μg fluoride/m 3 for 4 days. MacLean et al.

(1984a) exposed wheat ( T. aestivum ) and two sorg h um ( Sorghum sp.)

hybrids to hydrogen fluoride at concentrations ranging from 1.6 to

3.3 μg/m

3 for three successive 3-day periods. Anthesis (the maturing

of the stamens) was the most sensitive stage, and this occurred during

the first exposure period in wheat and the third exposure in sorghum.

Hydrogen fluoride-in duced foliar damage did not occur in wheat;

however, both sorghum hybrids developed foliar damage in proportion

to the exposure concentration. Pack (1971) found no effect of hydrogen

fluoride on the progeny of bean plants (no species stated) grown at

0.58 μg fluoride/m 3 . However, the primary leaves of some F

1 progeny

of plants grown at 

### $ 2.1 μg fluoride/m 3 w ere severely stunted and

distorted. MacLean et al. (1977) observed a significant reduction (25%)

in the fresh mass of pods from bean plants ( P haseolus vulgaris )

exposed to 0.6 μg fluoride/m 3 for 43 d ays (emergence to harvest) in

open-top fiel

d chambers. There was no effect of hydrogen fluoride

exposure (0.6 μg fluoride/m 3 ) on growth or fruiting in tom ato ( L ycopersicon esculentum ) plants.

Madkour & Weinstein (1988) found that hydrogen fluoride at

nominal concentrations of 1, 3 and 5 μg fluoride/m 3 inhibited the active

loading of [ 14 C]sucrose into the minor veins of soybean ( Glycine max )

leaf discs during 8- to 11-day exposures. Similar results were obtained

for both controlled-environment and field conditions.

Several species of eucalypt ( Eucalyptus spp.) have shown sensitivity to fluoride. Murray & Wilson (1988b) exposed E. tereticornis to

hydrogen fluoride (0.38 μg fluoride/m 3 ) for 90 days in open-top

chambers. Fluoride significantly reduced leaf surface area and weight

in mature and immature leaves. The same significant effects on immature leaves were noted for marri ( E

. calophylla ), tuart ( E. gomphocephala ) and jarrah ( E. marginata ) at 0.39 μg fluoride/m 3 for 120 days.Effects on Other Organisms in the Laboratory and Field

145 However, in mature leaves, leaf surface area and weight were reduced

in tuart, and surface area was reduced in marri. In jarrah, these two endpoints were unaffected (Murray & Wilson, 1988a).

Coniferous trees have also been identified as sensitive plant species. In field exposure chambers, significant dose–response relationships were observed between hydrogen fluoride e x posure and

developme n t of needle necrosis in 2-year-old black spruce ( Picea

mariana ) and 3-year-old w hite spruce ( P

. glauca ) (McCune et al.,

1991). Four test chambers, one of which served as a control, were used

for different hydrogen fluoride exposure regimens for each coniferous

species. Measurements of tiss ue necrosis were recorded 10 days

following hydrogen fluoride exposure for 78 h with black spruce and 20

days following hydrogen fluoride exposure for 50 h with white spruce.

Lowest-observed-effect concentrations (LOECs) for necrosis were 4.4

and 13.2 μg fluoride/m 3 for black spruce and white spruce, respectively.

Airborne fluoride can also affect plant disease development,

although the type and magnitude of the effects are dependent on the

specific plant–pathogen combination (Laurence, 1983). Van Bruggen

& Reynolds (1988) found that exposure of soybean ( Glycine max )

plants to hydrogen fluoride (2 μg fluoride/m 3 ) in a controlled chamber

led to sig nificantly larger hypocotyl lesions after inoculation with

either R hizoctonia solani or Phytophthora megasperma

. Plants w ere

exposed to hydroge n fluoride for 1 week before and after the

infestation. However, Laurence & Reynolds (1984) found no significant

effect of hydrogen fluoride (1 or 3 μg fluoride/m 3 for 5 days) on lesion

characteristics of the bacterium Xanthomonas campestris on the leaves

of red kidney bean ( Phase olus vulgaris ) plants. Similar findings were

reported by Reynolds & Laurence (1990) during both continuous (1, 3

or 5 μg fluoride/m 3 for 15, 5 or 3 days, respectively) and intermittent (3

or 5 μg fluoride/m 3 for 15 days) exposures.

Several studies on fluoride have been carried out in culture media.

Belandria et al. (1989) studied the effect of sodium fluoride on the

germination of

lichen ascospores. They found that 20% of the

Xanthoria parietina spores were able to germinate in the presence of

19 mg fluoride/litre (1000 μmol/litre), and similar results were obtained

for Physconia distorta and Peltigera canina

. P. distorta was found to

be 37% inhibited at a concentration of 0.95 mg fluoride/litre

(50 μmol/litre). The most resistant species was Lecanora conizaeoides

,EHC 227: Fluorides

146 which was only weakly inhibited (44% inhibition) at 38 mg fluoride/litre

(2000 μmol/litre). Ballantyne (1984) found that exposure of pea ( Pisum

sativum ) shoots to solutions containing 19 mg fluoride/litre (1

mmol/litre) for up to 3 days caused significant increases in ATP levels

in the yo ungest, fully expanded leaves and in entire shoots. These

increases occurred before significant decreases in fresh weight, water

content or water uptake and stem elongation. Neither in vitro exposure

of spinach ( Spinacia oleracea ) petioles to 38 mg fluoride /litre (2

mmol/litre) for 3 h nor

in vivo exposure of plants to gaseous hydrogen

fluoride at 5 μg fluoride/m 3 for 6 days resulted in visible injury.

However, there was evid ence from experiments on chlorophyll a

fluorescence of a reduced ability to develop or maintain a transthylakoid proton gradient in chloroplasts containing elevated levels of

fluoride (Boese et al., 1995).

Fluoride at concentrations of 190 mg/litre (10 mmol/litre) significantly reduced the in vitro photosynthetic capacity of azalea ( Rhododendron sp.) cultivars (Ballantyne, 1991).

Stevens et al. (1998a) grew tomato ( Lycopersicon esculentum ) and

oat ( Avena sativa

) plants in nutrient solutions (12–13 days) at nominal

sodium fluoride concentrations ranging from 1 to 128 mg fluoride/litre.

Fluoride ion concentrations greater than 28 mg/litre (1473 μmol/litre)

caused significant decreases in the dry weights of tomato shoots and

roots; oat plants were unaffected at all fluor ide exposure

concentrations. Stevens et al. (1998b) found that dry weights of tomato

and oat shoots and roots were significantly decreased as the pH of the

solution culture decreased below 4.3 at hydrogen fl uoride

concentrations of 1.4 mg fluoride/litre (71 μmol/litre) and 2.6 mg

fluoride/litre (137 μmol/litre) for tomatos and oats, respectively. Fluoride concentrations in tomato and oat shoots that corresponded with

significant reductions in plant dry weights were 228 and 125 mg/kg,

respectively. Aluminium–flu oride complexation increased fluoride

uptake (see chapter 4) and toxicity in oats relative to the free fluoride

ion; shoot and root dry weights were significantly limited at AlF 2 +

concentrations of 11–22 μmol/litre and AlF

2 + concentrations of 126–357

μmol/litre (Stevens et al., 1997).

Ratsch & Johndro (1986) calculated EC

50 s, based on inhibition of

root growth, for lettuce ( Lactuca sativa ) plants exposed to fluoride. ForEffects on Other Organisms in the Laboratory and Field

147 the 115-h paper substrate method, an EC

50 value of 450 mg fluoride/litre

was found, and for the 5-day solution method, the EC

50 was 660 mg

fluoride/litre.

Cooke (1976) studied the effect of fluoride (200 mg/litre) on

common sunflower ( Helianthus annus ) seeds grown in sand culture.

No effect on total dry weight was observed; however, there were significant reductions in leaf growth. Keller (1980) grew Norway spruce

( Picea abies ) cuttings in sand and watered with 1 00 mg fluoride/litre

during winter

until bud break. Watering with sodium fluoride significantly depressed the carbon dioxide uptake of shoots. Although the

previous year’s needles did not show signs of injury, most of the new

needles were killed immediately after flushing with fluoride. Exposure

to fluoride significantly increased the susceptibility of plants to sulfur

dioxide in subsequent fumigation experiments. Zwiazek & Shay (1987)

grew jack pine ( Pinus banksiana ) seedlings in sand cu lture at 3 or

15 mg fluoride/kg dry weight. Wilting was the firs t sign of fluoride

injury an d occurred in approximately 50% of plants after 25–26 h at

15 mg fluoride/kg and 2–6 h later in only 7% of plants exposed to

3 mg/kg. Fluoride-induced injuries to mesophyll and guard cells were

similar to tho se caused by drought and included the appearance of

lipid material in the cytoplasm during early stages of injury, suggesting

cell me mbrane damage. Plants exposed to 3 mg/kg for up to 168 h

showed significant redu ctions in water content. Respiration was

significantly reduced after 24 h, but not after longer exposure times,

while photosynthetic oxygen release was significantly reduced at 48

and 91 h but had recovered after 168 h (Zwiazek & Shay, 1988a).

Zwiazek & Shay (1988b) reported that 3 mg fluoride/kg significantly

reduced growth (as measured by fresh weight) and acid phosphatase

activity and increased total organic acid content of jack pine ( P.

banksiana ) seedlings.

A few studies have been carried out in which the fluoride exposures have been via the soil. However, the type of soil can greatly

a ffect the uptake and subsequent toxicity of fluorides. For example

,

Conover & Poole (1971) found that calcined clay prevented the uptake

of water-so luble fluoride, whereas sphagnum peat did not have the

same capability.

In pot expe riments, Singh et al. (1979) grew rice ( O ryza sativa )

plants in soil (pH >9.4) amended with 25–200 mg fluoride (a d ded as

sodium flu oride); the rice plants were harvested, and the soil wasEHC 227: Fluorides

148 subsequently sown with wheat ( Triticum aestiv um ). The authors

found that the critical water-extractable fluoride concentration in soil

for grain yield in wheat was 22 mg fluorid e/kg, which related to a

fluoride content of 35 mg/kg in mature wheat straw.

There are limited data available to determine the critical value for

fluoride in soil with respect to plant toxicity. The data are also complicated by plant species ranges of sensitivities, heterogeneity of soils,

soil chemical parameters that can influence fluor ide availability and

toxicity, and the relative toxicity of ionic species of fluoride found in

the soil solution. Ho w ever, more controlled solution culture studies

have attempted to define toxic concentrations of fluoride exposed to

the plant roots and are perhaps the best first approximation of toxic

concentrations of fluoride in soil solution.

Elrashidi et al. (1998) found that an application of 100 mg fluoride/kg significantly reduc ed dry matter yield of barley ( H ordeum

vulgare ) grown on both acid (pH 4.75) and neutral (pH 6.6) soils for 40

days; however, plants growing on alk aline soil (pH 7.5) were unaffected at 1000 mg/kg. The authors found no clear influence of phosph ate (50–550 mg/kg soil) on the adverse effect of fluoride on dry

matter yield.

Davis & Barnes (1973) found that an added soil fluoride concentration of 380 mg/kg (20 mmol/litre) significantly reduced the growth of

loblolly pine ( Pinus taeda ) and red maple ( Acer rubrum ) seedlings.

9.1.3.2 Invertebrates

Johansson & Johansson (1972) found that egg production and

survival were adversely affected in flour beetles ( Tribolium confusum )

exposed to flour containing 4524 mg fluoride/kg (0.1% sodium fluoride)

for up to 27 days. However, short-term (1–7 days) exposure to fluoride

concentrat ions of 452.4 mg/kg (0.01% sodium fluoride) produced

significant stimulation of egg production.

Hughes et al. (1985) fed c abbage looper ( T richoplusia ni ) larvae

on a wheat g erm diet dosed with sodium fluoride (50 and 187 mg

fluoride/k

g dry weight) or potassium fluoride (48 and 235 mg fluoride/kg dry weight) or a diet of hydrogen f luoride-fumigated leaves

(40–187 mg fluoride/kg dry weight). Larval feeding, growth and rate of

development were generally reduc ed on diets containing sodiumEffects on Other Organisms in the Laboratory and Field

149 fluoride and potassium fluoride. The same parameters were generally

greater with or unaffected by diets containing fumigated leaves.

Wang & Bian (1988) exposed silkworms ( Bombyx mori ) to mulberry ( Morus alba ) leaves containing fluoride concentrations ranging

from 10 to 200 mg/kg. The threshold concentration for mortality was 30

mg/kg; 30% mortality was observed at concentrations of 30–50 mg

fluoride/kg, 70% at 50–120 mg fluoride/kg and 95% at 120–200 mg

fluoride/kg. There was a close correlation between cocoon development and the fluoride content of le aves, with >80 mg fluoride/kg

severely inhibiting cocoon production.

Survival of isopods (woodlouse, Porcellio scaber ) was not

affected after 4 weeks of exposure to fluoride levels in litter up to

3230 mg/kg (170 μmol/g) (Van Wensem & Adema, 1991).

Davies et al. (1998) found no effect on the reproduction of aphids

( A phis fabae ) feeding on bean ( Vicia faba ) plants (12 days) that had

been previously exposed to either sodium fluoride in nutrient solution

(15 μg fluoride/cm 3 ) or hydrogen fluoride via fumigation (6.5 μg

fluoride/m

3 ). Plants accumulated more fluoride in t he shoots during

fumigation and at levels of up to 200 mg fluoride/kg; aphids accumulated up to 300 mg fluoride/kg from these plants. Similarly, Port et al.

(1998) found no effect of hydrogen fluoride on the growth and survival

of cabbage white caterpi l lars ( Pieris brassicae ) at a dietary concentration of 178.3 mg fluoride/kg.

9.1.3.3 Vertebrates

Guenter & Hahn (1986) fed white leghorn hens on a diet containing up to 1300 mg fluoride/kg for 252 days. Concentrations of



### $ 1000 mg/kg resulted in si g nificant depression of feed intake, body

weight gain, feed efficiency and egg quality. In a second experiment,

pullets were fed 1300 mg/kg for 49 days; similar results were obtained,

but the addition of al uminium (1040 mg/kg) to the diet reduced the

effects. Chan et al. (1973) found no effect on growth in Japanese quail

( Coturnix coturnix japonica ) fed diets resulting in av erage tibial

fluoride concentrations of 13–2223 mg/kg ash weight.EHC 227: Fluorides

150 Fleming et al. (1987) dosed nestling European starlings ( Sturnus

vulgaris ) with daily oral doses of 6–160 mg fluoride/kg body weight.

Dosing began 24–48 h after hatching and continued for 16 days. The

24-h LD 50 was 50 mg/kg body weight for 1-day-old chicks and 17 mg/kg

body weight for 16-day-old nestlings. Growth rates were significantly

reduced at 13 and 17 mg fluoride/kg body weight (the highest doses at

which growth was monitored). No histological damage due to fluoride

treatments was found in liver, spleen or kidney.

Carrière et al. (1987) fed nesting American kestrels ( F alco sparverius ) on a diet containing fluoride levels of 62.4 (background), 4512

or 7690 mg/kg for 10 days. The diet consisted of cockerels ( G allus

gallus ) that had been exposed to fluoride. Fluoride levels in femurs and

eggshells of treated kestrels were significantly highe r than those in

controls. There were no significant effects of fluoride on per cent

fertility or hatchability of eggs. Clutch sizes tended to be smaller with

increasing fluoride in the diet; however, the difference was not statistically significant. Seven-day-old kestrel chicks were fed on a cockerel

mash diet containing 0, 1120 or 2240 mg/k g for 27 days. Growth of

chicks and weights of internal organs were not significantly affected

by fluoride in the diet. Per cent bone ash was significantly increased,

while bone-breaking strength was significantly decreased by fluoride

(Bird et al., 1992). Bird & Massari (1983) fed kestrels on a diet to which

flour contaminated with fluoride (10, 50 or 500 mg/kg) had been applied.

The bir ds receiving the highest fluoride dose died within 6 days.

Fluoride at the lower doses had no effect on clutch size, hatchability or

fledging success but was associated with a higher fertility. Eggs laid

by kestrels at 50 mg/kg had significantly thicker shells. Lower

reproductive success of eastern screech-owls ( Otus asio ) w a s noted

when birds were fed 90 mg fluoride/kg diet wet weight (as sodium

fluoride), but not when fed 18 mg fluoride/kg diet (Hoffman et al., 1985;

Pattee et al., 1988).

Most of the early work on mammals was carried out on domesticated ungulates (Suttie, 1983). Fluorosis has been observed in experimental studies on cattle and sheep exposed to fluoride. Cattle are less

tolerant of fluoride toxicity than are other livestock (Phillips & Suttie,

1960). In long-term experiments with beef cattle, 30 mg/kg of dietary

fluoride caused excessive wear and staining of teeth (Hobbs & Merriman, 1959). In a further study, beginning with young calves and lasting

7 years, the tolerance for soluble fluoride was also 30 mg/kg dry diet

(Shupe et al., 1963). Suttie et al. (1957) found that lactating cows couldEffects on Other Organisms in the Laboratory and Field

151 tolerate 30 mg/kg, with a rate of 50 mg/kg causing fluorosis within 3–5

years.

Tolerance levels h a ve been identified for domesticated animals

based on clinical signs and lesions. Tolerance levels in feed range from

30–40 mg/kg dry weight in dairy cattle to 150 mg/kg in lambs; in water,

tolerance l evels range from 2.5–4.0 mg/litre in dairy cattle to 12–15

mg/litre in lambs (Shupe & Olson, 1983; Cronin et al., 2000). The lowest

dietary level observed to cause an effect on wild ungulates was in a

c ontrolled captive study, where white-tailed deer ( O docoileus

virginianus ) were exposed to 10 (control feed), 35 or 60 mg fluoride/kg

wet weight (as sodium fluoride) in their diet for 2 years (Suttie et al.,

1985). A general mottling of the incisors characteristic of dental

fluorosis was noted in the animals at the 35 mg/kg diet dose; those on

the higher dose also experienced minor increased wear of the molars,

as well as mild hyperostoses of the long bones of the leg. No gross

abnormalities of the mandible were observed. The mean fluoride content of the mandibles was approximately 1700 mg/kg ash weight for the

control, 4550 mg/kg for the low-dose grou p and 6600 mg/kg for the

high-dose group, the latter two levels being similar to those observed

in affected wild deer near sources of industrial pollution (Karstad, 1967;

Kay et al., 1975; Newman & Yu, 1976).

Deer mice ( Peromyscus maniculatus ) fed diet s of 38 (control),

1065, 1355 or 1936 mg fluoride/kg diet dry weight (as sodium fluoride)

for 8 weeks exhibited, at all concentrations above the control, marked

weight loss, mortality, changes in femur size and dental disfigurement

(Newman & Markey, 1976). Bank voles ( Clethrion omys glareolus )

showed a reduction in the number of litters per female, an increase in

the number of days from mating to producing the first litter, increased

mortality of offspring and a changed sex ratio (greater number of males)

in offspring of anim als fed 97 mg/kg diet (wet or dry basis not

specified). Animals fed 47 mg/kg diet also showed these effects, but

the differences were not significant from the control (Krasowska, 1989).

Boulton et al. (1995) exposed short-tailed field voles ( Microtus

agrestis ), bank voles ( Clethrionomys glareolus ) and wood mice

( Apodemus sylvaticus ) to drinking-water containing 0, 40 or 80 mg

fluoride/litre for up to 84 days. Both fluoride exposures inducedEHC 227: Fluorides

152 premature mortalities in both vole species. Severe dental lesions were

observed in animals surviving the highest dose. Voles were also fed on

a diet containing 100 mg fluoride/kg (vegetation c ontaminated by

atmospheric fluorides). Offspring of the vole s fed the contaminated

diet had si gnificantly lower growth rates and body weights during

stages of infancy and early adulthood. The incisors of newly born

young were not significantly different between the contaminated and

control diets; howeve r, incisors of offspring weaned on to the

contaminated diet showed marked morphological changes and severe

dental lesions (Boulton et al., 1994a).

Fluoride was suggested as the cause of reduced milk production

with subsequent mortality of kits in farm-raised red foxes ( Vulpes

vulpes ) fed a diet containing 98–137 mg fluoride/kg dry weight

(Eckerlin et al., 1986).

