Friday,

November 3, 2000

Part III

Environmental

Protection Agency

Revisions to the Methodology for

Deriving Ambient Water Quality Criteria

for the Protection of Human Health

(2000); Notice

66444 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

ENVIRONMENTAL PROTECTION

AGENCY

[WH–FRL–6893–6]

Revisions to the Methodology for

Deriving Ambient Water Quality

Criteria for the Protection of Human

Health (2000)

AGENCY: Environmental Protection

Agency (EPA).

ACTION: Notice of Availability.

SUMMARY: EPA is announcing the

availability of final revisions to the

Methodology for Deriving Ambient

Water Quality Criteria for the Protection

of Human Health (2000) (hereafter

‘‘2000 Human Health Methodology’’)

published pursuant to section 304(a)(1)

of the Clean Water Act (CWA). The 2000

Human Health Methodology supersedes

the existing Guidelines and

Methodology Used in the Preparation of

Health Effect Assessment Chapters of

the Consent Decree Water Criteria

Documents, published by EPA in

November 1980 (USEPA, 1980)

(hereafter ‘‘1980 AWQC National

Guidelines’’ or ‘‘1980 Methodology’’).

Today’s Notice is intended to support

the requirements of section 304(a)(1) of

the CWA that EPA periodically revise

criteria for water quality to accurately

reflect the latest scientific knowledge on

the kind and extent of all identifiable

effects on health and welfare that may

be expected from the presence of

pollutants in any body of water,

including ground water. These revisions

are prompted by the many significant

scientific advances that have occurred

during the past 20 years in such key

areas as cancer and noncancer risk

assessments, exposure assessments, and

bioaccumulation assessments. These

revisions are not regulations and do not

impose legally-binding requirements on

EPA, States, Tribes, or the public.

DATES: Technical Support Documents

(TSD) on exposure assessment guidance

and bioaccumulation guidance

applicable to the 2000 Human Health

Methodology are expected to become

available early in calendar year 2001.

ADDRESSES: The 2000 Human Health

Methodology is published in the

document entitled, Methodology for

Deriving Ambient Water Quality Criteria

for the Protection of Human Health

(2000). This document is available on

the EPA website at www.epa.gov/OST/

humanhealth. A Technical Support

Document (TSD) volume on risk

assessments applicable to the 2000

Human Health Methodology is also

available from the website. Materials in

the public docket will be available for

public inspection and copying during

normal business hours at the Office of

Water Docket, 401 M St., SW,

Washington, DC 20460 by appointment

only. Appointments may be made by

calling (202) 260–3027 and requesting

item W–97–20. A reasonable fee will be

charged for photocopies.

FOR FURTHER INFORMATION CONTACT:

Denis R. Borum, Health and Ecological

Criteria Division (4304), U.S. EPA, Ariel

Rios Building, 1200 Pennsylvania

Avenue, NW, Washington, DC 20460;

(202) 260–8996; borum.denis@epa.gov.

SUPPLEMENTARY INFORMATION: This

Supplementary Information Section is

organized as follows:

I. Background Information

A. What are human health ambient water

quality criteria?

B. How is the Human Health Methodology

used?

C. Why was the Methodology revised?

D. What specific scientific advances have

occurred since 1980?

E. What process did EPA follow in revising

the Methodology?

F. What are the major revisions to the

Methodology?

G. How will EPA use the Human Health

Methodology?

II. Implementation Issues

A. How does EPA use its recommended

304(a) water quality criteria?

B. What water quality criteria must a State

or authorized Tribe adopt into its water

quality standards?

C. May States and authorized Tribes adopt

water quality criteria based on local

conditions?

D. What cancer risk level should States and

authorized Tribes use when establishing

water quality criteria?

E. How does the Review and Approval of

State and Tribal Water Quality Standards

rule affect water quality criteria adopted

by States and authorized Tribes?

F. While EPA is re-evaluating a 304(a)

criterion, what criterion is in effect?

G. What design stream flow should be used

to implement human health criteria?

H. What is the relationship between the

Agency’s recommended Section 304(a)

water quality criteria and drinking water

standards?

