World Trade Center Indoor Environment Assessment:

Selecting Contaminants of Potential Concern and

Setting Health-Based Benchmarks

May 2003

Prepared by the Contaminants of Potential Concern (COPC) Committee

of the World Trade Center Indoor Air Task Force Working Group

Contributors:

U.S. Environmental Protection Agency

Mark Maddaloni

Charles Nace

Peter Grevatt

Terry Smith

Dore LaPosta

John Schaum

Dana Tulis

Jennifer Hubbard

New York City Department of Health and

Mental Hygiene

Nancy Jeffery

Ken Carlino

Jeanine Prudhomme

Chris D’Andrea

Caroline Bragdon

James Miller

Agency for Toxic Substances and Disease Registry

Sven Rodenbeck

Danielle DeVoney

New York State Department of Health

Robert Chinery

Occupational Safety and Health Administration

David Ippolito

Dan Crane
i

Table of Contents

1.0 Introduction ............................................................. 1

2.0 Selecting the Contaminants of Potential Concern (COPC) ........................... 3

2.1 Review of Multiple Data Sets to Identify Candidate Substances ................. 3

2.2 Initial Screen to Identify Contaminants Requiring Further Consideration ........... 5

2.2.1 Eliminating volatile compounds ................................... 5

2.2.2 Eliminating contaminants detected at low frequencies .................. 5

2.2.3 Comparing detected concentrations to health-based screening values ....... 5

2.3 Secondary Screen to Select COPC. .................................... 7

2.3.1 Contaminants with toxicity criteria ................................. 7

2.3.2 Contaminants with no toxicity criteria. . . . . ...................... 7

3.0 Setting Benchmarks for the Contaminants of Potential Concern (COPC) ............... 8

3.1 Use of Environmental Standards/Regulations ............................... 8

3.2 Developing Risk-based Criteria for Indoor Air and Settled Dust ................ 9

3.3 Developing Benchmark Levels Based on Occupational Health Standards ......... 9

3.4 Health-Based Benchmarks (Summary Table) ............................. 12

4.0 Uncertainties and Limitations ............................................... 12

5.0 References ............................................................ 16

Appendix A: Deriving Health-Based Screening Values for Air and Dust Exposure Pathways

Appendix B: Results of the COPC Selection Process

Appendix C: Basis for Screening Level of 1 x 10-4

Appendix D: Assessing Exposures to Indoor Air and to Residues on Indoor Surfaces

Appendix E: IEUBK Lead Model Results for Lead in Indoor Air
ii

This page intentionally left blank.
iii

Foreword

Following the collapse of the World Trade Center on September 11, 2001, federal, state, and

municipal health and environmental agencies initiated numerous studies to assess environmental

conditions in the area. A multi-agency task force was specifically formed to evaluate indoor

environments for the presence of contaminants that might pose long-term health risks to local residents.

As part of this evaluation, a task force committee was established to identify contaminants of primary

health concern and establish health-based benchmarks for those contaminants in support of ongoing

residential cleanup efforts in Lower Manhattan. In September 2002, the committee released a draft

document titled “World Trade Center (WTC) Indoor Air Assessment: Selecting Contaminants of

Potential Concern (COPC) and Setting Health-Based Benchmarks.” 

In October 2002, a panel of 11 experts conducted an independent peer review of the draft COPC

document to ensure that the evaluations presented in the document were technically based and

scientifically sound. A final report with peer reviewers’ conclusions and recommendations was released

in February 2003. The peer review report and the COPC Committee’s response to peer review

comments can be accessed on-line at: www.tera.org. 

The responsiveness summary provides the formal responses to peer reviewer comments. EPA, through

its chairmanship of the multi-agency committee that authored the response to peer review comments,

assumes ownership and fully endorses that report’s content. The responsiveness summary presents

background on the peer review process, an overview of the peer reviewers’ main conclusions and

recommendations, and the document authors’ responses to specific comments. The final COPC

document presents the updated approaches for selecting COPC and setting health-based benchmarks,

based on peer reviewer input. 

Copies of the final COPC document can be obtained on-line at www.epa.gov/WTC. Inquires

regarding the content of this document should be directed to:

Mark A. Maddaloni Dr.P.H., DABT

U.S. Environmental Protection Agency, Region 2

290 Broadway

New York, NY 10007-1866

212-637-3590

maddaloni.mark@epa.gov

This document is just one product that addresses environmental and public health concerns related to

the WTC. Individuals interested in other studies and research projects related to the WTC should refer

to the following Web pages:

1.01 U.S. EPA: www.epa.gov/WTC

1.02 ATSDR: www.atsdr.cdc.gov/

1.03 NYCDOHMH: http://home.nyc.gov/html/doh/html/alerts/911.html
iv

List of Abbreviations

ACGIH American Conference of Governmental Industrial Hygienists

ATSDR Agency for Toxic Substances and Disease Registry

COPC contaminant(s) of potential concern

CSF cancer slope factor

EPA U.S. Environmental Protection Agency

HEAST Health Effects Assessment Summary Tables

IEUBK Integrated Exposure Uptake Biokinetic 

IRIS Integrated Risk Information System 

IUR inhalation unit risk

μg/m3 microgram per cubic meter

mg/m3 milligram per cubic meter

MRL ATSDR minimal risk level 

NHANES National Health and Nutrition Examination Survey

NIOSH National Institute of Occupational Safety and Health

NJDEP New Jersey Department of Environmental Protection

NYCDEP New York City Department of Environmental Protection

NYCDOHMH New York City Department of Health and Mental Hygiene

NYSDOH New York State Department of Health

OSHA Occupational Safety and Health Administration

PAHs polycyclic aromatic hydrocarbons

PCM phase contrast microscopy

PEL OSHA permissible exposure limit

REL NIOSH recommended exposure limit

RfD reference dose

RfC reference concentration

SVOC semi-volatile organic compound

TERA Toxicology Excellence for Risk Assessment

TLV ACGIH threshold limit value 

VOC volatile organic compound

WTC World Trade Center
1

1.0 Introduction

Background

Since September 11, 2001, the outdoor (ambient) environment around the World Trade Center

(WTC) site and nearby areas has been extensively monitored by a group of federal, state, and

municipal environmental and health agencies. The agencies have taken samples of air, dust, water, river

sediments, and drinking water and analyzed them for the presence of contaminants that could pose a

health risk to response workers at the WTC site, office workers, and local residents. 

While some workers (WTC response as well as office) and local residents may have experienced acute

irritant and respiratory effects from the collapse of the towers and associated fires, extended monitoring

of the ambient air at and beyond the perimeter of the WTC site over the past year and a half indicates

that contaminant concentrations in the ambient air pose a low risk of long-term health effects (EPA

2002). In February 2002, A multi-agency task force headed by EPA was specifically formed to

evaluate indoor environments for the presence of contaminants that might pose long-term health risks to

local residents. As part of this evaluation, a task force committee was established (COPC Committee)

to identify contaminants of primary health concern and establish health-based benchmarks for those

contaminants in support of planned residential cleanup efforts in Lower Manhattan.

Purpose

The process of selecting contaminants of potential concern (COPC) and setting health-based

benchmarks—the subject of this document — is intended to determine which contaminants are likely

associated with the WTC disaster for the purpose of setting health-based benchmarks for the indoor air

and settled dust.

As depicted in Diagram 1, the COPC document informs the Indoor Air Residential Assistance/WTC

Dust Clean-up Program, which will be referred to as the WTC Clean-up Program through the

remainder of this document. In conventional hazardous waste site investigations, the COPC selection

process is intended to reduce what is typically an extensive contaminant sampling list to a manageable

“short list” of risk-driving chemicals. The risk from this “short list” is then calculated to determine if

remedial action is warranted. Regarding the WTC, there was an a priori decision to institute a clean-up

program rather than launch a formal remedial investigation to determine if remediation of residential

dwellings was necessary. The primary reason for this decision was to eliminate the time-consuming

process of initiating a remedial investigation (i.e., developing a sampling and analysis plan, conducting

representative sampling of residential dwellings, analyzing a large number of samples, and finally

interpreting results) at a time when re-habitation of residential dwellings in Lower Manhattan was nearly

complete. As a result of this decision, the COPC selection process associated with the WTC Clean-up

Program assumed a somewhat modified purpose. Rather than serve as a process to determine the need

for clean-up, the COPC selection process served to facilitate development of health-based benchmarks

for the WTC Clean-up Program. By identifying COPC, health-based clearance criteria for individual

contaminants could be developed for indoor air and settled dust. To summarize, first and foremost, the

intent of the COPC document is to identify risk-driving chemicals and to establish specific health-based

benchmarks for the WTC Clean-up Program.

As part of this initiative, the COPC selection process informed two complimentary studies that were

undertaken as part of the WTC Clean-up Program. The first was the WTC Residential Confirmation
2

Indoor Cleanup Program

Cleaning Confirmation

Study

COPC/Benchmark Report

Background

Study

Clearance

Criteria

Background

Concentration

Attainment of

Benchmarks

Indoor Cleanup Program

Cleaning Confirmation

Study

COPC/Benchmark Report

Background

Study

Clearance

Criteria

Background

Concentration

Attainment of

Benchmarks

Cleaning Study (EPA 2003a). This study was initiated to evaluate the effectiveness of various cleaning

methods (e.g., high-efficiency particulate air vacuuming, wet wiping) used to clean residences. The

COPC selection process provided the list of contaminants to sample for in the WTC Residential

Confirmation Cleaning Study. It also enabled the development of health-based benchmarks for indoor

air and settled dust so the effectiveness of cleaning methods could be assessed. The cleaning methods

employed also served to guide the clean-ups of other heavily impacted unoccupied buildings. Another

outcome of the WTC Residential Confirmation Cleaning Study was in streamlining the post-cleaning

sampling needs of the WTC Clean-up Program. Although not a specific goal, this effort identified an

indicator chemical (i.e., asbestos) that signaled the reduction of all COPC to concentrations below

health-based benchmarks. With thousands of residents signed up for cleaning, the use of an indicator

contaminant to establish cleaning effectiveness provided a powerful tool in facilitating the WTC Cleanup Program.

The other initiative that the COPC selection process informed was the WTC Background Study (EPA

2003b). The development of remediation goals is influenced by factors such as technical

implementation, analytical detection limits, and the background concentration of contaminants in the

environmental setting of interest. A literature review of contaminant background concentrations in

residential dwellings was conducted to inform the WTC Clean-up Program. Limited information was

obtained for asbestos in indoor air and lead and dioxin in settled dust, otherwise the search yielded very

little useful data. It was therefore deemed advantageous to conduct a site-specific background study to

inform risk management decisions regarding the setting of clean-up goals at health-based or

background concentrations. Consequently, The COPC selection process directed the group of

contaminants to be sampled for in the WTC Background Study. Conversely, the results of the WTC

Background Study provides data to enhance the value of the final COPC document. That is, it

provides an estimate of background for COPC in Lower Manhattan to be evaluated alongside healthbased benchmarks. 

Diagram 1
3

2.0 Selecting the Contaminants of Potential Concern (COPC)

A systematic risk-based approach was used to select COPC. As shown in Figure 1, the selection

process involved multiple steps. The process began with the review of an extremely large environmental

data set, including indoor and outdoor air and dust data. This was followed by a two-level screening

which considered individual contaminant toxicity, the prevalence of a contaminant within and across

media, and the likelihood that a detected contaminant was related to the WTC disaster. The goal of the

process was to identify those contaminants most likely to be present within indoor environments at

levels of health concern. 

This section details the steps and overall findings of the COPC selection process. Two appendices

provide supporting documentation for the screening process. Appendix A describes how the healthbased screening values used in the process were derived. Appendix B presents the findings of each

step of the process.

2.1 Review of Multiple Data Sets to Identify Candidate Substances

The collapse of the WTC released a very broad range of contaminants into the air, many of which

deposited with settled dust on surfaces in Lower Manhattan, both indoors and outdoors. To gain the

best possible sense of the contamination levels in indoor residential environments, multiple sets of

sampling data describing environmental conditions at and near the WTC site between September 11,

2001, and the present were reviewed. The primary goal of this exercise was to review data that might

provide insights on the contamination levels inside Lower Manhattan residences. As a result, a large set

of bulk dust and settled dust sampling results were reviewed, along with ambient and indoor air

sampling data, based on the premise that contaminants entered residences through atmospheric

transport.

Sampling data evaluated included those collected by the U.S. Environmental Protection Agency (EPA),

Agency for Toxic Substances and Disease Registry (ATSDR), Occupational Safety and Health

Administration (OSHA), New York City Department of Environmental Protection (NYCDEP), New

York City Department of Health and Mental Hygiene (NYCDOHMH), the New York City

Department of Education, the New Jersey Department of Environmental Protection (NJDEP),

academic institutions and independent investigators. Overall, we examined results from more than

500,000 environmental samples, with sampling results available for more than 300 contaminants. The

contaminants included volatile organic compounds (VOCs), semi-volatile organic compounds

(SVOCs), pesticides, polychlorinated biphenyls (PCBs), metals, asbestos, silica, other minerals, and

synthetic fibers. Every contaminant identified in the sampling data was considered a candidate

substance for the COPC selection process. A more complete description, including citations, of the

data bases evaluated for selecting COPC can be found in Appendix B.
4

Figure 1. COPC Selection Process
5

2.2 Initial Screen to Identify Contaminants Requiring Further Consideration

The goal of the initial screening procedure was to sort through a large volume of data in a consistent

manner to identify those substances requiring closer evaluation. In this analysis, ambient air, indoor air,

bulk dust, and settled dust data were evaluated separately. The initial screening involved three main

steps, as described below. The outcome of this process is detailed in Appendix B.

2.2.1 Eliminating volatile compounds

Volatile compounds were eliminated from the COPC selection process, because any volatile

compound that might have been released in or adhered to dusts from the WTC site have likely

evaporated or greatly dissipated since the time that air emissions from the site were controlled (i.e.,

since the time that the fires were extinguished - December, 2001). Any contaminant on the target

compound list for Method TO-15 (ambient air) and Method 8260 (waste) was considered volatile.

Further, chemical similarity to compounds on those lists and boiling point (as a surrogate for vapor

pressure) were used to identify additional volatile contaminants not on these methods’ target lists.

2.2.2 Eliminating contaminants detected at low frequencies 

All contaminants detected in fewer than 5% of samples were removed from the list of candidate

contaminants, but only if the contaminant was analyzed for in more than 20 samples. This screening

approach based on frequency of detection is consistent with EPA’s guidance on human health risk

assessment (EPA 1989). The purpose of this step was to focus the COPC selection process on

contaminants that were consistently detected, rather than on those that were infrequently detected.

The frequency of detection was calculated based on all relevant sampling data for a particular medium.

WTC related environmental samples were obtained throughout Lower Manhattan from 9/11/01

through the present time. Using this approach, a contaminant could be eliminated even if it were

detected at a relatively high concentration, but perhaps only in one location or at one point in time. We

therefore carefully reviewed the contaminants eliminated in this step of the process to ensure that

contaminants possibly linked with the WTC disaster and of potential public health importance did not

get eliminated using this procedure. For example, before eliminating PCBs from further consideration,

we confirmed that the PCBs detected in fewer than 3% of settled dust samples did not exceed healthbased screening values. 

2.2.3 Comparing detected concentrations to health-based screening values

For the contaminants that were not eliminated in the previous two steps, the maximum concentration

detected in each medium was compared to corresponding health-based screening values. Health-based

screening values were derived for air, bulk dust, and settled dust using methodologies, risk equations,

and exposure assumptions consistent with established EPA risk assessment guidance. Appendices A

and D present the specific risk equations, exposure parameters, and toxicity values used in deriving

health-based screening values. 

Exposure equations generally stem from EPA’s Risk Assessment Guidance for Superfund (RAGS)

(EPA 1989). Exposure assumptions used are those recommended in RAGS or supplemental risk

assessment guidance, including EPA’s Exposure Factors Handbook (EPA 1997b), Child-Specific

Exposure Factors Handbook (EPA 2002a), Dermal Exposure Assessment: Principles and Applications

(EPA 1992), and RAGS Part E, Supplemental Guidance for Dermal Risk Assessment (EPA 2001a).
6

To evaluate the settled dust pathway, EPA guidance for residential pesticide exposure assessment

(EPA 2001b) was used and further supported by procedures and re-entry guidelines previously

developed for scenarios evaluating fine dust particles more analogous to those associated with the

WTC collapse (Kim and Hawley 1985; NJDEP 1993; Michaud et al. 1994; Radian 1999).

In calculating health-based screening values, the following criteria were applied to all exposure

pathways:

# Evaluation of both cancer and non-cancer effects, with a target cancer risk of 10-4 and

a hazard quotient of 1 for non-cancer endpoints—the more sensitive of the two being

used to derive screening values.

# Evaluation of adult and child exposures, with child exposures factoring heavily into the

development of dust screening values.

# Use of the most current toxicity criteria on EPA’s Integrated Risk Information System

(IRIS) database. In the absence of IRIS toxicity criteria, the following hierarchy of

toxicity data sources was used: EPA’s Health Effects Assessment Summary Tables

(HEAST), ATSDR’s minimal risk levels (MRLs), provisional values derived by EPA’s

National Center for Environmental Assessment, and, in limited cases, the use of

surrogate toxicity values or cross-route extrapolations.

Three outcomes were possible from this initial screening:

1) If a contaminant’s maximum concentration was lower than the corresponding screening value,

that contaminant was eliminated from further consideration. Appendix B presents, by medium,

the contaminants that fall into this category, listing the maximum detected concentrations and

corresponding screening values.

2) If a contaminant’s maximum concentration was greater than the screening value, then we

evaluated the contaminant further in the secondary screening step (see Section 2.3.1 below).

Fifteen contaminants fell into this category, including:

Aluminum

Antimony

Arsenic

Asbestos

Barium

Chromium

Dioxins

Lead

Manganese

Naphthalene

Nickel

PAHs (carcinogenic)

Mercury

4,4'-Methylene diphenyl diisocyantate (MDI)

Thallium

3) If a contaminant did not have a toxicity value, and therefore did not have a screening value, we

reviewed other relevant information (e.g., trends among sampling data, comparisons to

background, the likelihood of the contaminant being related to site-specific releases) on a caseby-case basis to determine whether the contaminant should be evaluated further (see Section

2.3.2 below).

2.3 Secondary Screen to Select COPC. 

As noted in the previous section, two classes of contaminants required further evaluation after the initial

screen: (1) contaminants with a maximum concentrations greater than screening values and (2)
7

contaminants for which no screening values are available. Sections 2.3.1 and 2.3.2 describe the

secondary screening procedure for these two groups of contaminants. Appendix B (Section 5.0)

presents detailed justifications for the contaminants included and not included as COPC.

2.3.1 Contaminants with toxicity criteria

For those substances exceeding health-based screening criteria in at least one sample, a detailed 

review of findings across environmental media was conducted to assess the representativeness of

reported maximum concentrations, to study spatial and temporal trends, to determine the relationship of

detected concentrations to available background concentrations, and to examine whether there was

reason to believe a contaminant was site-related. Professional judgment entered into this part of the

process. In general, contaminants with reported concentrations deemed representative of exposure

conditions and detected above background (if appropriate comparison data were available) were

retained as COPC. 

The following list describes the final decisions reached for the 15 contaminants identified as requiring

further evaluation: 

# Asbestos, dioxins, lead, and PAHs. These contaminants were selected as COPC because

they were consistently detected across environmental media at concentrations above healthbased screening values.

# Aluminum, antimony, arsenic, barium, manganese, naphthalene, nickel, MDI, and

thallium. These contaminants were not selected as COPC. In each case, closer examination

presented strong evidence that these contaminants were not likely present in indoor dusts at

levels of health concern (See Appendix B for additional discussion).

# Chromium and mercury. These two contaminants were not retained as COPC but deserve

some additional discussion. Chromium in ambient air has been shown to exceed health-based

screening values, though chromium levels in available bulk and settled dusts collected in Lower

Manhattan are not above health-based screening values. Regarding mercury, wipe sampling

data indicated that in isolated instances settled dust in Lower Manhattan residences contained 

mercury at levels greater than health-based screening values. In both cases, it is unclear whether

detected levels were associated with the WTC. (See Appendix B for additional discussion.)

Regardless, as part of the WTC Clean-up Program, EPA is performing a limited number of

wipe samples for 21 non-COPC metals, including chromium and mercury.

2.3.2 Contaminants with no toxicity criteria

A subset of contaminants were detected for which no toxicity criteria or corresponding screening values

were available. For these contaminants we considered any occupational or environmental standards

and/or evaluated sampling trends, exposure potential, and the likelihood a contaminant was associated

with the WTC collapse. The following list describes the final decisions reached for these contaminants:

# Fibrous glass and crystalline silica. These contaminants were retained as COPC. Both are

components of building materials. Fibrous glass was consistently detected at high concentration

in both bulk and settled dust samples collected at and near the WTC site. Crystalline silica,

measured as alpha quartz, has been selected as a COPC for the following reasons: (1) indoor

dust levels of quartz in Lower Manhattan were found to be significantly higher than those in

comparison locations north of 59th Street; (2) quartz has been found in the respirable fraction of
8

air samples, demonstrating a potential for exposure; and (3) quartz is a known component of

building construction materials and was known to be released when the WTC collapsed.

# Calcite, gypsum, and portlandite. These contaminants were eliminated from further

consideration. Detected concentrations were more than 100 times lower than occupational

exposure limits for irritant effects.

# Essential nutrients (e.g., calcium, magnesium); a limited number of specific phthalates

and PAHs, and SVOCs that are not conventionally measured to support EPA risk

assessment. Due to the lack of appropriate comparison data, these substances were not

carried any further in the COPC selection process. See Section 4.0 (Uncertainties and

Limitations) for perspective on the impact that not evaluating these substances has on the

overall COPC selection process.

3.0 Setting Benchmarks for the Contaminants of Potential Concern (COPC)

Health-based benchmarks were developed to be protective of long-term habitability of residential

dwellings. The following hierarchal approach was employed for developing benchmark values: use of

relevant and appropriate environmental standards/regulations; calculation of health-based benchmarks

employing environmental risk assessment guidance, and adaptation of occupational standards with

additional safety factors. 

3.1 Use of Environmental Standards/Regulations

A review of environmental standards/regulations was conducted for each of the six COPC. The

COPC Committee identified an applicable and relevant existing standard to set a health-based

benchmark for lead in interior dust. The Residential Lead-Based Paint Hazard Reduction Act (Title X)

Final Rule (40 CFR, Part 745, 1/5/01) established uniform national standards for lead in interior dust.

Thus, both EPA and the United States Department of Housing and Urban Development (HUD) have

set a dust standard for lead of 40 μg/ft2 for floors (including carpeted floors) and 250 μg/ft2 for interior

window sills.To support the development of a dust standard EPA performed an analysis of the

Rochester Lead-in-Dust Study (HUD, 1995). At 40 μg/ft2 a multimedia analysis shows a 5.3%

probability that a child’s blood lead level would exceed 10 μg/dl. Thus, this standard meets the criteria

established by EPA (i.e., 95% probability to be below 10 μg/dl) (EPA 1994a) for managing

environmental lead hazards. However, the COPC Committee opted to set the benchmark at the more

stringent HUD screening level of 25 μg/ft2. 

The clearance criteria established in the Asbestos Hazard Emergency Response Act (AHERA 1986) of

70 structures/mm2 (0.022 f/cc) was utilized to evaluate asbestos samples from the WTC ambient

(outdoor) air monitoring effort. Although not specifically risk-based, the AHERA standard was deemed

an appropriate benchmark for evaluating ambient airborne asbestos data, especially since exposure to

potentially elevated levels of asbestos in the ambient air was not expected to exceed the duration of

time needed to clean-up Ground Zero (i.e., less than one year). However, given the potential for

extended exposure in residential dwellings, a risk-based approach specifically developed to address

long-term exposure was deemed more appropriate.

3.2 Developing Risk-Based Benchmarks for Indoor Air and Settled Dust
9

In cases where appropriate standards did not exist (e.g., asbestos), risk-based benchmarks were

developed using established EPA risk assessment methods: for indoor air, methods described in EPA’s

“Risk Assessment Guidance for Superfund” (EPA 1989) were used; for settled dust, the most formal

EPA guidance which addresses this issue is the “Standard Operating Procedures (SOPs) for

Residential Exposure Assessment” originally published by the Office of Pesticides in 1997 and updated

in 2001 (Appendix D - EPA 1997a and EPA 2001a). This methodology was employed with

modifications. (See Appendix D for a comprehensive discussion of the methods, exposure parameters

and equations used to develop risk-based benchmarks for indoor air and settled dust.) The risk-based

benchmarks reflect the most current toxicity criteria (Cancer Slope Factors and RfDs/RfCs) on EPA’s

Integrated Risk Information System (IRIS). IRIS is a regularly updated (quarterly), online database that

reports chemical toxicity reference values and information on human health effects that may result from

exposure to chemicals in the environment. In the absence of IRIS toxicity criteria, the following

hierarchy of toxicity data sources was used: EPA’s Health Effects Assessment Summary Tables

(HEAST), ATSDR’s minimal risk levels (MRLs), provisional values derived by EPA’s National Center

for Environmental Assessment, and, in limited cases, the use of surrogate toxicity values or cross-route

extrapolations. Health based benchmarks for asbestos, dioxin, and PAHs, were derived by this

process. 

EPA’s Integrated Exposure Uptake Biokinetic (IEUBK) Lead Model (EPA, 1994) was employed to

derive a health-based benchmark for lead in indoor air. EPA developed the IEUBK Lead Model to

evaluate multimedia lead exposure to children in residential settings. EPA established a goal of attaining

a 95% probability that blood lead levels in children be less than 10 :g g/dl (EPA 1994a). Setting the

indoor air lead concentration at 0.7 :g g/m3 and using site specific (i.e., New York City background)

concentrations for lead in water, diet, soil and dust, the IEUBK Lead Model estimates that 95% of the

blood lead probability distribution falls below 10 :g/dl. See Appendix E for a detailed discussion of

medium-specific lead concentrations, data input spreadsheets and a graphic display of the blood lead 

probability distribution for children 0-7 years old. 

3.3 Developing Benchmark Levels Based on Occupational Health Standards

For contaminants that lacked environmental toxicity criteria from sources listed in Section 3.2,

occupational standards served as the starting point for benchmark development. Additional safety

factors were added to account for higher exposure and greater sensitivity within the general population.

The health-based benchmarks for fibrous glass and crystalline silica in indoor air were developed in this

manner. A detailed discussion for each benchmark is provided below.

Fibrous glass. Although the TLV (1 f/cc) is based on irritant effects, the derived benchmark of 0.01

f/cc (100 fold safety factor) is believed to be protective for chronic residential exposure for glass and

mineral wool. The COPC Committee did not specifically apportion this adjustment as a duration

adjustment or an adjustment for application to a non-worker population. Although this total adjustment

of 100 could be considered to cover the 4.2 duration adjustment, and an adjustment above that for

application to non-worker population, there is considerable variation in how this second adjustment

may be set. The concern is not so much can we assign a specific number for the adjustment which is

accurate, but rather is the resulting benchmark protective?

Fibrous glass less than 3 microns in diameter are respirable and available to enter and deposit in the

pulmonary regions of the lung (ACGIH 2001). Clearance of these fibers from the lung will be

determined by fiber solubility and length (ACGIH 2001; ATSDR 2002a). Fibers cleared from the lung

have less potential to create long-term health effects. Less soluble materials have a longer residence

time in the lung and therefore have a greater potential to contribute to tissue damage or malignant

disease. Within synthetic vitreous fiber (SVF) types, glass fibers and slag wool are considered the most
1

Early studies often relied upon injection and implantation studies, which may not accurately predict a

pulmonary response from inhalation exposures. A review of inhalation studies indicates that glass wool did not

cause pulmonary fibrosis or lung cancer in these animal studies (Bonn et al. 1993). A recent study by Hesterberg

indicates no increase in pulmonary fibrosis or lung cancer even at doses of 222 f/cc, although cancer incidence in

control animals was considered high. 

10

soluble, and therefore least toxic. Mineral wool is less soluble than glass wool. The fibers observed in

indoor and outdoor dust samples from the WTC area contained glass wool and mineral wool, both of

which have lower biopersistence than other forms of synthetic vitreous fibers.

Although some animal studies have demonstrated both fibrotic and carcinogenic potential for glass and

mineral wools (ACGIH 2001; ATSDR 2002a; IARC 1988), more recent studies do not fully support

this finding.1 Epidemiologic studies on workers exposed to fibrous glass do not provide consistent

evidence of pulmonary effects, although some effects were noted (ATSDR 2002a; Bonn et al. 1993).

Similarly, when assessing deaths due to lung cancer in workers exposed to glass wool, studies do not

provide strong evidence for increased risk of cancer deaths attributable to the glass wool exposure.

The carcinogenic potential of fiberglass has been reviewed by several agencies. The IARC originally

classified both glass and mineral wools as Group 2B carcinogens, possibly carcinogenic to humans,

based on animal studies (IARC 1987). Similarly these materials were classified as carcinogens by the

National Toxicology Program and the American Conference of Governmental Industrial Hygienists

(ACGIH 2001; NTP 2001). However a review of the carcinogenic potential of these fibers by IARC

in 2001, which takes into account updated human studies, animal inhalation studies, and mechanistic

studies, recommends a change in this classification. The IARC has announced that the recent

monograph designates both glass and mineral wool as Group 3, unclassifiable as to carcinogenicity in

humans, because of inadequate evidence of carcinogenicity in humans and the relatively low

biopersistence of the materials. 

In contrast, the less soluble and more biopersistent refractory ceramic fibers are still considered

potentially carcinogenic and are believed to more toxic than glass and mineral wools. A recent review

of the toxicity of synthetic vitreous fibers by ATSDR proposes a Minimal Risk Level for chronic

exposure of 0.03 f/cc for these refractory ceramic fibers (ATSDR 2002b). Although ATSDR did not

set MRLs for glass and mineral wools, it notes that “insulation wools are markedly less durable and less

potent than refractory ceramic fibers.” Therefore the benchmark of 0.01 f/cc for glass and mineral

wools, which is lower, should be considered protective. 

Silica. No threshold has been established and it is possible health effects occur below the NIOSH

REL of 50 :g/m3. Although duration adjustments and uncertainty factors can be applied to this REL to

develop a benchmark for residential exposure, the resulting level would be below practical detection

limits. Therefore the COPC Committee is recommending a benchmark of 5 :g/m3, which is the lowest

amount that can be reliably reported in a reasonable sampling time.