Aulerich et al. (198 7) fed mink ( M ustela vison ) diets containing

35– 385 mg fluoride/kg for 382 days. No significant differences were

observed in body weight gains or fur quality between dosed and

control mink. No adverse effects of fluoride on breeding, gestation,

whelping or lactation were found. Survival was adversely affected at

385 mg fluoride/kg; some of the surviving mink at this concentration

had weakened frontal, pariet al and femoral bones. Fluoride did not

affect haematological parameters or serum calcium concentrations, but

serum alkaline phosphatase activity was significantly increa sed at

fluoride concentrations of 

### $ 229 mg/kg.

Mink ( Mustela vison ) kits and adult male mink were fed diets

containing fluoride (as sodium fluoride) at concentrations ranging from

26 to 287 mg fluoride/kg wet weight for up to 8 months. Gross,

radiographic and microradiographic changes were seen in bones from

animals ingesting the higher levels of fluoride. Chemical analyses for

fluoride generally reflected the levels ingested. After data were evaluated, a tolerance level in the feed of 50 mg fluoride/kg for breeding

stock was recommended (Shupe et al., 1987).Effects on Other Organisms in the Laboratory and Field

153 

### 9.2 Field observations

9.2.1 Microorganisms

Rao & Pal (1978) found a positive correlation between concentrations of fluoride in soil and soil organic matter content at eight sites

near an aluminium factory in India and inferred that fluoride decreased

the activity of soil microorganisms responsible for litter decomposition.

Significant increases in the organic matter of soils were not found until

total soil fluorid e concentrations were greater than approximately

1000 mg/kg.

Tscherko & Kandeler (1997) studied the influence of atmospheric

fluoride deposits on soil microbial biomass and its enzyme activities

near an aluminium smelter at Ranshofen, Upper Austria. Mean waterextractable fluoride concentrations ranged from 10 to 124 mg/kg dry

soil and were inversely correlated with microbial activity. In the most

contaminated soil (up to 189 mg/kg), the microbial activities were only

5–20% of those in unpolluted soil. At a fluoride concentration above

100 mg/kg, microbial biomass and dehydrogenase activity decreased

substantially, whereas arylsulfatase activity was in hibited at only

20 mg/kg. The accumulation of organic matter near the smelter (124 mg

fluoride/kg) also indicated severe inhibition of mi crobial activity by

fluoride.

9.2.2 Aquatic organisms

Kudo & Garrec (1983) simulated the accidental release of ammonium fluoride into a pond. Mean fluoride concentrations increased from

0.2 to 7.3 mg/litre fo llowing the release. Fluoride levels returned to

background concentrations within 30 days. No visible toxic effects on

plants, algae, molluscs or fish were observed during the 30-day period.

No details regarding the chemical character istics of the pond water

were given.

Ares et al. (1983) monitored fluoride concentrations and diatom

populations in seawater near an aluminium smelter in southern Argentina. Fluoride concentrations primarily ranged from 1.1 to 1.3 mg/litre.

Anthropogenic emissions accounted for 6–8% of the variance of fluoride levels in the waters. The correlations observed between fluorideEHC 227: Fluorides

154 concentrations and some structural characteristics of the diatom community did not show significant effects of the discharged fluoride.

Fluoride-loaded effluent adversely affected the species richness

of a marine encrusting community for up to 400 m from the point of

discharge. Fluoride concentrations greater than 50 mg/litre (the

concentration of fluoride in effluent at which mortality was observed

in the laboratory) seldom extended for more than 20 m from the outfall.

The authors concluded that a sublethal effect of fluoride and/or some

other effluent component appeared to be producing the observed

distribution (Pankhurst et al., 1980).

High mortality and delayed migration were observe d in Pacific

salmon ( Oncorhynchus sp.) migrating upstream near an al uminium

plant on the Columbia River, US A (Washington/Oregon border).

Fluoride levels in the water ranged between 0.3 and 0.5 mg/litre during

1982. Bioassay experiments on adult salmon suggested that fluoride

concentrations of 0.5 mg/litre would adversely affect migration.

Between 1983 and 1986, discharges from the aluminium plant were

reduced, there was a corresponding drop in fluoride concentrations,

and fish mortality and migration delays were decreased (Damkaer &

Dey, 1989).

Mishra & Mohapatra (1998) monitored toads ( Bufo melanosticus )

at a fluoride-contaminated site at Hirakud, India. Mean haemoglobin

content, total red blood cell count and haematocrit in blood samples

were found to be significantly reduced, whereas mean corpuscular

concentration and volume were significantly elevated when compared

with toads at an uncontaminated site. Mean bone fluoride concentrations were 2736 mg/kg at the contaminated site and 241 mg/kg at the

control site.

9.2.3 Terrestrial organisms

9.2.3.1 Plants

Aluminium smelters, brickworks, phosphorus plants and fertilizer

and fibreglass plants have all been shown to be sources of fluoride

that are correlated with damage to local plant communit ies. In 1970,

vegetation in the vicinity of a phosphorus plant in Newfoundland,

Canada, began to show symptoms of damage (tip burn and marginEffects on Other Organisms in the Laboratory and Field

155 burn). Samples collected during 1973–1975 revealed that the degree of

damage and fluoride levels in soil humus were inversely related to the

distance from the plant. Average levels of fluoride in vegetation ranged

from 281 m g/kg in severely damaged areas to 44 mg/kg in lightly

dam aged areas; at a control site, the fluoride concentration was 7

mg/kg (Thompson et al., 1979). Klumpp et al. (1994, 1996a) reported that

plants downwind of fertilizer industries in Brazil showed damage

(necrotic bands or tip burn). Bioin dicator plants have revealed that

severe damage corresponded to high leaf fluoride concentrations (no

statistical analysis performed). Klumpp et al. (1996b) found a highly

signifi cant linear regression between leaf damage and fluoride

accumulation in Gladiol us plants; the plants developed typical

fluoride-induced leaf lesions. Murray (1981) found that plant communities near an aluminium smelter showed differences in community

composition and structure due partly to variations in fluoride tolerance.

However, it must be noted that in the field, one of the main problems with the identification of fluoride effects is the presence of confounding variables, such as other atmospheric pollutants. McClenahen

(1978) examined stands of vegetation along pollution gradients recording species richness, evenness of stand, diversity index and concentrations of three pollutants. Most vegetation characteristics were altered

in areas of high pollution. Statistical analysis showed a sig nificant

positive correlation between fluorides and s hrub density; however,

chloride appeared to have the greatest impact on the same parameter.

Therefore, care must be taken when interpreting the many field studies

on fluoride pollution.

Lichens have been us ed widely as biomonitors of fluoride

pollution. LeBlanc et al. (1971) transplanted epiphytic lichens from an

unpo lluted area to various distances from an aluminium factory.

Lichens accumulated 600–900 mg fluoride/kg during periods of 4 or 12

months within 8 km of the factory compared with 70 mg/kg at a control

site. Lichen thalli ex

posed for 4 months at 1 km from the factory

contained some extractable chlorophyll; however, those exposed for 12

months did not. Soredia (viable structures with a potential to develop

into parent lichen thalli under favourable ecological conditions) were

absent in lichens growing within 4 km of the plant. Davies (1982) found

that visible damage to lichen ( X anthoria parietina ) thalli (growing

within a 30-km radius of the Bedfordshire brickfields, United Kingdom)EHC 227: Fluorides

156 was observed when internal fluor ide concentrations exceeded 68

mg/kg, and internal damage occurred at >90 mg fluoride/kg.

Gilbert (1985) monitored lichens near an aluminium smelter during

its 11-year operational life. Epiphytic lichens were severely damaged

(>50% injury) over a 25-km 2 area close to the smelter. Fluoride

concentrations in R a malina farinacea near the smelter increased from

9–11 mg/kg prior to the start of the smelting opera tion to 120–156

mg/kg within 4 months and had reached these higher levels up to 3 km

from the smelter within 3 years.

Perkins & Mil l ar (1987) studied the effect of airborne fluoride

emitted from an aluminium works on previously unpolluted assemblages of saxicolous lichens. Prior to emissions, lichens contained a

mean concentration of 16 mg fluoride/kg. Fruticose (shrubby) lichens,

such as Ramalina species, were the mo st sensitive to fluoride emissions, wi th lichens containing >100 mg fluoride/kg showing severe

damage. Some foliose (leaf-like) lichens tolerated >200 mg fluoride/kg,

and crus tose (crust-like) lichens were the most tolerant group, with

overall survival at 32% and 70% for the two groups, respe c tively,

within 1 km of the works. Damage to lichens was greatest less than

2 km from t he works, where 41% of R amalina thalli showed >50%

chlorosis or necrosis. Loss of lichens decreased with increasing distance from the works. The authors reported that lichens containing 300,

100 and 50 mg fluoride/kg dry weight lost 46, 15 and 10% of cover per

year, respectively (Perkins, 1992).

Several studies have been carried out on the effects of fluorides

on a variety of tree species and the subsequent damage to forests.

Infrared aerial photographs of forest near an aluminium plant in northwestern Montana, USA, revealed widespread damage to nearly

75 000 ha of pine ( Pinus sp .) trees. The authors identified several

factors that suggest fluoride as the cause, including proximity to the

plant, high fluoride concentrations in conifer leaves and the presence

of typical fluoride-induced leaf lesions (Carlson, 1978). Bunce (1984)

reported that the growth reduction of forest (2800 m 3 /year) estimated

for the years from the establishment of an aluminium smelter (Kitimat,

British Columbia, Canada) to 1974 dec lined by 78% for the period

1974–1979. The improvement in growth corresponded to a 79% decline

in fluoride content of foliage and a 64% decline in fluoride emissions.Effects on Other Organisms in the Laboratory and Field

157 The effects of fluoride emissions from a phosphorus plant (the

plant closed in 1989) in Long Harbour, Newfoundland, Canada, on the

conifers balsam fir (

Abies balsamea ) , black spruce ( P icea mariana )

and larch ( Larix laricina ) were monitored at sites downwind from the

plant during the su mmer of 1982 (Sidhu & Staniforth, 1986). Mean

fluoride concentrat ions ranged between 11.4 μg/m 3 at a distance of

1.4 km from the source and 0.08 μg/m 3 18.7 km from the source. At the

closest site, seed production in balsam fir, black spruce and larch was

impaired by 76.4%, 87.4% and 100%, re spectively, compared with

controls. At 10.3 km from the source (mean ambient air concentration

0.9 μg fluoride/m 3 ), the effects included reduction of 3–10% in seed size

and 23–30% in cone size and a dec rease of 17–72% (varied with

species) in the number of cones per tree. A significant negative correlation was observed between atmosph eric fluoride levels and seed

production for all three species. A significant negative correlation was

also observed between foliar injury in the three species (chlorosis and

necrosis) and mean atmospheric fluoride levels. Toxic effects of fluoride on these conifer species have resulted in their replacement by more

tolerant hardwood species, such as birch ( Betula sp.) and alder ( Alnus

sp.). Reproductive and vegetative characteristics of raspberry ( Rubus

sp.) and blueberry ( Vaccinium sp.) were monitored at six sites downwind from the plant. Within 1.4 km of the plant, flower mortality was

89% for blueberry and 78% for raspberry, compared with 27% and 26%,

respectively, for a control site; there were also significant decreases in

size, number and dry weight of fruit. Fluoride concentrations in foliage

were 403 mg/kg for raspberry and 216 mg/kg for blueberry, compared

with 8 and 9 mg/kg, respectively, for the control site (Staniforth &

Sidhu, 1984).

Taylor & Basabe (1984) established correlations between fluoride

concentrati o ns in pine needles (Douglas-fir, Pseudotsuga menziesii )

and annual growth increments, wind patter n, distance from fluoride

source (aluminium smelter) and hydrogen fluoride concentrations in

emissions. The authors noted that visible fluoride symptoms and over

40% growth reduction occurred in trees that were accumulating fluorides below established “injury threshold levels.” They suggested that

synergism between hydrogen fluoride a nd sulfur dioxide may have

given rise to these reduced threshold levels.

Vike & Håbjørg (1995) recorded fluoride content and leaf injury in

a variety of plant species growing in the vicinity of aluminium smeltersEHC 227: Fluorides

158 in Norway. Scots pine ( Pi nus sylvestris ) was the most sensitive

species, showing leaf injury symptoms at a leaf fluoride content of less

than 50 mg/kg at the northern-most locality and <1 00 mg/kg under

so u thern maritime conditions. Broad-leaved species such as downy

birch ( Betu l a pubescens ), goat willow ( Salix caprea ) and European

mountain-ash ( Sorbus aucu paria ) showed similar symptoms at

concentrations of 100 and 170 mg/kg for the two sites, respectively. In

a later study, Vike (1999) reported that leaf injury appeared at leaf

fluoride content levels as low as 30 mg/kg, and damage was restricted

to within 2 km of the emission sources. Regression analysis showed a

positive correlation between leaf injury and fluoride content of leaves

within a locality, but great variation between localities. The author

concluded that the establishment of tolerable emission levels must take

into account local dispersal patterns and climatic conditions.

Ivinskis & Murray (1984) found that reductions in photosynthetic

capacity, chlorophyll a and b and leaf area of grey gu m ( Eucalyptus

punctata ) were all significant ly correlated with leaf fluoride content,

fluoride in air and distance from an aluminium smelter. The authors also

foun d that dusky-leaved ironbark ( E ucalyptus fibrosa ), a species

believed to be tolerant of fluoride, showed no significant differences

between sites for any of the variables except leaf area.

9.2.3.2 Invertebrates

Mayer et al. (1988) conducted a 3-year study on honeybees ( Apis

mellifera ) in Puyallup Valley, Washing ton, USA, near an aluminium

plant. The mean fluoride content of bees from a site 0.8 km downwind

of the plant ranged from 82 to 261 mg/kg dry weight. No significant

effect of fluoride on brood survival , brood development or honey

production was found.

9.2.3.3 Vertebrates

Van Toledo (1978) found that the number of avian species near

fluoride-emitting aluminium factories in Europe was depressed. They

speculated that the reductions were due to fluoride emissions. Newman

(1977) believed that the nesting density of house mart ins ( D elichon

urbica ) was reduced near an aluminium plant with high fluoride

emissions. However, there were many other air pollutants present, and

so it is difficult to establish a causal relationship with fluoride inEffects on Other Organisms in the Laboratory and Field

159 particular. Henny & Burke (1990) monitored black-crowned night

herons ( Nycticorax nycticor a x ) living near a phosphate-processing

complex in Idaho, USA. Fluoride in femurs ranged from 540 to

11 000 mg/kg ash weight and increased with age. The authors studied

bon e strength, but, because of the strong relationship between age

and fluoride concentrations, it proved difficult to separate the effects

of fluoride from those of age.

The original findings of fluoride eff e cts on mammals were from

studies in the field on domestic animals such as sheep (Moule, 1944;

Harvey, 1952; Peirce, 1952) and cattle (Rand & Schmidt, 1952; Neeley

& Harbaugh, 1954; Burns & Allcroft, 1964; Allcroft & Burns , 1968;

Krook & Maylin, 1979), and more recent studies have shown this to be

a n ongoing problem in some areas (Jubb et al., 1993; Fidanci et al.,

1998; Swarup et al., 1998; Choubisa, 1999; Patra et al., 2000). Fluoride

can be taken up from vegetation, soil and drinking-water. Incidents

involving domesticat ed animals have originated both from natural

fluoride sources, such as volcanic eruptions an d the underlying

geology, and from anthropogenic sources, such as min eral supplements, fluoride-emitting industries and power stations. Symptoms of

chronic fluoride toxicity inc l ude emaciation, stiffness of joints and

dental and skeletal fluorosis. Other effects include lowered milk

production and detrimental e ffects on the reproductive capacity of

animals. Guidance is available on fluoride tolerance levels in feed and

w ater for domesticated animals based on clinical signs and l esions

(Shupe & Olson, 1983; Cronin et al., 2000) (see section 9.1.3.3).

Investigations of the effects of fluoride on wildlife have focused

on impacts on the structural integrity of teeth and bone. Most

observations have involved large herbivores. For example, dental and

skeletal le sions were found in mule deer ( O docoileus hemionus ), elk

( Cervus canadensis ) and American bison ( B ison bison ) exposed to

elevat ed levels (no specific anthropogenic sources identified) of

fluoride in Utah, Idaho, Montana and Wyoming, USA (Shupe et al.,

1984). Black-tailed dee r ( O docoileus hemionus columbianus ) near an

aluminium smelter in Washington, USA, were found to have dental

disfigurement, with the premolars of one individual deer being worn

down to the gumline. Fluoride levels in ribs ranged from 2800 to

6800 mg/kg on a fat-free basis, compared with control deer, which had

levels ranging from 160 to 460 mg/kg (Newman & Yu, 1976). Lameness

of deer adjacent to an aluminium smelter in Montana, USA, was notedEHC 227: Fluorides

160 by Kay et al. (1975). They speculated that fluorosis was the cause of

a change in age structure of the m ule deer population. Levels in

mandibles of the m

ule deer and white-tailed deer ( O docoileus

virginianus ) ranged from 1100 to 7000 and from 3400 to 9800 mg/kg,

respectively, on a fat-free basis, whereas those of control deer were

less than 200 mg/kg. White-tailed deer inhabiting an area adjacent to

an aluminium smelter in South Carolina, USA, exhibited dental fluorosis

but no osteofluorosis (Suttie et al., 1987). Mean levels in mandibles of

deer older than 2.5 years were 286 mg/kg ash weight before opening of

the smelter and 1275 mg/kg 3 years after start-up.

Karstad (1967) found that mandibular bone fluoride contents of

4300–7125 mg/kg in mule deer ( O docoileus hemionus ) near an industrial complex were associated with pitting and black discoloration of

teeth, abnormal tooth wear and fractures of teeth and jaw bones. All

red deer ( Cervus elaphus ) yearlings, sampled near Norwegian aluminium smelters, with mandibular fluoride levels exceeding 2000 mg/kg

were fou nd to have dental fluorosis. Gross osteofluorosis was

observed in deer with mandibular fluoride residues of greater than 8000

mg/kg (Vikøren & Stuve, 1996b). Pathological alterations in the teeth

of roe deer ( Capreolus capreolus ) in Germany were diagnosed as

dental fluorosis. The di agnosis was confirmed by analysis of

mandibles, which contained significant levels of fluoride (Kierdorf,

1988). The dental fluorosis was found to occur mainly in the heavily

industrialized Ruhr area of Germany. H. Kierdorf et al. (1996) and U.

Kierdorf et a l. (1996) monitored mandibular bone fluoride

concentrations and frequency and intensity of fluoride-induced dental

lesions in red deer in the Czech Republic and Germany (Figure 4). The

frequency and severity of dental fluorosis were positively correlated

with bone fluoride levels. Detailed macroscopic, microradiographic and

scanning electron m

i croscopic methods have revealed structural

changes in fluorosed dental enamel of both roe and red deer (U.

Kierdorf et al., 1993, 1996). Corresponding changes have also been

described in fluorosed enamel of wild boars ( Sus scrofa ) from fluoridepolluted areas (H. Kierdorf et al., 2000). Kier dorf & Kierdorf (1997)

concluded that periods of especially elevated plasma fluoride levels in

chronically fluoride- s tressed deer can cause a disruption in the

function of secretory ameloblasts similar to that following acute

fluoride dosing in laboratory rodents. Morphological imaging has

revealed a decreased width and an inc reased porosity of the antler

cortex in deer from highly fluoride polluted areas (U. Kierdorf et al.,

2000). Kierdorf et al. (1997) concluded that increased fluoride exposureEffects on Other Organisms in the Laboratory and Field

161 of deer leads to reduced mineral content and mineral density of antler

bone and that it is the rapidity of their growth and mineralization that

makes antlers especially susceptible to fluoride action. The occurrence

of osteofluorotic alterations has also been diagnosed in red deer ( C.

ela

phus ) with bone fluoride concentrations greater than 4000 mg/kg

dry weight (Schultz et al., 1998). The authors concluded that in addition

to fluoride-induced den tal lesions, the occurrence of marked

periodontal disease and tooth loss is an important factor responsible

for a reduction of life expectancy in severely fluorotic wild red deer. It

has been demonstrated that in the case of regional, long-term fluoride

pollution, dental fluoro sis can be used as a sensitive biomarker of

fluoride exposure in deer and thus as an indicato r of the level of

environme ntal contamination by fluorides (U. Kierdorf & Kierdorf,

1999).

Fig. 4. Row of permanent mandibular cheek teeth (from right to left, 2nd, 3rd,

4th premolar, 1st, 2nd, 3rd molar) of a red deer ( Cervus elaphus ) exhibiting

pronounced dental fluorosis. The premolars and the M 3 exhibit enamel

discoloration and increased wear. Note destruction of the tooth crown in the

P 3

(asterisk) and dysfunctional crown shape of the M 3 (arrow). Due to the

increased wear, the alveolar process has regressed in the region of P 3 and P 4 (arrowheads).