I. How are health risks to children

considered in the Methodology?

III. Summary of Comments Received on the

1998 Draft Methodology Revisions and

EPA’s Responses

A. Implementation

1. Application of Human Health Criteria

Within Mixing Zones

2. Application of Human Health Water

Quality Criteria to Marine Waters

3. Cancer Risk Range

4. Coordinating the Human Health

Methodology With Other EPA Programs

5. Designated Uses

6. Developing National 304(a) Criteria

7. Developing Organoleptic Criteria

8. Establishing EPA’s Most Recent

Federally Recommended Water Quality

Criteria

9. Flows

10. Implementation on a Waterbody Basis

11. Proposed Chemical List

12. Publishing Existing 304(a) Criteria

Information

13. Revising Existing 304(a) Criteria

14. State Evaluation of Data Supporting

Criteria

15. Streamlined Approach to Developing

Criteria Documents

16. Treaty Rights and Trust Obligations/

Government-to-Government Relations

B. General Policy

1. AWQC Derivation Equation Errors

2. Chronic Human Health Effects

Assumption

3. Protectiveness of the Methodology

4. Setting Criteria to Protect Both Fish and

Drinking Water Versus Fish Only

5. Setting Criteria to Protect Against

Multiple Exposures From Multiple

Chemicals

6. Uncertainty with the Derivation of

304(a) Criteria

7. Toxicity Equivalency Factors (TEFs) for

Dioxin-like Compounds

C. Cancer

1. Acceptable Risk Level for Carcinogens

2. ED10 (central estimate) versus LED10

(lower bound on dose)

3. Group C Contaminants

4. Guidance on Carcinogen Risk

Assessment

5. Hexachlorobutadiene (HCBD)

6. Integration of Analyses for Cancer and

Noncancer Effects

7. Margin of Exposure (MOE) Analysis

8. MOE Approach to Applying Uncertainty

Factors (UFs)

9. MOE and MOP

10. Oral Scaling Factor for Dose

Adjustment

11. Toxic Endpoints

12. Weight-of-Evidence Narrative and

Classification System

D. Noncancer

1. Benchmark Dose Methodology

2. Categorical Regression

3. Integrated Approach

4. Integrated Risk Information System

(IRIS)

5. NOAEL/LOAEL Approach

6. Nonthreshold Approach for

Noncarcinogens

7. RfD Range

8. Severity of Effects

9. Stochastic Modeling

10. Synergistic Effects

11. Target Population Adjustments

12. Uncertainty and Modifying Factors

13. Use of Less-Than-90-Day Studies in

Determining an RfD

E. Exposure Assessment

Default Intakes

1. Assumption That All of the Drinking

Water Consumed Is Contaminated at the

Criteria Level

2. Assumption That All Fish Consumed Is

Contaminated at the Criteria Level and

All Fish May Come from One Waterbody

3. Body Weight Assumptions

4. Combining Consumption Intakes and

Body Weights

5. Combining Fish Intake and Body

Weights

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66445

6. Default Drinking Water Intake Rates

7. Default Fish Intake Rates

8. Effect of Cooking on the Contaminant

Concentration

9. Inclusion of Marine Species in the

Default Rate

10. Precision of the Drinking Water

Parameter

11. Redesignation of Salmon as a Marine

Species

12. Studies on Sportfishers and

Subsistence Fishers

13. USDA Continuing Survey of Food

Intake by Individuals (CSFII)

14. Use of Uncooked or As Consumed Fish

Weight for Default Intake Rates

Relative Source Contribution (RSC)

15. Default Percentages and RSC Floor of

20% and Ceiling of 80%

16. Duplication of Fish Intake Assumptions

17. Exposure Route Differences

18. Need for an RSC Factor/Considering

Multiple Routes of Exposure

19. Use of RSC With Carcinogenic Effects

Based on Linear Low-Dose Extrapolation

20. Use of Subtraction or Percentage

Methods in RSC Apportionment

F. Bioaccumulation

1. Use of Bioaccumulation Factors (BAFs)

in General

2. Guidance for Deriving Field

Bioaccumulation Factors (BAFs)

3. Use of Biota-Sediment Accumulation

Factors (BSAFs)

4. Dissolved Organic Carbon (DOC) and

Particulate Orgain Carbon (POC)

5. Fish Lipid Content

6. Use of Food Chain Multipliers (FCMs)

7. Fish Tissue Criteria

G. Literature Cited

I. Background Information

A. What are Human Health Ambient

Water Quality Criteria?