The level of this benchmark is technically limited by sampling constraints, including time and weight

loading. It is based upon a reporting limit of 10 micrograms of crystalline silica with no more than about

3 milligrams of total dust on a single filter. (A reporting limit is the smallest amount of a substance for

which a quantitative value can be determined.) More than about 3 milligrams of dust on the filter will

decrease analytical sensitivity. Collection of 2 cubic meters of air over about 20 hours for a Dorr-Oliver

cyclone at 1.7 L/min or about 13.3 hours using an SKC cyclone at 2.5 L/min will provide sufficient

sensitivity to measure 5 μg/m3 crystalline silica so long as the total dust weight on the filter does not
11

exceed about 3 milligrams (an airborne dust concentration of 1.5 mg/m3). Using either the nylon DorrOliver or SKC Aluminum Cyclones, the following limits are possible:

Sampling Equipment

(Size selection

cyclones)

Duration of sampling Volume of air

(m3)

Effective reporting limit

(μg/m3)

Dorr-Oliver (OSHA)

at1.7 L/min

6 hours (360 min) 0.61 16.3

8 hours (480 min) 0 .81 12.3

10 hours (600 min) 1.02 9.8

19.6 hours (1176 min) 2.0 5.0

SKC Aluminum

(NIOSH) at 2.5

L/min

6 hours (360 min) 0.9 11.2

8 hours (480 min) 1.20 8.4

10 hours (600 min) 1.5 6.7

13.3 hours (800min) 2.0 5.0

3.4 Health-Based Benchmarks (Summary Table)

Table 1 lists the COPC health-based benchmarks for indoor air and settled dust. Benchmarks for

asbestos, fibrous glass and crystalline silica in settled dust are not provided for the following reason.

These three minerals exert their toxicity primarily through the inhalation route of exposure. Therefore, a

health-based benchmark for settled dust would be a function of the relationship between the mineral

content in settled dust and indoor air. Limited studies (Millette and Hays, 1994) have described the

empirical relationships (referred to be the authors as “ K factors”) between concentrations of asbestos

fibers in settled dust and indoor air. These K factors were developed by studying matched air and

settled dust samples taken from indoor environments at varying levels of activity. However, due to the

numerous factors that influence the relationship between fiber concentration in settled dust and indoor

air, including surface porosity, activity patterns, air exchange rates and interior volume, the COPC

Committee elected against setting benchmarks for COPC in settled dust based on projected

concentrations in indoor air. 

COPC Indoor Air Settled Dust

Asbestos* 0.0009 f/cc n/a

Lead 0.7 μg/m3 25 μg/ft2

MMVF 0.01 f/cc n/a

Dioxin 0.001 ng/m3 2 ng/m2

PAH 0.2 μg/m3 150 μg/m2

Silica 5 μg/m3 n/a

Table 1
12

*Risk-based criteria were used to develop the benchmark level for asbestos in air. Conservative

assumptions of continuous exposure to a constant level of airborne fibers were combined with the IRIS

Slope Factor to establish a benchmark equating to a 1x10-4 excess lifetime cancer risk. This approach

makes several assumptions, chief among those is the quantification of asbestos fibers in air based on the

PCM equivalent (PCMe) definition of a fiber (greater than 5um in length with an aspect ratio of 3:1 or

greater) and the use of the IRIS Slope Factor which was designed to apply to fibers so defined. 

Although there is some concern regarding shorter fibers, the approach used here represents the current

consensus by the US EPA for quantifying risk of airborne asbestos fibers. It should be noted there is

ongoing debate regarding the nature of health effects which may be attributed to shorter asbestos fibers. 

Both EPA and ATSDR are currently pursuing meetings to discuss and further refine these issues. 

However for the purposes of this response, addressing PCMe fibers is considered protective.

4.0 Uncertainties and Limitations

Overall, the COPC selection process used in evaluating WTC-related contamination enabled us to

select appropriate indicator contaminants, leading to the development of benchmark criteria which

support ongoing efforts to safely clean up residential environments in Lower Manhattan. However,

some uncertainties are inherent in the COPC selection and benchmark setting processes.

The primary uncertainties associated with the COPC selection process include the nature of the

environmental data sets used in the selection process and the absence of toxicity criteria for some

contaminants. Other uncertainties relate to the exposure assumptions used in setting benchmark values,

especially for settled dust. The impact of these factors on the outcome of the process are detailed

below.

# Data limitations. Outside of the WTC Clean-up Program itself, extensive, systematic sampling

of indoor air and dusts in Lower Manhattan residences has not occurred. However, in selecting

COPC, we drew from the much larger sampling data from other media to account for this

shortcoming. We feel that these data are sufficient to identify those contaminants most likely to

be present in indoor environments and to support the derivation of clean-up criteria. Ambient

air monitoring data need to be interpreted with caution before being used to evaluate indoor

environments. For example, samples collected months after the WTC collapse may not have

characterized much of what made it into the residences as dust. Fortunately, indoor air and

residual dust sampling being conducted as part of EPA’s ongoing residential clean-up program

offer additional insight to the nature and extent of contaminants found in indoor environments.

As discussed earlier, to promote a timely response to the WTC disaster, conventional remedial

investigation approaches were not used to generate our study data. That is, an investigation of

indoor environments with targeted sampling was not conducted. Instead, to expedite cleanup,

we relied on existing data sets realizing that many of the data sets were generated

independently, by multiple entities, for various purposes, and with varying data quality

objectives. Sampling and analytical methods varied across some studies, and that limited results

exist for some contaminants in some media. To the extent possible, we factored contaminantand study-specific considerations into final decisions on COPC (e.g., sample size, detection

limits, etc.). Lastly, environmental sampling data do not specifically “fingerprint” the possible

unique pattern of substances that may have been released from the WTC collapse and settled in

indoor dust. Nonetheless, we still screened hundreds of contaminants, many of which are

known to be associated with building materials or thermal or chemical degradation products

(e.g., asbestos, PAHs and other SVOCs, dioxins, and metals). Through a combined analysis of
13

air and settled dust data, the process enabled the identification of risk-driving contaminants

within indoor environments.

# Absence of contaminant-specific toxicity criteria. Though toxicity values are not currently

available for a subset of contaminants tested for and detected in some air and dust samples in

Lower Manhattan, the COPC selected are indicative of the most prevalent, most toxic

contaminants associated with the WTC releases. A wide range of contaminant classes were

captured, among which some of the more toxic members were identified and screened (e.g.,

dioxins, PAHs, metals). Basing COPC selection on the contaminants with known toxicity

criteria (and arguably some of the more toxic compounds) that are measured at higher levels

than the contaminants in question is believed to be appropriate and reasonably healthprotective.

The list of contaminants without toxicity criteria that were not carried through the COPC

selection process include (1) essential nutrients (e.g., calcium, magnesium), which EPA

generally does not carry through its risk assessments; (2) a limited number of specific phthalates

and PAHs; (3) and SVOCs that are not conventionally measured to support EPA risk

assessment. The lengthiest list of SVOCs for which no toxicity criteria exist comes from Lioy et

al. (2002)—a study of three outdoor bulk dust samples collected in Lower Manhattan on

September 16 and 17, 2001. Most of the SVOCs that do not have toxicity criteria were not

consistently detected across the three samples. Further, the concentrations measured were

consistently lower than other SVOCs (e.g., PAHs) that have been selected as COPC. Finally,

because many of the SVOCs identified by Lioy are rarely considered in environmental sampling

studies, we have no knowledge whether the measured levels are consistent with background

concentrations in urban settings or if the levels are unusually high.

# Absence of child-specific toxicity criteria. Ideally, toxicity criteria should consider the critical

exposure periods and toxicity endpoints relevant to children’s health. However, the

development of additional toxicity criteria for children to support the COPC selection process is

beyond the scope of this effort. Our screening process did consider, however, toxicity

endpoints relevant to children’s health where available (e.g., lead). As stated earlier, the critical

studies and endpoints used in developing IRIS and alternate toxicity values served as the basis

for our screening values. Currently, most consensus toxicity values are based on the evaluation

of adult exposures, not early-life exposures, though EPA does factor in relevant information on

reproductive and developmental endpoints (or the lack thereof) when deriving toxicity values.

It should be noted that research evaluating the significance of early-life exposures to toxic

chemicals is ongoing by EPA and others. For example, EPA recently developed draft guidance

for assessing cancer susceptibility from early-life exposure to carcinogens (EPA 2003).

Because most current cancer slope factors do not account for susceptibility differences with

respect to early life stages, agency scientists are exploring the possibility of applying additional

uncertainty factors when evaluating childhood carcinogenic risks to some (e.g., mutagenic)

carcinogens. Much of the impetus for such an approach is the growing knowledge and

understanding of how a particular carcinogen exerts its effect (i.e., its mode of action) and how

a particular mode of action may increase the risk of tumor response if exposure occurs during

early-life stages. The COPC Committee acknowledge that the current approach of applying

existing toxicity criteria to all age groups introduces some uncertainty to the evaluation biased

toward an underestimation of risk.

# Uncertainty in deriving settled dust screening and benchmark values. As detailed in

Appendix D, derivation of settled dust screening values required multiple assumptions in
14

estimating exposure to surfaces, which add uncertainty to our analysis. For example, factors

affecting surface loading and transfers to skin have not been well studied and are likely to be

highly variable (e.g., characteristics of different surfaces, activities patterns related to surface

contact, and surface cleaning techniques and frequency). As a result, limited data were available

for many of the input parameters used to estimate dose from exposure to contaminants in

settled dust. However, consistent with general human health risk assessment practice, every

effort was made to select exposure input parameters that would define a reasonable maximum

exposure and produce protective screening values. Upper-bound exposure estimates were

used whenever available. Therefore, overall, the process represents a reasonably protective

approach.

# Evaluating multiple-contaminant exposures. Benchmarks were developed on a

contaminant-by-contaminant basis. It is clearly recognized that the residents in Lower

Manhattan are not exposed to environmental contaminants singularly, but instead to

combinations of chemical and physical agents. Development of benchmarks, however, was

driven by a combined consideration of individual COPC-specific toxicity, background levels,

and practicalities and limitations related to sampling. Mixture toxicology was not factored into

the derivation process because little or no quantitative dose-response data exist regarding

specific interactions across the WTC COPC (asbestos,
2Note that combined effects within dioxin and PAH mixtures were accounted for in the development of

benchmarks using toxic equivalency (TEQ) approaches that account for the relative potency of the components of

these complex mixtures. Toxicity equivalent factors used in this approach are based on our understanding of the

most toxic component of each mixture (i.e., 2,3,7,8-TCDD for dioxins and benzo(a)pyrene for PAHs).

One EPA study looking at acute airway effects in mice exposed to WTC fine particulate matter (2.5 microns)

provides some insights to the magnitude of total dust exposures leading to observable effects. This study revealed

that components of WTC dust promotes respiratory inflammation at “high” doses only (EPA 2002). This study does

not evaluate the effects of long-term or repeated exposures to lower levels of WTC dust and is not directly useful in

the development of benchmarks.

15

 dioxins, lead, PAHs, fibrous glass, and crystalline silica)2. 

The contaminant-specific approach is believed to be health protective, however, for the

following reasons:

1) For non-carcinogens, COPC benchmarks are set at concentrations well below

observed effect levels and generally at or below no-observed-adverse-effect levels

(NOAELs). Presumably, exposures to one or multiple substances below or near the

NOAEL will not result in adverse effects (EPA 2000b). 

2) The likelihood of interactions are increased if substances behave similarly

toxicologically. A review of the toxicology of individual COPC (target organ toxicity,

mode of action) and any documented chemical interactions among WTC COPC

revealed the following:

< Target organs and critical effects resulting from ingestion and dermal exposures

generally differ across individual COPC, though lead, dioxins, and PAHs are

all considered potential human carcinogens via the ingestion route. Each of

these contaminants can affect a wide range of biological systems, but each

generally exerts its effects via different mechanisms. 

< At high concentrations, inhalation exposure to several of the COPC (asbestos,

PAHs, fibrous glass, and crystalline silica), as well as the small particulate

matter released during the WTC disaster, has been shown to result in point of

contact toxicity to the lung. Specific lung effects vary across these substances,

ranging from acute irritant effects produced by fibrous glass to cancers of the

lung associated with asbestos. Exposures to COPC at or below benchmark

concentrations—which are set at levels significantly lower than observable

effect levels—would be unlikely to produce effects individually or in

combination.
16

5.0 References

American Conference of Governmental Industrial Hygienists (ACGIH). 2001. TLV Documentation:

Manmade Vitreous Fibers (MMVF), 2001.

ATSDR. 1995. Toxicological Profile for Asbestos. U.S. Dept. of Health and Human Services, Atlanta,

GA.

ATSDR. 1998. Toxicological Profile for Chlorinated Dibenzo-p-dioxins. Atlanta: U.S. Department of

Health and Human Services. December 1998.

ATSDR 2000. Toxicological Profile for Arsenic. Atlanta: U.S. Department of Health and Human

Services. September 2000.

ATSDR. 2001. Guidance Manual for the Assessment of Joint Toxic Action of Chemical Mixtures.

Draft for Public Comment. Atlanta: U.S. Department of Health and Human Services. February 2001.

ATSDR. 2002a. Technical Briefing Paper: Health Effects from Exposure to Fibrous Glass, Rock Wool

or Slag Wool. Agency for Toxic Substances and Disease Registry, U.S. Department of Health and

Human Services, Atlanta, GA. 2002.

ATSDR 2002b. Toxicological Profile for Synthetic Vitreous Fibers. Atlanta: U.S. Department of

Health and Human Services. September 2002. 

Bonn WB, Bender JR, et. al. 1993. Recent Studies of Man-made Vitreous Fibers: Chronic Animal

Inhalation Studies. J Occup Med. 1993;35(2):101-113.

EPA. 1986. EPA’s Guidelines for the Health Risk Assessment of Chemical Mixtures. EPA/630/R98/002. September 1986.

EPA. 1989. Risk Assessment Guidance for Superfund. Volume 1. Human Health Evaluation Manual

(Part A). Interim Final. U.S. Environmental Protection Agency, Office of Emergency and Remedial

Response. EPA/540/1-89/002. December 1989.

EPA. 1992. Dermal Exposure Assessment: Principles and Applications. Interim Report. U.S.

Environmental Protection Agency, Office of Health and Environmental Assessment.

EP/600/891/001/B.

EPA 1994. Guidance Manual for the Integrated Exposure Uptake Biokinetic Model for Lead in

Children. Office of Emergency and Remedial Response. EPA/540/R-93/081 Washington D.C.

EPA 1994a. Revised Interim Soil Lead Guidance for CERCLA Sites and RCRA Corrective Action

Facilities. OSWER Directive 9355.4-12. Washington D.C.

EPA. 1997a. Health Effects Assessment Summary Tables. FY 1997 Update. Emergency Response.

EPA-540-R-97-036. July 1997.

EPA 1997b. Exposure Factors Handbook. U.S. Environmental Protection Agency, Office of Research

and Development, National Center for Environmental Assessment. EPA/600/P-95/002Fa. August

1997.
17

EPA 2000a. Science Policy Council Handbook: Peer Review. U.S. Environmental Protection Agency,

Office of Science Policy. EPA 100-B-00-001. December 2000.

EPA. 2000b. Supplementary Guidance for Conducting Health Risk Assessment of Chemical Mixtures.

Risk Assessment Forum Technical Panel. EPA/630/R-00/002. August 2000.

EPA. 2000c. Draft Exposure and Human Health Reassessment of 2,3,7,8-Tetrachlorodibenzo-pDioxin (TCDD) and Related Compounds. Office of Research and Development. 

EPA. 2001a. Risk Assessment Guidance for Superfund Volume 1: Human Health Evaluation Manual

(Part E, Supplemental Guidance for Dermal Risk Assessment). Review Draft. U.S. Environmental

Protection Agency, Office of Emergency and Remedial Response EPA/540/R/99/005.

EPA 2001b. Science Advisory Council for Exposure. Policy Number 12 on Recommended Revisions

to the Standard Operating Procedures (SOPs) for Residential Exposure Assessments. Revised:

February 22, 2001.

EPA 2002. Exposure and Human Health Evaluation of Airborne Pollution from the World Trade

Center Disaster. National Center for Environmental Assessment - Office of Research and

Development. (External Review Draft) EPA/600/P-2/002A

EPA 2002a. Child-Specific Exposure Factors Handbook (Interim Report). U.S. Environmental

Protection Agency, Office of Research and Development, National Center for Environmental

Assessment. EPA-600-P-00-002B. September 2002.

EPA. 2002b. Toxicological Effects of Fine Particulate Matter Derived from the Destruction of the

World Trade Center. National Health and Environmental Effects Research Laboratory. December

2002.

EPA 2003. Supplemental Guidance for Assessing Cancer Susceptibility from Early-Life Exposure to

Carcinogens. External Review Draft. EPA/630/R-03/003. February 2003.

EPA 2003a. World Trade Center Residential Confirmation Cleaning Study (Draft Report, March

2003). USEPA Region 2, New York, NY.

EPA 2003b. World Trade Center Background Study (Draft Report, March 2003) USEPA Region

2, New York, NY.

HUD 1995. The Relation of Lead-Contaminated House Dust and Blood Lead Among Urban Children.

Final Report to USHUD from the University of Rochester School of Medicine (Rochester, NY) and

the National Center for Lead Safe Housing (Columbia, MD).

International Agency for Research on Cancer (IARC). 1987. Monograph on Asbestos (Actinolite,

Amosite, Anthophyllite, Chrysotile, Crocidolite, Tremolite), in IARC Monographs of the Evaluation of

Carcinogenic Risks to Humans. International Agency for Research on Cancer, World Health

Organization, Lyon, France 1987;Supp 7:106.

International Agency for Research on Cancer (IARC). 1988. Monograph on Man-Made Mineral

Fibers, in IARC Monographs of the Evaluation of Carcinogenic Risks to Humans. International Agency

for Research on Cancer. World Health Organization. Lyon, France. 1988;43:39.
18

Kim NK, Hawley J. 1985. Re-entry guidelines: Binghamton State Office Building. New York State

Dept. of Health, Bureau of Toxic Substances Assessment, Division of Health Risk Control. Albany,

NY. August. Document 0549P.

Lioy P, Wiesel CP, Millette JR, Eisenreich S, Vallero D et al. 2002. Characterization of the

Dust/Smoke Aerosol that Settled East of the World Trade Center (WTC) in Lower Manhattan after

the Collapse of the WTC September 11, 2001. Environ. Health Perspectives. July 2002;110(7):703-

14.

New Jersey Department of Environmental Protection (NJDEP). 1993. Technical Basis and

Background for Cleanup Standards for Contaminated Sites. N.J.A.C. 7:26D (Draft).

Michaud JM, Huntley SL, Sherer RA, Gray MN, and Paustenbach DJ. 1994. PCB and Dioxin ReEntry Criteria for Building Surfaces and Air. Journal of Exposure Analysis and Environmental

Epidemiology; 4(2):197-227.

Milette JR, Hays SM. 1994. Settled Asbestos Dust Sampling and Analysis. Lewis Publishers. New

York, NY.

National Toxicology Program (NTP). 2001. Glasswool in Report on Carcinogens, 9th Edition. U.S.

Department of Health and Human Services, National Toxicology Program, Research Triangle Park,

NC. 2001.

NIOSH 2002. National Institute of Occupational Safety and Health. Health Effects of Occupational

Exposure to Respirable Crystalline Silica. NIOSH # 2002-129. US Department of Health and Human

Services.

NYCDOHMH 2003. Personal Communication with Ken Carlino - Lead Program. New York City

Department of Health and Mental Hygiene. New York, NY.

Radian International (Radian). 1999. Development of Risk-Based Wipe Sample Cleanup Levels at the

Claremont Polychemical Superfund Site in Old Bethpage, New York. Prepared for the U.S. Army

Corps of Engineers.

TERA 2003. World Trade Center (WTC) October 21–22, 2002, Peer Review Meeting Notes.

Prepared by Toxicology Excellence for Risk Assessment. Prepared for the U.S. Environmental

Protection Agency. February 7, 2003.

WHO. 1998. Environmental Health Criteria 205. Polybrominated Dibenzo-p-dioxins and

Dibenzofurans.
3

In the absence of IRIS values, the following hierarchy was used to obtain toxicity values: 

1.01 EPA Health Effects Assessment Summary Tables (HEAST) values (RfC/RfD, IUR/CSF).

1.02 ATSDR minimal risk level (MRL).

1.03 On a case-by-case basis, other sources were consulted (e.g., EPA’s National Center for

Environmental Assessment (NCEA) provisional values, National Ambient Air Quality Standards

(NAAQS), cross-route extrapolations after consideration of critical effect/target organ).

A-1

APPENDIX A

Deriving Health-Based Screening Values for Air and Dust Exposure Pathways

1.0 Introduction

As described in Section 2.0 of the main text, the initial screening step in the COPC selection process

involved the comparison of maximum detected air and dust concentrations against health-based

screening values. The purpose of this appendix is to describe how screening values used in this step of

the process were selected or derived. 

Health-based screening values were derived for three exposure pathways as follows:

• Air pathway. Contaminants detected in ambient and indoor air were compared to the lower of

the following EPA Integrated Risk Information System (IRIS) values: EPA reference

concentrations (RfCs) (for noncarcinogens) or air concentrations associated with a 10-4 cancer

risk (based on inhalation unit risks [IURs]). In the absence of IRIS values, a defined hierarchy

was used to obtain toxicity values for this and the other pathways evaluated3.

• Bulk dust pathway. Screening values were developed for bulk dust based on a soil ingestion

scenario, considering both child and adult exposures. The exposure equations and age-specific

assumptions are detailed below. Oral toxicity values (EPA reference doses [RfDs] for

noncarcinogens and cancer slope factors [CSFs]) were used when available. Otherwise, the

hierarchy described above was followed. 

• Settled dust pathway. Screening values were developed based on exposures associated with

ingestion and dermal contact with dust residues on indoor surfaces. The derivation of screening

values parallels that used in developing benchmark criteria for the settled dust pathway. To

evaluate this pathway, we adapted EPA guidance for residential exposure assessment, originally

developed to study pesticide residues (EPA 2001). This approach was further supported by

procedures and re-entry guidelines previously developed for scenarios evaluating fine dust

particles more analogous to those associated with the WTC collapse (Kim and Hawley 1985;

NJDEP 1993; Michaud et al. 1994; Radian 1999). Applicable parameters and the justification

for selected values are detailed in Appendix D. Toxicity criteria used included EPA’s RfDs and

CSFs.

2.0 Air 

When available, consensus inhalation toxicity values available through EPA’s IRIS served as the basis

for air screening values. (See above for hierarchy used to obtain toxicity values.) Screening values for

cancer and non-cancer risks were derived as follows, with the lower of the two values used in the
A-2

COPC selection process. A complete list of the toxicity criteria and screening values used in the

analysis of air concentrations is presented in Table A-1.

Carcinogens

SV = TR / IUR

Non-carcinogens 

SV = THI * RfC 

Where:

SV = screening value (mg/m3)

TR = target cancer risk of 1 x 10-4 (Appendix C explains the rationale for this

value)

IUR = inhalation unit risk (the upper-bound excess lifetime cancer risk

estimated to result from continuous exposure to an agent per unit

concentration)

THI = target hazard index of 1

RfC = reference concentration (mg/m3) (an estimate of a continuous inhalation

exposure to the human population [including sensitive subgroups] that is

likely to be without an appreciable risk of deleterious effects during a

lifetime) 

3.0 Bulk Dust

Screening values for bulk dust were derived based on a residential soil ingestion scenario. This

exposure scenario conservatively assumes that exposure to dust will be equivalent to that of incidental

ingestion of substances in soil. Because children are expected to ingest more soil per body weight than

adults, childhood exposure factors were included in the analysis. Screening values for carcinogens are

based on combined childhood and adult exposure. Screening values for non-carcinogens are based on

childhood exposure alone.

Equations and assumptions used in the derivation of bulk dust screening values follow, including sample

calculations. Table A-2 presents a complete list of the toxicity criteria and screening values used in the

analysis of bulk dust.

Carcinogens:

SVca =

TR AT CF

EF CSFo

EDc IRc

BWc

EDa IRa

BWa

× ×

×













 ×



 +

× 





− 1

Where:

SVca = screening value for cancer effects (mg/kg)

TR = target risk of 1 x 10-4 (Appendix C explains the rationale for this value)

AT = averaging time (70 years x 365 days/year = 25,500 days)

BWc = body weight, child (15 kg)

BWa = body weight, adult (70 kg)

CF = conversion factor (106 mg/kg)

EF = exposure frequency (365 days/year)
A-3

EDc = exposure duration child, 6 years

EDa = exposure duration adult, 24 years

IRc = ingestion rate, child (200 mg/day)

IRa = ingestion rate, adult (100 mg/day)

CSFo = oral cancer slope factor (mg/kg/day)-1

As an example, the SVca for heptachlor (CSF = 4.5 mg/kg/day-1) was derived as follows:

SVca = 

10 25 500 10

365 4 5

6 200

15

24 100

70

4 6 1

1

− − × ×

×













 ×



 +

× 





−

,

.

/

/ /

days year / /

days mg kg day

years mg day

kg

years mg day

kg

SVca = 14 mg/kg
A-4

Non-carcinogens: 

SVnc = 

THI RfDo AT BWc CF

EF ED IR

× × × ×

× ×

Where:

SVnc = screening value for non-cancer effects (mg/kg)

THI = target hazard index of 1

RfDo = oral RfD (mg/kg/day) 

AT = averaging time (6 years x 365 days/year = 2,190 days)

BWc = body weight, child (15 kg)

CF = conversion factor (106 mg/kg)

EF = exposure frequency (365 days/year)

ED = exposure duration, child (6 years)

IR = ingestion rate (200 mg/day)

For example, the SVnc for cadmium (RfD = 0.001 mg/kg/day) was derived as follows:

SVnc = 

1 0 001 2 190 15 10

365 6 200

6

× × × ×

× ×

. / / , /

/ /

mg kg day days year kg

days year years mg day

SVnc = 75 mg/kg

4.0 Settled Dust

Screening values for settled dust were developed based on exposures associated with ingestion and

dermal contact with dust residues on indoor surfaces. Continuous age-specific exposure parameters

from age 1 through 31 were factored into this approach. Dose rates were estimated based on a number

of assumptions—for example, the fraction of dust residues that can be transferred to the skin, daily skin

loads, mouthing behaviors for different age groups, and dissipation of surface loading over time. All of

these parameters and the justification for selected values are detailed in Appendix D. Table A-3

presents the screening values derived for settled dust, including the toxicity criteria (RfDs and CSFs)

used in the process.
A-5

Table A-1. Air Screening Values and Supporting Toxicity Criteria

Substance Name Screening Value

(mg/m3)

Toxicity Value Toxicity Value 

Source

Cancer

(mg/m3)

-1

Noncancer

(mg/m3)

SVOCs

Benzaldehyde 0.35 0.35 IRIS oral RfDa

(0.1 mg/kg/day)

2-Methylnaphthalene 0.07 0.07 NCEA oral RfDa

(0.02 mg/kg/day)

4,4'-Methylene diphenyl

diisocyanate (MDI)

0.0006 0.0006 IRIS RfC

Inorganics

Aluminum 0.0035 0.0035 NCEA oral RfDa

(0.001 mg/kg/day)

Antimony 0.0004 0.0004 NCEA RfC

Arsenic 0.00002 4.3 IRIS IUR

Asbestos 0.0004 f/cc 0.23 IRIS IUR

Barium 0.00049 0.00049 HEAST oral RfDa

(0.00014 mg/kg/day)

Chromium 0.000008 12 0.0001 IRISIURb, IRIS RfC

(chromium VI)

Copper 0.14 0.14 HEAST oral RfDa

(0.04 mg/kg/day)

Iron 1.05 1.05 NCEA oral RfDa

(0.3 mg/kg/day)

Lead 0.0015 0.0015 NAAQS

Manganese 0.00005 0.00005 IRIS RfC

Mercury 0.0003 0.0003 IRIS RfC

Naphthalene 0.003 0.003 IRIS RfC

Nickel 0.0002 0.0002 ATSDR c-MRL

Phosphoric Acid 0.01 0.01 IRIS RfC

Vanadium 0.0002 0.0002 ATSDR a-MRL

Zinc 1.05 1.05 IRIS oral RfDa

(0.3 mg/kg/day)

Dioxins

2,3,7,8 TCDD TEQ 3.5x10-10 2.9x10+5 EPA 2000 Dioxin

Reassessment CSFc

(1x106 mg/kg/day-1)

a Route-to-route extrapolation. RfD converted to RfC using the following equation: 

RfC mg/m3 = RfD mg/kg/day x 70 kg (body weight) / 20 m3/day (inhalation rate)

b The screening value is based upon the IRIS IUR.

c Route-to-route extrapolation. CSF converted to IUR using the following equation: 

IUR = CSF mg/kg/day-1 x 20 m3/day (inhalation rate)/ 70 kg (body weight)
A-6

Table A-2. Bulk Dust Screening Values and Supporting Toxicity Criteria

Substance Name Screening

Value

(mg/kg)

Toxicity Value Toxicity Value 

Source

CSF

(mg/kg/day)-1

RfD

(mg/kg/day)

SVOCs

Benzyl alcohol 22500 0.3 HEAST 

Benzyl butyl phthalate 15000 0.2 IRIS

Biphenyl 3750 0.05 IRIS

bis(2-Chloroethyl)ether 56 1.1 IRIS

bis(2-

Chloroisopropyl)ether

873 0.07 0.04 HEAST CSFa

IRIS RfD

bis(2-

Ethylhexyl)phthalate

1500 0.014 0.02 IRIS CSF

IRIS RfDa

2-Chlorophenol 375 0.005 IRIS 

Dibenzofuran 300 0.004 NCEA 

Dibutyl phthalate 7500 0.1 IRIS

3,3'-Dichlorobenzidine 136 0.45 IRIS

Diethylphthalate 60000 0.8 IRIS

2,4-Dimethylphenol 1500 0.02 IRIS

2,4-Dinitrophenol 150 0.002 IRIS 

4,6-Dinitro-2-

methylphenol

7.5 0.0001 NCEA

2,4-Dinitrotoluene 150 0.002 IRIS

2,6-Dinitrotoluene 75 0.001 HEAST

Di-n-octylphthalate 30000 0.4 ATSDR i-MRL

Hexachlorobenzene 38 1.6 0.0008 IRIS CSFa

IRIS RfD

Hexachloroethane 75 0.014 0.001 IRIS CSF

IRIS RfDa

Isophorone 15000 0.00095 0.2 IRIS CSF

IRIS RfDa

2-Methylnaphthalene 1500 0.02 NCEA

2-Methylphenol 3750 0.05 IRIS

4-Methylphenol 375 0.005 HEAST

Naphthalene 1500 0.02 IRIS

Naphthalene, 1-

(methylthio)-

1500 0.02 IRIS

Naphthalene, 1,3-

dimethylene

1500 0.02 IRIS

2-Nitroaniline 3750 0.05 IRIS

3-Nitroaniline 23 0.02 0.0003 NCEA CSF

NCEA RfDa

4-Nitroaniline 225 0.02 0.003 NCEA CSF

NCEA RfDa

Nitrobenzene 37.5 0.0005 IRIS

n-Nitroso-Di-npropylamine9 7 IRIS

n-Nitrosodiphenylamine 1500 0.0049 0.02 NCEA
Substance Name Screening

Value

(mg/kg)

Toxicity Value Toxicity Value 

Source

CSF

(mg/kg/day)-1

RfD

(mg/kg/day)

A-7

PAHs (total) 0.3 7.3 IRIS

(benzo[a]pyrene)

Pentachlorophenol 509 0.12 0.03 IRIS CSFa

IRIS RfD

Phenol 22500 0.3 IRIS

2,4,5-Trichlorophenol 7500 0.1 IRIS

2,4,6-Trichlorophenol 5557 0.011 IRIS

Pesticides and PCBs

Aldrin 2 0.00003 IRIS 

"-BHC 10 6.3 0.008 IRIS CSFa

 IRIS RfD

$-BHC 34 1.8 0.0006 IRIS CSFa

 IRIS RfD

(-BHC 23 0.0003 ATSDR i-MRL

Carbazole 3056 0.02 HEAST

"-Chlordane 38 0.01 0.0005 IRIS CSF

 IRIS RfDa

(technical chlordane)