E xposure of predatory wildlife is often minimal, as fluoride is

largely unavailable to those mammalian and avian predators that do not

digest bone. For example, barn-owls regurgitate pellets that contain

virtually intact skeletons of their prey (Thomson, 1987).EHC 227: Fluorides

162 Walton (1987c) found that severe dental damage in field voles

( Microtus agr estis ) and wood mice ( A podemus sylvaticus ) was evident

only within 200–300 m (dow nwind) of an aluminium smelter. A

significant increase in tooth wear was noted in moles ( Talpa europaea )

at between 4 and 15 km from the smelter. Radiographs of the skeletons

of voles and mice with bone fluoride levels of up to 15 000 mg/kg dry

weight showed no changes when compared with rodents from control

sites. Paranjpe et al. (1994) identified fluorosis in cotton rats ( Sigmodon

hispidus ) at a petrochemical waste site. Approximately 80% of the

cotton rats collected by Schroder et al. (1999) at the same site were

found to have dental fluorosis. Mean bone fluoride and mean soil total

fluoride levels were 1515 and 1954 mg/kg, respectively. Bone fluoride

was found to be an accurate predictor of dental fluorosis when it was

low (<1000 mg fluoride/kg; no fluorosis) or high (>3000 mg fluoride/kg;

fluorosis), but not when it was intermediate (Schroder et al., 2000). Field

voles ( M. agrestis ) and bank voles ( C lethrionomys glareolus ) showed

severe dental lesions on incisor and molar teeth near a chemical works

(549 mg total fluoride/kg dry weight of vegetation) and an aluminium

smelter (187 mg fluoride/kg vegetation), with less marked damage at a

mine tailings dam (80 mg fluoride/kg vegetation) (Boulton et al., 1994b).

Boulton et al. (1999) reported that the severity of lesions in both incisor

and molar teeth of field voles ( M. agrestis ) was positively correlated

with the respective tissue fluoride concentrations.Table 16 (contd).

Organism Size/age Temperatur

e (°C) Hardness

(mg/litre) b pH Salinit

y (‰) Parameter Concentration

(mg fluoride/

litre) c Reference

Sheepshead minnow

( Cyprinodon

variegatus ) 8–15 mm 25–31 10–31 96-h LC 50 >225 n Heitmuller et al. (1981)

Ambassid (

Ambassis

safgha ) adult 20–21 10–28 96-h LC 50 >100 n Hemens & Warwick (1972)

Crescent perch

( Therapon

jarbua ) adult 20–21 10–28 96-h LC 50 >100 n Hemens & Warwick (1972)

Mullet ( Mugil

cephalus ) juvenile 20–21 10–28 96-h LC 50 >100 n Hemens & Warwick (1972)

a All tests were conducted under static conditions (water unchanged for duration of test).

b Hardness expressed as mg calcium carbonate/litre.

c n = based on nominal concentrations; m = based on measured concentrations.163 

### 10. EVALUATION OF HUMAN HEALTH RISKS

AND EFFECTS ON THE ENVIRONMENT

10.1 Evaluation of human health risks

10.1.1 Exposure

Individuals are exposed to some level of fluoride from natural and/

or anthropogenic sources. The consumption of foodstuffs, drinkingwater and other beverages is generally the principal route of exposure.

Significant intake may also occur in younger children from the

ingestion of fluoridated dentifrice and supplements. Infants can receive

small amounts of fluoride from breast milk. The inhalation of fluorides

in air usually makes only a minor c ontribution to the overall total

intake. High intakes of fluoride have been noted in geographical areas

worldwide where the surrounding environment is rich in natural fluoride. In these areas, drinking-water, foodstuffs and the inhalat ion of

indoor air where coal rich in fluoride is used for heating and cooking all

contribute to the overall intake. Exposures might be increased somewhat in the vicinity of certain anthropoge n ic sources of fluoride. In

certain occupational environments, the inhalation of workroom air containing fluoride would contribute to higher than typical ambient exposures.

Estimates of daily fluoride intake by children in Canada range from

<0.01 mg (<1 μg/kg body weight for infants) to 2.1 mg (160 μg/kg body

weight for children up to 4 years of age and 80 μg/kg body weight for

adolescents aged 5–11 years). For adults, estimates of daily fluoride

intake range from 2.2 to 4.1 mg (approximately 30 to 60 μg/kg body

weight, assuming an average body weight of 64 kg). For individuals

residing in certain geographical areas rich in natural fluoride, daily

intakes as high as 27 mg (420 μg/kg body weight, assuming an average

body weight of 64 kg) have been reported. The esti mates of total

fluoride intake usually do not take into account its bioavailability (e.g.,

the degree of fluoride absorption from fluoride-containing food items).

Such information is needed in order to derive accurat e estimates of

daily total fluoride intake in individuals living in fluoridated as well as

non-fluoridated areas and in areas of endemic fluorosis.EHC 227: Fluorides

1 The effects of fluoride on dental health were reviewed in depth by

WHO (1994), and therefore only a brief summary is presented here.

164 10.1.2 Hazard identification 1

Fluoride has both positive and negative effects on human health,

similar to essential elements. Compared with many other chemicals,

there is a relatively na r row range between intakes associated with

beneficial effects and exposures causing adverse effects. The exposure

to low levels of fluoride in drinking-water (i.e., approximately 1 mg/litre)

has long been known to have a beneficial effect on the reduction of

dental caries. Clinical use of fluoride in the treatment of osteoporosis

(at doses generally greater than 25 mg/day) has been investigated in

a number of studies.

Based on the available data, it is evident that skeletal and dental

effects related to fluoride exposure in humans occur at doses or intakes

lower than those associated with other pot ential adverse tissue- or

organ-specific effects. This is likely a consequence of the accumulation

of fluoride almost exclusively in bones and teeth. In children, intakes

of fluoride associated with beneficial effects on dentition overlap with

those that lead to an increas e d prevalence of dental fluorosis. Consequently, public health programmes h ave sought to maximize the

beneficial effects of fluoride on dental health, while at the same time

minimizing its adverse fluorotic effects on the teeth.

Effects on the skeleton are the most consistent and best characterized of the toxic responses to fluoride and are considered to have

direct public heal th relevance. The skeletal changes that have been

observed in a number of animal species (i.e., cattle, sheep, poultry,

rodents) exposed to fluoride are not inconsistent with effects observed

in humans, although data from such studies have not been utilized in

the assessment of human exposure–response.

Case reports or descriptive ecological human studies of skeletal

fluorosis or osteosclerosis or studies on the occurrence of ende m ic

(crippling) skeletal fluorosis in which the levels of fluoride are naturally

very high provide little quantitative information useful in establishing

an adverse effect level associated with total fluoride intake. In such

studies, nutrition, the intake of fluoride (and additional minerals) fromEvaluation of Human Health Risks and Environmental Effects

165 other sources and potentially confounding concomitant exposures, all

of which have been suggested to play a role in the etiology of this

disease (for a r e view, see WHO, 1984; US EPA, 1985), were not

adequately documented. There is also limited quantitative information

on exposure to fluoride and the d evelopment of skeletal effects

(osteosclerosis or fluorosis) in occupationally exposed workers (see

Ho dge & Smith, 1977; Grandjean, 1982; Chan-Yeung et al., 1983a;

Czerwinski et al., 1988). Inconsistent results of inherently limited crosssectional studies of small populations exposed to often unspecifi e d

concentrations of fluoride in the vicinity of industrial sources (cited in

Hodge & Smith, 1977) contribute little to an assessme nt of

exposure–response for skeletal effects associated with exposure to

fluoride. Information obtained from clinical studies, in which sodium

fluoride was administered to patients for the treatment of osteoporosis,

is inadequate, owing to the nature of the protocols, characteristics of

the patients in these studies and inconsistencies in the results.

Moreover, these clinical studies were undertaken to assess the

considered beneficial effects of fluoride (i.e., its capacity to increase

bone mass and decrease vertebral fractures), rather than its potential

to produce adverse effects after long-term exposure.

Estimating a putative effect level for the development of skeletal

fluorosis (or related changes) in humans exposed to fluoride is further

complicated by differences in the radiological diagnosis of early-stage

skeletal fluorosis among health care professionals (Chan-Yeung et al.,

1983a), as well as by the multiplicity of factors that may influence the

amount of fluoride deposited in the bone, and hence the severity of the

disease. In case accounts, the development of crippling skeletal fluorosis was attributed to an intake of approximately 2 30–310 μg fluoride/kg body weight per day in adults weighing 64 kg (US DHHS, 1991).

Skeletal f

luorosis has been observed in cryolite workers having

estimated (occupational) intakes of approximately 310–1250 μg fluoride/kg body weight per day in adults weighing 64 kg (Grandjean, 1982)

.

Evidence from ecological studies suggests that there may be an

association between the consumption of fluoridated drinking- water

and an increased incidence of hip fracture (based on hospitalization

rates), particularly among the elderly. These results should be

interpreted with caution, however, in view of the limitatio ns of

epidemiological investigations of this design. Moreover, owing to theEHC 227: Fluorides

166 lack of data on individual exposure in such st udies, it is difficult to

derive meaningful conclusions concerning the exposure– response

relationship for possible skeletal effects associated with exposure to

fluoride from these studies.

Although the relative risk of hip, wrist or spina l fracture was

increased in some groups of women residing in an elevated-fluoride

community (with drinking-water containing 4 mg/litre, and having an

estimated [mean] intake of approximately 72 μg fluoride/kg body weight

per day) compared with those in a control community (with drinkingwat er containing 1 mg fluoride/litre) (Sowers et al., 1986, 1991), the

intake of fluoride by women in the elevated-fluoride community was

likely underestimated (since it was derived solely from the amount of

water-based beverages consumed), and the level of calcium in the

drinking-water from the elevated-fluoride community was

approximately 25% of the level in the control community.

Other studies, including analytical investigations, have not identified an increased risk of skeletal fracture associated with the consumption of drinking-water containing elevated levels of fluoride (Madans

et al., 1983; Simonen & Laitinen, 1985; Arnala et al., 1986; Jacobsen et

al., 1993; Suarez-Almazor et al., 1993; Kröger et al., 1994; Cauley et al.,

1995; Lehmann et al., 1998; Hillier et al., 2000).

Only two analytical studies evaluated the risk of fracture across

a range of fluoride exposures. Among 144 627 Finnish men and women,

no association was observed between hip fractures and the well-water

fluoride concentration, when all age groups were considered. However,

in women 50–65 years of age at the start of follow-up, the relative risk

of hip fracture increased with increasing well-water fluoride concentrations in the categories < 0.1, 0.1–0.3, 0.3–0.5, 0.5–1.0, 1.1–1.5 and >1.5

mg/litre. The respective relative risk of hip fracture was 1.0, 1.16, 1.31,

1.53 ( P < 0.05), 1.24 and 2.09 ( P < 0.05) (Kurttio et al., 1999).

Among 8266 Chinese men and women, the risk of all fractures and

hip fractures was examined across a range of fluoride exposures (see

Table 14 in chapter 8) (Li et al., 2001). There was an increased risk of

overall fracture and hip fracture that became statistically significant at

drinking-water levels in excess of 4.32 mg fluoride/litre.

Owing to the widespread controlled addition of fluoride to public

drinking-water supplies, numerous epidemiological and experimentalEvaluation of Human Health Risks and Environmental Effects

167 studies have attempted to address concerns related to the potential

carcinogenicity of this substance. There has been no consistent evidence of an association between the consumption of fluoridated

drinking-water and the incidence of, or mortality due to, cancer in a

large number of ecological studie s performed in many countries.

Although these results do not s upport the hypothesis of an

association, thei r considerable limitations preclude firm conclusions

from being drawn regarding the carcinogenicity of fluoride in humans.

For example, cancer of the bone was not assessed in the majority of

these human ecological studies. Case–control studies (Gelberg et al.,

1995; Moss et al., 1995) have not identified a relationship between

bone cancer and exposure to fluoride.

The incidence of, or death due to, cancer has also been investigated in a number of historic cohort studies of workers exposed to

fluoride predominantly in the aluminium smelting industry. While

excesses of cancers of different types have been reported in various

studies, the only site for which there was excess risk in several investigations is lung cancer; due to confounding by concomitant exposure

to known human carcinogens in analytical studies of occupationally

exposed workers, the observed excesses cannot be a ttributed to

fluoride exposure per se. Bone cancer was not assessed in the majority

of these studies.

Although the weight of evidence does not support the view that

fluoride causes canc er in humans, the data on bone cancer are

relatively limited.

In early carcinogenicity bioassays conducted by Kanisawa &

Schroeder (1969), Taylor (1954) and Tannenbaum & Silverstone (1949),

the incidence of tumours in mice administered sodium fluoride (in either

the diet or drinking-water) was, in general, not markedly greater than

that observed in controls. Owing to inadequate documentation and to

numerous methodological shortcomings, however, the results of these

investigations do not contribute meaningfully to an assessment of the

weight of evidence of the carcinogenicity of (sodium) fluoride.

The administration of drinking-water containing sodium fluoride

(in amounts estimated to provide intakes ranging from 0.6 to 9.1 mg

fluoride/kg body weight per day) to male and female B6C3F

1 mice overEHC 227: Fluorides

168 a period of 2 years produced a marginal (statistically ins ignificant)

increase in the incidence of hepatoblastoma, compared with the incidence in groups of controls administered drinking-water without added

fluoride; however, this minor increase was not considered “biologically

significant,” since the overall incidence of hepatic tumours (adenoma,

carcinoma, hepatoblastoma) was no t increased in animals receiving

sodium fluoride, and the incidence of all hepatic tumours in these

groups of mice was higher than that in previous NTP carcinogenicity

bioassays (NTP, 1990). Th e marginal increase in the incidence of

malignant lymphoma in female B6C3F

1 mice administe red drinkingwater containing sodium fluoride was considered not to be compoundrelated, since the incidence in the high-dose group was similar to that

obser ved in historical controls (NTP, 1990). No other increases in

tumour incidence were observed; however, failure to attain the maximum tolerated dose may have reduced somewhat the sensitivity of this

study in mice. In a less extensive carcinogenicity bioassay in which the

incidence of osteomas in male and female CD-1 mice receiving 11.3 mg

fluoride/kg body weight per day in the diet was increased compared

with controls (Maurer et al., 1993), the specific role of fluoride in the

etiology of the tumours cannot be determined with certainty, owing to

the infection of these animals with Type C retrovirus (US DHHS, 1991;

Maurer et al., 1993; US NRC, 1993).

The administration of drinking-water containing sodium fluoride

(in amounts estimated to provide intakes ranging from 0.2 to 4.5 mg

fluoride/kg body weight per day) to F344/N rats over a period of

2 years produced a marginal (not statistically significant) increase in

the incidence of oral cavity neoplasms (in males and females) and

tumours in the thyroid gland (in males) (NTP, 1990). The squamous cell

tumours o f the oral cavity were not considered to be compoundrelated, since the incidence of tumours in the high-dose group was not

significantly different from the controls, the incidence of these neoplasms was within the range observed in historical controls and there

was no supporting evidence of focal hyperplasia of the oral mucosa

(NTP, 1990). The marginal increase in thyroid (follicular cell) tumours

was also considered not to be compound-related, since the incidence

of these tumours in the high-dose group was not significantly different

from the co ntrols, the incidence of these neoplasms was within the

range observed in historical controls and the incidence of follicular cell

hyperplasia was not increased in fluoride-exposed animals (NTP, 1990).

The incidence of osteosarcoma in rats with intakes ranging from 0.8 toEvaluation of Human Health Risks and Environmental Effects

169 4.5 mg fluoride/kg body weight per day was not significantly increased,

compared with controls receiving approximately 0.2 mg fluoride/kg

body weight per day (NTP, 1990); however, for the male F344/N rats,

it was reported that “the osteosarcomas occurred wi th a significant

dose response trend ( P = 0.027, by logistic regression)” (NTP, 1990).

In a more limited carcinogenicity bioassay conducted by Maurer et al.

(1990), the administration of diets conta ining sodium fluoride (in

amounts e stimated to provide intakes ranging from 1.8 to 11.3 mg

fluoride/kg body weight per day) to male and female Sprague-Dawley

rats over a period of 95–99 weeks produced no significant increase in

the incidence of any types of tumours, compared with groups of

controls receiving approximately 0.1 mg fluoride/kg body weight per

day, although a small number of malignant tumours of the bone were

observed.

In assessing the evidence for the carcinog enicity of fluoride

derived from studies conducted with laboratory animals, some significance might be attributed to the observation of a dose–response

trend in the occurrence of osteosarcomas i n male F344/N rats

administered sodium fluoride in drinking-water (NTP, 1990). Such a

trend associated with the occurrence of a rare tumour in the tissue in

which fluoride is known to accumulate cannot be casually dismissed.

Moreover, the level of fluoride in the bones of the high-dose group of

male rats in the NTP carcinogenicity bioassay, in which a nonsignificant increase in osteosarcomas was observed, is similar to that

measured in huma ns with a preclinical phase of skeletal fluorosis.

However, the biolog i cal significance of this dose–response trend is

tempered by the lack of statistical significance of the observed excess

in the high-dose males in comparison with controls, as well as by the

absence of a comparable statistically significant trend in the incidence

of osteosarcomas in female F344/N rats or male and female B6C3F

1 mice

receiving comparable amoun ts of inorganic fluoride (NTP, 1990).

Indeed, the levels of fluoride in the bone of (male and female) F344/N

rats and B6C3F

1 mice administered sodium fluoride in drinking-water

were similar (NTP, 1990). No dose–response trend in the incidence of

osteosarcomas was observed in groups of male and female SpragueDawley rats administered diets containing sodium fluoride (Maurer et

al., 1990), even though the levels of fluoride in the bone in the highdose animals were greater than those in the male F344/N rats in which

there was an increase in osteosarco mas in the NTP (1990)

carcinogenicity bioassay; however, there may be variations inEHC 227: Fluorides

170 sen sitivity of the two strains to the effects of fluoride. There is

controversy concerning whether or not the osteomas in male and

female CD-1 mice observed in the carcinogenicity bioassay conducted

by Maure r et al. (1993) should be classified as neoplasms, and a

retrovirus (in addition to fluoride) has been implicated in their etiology;

however, the significant increases in (the highest-dose) fluorideexposed versus control groups (in animals infected with retrovirus), in

a tissue in which fluoride is known to accumulate, adds some weight,

albeit weak, to the evidence of carcinogenicity. Overall, the evidence

regarding the carcinoge nicity of fluoride in laboratory animals is

inconclusive.

There is evidence that fluoride is genotoxic based on the outcome

of in vitro studies. Fluoride is not mutagenic in bacterial cells but is

clastogenic in human and animal cells exposed i n vitro

. Sodium

fluoride induced recessive lethal mutations in Drosphila melanogaster

and cytogenetic damage after intraperitoneal injection in rodents.

Generally, however, in studies in which fluoride was administered to

laboratory animals by routes of expo sure similar to those by which

humans are normally exposed (i.e., orally), fluoride had no effect upon

the frequency of chromosomal aberrations, micronuclei, sister chromatid exchange, DNA strand breaks or sperm morphology. The mechanism by which fluoride could induce genetic alterations is not known;

however, it is not likely due to an interaction between the fluoride ion

and DNA. Rather, it may be a secondary effect of the actions of

flu oride that result from its inhibition of enzymes involved in DNA

synthesis and/or repair.

10.1.3 Exposure–response analysis for adverse effects in bone

A few investigations on skeletal fluorosis or the risk of fractures

include quantitative estimates of the dose–response relationship. Studies in Chin a and India report an increased prevalence of skeletal

fluorosis above the level of 1.4 mg fluoride/litre in drinking-water (Jolly

et al., 1968; Choubisa et al., 1997; Xu et al., 1997). However, su c h

studies suffer from limitations: the diagnostic criteria are not always

specified or consist of self-reported symptoms, and only drinkingwater is considered as a source of exposure. The latter problem is likely

to be important, since other stu dies (Liang et al., 1997; Ando et al.,

1998) estimate that, at least in some regions of China and Indi a

, the

contribution from food can greatly exceed that from water. Therefore,

one cannot rule out that high rates of skeletal fluorosis associated withEvaluation of Human Health Risks and Environmental Effects

171 a level greater than 1.4 mg/litre in drinking-water are due to o ther

exposures. While there is a clear excess of skeletal fluorosis in these

studies for a total intake of 14 mg/day, the quantitative relationship

between total intake of fluoride from different sources and the risk of

skeletal fluorosis cannot be estimated because of substantial

uncertainties in the prevalence of effects in the range of intakes

between 3 and 14 mg/day.

The studies on f

ractures are also difficult to interpret, but for

different reasons:

• Few studies report an interpretable range of exposures to fluoride.

• Results tend to be contradictory, with no clear-cut trend in both

men and women.

• Total intake of fluoride is not estimated.