Human health ambient water quality

criteria (AWQC) are numeric values for

pollutant concentrations in ambient

waters considered to be protective of

human health. The criteria are

developed under section 304(a) of the

Clean Water Act (CWA) and are based

solely on data and scientific judgments

on the relationship between pollutant

concentrations and environmental and

human health effects. Protective

assumptions are made regarding the

potential human exposure intakes.

These criteria do not reflect

consideration of economic impacts or

the technological feasibility of meeting

the chemical concentrations in ambient

water. Section 304(a)(1) of the CWA

requires EPA to develop and publish,

and from time to time revise, criteria for

water quality accurately reflecting the

latest scientific knowledge. The criteria

are used by States and authorized Tribes

to establish water quality standards and

ultimately provide a basis for

controlling discharges or releases of

pollutants. The criteria also provide

guidance to EPA when promulgating

Federal regulations under CWA Section

303(c) when such actions are necessary.

In 1980, we published AWQC (i.e.,

Section 304(a) criteria) for 64

pollutants/pollutant classes and

provided a methodology for deriving the

criteria. The 1980 AWQC National

Guidelines for developing human health

AWQC addressed three types of

endpoints: noncancer, cancer and

organoleptic (taste and odor) effects.

Criteria for the protection against

noncancer and cancer effects were

estimated by using risk assessmentbased procedures, including

extrapolation from animal toxicity or

human epidemiological studies. Basic

human exposure assumptions were

applied to the criterion equation. When

using cancer as the critical risk

assessment endpoint, which was

assumed not to have a threshold, the

AWQC were presented as

concentrations associated with specified

incremental lifetime risk levels. When

using noncancer effects as the critical

endpoint, the AWQC reflected an

assessment of a ‘‘no-effect’’ level, based

on an assumption of a threshold for

noncancer effects.

B. How Is the Human Health

Methodology Used?

The Methodology is used by EPA to

derive or revise its section 304(a)

criteria. It provides the detailed means

for developing the water quality criteria,

including systematic procedures for

evaluating cancer risk, noncancer health

effects, human exposure, and

bioaccumulation potential in fish. This

Methodology is also guidance for States

and authorized Tribes to help them

establish water quality criteria to protect

human health. States and authorized

Tribes must develop water quality

standards that include designated uses

and water quality criteria necessary to

support those uses.

C. Why Was the Methodology Revised?

EPA periodically revises water quality

criteria to ensure that they reflect the

latest scientific knowledge on the kind

and extent of all identifiable effects on

health and welfare that may be expected

from the presence of pollutants in any

body of water, including ground water.

Since 1980, many significant scientific

advances have occurred which prompt

revisions to the Methodology.

Specifically, advances in such key areas

as cancer and noncancer risk

assessments, exposure assessments, and

bioaccumulation make the revisions

appropriate at this time. We therefore

updated the Methodology to provide

States and authorized Tribes with the

most current procedures to reflect these

changes in risk and exposure

assessment. States and authorized

Tribes can use the Methodology to

modify their water quality criteria, as

appropriate, to ensure that their criteria

are protective of designated uses.

Another reason for these revisions is

the need to address differences in the

risk assessment and risk management

approaches used by the EPA Office of

Water for the derivation of AWQC—

under the authority of the CWA—and

Maximum Contaminant Level Goals

(MCLGs)—under the authority of the

Safe Drinking Water Act (SDWA). Three

notable differences in these revisions

include the treatment of chemicals

designated as Group C possible human

carcinogens under the 1986 Guidelines

for Carcinogen Risk Assessment

(USEPA, 1986a), the consideration of

non-water sources of exposure when

setting an AWQC or MCLG for a

noncarcinogen, and cancer risk ranges.