(-Chlordane 38 0.35 0.0005 IRIS CSF

 IRIS RfDa

(technical chlordane)

Chlordanes (total) 45 0.35 0.0006 IRIS CSF

 ATSDR c-MRLa

p,p'-D D D 255 0.24 IRIS

p,p'-D D E 180 0.34 IRIS 

p,p'-D D T 38 0.34 0.0005 IRIS 

Dieldrin 4 16 0.00005 IRIS CSF 

 IRIS RfDa

Endosulfan (I) 450 0.006 IRIS

Endosulfan (II) 450 0.006 IRIS 

Endosulfan Sulfate 450 0.006 IRIS 

Endrin 23 0.0003 IRIS 

Endrin Aldehyde 23 0.0003 IRIS 

Endrin Ketone 23 0.0003 IRIS 

Heptachlor 14 4.5 0.0005 IRIS CSFa

 IRIS RfD

Heptachlor Epoxide 1 9.1 0.000013 IRIS CSF

 IRIS RfDa

Methoxychlor 375 0.005 IRIS

Metribuzin 1875 0.025 IRIS 

Mirex 15 0.0002 IRIS 

Prometryn (caparol) 300 0.004 IRIS 

Toxaphene 56 1.1 IRIS 

PCBs (total) 1.5 2 0.00002 IRIS CSF

 IRIS RfDa

(Aroclor 1254)
Substance Name Screening

Value

(mg/kg)

Toxicity Value Toxicity Value 

Source

CSF

(mg/kg/day)-1

RfD

(mg/kg/day)

A-8

Inorganics

Aluminum 75000 1 NCEA

Antimony 30 0.0004 IRIS

Arsenic 23 1.5 0.0003 IRIS CSF

 IRIS RfDa

Barium 5250 0.07 IRIS

Beryllium 150 0.002 IRIS 

Cadmium 75 0.001 IRIS 

Chromium 225 0.003 IRIS (chromium VI) 

Cobalt 1500 0.02 NCEA

Copper 3000 0.04 HEAST

Fluoride 4500 0.06 ATSDR c-MRL

Iron 22500 0.3 NCEA

Lead 400 EPA Soil Screening 

Value

Lithium 1500 0.02 NCEA 

Manganese 1500 0.02 IRIS (non-food)

Mercury 11 0.00014 IRIS

(methylmercury) 

Molybdenum 375 0.005 IRIS

Nickel 1500 0.02 IRIS

Nitrate 120000 1.6 IRIS 

Selenium 375 0.005 IRIS 

Silver 375 0.005 IRIS 

Strontium 45000 0.6 IRIS 

Thallium 5 0.00007 RBC 

Titanium 300000 4 NCEA

Uranium 225 0.003 IRIS

Vanadium 525 0.007 HEAST

Zinc 22500 0.3 IRIS

Dioxins

2,3,7,8 TCDD TEQ 0.00006 1000000 EPA 2000 Dioxin 

Reassessment

a Toxicity value upon which screening value is based.
A-9

Table A-3. Settled Dust Screening Values and Supporting Toxicity Criteria

Substance Name Screening

Valuea

(μg/m2)

Toxicity Value Toxicity Value 

Source CSF

(mg/kg/day)-1

RfD

(mg/kg/day)

Inorganics

Aluminum 1567888 1.0 NCEA 

Antimony 627 0.0004 IRIS 

Arsenic 387 1.5 0.0003 IRIS CSF

 IRIS RfDb

Barium 109752 0.07 IRIS 

Beryllium 3136 0.002 IRIS 

Cadmium 1557 0.001 IRIS 

Chromium 4704 0.003 IRIS (chromium VI) 

Cobalt 31358 0.02 NCEA 

Copper 62716 0.04 HEAST 

Iron 940733 0.6 NCEA 

Lead 270 HUD standard

Manganese 31358 0.02 IRIS (non-food)

Mercury 157 0.0001 IRIS (methylmercury) 

Nickel 31358 0.02 IRIS 

Selenium 7839 0.005 IRIS

Silver 7839 0.005 IRIS 

Thallium 110 0.00007 RBC

Vanadium 10975 0.007 HEAST 

Zinc 470366 0.3 IRIS 

Other

PAHs (total) 145 7.3 IRIS (benzo[a]pyrene)

PCBs (total) 16 2.0 IRIS

Dioxins 0.0017 1000000 EPA 2000 Dioxin

Reassessment

a Refer to Appendix D for derivation of screening values.

b Toxicity value upon which screening value is based.
4

Tentatively identified compounds were not included in the list of contaminants. All measurements for

dioxins and furans are considered as one contaminant in this tally, and were screened using a TEQ analysis. All

measurements for asbestos are considered one contaminant, though measurements used different analytical

methods and counted different subsets of fiber types and sizes. All measurements for PCBs are considered one

contaminant, though the studies reported concentrations under several different groupings of congeners (e.g., total

PCBs, Aroclors).

B-1

APPENDIX B

Results of the COPC Selection Process

This appendix presents the results of each step of the COPC selection process. As described in Section

2.0 of the main text, the approach involved a review of multiple data sets to identify candidate

substances, followed by an initial and secondary screening process. Ambient air, indoor air, bulk dust,

and settled dust were evaluated. 

As part of the initial screen for each of these media, volatile contaminants and those detected at low

frequencies were eliminated from further consideration. Remaining contaminants were screened against

health-based screening values derived for air and dust (see Appendix A). Three outcomes were

possible for this step. If a contaminant’s maximum concentration was lower than the corresponding

screening value, that contaminant was eliminated from further consideration. If a contaminant’s

maximum concentration was greater than the screening value, then the contaminant was evaluated

further in the secondary screening step. If a contaminant did not have a toxicity value, and therefore did

not have a screening value, other relevant information (e.g., trends among sampling data, comparisons

to background, the likelihood of the contaminant being related to site-specific releases) were reviewed

to determine whether the contaminant should be evaluated further. Where possible, occupational or

environmental criteria were considered in determining whether contaminants needed further evaluation.

Any contaminant detected even once above a screening value within an individual medium was flagged

as requiring further consideration. In the secondary screen, we reviewed findings across environmental

media to assess representativeness of reported maximum concentrations, studied spatial and temporal

trends, determined the relationship of detected concentrations to available background concentrations,

and examined whether there was reason to believe a contaminant was site-related. From this, a

judgment was made whether or not to select the contaminant as a COPC.

Sections 1.0 through 4.0 below detail the findings of the initial screening process for each medium.

Section 5.0 presents the findings of the secondary screen; it reviews each of the contaminants identified

in the initial screen as requiring further consideration and provides justification for selecting a

contaminant as a COPC or eliminating it from further consideration.

1.0 Ambient Air

Ambient air sampling results were obtained from the following sources:

• EPA Region 2’s database of environmental sampling results. The processed database

contains more than 200,000 records, with more than half being asbestos sampling results. The

database includes sampling conducted by multiple agencies; EPA collected most of the

samples, but samples collected by the New York City Department of Environmental Protection

(NYCDEP) and New Jersey Department of Environmental Protection (NJDEP) are also

included. Sampling results are available for 137 contaminants.4 The database includes samples
B-2

with various averaging times (both grab and integrated samples), sampling locations (most

samples in Lower Manhattan, but some from locations outside of Manhattan), sampling dates

(September 2001 through July 2002), sampling methods, and detection limits.

• New York City Department of Health and Mental Hygiene (NYCDOHMH)/Agency for

Toxic Substances and Disease Registry (ATSDR) public health investigation (2002). This

study documents sampling results from 30 residential buildings in Lower Manhattan and 4

comparison buildings north of 59th Street. Samples were collected in November and

December, 2001. The study reports outdoor levels of fibers (PCM) for 32 samples collected in

Lower Manhattan, including results from co-located sampling devices. None of the samples

from outdoor locations was analyzed for asbestos or synthetic vitreous fibers. Additionally, the

study reports concentrations of six minerals in 354 air samples from Lower Manhattan. The

sampling results for minerals are applied to both the ambient air and indoor air COPC screening

process, because the final study report does not specify what fraction of the 354 samples were

collected indoors versus outdoors. 

• New York City Department of Education sampling in schools. This study documents

sampling results from six schools: PS-89, PS-150, PS-234, Stuyvesant High School (M-477),

High School for Leadership and Public Services (M-894), and High School of Economics and

Finance (M-833). Sampling occurred between September 2001 and June 2002, both indoors

and outdoors. Because the database does not clearly distinguish these two types of samples,

the COPC selection process considers all of the sampling results both for the indoor air and

ambient air analysis. The project database includes more than 30,000 records of air sampling

results. Asbestos sampling results account for more than half of these records, with the rest of

the results being for more than 70 other contaminants.1

• Chattfield and Kominsky’s (2001) survey of indoor air quality. This study characterizes

impacts of WTC dusts in two buildings in Lower Manhattan. The study focuses on the indoor

environment, but two outdoor air samples were collected and analyzed for asbestos.

COPC Selection Process for Ambient Air

Step 1: Do not consider volatile contaminants

Volatile contaminants were eliminated from the COPC selection process. Any contaminant on

the target analyte list for Method TO-15 (ambient air) and Method 8260 (waste) was

considered volatile. Further, chemical similarity to compounds on those lists and boiling point

(as a surrogate for vapor pressure) were used to identify additional volatile contaminants not on

these methods’ target lists.

• 83 contaminants removed from list (see Table B-1)

• 73 contaminants remained for further consideration 

Step 2: Do not consider contaminants detected in fewer than 5% of samples, only if

more than 20 samples were collected

• 43 contaminants removed from list (see Table B-2)

• 30 contaminants remained for further consideration 

Step 3: Compare maximum detected concentrations against health-based screening

values
B-3

Using the health-based screening values described in Appendix A:

• 8 contaminants removed from list (maximum concentration < screening value, see Table

B-3)

• 10 contaminant do not have health-based screening values (see Table B-4)

• 12 contaminants remained for further consideration (listed below) 

Contaminants requiring further consideration (see Section 5.0):

1) Aluminum

2) Arsenic

3) Asbestos

4) Barium

5) Chromium

6) Dioxins

7) Lead

8) Manganese

9) Mercury

10) 4,4'-Methylene diphenyl diisocyanate (MDI) 

11) Naphthalene

12) Nickel

Table B-1. Volatile Contaminants Removed from COPC Selection Process

1,1,1-Trichloroethane Carbon disulfide Methyl isobutyl ketone

1,1,2,2-Tetrachloroethane Carbon tetrachloride Methyl tert-butyl ether

1,1,2-Trichloroethane Chlorobenzene Methylcyclopentane

1,1-Dichloroethane Chlorodifluoromethane Methylene chloride

1,1-Dichloroethylene Chloroethane n-Butane

1,2,4-Trimethylbenzene Chloroform n-Heptane

1,2-Dibromoethane Chloromethane n-Hexane

1,2-Dichlorobenzene cis-1,2-Dichloroethylene Nitric acid

1,2-Dichloroethane cis-1,3-Dichloropropylene Nitric oxide

1,2-Dichloropropane Cyclohexane Nitrogen dioxide

1,3,5-Trimethylbenzene Dibromochloromethane n-Pentane

1,3-Butadiene Dibromomethane o-Xylene

1,3-Dichlorobenzene Dichlorodifluoromethane Ozone

1,3-Dichloropropane Dichlorotetrafluoroethane Propane

1,4-Dichlorobenzene Ethanol Propylene

1,4-Dioxane Ethyl acetate Styrene

1-Heptene Ethylbenzene Sulfur dioxide

2-Butanone Formaldehyde Tetrachloroethylene

2-Hexanone Hexachlorobutadiene Tetrahydrofuran

3-Chloropropylene Hydrogen bromide Toluene

4-Ethyltoluene Hydrogen chloride trans-1,2-Dichloroethylene

Acetone Hydrogen cyanide trans-1,3-Dichloropropylene

Acrylonitrile Hydrogen fluoride Trichloroethylene
B-4

a-Methylstyrene i-Propylbenzene Trichlorofluoromethane

Benzene Isopentane Trichlorotrifluoroethane

Bromodichloromethane Isopropyl alcohol Vinyl acetate

Bromoform m,p-Xylene Vinyl chloride

Bromomethane Xylene (total)

Table B-2. Contaminants Removed from the COPC Selection Process Due to Frequency of

Detection

Contaminant Samples Frequency of

Detection

Contaminant Samples Frequency of

Detection

1,2,4-Trichlorobenzene 1010 1.8% Dibenzo(a,h)anthracene 573 0.0%

1-Methylnaphthalene 573 2.1% Dibenzofuran 528 0.0%

2,4-TDI 48 0.0% Fluoranthene 573 0.0%

2,6-Dimethylnaphthalene 528 0.0% Fluorene 573 0.0%

2,6-TDI 48 0.0% Halite 354 3.4%

Acenaphthene 573 0.0% HDI 48 0.0%

Acenaphthylene 573 0.0% Indeno(1,2,3-cd)pyrene 573 0.0%

Anthracene 570 0.0% IPDI 48 0.0%

Benzo(a)anthracene 573 0.0% Isopropylbenzene 430 0.0%

Benzo(a)pyrene 573 0.0% HMDI 48 0.0%

Benzo(b)fluoranthene 576 0.0% Mica 354 2.0%

Benzo(e)pyrene 528 0.0% Molybdenum 471 0.0%

Benzo(g,h,i)perylene 572 0.0% Phenanthrene 573 0.2%

Benzo(k)fluoranthene 570 0.0% Potassium 738 3.1%

Benzyl Chloride 1010 1.4% Pyrene 573 0.2%

Beryllium 738 0.1% Selenium 737 1.2%

Biphenyl 528 0.0% Silica Dust 798 4.3%

Cadmium 1216 1.1% Silver 738 2.2%

Carbazole 528 0.0% Thallium 738 2.6%

Chrysene 573 0.0% Tridymite 597 0.0%

Cobalt 1209 4.4% Total PCBs 633 4.9%

Cristobalite 597 0.0%

Notes:

TDI toluene diisocyanate

HDI hexamethylene diisocyanate

HMDI methylene bis-(4-cyclohexylisocyanate)

IPDI isophorone diisocyanate

In addition to total PCB data, multiple Aroclors were not detected in any samples collected in six Lower Manhattan

schools.

Table B-3. Contaminants with Measured Levels Lower than Health-Based Screening Values

Contaminant Maximum

Concentration

(mg/m3)

Health-based

Screening Value

(mg/m3)

Basis for Screening Value

2-Methylnaphthalene 0.009 0.07 Extrapolation from oral RfD

Antimony 0.00033 0.0004 NCEA provisional RfC

Benzaldehyde 0.032 0.35 Extrapolation from oral RfD

Copper 0.063 0.14 Extrapolation from oral RfD

Iron 0.064 1.05 Extrapolation from oral RfD
B-5

Phosphoric acid ND 0.01 IRIS RfC

Vanadium 0.0001 0.0002 ATSDR acute MRL

Zinc 0.0081 1.05 Extrapolation from oral RfD
1

 Tentatively identified compounds were not included in the list of contaminants. All measurements for asbestos are

considered one contaminant, though measurements used different analytical methods and counted different subsets

of fiber types and sizes. All measurements for PCBs are considered one contaminant, though the schools study

reported concentrations for multiple Aroclors.

B-6

Table B-4. Contaminants with No Health-Based Screening Values

Bromobenzene Magnesium

Calcite Portlandite 

Calcium Quartz 

Fibers (PCM) Sodium

Gypsum Sulfuric Acid

2.0 Indoor Air

Indoor air sampling results were obtained from the following sources:

• EPA Region 2’s database of environmental sampling results. The processed database

contains 73 records of indoor air sampling results, all for asbestos. EPA collected these

samples from three buildings in Lower Manhattan in September and October, 2001. Of the 73

records, 20 document PCM analyses and 53 document TEM analyses.

• NYCDOHMH/ATSDR (2002) public health investigation. This study documents sampling

results from 30 residential buildings in Lower Manhattan and 4 comparison buildings north of

59th Street. Samples were collected in November and December, 2001. The study reports

indoor levels of fibers (PCM) for 96 samples collected in Lower Manhattan, including results

from co-located sampling devices. A small subset of these samples was analyzed further for

asbestos and synthetic vitreous fibers. Additionally, the study reports concentrations of six

minerals in 354 air samples from Lower Manhattan. The sampling results for minerals are

applied to both the ambient air and indoor air COPC screening process, because the final study

report does not specify what fraction of the 354 samples were collected indoors versus

outdoors.

• New York City Department of Education sampling in schools. This study documents

sampling results from six schools: PS-89, PS-150, PS-234, Stuyvesant High School (M-477),

High School for Leadership and Public Services (M-894), and High School of Economics and

Finance (M-833). Indoor and outdoor sampling occurred between September 2001 and June

2002. However, because the database does not clearly distinguish these two types of samples,

the COPC selection process considers all sampling results both for the indoor air and ambient

air analysis. The project database includes more than 30,000 records of air sampling results.

Asbestos sampling results account for more than half of these records, with the rest of the

results being for more than 70 other contaminants.1

• Chattfield and Kominsky’s (2001) survey of indoor air quality. This study characterizes

impacts of WTC dusts in two buildings in Lower Manhattan. The study includes 11 indoor air

samples that were collected and analyzed for asbestos. 

COPC Selection for Indoor Air

Step 1: Do not consider volatile contaminants
B-7

Volatile contaminants were eliminated from the COPC selection process. Any contaminant on

the target analyte list for Method TO-15 (ambient air) and Method 8260 (waste) was

considered volatile. Further, chemical similarity to compounds on those lists and boiling point

(as a surrogate for vapor pressure) were used to identify additional volatile contaminants not on

these methods’ target lists.

• 35 contaminants removed from list (see Table B-5)

• 44 contaminants remained for further consideration

Step 2: Do not consider contaminants detected in fewer than 5% of samples, only if

more than 20 samples were collected

• 27 contaminants removed from list (see Table B-6)

• 17 contaminants remained for further consideration

Step 3: Compare maximum detected concentrations against health-based screening

values

Using the health-based screening values described in Appendix A:

• 6 contaminants removed from list (maximum concentration < screening value, see Table

B-7)

• 7 contaminant do not have health-based screening values (see Table B-8)

• 4 contaminants remained for further consideration (listed below)
B-8

Contaminants requiring further consideration:

1) Aluminun

2) Asbestos

3) Chromium

4) Mercury

Table B-5. Volatile Contaminants Removed from COPC Selection Process

1,1,1-Trichloroethane Hydrogen cyanide

1,1,2,2-Tetrachloroethane m,p-Xylene

1,1-Dichloroethylene Methylene chloride

1,2-Dibromoethane n-Heptane

1,2-Dichloroethane n-Hexane

1,2-Dichloropropane Nitric oxide

1,3-Dichloropropane Nitrogen dioxide

1-Heptene n-Pentane

3-Chloropropylene o-Xylene

Acetone Ozone

Acrylonitrile Styrene

Benzene Sulfur dioxide

Bromoform Tetrachloroethylene

Carbon tetrachloride Toluene

Chlorobenzene Trichloroethylene

Chloroform Vinyl chloride

Ethylbenzene Xylene (total)

Formaldehyde

Table B-6. Contaminants Removed from the COPC Selection Process Due to Frequency of

Detection

Contaminant Samples Frequency of

Detection

Contaminant Samples Frequency of

Detection

Acenaphthene 45 0.0% Halite 354 3.4%

Acenaphthylene 45 0.0% Indeno(1,2,3-cd)pyrene 45 0.0%

Anthracene 42 0.0% Isopropylbenzene 430 0.0%

Benzo(a)anthracene 45 0.0% Magnesium 471 4.2%

Benzo(a)pyrene 45 0.0% Manganese 471 0.0%

Benzo(b)fluoranthene 48 0.0% Mica 354 2.0%

Benzo(g,h,i)perylene 45 0.0% Molybdenum 471 0.0%

Benzo(k)fluoranthene 42 0.0% Nickel 471 0.6%

Cadmium 478 0.0% PCBs 32 0.0%

Chrysene 45 0.0% Phenanthrene 45 2.2%

Cobalt 471 0.0% Pyrene 45 2.2%

Dibenzo(a,h)anthracene 45 0.0% Silica Dust 798 4.3%

Fluoranthene 45 0.0% Zinc 471 0.6%

Fluorene 45 0.0%

Table B-7. Contaminants with Measured Levels Lower than Health-Based Screening Values

Contaminant Maximum

Concentration

(mg/m3)

Health-based Screening

Value (mg/m3)

Source of Screening Value

2-Methylnaphthalene 0.00092 0.07 Extrapolation from oral RfD
Contaminant Maximum

Concentration

(mg/m3)

Health-based Screening

Value (mg/m3)

Source of Screening Value

B-9

Copper 0.00389 0.14 Extrapolation from oral RfD

Iron 0.00577 1.05 Extrapolation from oral RfD

Lead 0.00136 0.0015 NAAQS

Naphthalene 0.00099 0.003 RfC

SVF 0.00025 f/cc 0.03 f/cc Proposed ATSDR MRL

Table B-8. Contaminants with No Health-Based Screening Values

1-Methylnaphthalene Gypsum 

Bromobenzene Portlandite 

Calcite Quartz 

Fibers

3.0 Bulk Dust

Bulk dust sampling results were obtained from the following sources:

• EPA Region 2’s database of environmental sampling results. The processed database

contains 1,936 records of bulk dust sampling; 1,930 of the records were from EPA sampling,

and 6 were from NYCDEP sampling. Most samples were collected in September and

October, 2001; the database also includes results from multiple samples collected in May,

2002. The majority of sampling occurred in Lower Manhattan, but some results are also

available for Brooklyn and the Fresh Kills Landfill. The database includes dust samples from

indoor and outdoor locations. Samples were analyzed for asbestos, metals, pesticides, PAHs,

and other semi-volatile organic compounds.

• NYCDOHMH/ATSDR (2002) public health investigation. This study documents sampling

results from 30 residential buildings in Lower Manhattan and 4 comparison buildings north of

59th Street. Samples were collected in November and December, 2001. This data summary

considered only the dust samples (both indoor and outdoor) collected in Lower Manhattan, and

not those from the comparison population. Data are available for asbestos, synthetic vitreous

fibers, and six minerals.

• New York City Department of Education sampling in schools. This study documents

sampling results from six schools: PS-89, PS-150, PS-234, Stuyvesant High School (M-477),

High School for Leadership and Public Services (M-894), and High School of Economics and

Finance (M-833). Sampling occurred between September 2001 and June 2002. The project

database includes nearly 3,000 records of sampling results for bulk settled dust; these samples

were collected at various indoor and outdoor locations. The only contaminants analyzed for in

the samples were asbestos and fiberglass. All samples were analyzed using polarized light

microscopy (PLM).

• Chattfield and Kominsky’s (2001) survey of indoor air quality. This study characterized

impacts of WTC dusts in two buildings in Lower Manhattan. During the study, an indoor dust

sample and two outdoor dust samples (rooftop and exterior window ledge) were analyzed for

dioxins, PCBs, and metals. Additionally, four exterior dust samples were analyzed for asbestos.

All sampling occurred in September, 2001.
B-10

• Lioy et al. (2002) study. This study documents results from three outdoor bulk dust samples

collected in Lower Manhattan on September 16 and 17, 2001. The samples were analyzed for

a wide range of compounds, including metals, PCBs, dioxins, pesticides, asbestos, and semivolatile organic compounds.

• OSHA’s data set. Results from 11 bulk dust samples collected on June 5, 2002, in a Lower

Manhattan building were reviewed. All samples were apparently collected indoors and

analyzed for 13 metals.

COPC Selection for Bulk Dust

Step 1: Do not consider volatile contaminants

Volatile contaminants were eliminated from the COPC selection process. Any contaminant on

the target analyte list for Method TO-15 (ambient air) and Method 8260 (waste) was

considered volatile. Further, chemical similarity to compounds on those lists and boiling point

(as a surrogate for vapor pressure) were used to identify additional volatile contaminants not on

these methods’ target lists.

• 12 contaminants removed from list (see Table B-9)

• 176 contaminants remained for further consideration

Step 2: Do not consider contaminants detected in fewer than 5% of samples, only if

more than 20 samples were collected

• 1 contaminant (fiberglass) removed from list

• 175 contaminants remained for further consideration
B-11

Step 3: Compare maximum detected concentrations against health-based screening

values

Using the health-based screening values for bulk dust described in Appendix A (based on a soil

ingestion scenario):

• 84 contaminants removed from list (maximum concentration < screening value, see

Table B-10)

• 83 contaminant do not have health-based screening values (see Table B-11)

• 8 contaminants remained for further consideration (listed below)

Contaminants requiring further consideration:

1) Antimony

2) Asbestos

3) Chromium

4) Dioxins

5) Lead

6) Manganese

7) PAHs

8) Thallium

Table B-9. Volatile Contaminants Removed from COPC Selection Process

1,2,4-Trichlorobenzene 2,4-Dimethylheptane

1,2-Dichlorobenzene 2,4-Dimethylhexane

1,3-Dichlorobenzene 3,3-Dimethylhexane

1,4-Dichlorobenzene Hexachlorobutadiene

2,3,4-Trimethylhexane Hexachlorocyclopentadiene

2,3-Dimethyl-1-pentanol n-Octane
B-12

Table B-10. Contaminants with Measured Levels Lower than Health-Based Screening Values

Contaminant Maximum

(mg/kg)

Screening

Value

(mg/kg)

Contaminant Maximum

(mg/kg)

Screening

Value

(mg/kg)

2,4,5-Trichlorophenol ND 7500 NC Endrin ND 22.5 NC 

2,4,6-Trichlorophenol ND 5557 C Endrin Aldehyde ND 22.5 NC 

2,4-Dimethylphenol ND 1500 NC Endrin Ketone ND 22.5 NC 

2,4-Dinitrophenol ND 150 NC Fluoride 0.22 4500 NC 

2,4-Dinitrotoluene ND 150 NC g-BHC ND 22.5 NC 

2,6-Dinitrotoluene ND 75 NC g-Chlordane 0.0081 37.5 NC 

2-Chlorophenol ND 375 NC Heptachlor ND 13.6 C 

2-Methylnaphthalene 5.1 1500 NC Heptachlor Epoxide ND 0.975 NC 

2-Methylphenol 0.57 3750 NC Hexachlorobenzene 0.0019 38 C 

2-Nitroaniline ND 3750 NC Hexachloroethane ND 75 NC 

3,3'-Dichlorobenzidine 10 136 C Iron 21000 22500 NC 

3-Nitroaniline ND 22.5 NC Isophorone ND 15000 NC 

4,6-Dinitro-2-

methylphenol

ND 7.5 NC Lithium 29.52 1500 NC 

4-Methylphenol 0.93 375 NC Mercury 0.38 10.5 NC 

4-Nitroaniline ND 225 NC Methoxychlor ND 375 NC 

a-BHC ND 10 C Metribuzin 22.1 1875 NC 

a-Chlordane ND 38 NC Mirex 0.0008 15 NC 

Aldrin ND 2 NC Molybdenum ND 375 NC 

Aluminum 31000 75000 NC Naphthalene 13 1500 NC 

Arsenic 11 23 NC Naphthalene, 1-

(methylthio)-

7.5 1500 NC 

Barium 500 5250 NC Naphthalene, 1,3-

dimethylene

5.3 1500 NC 

b-BHC ND 34 C Nickel 47.29 1500 NC 

BDE 3.3 150 NC Nitrate 0.33 120000 NC 

Benzyl alchohol 0.62 22500 NC Nitrobenzene ND 37.5 NC 

Benzyl butyl phthalate 94.1 15000 NC N-Nitroso-Di-npropylamineND 8.7 C 

Beryllium 3.754 150 NC NNitrosodiphenylamineND 1500 NC 

Biphenyl 6.5 3750 NC p,p'-D D D ND 255 C 

bis(2-Chloroethyl)Ether ND 56 C p,p'-D D E 0.003 180 C 

bis(2-

Chloroisopropyl)ether

ND 873 C p,p'-D D T 0.046 37.5 NC 

bis(2-

Ethylhexyl)phthalate

21 1500 NC PCBs (Aroclor 1260) 1.6 30.6 C

Cadmium 8.454 75 NC Pentachlorophenol ND 509 C 

Carbazole 35 3056 C Phenol 5.6 22500 NC 

Cobalt 14 1500 NC Prometryn (caparol) 10.7 300 NC 

Copper 1327 3000 NC Selenium ND 375 NC 

Dibenzofuran 18 300 NC Silver 54 375 NC 

Dibutyl phthalate 19.7 7500 NC Strontium 720.8 45000 NC 

Dieldrin 0.0028 3.75 NC Titanium 1797 300000 NC 

Diethylphthalate 31.7 60000 NC Total chlordanes 0.0056 45 NC 

Di-n-octylphthalate 4.4 30000 NC Toxaphene ND 56 C 

Endosulfan (I) ND 450 NC Uranium 4.213 225 NC 
Contaminant Maximum

(mg/kg)

Screening

Value

(mg/kg)

Contaminant Maximum

(mg/kg)

Screening

Value

(mg/kg)

B-13

Endosulfan (II) ND 450 NC Vanadium 42.61 525 NC 

Endosulfan Sulfate ND 450 NC Zinc 3000 22500 NC 

Notes:

NC Screening value based on non-cancer endpoint (HQ=1; child exposure)

C Screening value based on cancer endpoint (10-4 risk)

BDE Total bromodiphenyl ethers (BDE47, 99, 100, 153, 154, 209)

Table B-11. Contaminants with No Health-Based Screening Values

Lioy et al. Database

 (E)-2-(6-Nonexnoxy)-tetrahydropyran Bismuth 

 1,2,3-Triphenyl-3-vinyl-cyclopropene Cellulose (%) 

 12-Acetoxydaphnetoxin Cesium 

 1-Azabicyclo[2.2.2]octan-3-one Chloride 

 1-Dodecanol, 2-methyl-, (S)- Chrysotile asbestos (%) 

 1H-1,2,4-Triazole, 1-ethyl 2-Hexyl-1-decanol 

 1-Hexadecanol, 2-methyl 3,4-Dihydrocyclopenta(cd)pyrene (acepyrene) 

 1-Hexyl-2-nitrocyclohexane Cycloate 

 1H-Indene, 1-(phenylmethylene)- Cyclohexanemethanol 

 1H-Pyrrole-3-propanoic acid, 2,5-dihydro-4-methyl2,5-dioxo  Dibenzothiophene 

1-Hydroxypyrene Dicyclohexyl phthalate 

 1-Methylanthracene Didodecyl phthalate 

 1-Methylphenanthrene Dihydrogeraniol 

 1-Pentacontanol Diisobutyl phthalate 

 2-(3'-Hydroxyphenylamino)-5-methyl-4-oxo-3,4-

dihydrophyrimidine 

 Dimethylcyanamide 

 2,3-Dihydrofluoranthene Droserone (2,8-dihydroxy-3-methyl-1,4-

naphthoquinone) 

 2,4-DDT Ether, hexyl pentyl 

 2-Benzylquinoline Gallium 

 3-Methoxycarbonyl-2-methyl-5-(2,3,5-tri-O-acetylbeta-d-ribofuranosyl)  Hexyl N-butyrate 

 4,4'-Biphenyldicarbonitrile Methyl alpha-ketopalmitate 

 4-Hydroxymandelic acid-TRITMS Monobutyl phthalate 

 4-Methyl-2-propyl-1-pentanol Nefopam 

 4-Methylphenanthrene Pentanoic acid, 4,4-dimethyl-3-methylene-, ethyl

ester 

 7-Methyl-3,4,5(2H)-tetrahydroazepine Phthalate 

 9,10-Anthraquinone Phthalic acid, 2-hexyl ester 

 9H-Fluorene, 9-(phenylmethylene) Rubidium 

 Auraptenol Sulfate 

 Benzamide, N-acetyl- Vernolate (vernam) 

 Benzene, 1,1'-(1,3-butadiyne-1,4-diyl)bis- Xanthene 

 Benzimidazo [2,1-a] isoquinoline 

EPA Region 2 Database

 1-Methylnaphthalene 4-Nitrophenol 

 2,4-Dichlorophenol bis(2-Chloroethoxy)methane 

 2,6-Dimethylnaphthalene d-BHC 

 2-Chloronaphthalene Dimethylphthalate 

 2-Nitrophenol Calcium 

 4-Bromophenyl ether Magnesium 
B-14

 4-Chloro-3-Methylphenol Potassium 

 4-Chloroaniline Sodium 

 4-Chlorophenyl-phenylether 

ATSDR-NYCDOH Database

 Calcite Portlandite 

 Gypsum Quartz 

 Halite SVF (PLM) 

 Mica 

4.0 Settled Dust

Settled dust sampling results were obtained from the following sources:

• EPA Region 2’s database of environmental sampling results. The processed database

contains more than 500 records of settled dust sampling results. EPA collected wipe samples

from three schools (Manhattan Community College, Stuyvesant High School, and PS234) in

September 2001. The samples were analyzed for loadings of metals, PCBs, and dioxins.