One exception is represented by a study in China (Li et al., 2001) in

which different sources of exposure have been considered and an

estimate of total intake is presented. In this study, there is an upward

trend for the risk of total fractures above an expos ure of 1.45 mg

fluoride/litre in drinking-water, but only for the highest level of exposure (i.e., >4.32 mg fluoride/litre in drinking-water) was the relative risk

statistically significant (RR

= 1.47; P

= 0.01). In the concentration range

of 1.45–2.19 mg fluoride/litre in drinking-water, corresponding to a total

intake of 6.54 mg/day, there was a relative risk for all fractures of 1.17

and for hip fractures of 2.13 (both not statistically significant).

In summary, estimates based on studies from China and India

indicate that:

• for a total intake of 14 mg/day, there is a clear excess ri s k of

skeletal adverse effects; and

• there is suggestive evidence of an increased risk of effects on the

skeleton at total fluoride intakes above about 6 mg/day.EHC 227: Fluorides

172 

### 10.2 Evaluation of effects on the environment

10.2.1 Exposure

Fluorides are released into the environment naturally through the

weathering and dissolution of minerals, in emissions from volcanoes

and in marine aerosols. Fluorides are also released into the environment via coal combustion and process waters and waste from various

industrial processes, including steel manufacture, primary aluminium,

copper and nickel produc tion, phosphate ore processing, fertilizer

production and use, glass, brick and ceramic manufacturing, and glue

and adhesive production.

Atmospheric fluorides can be transported over large distances as

a result of wind or atmospheric turbulence or removed from the

atmosphere via wet or dry deposition or hydrolysis. Fluoride concentrations in groundwater are primarily due to dissolution fro m local

geological sources. The transport of fluorides in water is influenced by

pH and water hardness and the presence of ion-exchange mate rials

such as clays, and fluoride is usually complexed with aluminium and

calcium. Fluoride is not readily leached from s oils, with adsorption

being strongest at pH 5.5–6.5. Soluble fluorides are bioaccumulated by

some aqu atic and terrestrial biota; however, no information was

identified concerning the biomagnification of fluoride. Terrestrial plants

m ay accumulate fluorides from airborne deposition and, to a lesser

extent, via uptake from soil, as fluoride adsorbs strongly to soil.

Fluoride accumulates in the exoskeleton of invertebrates and the bone

and dental hard tissues of vertebrates.

Surface freshwater fluoride concentrations tend to range from 0.01

to 0.3 mg/litre, whereas typical marine concentrations range from 1.2 to

1.5 mg/litre (Figure 5). Higher concentrations are found in areas where

there is geothermal or volcanic activity. Anthropogenic discharges

lead to increased levels of f l uoride in the environment. Airborne

fluoride exists in gaseous and particulate forms, which are emitted from

both natural and anthropogenic sources. Mean fluoride concentrations

in ambient air are generally less than 0.1 μg/m 3

. Levels may be slightly

higher in urban than in rural locations; however, even in the vicinity of

emission sources, the levels of airborne fluoride usually do not exceed

2–3 μg/m

3 (Figure 6). Fluoride is a component of most types of soil,

with concentrations ranging from 20 to 1000 mg

### 10 -3 

### 10 -2 

### 10 -1 

### 10 0 

### 10 1 

### 10 2Concentration mg F/litre

sea water

freshwater; background

freshwater; geothermal/volcanic

freshwater; local industrial 

## Figure 5: Reported concentrations of fluoride in surface waters Evaluation of Human Health Risks and Environmental Effects

173 

### 10 -3 

### 10 -2 

### 10 -1 

### 10 0 

### 10 1Concentration ug F/m3

Ambient: remote

Ambient: rural

Ambient: urban

Local industrial 

## Figure 6 : Reported concentrations of fluoride in airEHC 227: Fluorides

174 total fluoride /kg in are as without natural phosphate or fluoride

deposits and up to several thousand milligrams per kilogram in mineral

soils with deposits of fluoride (Figure 7). Reported concentrations of

fluoride in vegetation are plotted in Figure 8.



### 10 -2 

### 10 -1 

### 10 0 

### 10 1 

### 10 2 

### 10 3 

### 10 4Concentration mg F/kg

Natural: total

Natural: water soluble

Anthropogenic: total

Anthropogneic: water soluble 

## Figure 7: Reported concentrations of fluoride in soil

10 -1 

### 10 0 

### 10 1 

### 10 2 

### 10 3Concentration mg F/kg

Natural

Natural: lichens

Natural: tree foliage

Local industrial

Local industrial: lichens

Local industrial: tree foliage

Mining

Volcanic: lichens 

## Figure 8: Reported concentrations of fluoride in vegetationEvaluation of Human Health Risks and Environmental Effects

175 10.2.2 Effects

The most sensitive aquatic invertebrate species tested were the

freshwater fingernail clam ( Musculium transversum ), with an 8-week

LC

50 of 2.8 mg fluoride/litre, freshwater net-spinning caddisflies

(Hydropyschidae), with estimated “safe concentrations” ranging from

0.2 to 1.2 mg fluoride/litre, and the marine brine shrimp ( Artemia

salina ), with significant impairment of growth being observed in a 12-

day static test at 5 mg/litre. F o r fish, 20-day LC

50 s for rainbow trout

( Oncorhynchus mykiss ) ranged from 2.7 to 4.7 mg fluoride/litre; in

another study under different conditions (such as higher water hardness), a “safe concentration” of 5.1 mg/litre was estimated. The hatching of fish eggs ( Catla catla ) was delayed at fluoride concentrations

greater than or equal to 3.6 mg fluoride /litre. Behavioural experiments

on adu lt Pacific salmon in soft-water rivers indicate that changes in

water chemistry, due to an incre ase in the fluoride concentration to

0. 5 mg/litre, can adversely affect migration; migrating salmon are

extremely sensitive to changes in the water chemistry of their river of

origin. (Reported toxicity test results for a range of freshwater

organisms are plotted in Figure 9.)



## 10 -1 

## 10 0 

## 10 1 

## 10 2 

## 10 3Concentration mg F/litre Algae: EC50

Algae: LOEC

Algae: NOEC

Invertebrates: LC50

Invertebrates: LOEC

Invertebrates: NOEC

Invertebrates -"Safe concentration"

Fish: LC50

Fish: LOEC

Fish: NOEC

Fish - "Safe concentration"

* - chronic

Fish behaviour LOEC 

## Figure 9: Reported toxicity of fluoride to freshwater organisms



# * *

*EHC 227: Fluorides

176 In laboratory studies, fluoride seems to be toxic for microbial

processes at concentrations found in moderately fluoride-polluted

soils; similarly, in the field, accumulation of organic matter in the

vicinity of smelters has been attributed to severe inhibition of microbial

activity by fluoride.

The LOELs for leaf necrosis in terrestrial plants were at fluoride

concentrations of 0.2–0.4 μg/m 3

. On the basis of effect concentrations

and no-effect concentrations for fumigation experiments, a relationship

was der i ved between the NOEC and the exposure period. If this

relationship is extrapolated to two growing seasons, the derived NOEC

is approximately 0.2 μg fluoride/m 3

. Several short-term solution culture

studies have identified a toxic threshold for fluoride ion act ivity

ranging from approximately 50 to 2000 μmol fluoride/litre. Toxicity is

specific not only to plant species, but also to ionic species of fluoride,

where some aluminium–fluoride complexes present in solution culture

may be toxic at activities of 22–357 μmol fluoride/litre, whereas

hydrogen fluoride is toxic at activities of 71–137 μmol/litre. Due to the

complexity of fluoride availability in soil and the high concentrations

generally required for plant toxicity, no soil effect range was defined.

The growth rate of young starlings was significantly reduced at

a fluoride concentration of 13 mg /kg body weight. Fluoride has been

shown to cause adverse effects on domesticated animals in both the

laboratory an d the field. Recent studies have shown this to be an

ongoing problem. Tolerance le vels have been identified for domesticated animals, with the lowest values for dairy cattle at 30 mg/kg feed

or 2.5 mg/litre drinking-water. The lowest dietary concentration of

fluoride to cause fluoros is in white-tailed deer ( O docoileus virginianus ) was 35 mg/kg. Field surveys have found that bone fl uoride

concentrations of >2000 mg /kg in young deer and >3000 mg /kg in

cotton rats ( Sigmod on hispidus ) are associated with fluorosis in all

individuals. Osteofluorotic alterations have been diagnosed in deer

with bone fluoride concentrations of >4000 mg /kg.

10.2.3 Evaluation

In the freshwater environment, natural fluoride concentrations are

usually lower than those expected to cause toxicity in aquatic organisms. However, aquatic organisms might be adversely affected in theEvaluation of Human Health Risks and Environmental Effects

177 vicinity of anthropogenic discharges. Fluoride toxicity is dependent on

water hardness, with organisms living in soft-water environments at

greater risk than those in hard-water areas. Because of the particular

sensitivity of some freshwater invertebrates and Pacific salmon, fluoride concentrations in soft-water ecosystems (low in calcium) should

not be increased by anthropogenic inputs to values exceeding 0.5 mg

fluoride/litre. Aquatic organisms that inhabit areas with high natural

fluoride levels from geothermal or volcanic activity would be expected

to be adapted to such conditions.

Comparing the long-term NOEC for plants with air concentrations

reveals that sensitive species growing near anthropogenic sources of

fluoride are at risk. In the field, anthropogenic sources of fluoride have

been shown to be corr e lated with damage to local terrestrial plant

communities. However, these adverse e ffects are often difficult to

attribute to fluoride alone, due to the presence of other atmospheric

poll utants. Fluoride is generally strongly adsorbed by soils. Consequently, plant uptake via this pathway is relatively low, and leaching

of fluoride through soil is minimal. However, high fluoride concentrations in soil from natural and anthropogenic sources, combined with

soil properties that minimize fluoride adsorpt ion (below pH 5.5, low

carbon and clay content), can lead to increased pla n t availability of

fluoride. Plant availability is also dependent on the io nic species of

fluoride prese nt in the soil solution. Above soil pH 5.5, fluoride in

solution is predominantly the free fluoride ion, CaF + or MgF + , which is

relatively less available to uptake via the plant root. Below soil pH 5.5,

aluminium–fluoride complexes can become dominant in soil solution,

potential ly increasing plant availability of fluoride. However, plant

toxicity from uptake of fluoride from soil is rare.

Concentrations of fluoride in vegetation in the vicinity of fluoride

emission sources, such as aluminium smelters, can be higher than the

lowest dietary effect concentration reported for mammals in laboratory

experiments. Fluorosis in do mesticated animals has been reported.

Incidents have originated both from natural fluoride sources, such as

volcanic eruptions and the underlying geology , and from

anthropogenic sources, such as fluoride-emitting industries and power

stations. Guidance is available on fluoride tolerance levels in feed and

water; however, there are still some areas reporting fluorosis incidents

in livestock due to uptake of fluoride-rich mineral supplements and

drinking-wa ter. Furthermore, there is a potential risk from fluoridecontaminated pasture and soil ingestion due to the long-term use ofEHC 227: Fluorides

178 pho sphate fertilizers containing fluoride as an impurity. Fluorideinduced effects, such as lameness and tooth damage, have also been

reported in wild ungulates, such as deer, and in small mammals close

to anthropogenic sources of fluoride. Several studies have demonstrated that wild deer and rodents are sensitive bioindicators of

environmental pol lution by fluorides and can, therefore, be used as

sentinels for the identification of fluoride hazards to the environment.

Within some areas of Europe, where effective emission control measures have been introduced following clean air legislation, the bone

fluoride levels in deer have fal len by around 70% in the last 15–

20 years. Based on the correlation between bone fluoride levels and

fluorosis, it can be assumed that the prevalence and severity of fluoride-induced effects in the wild deer population in these areas will

probably have fallen at a similar rate. However, it should be noted that

in other regions of Europe, fluoride discharges to the environment

have not shown the same downward trend during this period, and this

is reflected in the bone fluoride levels of mammals from these areas.179 

### 11. CONCLUSIONS AND RECOMMENDATIONS

FOR PROTECTION OF HUMAN HEALTH AND THE

ENVIRONMENT

11.1 Conclusions

All organisms are exposed to various levels of fluoride from

natural and/or anthropogen i c sources. Very high intakes have been

observed in areas worldwide in which the environment is rich in natural

fluoride and where groundwater high in fluoride is consumed.

Fluor ide in dental products may form a source of exposure for

many individuals. Increased exposures migh t be experienced in the

vicinity of anthropogenic point sources.

Fluoride has both beneficial and detrimental effects on human

health, with a narr ow range between the intakes associated with its

beneficial and adverse health effects.

Effects on the teeth and skeleton are observed at exposures below

those associated with the development of other organ - or tissuespecific adverse health effects. Effects on the bone are considered the

most relevant in assessing the adverse effects of long-term exposure

of humans to fluoride.

Skeletal fluorosis is a crippling disabilit y affecting millions of

people in various regions of Africa, India and China, which has major

public health and socioeconomic impact. Intake of fluoride in the water

and/or foodstuffs is the primary causative factor in the incidence of

endemic skeletal fluorosis. In parts of China, a large number of people

have been shown to be impacted by the indoor burning of coal with a

high fluoride content. There are few data from which to estimate total

exposure to and the bioavailability of fluoride, and there are inconsistencies in the characterization of its adverse effects.

There is clear evidence from India and China that skeletal fluorosis

and an increased risk of bone fractures occur at a total intake of 14 mg

fluoride/day, and there is evidence suggestive of an increased risk of

bone effects at total intakes above about 6 mg fluoride/day.EHC 227: Fluorides

180 Excess exposure to bioavailable fluori de constitutes a risk to

aquatic and terrestrial biota.

Fluoride-sensitive species can be used as sentinels for the identification of fluoride hazards to the environment.



### 11.2 Recommendations

Consideration should be given to the levels of fluoride and the

means of applica tion required to maximize the beneficial effects of

fluoride while minimizing the potential for adverse effects on the

skeleton and teeth.

It is recommended that international and nati onal agencies

identify areas in which health effects related to fluoride are found,

identify the primary sources of fluoride exposure and take appropriate

action(s) to reduce exposure.

It is reco mmended that international and national agencies

support rese arch to better characterize total fluoride exposure,

exposure–health relationships and the various factors that modify and

influence these.

In areas exposed to increased fluoride from an thropogenic

sources, fluoride levels in the environment should be mo n itored for

changes using appropriate bioindicators.181 

### 12. FURTHER RESEARCH

There is a need to improve knowledge on the accumulat ion of

fluoride in organisms and on how to monitor and control this.

The biological effects associated with fluoride exposure should be

better characterized.



### 12.1 Health effects research

There is a need:



### # to determine total dietary fluoride intakes and bioavailab ility

and elucidate the relative contribution of water and foodstuffs

to fluoride intake;



### # to develop robust markers of fluoride exposure and effects in

animals and humans to further elucidate the mechan i sms

(including work on a molecular level) of fluoride’s effects on

bone, and how these might be reversed;



### # to des ign high-quality studies at population and individual

levels, to characterize the adverse effects of fluoride on bone,

cancer and reproductive outcomes; available data sets should

be exploited to generate sound epidemiological observations

—

for example, through a linkage between population registries in

high-exposure areas and cancer or other disease registries;



### # to characterize the potential interactions of fluoride with other

elements

— aluminium, copper, lead, arsenic, selenium

— in the

environment and their influence on fluoride bioavailability and

mobility;



### # to clarify quantitatively and mechanistically how environmental

f actors (e.g., atmospheric pollution, coal burning, climate,

rainfall, altitude) and lifestyle (including occupation) influence

fluoride exposure;EHC 227: Fluorides

182 

### # to characterize the short- and long-term turnover of fluoride in

the body and how factors such as bone remodelling and renal

function influence this;



### # to improve the routine quantitative analysis of fluoride in body

fluids;



### # to develop robust biomarkers in animals and humans;



### # to investigate the passage of fluoride through the food-chain

from the geochemical environment to the diet;



### # to determine if fluoride has potential adverse effects on other

systems, including the neurological system;



### # to investigate what factors (age, genetic polymorphisms, diet,

etc.) might make particula r population subgroups more

susceptible to the effects of fluoride; and



### # to determine the mechanisms associated with the clastogenicity

of fluoride.

Additional research needs include studies on the interactions

of fluoride with nuclear proteins (i.e., histones) and polyamines as well

as on factors influencing the membrane transport of fluoride.



### 12.2 Environmental effects research

There is a need:



### # for the identification of more fluoride-sensitive species from different environmental compartments for use as bioindicators;



### # to define critical measures of fluoride concentrations in soil to

assess plant fluoride availability (i.e., when plant fluoride concentrations increase significantly from background or, to a lesser

extent, become toxic to plants);



### # to determine the bioavailability of fluoride in animals that ingest

significant quantities of soil in their diet (e.g., cattle);Further Research

183 

### # for the standardization of the assessment of the effects of fluoride

on wild animals; and



### # to improve the quantitative routine analysis of fluoride in soil and

plants.184 

### 13. PREVIOUS EVALUATIONS BY

INTERNATIONAL BODIES

Fluoride (used in dri nking-water) is considered to be “not

classifiable as to its carcinog enicity to humans” (Group 3) in the

classification scheme of the International Agency for Research on

Cancer (IARC, 1987).

The WHO recommended guideline value for fluoride in drinkingwater is 1.5 mg/litre (WHO, 1993, 1996b). It was also noted that “in

setting national standards for fluoride, it is particularly important to

consider climatic conditions, water intake and intake of fluoride from

other sources (e.g ., from food and air). In areas with high natural

fluoride levels, it is recognized that the guideline value may be difficult

to achieve in some circumst ances, with the treatment technology

available” (WHO, 1996b).

An expert consultation of the WHO on trace elements in human

nutr ition and health (WHO, 1996c) categorized fluoride among

“potentially toxic elements, som e of which may nevertheless have

some essential functions at low leve ls.” Fluoride was regarded as

“essential,” sin ce the consultation “considered resistance to dental

caries to be a physiologically important function.” The consultation

indicated that total intakes at 1, 2 and 3 years of age “should, if

possible, be limited to 0.5, 1.0 and 1.5 mg/day, respectively,” with not

more than 75% coming in the form of soluble fluorides from drinkingwater. It was also noted that “adult intakes exceeding 5 mg of fluoride

per day from all sources probabl y pose a significant risk of skeletal

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### RESUME ET CONCLUSIONS

Ce document est consacré à l’exposition environn e mentale aux

fluorures, minéraux principalement, et à ses effets sur l’Homme, les

animaux et les autres êtres vivants. Les données prises en compte

concernent le fluorure d’hydrogène, le fluorure de calcium, le fluorure

de sodium, l’hexafluorure de soufre et les silicofluorures étant donné

que ce sont les fluorures minéraux les plus importants du point de vue

des quantités libérées et des concentrations dans l’environnement

ainsi que des effets toxicologiques exercés sur les organismes vivants.



### 1. Identité, propriétés physiques et chimiques et

méthodes d’analyse

Le fluorure d’hydrogène (HF) s e présente sous la forme d’un

liquide ou d’un gaz incolore, à l’odeur âcre, qui est très soluble dans

les solvants organiques et dans l’eau avec laquelle il donne de l’acide

fluorhydrique. Le fluorur e de calcium (CaF

2 ) est un solide incolore,

relativement insoluble dans l’eau et les acides ou bases diluées. Le

fluorure de sodium (NaF) est un solide incolore à blanc, modérément

soluble dans l’eau. L’hexafluorure de soufre (SF

6 ) est un gaz incolore

et inodore, chimiquement inerte, qui est légèrement soluble dans l’eau

et facilement soluble dans l’éthanol et les bases.

Le dosage des fluorures libres s’effectue le plus couramment par

voie électrochimique au moyen d’une électrode sélective. On estime

que les techniques de microdiffusion constituent le moyen le plus

fiable pour la préparation des échantillons (c’est-à-dire par libération

de d’anions fluorure libres à partir de complexes organiques ou minéraux).



### 2. Sources d’exposition humaine et environnementale

Il y a libération naturelle de fluorures dans l’environnement par

suite de l’érosion et de la dissolution des roches et des minéraux, à la

faveur d’émissions par les volcans ou par l’ i ntermédiaire d’aérosols

marins. La combustion du charbon ainsi que les eaux usées provenant

de diverses opérations industrielles, comme la fabrication de l’acier, la

producti on d’aluminium, de cuivre et de nickel, le traitement desRésumé et Conclusions

233 minerais de phosphates, la production et l’utilisation d’engrais

phosphatés, la fabr

ication de verre, de briques et de céramiques ou

encore la production de colles et d’adhésifs. L’épandage de pesticides

fluorés ainsi que la fluoration de l’eau destinée à la boisson sont également des sources anthropogéniques de fluor. Les données disponibles

montrent que l’extraction et l’utilisation des phosphates ainsi que la

production de l’aluminium sont les sources industrielles qui rejettent

le plus de fluorures dans l’environnement.