1. Group C Chemicals. Chemicals

classified as Group C—i.e., possible

human carcinogens’under the existing

(1986) EPA cancer classification scheme

have been typically classified as such

for any of the following reasons.

(1) Carcinogenicity has been

documented in only one test species

and/or only one cancer bioassay, and

the results do not meet the requirements

of ‘‘sufficient evidence.’’

(2) Tumor response is of marginal

statistical significance due to inadequate

design or reporting.

(3) An agent causes benign, but not

malignant, tumors and no response in a

variety of short-term tests for

mutagenicity.

(4) There are responses of marginal

statistical significance in a tissue known

to have a high or variable background

rate.

The 1986 Guidelines for Carcinogen

Risk Assessment (hereafter ‘‘1986 cancer

guidelines’’) specifically recognized the

need for flexibility with respect to

quantifying the risk of Group C agents

(USEPA, 1986a). The 1986 cancer

guidelines noted that agents judged to

be in Group C, possible human

carcinogens, may generally be regarded

as suitable for quantitative risk

assessment, but that case-by-case

judgments may be made for them.

EPA has historically treated Group C

chemicals differently under the CWA

and the SDWA. It is important to note

that the 1980 AWQC National

Guidelines for setting AWQC under the

CWA predated EPA’s carcinogen

classification system, which was

proposed in 1984 and finalized in 1986

(USEPA, 1984, 1986a). The 1980 AWQC

National Guidelines did not explicitly

66446 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

differentiate among agents with respect

to the weight of evidence for

characterizing them as likely to be

carcinogenic to humans. For all

pollutants judged as having adequate

data for quantifying carcinogenic risk—

including those now classified as Group

C—AWQC were derived based on

cancer incidence data. In the November

1980 Federal Register Notice, we

emphasized that the AWQC for

carcinogens should state that the

recommended concentration for

maximum protection of human health is

zero. At the same time, the criteria

published for specific carcinogens

presented water concentrations for these

pollutants corresponding to individual

lifetime cancer risk levels in the range

of 10¥7 to 10¥5 (ranging from one case

in a population of ten million to one

case in a population of one hundred

thousand).

In the development of national

primary drinking water regulations

under the SDWA, EPA is required to

promulgate a health-based MCLG for

each contaminant. Our policy has been

to set the MCLG at zero for chemicals

with strong evidence of carcinogenicity

associated with exposure from water.

For chemicals with limited evidence of

carcinogenicity, including many Group

C agents, the MCLG was usually

obtained using a Reference Dose (RfD)

based on its noncancer effects with the

application of an additional factor of 1

to 10. If valid noncancer data for a

Group C agent were not available to

establish an RfD, but adequate data were

available to quantify the cancer risk,

then the MCLG was based upon a

nominal lifetime excess cancer risk

calculation in the range of 10¥6 to 10¥5

(ranging from one case in a population

of one million to one case in a

population of one hundred thousand).

Even in those cases where the RfD

approach has been used for the

derivation of the MCLG for a Group C

agent, the drinking water concentrations

associated with excess cancer risks in

the range of 10¥6 to 10¥5 were also

provided for comparison.

It should also be noted that in actions

taken under the Federal Insecticide,

Fungicide, and Rodenticide Act

(FIFRA), EPA’s pesticides program has

applied both of these methods for

addressing Group C chemicals and finds

both methods (quantified ‘‘C’s’’ and

nonquantified ‘‘C’s’’) applicable on a

case-by-case basis. Unlike the drinking

water program, however, the pesticides

program does not add an extra

uncertainty factor to account for

potential carcinogenicity when using

the RfD approach.

The EPA is in the process of revising

its cancer guidelines, including its

descriptions of human carcinogenic

potential. Once final guidelines are

published, they will be the basis for

assessment under this Methodology. In

the meanwhile, the 1986 cancer

guidelines are used and extended with

principles discussed in EPA’s 1999

Guidelines for Carcinogen Risk

Assessment—Review Draft (hereafter

‘‘1999 draft revised cancer guidelines’’).