• EPA’s wipe sampling data. Preliminary results from EPA’s ongoing wipe sampling study of

Lower Manhattan residences were reviewed. Only those records labeled as “special pre

monitoring” (excluding field blanks) were considered. Overall, 187 samples were analyzed for

metals, and 191 samples were analyzed for dioxins. Samples were collected from various

indoor locations (e.g., counter tops, floors, walls, window sills).

• New York City Department of Education sampling in schools. This study documents

sampling results from six schools: PS-89, PS-150, PS-234, Stuyvesant High School (M-477),

High School for Leadership and Public Services (M-894), and High School of Economics and

Finance (M-833). Settled dust sampling occurred between October 2001 and December

2002. The project database includes more than 6,000 records of sampling results for settled

dust; these samples were collected at various indoor and outdoor locations. Samples were

analyzed for PAHs, PCBs, dioxins, and metals.

• Chattfield and Kominsky’s survey of indoor air quality. This study characterized impacts of

WTC dusts in two buildings in Lower Manhattan. During the study, six wipe dust samples were

analyzed for dioxins, PCBs, and metals. All sampling occurred in September 2001.

• PCB study by Butt et al. (2002). In October 2001, wipe samples were collected to

characterize PCB contamination in organic films on building surface, mostly windows. Overall,

9 samples were collected and analyzed for total PCB concentrations.

COPC Selection for Settled Dust

Step 1: Do not consider volatile contaminants

Volatile contaminants were eliminated from the COPC selection process. Any contaminant on

the target analyte list for Method TO-15 (ambient air) and Method 8260 (waste) was

considered volatile. Further, chemical similarity to compounds on those lists and boiling point

(as a surrogate for vapor pressure) were used to identify additional volatile contaminants not on

these methods’ target lists.

• No contaminants removed from list
B-15

• 44 contaminants remained for further consideration

Step 2: Do not consider contaminants detected in fewer than 5% of samples, only if

more than 20 samples were collected

• 25 contaminants removed from list (see Table B-12)

• 19 contaminants remained for further consideration
B-16

Step 3: Compare maximum detected concentrations against health-based screening

values

Using the health-based screening values for settled dust described in Appendix A (based on

ingestion/dermal contact scenario):

• 11 contaminants removed from list (maximum concentration < screening value, see

Table B-13)

• 5 contaminant do not have health-based screening values (see Table B-14)

• 3 contaminants remained for further consideration (listed below)

Contaminants requiring further consideration:

1) Dioxins

2) Lead

3) Mercury

Table B-12. Contaminants Removed from the COPC Selection Process Due to Frequency of

Detection

Contaminant Samples Frequency of

Detection

Contaminant Samples Frequency of

Detection

Acenapthene 35 0% Dibenzo(a)anthracene 35 0%

Acenaphthylene 35 0% Fluoranthene 35 0%

Anthracene 35 0% Fluorene 35 0%

Arsenic 215 4.7% Indeno(1,2,3-cd)pyrene 35 0%

Benzo(a)anthracene 35 0% Molybdenum 38 0%

Benzo(a)pyrene 35 0% Naphthalene 35 0%

Benzo(b)fluoranthene 35 0% PCBs 371 2.7%

Benzo(g,h,I)perylene 35 0% Phenanthrene 35 0%

Benzo(k)fluoranthene 35 0% Pyrene 35 0%

Beryllium 215 0% Silver 215 1.4%

Chrysene 35 0% Thallium 215 0.5%

Cobalt 250 2.8% Vanadium 215 3.7%

Decaclhorobiphenyl 1 0%

Notes:

The number of samples for “PCBs” is the total number of samples that were analyzed for any grouping of PCB

congeners, including Aroclors or total PCBs. It should be noted that the highest total PCB concentration reported

for a surface measurement (1.398 :g/m2) is lower than the corresponding health-based screening value (15.6 :g/m2).
B-17

Table B-13. Contaminants with Measured Levels Lower than Health-Based Screening Values

Contaminant Maximum

(:g/m2)

Screening

Value

(:g/m2)

Contaminant Maximum

(:g/m2)

Screening

Value

(:g/m2)

Aluminum 102,000 1,570,000 Iron 212,000 941,000

Antimony 377 627 Manganese 3,910 31,400

Barium 3,100 110,000 Nickel 1,160 31,400

Cadmium 429 1,560 Selenium 590 7,840

Chromium 1,900 4,700 Zinc 72,000 470,000

Copper 7,150 62,700

Table B-14. Contaminants with No Health-Based Screening Values

 Asbestos (inhalation value only) Potassium

 Calcium Sodium

 Magnesium
B-18

5.0 Analysis of Contaminants Requiring Further Consideration

Two classes of contaminants required further evaluation after the initial screening described above: (1)

contaminants with maximum concentrations greater than screening values and (2) contaminants for

which no screening values are available. Sections 5.1 and 5.2 describe the results of this secondary

analysis, providing justification for all contaminant-specific decisions.

5.1 Contaminants Found to Exceed Toxicity Criteria

From the initial screening results presented above, fifteen contaminants were detected in at least one

sample from at least one medium at concentrations greater than corresponding health-based screening

values. This section presents the findings of the secondary screen conducted to determine whether these

contaminants would be selected or eliminated as a COPC. The decision process involved assessing the

representativeness of reported maximum concentrations, studying spatial and temporal trends,

determining the relationship of detected concentrations to available background concentrations, and

examining whether there was reason to believe a contaminant was site-related.

From this evaluation, the following contaminants were selected as COPC:

< Asbestos

< Dioxins

< Lead

< PAHs

This evaluation eliminated the following contaminants from further consideration:

< Aluminum

< Antimony

< Arsenic

< Barium

< Manganese

< Naphthalene

< Nickel

< MDI

< Thallium

Two of the metals (chromium and mercury) did not fully meet all the criteria for selection as a COPC

and were not designated as such, but some evidence exists that they may be present in indoor

environments. Chromium and mercury are therefore highlighted separately below. EPA will continue to

sample for these and other non-COPC metals as part of the WTC Clean-up Program.

Contaminants selected as COPC:

1) Asbestos: Ambient air sampling conducted by multiple parties has found asbestos

concentrations greater than the air screening value (0.0004 fibers/cubic centimeter) based on

cancer risk. Additionally, asbestos fibers have been found in indoor and outdoor dust samples

collected at various Lower Manhattan locations. Based on these and other trends among the

sampling data, our knowledge of the construction materials in the WTC buildings, and ongoing

health concerns regarding potential exposure to asbestos, asbestos is being selected as a

COPC.
1 The frequency with which dioxin levels in settled dust exceeds health-based screening values depends on

how one interprets non-detect observations. Whether one assigns non-detects a value of zero or one-half

the detection limit, however, at least one measurement of surface loading exceeds a health-based screening

value.

B-19

2) Dioxins: As the peer review draft COPC document notes, ambient air concentrations of dioxin

in samples collected in September and October, 2001, exceeded EPA’s screening criteria for

dioxin, regardless of whether toxicity screening was based on the current cancer slope factor or

on EPA’s proposed updated cancer slope factor. Since 2001, EPA has collected and analyzed

nearly 200 settled dust samples from Lower Manhattan residences, and dioxin levels in this

medium also were found to exceed health-based screening values.1 Given these observations,

and the knowledge that high-temperature combustion sources (like that which occurred at

Ground Zero on and following September 11, 2001) release dioxins to the air, dioxins are

being considered as a COPC.

3) Lead: EPA’s ambient air monitoring database includes five samples with lead concentrations

greater than the National Ambient Air Quality Standard for lead (0.0015 mg/m3). This standard

is based on a quarterly average air concentration, and quarterly average lead levels near the

WTC site have not exceeded this standard. Lead was more commonly found at concentrations

greater than 0.0001 mg/m3, which has been reported as the upper bound of average air

concentrations of lead in urban environments. These sampling results, taken alone, do not

present extraordinarily high concentrations. However, when considering the lead levels reported

in WTC dusts and the mass of material released from the collapse of the towers, potentially

significant amounts of lead might have deposited in Lower Manhattan. As evidence of this,

EPA’s ongoing study of Lower Manhattan residences has found that lead levels in more than

90% of the indoor wipe samples collected to date have exceeded the reported background

loading (1.78:g/ft2, the 95% UCL based on residential data). Therefore, lead is considered a

COPC.

4) PAHs: Limited ambient air sampling was conducted for PAHs between September and

December, 2001, when fires continued to burn at Ground Zero. However, bulk dust samples

collected by EPA and an independent researcher contained PAHs at levels greater than healthbased screening values. Based on this observation and the knowledge that combustion

processes release soot particles containing PAHs into the air, PAHs are being considered a

COPC.

Contaminants eliminated from further consideration:

1) Aluminum: Aluminum levels have been measured in more than 200 settled dust samples, 18

bulk dust samples, and more than 1,000 air indoor or ambient air samples. None of the bulk

dust samples or settled dust samples collected to date have contained aluminum levels greater

than health-based screening values. Fewer than 5% of the air samples had concentrations

greater than NCEA’s provisional reference concentration (0.0035 mg/m3). However, no clear

spatial or temporal trends are apparent among these samples. The ranges of aluminum

concentrations documented in these studies are generally consistent with those that have been

reported for other urban areas in the United States (ATSDR 1999a). Based on this review of

the data, there is no evidence that aluminum concentrations are unusually high or consistently

greater than health-based screening values. As a result, aluminum is not being considered a

COPC. However, as part of ongoing cleanup efforts, EPA continues to analyze indoor dust

samples for aluminum to evaluate surface loadings.
B-20

2) Antimony: Levels of antimony were measured in more than 200 settled dust samples, 25 bulk

dust samples, and nearly 750 air samples. None of the air concentrations or settled dust

loadings measured exceeded health-based screening values. Of the 25 bulk dust samples

reviewed, only one sample contained antimony (42.1 mg/kg) at levels greater than the healthbased screening value (30 mg/kg). That sample was collected from a rooftop in Lower

Manhattan. Antimony is not being selected a COPC because the overwhelming majority of

sampling results (>99%) are below health-based screening values. To be protective, EPA

continues to analyze indoor dust samples for antimony to evaluate surface loadings.

3) Arsenic: Arsenic levels have been measured in 17 bulk dust samples and in 215 settled dust

samples, but never detected at concentrations or loadings greater than corresponding healthbased screening values. On the other hand, since September 11, 2001, 738 air samples

collected in and near Lower Manhattan were analyzed for arsenic, and arsenic was detected in

64 (9%) of the samples. The measured concentrations ranged from 0.000007 mg/m3 to

0.000343 mg/m3. Thirty-two samples contained arsenic above the screening value (10-4 cancer

risk) for arsenic (0.00002 mg/m3). A clear majority of the highest concentrations were

observed in samples collected in April and May, 2002, suggesting that sources other than WTC

dust likely account for a considerable portion of the ambient levels. This is supported by the

observation that the measured ambient air concentrations fall within the range of arsenic levels

reported as being observed in urban settings (ATSDR 2000a). Local background data are a

little more difficult to interpret. Annual average arsenic levels in Midtown Manhattan between

1992 and 1998 ranged from 0.0000017 mg/m3 to 0.0000031 mg/m3 (NYSDEC 2000).

However, a direct comparison cannot be made between NYSDEC’s Midtown sampling and

EPA’s Lower Manhattan sampling due to the differences in detection limits and the high

frequency of non-detects. Overall, the observations suggest that arsenic in the WTC dusts is not

at levels greater than health-based screening values and that airborne arsenic in Lower

Manhattan is not unusually high when compared to the arsenic levels routinely observed in

urban settings. Consequently, arsenic is not being considered a COPC, but EPA will continue

to measure arsenic levels in indoor dust samples to ensure that ongoing exposures to arsenic

from WTC dusts, if any, are not at levels of health concern.

4) Barium: Since September 11, 2001, barium levels have been measured in 738 ambient air

samples, 17 bulk dust samples, and 215 settled dust samples. Of all these measurements, only

two air samples had barium concentrations greater than an ambient air screening value

(0.00049 mg/m3) derived from a “HEAST alternate RfDi” reported in EPA Region 3’s RiskBased Concentration Table. Furthermore, EPA’s ongoing indoor wipe sampling has found no

barium levels greater than corresponding health-based screening values. These observations

provide little evidence of barium consistently being greater than screening values, and barium is

not being considered a COPC.

5) Manganese: Concentrations of manganese have been measured in more than 1,200 air

samples, in 28 bulk dust samples, and in 218 settled dust samples. According to EPA’s

database of air sampling results, manganese levels in 236 air samples collected to date were

greater than the RfC (0.00005 mg/m3). However, the 95% UCL of the mean concentration is

lower than the RfC. In bulk dust, the health-based screening value (1,500 mg/kg) was only

slightly exceeded (1,600 mg/kg) in a single sample. EPA’s ongoing indoor dust sampling events

provide further insights into the significance of manganese levels for the indoor environment: to

date, all 218 manganese concentrations measured in dusts from Lower Manhattan residences

have been lower than corresponding health-based screening values. Based on these trends

among the air and dust sampling data, manganese is not being selected a COPC. Nonetheless,
B-21

EPA will continue to analyze indoor dust samples for manganese to ensure that surface loadings

are not at levels of health concern.

6) 4,4'-Methylene diphenyl diisocyanate (MDI): The only sampling data available for MDI

are 48 ambient air samples collected between December 2001 and February 2002. MDI was

detected in three of these samples, all of which were collected on December 19, 2001. The

levels measured in the three samples were higher than the RfC (0.0006 mg/m3). The multiple

detections on one day suggest that MDI might be released sporadically by one or more sources

in Lower Manhattan. Regardless of the source of the airborne levels, MDI is a highly reactive

compound and it is unlikely that MDI released during the collapse of the WTC towers, if any,

would still be present in indoor environments today. MDI is not being considered as a COPC,

nor will it be analyzed for during the ongoing residential dust sampling effort.

7) Naphthalene: The available sampling data include 573 air samples and 22 bulk dust samples.

Of these measurements, only a single ambient air sample had a concentration (0.0073 mg/m3)

greater than the RfC (0.003 mg/m3). This sample is J-qualified and was collected on April 18,

2002, well after WTC-related emissions subsided. Given the extremely limited evidence of

naphthalene being found at levels greater than health-based screening values, this contaminant is

not being considered as a COPC and indoor dust samples collected in Lower Manhattan

residences will not be analyzed for naphthalene.

8) Nickel: Levels of nickel have been measured in more than 1,000 ambient air samples, in 28

bulk dust samples, and in more than 200 settled dust samples. The only samples found to have

nickel levels greater than health-based screening values are six ambient air samples, which

contained nickel at levels greater than ATSDR’s inhalation MRL for chronic exposure (0.0002

mg/m3). However, the 95% UCL nickel concentration (a better indicator of chronic exposure

levels) is considerably lower than this screening value. Moreover, EPA’s ongoing indoor dust

sampling efforts show that all of the nickel levels measured in indoor wipe samples at Lower

Manhattan residences have been lower than their corresponding health-based screening level.

Therefore, nickel is not being considered as a COPC. Nonetheless, EPA will continue to

analyze indoor dust samples for nickel to ensure that surface loadings are not at levels of health

concern.

9) Thallium: Thallium levels have been measured in 738 ambient air samples, 17 bulk dust

samples, and 215 settled dust samples. To date, only a single measurement—a bulk dust

sample collected in September 2001—had a thallium concentration (11 mg/kg) greater than the

corresponding health-based screening value (7 mg/kg). However, EPA’s ongoing indoor wipe

sampling results are more representative of current and future exposures, and this study has

detected thallium in only 1 out of the 187 samples analyzed to date. Thus, thallium is not being

considered a COPC, but the indoor wipe sampling program will continue to measure thallium

levels to ensure that Lower Manhattan residents are not at risk from ongoing thallium

exposures, if any measurable exposures exist.
B-22

Chromium and mercury:

1) Chromium: In the past 2 years, chromium levels in Lower Manhattan have been measured in

air (more than 1,000 samples), bulk dust (28 samples) and settled dust (225 samples). None of

the dust samples, including the 187 samples EPA recently collected from Lower Manhattan

residences, have contained chromium at levels greater than health-based screening values.

These samples are most representative of the current and future exposures that may be

occurring in the indoor environment. The air sampling results provide somewhat conflicting

results:

• Chromium was detected in 449 of the 478 samples collected in and near Lower

Manhattan schools. Every detected chromium concentration was greater than the

screening value for 10-4 cancer risk (0.000008 mg/m3) and the RfC (0.0001 mg/m3),

but additional observations must be noted. Most importantly, these concentrations were

measured using NIOSH Method 7300M. NIOSH reports a “working range” for this

method as 0.005 to 2.0 mg/m3, based on a 500-liter sample. However, even the

highest level measured in this sampling (0.00119 mg/m3) is below the working range of

the method. Moreover, chromium was consistently detected in blank samples, raising

further questions about the validity of the measured concentrations.

• The other information on ambient chromium levels is documented in EPA’s sampling

database, which documents the results of 738 samples. Chromium was detected in

23% of these samples; the highest concentration measured was 0.00051 mg/m3 and the

95% UCL of the mean concentration was 0.000040 mg/m3. Comments in the EPA

database indicate that chromium was detected in several field blanks; however, none of

the sampling results are B-qualified. 

Overall, the sampling data provide compelling evidence that chromium in bulk and settled dusts

that remain in Lower Manhattan residences are below health-based screening values. Though

some questions remain about the chromium found in the ambient air, the 95% UCL

concentration of total chromium (0.000040 mg/m3) collected with the most sensitive method

falls within the range of chromium levels typically observed in urban environments (ATSDR

2000). While chromium is not being considered a COPC, EPA will continue to analyze dusts

from Lower Manhattan residences for chromium to identify and clean homes found to have

elevated levels, even though the available data suggest that chromium in settled dust is

consistently less than screening values. 
B-23

2) Mercury: Multiple studies have measured mercury levels in air and dust in Lower Manhattan

following September 11, 2001, and these studies have not reached consistent findings:

• Three different parties have analyzed 13 bulk dust samples for concentrations of

mercury. The highest concentration measured (0.38 mg/kg) is lower than the

corresponding health-based screening value (22.5 mg/kg).

• An independent researcher prepared a report indicating that airborne mercury levels in

Lower Manhattan after the WTC collapse were greater than EPA’s RfC (0.0003

mg/m3) and orders of magnitude greater than mercury levels found in non-industrial

urban environments (Singh 2002). These conclusions were based on measurements

made with a Jerome Mercury Vapor Analyzer, a hand-held field surveying tool with a

reported mercury detection limit of 0.003 mg/m3. These results could not be

reproduced, however. A subsequent review questioned the findings from the study,

noting that the sampling results could be biased due to low measurement selectivity and

various positive interferences (Johnson 2002). Further, EPA initiated a follow-up

mercury sampling project, during which mercury levels were measured in four occupied

Lower Manhattan residences and at selected outdoor locations (Johnson 2002). In this

study, both the maximum air concentration (0.0002 mg/m3) and the 95% UCL of the

mean concentration (0.00006 mg/m3) were lower than EPA’s RfC. Sampling in this

study was performed with a Lumex Mercury Vapor Analyzer, which has a detection

limit of 0.000002 mg/m3.

• The New York City Department of Education sampled airborne mercury levels in six

Lower Manhattan schools using NIOSH Method 6009. The database of sampling

results indicates that some individual measurements were greater than the RfC (0.0003

mg/m3) and that the 95% UCL of the mean concentration (0.00029 mg/m3) was just

below this screening value. However, the reliability of these measurements is

questionable for two reasons. First, the accuracy of the NIOSH method has only been

established for concentrations ranging from 0.002 to 0.8 mg/m3, and the levels reported

in this study are typically more than an order of magnitude lower than this range.

Second, mercury was detected in about 75% of the blank samples, and the mass of

mercury collected in the majority of field samples was indistinguishable from the levels

observed in the blanks. Thus, the sampling methodology used in this study does not

appear to be capable to measure mercury accurately and precisely at concentrations

near the screening level for this evaluation.

• Finally, the sampling results available from EPA’s ongoing study of settled dust in

Lower Manhattan residences includes 182 measured surface loadings of mercury. Two

of the samples collected to date contained mercury at levels greater than the

corresponding health-based screening value (157 :g/m2). Of the 24 contaminants for

which data are currently available, mercury is one of only three contaminants (dioxin

and lead being the others) that had any measured levels greater than screening values.

Overall, the air sampling study using the most sensitive methodology found that airborne

mercury levels in Lower Manhattan (both indoor and outdoor) were lower than the RfC. The

two other studies with conflicting conclusions were based on air sampling methodologies that

are not designed to generate accurate readings at levels near the screening value. On the other

hand, EPA’s indoor dust sampling project has found that a very small fraction of Lower

Manhattan residences contain settled dust with mercury levels greater than the screening value.

The origin of the mercury in this limited number of homes is not known, and it may come from
B-24

indoor or outdoor sources. Indoor sources of mercury include industrial instruments (e.g.,

fluorescent lights, thermometers), some paints, consumer products used for traditional or herbal

remedies or religious practices, among others (ATSDR 1999b).

The available data suggest that settled dusts in some Lower Manhattan residences contain

mercury at levels greater than health-based screening values; however, it is not clear whether

this mercury is related to the WTC site. EPA will continue to analyze dusts from Lower

Manhattan residences for mercury to identify and clean homes found to have elevated levels,

regardless of the source.)

5.2 Contaminants with No Toxicity Criteria

Contaminants for which no toxicity criteria are available are listed in Tables B-4, B-8, B-11, and B-14.

This section presents the findings of a more in-depth evaluation to determine whether any of these

contaminants require further consideration. From this evaluation, two additional COPC were identified:

fibrous glass and crystalline silica.

Contaminants selected as COPC:

1) Fibrous glass: Analysis of WTC bulk dust and debris has consistently identified fibrous glass

to be a major constituent of the material (Lioy et al. 2002, USGS 2001). In addition, the

NYCDOHMH/ATSDR (2002) study found fibrous glass in the interior settled dust. Air

samples collected in areas with fibrous glass in settled dust indicate no fiber levels of immediate

concern. Although fiber counts were found in four areas with slightly greater than background

(0.004-0.006 fiber/cc), subsequent re-analysis indicated actual fibrous glass concentrations

from these areas as 0.00004 to 0.00026 fiber/cc. Air samples from remaining areas showed a

maximum 0.003 f/cc total fiber count by Phase Contrast Microscopy. These fibers may be skin,

eye, and respiratory tract irritants. Although there are no standards to evaluate the settled dust

content, the presence of fibrous glass in settled dust does indicate a potential for exposure.

Therefore, fibrous glass is included as a COPC.

2) Crystalline silica: Settled dust and air samples taken in indoor and outdoor areas of

residential buildings in November and December of 2001 indicate the presence of alpha-quartz.

Other forms of crystalline silica were not found. This is consistent with outdoor dust and debris

samples collected by the USGS (USGS, 2001) and subjected to mineral analysis. Quartz was

found in approximately 49% of the settled dust samples from indoor areas of residential

buildings and all of the associated outdoor areas sampled. Levels of quartz ranged as high as an

estimated 31.4% of the dust by weight in a residence. Since quartz is a common material in

sand, finding this mineral in a city where there is a great deal of concrete is not unusual.

However, quartz in dust from a comparison area unaffected by the WTC collapse ranged from

non-detect only up to an estimated 2.2% in the residence (NYCDOHMH, 2002). Seventeen

residential areas and eleven common areas had quartz levels greater than the associated

comparison area. Therefore, quartz was deemed to be elevated in some indoor areas of lower

Manhattan relative to the comparison area. Additionally, quartz was found in 13% of the

respirable fraction air samples taken in these areas, ranging from an estimated 4-19 μg/m3,

demonstrating a potential for exposure. Although below occupational standards, this estimated

concentration is above the effective NAAQS standard for the silica fraction of respirable

particulate matter. Therefore crystalline silica, measured as alpha-quartz, is included as a

COPC.

Contaminants eliminated from further consideration:
B-25

1) Calcite, gypsum, and portlandite: In addition to crystalline silica, calcite, portlandite and

gypsum were the most abundant minerals detected in settled dust samples from residential areas

in lower Manhattan following the WTC collapse. Mica was detected with much less frequency,

generally at less than 0.1% of the dust. Halite (salt) was also detected at trace levels. Calcite,

portlandite, and gypsum are typical components of concrete and gypsum based wallboard

products, which were present in the WTC buildings. While high concentrations of these

minerals in airborne dust constitute a short-term health concern in the form of eye, nose and

throat irritation, persisting adverse heath effects would not be anticipated, unless these minerals

remained suspended in high concentrations. Indoor and street-level outdoor air sampling done

in November and December of 2001 show that the levels of these chemicals, over a timeweighted sample, were below levels associated with irritant effects (see table below).

 NIOSH and OSHA exposure limits and estimated maximum values in Lower Manhattan

Mineral NIOSH REL (:g/m3) OSHA PEL (:g/m3)

*Maximum Estimated Value

(J) in Lower Manhattan

(:g/m3)

Gypsum 10,000 :g/m3

 (total)

5,000 (:g/m3 resp)

15,000 :g/m3 (total)

5,000 (resp)

14J (PM100)

15J (PM4)

Portlandite 5,000 :g/m3 15,000 :g/m3

 (total)

5,000 :g/m3 (resp)

95J (PM100)

84J (PM4)

Calcite 10,000 :g/m3

 (total)

5,000 :g/m3 (resp)

15,000 :g/m3 (total)

5,000 :g/m3 (resp)

14J (PM100)

10J (PM 4)

NIOSH = National Institute of Occupational Safety and Health, Centers for Disease 

Control and Prevention

REL = recommended exposure level/limit

OSHA = Occupational Safety and Health Administration

PEL = permissible exposure limit.

resp = respirable

* [ATSDR/NYCDOHMH, 2002]

2) Essential nutrients (e.g., calcium, magnesium, sodium): EPA does not generally carry

these elements through its risk assessments because of their natural occurrence, presence in our

diets, and relatively low toxicity. 

3) A limited number of specific phthalates and PAHs and other SVOCs. The lengthiest list

of SVOCs for which no toxicity criteria exist comes from Lioy et al. (2002)—a study of three

outdoor bulk dust samples collected in Lower Manhattan on September 16 and 17, 2001.

Most of these SVOCs were not consistently detected across the three samples. Further, the

concentrations measured were consistently lower than other SVOCs (e.g., PAHs) that have

been selected as COPC. Finally, because many of the SVOCs identified by Lioy are rarely

considered in environmental sampling studies, we have no knowledge whether the measured

levels are consistent with background concentrations in urban settings or if the levels are

unusually high.
B-26

References

Agency for Toxic Substances and Disease Registry (ATSDR), New York City Department of Health

and Mental Hygiene (NYCDOHMH). 2002. Final Technical Report of the Public Health Investigation

to Assess Potential Exposures to Airborne and Settled Surface Dust in Residential Areas of Lower

Manhattan. September 2002.

ATSDR. 1999a. Toxicological profile for aluminum. Atlanta: U.S. Department of Health and Human

Services. July 1999.

ATSDR. 1999b. Toxicological profile for mercury. Atlanta: U.S. Department of Health and Human

Services. March 1999.

ATSDR. 2000a. Toxicological profile for arsenic. Atlanta: U.S. Department of Health and Human

Services. September 2000.

ATSDR. 2000b. Toxicological profile for chromium. Atlanta: U.S. Department of Health and Human

Services. September 2000.

Butt CM, Truong J, Diamond ML, Stern GA. 2002. Polychlorinated Biphenyl (PCB) Concentrations in

Atmospherically Derived Organic Films From Lower Manhattan After September 11, 2001. Formation

and Sources: Field Cases. Organohalogen Compounds 59:219–222.

Chattfield EJ, Kominsky JR. 2001. Summary Report: Characterization of Particulate Found in

Apartments After Destruction of the World Trade Center. Report Requested by: “Ground Zero”

Elected Officials Task Force.

Johnson C. 2002. Mercury vapor levels in dwellings in close proximity to the WTC site. Medgar Evers

College (CUNY) Bklyn, NY 

Lioy PJ, Weisel CP, Millette JR, Eisenreich S, Vallero D, Offenberg J, Buckley B, Turpin B, Zhong M,

Cohen MD, Prophete C, Yang I, Stiles R, Chee G, Johnson W, Porcja R, Alimokhtari S, Hale RC,

Weschler C, Chen LC. 2002. Characterization of the Dust/Smoke Aerosol that Settled East of the

World Trade Center (WTC) in Lower Manhattan after the Collapse of the WTC 11 September 2001.

Environmental Health Perspectives 110:703–14.

New York State Department of Environmental Conservation (NYSDEC). 2000. 1999 New York

State air quality report: ambient air monitoring system. NYSDEC. Division of Air Resources. Bureau of

Technical Support. 

Singh U. 2002. Mercury Contamination after September 11, 2001: A Potential Public Health Risk in

Lower Manhattan. I.H. Consultants Inc. Upper Monclair, NJ

U.S. Geological Survey (USGS). 2001. Environmental studies of the world trade center after the

September 11, 2001 attack. Open File Report OFR-010429.
C-1

APPENDIX C

Basis for Screening Level of 1 E-04 (1 x 10 -04)

Defensible analytical methodologies and sampling protocols have been chosen for indoor sampling and

analysis activities. The methods chosen are ones that have been published by reputable agencies and

are in common practice among testing laboratories. In some cases, minor modifications may be made

to the sampling and analytical protocols, but these are modifications that are well established in the

laboratory community. 