Le fluorure d’hydrogène est un produit industriel important qui

est principalement utilisé pour la production de cryolithe synthétique

(Na

3 AlF

6 ), de fluorure d’aluminium (AlF

3 ), des alkylates ou isoparaffines qui entrent dans la composition de l’essence automobile et de

chlorofluorocarbures, avec une consommation annuelle mondiale de

plus de 1 million de tonnes. On l’emploie également pour le décapage

d es dispositifs à semi-conducteurs, le décapage, la gravure et le

dépolissage du verre, le décapage de la brique et de l’aluminium, le

tannage du cuir ainsi que pour la préparation des produits antirouille

vendus dans le commerce. Le fluorure de calcium est utilisé comme

fondant dans la production de l’acier, du verre et de l’émail et il sert de

matière première pour la préparation de l’acide fluorhydr ique et du

fluorure d’hydrogène anhydre ou encore d’électrolyte dans la préparation de l’aluminium. Le fluorure de sodium est utilisé pour la fluoration

réglementée de l’eau de boisson, comme conservateur dans les colles,

le verre et l’émail, comme fondant dans la production de l’acier et de

l’aluminium et comme agent conservateur du bois. L’acide fluorosilicique (H

2 SiF

6 ) et l’hexafluorosilicate de disodium (Na

2 SiF

6 ) sont

utilisés pour la fluoration de l’eau.



### 3. Transport, distribution et transformation dans

l’environnement

Les fluorures présents dans l’atmosphère peuvent s e trouver sous

forme de gaz ou de particules. Ils sont susceptibles d’être transportés

sur de grandes distances par les vents ou par suite des turbulences

atmosphériques ou être éliminés de l’atmosphère par dépôt à sec, par

les précipitations ou encore par hy drolyse. A l’exception de l’hexafluorure de soufre, on estime que les fluorures ne restent vraisemblablement pas très longtemps dans la troposphère et qu’ils me migrentEHC 227: Fluorides

234pas vers la stratosphère. La durée de séjour atmosphérique de l’hexafluorure de soufre va de 500 ans à plusieurs milliers d’années.

Le transport et la transformation des fluorures dans l’eau dépendent du pH, de la dureté de l’eau et de la présence de substances échangeuses d’ions comme les argiles. Le transport des fluorures s’effectue

par le cycle de l’eau sous forme de complexes avec l’aluminium.

Dans le sol, le transport et la transformation des fluorures

dépendent également du pH, mais aussi de la formation de complexes,

notamment avec l’aluminium et le calcium. L’adso rption à la phase

solide du sol est plus forte lorsque le pH est acide (5.5-6.5). Le lessivage des fluorures présents dans le sol ne se fait pas spontanément.

L’absorption des fluorures par les êtres vivants dépend de la voie

d’exposition, de la biodisponibil ité des composés et de la cinétique

d’absorption et d’excrétion dans les divers organismes. Certains biotes

aquatiques et terrestres accumu lent les fluorures solubles. On ne

possède cependant aucune information sur la bioamplificati o n des

fluorures dans les chaînes alimentaires aquatiques et terrestres.

Les plantes terrestres peuvent accumuler des fluorures aéroportés

qui se sont déposés ou fixer ceux qui étaient déjà présents dans le sol.



### 4. Concentrations dans l’environnement et exposition

humaine

La teneur des eaux de surface en fluorures peut varier selon le lieu

et la proximité des sources d’émission. Elle va généralement de 0,01 à

0,3 mg/litre. L’eau de mer contient plus de fluorures que l’eau douce,

avec une concentration comprise entre 1,2 et 1,5 mg/litre. Des concentrations plus fortes ont été relevées dans des zones où les roches sont

riches en fluorures et une teneur élevée en fluorure minéral s’observe

généralement dans les région où existe une activité géothermique ou

volcanique (par ex. 25-50 mg/litr e dans les sources chaudes et les

geysers et même 2800 mg/litre dans certains lacs de la vallée du Rift, en

Afrique orienta le). Les décharges résultant de l’activité humaine

peuvent également entraîner la présence de concentrations élevées de

fluorures dans l’environnement.Résumé et Conclusions

235 Les fluorures peuvent être présents dans l’air sous forme gazeuse

ou particulaire par suite d’émissions naturelles ou anthropogéniques.

Les fluorures émis sous forme gazeuse ou particul aire se déposent

généralement au voisinage de la source de l’émission, encore que ceux

qui sont présents dans certaines particules puissent réagir sur d’autres

constituants atmosphériques. La distribution et le dépôt des fluorures

aéroportés dépend de l’intensité de l’émission, des conditions météorologiques, de la granulométrie des particules et de leur réactivité

chimique. Dans les zones qui ne sont pas situées au voisinage

immédia t des sources d’émissions, la concentration moyenne en

fluorures dans l’air ambiant est généralement inférieure à 0,1 μg/m 3

. Elle

peut être légèrement plus élevée en ville qu’à la campagne. Toutefois,

même à proximité de sources d’émissions, la teneur de l’air en fluorures

ne dépasse généralement pas 2 à 3 μg/m 3

. Dans les régions de la Chine

où l’on utilise de la houille riche en fluorures comme combustible, on

fait état de concentrations dans l’air ambiant pouvan t atteindre 6

μg/m 3

.

Les fluorures sont des constituants de presque tous les types de

sols, avec des teneurs totales allant de 20 à 1000 μg/g dans les régions

où il n’y a pas de gisements naturels de phosphates ou de fluorures et

à des concentrations de plusieurs milliers de microgrammes par gramme

dans les sols où existent de tels gisements. Les fluorures présents dans

l’atmosphère à l’état gazeux ou particulaire ont tendance à s’accumuler

dans les couches superficielles du sol, mais peuvent m igrer vers la

zone radiculaire, même dans les sols calca ires. La rétention des

fluorures dans le sol dépend essentiellement de la teneur en argile et en

carbone organique ainsi que du pH. Les fluorures présents dans le sol

y sont surtout associés à la fraction colloïdale ou argileuse. Pour tous

les types de sols, c’est la teneur en fluor ures solubles qui est

biologiquement importante pour la faune et la flore.

Les organismes aquatiques peuvent absorber des fluorures soit

directement à partir de l’eau, soit, dans une moindre mesure, à partir de

leur nourriture. Les fluorures ont tendance à s’accumuler dans l’exosquelette ou dans les tissus osseux des animaux aquatiques, selon le

cas. Chez le krill, par exemple, on a mesuré des concentrations

moyennes de fluorures supérieures à 2000 mg/kg dans l’exosquelette.

Chez les mammifères marins comme le phoque ou la baleine, la teneur

moyenne des os en fluorures peut aller de 135 à 18 600 mg/kg de poids

sec.EHC 227: Fluorides

236 Chez les biotes terrestres, la concentration en fluorures est plus

élevée dans les zones où la présence de fluorures d’origine naturelle ou

anthropogénique est plus importante. On utilise beaucoup les lichens

comme bioindicateurs de la présence de fluorures. Dans des lichens

poussant dans un rayon de 2 à 3 km autour de sources d’émission de

fluorures, on a trouvé des concentrations de l’ordre de 150-250 mg/kg,

alors que la concentration de fond est de moins de 1 mg/kg.

La majorité des fluorures présents dans le sol sont insolubles et

par conséquent, peu biodisponibles pour les végétaux. Toutefois, une

forte teneur du sol en fluorures, un pH acide ou la présence d’argile ou

de matières organiques peuvent accroître la teneur de f luorures en

solution, ce qui va en favoriser leur fixation par le système radiculaire

de la plante. Si des fluorures sont captés au niveau de la racine, leur

concentration sera souvent plus élevée dans cette dernière que dans

les pousses en raison de leur faible mobilité dans la plante. La plupart

des fluorures pénètrent dans les tissus végétaux sous forme gazeuse

au nivau des stomates et ils s’accumulent dans les feuilles. De petites

quantités de particules fluorées peuvent également pénétrer dans la

plante en traversant l’épiderme et la cut icule. Une très large surveillance s’exerce sur la végétation située aux alentours des sources

d’émission anthropogéniques. On a constaté l’existence d’une corrélation entre la concentration de fluorures dans la végétation et la croissance annuelle, le régime des vents, la distance à la source d’émission

de fluorures et la teneur en fluorure d’hydrogène des rejets atmosphériques.

Les fluorures s’accumulent dans les tissus osseux des vertébrés

terrestres en fonction d’un certain nombre de facteurs tels que le

régime alimenta ire et la présence d’émissions de fluorures dans le

voisinage. Par exemple, on a trouvé des une concentration moyenne de

fluorures comprise entre 7000 et 8000 mg/kg dans les os de pe t its

animaux vivant à proximité d’une usine de production d’aluminium.

Les fluorures se retrouvent dans tout l’environnement, aussi les

sources d’eau potable ont-elles des chances d’en contenir au moins

une petite quantité. La teneur de l’eau de boisson non fluorée en

fl uorures d’origine naturelle (il s’agit de l’eau à laquelle on n’a pas

ajouté de flurorures pour prévenir les caries) varie dans d’importantes

proportions, en fonction de l’environnement géologique de la source.

La concentration peut atteindre 2,0 mg/litre; toutefois, dans les régionsRésumé et Conclusions

237 du monde où existe une endémie fluorot ique osseuse ou dentaire

parfaitement attest é e, la concentration des fluorures dans l’eau de

consommation va de 3 à plus de 20 mg/lit re. Là où l’eau de

consommation est fluorée intentionnellement pour prévenir les caries,

la teneur en fluorures est de 0,7 à 1,2 mg/litre.

Presque toutes les denrées alimentaires contiennent au moins des

traces de fluorures. Ils sont présents à forte concentration dans le

poisson et les feuilles de thé en sont particulièrement riches. La

quantité de fluorures dans le thé infusé dépend de la concentration en

fluorures solubles dans les feuilles et de la durée d’infusion. L’utilisation d’engrais à base de superphosphates, qui contiennent une forte

p roportion de fluorures (1 à 3 %) comme impuretés, pour traite r les

terres agri coles, n’accroît pas sensiblement la teneur des produits

alimentaires en fluorures, car le coefficient de transfert du sol à la

plante est généralement faible. Toutefois, selon une étude récente, si

les conditions pédologiques s’y prêtent et que l’on traite les sols avec

des phosphates suffisamment riches en impuretés flurorées, la fixation

de fluorures par la plante peut augmenter. En revanche, l’irrigation des

cultures avec de l’eau relativement pauvre en fluorures (moins de

3,1 mg/litre), n’entraîne généralement pas d’augmentation de la teneur

des produits alimentaires en fluorures. Ce la dépend cependant de

l’espèce végétale en cause et de la concentration des fluorures dans le

sol et l’eau. La concentration des fluorures dans les aliments est

sensiblement modifiée par la teneur en fluorures de l’eau utilisée pour

leur préparation ou leur fabrication, notamment dans le cas des boissons et des aliments secs - comme par exemple les aliments pour

nourrissons que l’on dilue dans l’eau avant consommation. La concentration des fluorures dans les cultures vivrières situées à proximité de

s ources d’émission industrielles peut être plus élevée, lorsque les

produits n e sont ni lavés ni transformés, que dans des cultures

identiques mais situées dans des zones où il n’y a pas d’exposition

d’origine industrielle. On a constaté que dans des aliments pour

nourrissons vendus aux Etats-Unis et qui s e présentaient sous la forme

de produits à base de soja prêts à être consommés ou encore de concentrés liquides, la concentration en fluorures était plus élevée que

dans les produits à base de lait; on n’a cependant constaté a u cune

différence entre ces derniers et les aliments pour nourrissons à base de

poudre de s oja. La présence de fluorures a été décelée dans le lait

maternel à des concentrations comprises entre <2 à et environ 100

μg/litre, la plupart des valeurs se situant entre 5 et 10 μg/litre.EHC 227: Fluorides

238 On ne dispose que de données limitées sur la teneur de l’air

intérieur en fluorures. Aux Pays-Bas, on a observé une concentration

en fluorures gazeux qui allait de <2 à 49 μg/m 3 dans l’air de cinq

habitations cons t ruites avec du bois traité par un conservateur

contenant 56 % de fluorure. En Chine, on a trouvé des concentrations

pouvant atteindre 155 μg/m 3 dans des échantillons d’air prélevés dans

des maisons où l’on brûlait du charbon à forte teneur en fluorures.

Les produit s dentifrices destinés aux adultes qui sont comm ercialisés dans de nombreux pays contiennent généralement des

fluorures à des concentrations comprises entre 1 0 00 et 1500 μg/g;

certains produits plus spécialement destinés aux enfants ont une

teneur plus faible en fluorures, qui va de 250 à 500 μg/g. Les produits

d’hygiène bucco-dentaire tels que pâtes dentifrices, bains de bouche

et suppléments fluorés, s e révèlent être une so urce importante de

fluorures. Les bains de bouche destinés à un usage quotidien contiennent généralement de 230 à 500 mg de fluorures par litre, alors que ceux

qui sont destinés à être utilisés toutes les semaines ou tous les 14 jours

peuvent en contenir entre 900 et 1000 mg/litre.

L’exposition individuelle aux fluorures varie probablement beaucoup, mais l’inhal ation de fluorures présents dans l’atmosphère ne

contribue en général que faiblement à l’apport total de ces substances.

Chez l’adulte, ce sont les produits alimentaires et l’eau de boisson qui

en constituent la principale voie d’apport. Dans les régions du monde

où l’on utilise du charbon riche e n fluor pour se chauffer et faire la

cuisine, l’air intérieur et les aliments, qui contiennent dès lors une

proportion plus importante de fluorures, contribuent également pour

une part imp ortante à l’apport de ces substances. Les nourrissons

alimentés à l’aide de produits formulés reçoivent 50 à 100 fois plus de

fluorures que ceux qui sont nourris exclusivement au sein. L’ingestion

de dentifrice par les jeunes enfants représente une fraction importante

de la dose totale de fluor qu’ils absorbent. On estime en général que

l’absorption de fluorures par les enfants et les adolescents ne dépasse

pas environ 2 mg/jour. Bien que la dose de fluorures absorbée

quotidiennement par un adulte puisse être supérieure en valeur

absolue à celle qui est absorbée par un enfant, cette dernière, exprimée

en mg par kg de poids corpo rel, peut être plus élevée que pour un

adulte. Dans les régions du monde où la concentration des fluorures

dans l’environnement peut être excessivement élevée et où le régime

alimentaire peut comporter des produits riches en fluor, on estimeRésumé et Conclusions

239 qu’ un adulte peut en absorber jusqu’à 27 mg par jour, la principale

source étant l’eau de boisson provenant de sour ces souterraines

captées dans des couches géologiques riches en fluor.

Les personnes qui utilisent du matériel de soudage ou qui sont

e mployées au traitement des minerais d’aluminium, de fer ou de

phosphates subissent vraisemblablement une exposition

professionnelle par inhalation ou contact cutané. Selon d es études

relativement récentes, la concentration en fluorures dans l’air des halls

d’électrolyse des usines de production d’aluminium est de l’ordre de

1 mg/m

3

.



### 5. Cinétique et métabolisme chez l’Homme et les

animaux de laboratoire

Chez l’Homme comme chez les anima ux de laboratoire, c’est

principalement au niveau de l’estomac et de l’intestin que les fluorures

ingérés passent dans la circulation générale et cette résorption dépend

de la solubilité aqueuse relative de la substance en cause. Les fluorures

solubles sont presque entièrement résorbés dans les voies digestives,

mais le taux de résorption peut être réduit par la formation de complexes

avec l’aluminium, le phosphore, le magnésium ou le calcium. Les

fluorures particulaires ou gazeux qui pénètrent dans les voies

respiratoires sont partiellement à totalement résorbés, le taux de résorption étant fonction de la solubilité et de la granulométrie.

Les fluorures sont rapidement amenés par le courant sanguin dans

l’eau intracellulaire et extracellulaire des différents tissus; cependant

chez l’Homme et les animaux de laboratoire, environ 99 % de la charge

totale de l’organisme en fluorures est retenue par les os et les dents.

Les fluorures sont incorporés dans le réseau cristallin des tissus

dentaire et osseux.

Les fluorures traversent la barrière placentaire et il passent ainsi

de la mère au foetus. Ils sont pr incipalement éliminés par la voie

urinaire. Chez le nourrisson, le fluor est retenu à environ 80-90 %; chez

l’adulte, le chiffre correspondant est d’environ 60 %. Une modification

du débit urinaire ou du pH peut faire varier ces valeurs.

Les fluorures sont prés ents dans tous les organes, tissus et

liquides de l’organisme. Dans une communauté des Etats-UnisEHC 227: Fluorides

240 alimentée en eau fluorée, on a relevé des concentrations dans le sang

total qui allaient de 20 à 60 mg/litre. Chez 127 sujets dont l’eau de

boisson avait une teneur en fluorures de 5,03 mg/litre, on a trouvé un

taux plasmatique moyen de 106 ± 76 ( 

### F ) μg/litre. Le plasma et le sérum

ont pratiquement la même teneur en fluorures. En ce qui concerne les

tissus calcifiés, c’est généralement dans les os, la dentine et l’émail que

la concentration est la plus élevée. Dans les os, cette concentration

varie en fonction de l’âge et du sexe ainsi que de la nature et de la

partie de l’os concernée. On estime qu’elle est le reflet de l’exposition

à long terme du sujet. Dans l’ém a il dentaire, la concentration en

fluorures diminue exponentiellement avec la distance à la surface et elle

dépend de la localisation, de l’usure des faces de la dent, de

l’exposition pa r la voie générale et des applications topiques de

fluorures auxquelles il a pu être procédé. La teneur en fluorures des

tissus mous correspond à la concentration sanguine. Chez un sujet en

bonne santé, la concentration urinaire des fluorures est liée à l’apport

de fluor. Chez des sujets exposés de par leur profession à des fluorures

présents dans l’air ou résidant dans des zones où la fluorose est

endémi que, on constate une élévation de la teneur des urines en

fluorures.



### 6. Effets sur les mammifères de laboratoire et les

systèmes d’épreuve in vitro

Chez des rats recevant des fluorures par voie orale pendant des

périodes allant de 3 à 5 semaines, diverses études ont mis en évidence

des effets au niveau du squelette consistant en une inhibition de la

minéralisation et de la formation du tissus osseux, un retard dans la

guérison des fractures ainsi qu’une réduction du volume osseux et de

la synthèse du collagène. Des études à moyen terme au cours

desquelles des souris ont reçu pendant 6 mois une eau de boisson

contenant des fluorures à une concentration supérieure à 4,5 mg/kg de

poids corporel, ont révélé les effets suivants : anomalies du remodelage

osseux, mégalocytose hépatique, néphrose, minéralisation du myocarde, nécrose ou dégénérescence des tubes séminifères du testicule.

Une étude de cancérogénicité très complète au cours de laquelle

des groupes de rats F344/N et des souris B6C3F

1 des deux sexes ont

reçu pendant 2 ans une eau de boisson contenant jusqu’à 79 mg/litre

de fluorure de sodium, n’a révélé aucune augmentation significative,

dans l’un et l’autre groupe, de l’incidence des tumeurs, quelles qu’ellesRésumé et Conclusions

241 soient. On a bien observé une tendance statistiquement significative

à l’accr oissement des ostéosarcomes chez les mâles lorsqu’on

augmentait l’exposition au fluorure, mais l’incidence restait cependant

dans les mêmes limites que chez les témoins historiques.

Une autre étude de cancérogénicité de 2 ans a été effectuée sur

des rats Sprague-Dawley, qui ont été exposés par voie alimentaire à des

doses quotidiennes de fluorures allant jusqu’à 11,3 mg/kg p.c.; aucune

augmentation statistiquement significative n’a été relevée dans l’incidence des ostéosarcomes ou d’autres tumeu rs. Il existe une autre

étude, qui fait état d’un accroissement de l’inc i dence des ostéosarcomes chez des souris qui avaient reçu des doses quotidienne de

fluorures allant jusqu’à 11,3 mg/kg p.c., mais les résultats sont difficiles

à interpréter car les animaux étaient infectés par un rétrovirus de type

C.