All protocols chosen are designed to reach the lowest level of detection that is reasonable for the

established methods. For dioxin, asbestos and PAHs in indoor air the sampling and analytical protocols

are designed to reach detection limits that represent risk estimate levels of 1 E-04. To reach risk

estimates of 1E-06, extraordinary modifications would have to be employed. These modifications

would either have to be incorporated into the analytical protocols to increase the sensitivity of the

required instrumentation, incorporated into the sampling protocols to achieve a larger sample, or a

combination of both. For the Chemicals of Potential Concern (COPC) list, the analytical protocols

chosen are already incorporating the maximum sensitivity of the instrumentation. Therefore, the only

legitimate mechanism to lower the overall limits of detection is to modify the sampling protocol. The

two means of achieving this goal are to either run the sampling equipment (pumps) at a higher flow rate,

or for longer periods of time. For the COPC list modifying flow rates would involve operating the

equipment to achieve flow rates on the order of 500 to 1000 liters per minute. The only equipment

available to operate at such flow rates are large units that can not be brought inside a residence. Rates

this high also present problems with creating excessive negative pressure for indoor environments, plus

flow rates this high have not been tested using the sampling protocols, and there is high likelihood of

having analyte breakthrough on the collection filters. Therefore, this is not practical. The other option is

to run the equipment for long periods of time. Again with the COPC list, sampling periods of up to 800

hours (33 days of continuous operation) would be needed to reach the E-06 risk detection levels.

For silica, the analytical and sampling protocols chosen will give detection levels in the neighborhood of

5 :g/m3 (see Section 3.3 for more detailed discussion). Instrumental sensitivity can not be set any

higher to reach lower detection levels. Also, the sampling protocols involved for this analysis have been

thoroughly validated by NIOSH. Any change in pump flow rate or sampling duration beyond what is

documented in the method will produce results that have not been validated. Therefore, the sampling

protocol should not be changed from that which is documented.

For fibrous glass the methodology is such that detection levels as low as 0.00001 f/cc can be achieved. 

This is well below required levels of detection for future indoor studies.

Another consideration in setting the target risk level involved the anticipated background level of

contaminants such as asbestos, dioxin and PAHs in urban indoor environments. EPA has conducted a

study (WTC Background Study - EPA 2003b) to characterize background conditions for WTC

COPC in New York City residential dwellings. Preliminary results indicate that background

concentrations of asbestos in indoor air and dioxin in settled dust are within the same order-ofmagnitude as the analogous health-based benchmarks set at the E-04 risk level. Practical quantitation

limits constrain the ability to measure PAH congeners below the E-04 risk level. As part of the WTC

Background study, a literature review was conducted to provide a general estimate of background

concentrations for carcinogenic COPC in urban indoor environments. It should be noted that the

literature is limited in this regard. For asbestos, ATSDR reports that “measured indoor air values range

widely, depending on the amount, type, and condition (friability) of asbestos-containing materials used
C-2

in the building” (ATSDR, 1995). In its review ATSDR notes that the studies suffer from lack of

common measurement reporting units. Study results have been reported as ng/m3, f/cc (TEM) and f/cc

(PCM). Using unit conversion factors recommended by the National Research Council in 1984,

ATSDR (1995) reports that the arithmetic mean concentrations of monitoring data from a variety of

indoor locations ranged from .00003 - .006 f/cc (PCM). The clearance level for WTC-impacted

residential dwellings (.0009 PCM equivalents) is within this background range. Additional literature

review (ATSDR 2000, EPA 2003 b) indicates that the background levels of PCM equivalent fibers in

residential indoor environments ranges from non-detect (ND) - .002 f/cc.
D-1

APPENDIX D

Assessing Exposures to Indoor Air and to Residues on Indoor Surfaces

1.0 Introduction

The purpose of this Appendix is to provide further details on how procedures were selected to estimate

exposure to indoor air and to residues on indoor surfaces in residences impacted by the WTC attack.

2.0 Indoor Air

Indoor air clearance criteria were derived using methods described in EPA’s “Risk Assessment

Guidance for Superfund” [RAGS, 1989]. These methods were developed to assess the risk from

contaminants at Superfund sites. The risk based clearance criteria were calculated using the formulas

below:

Carcinogens: Clearance Criteria = (TR * AT) / (ED * EF * IUR)

Non-Carcinogens: Clearance Criteria = Target Hazard Index * RfC

where:

TR = Target Risk EF = Exposure Frequency (d/yr)

AT = Averaging Time (d) IUR = Inhalation Unit Risk (risk per :g/m3)

ED = Exposure Duration (yr) RfC = Reference Concentration ( :g/m3)

Target Risk (TR) and Target Hazard Index

The target risk identified for these calculations was 1 x 10-4 and the target hazard index was 1.0. 

Appendix C explains the rationale for these values.

Averaging Time (AT) - Carcinogens

For carcinogens, exposure is averaged over a 70-year lifetime (the factor on which the cancer slope

factors are based), and the AT is 70 years, in days (25,550).

Exposure Duration (ED)

A value of 30 years is assumed to match upper bound estimate of time in a residence (EPA, 1997b).

Exposure Frequency (EF)

A value of 365 days/year is used to represent a full time resident. Implicitly this approach also assumes

exposure occurs continuously, i.e. 24 hr/d. 

Inhalation Unit Risk (IUR)

The upper-bound excess lifetime cancer risk estimated to result from continuous exposure to an agent

at a unit concentration. The inhalation unit risk values used in this report are summarized in Table A-1

(Appendix A). Cancer risks for dioxin were evaluated on the basis of a range of unit risk values. An

inhalation unit risk of 50,000 per mg/m3 can be calculated from the oral slope factor of 1.6 x 105 kgd/mg given in EPA, 1985. The draft Dioxin Reassessment (EPA, 2000) proposes an oral slope factor

of 1 x 106 kg-d/mg which can be converted to an inhalation unit risk of 290,000 per mg/m3. 

Reference Concentration (RfC)
D-2

The RfC represents an estimate (with uncertainty spanning perhaps an order of magnitude) of a

continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to

be without an appreciable risk of deleterious effects during a lifetime. The RfC values used in this

report are summarized in Table A-1 (Appendix A). 

3.0 Residues on Indoor Surfaces

The most formal EPA guidance which addresses this issue is the “Standard Operating Procedures

(SOPs) for Residential Exposure Assessment” originally published by the Office of Pesticides in 1997

and updated in 2001 (EPA, 1997a and EPA, 2001a). This guidance was designed for estimating

exposures to pesticides. Pesticides are typically applied to indoor surfaces as liquid or sprayed

formulations which would create surface residues which are likely to be somewhat different than the fine

dust particles associated with the WTC attack. So while this guidance was selected as the starting

point for developing these procedures, a number of other sources were also reviewed including the

Superfund guidance on dermal contact (EPA,1989), the procedures used to develop re-entry

guidelines for the Binghamton State Office Building (Kim and Hawley, 1985), procedures used by

NJDEP for setting interior building surface clean-up goals (NJDEP, 1993), the building clean-up

procedures presented by Michaud et al (1994) and an approach developed by the EPA Region III

Superfund program that has been employed by the U.S. Army Corps of Engineers to develop riskbased clean-up goals for interior surfaces at the Claremont Polychemical Superfund site in Region II

(Radian, 1999). The discussion below presents the OPP procedures and how they were adopted for

application to residences near WTC.

The scenario for indoor surface exposures is assumed to be 30 years which represents an upper

estimate for how long individuals may live in one residence (EPA, 1997). This contact begins at about

6-12 mo age when infants become mobile. Thus, this exposure scenario is assumed to begin at age 1

and end at 31.

3.1 Dermal Contact

The OPP guidance specifies the following procedure to estimate the Potential Dose Rate (PDR, 

:g/kg-day) from dermal contact with indoor surfaces:

PDR = (ISR * TC * ET)/ BW

ISR = Indoor Surface Transferable Residue (:g/cm2)

TC = Transfer Coefficient (cm2/hr)

ET = Exposure Time (hr/d)

BW = Body Weight (kg)

ISR represents the amount of residue on a surface that can be transferred to skin. The OPP defaults

calculate this initially as a fraction of the application rate. Pesticide application rates are not relevant to

the WTC situation. Instead, the following approach is recommended. 

ISR = CSL * FTSS

CSL = Contaminant Surface Load (:g/cm2)

FTSS = Fraction Transferred from Surface to Skin (unitless fraction)
D-3

Making this substitution and rearranging to allow different parameter values for hard vs soft surfaces

gives the following:

PDR = [(TC*EThard*FTSShard*CSLhard)+(TC*ETsoft*FTSSsoft*CSLsoft)]/BW

The discussion below defines these parameters, provides the OPP default and discusses how they

should be changed for the WTC assessment. The OPP procedures provide defaults for two age

classes: toddlers (ages 1-6 yr) and adults. The OPP estimate of the surface residue level includes

dissipation over time. Dissipation is also expected to occur in the WTC situation, but at potentially

different rates and mechanisms than pesticides. This issue is discussed separately below in Section 3.3. 

Fraction Transferred from Surface to Skin (FTSS, unitless fraction) - This is the fraction of residue on a

surface that can be transferred to skin. The OPP defaults calculate this initially as 5% of application

rate for carpets and 10 % for hard surfaces with a subsequent dissipation rate. FTSS will vary

depending on type of surface, type of residue, hand condition, force of contact, etc. USEPA has

previously assumed a transfer fraction of 0.5 for PCBs (EPA, 1987) based on an Office of Toxic

Substances (OTS) assessment. Michaud et al (1994) assumed 0.5 for PCBs and dioxins, but stated

that 0.1 might be more realistic. In developing re-entry guidelines for the Binghamton State Office

Building after a fire, a 100% transfer was assumed (Kim and Hawley, 1985). In a study of Malathion

uptake from different surfaces, USEPA-EMSL found that FTSS of Malathion from painted Sheetrock

to human hands was only 0.0003. (Mean transfer from vinyl flooring to hands was 0.0018, and from

carpet to hands was 0.0152.) Malathion is a pesticide assumed to have lipophilicity more similar to

PCBs than to volatiles or metals. However, the representativeness of such a number for PCBs and

dioxins is unknown. PCBs are more lipophilic (have higher Kows) than malathion. Rodes et al. 2001

conducted hand press experiments on particle transfer to dry skin and measured transfers with central

values of about 10% from carpets and 50% from hard surfaces. These are considered most relevant to

the WTC situation and were adopted in this assessment for transfers to hands leading to ingestion (see

discussion below). For dermal contact, it is important to consider that much less transfer will occur to

body parts with less intensive surface contact than hands such as the arms, legs, and face. Therefore

these values were reduced by half to represent an area weighted transfer to the all exposed skin (i.e.

5% from soft surfaces and 25% from hard surfaces).

Transfer Coefficient (TC, cm2/hr) - This represents the rate of skin contact with the surface. The OPP

defaults are 6000 cm2/hr for toddlers and 16,700 cm2/hr for adults. These were derived from pesticide

specific studies involving very high activity levels and minimal clothing protection. For chronic

exposures assumed for the WTC situation, where exposure is to dust, much lower transfer coefficients

would be applicable. A value more representative of this scenario was derived by selecting a TC which

yielded total dust on skin loads comparable to measured values in indoor settings. Using the model

presented above, the total dust load on skin can be computed and averaged over the exposed skin area

(SA) as follows:

Daily Skin Load = [(TC*EThard*FTSShard*CSLhard)+(TC*ETsoft*FTSSsoft*CSLsoft)]/SA

The CSL values were set at 50 :g/cm2 of total dust which represents typical indoor horizontal surfaces

based on Rodes et al., 2001 (this value is also consistent with ranges shown in Table 2). The exposed

skin surface area was set to 5000 cm2 for children (half the skin area of 7-8 yr old) and 9000 cm2 for

adults (half the skin area of an adult) (EPA, 1997). The other parameters were set at the values

presented above. A TC value of 1200 cm2/hr was judged to provide reasonably comparable skin

loads to measured levels and adopted here (see Table 1).
D-4

Table 1. Skin Load Comparisons

Calculated Skin

Load ( :g/cm2)

Measured Skin Load ( :g/cm2)

Child 17 10 - area weighted average for indoor children (EPA, 2000)

40 - area weighted average for daycare children (EPA, 2000)

Adult 9 2 to 6 - range across body parts for Tai Kwon Do students (EPA,

1997b)

2 to 43 - range across body parts for greenhouse workers (EPA,

1997b)

Exposure Time (ET, hr/d) - The OPP defaults are 8 hr/d for carpets and 4 hr/d for hard surfaces. Hard

surface time is based on time in kitchen and bathroom. Carpet time is based on remaining indoor time

not including sleeping. This was judged to be representative of many children under age 6 who spend

most of their time at home. Normally children begin school at age 6 and spend less time at home. So

for ages 6-18 this was reduced to 6 hr/d for carpets and 2 hr/d for hard surfaces. After 18, many

individuals will spend more time in school or at work. Others, however, may not work or attend school

and spend more time at home. To be conservative, it was decided to represent this second scenario

and assume that after 18 individuals would spend 8 hr/d on carpets and 4 hr/d on hard surfaces.

Body Weight (BW, kg) - The OPP defaults are 15 kg for toddlers and 71.8 kg for adults. Since this

assessment spans ages 1-31, mean weights were used to represent each year based on national data in

EPA, 1997.

3.2 Dust Ingestion

The OPP guidance specifies the following procedure to estimate the Potential Dose Rate (PDR, 

:g/kg-day) from incidental nondietary ingestion of residues on indoor surfaces from hand-to-mouth

transfer.

PDR = (ISR * SA * FQ * SE * ET)/ BW

ISR = Indoor Surface Transferable Residue (:g/cm2)

SA = Surface Area (cm2/event)

FQ = Frequency of hand to mouth events (events/hr)

SE = Saliva Extraction factor (unitless fraction)

ET = Exposure Time (hr/d)

BW = Body Weight (kg)

As discussed above, ISR is calculated here by multiplying the Contaminant Surface Load (CSL) by the

Fraction Transferred from Surface to Skin (FTSS). Making this substitution and rearranging to allow

different parameter values for hard vs soft surfaces gives the following:

PDR = [(EThard*FTSShard*CSLhard)+(ETsoft*FTSSsoft*CSLsoft)]*SA*FQ*SE/BW

The discussion below defines these parameters, provides the OPP default and discusses how they

should be changed for the WTC assessment. The OPP guidance provides defaults for toddlers (ages 1-

6 yr) only.
D-5

Fraction Transferred from Surface to Skin (FTSS, unitless) - Rodes et al. 2001 conducted hand press

experiments on particle transfer to dry skin and measured transfers with central values of about of 10%

from carpets and 50% from hard surfaces. These are considered representative of the WTC situation

and were adopted in this assessment for transfers to hands leading to ingestion. Rodes et al. presented

some data suggesting that transfers to wet skin (which would be associated with mouthing behavior)

would be higher than dry skin, but these results were not used since they appeared less reliable. 

Surface Area (SA, cm2/event) - This is the skin area contacted during the mouthing event. The OPP

default is 20 cm2 based on the area of a child’s 3 fingers. Total skin surface area increases by about 3

fold from age 2 to an adult (EPA, 1997). Average area of both hands for an adult is about 900 cm2, so

it would be about 300 cm2 for a 2 year old. Assuming 3 fingers of one hand represents about 5% of

the total area of both hands, it would increase from 15 cm2 to 45 cm2 from age 2 to adult. On this basis,

the SA values used here are assumed to start at 15 cm2 and increase linearly to 45 cm2 at age 17 and

remain constant after that. 

Frequency of hand to mouth events (FQ, events/hr) - The OPP defaults suggest 9.5 events/hr for

toddlers, based on observations at day care centers. This will decline with age, but very little data are

available for other ages. Michaud et al (1994) assumed a mouthing frequency of twice per day for

adults. It was decided to step down this frequency as follows: 1 to 6 yr - 9.5 times/hr, 7 to 12 - 5

times/hr, 8 to 18 yr - 2 times/hr and 19 to 31 yr - 1 time/hr. 

Saliva Extraction factor (SE, unitless fraction) - The fraction transferred from skin to mouth will depend

on the contaminant, mouthing time and other behavioral patterns. The OPP default is 50%, based on

pesticide studies. Michaud et al (1994) assumed that all of the residues deposited on the fingertips

would be transferred to the mouth, twice per day. In the Binghamton re-entry guideline derivation, a

range of factors were used: 0.05, 0.1, and 0.25 representing the fraction of residue on hand that is

transferred to the mouth (Kim and Hawley, 1985). For purposes of this assessment, the OPP default

of 50% was selected for all ages.

Exposure Time (ET, hr/d) - Same as dermal contact, see discussion above.

Body Weight (BW, kg) - Same as dermal contact, see discussion above.

3.3 Dissipation

The surface loading of the contaminant in the dust is likely to diminish over the 30 year exposure period

as a result of volatilization, chemical degradation, surface cleaning and transfers to skin/clothing. While

some redeposition will also occur, the net long term effect should be a gradual decline. The discussion

below provides a review of the literature related to this issue.

Several studies indicate that the main source of new dust indoors is track-in from footwear. Thatcher

and Layton (1995) found a mass increase on tracked but not cleaned/vacuumed floor surfaces of 0.01

grams/day-m2for linoleum, 0.15 for upstairs carpet and 0.31 for downstairs carpet. They reported a

value for the front doormat of 6.2 grams /day-m2. Allot (1992) also indicated that the main mechanism

for introduction of dust indoors is tracking by footwear and noted a smaller contribution from deposition

dust particles suspended in air. Without regular indoor cleaning the dust inputs would accumulate. With

time, they would likely become noticeable or objectionable to the inhabitants, prompting cleaning. Lioy

(2002) indicates that in a survey of 36 homes, an average time since the last cleaning was 14.2 days

(range 1-150 days). Roberts et al. (1999) determined that the median value of dust loading on 11

carpets before cleaning was 1.3 g/m2. This agrees with Camann and Buckley’s (1994) estimate of the
D-6

median surface loading on 362 carpets of 1.4 g/m2. Lioy et al. (2002) report ranges of dust loadings in

homes from 0.05-7 g/m2 for floors and <1 to 63 g/m2 for rugs. See summary in Table 2.

Table 2. Dust Loads on Indoor Surfaces

Dust Load (:g/cm2) Reference

Hard

Surfaces

5-700 floors Lioy et al. (2002)

Soft

Surfaces

130 - median for carpets before cleaning (n=11)

10 - median for carpets after cleaning (n=10)

140 - median for carpets (n=362) 

<100 to 6300 - range for rugs

Roberts et al. (1999)

Roberts et al. (1999)

Camann and Buckley (1994)

Lioy et al. (2002)

Elevated non-porous surfaces such as walls, table tops, counters, etc. receive much of their dust loads

from deposition of suspended dust. The mean dustfall rate in 100 American homes in five cities was

0.02 g/day-m2( Schaefer et al 1972, quoted in Roberts, Budd, et al. 1992) . This indicates that the dust

inputs to these surfaces are considerably smaller than track-in for carpets near entryways. 

 In order to maintain a fairly constant dust loading on surfaces, dust would have to be removed by

cleaning at a rate equal to the rate of input from outside sources. Otherwise dust will accumulate and

probably further prompt cleaning because it would be noticeable or objectionable. Assuming an input of

0.31 grams /day-1 m-2 for track-in to a downstairs carpet (Thatcher and Layton (1995)), dust must be

removed by cleaning at this rate to maintain a constant dust load on carpet. At a track-in rate of 0.31

g/day/m2, an initially clean carpet would require about 5 days to achieve a dust loading of 1.3 g/m2. 

If cleaning occurred on a periodic basis as it normally does, newly tracked-in dust would continually be

mixed with and removed by cleaning with dust in the carpet from previous tracking events. With

continued cleaning eventually the dust reservoir (from past tracking events) would be replaced with

newly tracked-in dust. This means that any initial, residual load of dust containing contaminants in a

carpet would be gradually removed over time with periodic cleaning and no new significant input of

contaminated dust. Roberts et al. (1999) determined that the residual lead loading in carpets could be

reduced by 90 to 99% in 6 months by removing shoes on entering (lead was being tracked in from the

outside), use of a doormat, and use of an efficient vacuum twice a week. They determined that vigorous

vacuuming was efficient in removing the contaminated dust reservoir from carpets. If a carpet is initially

loaded with a contaminated dust, a half-life for its removal can be calculated assuming 90% removal in

6 months using the Roberts et al. (1999) data. This results in a 2-month half-life for dust removal from

carpets using vigorous cleaning by vacuuming. It would take roughly 12 months to reduce the initial

contaminant load by 99.9% using the above scenario. With no new, significant inputs of contaminated

dust to a carpet an initial, residual load would be reduced over time with regular vigorous cleaning. 

Roberts (1999) also determined that the dust on the surface of 11 carpets could be reduced by 90% in

1 week with the use of a Hoover Self-Propelled Vacuum with Embedded Dirt Finder (HSPF). The

pre- and post-cleaning surface loadings were as follows: pre-cleaning fine dust loading: min. 0.32 g/m2,

max. 14.4 g/m2, median 1.30 g/m2; final fine dust loading: min. 0.019 g/m2, max. 0.289 g/m2, median

0.102 g/m2. A cumulative vacuuming rate of 6 to 45 min/m2 of vacuuming with the HSPF removed

deep dust from these carpets. The median surface loadings of fine dust in these carpets were reduced

by 91%, in 1 to 15 hours of cumulative vacuuming
D-7

The above analysis deals with a carpeted surface that can act as a dust reservoir and which is a difficult

surface to clean. Non-porous surfaces such as floors and tables, etc. don’t have the same degree of

storage potential for dust and are easily cleaned. These surfaces will have a faster removal half-life than

the approximately 2 months for carpets calculated above. However, they may get re-contaminated

from dust re-suspension from the carpets (carpets become the source of contamination) until the carpet

contaminant load is reduced.

Further data concerning the removal half-life of dioxins in indoor dust is available from the study of the

Binghamton State Office Building (BSOB) (NYSDOH 2002). The building had closed in February

1981 after an intense transformer fire spread an oily soot contaminated with polychlorinated biphenyls

(PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs)

throughout the 18-story structure. After extensive decontamination, testing and reconstruction, the

BSOB was reopened late in 1994. Pre-occupancy sampling in July 1994 found that PCB and PCDD/F

levels in air and on surfaces in workspaces were considerably less than the guidelines set for

reoccupancy. In fact, they were similar to levels found in buildings that have never experienced a

transformer fire. Seven rounds of dust wipe sampling of tops of in-ceiling light fixtures were performed

post-occupancy. PCDD/F levels on the tops of in-ceiling light fixtures averaged 1.1 nanograms per

square meter at the final round of sampling, less than any previous measurements. The seven dust wipe

sampling rounds indicated a gradual decline of PCDDs over-time on the light fixtures (see Figure 1).

Since reoccupancy, surfaces above the ceiling were cleaned twice, once before the March 1997

sampling and again before the sixth round of sampling in August 1998. Since reoccupancy, average

PCDD/F levels in dust on light fixtures have declined steadily by about one-half every 20-22 months (a

half-life of 20-22 months).
D-8

The BSOB PCDD dust half-life value shown above was based on dust wipe sampling of the tops of

light fixtures which were inaccessible to regular cleaning and only cleaned twice in 5 years. The

mechanism of removal of the contaminated dust was probably a combination of cleaning, resuspension

and dilution with uncontaminated dust (and possibly some volatilization). This half-life is a conservative,

upper bound estimate of a removal half-life for dioxins in dust for areas that are cleaned routinely (such

as would be expected were people would have daily contact). The BSOB half-life should be

acceptable and conservative for use in the COPC risk assessment scenario which addresses exposure

to accessible surfaces. It will capture the mechanism of dust removal from a residence due to regular

cleaning that is discussed by Roberts et al. (1999) and Allot (1992) cited above and is a slower

removal of dioxins in dust than would be predicted using these carpet vacuuming studies.

Further support for considering dissipation is presented below: 

• The OPP guidance (EPA, 1997a and EPA, 2001a) uses a “dissipation” factor to account for

degradation and other loss mechanisms after pesticide application. Similarly, Durkin et al

(1995) has proposed a time-dependent transfer coefficient method for lawn treatment

pesticides.

• Michaud et al (1994) proposed a mass balance model which accounts for losses from surfaces

associated with building clean-ups.

Based on the above discussion, there is strong support for considering dissipation in setting criteria for

building clean-ups. The recently completed study at the Binghamton State office Building described

above found that dioxin has dissipated over time according to first order kinetics with a 20 to 22 month

half life. As discussed above this dissipation is thought to occur from a combination of cleaning,

resuspension and dilution with uncontaminated dust (and possibly some volatilization). These same

physical dissipation processes would apply to other compounds addressed in this study as well. 

Therefore the other compounds were assumed to dissipate at the same rate as dioxin. Note that this

leads to some overestimate of risk for the organic compounds with higher volatility than dioxin. In

summary, a 22 month half life (decay rate constant of 0.38 yr-1) was adopted here and assumed to

apply to all contaminants. Exposures were calculated in a in a series of time steps where the residue

level was assumed to dissipate according to first order kinetics:

CSL = CSLinitial e-kt

CSL = Contaminant Surface Load (:g/cm2)

CSLinitial = Initial Contaminant Surface Load (:g/cm2)

k = Dissipation Rate Constant (yr-1)

t = Time (yr)

3.4 Calculating Clearance Criteria

The dose rates for dermal contact and ingestion were used to estimate cancer risk and noncancer

hazard. The clearance criteria for surface dust loadings were derived by adjusting the levels iteratively

until the risks reached the target levels. Cancer risks and noncancer hazards were calculated as

follows:

Cancer Risk = LADD * CSF

Noncancer Hazard = ADD/RfD
D-9

LADD = Lifetime Average Daily Dose (:g/kg-d)

CSF = Cancer Slope Factor (kg-d/:g)

ADD = Average Daily Dose (:g/kg-d)

RfD = Reference Dose (:g/d)

For carcinogens, LADD is calculated by summing daily doses (PDR) over ages 1 to 31 and then

averaging over a lifetime of 70 years. For noncarcinogens, ADD is calculated by summing daily doses

over ages 1-6 and averaging over this 5 year period. Implicitly this procedure assumes that the

exposure frequency is every day during the exposure period. This procedure also involves multiplying

the potential dermal dose by an absorption fraction to get the absorbed dose. Absorption fraction and

toxicity values are discussed below.

Oral Absorption Fraction (ABSo)

For chemicals whose dose-response parameters are based on experiments in which the absorption

fraction is similar to the one expected in the exposure scenario, there is no need to adjust the RfD or

CSF.

Dermal Absorption Fraction (ABSd)

This parameter is chemical-specific. Dermal absorption fractions of 0.06 for PCBs and 0.03 for

dioxins from soil were first proposed in USEPA, 1992 and more recently adopted in EPA 2001b. 

Michaud et al (1994) used 0.02 for dioxins and 0.03 for PCBs uptake from a sooty surface, based on

the ranges of estimated ABSd values for soil. The Binghamton panel used a range of values for PCBs

(0.01, 0.1, and 0.5) and dioxins (0.01 and 0.1) ( Kim and Hawley, 1985).

Reported ranges for dermal uptake for PCBs in solvent vehicles are reported to range from 15 to 56%,

with most of the values clustering around 20% (ATSDR, 1993). Reported ranges for 2,3,7,8-TCDD

in solvent vehicles are reported to range from 1 to 40% (ATSDR, 1988). Therefore, it seems that even

if absorption from the wall material might be enhanced by residual solvent, the maximum possible

absorption of 100% would be unrealistic even for worst-case exposure.

The values recommended here of 3% for dioxins and 13% for PAHs are based on EPA, 2001b. 

Toxicity Values

Two toxicity values are used here, a Reference Dose (RfD) for non-carcinogenic compounds and a

Cancer Slope Factor (CSF) for carcinogenic compounds. The RfD is defined as an estimate (with

uncertainty spanning perhaps an order of magnitude) of a daily oral exposure to the human population

(including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects

during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark dose, with uncertainty

factors generally applied to reflect limitations of the data used. The CSF is defined as an upper bound,

approximating a 95% confidence limit, on the increased cancer risk from a lifetime exposure to an

agent. This estimate, usually expressed in units of proportion (of a population) affected per mg/kg/day,

is generally reserved for use in the low-dose region of the dose-response relationship, that is, for

exposures corresponding to risks less than 1 in 100. The RfD and Cancer Slope Factor values used in

this report are summarized in Table A-1 (Appendix A).

Cancer risks for dioxin were evaluated on the basis of a range of slope factors. EPA (1985) provides

an oral slope factor of 1.6 x 105 kg-d/mg and the draft Dioxin Reassessment (EPA, 2000) proposes an

oral slope factor of 1 x 106 kg-d/mg. 
D-10

3.5 Uncertainties

Dose Adjustments

The procedure used here, estimates the absorbed dose from dermal contact. Since dose-response

relationships are typically based on an administered oral dose, ideally some adjustment is needed

before calculating risks. EPA (2000) states that about 80% of dioxin in food is absorbed and therefore

recommends multiplying an absorbed dose by 1.25 (100%/80%) to adjust it to a comparable

administered oral dose. Since the basis for this dioxin adjustment is somewhat uncertain and similar

data for other chemicals were not available, no adjustments were made for this purpose in this

document. This could lead to relatively small under estimates of risk.

A similar issue applies to the ingestion pathway. Organic contaminants are likely to be more tightly

bound (i.e. less bioavailable) from dust than food used in calculating dose-response relationships. 

About 30% of dioxins in soil are absorbed orally (EPA, 2000). On this basis, EPA recommended

multiplying the ingested dose of dioxin in soil by 0.375 (80%/30%) to adjust it to a comparable basis. 

Given the similarity of dust and soil, this adjustment may also apply to dust. Since the basis for this

dioxin adjustment is somewhat uncertain and similar data for other chemicals were not available, no

adjustments were made for this purpose in this document. This could lead to over estimates of risk.

Surface to Skin Transfers

No standardized procedures have been established for estimating dust transfers to skin in indoor

settings. As discussed above, the procedure used here is derived from the pesticide guidance. 

Pesticides are clearly different than dust. The default values for key parameters provided in the

pesticide guidance (transfer fractions and transfer coefficients) were derived from experiments specific

to pesticides. Although considerable judgement was used to adjust these to indoor dust, the adjusted

values give total dust on skin loads that are consistent with measured values (as shown in Table 1). 

These uncertainties could lead to either over or under estimates of risk.

Dust Ingestion

No standardized procedures have been established for estimating indoor dust ingestion. As discussed

above, the procedure used here is derived from the pesticide guidance which has uncertain application

to the WTC scenarios. One way to evaluate this approach is to compute the implied dust ingestion

rate: 

Ingestion Rate = [(EThard*FTSShard*CSLhard)+(ETsoft*FTSSsoft*CSLsoft)]*SA*FQ*SE

The CSL values were set at 50 :g/cm2 of total dust which represents typical indoor horizontal surfaces

based on Rodes et al., 2001 (this value is also consistent with ranges shown in Table 2). The other

parameters were set at the values presented above. This yields an ingestion rate of 13 mg/d for

children and 6 mg/d for adults. EPA (1997) recommends central estimates of total soil ingestion rates

of 100 mg/d for children and 50 mg/d for adults. It is logical that lower ingestion rates would apply to

dust only, however, it is uncertain how much less. This uncertainty appears to have more potential for

leading to under than over estimates of risk.

Dioxin Toxicity
D-11

The toxicity of dioxin-like compounds have been intensively debated over many years. EPA currently

uses an oral slope factor of 1.6 x 105 kg-d/mg based on EPA, 1985. The draft Dioxin Reassessment

(EPA, 2000) proposes an oral slope factor of 1 x 106 kg-d/mg. Thus, the uncertainty in this factor

spans a range of at least 6 fold. 
D-12

References

Agency for Toxic Substances and Disease Registry (ATSDR). 1988. Toxicological Profile for 2,3,7,8-

Tetrachlorodibenzo-p-dioxin. United States Public Health Service, ATSDR, Atlanta, GA.

Allot RW, Kelly M, Hewitt C. 1992. Behavior of Urban Dust Contaminated by Chernobyl Fallout:

Environmental Half-lives and Transfer Coefficients. Environ. Sci. Technol. 26: 2142-2147

ATSDR. 1993. Toxicological Profile Update for Polychlorinated Biphenyls. United States Public

Health Service, ATSDR, Atlanta, GA.

Durkin, P.R., L. Rubin, J. Withey, and W. Meylan. 1995. Methods of assessing dermal absorption

with emphasis on uptake from contaminated vegetation. Toxicology and Industrial Health 11(l):63-79.

Kim N.K. and J. Hawley. 1985. Re-Entry Guidelines: Binghamton State Office Building. New York

State Dept. of Health, Bureau of Toxic Substances Assessment, Division of Health Risk Control. 

Albany, NY. August. Document 0549P.

EPA. 1985. Health effects assessment document for polychlorinated dibenzo-p-dioxins. Prepared by

the Office of Health and Environmental Assessment, Environmental Criteria and Assessment Office,

Cincinnati, OH, for the Office of Emergency and Remedial Response, Washington, DC. EPA/600/8-

84/014F.

EPA. 1987. Polychlorinated Biphenyls: Spill Cleanup Policy. Final Rule. Federal Register, Volume

52, Number 63. April 2.

EPA. 1989. Risk Assessment Guidance for Superfund. Volume I: Human Health Evaluation Manual

(Part A). Interim Final. Office of Emergency and Remedial Response, Washington, D.C. December.

EPA. 1992. Dermal Exposure Assessment: Principles and Applications. Interim Report. Office of

Health and Environmental Assessment, Washington, D.C. January. EPA/600/891/011/B.

EPA, 1997a. Draft Standard Operating Procedures (SOPs) for Residential Exposure Assessment. 

Office of Pesticides Programs. December 19, 1997.

EPA, 1997b. Exposure Factors Handbook. EPA/600/P95/002

EPA, 2000. Exposure and Human health Reassessment of 2378-TCDD and Related Compounds.

EPA/600/P-00/001. http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=55265

EPA, 2001a. Science Advisory Council for Exposure. Policy Number 12 on Recommended

Revisions to the Standard Operating Procedures (SOPs) for Residential Exposure Assessments .

Revised: February 22, 2001

EPA, 2001b. Risk Assessment Guidance for Superfund Volume 1: Human Health Evaluation Manual

(Part E, Supplemental Guidance for Dermal Risk Assessment) Interim. EPA/540/R/99/005. Review

Draft.

Lioy JL, Freeman CG, Millette JR. 2002. Dust: A Metric for Use in Residential and Building Exposure

Assessment and Source Characterization. Environ. Health Persp. 110: 969-983.
D-13

Michaud, J.M., S.L. Huntley, R.A. Sherer, M.N. Gray, and D.J. Paustenbach. 1994. PCB and dioxin

re-entry criteria for building surfaces and air. Journal of Exposure Analysis and Environmental

Epidemiology 4(2):197-227.

New Jersey Department of Environmental Protection (NJDEP). 1993. Technical Basis and

Background for Cleanup Standards for Contaminated Sites. N.J.A.C. 7:26D (Draft).

New York State Department of Health. 2002. Binghamton State Office Building: Post-occupancy

Environmental Sampling, Final Round. Center for Environmental Health, Troy, NY. 

Radian International. 1999. Development of risk-based wipe sample cleanup levels at the Claremont

Polychemical Superfund site in Old Bethpage, New York. Prepared for: U.S. Army Corps of

Engineers.

Roberts JW, Budd WT, Camann DE, Fortmann RC, Lewis RG, Ruby MG, Stamper VR, Sheldon LS.

1991. A small high volume surface dust sampler (HVS3) for lead, pesticides, and other toxics

substances in house dust.[Anonymous] Proceedings Annual Meeting of Air and Waste Management

Association, Vancouver, June1991. Vol.15. Pittsburgh:Air and Waste Management Assoc. p 150.2

Roberts JW, Clifford WS, Glass G, Hummer PG. 1999. Reducing Dust, Lead, Dust Mites, Bacteria,

and Fungi in Carpets by Vacuuming. Arch. Environ. Contam. Toxicol. 36:477-484.

Thatcher TL, Layton DW. 1995. Deposition, Resuspension and Penetration of Particles Within A

Residence. Atmos Environ 29(13):1487-97.

Rodes, C., R. Newsome, R Vanderpool, J Antley, R. Lewis. 2001. Experimental methodologies and

preliminary transfer factor data for estimation of dermal exposure to particles. Journal of Exposure

Analysis and Environmental Epidemiology, 11:123-139.
E-1

APPENDIX E

IEUBK Lead Model Results for Lead in Air

EPA developed the Integrated Exposure Uptake Biokinetic (IEUBK) Lead Model (EPA 1994) to

evaluate multimedia lead exposure to children in residential settings. EPA established a goal of attaining

a 95% probability that blood lead levels in children be less than 10 μg/dl (EPA 1994a). To meet the

aforementioned goal, The IEUBK Lead Model was run using multimedia input parameters that are

applicable to the residential community in Lower Manhattan. To be conservative, the IEUBK Lead

Model was run under the assumption that a child would be indoors 24 hours a day. The following

discussion details the basis for individual input parameters.

Lead in Drinking Water - The source of NYC’s drinking water (the Catskill/Delaware and Croton

systems) is remarkably low in lead. The average lead concentration is 1 μg/l in the Catskill/Delaware

system and <1 μg/l in the Croton system (NYCDEP - Drinking Water Quality Test Results, 2001 - see

www.nyc.gov/dep). However, the concentration of lead in tap water can be increased by lead

containing components (pipes, solder) of a building’s distribution system. Consequently, the Safe

Drinking Water Act “Lead and Copper Rule” (Federal Register, June 7, 1991) requires large water

systems to monitor led concentration at the tap. If more than 10% of the samples exceed the federal

“Action Level” of 15 μg/l, corrective steps (e.g., source treatment, corrosion control) must be carried

out. The IEUBK Lead Model is intended to run with input values that represent the average lead

concentration in the environmental media of interest. As reported by NYCDEP, 2001, the median lead

concentration from a total of 107 samples obtained at the tap was 3 μg/l. It should be noted that these

samples represent a high bias in that they were obtained from homes where there is reason to believe

that lead service lines exist. The median lead concentration in tap water city-wide is likely to be lower.

However, for the purpose of this site-specific application of the IEUBK Lead Model, a value of 3 μg/l

is used as a conservative central tendency estimate of lead in tap water.

Lead in Diet - No data could be located relating to the lead content in food items for residents living in

Lower Manhattan. Since there is very little home gardening taking place in this community it was

deemed appropriate to use data that reflects national trends for commercially available food items. EPA

recently evaluated dietary lead content in children in support of revising default input parameters for the

IEUBK Lead Model (EPA 2002). Lead residues in food were obtained from the Food and Drug

Administration’s (FDA’s) Total Dietary Survey. Food consumption trends were obtained from the

National Health and Nutrition Examination Survey (NHANES) . The average lead content in the diet of

children 0 - 7 years old is 2.8 μg/day. Consequently, the input value of 2.8 μg/day was employed as the

estimate of average daily lead intake from diet.

Lead in Soil - Numerous studies have been conducted to evaluate soil and street dust lead

concentrations in New York City (NYCDOHMH, 2003). In the studies reviewed, soil/dust samples

were taken by a variety of methods over a long period of time (1924 - 1993). Summary statistics were

compiled by the NYCDOHMH based on whether the studies assessed known lead sources or

background conditions. Ruling out studies on specific sources such as bridges, a median soil lead

concentration of 200 ppm and street dust lead concentration of 895 ppm was reported. Data are

lacking with regard to the relative contribution of street dust to a child’s daily “soil” intake. Given this

uncertainty, the median values of soil and dust were averaged to provide a composite soil/dust

concentration of 548 ppm. This value was used as the soil lead concentration in the site-specific

application of the IEUBK Lead Model 
E-2

Lead in Indoor Dust - Although there exists a substantial amount of lead “load” data (i.e., mass per

unit area - typically recorded in units of micrograms per square foot as per HUD reporting

requirements) as a measure of lead contamination in residential dwellings, the IEUBK Lead Model

requires lead concentration in settled dust to be reported in terms of concentration (i.e., mass per unit

mass - typically recorded as parts per million). The WTC Background Study reported lead in house

dust both in terms of lead load (μg/ft2) and concentration (ppm) although more limited sampling was

obtained of lead concentration (ppm) measurements. Nonetheless, because these data were specifically

intended the assess background conditions in Lower Manhattan, they were used in the site-specific

application of the IEUBK Model. The mean concentration of lead in settled dust in the WTC

Background Study was 126 ppm (EPA 2003a). Consequently, this was the value used for lead in

indoor dust for the site-specific application of the IEUBK Lead Model. 

Site specific application of the IEUBK resulted in a lead benchmark for indoor air of 0.7 μg/m3. 

Displayed below are data input spreadsheets and a graphic display (Page E-6) of model results.

LEAD MODEL FOR WINDOWS Version 1.0 Build 251

 

=====================================================================

 Model Version: 1.0 Build 251

 User Name: 

 Date: 

 Site Name: 

 Operable Unit: 

 Run Mode: Research

 

=====================================================================

 The time step used in this model run: 1 - Every 4 Hours (6 times a day).

 ****** Air ******

 Indoor Air Pb Concentration: 100.000 percent of outdoor.

 Other Air Parameters:

 Age Time Ventilation Lung Outdoor Air

 Outdoors Rate Absorption Pb Conc

 (hours) (m^3/day) (%) (ug Pb/m^3)

 ----------------------------------------------------------------------

 .5-1 0.000 2.000 32.000 0.700

 1-2 0.000 3.000 32.000 0.700

 2-3 0.000 5.000 32.000 0.700

 3-4 0.000 5.000 32.000 0.700

 4-5 0.000 5.000 32.000 0.700

 5-6 0.000 7.000 32.000 0.700

 6-7 0.000 7.000 32.000 0.700

 ****** Diet ******

 Age Diet Intake(ug/day)

 -----------------------------------
E-3

 .5-1 2.800

 1-2 2.800

 2-3 2.800

 3-4 2.800

 4-5 2.800

 5-6 2.800

 6-7 2.800

 ****** Drinking Water ******

 Water Consumption: 

 Age Water (L/day)

 -----------------------------------

 .5-1 0.200

 1-2 0.500

 2-3 0.520

 3-4 0.530

 4-5 0.550

 5-6 0.580

 6-7 0.590

 Drinking Water Concentration: 3.000 ug Pb/L

 ****** Soil & Dust ******

 Age Soil (ug Pb/g) House Dust (ug Pb/g)

 --------------------------------------------------------

 .5-1 548.000 126.000

 1-2 548.000 126.000

 2-3 548.000 126.000

 3-4 548.000 126.000

 4-5 548.000 126.000

 5-6 548.000 126.000

 6-7 548.000 126.000

 ****** Alternate Intake ******

 Age Alternate (ug Pb/day)

 -----------------------------------

 .5-1 0.000

 1-2 0.000

 2-3 0.000

 3-4 0.000

 4-5 0.000

 5-6 0.000

 6-7 0.000

 ****** Maternal Contribution: Infant Model ******

 Maternal Blood Concentration: 2.500 ug Pb/dL 
E-4

 *****************************************

 CALCULATED BLOOD LEAD AND LEAD UPTAKES: 

 *****************************************

 Year Air Diet Alternate Water

 (ug/dL) (ug/day) (ug/day) (ug/day)

 -------------------------------------------------------------------------------

 .5-1 0.448 1.265 0.000 0.271

 1-2 0.672 1.244 0.000 0.667

 2-3 1.120 1.265 0.000 0.705

 3-4 1.120 1.282 0.000 0.728

 4-5 1.120 1.318 0.000 0.777

 5-6 1.568 1.332 0.000 0.828

 6-7 1.568 1.340 0.000 0.847

 

Year Soil+Dust Total Blood

 (ug/day) (ug/day) (ug/dL)

 ---------------------------------------------------------------

 .5-1 7.280 9.264 5.0

 1-2 11.373 13.956 5.7

 2-3 11.558 14.647 5.4

 3-4 11.718 14.848 5.2

 4-5 8.920 12.135 4.3

 5-6 8.113 11.841 3.7

 6-7 7.708 11.462 3.3

 
E-5
World Trade Center Indoor Environment Assessment:

Response to Peer Review Comments on the Report for

Selecting Contaminants of Potential Concern and

Setting Health-Based Benchmarks

May, 2003

Prepared by the Contaminants of Potential Concern (COPC) Committee

of the World Trade Center Indoor Air Task Force Working Group

Contributors:

U.S. Environmental Protection Agency

Mark Maddaloni

Charles Nace

Peter Grevatt

Terry Smith

Dore LaPosta

John Schaum

Dana Tulis

Jennifer Hubbard

New York City Department of Health and

Mental Hygiene

Nancy Jeffery

Ken Carlino

Jeanine Prudhomme

Chris D’Andrea

Caroline Bragdon

James Miller

Agency for Toxic Substances and Disease Registry

Sven Rodenbeck

Danielle DeVoney

New York State Department of Health

Robert Chinery

Occupational Safety and Health Administration

David Ippolito

Dan Crane
i

Table of Contents

Foreword .................................................................... ii

List of Abbreviations ........................................................... iii

I. Introduction ............................................................. 1

II. Overview of the Peer Review Process ......................................... 1

III. Responses to Peer Review Comments ......................................... 2

A. Responses to Comments on Selecting Contaminants of Potential Concern ......... 2

B. Responses to Comments on Setting Health-Based Benchmarks ................ 12

IV. References ............................................................. 24
ii

Foreword

Following the collapse of the World Trade Center on September 11, 2001, federal, state, and

municipal health and environmental agencies initiated numerous studies to assess environmental

conditions in the area. A multi-agency task force was specifically formed to evaluate indoor

environments for the presence of contaminants that might pose long-term health risks to local residents.

As part of this evaluation, a task force committee was established to identify contaminants of primary

health concern and establish health-based benchmarks for those contaminants in support of ongoing

residential cleanup efforts in Lower Manhattan. In September 2002, the committee released a draft

document titled “World Trade Center (WTC) Indoor Air Assessment: Selecting Contaminants of

Potential Concern (COPC) and Setting Health-Based Benchmarks.” 

In October 2002, a panel of 11 experts conducted an independent peer review of the draft COPC

document to ensure that the evaluations presented in the document were technically based and

scientifically sound. A final report with peer reviewers’ conclusions and recommendations was released

in February 2003. The authors of the draft COPC document have reviewed and responded to all peer

reviewer comments.

This report—or responsiveness summary—provides the formal responses to peer reviewer comments.

EPA, through its chairmanship of the multi-agency committee that authored the response to peer

review comments, assumes ownership and fully endorses the report’s content. The responsiveness

summary presents background on the peer review process, an overview of the peer reviewers’ main

conclusions and recommendations, and the document authors’ responses to specific comments. In

addition to preparing this responsiveness summary, which will become part of EPA’s peer review

record for the WTC site, document authors have prepared a revised, and final, COPC document. The

final document presents the updated approaches for selecting COPC and setting health-based

benchmarks, based on peer reviewer input. 

Copies of the final COPC document can be obtained on-line at www.epa.gov/WTC. Copies of this

report are available at www.tera.org. Inquires regarding this report should be directed to: 

Mark A. Maddaloni Dr.P.H., DABT

U.S. Environmental Protection Agency, Region 2

290 Broadway

New York, NY 10007-1866

212-637-3590

maddaloni.mark@epa.gov

This report is just one response to environmental and public health concerns related to the WTC.

Individuals interested in other studies and research projects related to this site should refer to the

following Web pages:

< U.S. EPA: www.epa.gov/WTC

< ATSDR: www.atsdr.cdc.gov/

< NYCDOHMH: http://home.nyc.gov/html/doh/html/alerts/911.html
iii

List of Abbreviations

ACGIH American Conference of Governmental Industrial Hygienists

ATSDR Agency for Toxic Substances and Disease Registry

COPC contaminant(s) of potential concern

CSF cancer slope factor

EPA U.S. Environmental Protection Agency

HEAST Health Effects Assessment Summary Tables

IEUBK Integrated Exposure Uptake Biokinetic 

IRIS Integrated Risk Information System 

IUR inhalation unit risk

μg/m3 microgram per cubic meter

mg/m3 milligram per cubic meter

MRL ATSDR minimal risk level 

NHANES National Health and Nutrition Examination Survey

NIOSH National Institute of Occupational Safety and Health

NJDEP New Jersey Department of Environmental Protection

NYCDEP New York City Department of Environmental Protection

NYCDOHMH New York City Department of Health and Mental Hygiene

NYSDOH New York State Department of Health

OSHA Occupational Safety and Health Administration

PAHs polycyclic aromatic hydrocarbons

PCM phase contrast microscopy

PEL OSHA permissible exposure limit

REL NIOSH recommended exposure limit

RfD reference dose

RfC reference concentration

SVOC semi-volatile organic compound

TERA Toxicology Excellence for Risk Assessment

TLV ACGIH threshold limit value 

VOC volatile organic compound

WTC World Trade Center
1

I. Introduction

Following the collapse of the World Trade Center (WTC) towers and nearby buildings on September

11, 2001, federal, state, and municipal health and environmental agencies have been characterizing and

evaluating levels of contamination near the site. Under EPA’s leadership, these agencies participated in

a task force to assess the potential impact to the indoor environment from contaminants that might pose

long-term health risks to local residents. The working group is called the “World Trade Center Indoor

Air Task Force Working Group.” Agencies participating in this task force working group include the

U.S. Environmental Protection Agency (EPA), the Agency for Toxic Substances and Disease Registry

(ATSDR), the Occupational Safety and Health Administration (OSHA), the New York State

Department of Health (NYSDOH), the New York City Department of Health and Mental Hygiene

(NYCDOHMH), and the New York City Department of Environmental Protection (NYCDEP).

The task force working group formed a committee—the “Contaminants of Potential Concern (COPC)

Committee”—to address potential contamination of the indoor environment near the WTC site. The

primary activity of the COPC Committee was to prepare a document that identifies COPC for indoor

environments and sets health-based benchmarks for long-term exposures. In September, 2002, the

committee released its draft peer review document, titled “World Trade Center Indoor Air Assessment:

Selecting Contaminants of Potential Concern and Setting Health-Based Benchmarks” (COPC 2002).

For ease of reference, the draft peer review document will be referred to throughout this report as “the

draft COPC document.” EPA decided to have the draft COPC document peer reviewed by a panel of

independent experts to ensure that the committee’s evaluations are technically based and scientifically

sound.

This report is the COPC Committee’s responsiveness summary to the independent peer review.

Section II of this report presents important background on the peer review process, including an

overview of the peer reviewers’ main conclusions and recommendations. The COPC Committee’s

specific responses to the peer reviewers’ findings are documented in Section III. In addition to

preparing this report, which will become part of EPA’s peer review record for the WTC site, the

committee is also preparing a revised, and final, COPC document (COPC 2003). As EPA’s peer

review policy requires, this report explains how the peer reviewers’ recommendations will be reflected

in the final COPC document, or reasons are provided for why certain recommendations are not

incorporated.

The final COPC document, therefore, presents the COPC Committee’s updated approach for selecting

COPC and setting health-based benchmarks. Copies of that report can be obtained by contacting

EPA, using the contact information provided in the Foreword to this report. The report will also be

available on the EPA Web site (www.epa.gov/WTC).

II. Overview of the Peer Review Process

The independent peer review was implemented through Toxicology Excellence for Risk Assessment

(TERA), a contractor to EPA, in accordance with specifications in EPA’s “Peer Review Handbook”

(EPA 2000a). TERA identified 11 independent peer reviewers from different affiliations and with

expertise in various relevant fields, including risk assessment, exposure assessment, indoor air sampling

techniques, and toxicology. According to the peer review report, “most of the peer reviewers stated

that they had no prior work activity related to the WTC disaster or any known conflicts and felt they

could participate fully in the meeting” (TERA 2003).

The peer reviewers provided their feedback on the review document during a 2-day meeting on

October 21–22, 2002, in New York City. The meeting, which was open to the public, was split into
2

two general sessions: reviewing the approach used to select COPC, and reviewing the approach used

to set health-based benchmarks. At the beginning of each session, authors of the draft COPC

document gave brief presentations, after which the peer reviewers discussed and debated the scientific

merits of the document. This open discussion was framed around a series of charge questions that

TERA asked the peer reviewers to address. Observers were allowed to comment at designated times

during the peer review meeting.

TERA released a final summary report in February 2003 that documents the discussions among the

independent peer reviewers (TERA 2003). These discussions ultimately led to 16 specific conclusions

and recommendations that are documented in the peer review report. To respond to the peer

reviewers’ comments, the COPC Committee addressed each of these conclusions and

recommendations. When preparing our responses, we referred to the summary of the peer reviewers’

discussions related to each conclusion or recommendation. Therefore, this responsiveness summary

addresses the major themes and issues expressed throughout the peer review report, but our responses

are framed around the final conclusions and recommendations.

In addition, the COPC Committee reviewed both verbal and written comments submitted by observers

to the peer review meeting. Some observer comments addressed components of the WTC Clean-up

Program that were outside the scope of the peer review. Substantive comments relating to the draft

COPC document (e.g., data sources for COPC screening, target risk range) have been addressed in

the course of responding to the peer reviewers’ comments. 

III. Responses to Peer Review Comments

When responding to peer review comments, EPA prepares (as per its guidance on peer review) a

written record “responding to the peer review comments specifying acceptance or, where thought

appropriate, rebuttal and non-acceptance” (EPA 2000a). This section presents the COPC

Committee’s responses to the peer reviewers’ 16 main conclusions and recommendations: 7 that

pertain to selecting COPC (see Section III.A), and 9 that pertain to setting health-based benchmarks

(see Section III.B). Each conclusion and recommendation is addressed individually, and our response

indicates what, if any, changes were made to the draft COPC document to address the comment. If no

changes were made, our response explains why.

A. Responses to Comments on Selecting Contaminants of Potential Concern

The peer reviewers made seven conclusions and recommendations related to the COPC selection

process in the draft COPC document. These are presented on pages 16–17 of the peer review report,

and are reproduced below. Each conclusion and recommendation is followed immediately by the

COPC Committee’s response to the comment.

Comment COPC #1:

The document should more clearly state the intended use of the COPC selection process.

Response:

The selection of COPC was intended to inform the Indoor Air Residential Assistance - WTC

Dust Clean-up Program, which we will refer to as the WTC Clean-up Program. In

conventional hazardous waste site investigations, the COPC selection process is intended to

reduce what is typically an extensive contaminant sampling list to a manageable “short list” of

risk-driving chemicals. The risk from this “short list” is then calculated to determine if remedial

action is warranted. Regarding the WTC, there was an a priori decision to institute a clean-up
3

program rather than launch a formal remedial investigation to determine if remediation of

residential dwellings was necessary. The primary reason for this decision was to eliminate the

time-consuming process of initiating a remedial investigation (i.e., developing a sampling and

analysis plan, conducting representative sampling of residential dwellings, analyzing a large

number of samples, and finally interpreting results) at a time when re-habitation of residential

dwellings in Lower Manhattan was nearly complete. As a result of this decision, the COPC

selection process associated with the WTC Clean-up Program assumed a somewhat modified

purpose. Rather than serve as a process to determine the need for clean-up, the COPC

selection process served to facilitate development of health-based benchmarks for the WTC

Clean-up Program. By identifying COPC, benchmarks for individual contaminants could be

developed for indoor air and settled dust. To summarize, first and foremost, the intent of the

COPC selection process was to identify risk-driving chemicals and to establish specific healthbased benchmarks for the WTC Clean-up Program.

As part of this initiative, the COPC selection process informed two complimentary studies that

were undertaken as part of the WTC Clean-up Program. The first was the WTC Residential

Confirmation Cleaning Study (EPA 2003a). This study was initiated to evaluate the

effectiveness of various cleaning methods (e.g., high-efficiency particulate air vacuuming, wet

wiping) used to clean residences. The COPC selection process provided the list of

contaminants to sample for in the WTC Residential Confirmation Cleaning Study. It also

enabled the development of health-based benchmarks for indoor air and settled dust so the

effectiveness of cleaning methods could be assessed. The cleaning methods employed also

served to guide the clean-ups of other heavily impacted unoccupied buildings. Another outcome

of the WTC Residential Confirmation Cleaning Study was in streamlining the post-cleaning

sampling needs of the WTC Clean-up Program. Although not a specific goal, this effort

identified an indicator chemical (i.e., asbestos) that signaled the reduction of all COPC to

concentrations below health-based benchmarks. With thousands of residents signed up for

cleaning, the use of an indicator contaminant to establish cleaning effectiveness provided a

powerful tool in facilitating the WTC Clean-up Program.

The other initiative that the COPC selection process informed was the WTC Background

Study (EPA 2003b). The development of remediation goals is influenced by factors such as

technical implementation, analytical detection limits, and the background concentration of

contaminants in the environmental setting of interest. A literature review of contaminant

background concentrations in residential dwellings was conducted to inform the WTC Cleanup Program. Limited information was obtained for asbestos in indoor air and lead and dioxin in

settled dust, otherwise the search yielded very little useful data. It was therefore deemed

advantageous to conduct a site-specific background study to inform risk management decisions

regarding the setting of clean-up goals at health-based or background concentrations.

Consequently, The COPC selection process directed the group of contaminants to be sampled

for in the WTC Background Study. Conversely, the results of the WTC Background Study

provides data to enhance the value of the final COPC document. That is, it provides an

estimate of background for COPC in Lower Manhattan to be evaluated alongside health-based

benchmarks. 

Comment COPC #2:

The document should “include a clear presentation of the logic used to select COPC.”
4

Response:

As noted in the previous response, the COPC selection process described in the draft COPC

document was driven by the need to develop clean-up criteria for those contaminants with the

potential to pose the greatest public health risk. The semi-quantitative approach initially used to

select COPC examined the contaminants detected in environmental samples collected in Lower

Manhattan and contaminants believed to be released from the WTC disaster (e.g., combustion

by-products, building materials). COPC were originally selected based on a combined

consideration of the substances’ toxicities, the frequencies at which substances were detected,

and the likelihood that detected substances were related to the WTC disaster. 

Peer reviewers acknowledged the constraints under which the COPC selection approach was

developed, but commented that the COPC list seemed to have been narrowed fairly rapidly

and recommended that additional data sets be considered and the description of the process be

more transparent. In response to this comment, the authors conducted a systematic review of

the COPC selection process. This involved a careful re-examination of multiple supporting

environmental data sets, consideration of newly available data sets, and a review of the

exposure assumptions and toxicity criteria used in establishing screening values. 

Though we made some modifications in approach, the final COPC list remains unchanged. The

authors revised the COPC document, however, to more clearly present the steps taken and the

logic followed in selecting COPC. We hope that these revisions will help readers fully

understand the COPC selection process and will demonstrate that the selection process was

comprehensive, technically sound, and, most importantly, protective of public health. Our

conceptual approach for selecting COPC, including the underlying logic, is summarized below.

Appendix B of the final COPC document describes in greater detail how each step was applied

and what contaminants, by medium, were eliminated or retained for further consideration.

# Review of multiple data sets to identify candidate substances. The collapse of the

WTC released a very broad range of contaminants into the air, many of which

deposited with settled dust on surfaces in Lower Manhattan, both indoors and

outdoors. To gain the best possible sense of the contamination levels in indoor

residential environments, the authors reviewed an extremely large set of sampling data

describing environmental conditions at and near the WTC site between September 11,

2001, and the present. Our goal was to review data that might provide insights on the

contamination levels inside Lower Manhattan residences. As a result, we reviewed a

large set of bulk dust and settled dust sampling results, and we also reviewed ambient

and indoor air sampling data, based on the premise that contaminants entered

residences through atmospheric transport.

We reviewed sampling data collected by EPA, ATSDR, OSHA, NYCDEP,

NYCDOHMH, the New York City Department of Education, the New Jersey

Department of Environmental Protection, and independent investigators. A complete list

of the data sources we reviewed is included in the final COPC document. Overall, we

examined results from more than 500,000 environmental samples, with sampling results

available for more than 300 contaminants. The contaminants included volatile organic

compounds (VOCs), semi-volatile organic compounds (SVOCs), pesticides,

polychlorinated biphenyls (PCBs), metals, asbestos, silica, other minerals, and synthetic

fibers. Every contaminant identified in the sampling data was considered a candidate

substance for the COPC selection process.
5

# Initial screen to identify contaminants requiring further consideration. The authors

used an initial screening procedure to identify the contaminants that require further

consideration before being selected as COPC. This initial screening procedure

identified contaminants that are most likely to be present in dust at levels greater than

health-based screening values. This initial screening involved three steps:

< First, all VOCs were eliminated from the COPC selection process, because

any VOCs that might have been released in or adhered to dusts from the WTC

site have likely evaporated or greatly dissipated since the time that air emissions

from the site were controlled (i.e., since the time, December, 2001, that the

fires were extinguished).

< Second, all contaminants detected in fewer than 5% of samples were removed

from the list of candidate contaminants, but only if the contaminant was

analyzed for in more than 20 samples. This screening approach based on

frequency of detection is consistent with EPA’s guidance on human health risk

assessment (EPA 1989). By requiring a minimum of 20 samples to apply the

frequency of detection screening step, we believe we have addressed the peer

reviewers’ concern that the frequency of detection might not be an appropriate

screening criterion because the “available data reviewed were limited” and the

“goal of the screening process was to be inclusive.” A review of the

contaminants that were screened out by frequency of detection revealed that

none were found at concentrations above health-based screening values. 

< Third, for the contaminants that were not eliminated in the previous two steps,

we compared the maximum concentration detected in each medium to

corresponding health-based screening values. (Refer to our response to COPC

#3 for further information on how these screening values were derived.) Three

outcomes were possible for this step. If a contaminant’s maximum

concentration was lower than the corresponding screening value, that

contaminant was eliminated from further consideration. If a contaminant’s

maximum concentration was greater than the screening value, then we

evaluated the contaminant further in the secondary screening step, described

below. If a contaminant did not have a toxicity value, and therefore did not have

a screening value, we reviewed other relevant information (e.g., occupational or

environmental standards, trends among sampling data, comparisons to

background, the likelihood of the contaminant being related to site-specific

releases) to determine whether the contaminant should be evaluated further.