En règle générale, les fluorures n’ont pas d’action mutagène sur

les cellules procaryotes. On a montré qu’ils augmentaient la fréquence

des mutations au n iveau de certains locus dans des cellules de

lymphome murin et des cellules lymphoblastoïdes humaines en culture,

mais ces mutations ne semblent pas être des mutations ponctuelles et

sont probablement plutôt dues à des lésions chromosomi ques. Les

fluorures ont des effets clastogènes sur divers types de cellules. On

pense que cette activité clastogène s’explique par un effet sur la

synthèse ou la réparation de l’ADN, plutôt que par une interaction

directe avec cette molécule. Dans la plupa rt des études au cours

desquelles des fluorures ont été administrés par voie orale à des

rongeurs, on n’a relevé aucun effet sur la morph ologie des spermatozoïdes, ni sur la fréquence des aberrations chromosomiques, des

micronoyaux, des échanges entre chromatides-soeurs ou des ruptures

des brins de l’ADN. On a toutefois ob s ervé des lésions

cytogénétiques au niveau de la moelle osseuse ainsi que des anomalies

affectant la morphologie des spermatozoïdes lorsque ces substances

étaient administrées par voie intrapéritonéale à des rongeurs.

Des études récentes au cours desquelles des animaux de

laboratoire ont reçu des fluorures ajoutés à leur eau de boisson, n’ont

pas mis en évidence d’effets sur la reproduction ou le développement.

Des anomalies histopathologiques ont cependant été relevées au

niveau des organes reproducteurs chez des lapins mâles qui avaient

reçu par voie orale pendant 18 à 29 mois une dose quotidienne de 4,5

mg de fluorures par kg de poids corporel, chez des souris mâlesEHC 227: Fluorides

242 soumises quotidiennement pendant 30 jours à u ne dose orale de

fluorures supérieure ou ég ale à 4,5 par kg p.c. ainsi que chez des

lapines qui en avaient reçu pendant 100 jours une dose quotidienne

supérieure ou égale à 10 mg/kg p.c. administrée par voie sous-cutanée.

Des effets génésiques indésirables ont également été observés chez

des souris femelles à qui on avait administré par voie orale une dose de

fluorures supérieure ou égale à 5.2 mg/kg p.c. 6 à 15 jours après

l’accouplement ainsi que chez des lapins mâles qui en avaient reçu une

dose quotidienne supérieure ou égale à 9.1 mg/kg p.c. pendant 30

jours.



### 7. Effets sur l’Homme

Les études épidémiologiques consacrées aux effets des fluorures

sur la santé humaine concernent l’exposition professionnell e des

travailleurs, notamment ceux qui sont affectés à la production de

l’aluminium, ain si que l’exposition des populations consommant de

l’eau fluorée. Un certain nombre d’études d’épidémiologie analytique

porta n t sur des travailleurs exposés à des fluorures de par leur profession, font ressortir une augmentation de l’incidence des cancers du

poumon et de la vessie ainsi qu’un accroissement de la mortalité due

à ces cancers ou à des tumeurs d’autre localisation. Il n’y a toutefois

généralem

ent pas de tendance cohérente et dans certaines de ces

études l’augmentation constatée de la morbidité et de la mortalité par

cancer peut être attribuée à l’exposition des travailleurs à d’autres

substances que les fluorures.

Un grand nombre d’études épidémiologiques ont été menée dans

de nombreux pays pour étudier la relation entre la consommation d’eau

fluorée et la morbidité ou la mortalité par cancer. Il n’existe aucune

preuve solide d’un lien entre la consommation d’eau réglementairement

fluorée une augmentation de la morbidité ou de la mortalité dues au

cancer.

Les effets des fluorures sur l’émail dentaire peuvent être bé n éfiques mais également nocifs. La prévalence des caries dentaires est

inversement proportionnelle à la teneur de l’eau de boisson en

fluorures. La prévalence de la fluorose dentaire est en rapport étroit

avec cette teneur, avec une relation dose-réponse positive.Résumé et Conclusions

243 On continue à observer des cas de fluorose osseuse liés à la consommation d’eau à forte teneur en fluorures. Un certain nombre de

facteurs tels que l’état nutritionnel, le régime alimentaire, le climat (qui

influe sur la prise de liquides), une exposition concomitante à d’autres

substances et un apport de fluorures provenant d’autres sources que

l’eau de boisson jouent, semble-t-il, un rôle important dans l’apparition

de cette maladie. Des cas de fluorose osseuse peuvent survenir parmi

les trava illeurs que leur profession expose à des concentrations

élevées de fluorures aéroportés , mais on n’a guère obtenu

d’informations nouvelles à ce sujet.

Les résultats d’un certain nombre d’études écologiques incitent

à penser qu’il existe un lien entre la consommation d’eau fluorée et les

fractures du col du fémur. Ces conclusions ne sont pas confirmées par

d’autres travaux notamment par l’analyse épidém i ologique du problème. Dans certains cas, on a même constaté un effet protecteur des

fluorures contre ces fractures.

Deux études permettent d’évaluer le risque de fracture pour toute

une gamme d’apports en fluor. La première a montré que le risque relatif

de fractures de toute nature ainsi que de fracture du col du fémur était

élevé dans des groupes consomm ant de l’eau dont la teneur en

fluorures était 

### $ 1,45 mg/litre (apport total 

### $ 6,5 mg/jour); la différence

atteignait le seuil de signification statistique pour le groupe dont l’eau

de boisson avait une teneur en fluorures 

### $ 4,32 mg/litre (apport total

14 mg/jour). Dans l’autre étu de, on a observé un accroissement de

l’incidence des fractures indépendant de la dose dans un groupe d’âge

constitué de femmes exposées aux fluorures par l’eau qu’elles consommaient.

Selon les études épidémiologiques, rien n’indique que la consommation d’ea u fluorée par les femmes enceintes augmente le risque

d’avortement spontané ou de malformations congénitales. D’autres

études épidémiologiques portant sur des travailleurs exposés de par

leur professio n n’ont pas décelé de véritable preuve d’effets génotoxiques ou systémiques au niveau du systèm e respiratoire, des

organes hématopoïétiques, du foie ou du rein qui puisse être

directement attribué à l’exposition aux fluorures en tant que telle.EHC 227: Fluorides

244 

### 8. Effets sur les autres êtres vivants au laboratoire et

dans leur milieu naturel

La présence de fluorures à la concentration de 100 mg/litre n’a pas

affecté la c roissance bactérienne ni la capacité de dégradation de

boues activées mesurée par la demande chimique d’oxygène. La CE

50

relative à l’inhibition de la nitrification bactérienne a été trouvée égale

à 1218 mg de fluorures/litre. La CE

50 à 96 h relative à la croissance des

algues a été trouvée égale à 123 mg/litre pour les algues d’eau douce

et à 81 mg/litre pour les algues marines.

Les valeurs de la CL

50 à 48 h pour les invertébrés aquatiques vont

de 53 à 304 mg/litre. Les invertébrés d’eau douce les plu s sensibles

s o nt le sphéridé Musculium transversum avec une mortalité

statistiquement significative ( 50 %) observée à la concentration de

2,8 mg de fluorures par litre lors d’une étude de 8 semaines, ainsi que

plusieu rs phryganes (dulçaquicoles; famille : hydropsychidés) pour

l esquelles les valeurs « sans danger » de la concentration (CE

0 ,01 à

8760 h) vont de 0, 2 à 1,2 mg/litre. L’artémia ( A rtemia salina ) a été

l’espèce marine la plus sensible observée. Lors d’un test de 12 jours

avec r enouvellement statique de l’eau, on a constaté une réduction

statistiquement significative de la croissance à la concentration de

5,0 mg/litre.

Les valeurs de la CL

50 à 96 h pour divers poissons d’eau douce

vont de 51 mg/litre (truite arc-en-ciel, O ncorhynchus mykis s ) à

460 mg/litre (épinoche à trois épines, Gasterosteus aculeatus ). Dans

tous les tests de toxicité aiguë à 96 h, on a trouvé des valeurs

su périeures à 100 mg/litre pour les poissons de mer. Il existe une

corrélation négative entre la toxicité des fluorures minéraux pour les

poissons d’eau douce et la dureté de l’eau (carbonate de calcium) et

une corrélation positiv e entre cette toxicité et la température. Les

symptômes d’une intoxication aiguë par les flu orures consistent

notamment en léth argie, mouvements violents et erratiques et mort.

Lors de tests de 20 jours avec renouvellement statique de l’eau, on a

trouvé une CE

50 de 2,7 à 4,7 mg/litre pour la truite arc-en-ciel. On estime

que la concentration « sans danger » (CL 0,01 à durée infinie) est de 5,1

mg/litre pour la truite arc-en-ciel et de 7,5 mg/litre pour la truite brune

(truite d’Europe, Salmo trutta ). A des concentrations 

### $ 3,2 (effluents)Résumé et Conclusions

245 ou 

### $ 3,6 (fluorure de sodium) de fluorure par litre, l’éclosion des oeufs

de la carpe indienne Catla catla a été retardée de 1 à 2 h.

Les études éthologiques effectuées en rivière (eau douce) sur des

saumons coho adultes ( Oncorhynchus sp.) montrent qu’une modification de la composition chimique des eaux consistant à augmenter la

concentration en fluorures pour la faire passer à 0,5 mg/litre peut avoir

un effet négatif sur la migration; les saumons en migration sont

extrêmement sensibles aux variation de composition chimique de leur

rivière d’origine. Au laboratoire, les fluorures semblent avoir des effets

toxiques sur les processus microbiens à des concentrations qui sont

celles des sols dont la pollution fluorée est modérée; de même, l’accumulation de matières organiques dans les zones situées au voisinage

d’usines de production d’aluminium est attribuée à une forte inhibition

de l’activité microbienne par les fluorures.

C’est au niveau des jeunes tissus en développement des arbres

feuillus et des aiguilles de conifères en phase d’allongement que l’on

a le plus de chances de constater des signes de phytotoxicité fluorotique (fluorose) tels que chlorose, nécrose et réduction du rythme de

croissance. Le déclenchement de la fluorose a été clairem e nt mis en

évidence en laboratoire, en serre ainsi que lors d’essais contrôlés sur

des parcelles expérimentales de pl e in champ. Une proportion importante des articles publiés au sujet de la toxicité des fluorures pour les

plantes portent sur la fumigation des serres avec du fluorure d’hydrogène. La nécrose foliaire a été observée pour la première fois sur des

plants de vigne ( Vitis vinifera ) exposés à des concentrations de 0,17

et 0,27 μg/m

3

, au bout de 99 et 83 jours respectivement. La dose la plus

faible produisant un effet nécrotique observable (65 % des feuilles) sur

le glaïeul à grandes fleurs ( Gladiolus grandiflorus ) a été trouvée égale

à 0,35 μ g de fluorure par m 3 . Les fluorures aéroportés peuvent également avoir un effet sur l’apparition des maladies végétales, mais la

nature et l’ampleur de cet effet dépendent du couple plante-germe

pathogène en cause.

Plusieurs études de brève durée portant sur des cultures en

solution nutritive ont permis de déterminer le seuil de toxicité de l’ion

fluor, qui s e situerait dans les limites approximatives de 50 à

2000 μmol/litre. La spécificité toxicologique observée n’est pas

uniquement fonction de l’espèce végétale, elle dépend également de laEHC 227: Fluorides

246 nature des ions fluor en cause; ainsi, certains fluorures complexes

d’aluminium présents dans des cultures en solution nutritive peuvent

s e révéler toxiques à des concentration de 22-357 μmol de fluorure par

litre, alors que le fluorure d’hydrogène est toxique aux concentrations

de 71-137 μmol/litre. Quelques études ont été consacrées à des cas

d’exposit ion aux fluorures présents dans le sol. Elles ont permis de

déterminer que la fixation et la toxicité potentielle de ces substances

dépendait beaucoup de la nature du sol.

Dans le cas des oiseaux, on a obtenu une valeur de 50 mg/kg de

poids corporel pour la DL 50 à 24 h d’étourneaux sansonnets ( Sturnus

vulgaris ) âgés de 1 jour et de 17 mg/kg p.c. chez des oisillons de

16 jours. Le taux de croissance a été sensiblement réduit aux doses de

13 et de 17 mg de fluorure par kg p.c. (doses les plus fortes auxquelles

ont a mesuré le taux de croissance). La plupart des premiers travaux

consacrés aux mammifères portent sur les ongulés domestiques. On a

ains i observé des cas de fluorose chez des bovins et des ovins. La

dose alimentaire la plus faible ayant causé un effet sur des ongul é s

sauvages a été déterminée dans le cadre d’une étude contrôlée sur des

cerfs de Virginie en captivité ( Odocoileus virginianus ); il s’agissait de

l’apparition de tachetures sur l’ensemble des incisives des animaux à

partir de 35 mg/kg de nourriture.

On a montré que les usines de production d’aluminium, de phosphates et d’engrais, les briquetteries, ainsi que les usines de

production de fibres de verre constituaient toutes des sources de

pollution fluorée et qu’il existait une corrélation entre leur présence et

les dommages constatés sur la végétation du voisinage. L’étude de la

végétation située au voisinage d’une usine de production de

phosphore a montré que l’ampleur des dommages infligés aux plantes

et la concentration en fluorures dans le sol étaient inversement

proportionnelles à la distance de l’installatio n

. La concentration

moyenne des fluorures allait de 281 mg/kg dans les secteurs où la

végétation était très endommagée, à 44 mg/kg dans les zones où les

dommages étaient moindres; sur le site témoin, la concentration des

fluorures était de 7 mg/kg. Dans des communautés végétales situées

à proximité d’une usine de production d’aluminium, on a constaté des

d ifférences de composition et de structure dues en partie à des

variations dans la tolérance au fluor. Il est toutefois à noter que, dans

la nature, l’un des principaux problè mes qui se posent pour

l’identification des effets de la pollution fluoré e tient à la présence

d’autres polluants atmosphériques qui jouent de rôle de variables deRésumé et Conclusions

247 confusion. La prudence doit donc être de règle lors de l’interprétation

des nomb reuses études consacrées à la pollution fluorée dans

l’environnement naturel.

Les premières observations d’effets de la pollution fluorée sur des

mammifères ont été faites dans le cadre d’études de terrain consacrées

à des animaux domestiques tels que les bovins et les ovins. Les

fluorures peuvent passer chez l’animal à partir de la végétation, du sol

et de l’eau qu’i l boit. Les niveaux de tolérance pour les animaux

domestiques se situent à 30 mg par kg de nourriture ou à 2,5 mg/litre

d’eau de boisson pour les animaux laitiers. Les incidents dont ont été

victimes des animaux domestiq ues avaient pour origine soit des

sources naturelles comme les éruptions volcaniques ou la nature

géologique du sol, soit des sources anthr opogéniques, telles que

l’administration au bétail de suppléments minér aux ou la présence

d’industries responsables d’émissions de fluorures et de centrales

électriques. Les symptômes constatés consistent en émaciation,

raideur des articulations et anomalies des dents et du squelette. Parmi

les autres effets, on peut citer une baisse de la production de lait et des

effets nocifs sur la capacité de reproduction des animaux. La

concentration alimentaire la plus faible ayant causé une fluorose chez

des cervidés sauvages était égale à 35 mg/kg. Les études consacrées

aux effets du fluor sur la faune s auvage concernent son action sur

l’intégrité de la denture et du squelette. Au voisinage des usines de

production d’aluminium, les effets de la pollution fluorée se traduisent

par de la boiterie et une atteinte lésionnelle des dents.



### 9. Evaluation des risques pour l’Homme et des effets

sur l’environnement

Les effets des fluorures sur la santé humaine peuvent être positifs

ou négatifs avec un fai ble écart entre les doses correspondantes. Il

existe une exposition importante à l’ensemble des sou rces de fluor,

parmi lesquelles les aliments et l’eau de consommation.

On possède peu de données qui permettraient de caractériser les

relations dose-réponse concernant l e s divers effets indésirables. En

particulier, les données relatives à l’exposition totale aux fluorures sont

peu nombreuses, notamment concernant l’apport et l’absorption.EHC 227: Fluorides

248 Les effets les plus graves résultent d’une accumulation de fluor

dans le squelette p ar suite d’une exposition excessive et de longue

durée et ils s e traduisent par une ostéopathie non maligne, en particulier une fluorose osseuse avec tendance aux fractures. Des données

en provenance de Chine et du sous-continent indie n montrent à

l’évidence que la fluorose osseuse et l’augmentation du risque de

fractures s e manifestent lorsque la dose totale de fluor atteint

14 mg/jour et on est fondé à penser que pour un apport fluoré

supérieur à environ 6 mg/jour, le risque de fracture est déjà augmenté.

Dans les eaux douces, la concentration naturelle des fluorures est

généralement inférieure au seuil de toxicité pour les organismes aquatique s

. Ces derniers peuvent cependant souffrir de la proximité de

décharges anthropogéniques. La toxicité des fluorures dépend de la

dureté de l’eau.

Il existe un risque pour les espèces végétales sensibles qui

poussent à proximité des sources anthropogéniques de fluorures. La

libération de ces substances dans l’environnement à partir de telles

sources cause des dégâts à la végétation terrestre locale, mais il est

difficile de savoir quelle est la part des seuls fluorures dans ces effets,

car d’autres polluants sont également présents dans l’atmosphère. Les

fluorures sont habituellement fortement adsorbés aux particules du sol.

Il en résulte que les plantes fixent relativement peu de fluorures par

cette voie et que le lessivage est minime.

La concentration en fluorures dans la végétation au voisinage de

diverses sources d’émission comme les usines de production

d’aluminium, peut être supérieure au seuil de toxicité alimentaire pour

les mammifères déterminé par l’expérimentation animale. On observe

des cas de fluorose parmi les animaux domestiques. Il existe des

régions où l’on signale encore des problèmes de fluorose dans le bétail

à qui l’on donne des suppléments minéraux et une eau de boisson riche

en fluor. En outre, l’utilisation prolongée d’engrais phosphatés contenant des impuretés fluorées fait courir un risque d’intoxication aux

animaux qui broutent dans des pâturages contaminés ou ingèrent de

la terre polluée. Des effets due à une intoxication par le fluor, tels que

boiterie et lésions dentaires, s’observent également chez des mammifères sauvages vivant à proximité de sources d’émission anthropogéniques.Résumé et Conclusions

249 

### 10. Conclusions

Tous les êtres vivants sont exposés aux fluorures provenant de

s ources naturelles ou anthropogéniques. L’apport en fluor es t très

important dans les régions du monde où l’environnement est riche en

cet élément et où l’Homme consomme l’eau de sources souterraines à

forte teneur en fluorures. L’exposition peut être encore plus importante

à proximité de sources d’émission ponctuelles. La fluoration des

produits d’hygiène dentaire constitu e pour beaucoup de gens une

source supplémentaire d’exposition.

Les effets des fluorures peuvent être bénéfiques ou indésirables

et l’écart entre les doses correspondantes est étroit.

Des effets sur les dents et les os peuvent s’observer à des doses

inférieures à celles qui produisent des effets indésirables spécifiques

sur d’autres organes ou tissus.

Chez l’Homme, les effets sur les os (fluorose osseuse et tendance

aux fracture s) sont considérés comme les plus significatifs pour

l’évaluation des effets indésirables d’une exposition prolo ngée aux

fluorures.

La fluorose osseuse est une maladie invalidante qui touche des

millions de gens dans diverses régions d’Afrique, de Chine et de l’Inde

et dont les conséquences sanitaires et socio-économiques sont très

importantes.

La principale cause de fluorose osseuse endémique est l’absorption de fluorures présents dans l’eau de boisson et les aliments. Dans

certaines régions, l’utilisation de charbon riche en fluor co mme

combustible à l’intérieur des habitations est également une source

importante d’exposition.

On ne possède guère de données à pa rtir desquelles estimer

l’exposition totale aux fluorures ou leur biodisponibilité et les documents relatifs à la caractérisation de leurs effets indésirables contiennent un certain nombre d’incohérences.EHC 227: Fluorides

250 Il apparaît clairement, à la lumière des données en provenance de

Chine et du sous-continent indien, que l a fluorose osseuse et la

tendance aux fractures s e manifestent pour des doses totales de 14 mg

de fluor ure/jour et on est incité à penser qu’à partir d’environ

6 mg/jour, le risque d’atteinte osseuse est d’ores et déjà augmenté.

Une exposition excessive aux fluorures biodisponibles constitue

un risque pour la faune et la flore aquatiques et terrestres.

On peut utiliser les espèces fluoro-sensibles comme sentinelles

pour attirer l’attention sur les dangers dus à la présence de fluorures

dans l’environnement.

Une meilleure connaissance de l’accumulation des fluorures par

les êtres vivants est nécessaire et il faut également déterminer comment

surveiller et réduire cette accumulation.

Il convient de mieux caractériser les effets biologiques de

l’exposition aux fluorures.251 

### RESUMEN Y CONCLUSIONES

Este documento se centra en la exposición en el medio ambiente

a los fluoruros derivados fundamentalmente de fuentes inorgánicas y

sus efectos en las personas, los animales y otra biota. Contiene datos

sobre el fluoruro de hid rógeno, el fluoruro de calcio, el fluoruro de

sodio, el hexafluoruro de azufre y los s i licofluoruros, puesto que s e

considera que estos compuestos son los fluoruros inorgánicos más

importantes, teniendo en cuenta el volu men de las emisiones en el

medio ambiente , las concentraciones en éste y los efectos

toxicológicos en los organismos vivos.