# Secondary screen to select COPC. For those substances exceeding health-based

screening criteria in at least one sample, we reviewed findings across environmental

media to assess representativeness of reported maximum concentrations, studied spatial

and temporal trends, determined the relationship of detected concentrations to available

background concentrations, and examined whether there was reason to believe a

contaminant was site-related. Professional judgment entered into this part of the

process, as the peer reviewers noted would be necessary. In general, contaminants with

reported concentrations deemed representative of exposure conditions and detected

above background (if appropriate comparison data were available) were retained as

COPC. The final COPC document provides detailed justification for contaminants

eliminated as part of the secondary screen. 
6

This selection process yielded the final list of COPC:

< Asbestos

< Dioxins

< Lead

< Polycyclic aromatic hydrocarbons (PAHs)

< Fibrous glass

< Crystalline silica

Asbestos, dioxins, lead, and PAHs were selected as COPC because they were

consistently detected across environmental media at concentrations above health-based

screening values. Fibrous glass and crystalline silica also were selected as COPC,

but from the list of contaminants that do no have health-based screening values. In the

absence of consensus toxicity criteria to apply in the quantitative screening used for

most other contaminants, we used environmental and occupational standards coupled

with an evaluation of overall exposure potential knowing that these and other building

materials were deposited in a large cloud from the collapse of the WTC. Section 2.3.2

of the final COPC document lists the specific reasons why fibrous glass and silica were

selected as COPC.

As a final note, the committee reviewed preliminary data from settled dust wipe samples

in Lower Manhattan residences which infrequently identified mercury at levels greater

than health-based screening values. Further, chromium in ambient air has been shown

to exceed health-based screening values, though chromium levels in available bulk and

settled dusts collected in Lower Manhattan are not above health-based screening

values. A more detailed discussion of the evaluation of environmental sampling data for

mercury and chromium can be found in Appendix B of the final COPC document. In

both cases, it is unclear whether detected levels are associated with the WTC collapse.

Regardless, as part of the WTC Clean-up Program, EPA is conducting wipe sample 

testing for 21 non-COPC metals, including mercury and chromium in approximately

250 apartments. 

Comment COPC #3:

The document should “more clearly describe the basis for the choice of toxicity values and

exposure assumptions used to estimate COPC screening criteria.”

Response:

Upon examination of peer reviewer comments, we agree that the document would benefit from

a more detailed description of and justification for the toxicity values and exposure assumptions

used in estimating WTC screening values. Therefore, the document will be revised to further

describe the basis for developing air and dust screening values. The toxicity and exposure

parameters used to develop screening values for bulk and settled dust will therefore be included

in the final COPC document.

The methodology, risk equations, and exposure assumptions used in developing WTC

screening values are consistent with established EPA risk assessment guidance. Exposure

equations generally stem from EPA’s Risk Assessment Guidance for Superfund (RAGS) (EPA
7

1989). For deriving screening values for residues on indoor surfaces (settled dust), we adapted

EPA guidance for residential exposure assessment, originally developed to study pesticide

residues (EPA 2001a). This approach was further supported by procedures and re-entry

guidelines previously developed for scenarios evaluating fine dust particles more analogous to

those associated with the WTC collapse (Kim and Hawley 1985; NJDEP 1993; Michaud et al.

1994; Radian 1999). Exposure assumptions used are those recommended in RAGS or

supplemental risk assessment guidance, including EPA’s Exposure Factors Handbook (EPA

1997b), Child-specific Exposure Factors Handbook (EPA 2002a), Dermal Exposure

Assessment: Principles and Applications (EPA 1992), and RAGS Part E, Supplemental

Guidance for Dermal Risk Assessment (EPA 2001b).

The final COPC document will present the following general framework used in deriving

screening values:

< The consideration of cancer and non-cancer effects, with a target cancer risk of 10-4

and a hazard quotient of 1 for non-cancer endpoints—the more sensitive of the two

being used to derive screening values.

< The evaluation of adult and childhood exposures, with child exposures factoring heavily

into the development of screening values for dioxin and PAHs in settled dust.

< The use of the most current toxicity criteria on EPA’s Integrated Risk Information

System (IRIS) database. In the absence of IRIS toxicity criteria, the following hierarchy

of toxicity data sources was used: EPA’s Health Effects Assessment Summary Tables

(HEAST), ATSDR’s minimal risk levels (MRLs), provisional values derived by EPA’s

National Center for Environmental Assessment, and, in limited cases, the use of

surrogate toxicity values or cross-route extrapolations.

Medium-specific approaches and assumptions are detailed in the final COPC document, as

outlined below: 

< Air pathway. Contaminants detected in ambient and indoor air were compared to the

lower of the following IRIS values: EPA reference concentrations (RfCs) (for noncarcinogens) or air concentrations associated with a 10-4 cancer risk (based on

inhalation unit risks [IURs]). In the absence of IRIS values, the hierarchy presented

above was used.

< Bulk dust pathway. Screening values were developed for bulk dust based on a soil

ingestion pathway scenario, considering both childhood and adult exposures. The

exposure equations and age-specific assumptions used are detailed in Appendix A of

the final COPC document. Oral toxicity values (EPA reference doses [RfDs] for noncarcinogens and cancer slope factors [CSFs]) were used when available. Otherwise,

the hierarchy described above was followed. 

< Settled dust pathway. Screening values were developed based on exposures

associated with ingestion and dermal contact with dust residues on indoor surfaces. As

per peer review comments, a childhood exposure scenario was incorporated into this

pathway. Dose rates were estimated based on a number of assumptions—for example,

the fraction of dust residues that can be transferred to the skin, daily skin loads,

mouthing behaviors for different age groups, and dissipation of surface loading over

time. All of these parameters and the justification for selected values are detailed in
8

Appendix D of the final COPC document. Toxicity criteria used included EPA’s RfDs

and CSFs.

Contaminants for which no consensus or provisional toxicity values are available were reviewed

on a case-by-case basis. In some cases, occupational standards and environmental standards

were considered in developing COPC screening criteria (e.g., crystalline silica and other

minerals).

Comment COPC #4:

The document should “more clearly describe the limitations of the methods used to screen

COPC.”

Response:

Overall, we are confident that the COPC selection process used in evaluating WTC-related

contamination enabled us to select appropriate indicator contaminants, leading to the

development of benchmark criteria which support ongoing efforts to safely clean up residential

environments in Lower Manhattan. The authors recognize, however, that limitations associated

with the COPC selection process exist. The primary limitations include the nature of the

environmental data sets used in the selection process and the absence of toxicity criteria for

some contaminants. However, the general framework for selecting COPC was developed

based on our complete understanding of these limitations. The impact of these factors on the

outcome of the COPC selection process is described in more detail below. An uncertainty

section will be added to the final COPC document to clearly describe these limitations.

# Data limitations. Extensive systematic sampling of indoor air and settled dust in Lower

Manhattan residences had not occurred at the time the draft COPC document was

released. However, partial results of sampling associated with the WTC Residential

Clean-up Program will be available to inform the final COPC document. In selecting

COPC, we drew from the much larger sampling data from other media to account for

this shortcoming. We feel that these data are sufficient to identify those contaminants

most likely to be present in indoor environments and to support the derivation of cleanup criteria. We agree with peer reviewer comments that ambient air monitoring data

need to be interpreted with caution before being used to evaluate indoor environments.

For example, peer reviewers expressed concern that samples collected weeks and

months after the building collapse would not have characterized much of what made it

into the residences as dust. Fortunately, as mentioned above, indoor air and residual

dust sampling being conducted as part of EPA’s WTC Residential Clean-up Program

offer additional insight to the nature and extent of contaminants found in indoor

environments.

As described in our response to COPC #1, to promote a timely response to the WTC

disaster, conventional remedial investigation approaches were not used to generate our

study data. That is, an investigation of indoor environments with targeted sampling was

not conducted. Instead, to expedite cleanup, we relied on existing data sets realizing

that many of the data sets were generated independently, by multiple entities, for

various purposes, and with varying data quality objectives. We recognize that sampling

and analytical methods varied across some studies, and that limited results exist for

some contaminants in some media. To the extent possible, we factored contaminantand study-specific considerations into our final decisions on COPC (e.g., sample size,
9

detection limits, etc.). Lastly, we also acknowledge, as noted by the peer reviewers,

that environmental sampling data do not specifically “fingerprint” the possible unique

pattern of substances that may have been released from the WTC collapse and settled

in indoor dust. Nonetheless, we still screened hundreds of contaminants, many of which

are known to be associated with building materials or thermal or chemical degradation

products (e.g., asbestos, PAHs and other SVOCs, dioxins, and metals). Through a

combined analysis of air and settled dust data, we believe that the process has enabled

us to identify risk-driving contaminants within the indoor environment.

# Absence of contaminant-specific toxicity criteria. Though toxicity values are not

currently available for a subset of contaminants tested for and detected in some air and

dust samples in Lower Manhattan, the COPC selected are indicative of the most

prevalent, most toxic contaminants associated with the WTC releases. A wide range of

contaminant classes were captured, among which some of the more toxic members

were identified and screened (e.g., dioxins, PAHs, metals). Basing COPC selection

on the contaminants with known toxicity criteria (and arguably some of the more toxic

compounds) that are measured at higher levels than the contaminants in question is

believed to be appropriate and reasonably health-protective.

The list of contaminants without toxicity criteria that were not carried through the

COPC selection process include (1) essential nutrients (e.g., calcium, magnesium),

which EPA generally does not carry through its risk assessments; (2) a limited number

of specific phthalates and PAHs; (3) and SVOCs that are not conventionally measured

to support EPA risk assessment. The lengthiest list of SVOCs for which no toxicity

criteria exist comes from Lioy et al. (2002)—a study of three outdoor bulk dust

samples collected in Lower Manhattan on September 16 and 17, 2001. Most of the

SVOCs that do not have toxicity criteria were not consistently detected across the

three samples. Further, the concentrations measured were consistently lower than other

SVOCs (e.g., PAHs) that have been selected as COPC. Finally, because many of the

SVOCs identified by Lioy are rarely considered in environmental sampling studies, we

have no knowledge whether the measured levels are consistent with background

concentrations in urban settings or if the levels are unusually high.

# Uncertainty in deriving settled dust screening values. As described in the response

to COPC #3 and detailed in Appendix D of the final COPC document, derivation of

settled dust screening values required multiple assumptions in estimating exposure to

surfaces, which add uncertainty to our analysis. For example, factors affecting surface

loading and transfers to skin have not been well studied and are likely to be highly

variable (e.g., characteristics of different surfaces, activities patterns related to surface

contact, and surface cleaning techniques and frequency). As a result, limited data were

available for many of the input parameters used to estimate dose from exposure to

residues on surfaces. However, consistent with general human health risk assessment

practice, every effort was made to select exposure input parameters that would define a

reasonable maximum exposure and produce protective screening values. For the most

part, upper-bound exposure estimates were used whenever available. Overall, we feel

the process represents a reasonably protective approach.

Comment COPC #5:

The document should “include a spreadsheet or sample calculations to document how the

screening values were calculated.”
10

Response:

The final COPC document has been revised to present the results of the step-by-step screening

process used in this assessment. The equations used in developing the screening values for bulk

and settled dust are included, with all assumptions clearly stated. Sample calculations are now

provided to illustrate the derivation process.

Comment COPC #6:

“COPC selection should primarily be based on a risk-based screening approach for settled

dust and air pathways that uses exposure parameters appropriate for children and reflects

toxicity endpoints relevant to children’s health. The panel suggested three exposure scenarios:

including a child at home for a 1-year exposure duration, an adult at home for a 30-year

exposure duration (time-weighted average 6 years of child exposure parameters and 24 years

of adult exposure parameters), and an adult at work for a 25-year exposure duration.”

Response:

The authors agree that COPC selection should be based on a risk-based screening approach

for the settled dust and air pathways and adjusted the process accordingly. The revised COPC

selection process evaluates a chronic residential exposure scenario, considering both child and

adult exposures. We did not, however, specifically evaluate exposures to a child at home for 1

year or to adult workers for the following reasons:

# The tiered approach in the original COPC document was designed to evaluate subchronic exposure (i.e., 1 year). That approach has been replaced in the final COPC

document to consider chronic exposures only. The incorporation of child-specific

exposure parameters in the chronic (i.e., 30 year) exposure scenario, as recommended

by the peer reviewers, will be protective of sub-chronic exposure to more highlyexposed child receptors.

# A worker exposure scenario was not adopted due to the residential nature of the cleanup program. However, screening values developed for the residential exposure

scenario are considered to be adequately protective of workers.

Consistent with peer reviewer recommendations, child exposure considerations now factor into

our COPC selection process. The methodologies used to develop WTC screening values

account for differences between adults and children with respect to exposure factors (e.g.,

body weight, intake rates, mouthing behaviors). For bulk dust, the chronic residential exposure

scenario is time-weighted to include 6 years of child exposure and 24 years of adult exposure

for screening carcinogens. A child soil ingestion scenario serves as the basis for non-cancer

screening values. For the evaluation of residues on indoor surfaces, we considered continuous

age-specific exposure parameters from age 1 through 31 for carcinogens and 1 through 6 for

non-carcinogens.

Peer reviewers also noted that, ideally, the process needs to consider the critical exposure

periods and toxicity endpoints relevant to children’s health. Peer reviewers acknowledged,

however, and we agree that development of additional toxicity criteria for children to support

this COPC selection process is beyond the scope of this effort. Our screening process did

consider, however, toxicity endpoints relevant to children’s health where available (e.g., lead).

As stated earlier, the critical studies and endpoints used in developing IRIS and alternate
11

toxicity values served as the basis for our screening values. Currently, most consensus toxicity

values are based on the evaluation of adult exposures, not early-life exposures, though EPA

does factor in relevant information on reproductive and developmental endpoints (or the lack

thereof) when deriving toxicity values.

It should be noted that research evaluating the significance of early-life exposures to toxic

chemicals is ongoing by EPA and others. For example, EPA recently released draft guidance

for assessing cancer susceptibility from early-life exposure to carcinogens (EPA 2003).

Because most current cancer slope factors do not account for susceptibility differences with

respect to early life stages, agency scientists are exploring the possibility of applying additional

uncertainty factors when evaluating childhood carcinogenic risks to some (e.g., mutagenic)

carcinogens. Much of the impetus for such an approach is the growing knowledge and

understanding of how a particular carcinogen exerts its effect (i.e., its mode of action) and how

a particular mode of action may increase the risk of tumor response if exposure occurs during

early-life stages.

In the meantime, we acknowledge that the current approach of applying existing toxicity criteria

to all age groups introduces some uncertainty to the evaluation biased toward an

underestimation of risk. Nevertheless, the overall conservative assumptions built into standard

risk assessment methodology used in the COPC selection process offer a health protective

screen. As pointed out by one peer reviewer, “it would be hard to imagine a more conservative

approach than applying Appendix D [settled dust screening values] with childhood parameters

as a COPC screening process,” which is the final approach that we used.

Comment COPC #7:

“The panel recognized that once risk-based screening criteria based on dust have been

developed, the list of COPC could potentially change. In addition, the panel observed that

additional sources of relevant data discussed during the meeting suggest that contaminants

which should be further evaluated to determine whether they should be listed as COPC include

phthalates, arsenic, beryllium, polybrominated diphenyl ethers, and polybrominated

dibenzofurans, as well as other potential COPC identified in the public observer comments.”

Response:

The inclusion of risk-based screening criteria for the dust pathway and consideration of data

sets made available subsequent to the release of the draft COPC document did not change the

final list of COPC. We examined the contaminants noted by peer reviewers with consideration

to factors applied to all candidate contaminants. The specified contaminants were not included

as COPC for the following reasons:

< Phthalates. Phthalates were sampled for and detected in a limited number of bulk dust

samples. Phthalates for which toxicity criteria are available (e.g., benzyl butyl phthalate,

bis[2-ethylhexyl phthalate], diethylphthalate, di-n-octylphthalate) were detected at

levels orders of magnitude lower than respective screening values providing justification

for their exclusion as COPC. Phthlates for which no toxicity criteria are available were

reported at comparably low concentrations.
12

< Arsenic. Arsenic levels have been measured in 17 bulk dust samples and in 215 settled

dust samples, but never detected at concentrations or loadings greater than

corresponding health-based screening values. Arsenic has been detected in 64 out of

738 (9%) ambient air samples. Half of these detections exceeded health-based

screening values, but generally fall within the range of arsenic levels reported in urban

settings, based on our review of national and regional background data (ATSDR

2000). Because arsenic has not been detected at levels of potential health concern in

dust samples and detected levels in ambient air are consistent with urban background, it

has not been selected as a COPC. Note, however, as part of the WTC Clean-up

Program, EPA will continue to analyze indoor dust samples for non-COPC metals,

including arsenic.

< Beryllium. Beryllium was detected infrequently and at low concentrations. Beryllium

was detected in only 0.1% of 738 ambient air samples and in none of the 215 settled

dust samples. It was detected in 17 out of 28 bulk dust samples, but the maximum

reported concentration (3.754 mg/kg) was considerably lower than the screening value

(150 mg/kg).

< Polybrominated diphenyl ethers (PBDEs). Due to the use of PBDEs as a flame

retardant in building materials and textiles, it is reasonable to consider this class of

compounds as a possible WTC-related contaminant. Lioy et al. (2002) sampled for

PBDEs in bulk dust. Though available results represent three samples only, PBDEs

were detected at concentrations below the bulk dust screening value (150 mg/kg),

which is based on the RfD for pentabromodiphenyl ether. The highest total

concentration of PBDEs across available samples was 3.3 mg/kg.

< Polybrominated dibenzo-p-dioxins and dibenzofurans (PBDDs/PBDFs). Based on

the presence of phthalates and PBDEs (albeit at relatively low concentrations), one

peer reviewer suggested that PBDFs be considered or at least mentioned in the COPC

document. No sampling results are available for PBDDs/PBDFs, nor do toxicity criteria

exist for this class of compounds. Therefore, interpretation of data, if they were to exist,

would be highly uncertain. We do know that this group of contaminants is more or less

similar to the chlorinated dioxins and dibenzofurans (dioxins) in their persistence and

toxicity (WHO 1998), which have been retained as a COPC.

B. Responses to Comments on Setting Health-Based Benchmarks

The peer reviewers made nine conclusions and recommendations related to how the COPC Committee

proposed setting health-based benchmarks in the draft COPC document. These are presented on

pages 32–33 of the peer review report, and are reproduced below. Each conclusion and

recommendation is followed immediately by the Committee’s response to the comment.

Comment BENCH #1:

“The rationale and purpose of each tier should be more fully described in the document.

Specifically, the document should describe the application for each tier and indicate how the

benchmarks for that tier are constructed to fulfill the intended application. This recommendation

particularly applies to the Tier II criteria. In addition, the document needs to more clearly

describe the ‘aggressive cleaning’ versus ‘diligent cleaning’ that are used to define Tier I
13

compared with Tier II benchmarks and show a difference in risk would result from using these

two different cleaning approaches.”

Response:

A tiered approach for health-based benchmarks was initially intended to address sub-chronic,

as well as chronic, exposures associated with the WTC collapse. At the time the draft COPC

document was initially conceived (March 2002), it was 6 months post-disaster and the

assessment of sub-chronic exposure was still a significant concern. However, the development

of health-based benchmarks (tiered, or otherwise) were not specifically intended to address the

methods or intensity of cleaning protocols associated with the WTC Clean-up Program. These

engineering issues were evaluated in a separate study (The WTC Residential Cleaning

Confirmation Study) (EPA 2003a). The inclusion of cleaning methods associated with each

benchmark was more intended for illustrative purposes rather than as particular

recommendations for cleaning. The authors regret the inclusion of cleaning methods in this

context as it directs attention away from the primary purpose of the document (i.e., to identify

COPC and set health-based benchmarks). The final COPC document will not include any

recommendations on cleaning methods.

As previously mentioned, the tiered approach was originally intended to address multiple

exposure scenarios. The WTC Clean-up Program that was put in place focused on long-term

protectiveness from residual contamination in residential dwellings. As such, the Tier III

benchmark (equating to a 30 year exposure duration) was most applicable to this purpose. 

Also noteworthy is that The WTC Clean-up Program was available to any resident regardless

of extent of residual contamination in their dwelling. Since this program was not linked to a

particular level of risk that might be represented by a tiered benchmark approach, establishment

of multiple tiers was deemed of less utility than originally construed. The Tier III benchmark

which has and continues to serve as a benchmark for long-term habitability of residential

dwelling is therefore the primary focus in revising the COPC document.

The peer review panel articulated the benefit of a tiered benchmark approach as potentially

useful in the prioritization of clean-up actions/decisions. Since the decision was made to clean

without the need for pre-cleaning sampling to establish an unacceptable level of risk, this

potential benefit was not realized. Conversely, the peer review panel also expressed

apprehension over the lack of clarity in how the tiered benchmarks would inform the WTC

Clean-up Program. As per the meeting notes: “Some panelists considered whether the Tier I

and Tier II criteria should be removed from the existing document, leaving just a single criterion

for each COPC equivalent to the respective Tier III criteria.” Upon reviewing the entirety of the

peer review comments on this subject, the authors agree with the position of panel members as

quoted above. Accordingly, the final COPC document will contain only Tier III (i.e., long-term)

health-based benchmarks.

Comment BENCH #2:

“In general, the panel recommends using a risk-based approach to develop benchmarks for the

COPC, but indicated that when a benchmark is based on occupational or existing

environmental standards, the document should clearly describe the underlying risk assessment

for the standard, and discuss how the scientific basis of the standard is

 relevant to the WTC situation. Also, it was suggested that the document specify a confidence

level in each benchmark developed.”
14

Response:

The comment applies to benchmarks based on occupational or existing environmental

standards. The COPC document currently uses such standards to derive benchmarks for

fibrous glass, silica and lead. Following are the responses to this comment for each of these

contaminants:

# Fibrous glass. The fibrous glass benchmark is based on the American Conference of

Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) of 1 f/cc

(ACGIH 2001). Fibrous glass was observed to be an upper respiratory tract and skin

irritant to workers in environments where air sampling indicated greater than 1 f/cc

fibers as measured by phase contrast microscopy (PCM) (ACGIH 2001; ATSDR

2002a). The ACGIH standard is written with the intention of preventing this irritant

effect. To the COPC Committee=s knowledge, no quantitative risk assessment was

used to establish this standard. Little data exist to provide a threshold below which

fibrous glass would not be an airborne or contact irritant, especially when considering

the effects on the general public, which may include sensitive individuals. 

Irritant effects are not the only health effects possible from fibrous glass exposure.

Fibrous glass less than 3 microns in diameter are respirable and available to enter and

deposit in the pulmonary regions of the lung (ACGIH 2001). Clearance of these fibers

from the lung will be determined by fiber solubility and length (ACGIH 2001; ATSDR

2002a). Fibers cleared from the lung have less potential to create long-term health

effects. Although some animal studies have demonstrated both fibrotic and carcinogenic

potential for glass and mineral wools (ACGIH 2001; ATSDR 2002a; IARC 1988),

more recent studies do not fully support this finding. Although the potential for these

adverse health effects is not the scientific basis of the ACGIH TLV, it is believed the

resulting benchmark is adequately protective (see response to BENCH Comment 9). It

should be noted this benchmark is lower than the proposed ATSDR chronic minimal

risk level (MRL) for refractory ceramic fibers (0.03 f/cc), which are considered more

toxic than the glass and mineral wools described in dust from both indoor and outdoor

dust around the WTC. Therefore, there is fair confidence this level should be

protective.

# Lead. The COPC Committee identified an applicable and relevant existing standard to

set a health benchmark for lead in interior dust. The Residential Lead-Based Paint

Hazard Reduction Act (Title X) Final Rule (40 CFR, Part 745, 1/5/01) established

uniform national standards for lead in interior dust. Thus, both EPA and the United

States Department of Housing and Urban Development (HUD) have set a dust

standard for lead of 40 μg/ft2 for floors (including carpeted floors) and 250 μg/ft2 for

interior window sills.To support the development of a dust standard EPA performed an

analysis of the Rochester Lead-in-Dust Study (HUD, 1995). At 40 μg/ft2 a multimedia

analysis shows a 5.3% probability that a child’s blood lead level would exceed 10

μg/dl. Thus, this standard meets the criteria established by EPA (i.e., 95% probability

to be below 10 μg/dl) (EPA 1994a) for managing environmental lead hazards.

However, the COPC Committee opted to set the benchmark at the more stringent

HUD screening level of 25 μg/ft2.

# Silica. The crystalline silica benchmark presented in the draft COPC document was

based on the OSHA Permissible Exposure Limit (PEL) for “dust containing quartz.”

This standard varies with the crystalline silica content of the dust and applies to dust
15

samples which may contain as little as 1% crystalline silica. Because this standard is for

respirable dust, and varies by crystalline silica content, different conditions would yield

different standards viewed either as total dust or effective silica concentration. For

example, in the case where the dust is 100% crystalline silica, the standard is 100

:g/m3. In contrast, in the case where a dust is 1% crystalline silica, the PEL is 3.3

mg/m3 for respirable dust containing crystalline silica. Because only 1% of this total dust

is crystalline silica, the effective crystalline silica concentration in this case is 33 :g/m3.

This OSHA standard is based on the 1969 ACGIH TLV value, adopted by OSHA in

1971. Subsequent follow-up to the original occupational cohorts on which this standard

was based and other cohorts studied show mixed results. Some studies uphold the

standard and others show a need to lower it. OSHA is considering a change. Because

of the complicated nature of the data and sampling issues, OSHA has not yet decided

on a new standard. And until such time, the PEL stands in effect. 

However, both the ACGIH and National Institute of Occupational Safety and Health

(NIOSH) have examined the data and have lowered their recommended exposure

limits to 50 :g/m3. This is based upon concern that there appears to be more silicosis in

exposed cohorts than was recognized by the older recommendation. A recent review

by NIOSH of their recommended exposure limit (REL) indicates that adverse health

effects may be observed in workers exposed at or below the current REL (NIOSH

2002). However, technical concerns regarding the ability to reliably measure respirable

crystalline silica in the workplace below the REL (see response to BENCH #9) prevent

NIOSH from lowering their REL at this time (NIOSH 2002). Although not the

quantitative basis for the current REL, NIOSH reviewed several health effects

associated with chronic exposure to crystalline silica in the workplace including:

silicosis, lung cancer, emphysema and chronic obstructive pulmonary disease. A

threshold for these health effects has not been defined although some analyses do

provide exposure response relationships and suggest a point of departure for

observable health effects. Cumulative exposure, peak exposure, duration of exposure

and latency time have all been positively related to adverse pulmonary health effects. In

light of these considerations, the benchmark for silica is now being based on the

NIOSH REL. (See the response to BENCH #9 for additional information on the

derivation of the silica benchmark from the REL.) 

Comment BENCH #3:

“For defining the different tiers, the panel recommended that Tier I benchmarks be based on a

1-year exposure, child exposure parameters, and where available, child-specific toxicological

endpoints. The panel recommended that Tier III benchmarks be based on a 30-year exposure,

where 6 years are based on child exposure parameters and 24 years are based on adult

exposure parameters.”

Response:

As discussed in our response to BENCH #1, the Tier III benchmark which has and continues

to serve as a benchmark for long-term habitability of a residential dwelling, will be the focus of

the revised COPC document. Benchmark criteria have been developed therefore to evaluate

chronic (30-year) exposures only, with consideration of childhood exposure within that time

frame. For the evaluation of residues on indoor surfaces, we factored in continuous age-specific

exposure parameters from age 1 through 31. Appendix D in the final COPC document details
16

the approach and exposure parameters used in deriving benchmark criteria for long-term

exposures.

Child-specific toxicological criteria were considered where available (e.g., lead). As described

in the responses to COPC #6, EPA’s IRIS database served as the primary source for toxicity

criteria most of which are based on animal and human data looking at adult exposures. The final

COPC document will note this factor as an additional uncertainty in the process. However, we

feel that the approach used relied on the best available science and risk assessment

methodologies and enabled the generation of reasonably protective benchmark criteria. As

stated earlier, development of child-specific toxicity criteria for screening COPC and setting

health-based benchmarks is beyond the scope of this project.

Comment BENCH #4:

“Panel members disagreed with the rationale provided in the document for using an upper level

excess lifetime cancer risk level of 1 x 10-4 in calculating the benchmarks for each tier. The

panel noted that the sampling and analysis limitations described in the document for asbestos

that limit the risk evaluation to a 1 x 10-4 risk level could be easily overcome and lower risk

levels could be achieved for other COPC. The panel did not address specifically the risk

management decision of whether using a 1 x 10-4 versus a risk level of 1 x 10-5 or 1 x 10-6

would be most appropriate.”

Response:

The level of 10-4 lifetime risk was chosen on the basis of practical sampling limitations particular

for asbestos. The level specified by the document, 0.0009 fibers/cc, is near the practical

detection level given the large scope of the WTC Clean-up Program. The reviewers suggested

that a somewhat lower risk, perhaps as low as 10-6, might be achieved by compositing multiple

samples. Measuring to a risk level of 10-6 requires 100 times more air volume per sample. 

The detection limit for a sample varies based on the volume of air which passes through the

filter, and/or by the number of grids (i.e., area) on the filter read by the microscopist.

Resources, both human and financial, prohibited the analysis of additional filter grids as a means

of lowering detection limits. Still, lower detection limits could be achieved by higher volumes of

air. However, in order to lower the detection limit 10 fold (to target a 10-5 risk instead of 10-4

risk) 10 times the air would need to be drawn through the filter. So a sample would run for 80

hours instead of 8, assuming the volumetric flow rate (already at the high end of the

recommended range) of the sample remains constant. Similarly, a risk level of 10-6 would

require a sampling time of 800 hours. In addition to the logistical problems of running a pump in

someone’s home for such an extended time, there are additional technical concerns. 

In urban atmospheres, there are many substances in the air other than asbestos fibers, which

interfere with detection of asbestos in ways that increase with the volume of air sampled.

Asbestos is unlike chemical species analysis where samples might be combined. Non-fibrous

dust and other general particulate matter collect on the filter along with any asbestos fibers. This

dust obscures fibers, and because asbestos fibers are counted manually on a known surface

area of filter, this limits the detectable level of asbestos. The authors acknowledge that

running multiple pumps concurrently, in theory, might mitigate overloading potential and reduce

total sample time. The WTC Clean-up Program was set up such that every room in a

residential dwelling (with a minimum of three samples) would need to meet the clearance criteria
17

before the residence was deemed effectively cleaned. Given that more than 6,000 individual

residences signed up for the cleaning test only program, the prospect of running multiple pumps

to obtain a single sample was determined to be beyond practical implementation. Additional

discussion in support of a 10-4 risk level for asbestos and other carcinogenic COPC is

presented in Appendix C of the final COPC document. 

Comment BENCH #5:

“The panel recommended that for some COPC, the authors should develop benchmarks for

contaminants on hard surfaces and benchmarks for contaminants on soft surfaces, instead of

just developing a single benchmark for contaminants in settled dust. The panel noted that,

although there are limited data available in order to recommend soft-surface benchmarks, some

methods for this have been developed to address exposure to pesticides. These methods could

be applied to the WTC situation. The panel recommended that for each COPC, the document

clearly analyze the chemical properties and the potential exposure pathways to that contaminant

before determining whether an air, hard-surface, or soft-surface benchmark is needed.”