### 1. Identidad, propiedades físicas y químicas y métodos

analíticos

El fluoruro de hidrógeno (HF) es un líquido o gas incoloro picante

muy soluble en disolventes orgánicos y en agua, con l a que forma

ácido fluorhídrico. El fluoruro de calcio (CaF

2 ) es un sólido incoloro

relativamente insoluble en agua y ácidos y bases diluidos. El fluoruro

de sodio (NaF) es un sólido entre incoloro y blanco moderadamente

soluble en agua. El hexafluoruro de azufr e (SF

6 ) es un gas inerte

incoloro e inodoro ligeramente soluble en agua y fácilmente soluble en

etanol y en bases.

El procedimiento más común utilizado para cuantificar la concentraci ón de aniones fluoruro libres es el electrodo selectivo de iones

fluoruro. Se considera que las técnicas de microdifusión son los métodos más exactos de preparación de muestras (es decir, la liberación de

fluoruro iónico a partir de complejos orgánicos e inorgánicos).



### 2. Fuentes de exposición humana y ambiental

Los fluoruros se liberan en el medio ambiente de manera natural

a través de la meteorización y disolución de minerales, las emisiones de

volcanes y los aerosoles marinos. También s e liberan a través de la

combustión del carbón y las aguas indust riales y los desechos de

diversos procesos industriales, en particular la fabricación de acero, la

producción primaria de aluminio, de cobre y de níquel, la elaboración

de minerales de fosfato, la producción y uso de fertilizantes fosfatados,EHC 227: Fluorides

252 la fabricación de vidrio, ladrillos y cerámica y la producción de cola y

adhesivos. La utilización de plaguicidas que contienen fluoruros, así

como la fluoración del abastecimiento de agua potable contribuyen a

la emisión de fluoruros a partir de actividades humanas. S egún los

d atos disponibles, la obtención y uso de minerales de fluoruro, así

como la fabricaci ón de aluminio, son las principales fuentes industriales de emisiones de fluoruros en el medio ambiente.

El fluoruro de hidrógeno es un producto industrial importante que

s e utiliza fundamentalment e en la producción de criolita sintética

(Na

3 AlF

6 ), trifluoruro de aluminio (AlF

3 ) y los alquilatos y los clorofluorocarbur

os de la gasolina para motores, con un consumo anual

mundial superior a un millón de toneladas. Se utiliza también en el

tratamiento químico de los dispositivos semiconductores, la limpieza

y el tratamiento químico del vidrio, la limpieza de los ladri llos y del

aluminio y el curtido de pieles, así como en los anticorrosivos comerciales. El fluoruro de calcio se utiliza como fundente en la producción

de acero, vidrio y esmalte, como materia prima para la producción de

ácido fluorhídrico y fluoruro de hidrógeno anhidro y como electrolito

en la producción de aluminio. El fluoruro de sodio se utiliza en la fluoración controlada del agua de bebida, como conservante en la cola, en

la producción de vidrio y esmalte, como fundente en la producción de

acero y aluminio, como insecticida y como conservante de la madera.

El he xafluoruro de azufre se utiliza ampliamente en diversos

componentes electrónicos y en la producción de magnesio y aluminio.

El ácido hexafluorosilícico (H

2 SiF

6 ) y el hexaflu orosilicato disódico

(Na

2 SiF

6 ) s e utilizan para la fluoración de los sistemas de abast ecimiento de agua potable.



### 3. Transporte, distribución y transformación en el

medio ambiente

Los fluoruros s e pueden encontrar en la atmósfera en forma gaseosa o particulada. Los fluoruros atmosféricos pueden recorrer largas

distancias transportados por el viento o por turbulencias atmosféricas,

o eliminarse mediante deposición húmeda y seca o hidrólisis. No cabe

esperar de los compu estos de fluoruro, con la excepción del hexafluoruro de azufre, una permanencia prolongada en la troposfera o su

desplazamiento hacia la estratosfera. El hexafluoruro de azufre tiene unResumen y Conclusiones

253 tiempo de permanencia en la atmósfera que oscila entre 500 y varios

miles años.

El transporte y la transformación de los fluoruros en el agua

dependen del pH, la dureza del agua y la presencia de materiales intercambiadores de iones, como la arcilla. Los fluoruros s e suelen transportar a través del ciclo hidrológico formando complejos con el aluminio.

E l transporte y la transformación de los fluoruros en el suelo

dependen del pH y de la formación de complejos, sobre todo con el

aluminio y el calcio. La adsorción a la f ase sólida del suelo es más

fuerte con un pH ligeramente ácido (5,5-6,5). No es fácil su lixiviación

del suelo.

La absorción de los fluoruros por la biota depende de la vía de

exposición, de su biodisponibilidad y de la cinética de absorción/excreción del organismo. Cierta biota acuática y terrestre bioacumula fluoruros solubles. Sin embargo, no se encontró información relativa a la

bioamplificación de los fluoruros en las cadenas alimentarias acuática

o terrestre.

Las plantas terrestres pueden acumular fluoruros a través de la

deposición de partículas suspendidas en el aire y la a bsorción del

suelo.



### 4. Niveles ambientales y exposición humana

Los niveles de fluoru ros en las aguas superficiales varían en

función del lugar y de la proximidad a fuentes de emisión. Las concentraciones en aguas superficiales generalment e oscilan entre 0,01 y

0,3 mg/l. El agua marina contiene más fluoruros que el agua dulce, con

concentraciones que van de 1,2 a 1,5 mg/l. Se han registrado niveles

más altos de fluoruros en zonas cuyas rocas naturales los contienen en

una elevada proporción, y s e observan con frecuencia niveles altos de

fluoruros inorgánicos en regi ones con actividad geotérmica o

volcánica (p. ej., 25-50 mg/l en fuentes term ales y géiseres y hasta

2800 mg/l en cie rtos lagos del valle del Rift, en la región oriental de

África). Las descargas de origen humano pueden provocar también un

aumento de su concentración en el medio ambiente.EHC 227: Fluorides

254 Los fluoruros suspendidos en el aire se encuentran en forma

gaseosa y particulada, procedentes de fuentes tanto naturales como

humanas. Estos fluoruros emitidos como materia gaseosa y particulada

s e suele n depositar en las proximidades de la fuente de emisión,

aunque algunas partículas pueden reaccionar con otros componentes

de la atmósfera. La distribución y deposición de los fluoruros

suspendidos en el aire dependen d e la intensidad de la emisión, las

condiciones meteorológicas, el tamaño de las partículas y la reactividad

química. En zonas no situadas en las inmediaciones de las fuentes de

emisión, las concentraciones medias de fluoruros e n el aire son

generalmente inferiores a 0,1 μg/m 3

. Los niveles pueden ser ligeramente

más altos en las zonas urbanas que en las rurales; sin embargo, incluso

en las proximidades de las fuentes de emisión los niveles de fluoruros

suspendidos en el aire no suelen ser superiores a 2-3 μg/m 3

. En algunas

zonas de China donde se utiliza carbón con un contenido elevado de

fluoruros como fuente de combustible, s e han notificado concentraciones de fluoruros en el aire de hasta 6 μg/m 3

.

Los fluoruros forman parte de la mayoría de los tipos de suelos,

con concentraciones totales de entre 20 y 1000 μg/g en zonas sin

depósitos naturales de fosfatos o fluoruros y de hasta varios miles de

μg por gramo en suelos minerales con depós itos de fluoruros. Los

fluoruros gaseosos y particulados suspendidos en el aire tienden a

acumularse en la capa superficial del suelo, pero pueden desplazarse

por toda la rizosfera, incluso en suelos calcáreos. La retención de

fluoruros en el suelo depende fundamentalmente del contenido de

arcilla y carbono orgánico, así como del pH del suelo. Los fluoruros del

suelo están asociados fundamentalmente con su fracción coloidal o

arcillosa. En todos los tipos de suelos, los fluoruros biológicamente

importantes para las plantas y los animales son los solubles.

Los organismos acuáti cos pueden absorber fluoruros

directamente del agua o en menor medida a través de los alimentos. Los

fluoruros tienden a acumularse en el exoesqueleto o en el tejido óseo

de los animales acuáticos. Se han registrado concentraciones medias

de fluoruros > 2000 mg/kg en el exoesqueleto del krill; las concentraciones medias de fluoruros en los huesos de mamíferos acuáticos,

como focas y ballenas, oscilan entre 135 y 18 600 mg/kg de peso seco.

Las concentraciones de fluoruros en la biota terrestre son superiores en las zonas con niveles de fluoruros más elevados procedentesResumen y Conclusiones

255 de fuentes naturales y humanas. Con frecuencia se han utilizado

líquenes como bioindicadores de fluoruros. En los líquenes que crecían

en un radio de 2-3 km de las fuentes de emisión se determinaron

concentraciones medias de fluoruros de 150-250 mg/kg, en

comparación con un nivel de fondo < 1 mg de fluoruros/kg.

La mayor parte de los fluoruros presentes en el suelo son insolubles y, por consiguiente, están menos disponibles para las plantas.

Sin embargo, factores como una concentración alta de fluoruros en el

suelo o un pH bajo y la presenci a de arcilla y/o materia orgánica

pueden aumentar sus niveles en solución, aumentando la absorción a

través de las raíces de las plantas. Si se absorben fluoruros a través de

las raíces, sus concentraciones son con frecuencia más altas en éstas

que en los brotes, debido a su baja movilidad en la planta. La mayor

parte de los fluoruros s e introducen en los tejidos de las plantas en

forma de gases por los estomas y s e acumulan en las hojas. Pueden

entrar en la pl anta pequeñas cantidades de fluoruros particulados

suspendidos en el aire a través de la epidermis y la cutícula. Se ha

vigilado de cerca la vegetación de las proximid a des de fuentes de

emisión de fluoruros de origen humano. Se ha observado una correlación entre la concentración de fluoruros en la vegetación y los incrementos del crecimiento anual, las características del viento, la distancia

de la fuente de fluoruros y la concentración de fluoruro de hidrógeno

en las emisiones aéreas.

Los fluoruros se acumulan en el tejido óseo de los vertebrados

terrestres, en función de factores como la alimentación y la proximidad

de las fuentes de emisión. Por ejemplo, s e han registrado con c entraciones medias de fluoruros de 7000-8000 mg/kg en los huesos de

pequeños mamíferos en las cercanías de una fundición de aluminio.

Los fluoruros son ubicuos en el medio ambiente; por ello, es frecuente que las fuentes de agua de bebida los contengan por lo menos

en pequeñas cantidades. La cantidad de fluoruros presentes de manera

natural en el agua potable no fluorada (es decir, agua de bebida a la

cual no se han añadido deliberadamente fluoruros para prevenir la

caries dent al) es muy variable, dependiendo del entorno geológico

concreto de procedencia del agua. Los niveles pueden alcanzar hasta

unos 2,0 mg/l; sin embargo, en las zonas del mundo con fluorosis

endémica del esquel eto y/o los dientes bien documentada, las

concentraciones de fluoruro s en la red de abastecimiento de agua

potable van de 3 a más de 20 mg/l. En zonas con agua potable fluoradaEHC 227: Fluorides

256 (es decir, con adición deliberada de fluoruros para la prevención de la

caries dental), la concentración de fluoruros en ella generalmente oscila

entre 0,7 y 1,2 mg/l.

Prácticamente todos los productos alimenticios contienen por lo

menos cantidades ínfimas de fluoruros. Se observan concentraciones

elevadas en los peces. Las hojas de té son particularmente ricas en

ellos; la cantidad en el té en infusión depende de la concentración de

fluoruros solubles en las hojas de té, del nivel de fluoruros en el agua

utilizada en su preparación y del tiempo de permanencia de las hojas en

el agua. La concentración de fluoruros en los productos alimenticios

no aumenta de manera signific ativa por el uso de fertilizantes

superfosfatados, que contienen concentraciones importantes de fluoruros (1%-3%) como impurezas, en las tierras agrícolas, debido a que el

coeficiente de tr ansferencia del suelo al material de las plantas es

generalmente bajo. Sin embargo, un estudio reciente p arece indicar

que, en condiciones apropiadas del su elo y con la aplicación de

suficientes fluoruros como impurezas en los fertilizantes fosfatados,

puede aumentar la absorción de fluoruros por las plantas. El uso de

agua de riego con niveles relativamente bajos (< 3,1 mg/l) de fluoruros

en los cultivo s no suele aumentar sus concentraciones en los

productos alimenticios. Sin embargo, esto depende de la especie de la

planta y de las concentraciones de fluoruros en el suelo y el agua. El

nivel de fluoruros en los alimentos depende sobre todo del contenido

de fluoruros del agua utilizada en su preparación o elaboración, sobre

todo en las bebidas y los productos alimenticios secos - por ejemplo,

las preparaciones en polvo para lactantes - a los cuales se añade agua

antes del consumo. Las concentraciones de fluoruros en los alimentos

no lavados o no elaborados en las cercanías de fuentes industriales

(emisiones) de fluoruros pueden ser superiores a las de los mismos

ali m entos cultivados en otras zonas no industriales. En las preparaciones infantiles disponibles en el comercio en los Estados Unidos, los

concentrado s a base de soja listos para el consumo y líquidos

contenían niveles de fluoruros superiores a los de los productos

lácteos equ ivalentes; sin embargo, no se observó una diferencia

significativa entre las preparaciones infantiles en polvo a base de soja

y de leche. Se han detectado fluoruros en la leche materna, habiéndose

notificado niveles comprendidos entre < 2 y aproximadamente 100 μg/l,

con la mayoría de los valores situados en el intervalo de 5 a 10 μg/l.Resumen y Conclusiones

257 Los datos disponibles sobre la concentración de fluoruros en el

aire de espacios cerrados son lim itados. En los Países Bajos, las

concentraciones de fluoruros gaseosos eran de < 2 a 49 μg/m 3 en el aire

del interior de cinco viviendas construidas con madera tratada con un

conservante que contenía un 56% de fluoru ros. En China, se han

notificado concentracione s de hasta 155 μg/m 3 en muestras de aire

recogido en el interior de viviendas donde s e utilizaba como combustible carbón que contenía concentraciones elevadas de fluoruros.

Los productos dentífricos para adultos presentes en el mercado

de muchos países suelen contener fluoruros en concentraciones

de 1000 a 1500 μg/g; algunos productos infantiles contienen niveles

más bajos, de 250 a 500 μg/g. Se han identificado productos dentales,

por ejemplo pasta de dientes, colutorios y suplementos de fluoruros,

como fuentes importantes de éstos. Los enjuagues bucales

comercializados para uso doméstico cotidiano suelen c ontener

entre 230 y 500 mg de fluoruros/l, mientras que los colutorios

destinados a un uso semanal o quincenal suelen contener 900-1000 mg

de fluoruros/l.

Aunque es probable que la exposición individual al fluoruro sea

muy variable, la inhalación de fluoruros suspendidos en el aire

generalmente representa una contribución de escasa importancia a la

ingesta total de esta sustancia. En adultos, la vía principal de ingesta

de fluoruros es el consumo de productos alimenticios y agua de

bebida. En las zonas del mundo en las cuales se utiliza carbón con un

alto contenido de fluoruros en la calefacción y la preparación de los

alimentos, la inhalación del aire i nterno y el consumo de productos

alimenticios con niveles altos de fluoruros también contribuyen a

aumentar la ingesta. Los lactantes alimenta dos con preparaciones

reciben 50-100 veces más fluoru ros que los que se nutren exclusivamente con leche materna. La ingestión de dentí frico por los niños

pequeños representa una contribución importante a su ingesta total.

En general, la ingesta estimada de fluoruros en niños y adolescentes

no sobrepasa los 2 mg/día. Aunque las personas adultas pueden tener

una ingesta diaria absoluta má s alta de fluoruros en mg, la ingesta

diaria de f

luoruros por los niños, expresada en mg por kg de peso

corporal, puede ser superior a la de los adultos. Se ha notificado que

en ciertas zonas del mundo en las cuales la concentración de fluoruros

en el ambie nte circundante puede ser sumamente alta y/o donde el

régimen alimenticio se basa en productos que los contienen enEHC 227: Fluorides

258 abundancia, se estimó una ingesta de fluoruros en adultos de hasta

27 mg/día, siendo l a fuente principal el agua de bebida obtenida de

fuentes freáticas situadas en zonas geológicas ricas en fluoruros.

Probablemente s e produce exposición ocupacional a los fluoruros

por inhalación o contacto cutáneo en las personas que trabajan con

equipo de soldadura o en la elaborac ión del aluminio, el mineral de

hierro o el de fosfato. En est udios relativamente recientes se

n o tificaron concentraciones de fluoruros suspendidos en el aire del

cuarto de crisoles de las fundiciones de aluminio del orden de 1 mg/m 3

.



### 5. Cinética y metabolismo en el ser humano y en

animales de laboratorio

En las personas y los animales de laboratorio, el paso de los fluoruros ingeridos a la circulación general se produce fundamentalmente

en el estómago y el intestino y depende de la solubilidad acuosa relativa de la forma consumida. Los fluoruros solubles se absorben casi

completamente del tracto gastrointestin al; sin embargo, el grado de

absorción s e puede ver reducido por la formación de complejos con el

aluminio, el fósforo, el magnesio o el calcio. En función de la solubilidad y del tamaño de las partículas, la absorción de los fluoruros gaseosos y particulados del tracto respiratorio puede ser parcial o completa.

Los fluoruros s e distribuyen rápidamente por la circulación sistémica al agua intracelular y extracelular de los tejidos; sin embargo, en

las personas y los animales de laboratorio, los huesos y los dientes

retienen alrededor del 99% de la carga corporal total de fluoruros. En

los dientes y el tejido esquelético, los fluoruros se incorporan al

retículo cristalino.

Los fluoruros atraviesan la placenta y pasan de la madre al feto.

Se elimin an del organismo fundamentalmente en la orina. En los

lactantes, s e retiene alrededor del 80%-90% de la dosis de fluoruros; en

los adultos, l a cifra correspondiente es de alrededor del 60%. Estos

valores pueden verse modificados por alteraciones del flujo urinario y

el pH de la orina.

Hay fluoruros presentes en los órganos, los tejidos y los fluidos

del cuerpo. Las concentraciones de fluoruros en la sangre entera deResumen y Conclusiones

259 personas residentes en una comunidad d e los Estados Unidos que

recibía agua de bebida fluorada eran de 20 a 60 μg/l. La concentración

media en el plasma de 127 personas con 5,03 mg de fluoruros/l en su

agua de bebida era de 10 6 ± 76 (SD) μg/l. El suero y el plasma

contienen prácticamente la misma cantidad de fluoruros. Las concentraciones más altas de fluoruros en los tejidos calcificados se suelen

dar en el hueso, la dentina y el esmalte. La concentración de fluoruros

en los huesos varía con la edad, el sexo y el tipo y parte específica de

hueso y s e considera que corresponde a una exposición prolongada de

la persona a los fluoruros. La concentración de fluoruros en el esmalte

dental disminuye exponencialmente con la distancia desde la superficie

y varía en función del lugar, el desg aste superficial, la exposición

sistémica y la exposición a los fluoruros de aplicación extern a. La

concentración de fluoruros en los tejidos blandos está relacionada con

la de la sangre. Los niveles de fluoruros en la orina de los individuos

sanos dependen de su ingesta. S e han registrado aumentos de la

concentración de fluoruros en la orina en personas tras la exposición

ocupacional a fluoruros suspendidos en el aire y entre los residentes

en zonas asociadas con fluorosis endémica.



### 6. Efectos en mamíferos de laboratorio y en sistemas

de ensayo in vitro

En varios estudios con ratas tratadas con fluoruros por vía oral

durante periodos de tres a cinco semanas s e observaron en el

esqu eleto efectos como una inhibición de la mineralización y la

formación de los huesos, retraso en la curac i ón de las fracturas y

reducción del volumen de hueso y la síntesis de colágeno. En estudios

de duración media con ratones tratados con fluoruros en el agua de

bebida (> 4,5 mg/kg de peso corporal al día) durante un periodo de seis

meses s e observó una remodelación alterada de los hues os,

megalocitosis hepática , nefrosis y/o degeneración de los túbulos

seminíferos de los testículos.

En una biovaloración amplia de la carcinogenicidad con grupos

de ratas F344/N y ratones B6C3F

1 macho y hembra a los que s e administró en el agua de bebida una concentración de hasta 79 mg de fluoruros/l en forma de fluoruro de sodio durante un periodo de dos años

no se observó un aumento estadísticamente significativo de la

incidencia de tumores en ninguno de los grupos expuestos. Se detectó

una tendencia estadísticament e significativa al aumento de laEHC 227: Fluorides

260 incidencia de osteosarcomas en ratas macho con la ex posición

creciente al

fluoruro. Sin embargo, la incidencia quedaba dentro del

margen de los testigos históricos.

En otra biovaloración de la carcinogenicidad de dos años con

ratas Sprague-Dawley expuestas a concent raciones de hasta

11 ,3 mg/kg de peso corporal al día con los alimentos tampoco se

observó un aumento estadí sticamente significativo de los

osteosarcomas u otros tumores. Otro estudio, en el que s e notificó un

aumento de la incidencia de osteomas en ratones que recibieron hasta

11,3 mg/kg de peso corporal al día, es difícil de interpretar, porque los

animales estaban infectados por un retrovirus de tipo C.

En general, los fluoruros no son mutagénicos en células procarióticas. Aunque s e ha demostrado que en cultivos de células de linfoma

de ratón y linfoblastoides humanas los fluoruros aumentan la frecuencia de mutaciones en loci específicos, estas mutaciones probablemente

s e deben más al daño cromosómico que a mutaciones puntuales. Se ha

demostrado también que los fluoruros son clastogénicos en diversos

tipos de células. El mecanismo de la clastogenicidad se ha atribuido al

efecto de los fluoruros en la formación de proteínas que intervienen en

la síntesis y/o reparación del ADN, más que a la interacción d i recta

entre los fluoruros y el ADN. En l a mayoría de los estudios en los

cuales se administraron fluoruros por vía oral a roedores, no se observaron efectos en la morfol ogía del esperma o en la frecuencia de

aberraciones cromosómicas, micronúcleos, intercambio de cromátidas

hermanas o rotura de la cadena del ADN. Sin embargo, se notificaron

daños citogenéticos en la médula ósea o alteraciones en la morfología

de las célul as espermáticas cuando se administraba la sustancia a

roedores por inyección intraperitoneal.

En estudios recientes con animales de lab oratorio a los que se

administraba fluoruro en el agua de bebida no s e observaron efectos

reproductivos o en el desarrollo. Sin embargo, se han notificado cambios histopatológicos en los órganos reproductivos de conejos macho

tratados (por vía oral) con 4,5 mg de fluoruros/kg de peso corporal al

día durante 18-29 meses, de ratones macho tratados (por vía oral) con



### $ 4,5 mg de fluoruros/kg de peso corporal al día durante 30 días y de

conejos a los que se administraron por inyección subcutánea 

### $ 10 mg

de fluoruro s/kg de peso corporal al día durante 100 días. Se han

notificado efectos adversos en la función reproductiva de ratones

hembra tratados (por vía oral) con 

### $ 5,2 mg de fluoruros/kg de pesoResumen y Conclusiones

261 cor p oral al día durante los días 6-15 después del apareamiento y de

conejos macho tratados (por vía oral) con 

### $ 9,1 mg de fluoruros/kg de

peso corporal al día durante 30 días.



### 7. Efectos en el ser humano

En las investigaciones epidemiológicas sobre los efectos de los

fluoruros en la salud humana s e han examinado trabajadores expuestos

en el lugar de trabajo empleados fundamentalmente en la industria de

la fundición del aluminio y poblaciones consumidoras de agua potable

fluorada. En algunos estudios epidemiológicos analíticos de trabajadores expuestos en el lugar de trabajo a fluoruros, s e ha detectado una

mayor incidencia de cáncer de pulmón y de vejiga y un aumento de la

mortalidad debida al cáncer de estos y otros órganos. En general, sin

embargo, no s e ha observado una pauta uniforme; en algunos de estos

estudios epidemiológicos, el aumento de la morbilidad o la mortalidad

debidas al cáncer se puede atribuir a la exposición de los trabajadores

a sustancias distintas de los fluoruros.

Se ha examinado en un gran número de estudios epidemiológicos

realizados en numerosos países la relación entre el consumo de agua

potable fluo rada y la morbilidad o la mortalidad por cáncer. No hay

pruebas convi ncentes de una asociación entre el consumo de agua

potable fluorada controlada y el aumento de la morbilidad o la mortalidad por cáncer.

Los fluoruro s tienen efectos tanto beneficiosos como

perjudiciales en el esmalte dental. La prevalencia de la caries dental es

inversamente proporcional a la concentración de fluoruros en el agua

potable. La prevalencia de la fluorosis crónica está muy asociada con

la concentració n de fluoruros, con una relación dosis-respuesta

positiva.

Se siguen notificando casos de fluorosis esquelética asociada con

el consumo de agua pot able que contiene niveles elevados de

fluoruros. Se conside ra que algunos factores, como el estado

n utricional y el régimen alimenticio, el clima (en relación con el

consumo de líquidos), la exposición simultánea a otras sustancias y la

ingesta de fluoruros de fuentes distintas del agua d e bebida,

desempeñan una función importante en la aparición de esta

enfermedad. La fluorosis esquelética puede aparecer en trabajadoresEHC 227: Fluorides

262 ocupacionalmente expuestos a concentraciones elevadas de fluoruros

suspendidos en el aire; sin embargo, sólo se ha encontrado

información nueva limitada.

Algunas pruebas obtenidas en varios estudi o s ecológicos

parecen indicar que podría haber una asociación entre el consumo de

agua fluorada y las fracturas de cadera. Sin embargo, otros estudios,

incluidas algunas investigaciones epidemiológicas, no respaldan esta

conclusión. En algunos casos se ha notificado un efecto protector de

los fluoruros en las fracturas.

Hay dos estudios que permiten evaluar el riesgo de fractura teniendo en cuenta una serie de ingestas de fluoruros. En un estudio, los

riesgos relativos de todas las fracturas y de la fractura de cadera eran

elevados en los grupos que utilizaban agua de bebida con 

### $ 1,45 mg

de fluoruros/l (ingesta total 

### $ 6 ,5 mg/día); esta diferencia alcanzó

significación estadística para el grupo expuesto al agua de bebida con



### $ 4,32 mg de fluoruros/l (ingesta total, 14 mg/día). En el otro estudio s e

observó un aumento no dependiente de la dosis de la incidencia de

fracturas en un grupo de edad de mujeres expuestas a fluoruros en el

agua de bebida.

Según los estudios epidemiol ógicos, no hay pruebas de una

asociación entre el consumo de agua de bebida fluorada por las madres

y el aumento del riesgo de aborto espontáneo o malformación congénita. Otras investigaciones epidemiológicas de trabajadores expuestos

en el lugar de trabajo no han proporcionado p ruebas razonables de

efectos genotóxicos o efectos sistémicos en los sistemas respiratorio,

hematopoyético, hepático o renal que puedan ser directamente atribuibles a la exposición en sí a los fluoruros.



### 8. Efectos en otros organismos en el lab oratorio y en el

medio ambiente

El fluoruro no afectó al crecimiento o a la capacidad de reducción

de la demanda química de oxígeno de los lodos activados a concentraciones de 100 mg/l. La CE

50 para la inhibición de la tasa de nitrificación

bacteriana fue de 1218 mg de fluoruros/l. La CE

50 a las 96 horas, basada

en el crecimiento, para algas de agua dulce y marinas fue de 123 y 81

mg de fluoruros/l, respectivamente.Resumen y Conclusiones

263 La CL

50 a las 48 horas para invertebrados acuáticos fue del orden

de 53 a 304 mg/l. Los invertebrados de agua dulce más sensibles fueron

Musculium transversum

, habiéndose observ ado una mortalidad

estadísticamente significativa (50%) a una concentración de 2,8 mg de

fluoruros/l en un experimento de flujo continuo de ocho semanas, y

var ias especies de insectos de agua dulce de la familia

Hydropsychidae, con «concentr aciones inocuas» (CE 0,01 a las

8760 horas) del orden de 0,2 a 1,2 mg de fluoruros/l. La especie marina

más sensible sometida a prueba fue la artemia ( Artemia salina ). En una

prueba estática con renovación de 12 días, s e produjo un trastorno del

crecimiento estadísticamente significativo con 5,0 mg de fluoruros/l.

La CL

50 a las 96 horas para los peces de agua dulce osciló entre

51 mg/l (trucha arco iris, Oncorhynchus mykiss ) y 460 mg/l (espinoso,

Gasterosteus aculeatus ). T odas las pruebas de toxicidad aguda

(96 horas) en peces marinos dieron resultados superiores a 100 mg/l. La

toxicidad del fluoruro inorgánico para los peces de agua dulce parece

tener una correlación negativa con la dureza del agua (carbonato de

calcio) y positiva con la temperatura. Entre los síntomas de intoxicación

aguda por fluoruros cabe mencionar el letargo, el movimiento violento

e incierto y la muerte. En pruebas estáticas con renovación la CL

50 a los

20 días para la trucha arco iris osciló entre 2,7 y 4,7 mg de fluoruros/l.

Se han estimado «concentraciones inocuas» (CL 0,01 en un número

indeterminado de horas) para la trucha arco iris y el reo ( Salmo trutta )

de 5,1 y 7,5 mg de fluoruros/l, respectivamente. A concentraciones



### $ 3,2 (efluente) o 

### $ 3,6 (fluoruro de sodio) mg de fluoruros/l, la

eclosión de los huevos del pez catla ( Catla catla ) se retrasó 1-2 horas.

Los experimentos sobre comportamiento realizados en el salmón

del Pacífico adulto ( Oncorhynchus sp.) en ríos de aguas blandas indican que los cambios en la química del agua, debido a un aumento de la

concentración de fluoruros hasta 0,5 mg/l, puede afectar negativamente

a la migraci

ó n; durante la migración los salmones son enormemente

sensibles a los cambios de la química del agua de sus ríos de origen. En

estudios de la boratorio, los fluoruros parecen ser tóxicos para los

procesos microbianos a concentraciones presentes en suelos

moderadamente contaminados con fluoruros; análogamente, la acumulación de materia orgánica sobre el terreno en las cercanías de fundiciones s e ha atribuido a una inhibición grave de la actividad microbiana

por esta sustancia.EHC 227: Fluorides

264 Los signos de fitotoxicidad de los fluoruros inorgánicos (fluorosis) como la clorosis, la necrosis y la disminución de la tasa de

crecimiento es más probable que se produzcan en los tejidos jóvenes

en expansión de las plantas latifolias y las agujas en fase de alargamiento de las coníferas. La inducción de fluorosis s e ha demostrado

claramente en experimentos realizados en laboratorios, en invernaderos

y en parcelas de terreno controladas. Se han publicado nu merosos

estudios sobre la toxicidad de los fluoruros para las plantas en relación

con la fumigación de los invernaderos con fluoruro de hidrógeno. Se

observó por primera vez necrosis foliar en vides ( V itis vinifera )

expuestas a 0,17 y 0,27 μg/m 3 a los 99 y los 83 días, respectivamente. El

nivel más bajo con efectos observados para la necrosis foliar (65% de

las hojas) en el gladiolo ( Gladiolus grandiflorus ) fu e de 0,35 μg de

fluoruros/m

3

. Los fl uoruros suspendidos en el aire pueden afectar

también al desarrollo de la enfermedad de la planta, aunque el tipo y la

magnitud de los efectos dependen de la combinación específica plantapatógeno.

En varios estudios breves de cultivos en solución s e ha determinado un umbral tóxico para la actividad del ión fluoruro que oscila

en tre alrededor de 50 y 2000 μmoles de fluoruro/l. La toxicidad es

específica no sólo para las especies de plantas, sino también para las

especies iónicas de fl u oruro; algunos complejos de fluoruro de aluminio presentes en cultivos en solución pueden ser tóxicos con activi dades de 22-357 μmoles de fluoruro/l, mientras que el fluoruro de

hidrógeno es tóxico con actividades de 71-137 μmoles de fluoruro/l. Se

ha realizado un pequeño número de estudios sobre la exposición a los

fluoruros a través del suelo. El tipo de suelo puede afectar enormemente a la absorción y la posible toxicidad de los fluoruros.

En las aves, la DL 50 en 24 horas fue de 50 mg/kg de peso corporal

para las crías de un día de estornino ( Sturnus vulgaris ) y de 17 mg/kg

de peso corporal para los pajaritos de 16 días. Las tasas de crecimiento

registraron una reducción significativa con 13 y 17 mg de fluoruros/kg

de peso corporal (las dosis más altas a las cuales se vigiló el crecimiento). Gran parte del trabajo inicial sobre mamíferos se realizó en

ungulados domesticados. Se ha observado fluorosis en el gan a do

bovino y ovino. La concentración más baja con los alimentos con

efecto en los ungulados salvajes se obtuvo en un estudio controlado

en cautividad con el venado de cola blanca ( Odocoileus virginianus ),

en el cual s e observó un moteado general de los incisivosResumen y Conclusiones

265 característico de la fluorosis dental con la dosis de 35 mg/kg de

alimentos.

Se ha demostrado que las fundiciones de aluminio, las fábricas de

ladrillos, las fábricas de fósforo y las instalaciones de fertilizantes y de

fibra de vidrio son fuentes de fluoruros que están en correlación con

el daño a las comunidades de plantas locales. En la vegetación en las

proximidades de una fábrica de fósforo s e observó que el grado del

daño y las concentraciones de fluoruros en el humus del suelo eran

inversamente proporcionales a la distancia de la fábrica. El promedio de

las concentraciones de fluoruros en la vegetación oscilab a entre

281 mg/kg en las zonas gravemente dañadas y 44 mg/kg en las zonas

menos dañadas; en una zona testigo, la concentración de fluoruro fue

de 7 mg/kg. Las comunidades de plantas en las cercanías de una

fund ición de aluminio mostraban diferencias en la composición y

estructura de la comunidad debi do en parte a variaciones en la

tolerancia a los fluoruros. Sin embargo, hay que señalar que uno de los

principales problemas con la id entificación de los efectos de los

fluoruros en la naturaleza es la presencia de variables confundidoras,

como por ejemplo otros contaminantes atmosféricos. Por consiguiente,

se ha de actuar con prudencia a la hora de interpretar los numerosos

estudios sobre el terreno relativos a la contaminación por fluoruros.

Las conclusiones iniciales de los efectos de los fluoruros en los

mamíferos procedían de estudios sobre animales domésticos, como el

ganado ovino y bovino. Los fluoruros se pueden recibir de la vegetación, el suelo y el agua de bebida. Se han determinado los niveles de

tolerancia para los animales domesticados, siendo los niveles más

bajos para las vacas lecheras de 30 mg/kg de pienso o 2,5 mg/l de agua

de bebida. Se han producido incidentes que afectaban a an imales

domesticados tanto a causa de fuentes naturales de fluoruros, como

las erupciones volcánicas y la geología subyacente, como por fuentes

de origen humano, por ejemp lo los suplementos minerales, las

industrias emisoras de fluoruro y las centrales eléctricas. Entre los

síntomas de la toxicidad por fluoruros cabe mencionar la emaciación,

la rigidez de las articulaciones y anomalías en dientes y huesos. Otros

efectos son un a reducción de la producción de leche y efectos

negativos en la capacid ad reproductiva de los animales. La

c oncentración más baja de fluoruros en los alimentos que pr ovocó

fluorosis en el ciervo salv aje fue de 35 mg/kg. Las investigaciones

acerca de los efectos de los fluoruros en la flora y fauna silvestres se

han concentrado en las repercusiones sobre la integridad estructuralEHC 227: Fluorides

266 de los dientes y los huesos. En las proximidades de las fundiciones se

han observado efectos inducidos por los fluoruros, por ejemplo cojera,

afeamiento dental y daños en los dientes.



### 9. Evaluación del riesgo para la salud humana y de los

efectos en el medio ambiente

Los fluoruros tienen efectos tanto positivos como negativos para

la salud humana, pero el margen entre las ingestas asociadas con estos

efectos es reducido. Es importante la exposición a todas las fuentes de

fluoruros, en particular el agua de bebida y los productos alimenticios.

Se dispone de poca información para caracterizar la relación dosisrespuesta relativa a los distintos efectos adversos. Son escasos, sobre

todo, los datos acerca de la exposición total, en particular la ingesta y

la absorción de fluoruros.

El efecto más grave es la acumulación esquelética de fluoruros

debid a a una exposición excesiva prolongada y sus efectos en las

enfermedades óseas no neoplásicas, en particular la fluorosis esquelética y las fracturas óseas. Hay pruebas claras obtenidas en la India y

en China de que una ingesta total de 14 mg de fluoruros/día provoca

fluorosis esquelética y un aumento del riesgo de fracturas óseas y

otras pruebas hacen pensar en un mayor riesgo de efectos óseos con

una ingesta total superior a unos 6 mg de fluoruros/día.

En el entorno de agua dulce, las concentraciones de fluoruros

naturales suelen ser inferiores a las supuestamente tóxicas para los

organismos acuáticos. Sin embargo, estos organismos podrían verse

afectados negativamente en las proximidades de descargas de origen

humano. La toxicidad de los fluoruros depende de la dureza del agua.

Las especies de plantas sensibles que crecen cerca de fuentes de

fluoruros de origen humano están expuestas a riesgos. La emisión de

fluoruro de fuentes humanas está asociada con daños para las

comunid ades de plantas terrestres locales, pero con frecuencia es

difícil atribuir estos efectos exclusivamente a los fluoruros, debido a la

presencia de otros contaminantes atmosféricos. Los suel o s suelen

adsorber fuertemente los fluoruros. En consecuencia, la absorción porResumen y Conclusiones

267 las plantas mediante esta vía es relativamente baja y la lixiviación de los

fluoruros a través del suelo mínima.

Las concentraciones de fluoruros en la vegetació n cercana a

fuentes de emisión, como las fundiciones de aluminio, pueden ser

superiores a la concentración más baja con efecto por vía alimentaria

notificada para los mamíferos en experimentos de laboratorio. Se ha

notificado fluorosis en animales domesticados. Todavía hay algunas

zonas que notifican incidentes de fluorosis en el ganado bovino

debido al consumo de suplementos minerales y agua de bebida con un

contenido elevado de fluoruros. Además, existe un posible riesgo de

ingestión de pastos y suelo contaminados por fluoruros debido al uso

prolongado de fertilizantes fosfatados que contienen fluoruros como

impureza. Se han notificado efectos inducidos por los fluoruros, como

cojera y daños en los dientes, en mamíferos salvajes de las cercanías

de fuentes humanas.



### 10. Conclusiones

Todos los organismos están expuestos a fluoruros de fuentes

naturales y/o humanas. Se han observado ingestas muy elevadas en

zonas de todo el mundo donde abundan los fluoruros en la naturaleza

y donde las personas utilizan agua freática con un contenido elevado

de fluoruros como agua de bebida. Podría haber una mayor exposición

en las cercanías de fuentes puntuales. Los fluoruros de los productos

dentales son una fuente adicional para muchas personas.

Los fluoruros tienen efectos tan to beneficiosos como

perjudiciales en la salud humana, con un margen de ingesta reducido

entre ambos.

Se pueden observar efectos en los dientes y en el esqueleto con

exposiciones inferiore s a las asociadas con la aparición de otros

efectos adversos para la salud específicos de órganos o tejidos.

Se considera que los efectos en los huesos (por ejemplo, la

fluorosis esquelética y las fracturas) son los resultados más

importantes en la evaluación de los efectos adversos de la exposición

prolongada de las personas a los fluoruros.EHC 227: Fluorides

268 La fluorosis esquelética es una discapacidad invalid ante que

afecta a millones de personas en diversas regiones de África, China y

la India, con repercusiones importantes para la salud pública y socioeconómicas.

La ingestión de fluoruros con el agua y los productos alimenticios

es el factor causal primordial de la fluorosis esquelética endémica. En

algunas regiones, la combustión en recintos cerrados de carbón con un

contenido elevado de fluoruros puede contribuir asimismo como una

fuente importante.

Hay pocos datos para estimar la exposición total a los fluoruros

y su biodisponibilidad, y s e han detectado contradicciones en los

informes sobre la caracterización de sus efectos adversos.

Hay pruebas convincentes obtenidas en la India y en China de

que una ingesta total de 14 mg de fluoruros/día produce fluorosis

esquelética y un mayor riesgo de fracturas óseas, y p ruebas que

parecen indicar un mayor riesgo de efectos óseos con ingestas totales

superiores a unos 6 mg de fluoruros/día.

Una exposición excesiva a fluoruros biodisponibles representa un

riesgo para la biota acuática y terrestre.

Se pueden utilizar especies sensibles a los fl u oruros como

indicadores a fin de identificar sus peligros para el medio ambiente.

Es necesario mejorar los conocimientos sobre la acumulación de

fluoruros en los organismos y sobre su vigilancia y control.

Se deben caracterizar mejor los efectos biológicos asociados con

la exposición a los fluoruros.