Response:

The committee generally agrees with this comment and has modified the assessment procedures

to explicitly consider differences in exposure to soft and hard surfaces. The revised procedure

has been adopted from EPA’s pesticide guidance (as suggested in the comment) and treats the

surfaces differently in terms of degree of particle transfer to skin and contact time. The

comment also implies that the clearance criteria for the two surfaces may differ. The assessment

procedure assumes a residence has both soft and hard surfaces and the total exposure results

from contact with both surfaces. For the sake of simplicity, the committee decided to set equal

criteria for the two surfaces. Also as suggested in the comment, this procedure is applied on a

chemical-by-chemical basis and considers chemical properties such as dermal absorption. 

It should be understood, however, that the procedures for estimating exposure to surfaces is

highly uncertain. The factors affecting surface loading and transfers to skin have not been well

studied and are likely to be highly variable. These include:

< Surface characteristics affecting deposition and removal (e.g., porosity, roughness,

static charge)

< Activity patterns related to surface contact.

< Surface cleaning techniques and frequency.

These uncertainties are highlighted in the final COPC document, both in the newly included

section on uncertainties and limitations and in Appendix D. 

Comment BENCH #6:

“The panel suggested that the document more clearly describe how mixture toxicology is being

considered in developing benchmarks.”

Response:

Benchmark criteria were developed on a contaminant-by-contaminant basis. The final COPC

document will explain why this approach was taken and is considered health protective, as

summarized below.
1Note that combined effects within dioxin and PAH mixtures were accounted for in the development of

benchmarks using toxic equivalency (TEQ) approaches that account for the relative potency of the components of

these complex mixtures. Toxicity equivalent factors used in this approach are based on our understanding of the

most toxic component of each mixture (i.e., 2,3,7,8-TCDD for dioxins and benzo(a)pyrene for PAHs).

One EPA study looking at acute airway effects in mice exposed to WTC fine particulate matter (2.5 microns)

provides some insights to the magnitude of total dust exposures leading to observable effects. This study revealed

that components of WTC dust promotes respiratory inflammation at “high” doses only (EPA 2002). This study does

not evaluate the effects of long-term or repeated exposures to lower levels of WTC dust and is not directly useful in

the development of benchmarks. 

18

The COPC Committee clearly recognizes that the residents in Lower Manhattan are not

exposed to environmental contaminants singularly, but instead to combinations of chemical and

physical agents. Development of benchmarks, however, was driven by a combined

consideration of individual COPC-specific toxicity, background levels, and practicalities and

limitations related to sampling. Mixture toxicology was not factored into the derivation process

because little or no quantitative dose-response data exist regarding specific interactions across

the WTC COPC (asbestos, dioxins, lead, PAHs, fibrous glass, and crystalline silica)1. 

We feel the contaminant-specific approach is health protective for the following reasons:

# The process for developing benchmarks based on non-cancer effects sets

concentrations well below observed effect levels and generally at or near no-observedadverse-effect levels (NOAELs). Presumably, exposures to one or multiple substances

below or near the NOAEL will not result in adverse effects (EPA 2000b). 

# The likelihood of interactions are increased if substances behave similarly

toxicologically. We therefore qualitatively examined the toxicology of individual COPC

to review what is known about target organ toxicity, mode of action, and any

documented chemical interactions among WTC COPC. Review of EPA’s toxicological

reviews (including the 2000 dioxin reassessment) and ATSDR’s toxicological profiles

revealed the following:

< Target organs and critical effects resulting from ingestion and dermal exposures

generally differ across individual COPC, though asbestos, lead, dioxins, and

PAHs are all considered potential human carcinogens via the ingestion route.

Each of these contaminants can affect a wide range of biological systems, but

each generally exerts its effects via different mechanisms. 

< At high concentrations, inhalation exposure to several of the COPC (asbestos,

fibrous glass, and crystalline silica), as well as the small particulate matter

released during the WTC disaster, has been shown to result in point of contact

toxicity to the lung. Specific lung effects vary across these substances, ranging

from acute irritant effects produced by fibrous glass to cancers of the lung

associated with asbestos. Again, although uncertainty exists due to the limited

study of chemical mixtures, exposures to COPC at or below benchmark

concentrations—which are set at levels significantly lower than observable

effect levels—would not be expected to produce effects individually or in

combination.
19

Comment BENCH #7:

“For the air benchmark for lead, the panel recommended incorporating local exposure loading

data into the IEUBK model.”

Response:

The draft COPC document utilized average background concentrations for multi-media sources

of lead based on national data for lead in drinking water, diet, soil and indoor dust as input

parameters for the IEUBK Lead Model. As per the peer review recommendations, local data

was researched for site-specific input parameters. The discussion below details the source,

analysis and application of these data.

EPA developed the Integrated Exposure Uptake Biokinetic (IEUBK) Lead Model (EPA

1994) to evaluate multimedia lead exposure to children in residential settings. EPA established

a goal of attaining a 95% probability that blood lead levels in children be less than 10 μg/dl

(EPA 1994a). To meet the aforementioned goal, The IEUBK Lead Model was run using

multimedia input parameters that are applicable to the residential community in Lower

Manhattan. The following discussion details the basis for individual input parameters.

Lead in Drinking Water - The source of NYC’s drinking water (the Catskill/Delaware and

Croton systems) is remarkably low in lead. The average lead concentration is 1 μg/l in the

Catskill/Delaware system and <1 μg/l in the Croton system (NYCDEP - Drinking Water

Quality Test Results, 2001 - see www.nyc.gov/dep). However, the concentration of lead in tap

water can be increased by lead containing components (pipes, solder) of a building’s

distribution system. Consequently, the Safe Drinking Water Act “Lead and Copper Rule”

(Federal Register, June 7, 1991) requires large water systems to monitor led concentration at

the tap. If more than 10% of the samples exceed the federal “Action Level” of 15 μg/l,

corrective steps (e.g., source treatment, corrosion control) must be carried out. The IEUBK

Lead Model is intended to run with input values that represent the average lead concentration in

the environmental media of interest. As reported by NYCDEP, 2001, the median lead

concentration from a total of 107 samples obtained at the tap was 3 μg/l. It should be noted that

these samples represent a high bias in that they were obtained from homes where there is

reason to believe that lead service lines exist. The median lead concentration in tap water citywide is likely to be lower. However, for the purpose of this site-specific application of the

IEUBK Lead Model, a value of 3 μg/l is used as a conservative central tendency estimate of

lead in tap water.

Lead in Diet - No data could be located relating to the lead content in food items for residents

living in Lower Manhattan. Since there is very little home gardening taking place in this

community it was deemed appropriate to use data that reflects national trends for commercially

available food items. EPA recently evaluated dietary lead content in children in support of

revising default input parameters for the IEUBK Lead Model (EPA 2002). Lead residues in

food were obtained from the Food and Drug Administration’s (FDA’s) Total Dietary Survey.

Food consumption trends were obtained from the National Health and Nutrition Examination

Survey (NHANES) . The average lead content in the diet of children 0 - 7 years old is 2.8

μg/day. Consequently, the input value of 2.8 μg/day was employed as the estimate of average

daily lead intake from diet.
20

Lead in Soil - Numerous studies have been conducted to evaluate soil and street dust lead

concentrations in New York City (NYCDOHMH, 2003). In the studies reviewed, soil/dust

samples were taken by a variety of methods over a long period of time (1924 - 1993).

Summary statistics were compiled by the NYCDOHMH based on whether the studies

assessed known lead sources or background conditions. Ruling out studies on specific sources

such as bridges, a median soil lead concentration of 200 ppm and street dust lead concentration

of 895 ppm was reported. Data are lacking with regard to the relative contribution of street

dust to a child’s daily “soil” intake. Given this uncertainty, the median values of soil and dust

were averaged to provide a composite soil/dust concentration of 548 ppm. This value was used

as the soil lead concentration in the site-specific application of the IEUBK Lead Model 

Lead in Indoor Dust - Although there exists a substantial amount of lead “load” data (i.e.,

mass per unit area - typically recorded in units of micrograms per square foot as per HUD

reporting requirements) as a measure of lead contamination in residential dwellings, the IEUBK

Lead Model requires lead concentration in settled dust to be reported in terms of concentration

(i.e., mass per unit mass - typically recorded as parts per million). The WTC Background

Study reported lead in house dust both in terms of lead load (μg/ft2) and concentration (ppm)

although more limited sampling was obtained of lead concentration (ppm) measurements.

Nonetheless, because these data were specifically intended the assess background conditions in

Lower Manhattan, they were used in the site-specific application of the IEUBK Model. The

mean concentration of lead in settled dust in the WTC Background Study was 126 ppm (EPA

2003a). Consequently, this was the value used for lead in indoor dust for the site-specific

application of the IEUBK Lead Model. 

Site specific application of the IEUBK resulted in a reduction of the lead benchmark for indoor

air form 1 μg/m3 to 0.7 μg/m3. See Appendix E of the final COPC document for data input

spreadsheets and graphic display of model results.

Comment BENCH #8:

“The panel did not endorse the asbestos settled dust benchmark because the only relevant

exposure pathway for asbestos is inhalation and K-factor methodology is, at this time,

inadequate for predicting inhalation exposure from asbestos surface loading measurement.

However, the panel did note that settled asbestos is a potential source of airborne asbestos if

disturbed or not remediated.”

Response:

The comment addresses the use of K-factors in the draft COPC document to derive Tier I

benchmarks for asbestos and fibrous glass in settled dust. As our response to comment

BENCH #1 indicates, we are now assigning one health-based benchmark to each COPC,

rather than using three tiers of benchmarks for each contaminant. As per the peer review

recommendations, the benchmarks for asbestos and fibrous glass in the final COPC

document have been developed only for indoor air, and reflect an environmental risk-based

paradigm and modified occupational standards, respectively. None of the benchmarks in the

final COPC document are based on the K-factor methodology. The COPC Committee agrees

with observations made by members of the peer review panel that due to the numerous factors

that influence the relationship between fiber concentration in settled dust and indoor air,

including surface porosity, activity patterns, air exchange rates and interior volume, benchmarks

for asbestos and fibrous glass in settled dust should be omitted. Our responses to comments
21

BENCH #2 and BENCH #9 further discuss the rationale behind the final set of health-based

benchmarks.

Comment BENCH #9:

“For setting benchmarks based on occupational standards, duration-based adjustment factors

should be used that weigh chemical-specific issues. Specifically, the panel suggested that a

duration adjustment of 4.2 is typical to extrapolate from occupational to environmental

exposure, and that additional adjustments of 10 or 100 (for a total factor of 42 or 420) may be

needed to address the underlying, chemical-specific biological factors (toxicokinetics and

toxicodynamics).”

Response:

The comment applies to benchmarks based on occupational standards. The draft COPC

document used such standards to derive benchmarks for fibrous glass and silica. Our

responses to this comment for these two COPC follow:

# Fibrous glass. Although the TLV is based on irritant effects the resulting benchmark of

0.01 f/cc is believed to be protective for chronic residential exposure for glass and

mineral wool. In developing the three tiered approach initially designed to prioritize and

define the level of response needed in different environments surrounding the WTC

area, the committee worked from the existing TLV. Anything above the TLV was not

considered acceptable for residential use. The TLV was adjusted by a factor of ten for

each Tier resulting in a total adjustment of 100 for the Tier III level. The committee did

not specifically apportion this adjustment as a duration adjustment or an adjustment for

application to a non-worker population. Although this total adjustment of 100 could be

considered to cover the 4.2 duration adjustment, and an adjustment above that for

application to non-worker population, there is considerable variation in how this second

adjustment may be set. The Peer review committee itself recommends a range between

10 and 100 resulting in a total adjustment between 42 and 420. The question is not so

much can we assign a specific number for the adjustment which is accurate, but rather

is the resulting standard protective. 

Fibrous glass less than 3 microns in diameter are respirable and available to enter and

deposit in the pulmonary regions of the lung (ACGIH 2001). Clearance of these fibers

from the lung will be determined by fiber solubility and length (ACGIH 2001; ATSDR

2002a). Fibers cleared from the lung have less potential to create long-term health

effects. Less soluble materials have a longer residence time in the lung and therefore

have a greater potential to contribute to tissue damage or malignant disease. Within

synthetic vitreous fiber (SVF) types, glass fibers and slag wool are considered the most

soluble, and therefore least toxic. Mineral wool is less soluble than glass wool. The

fibers observed in indoor and outdoor dust samples from the WTC area contained

glass wool and mineral wool, both of which have lower biopersistence than other forms

of synthetic vitreous fibers.

Although some animal studies have demonstrated both fibrotic and carcinogenic potential for

glass and mineral wools (ACGIH 2001; ATSDR 2002a; IARC 1988), more recent studies do
2

Early studies often relied upon injection and implantation studies, which may not accurately predict a

pulmonary response from inhalation exposures. A review of inhalation studies indicates that glass wool did not

cause pulmonary fibrosis or lung cancer in these animal studies (Bonn et al. 1993). A recent study by Hesterberg

indicates no increase in pulmonary fibrosis or lung cancer even at doses of 222 f/cc, although cancer incidence in

control animals was considered high. 

22

not fully support this finding.2 Epidemiologic studies on workers exposed to fibrous glass do not

provide consistent evidence of pulmonary effects, although some effects were noted (ATSDR

2002a; Bonn et al. 1993). Similarly, when assessing deaths due to lung cancer in workers

exposed to glass wool, studies do not provide strong evidence for increased risk of cancer

deaths attributable to the glass wool exposure.

The carcinogenic potential of fiberglass has been reviewed by several agencies. The

IARC originally classified both glass and mineral wools as Group 2B carcinogens,

possibly carcinogenic to humans, based on animal studies (IARC 1987). Similarly these

materials were classified as carcinogens by the National Toxicology Program and the

American Conference of Governmental Industrial Hygienists (ACGIH 2001; NTP

2001). However a review of the carcinogenic potential of these fibers by IARC in

2001, which takes into account updated human studies, animal inhalation studies, and

mechanistic studies, recommends a change in this classification. The IARC has

announced that the recent monograph designates both glass and mineral wool as Group

3, unclassifiable as to carcinogenicity in humans, because of inadequate evidence of

carcinogenicity in humans and the relatively low biopersistence of the materials. 

In contrast, the less soluble, and more biopersistent refractory ceramic fibers, are still

considered potentially carcinogenic and are believed to more toxic than glass and

mineral wools. A recent review of the toxicity of synthetic vitreous fibers by ATSDR

proposes a Minimal Risk Level for chronic exposure of 0.03 f/cc for these refractory

ceramic fibers (ATSDR 2002b). Although ATSDR did not set MRLs for glass and

mineral wools, it notes that “insulation wools are markedly less durable and less potent

than refractory ceramic fibers.” Therefore the benchmark of 0.01 f/cc for glass and

mineral wools, which is lower, should be considered protective. 

# Silica. In response to other peer review comments on this document, as well as the

current stage of clean-up and assessment projects ongoing in Lower Manhattan, it has

been decided to remove the tiered approach provided to screen and prioritize clean-up

and response efforts. Therefore the only benchmark needed for crystalline silica is that

which would be protective for the general public in a chronic exposure scenario. No

threshold has been established and it is possible health effects occur below the NIOSH

REL of 50 :g/m3. Although duration adjustments and uncertainty factors can be

applied to this REL to develop a benchmark for residential exposure, the resulting level

would be well below practical sampling limits. Therefore this committee is

recommending a benchmark of 5 :g/m3, which is the lowest amount that can be reliably

reported in a reasonable sampling time.

The level of this benchmark is technically limited by sampling constraints, including time

and weight loading. It is based upon a reporting limit of 10 micrograms of crystalline

silica with no more than about 3 milligrams of total dust on a single filter. (A reporting

limit is the smallest amount of a substance for which a quantitative value can be
23

determined.) More than about 3 milligrams of dust on the filter will decrease analytical

sensitivity. Collection of 2 cubic meters of air over about 20 hours for a Dorr-Oliver

cyclone at 1.7 L/min or about 13.3 hours using an SKC cyclone at 2.5 L/min will

provide sufficient sensitivity to measure 5 μg/m3 crystalline silica so long as the total dust

weight on the filter does not exceed about 3 milligrams (an airborne dust concentration

of 1.5 mg/m3). Using either the nylon Dorr-Oliver or SKC Aluminum Cyclones, the

following limits are possible:

Sampling Equipment

(Size selection

cyclones)

Duration of sampling Volume of air

(m3)

Effective reporting limit

(μg/m3)

Dorr-Oliver (OSHA)

at1.7 L/min

6 hours (360 min) 0.61 16.3

8 hours (480 min) 0 .81 12.3

10 hours (600 min) 1.02 9.8

19.6 hours (1176 min) 2.0 5.0

SKC Aluminum

(NIOSH) at 2.5

L/min

6 hours (360 min) 0.9 11.2

8 hours (480 min) 1.20 8.4

10 hours (600 min) 1.5 6.7

13.3 hours (800min) 2.0 5.0
24

IV. References

American Conference of Governmental Industrial Hygienists (ACGIH). 2001. TLV Documentation:

Manmade Vitreous Fibers (MMVF), 2001.

ATSDR. 1998. Toxicological Profile for Chlorinated Dibenzo-p-dioxins. Atlanta: U.S. Department of

Health and Human Services. December 1998.

ATSDR 2000. Toxicological Profile for Arsenic. Atlanta: U.S. Department of Health and Human

Services. September 2000.

ATSDR. 2001. Guidance Manual for the Assessment of Joint Toxic Action of Chemical Mixtures.

Draft for Public Comment. Atlanta: U.S. Department of Health and Human Services. February 2001.

ATSDR. 2002a. Technical Briefing Paper: Health Effects from Exposure to Fibrous Glass, Rock Wool

or Slag Wool. Agency for Toxic Substances and Disease Registry, U.S. Department of Health and

Human Services, Atlanta, GA. 2002.

ATSDR 2002b. Toxicological Profile for Synthetic Vitreous Fibers. Atlanta: U.S. Department of

Health and Human Services. September 2002. 

Bonn WB, Bender JR, et. al. 1993. Recent Studies of Man-made Vitreous Fibers: Chronic Animal

Inhalation Studies. J Occup Med. 1993;35(2):101-113.

COPC 2002. World Trade Center Indoor Air Assessment: Selecting Contaminants of Potential

Concern and Setting Health-Based Benchmarks. Peer Review Draft. Prepared by the Contaminants of

Potential Concern (COPC) Committee of the World Trade Center Indoor Air Task Force Working

Group. September 2002.

COPC 2003. World Trade Center Indoor Environment Assessment: Selecting Contaminants of

Potential Concern and Setting Health-Based Benchmarks. Final Report. Prepared by the Contaminants

of Potential Concern (COPC) Committee of the World Trade Center Indoor Air Task Force Working

Group. May, 2003.

EPA 1980. Man-Made Vitreous Fibers and Health, In Proceedings from the Natrional Workshop on

Substitutes for Asbestos. USEPA, EPA/560/3-80-001. 

EPA 1986. EPA’s Guidelines for the Health Risk Assessment of Chemical Mixtures. EPA/630/R98/002. September 1986.

EPA 1989. Risk assessment guidance for Superfund. Volume 1. Human Health Evaluation Manual

(Part A). Interim Final. U.S. Environmental Protection Agency, Office of Emergency and Remedial

Response. EPA/540/1-89/002. Washington D.C.

EPA 1992. Dermal Exposure Assessment: Principles and Applications. Interim Report. U.S.

Environmental Protection Agency, Office of Health and Environmental Assessment.

EPA/600/891/001/B.

EPA 1994. Guidance Manual for the Integrated Exposure Uptake Biokinetic Model in Children. Office

of Emergency and Remedial Response. EPA/540/R-93/081 Washington D.C.
25

EPA 1994a. Revised Interim Soil Lead Guidance for CERCLA Sites and RCRA Corrective Action

Facilities. OSWER Directive 9355.4-12. Washington D.C.

EPA. 1997a. Health Effects Assessment Summary Tables. FY 1997 Update. EPA-540-R-97-036.

July 1997.

EPA 1997b. Exposure Factors Handbook. U.S. Environmental Protection Agency, Office of Research

and Development, National Center for Environmental Assessment. EPA/600/P-95/002Fa. August

1997.

EPA 2000a. Science Policy Council Handbook: Peer Review. U.S. Environmental Protection Agency,

Office of Science Policy. EPA 100-B-00-001. December 2000.

EPA. 2000b. Supplementary Guidance for Conducting Health Risk Assessment of Chemical Mixtures.

Risk Assessment Forum Technical Panel. EPA/630/R-00/002. August 2000.

EPA. 2000c. Draft Exposure and Human Health Reassessment of 2,3,7,8-Tetrachlorodibenzo-pDioxin (TCDD) and Related Compounds. Office of Research and Development. 

EPA. 2001a. Science Advisory Council for Exposure. Policy Number 12 on Recommended Revisions

to the Standard Operating Procedures (SOPs) for Residential Exposure Assessments. Revised:

February 22, 2001.

EPA. 2001b. Risk Assessment Guidance for Superfund Volume 1: Human Health Evaluation Manual

(Part E, Supplemental Guidance for Dermal Risk Assessment). Review Draft. U.S. Environmental

Protection Agency, Office of Emergency and Remedial Response EPA/540/R/99/005.

EPA 2002. IEUBK Dietary Intake Update. (Revised Draft, 12/02) Technical Review Workgroup for

Lead. OSWER Washington D.C.

EPA. 2002a. Child-Specific Exposure Factors Handbook (Interim Report). U.S. Environmental

Protection Agency, Office of Research and Development, National Center for Environmental

Assessment. EPA-600-P-00-002B. September 2002.

EPA. 2002b. Toxicological Effects of Fine Particulate Matter Derived from the Destruction of the

World Trade Center. National Health and Environmental Effects Research Laboratory. December

2002.

EPA 2003. Supplemental Guidance for Assessing Cancer Susceptibility from Early-Life Exposure to

Carcinogens. External Review Draft. EPA/630/R-03/003. February 2003.

EPA 2003a. World Trade Center Residential Confirmation Cleaning Study (Draft Report, March

2003). USEPA Region 2, New York, NY.

EPA 2003b. World Trade Center Background Study (Draft Report, March 2003) USEPA Region

2, New York, NY.

Heisel EB and Hunt FE. 1968. Further Studies in Cutaneous Reactions to Glass Fibers. Arch Env

Health. 1968;17:705-711.
26

HUD 1995. The Relation of Lead-Contaminated House Dust and Blood Lead Among Urban Children.

Final Report to USHUD from the University of Rochester School of Medicine (Rochester, NY) and

the National Center for Lead Safe Housing (Columbia, MD).

International Agency for Research on Cancer (IARC). nd. IARC Monographs Program Re-evaluates

Carcinogenic Risks from Airborne Man-Made Vitreous Fibers, International Agency for Research on

Cancer, World Health Organization, Lyon, France. 

International Agency for Research on Cancer (IARC). 1987. Monograph Asbestos (Actinolite,

Amosite, Anthophyllite, Chrysotile, Crocidolite, Tremolite), in IARC Monographs of the evaluation of

carcinogenic risks to humans, International Agency for Research on Cancer, World Health

Organization, Lyon, France 1987;Supp 7:106.

International Agency for Research on Cancer (IARC). 1988. Monograph on Man-Made Mineral

Fibers, in IARC Monographs of the Evaluation of Carcinogenic Risks to Humans. International Agency

for Research on Cancer. World Health Organization. Lyon, France. 1988;43:39.

Kim NK and Hawley J. 1985. Re-Entry Guidelines: Binghamton State Office Building. New York

State Dept. of Health, Bureau of Toxic Substances Assessment, Division of Health Risk Control.

Albany, NY. August. Document 0549P.

Lioy P, Wiesel CP, Millette JR, Eisenreich S, Vallero D et al. 2002. Characterization of the

Dust/Smoke Aerosol that Settled East of the World Trade Center (WTC) in Lower Manhattan after

the Collapse of the WTC September 11, 2001. Environ. Health Perspectives. July 2002;110(7):703-

14.

Michaud JM, Huntley SL, Sherer RA, Gray MN, and Paustenbach DJ. 1994. PCB and Dioxin Reentry Criteria for Building Surfaces and Air. Journal of Exposure Analysis and Environmental

Epidemiology; 4(2):197-227.

Milette JR, Hays SM. 1994. Settled Asbestos Dust Sampling and Analysis. Lewis Publishers. New

York

National Toxicology Program (NTP). 2001. Glasswool in Report on Carcinogens, 9th Edition. U.S.

Department of Health and Human Services, National Toxicology Program, Research Triangle Park,

NC. 2001.

NIOSH 2002. National Institute of Occupational Safety and Health. Health Effects of Occupational

Exposure to Respirable Crystalline Silica. NIOSH # 2002-129. US Departmnet of Health and Human

Services.

New Jersey Department of Environmental Protection (NJDEP). 1993. Technical Basis and

Background for Cleanup Standards for Contaminated Sites. N.J.A.C. 7:26D (Draft).

NYCDOHMH 2003. Personal Communication with Ken Carlino - Lead Program. New York City

Department of Health and Mental Hygiene. New York, NY.

Radian International (Radian). 1999. Development of Risk-Based Wipe Sample Cleanup Levels at the

Claremont Polychemical Superfund site in Old Bethpage, New York. Prepared for the U.S. Army

Corps of Engineers.
27

Stam-Westerveld EB, Coenraads PJ, Van Der Valk, et.al. 1994. Rebbing Test Response of the Skin

to Man-Made Vitreous Fibers of Different Diameters. Contact Dermatitis 1994;31(1):1-4.

TERA 2003. World Trade Center (WTC) October 21–22, 2002, Peer Review Meeting Notes.

Prepared by Toxicology Excellence for Risk Assessment. Prepared for the U.S. Environmental

Protection Agency. February 7, 2003.

WHO. 1998. Environmental Health Criteria 205. Polybrominated Dibenzo-p-dioxins and

Dibenzofurans.
Addendum/Errata to the report titled 

“World Trade Center Indoor Environmental Assessment: 

Selecting Contaminants of Potential Concern and Setting

Health-Based Benchmarks (May, 2003).”

February, 2004

Copies of the “World Trade Center Indoor Environmental Assessment: Selecting Contaminants of

Potential Concern and Setting Health-Based Benchmarks (May, 2003) report and this

“Addendum/Errata” sheet can be obtained on-line at www.epa.gov/WTC. Inquiries regarding the 

content of both of these documents should be directed to:

Mark A. Maddaloni Dr. P.H., DABT

U.S. Environmental Protection Agency, Region 2

290 Broadway

New York, NY 10007-1866

Phone (212) 637-3590

E-mail maddaloni.mark@epa.gov
Section 3.4 Health Based Benchmarks - Expanded Discussion of PCM Equivalence

Asbestos clearance criteria was based on long (i.e., > 5 um) fiber counts. The use of a minimum fiber

length of 5 um for carcinogenic activity represents current scientific consensus and is documented in

both NIOSH methods 7400 & 7402 and EPA’s Integrated Risk Information System (IRIS) toxicity

data base.

The footnote to Table 1 in the report titled “World Trade Center Indoor Environmental Assessment:

Selecting Contaminants of Potential Concern and Setting Health-Based Benchmarks” documents this

minimum length requirement along with a minimum length-to-width aspect ratio of 3:1 as prescribed in

the NIOSH asbestos analytical methods 7400 & 7402. This counting method applies to phase contrast

microscopy (PCM) analysis.

The asbestos counting rules employed for the WTC Indoor Clean-up Program was designed to record

phase contrast microscopy equivalent (PCMe) fibers. This analytical method utilized transmission

electron microscopy (TEM) and followed AHERA (Asbestos Hazard Emergency Response Act)

counting rules. Fibers > 5 um were distinguished from total (i.e., >0.5 um) fiber counts. AHERA also

stipulates a minimum 5:1 aspect ratio. Modification was made to AHERA (by obtaining larger samples

volumes) in order to achieve the lower detection limits necessitated by use of risk-based clearance

criteria. 

NIOSH method 7402 is an alternative approach for estimating PCMe fibers by TEM analysis. The

method counting rules differs slightly from the above approach in the it stipulates a minimum aspect ratio

of 3:1 and a minimum fiber width of 0.25 um. The minimum fiber width reflects the optical resolution of

PCM. Compared to NIOSH method 7402, the PCMe counts recorded for the WTC Indoor Clean-up

Program may be marginally higher or lower. Extremely thin fibers (width < 0.25 um) were recorded but

would have been excluded using NIOSH 7402 counting rules. The actual magnitude of this over count

(relative to NIOSH 7402) is unknown but likely to be small. Conversely, asbestos fibers with an aspect

ratio between 3:1 and 5:1 were not counted but would have been recorded using NIOSH 7402

counting rules. Similarly, the actual magnitude of this undercount is unknown but likely to be small -

especially since the vast majority of identified asbestos fibers were chrysotile (which typically has a

relatively high aspect ratio).

Appendix A: Deriving Health-Based Screening Values for Air and Dust Exposure Pathways

The screening values for settled and bulk dust employed a 30 year exposure duration to reflect an

upper-bound estimate of time in residence, as per the recommendations in the Risk Assessment

Guidance for Superfund (RAGS, 1989). (Screening values for asbestos in settled and bulk dust were

not developed due to the highly uncertain relationship between settled and airborne asbestos.) Where

applicable, the health-based benchmarks for the contaminants of potential concern listed in Table 1 of
the report also reflect a 30 year exposure duration. However, an oversight occurred in the screening

values for inhalation carcinogens (e.g., asbestos). Rather than using the same 30 exposure duration

employed for the dust pathway, the screening value employed the inhalation unit risk (IUR) which is

based on lifetime (i.e., 70 yr) exposure duration. Consequently, the air screening value for asbestos

listed in Appendix A (Table A-1) is 0.0004 f/cc (reflecting a 70 year exposure duration), while the

health-based benchmark for asbestos listed in Section 3.4 (Table 1) is 0.0009 f/cc (reflecting a 30 year

exposure duration). 

Appendix D: Assessing Exposures to Indoor Air and Residues on Indoor Surfaces

The paradigm for assessing exposure from residues on indoor surfaces captures mouthing activity

through an input parameter then assigns the number of hand-to-mouth contacts per hour as a function

of age. The following mouthing frequency is listed in Appendix D (P. D-5): 1 to 6 yr - 9.5 times/hr; 7

to 12 yr - 5 times /hr; 8 to 18 yr - 2 times/hr; and, 19 to 31 yr - 1 time/hr. As listed in the report, two

age groups (7 to 12 and 8 to 18) overlap. The actual breakdown by age is correctly listed in the table

below under the column “COPC Spreadsheet.” In addition, Appendix D lists mouthing activity for

adults (19 to 31 yr) as 1 time/hr, when in reality the spreadsheet (and therefore the calculations used to

develop heath-based benchmarks for indoor surfaces) employed an adult (19 to 31 yr) mouthing rate

of 2 times/hr. The impact of using two rather than one mouthing events per hour for adults has a

negligible impact on the health-based benchmark and what little effect it has is biased toward a more

stringent value. 

Ages (yr) COPC

Report

COPC 

Spreadsheet

1 - 6 9.5 9.5

7 - 12 5 5

8 - 18 2 2 (age 13 -18 )

19 - 31 1 2