These principles arise from scientific

discoveries about cancer made in the

last 15 years and from EPA policy of

recent years supporting full

characterization of hazard and risk both

for the general population and

potentially sensitive groups such as

children. These principles are

incorporated in recent and ongoing

assessments such as the reassessment of

dioxin, consistent with the 1986 cancer

guidelines. Until final guidelines are

published, information is presented to

describe risk under both the 1986

guidelines and the 1999 draft revisions.

To bring in new science and

characterization principles, draft

revisions have weight-of-evidence

narratives for hazard characterization

that use consistent descriptive terms

(USEPA, 1999a). In order to provide

some measure of consistency in an

otherwise free-form, narrative

characterization, standard descriptors

are utilized as part of the hazard

narrative to express the conclusion

regarding the weight of evidence for

carcinogenic hazard potential. There are

five standard hazard descriptors:

‘‘carcinogenic to humans’’, ‘‘likely to be

carcinogenic to humans’’, ‘‘suggestive

evidence of carcinogenicity but not

sufficient to assess human carcinogenic

potential’’, ‘‘data are inadequate for an

assessment of human carcinogenic

potential’’, and ‘‘not likely to be

carcinogenic to humans.’’ Each standard

descriptor may be applicable to a wide

variety of data sets and weights of

evidence and are presented only in the

context of a weight-of-evidence

narrative. Furthermore, more than one

conclusion may be reached for a

pollutant. For instance, using a

descriptor in context, a narrative could

say that a pollutant is likely to be

carcinogenic by inhalation exposure and

not likely to be carcinogenic by oral

exposure.

In the 2000 Human Health

Methodology, we quantify those

pollutants considered ‘‘carcinogenic to

humans’’ or ‘‘likely to be carcinogenic to

humans.’’ In practice, even though the

terminology of the 1999 draft revised

cancer guidelines differs, this is the

approach currently used by the EPA

pesticides program.

2. Consideration of Non-water

Sources of Exposure. The 1980 AWQC

National Guidelines for setting AWQC

recommended that contributions from

non-water sources, namely air and nonfish dietary intake, be subtracted from

the Acceptable Daily Intake (ADI), thus

reducing the amount of the ADI

‘‘available’’ for water-related sources of

intake. In practice, however, when

calculating human health criteria, those

other exposures were generally not

considered because reliable data on

those exposure pathways were not

available. Consequently, the AWQC

were usually derived such that drinking

water and fish ingestion accounted for

the entire ADI (now called RfD).

Through the mid-1980s, the drinking

water program generally used a similar

‘‘subtraction’’ method in the derivation

of MCLGs, albeit inconsistently. More

recently, the drinking water program

has used a ‘‘percentage’’ method in the

derivation of MCLGs for

noncarcinogens. In this approach, the

percentage of total exposure typically

accounted for by drinking water is

applied to the RfD to determine the

maximum amount of the RfD

apportioned to drinking water reflected

by the MCLG value. This percentage is

called the relative source contribution

(RSC). In using this percentage

procedure, the drinking water program

also applies a ceiling of 80 percent of

the RfD and a floor of 20 percent of the

RfD. That is, the MCLG cannot account

for more than 80 percent of the RfD, nor

less than 20 percent of the RfD.

The drinking water program usually

takes a conservative approach to public

health by applying an RSC factor of 20

percent to the RfD when adequate

exposure data do not exist, assuming

that the major portion (80 percent) of

the total exposure comes from other

sources, such as diet.

The 2000 Human Health Methodology

includes guidance for routine

consideration of non-water sources of

exposure [both ingestion exposures (e.g.,

food) and exposures other than the oral

route (e.g., inhalation)] via an approach

called the Exposure Decision Tree. RSC

estimates will be made by EPA using

this approach, which allows for use of

either subtraction or percentage

methods, depending on chemicalspecific circumstances, within the 20 to

80 percent range described above.

3. Cancer Risk Ranges. In addition to

the different risk assessment approaches

discussed above for deriving AWQC and

MCLGs for Group C agents, there have

been different risk management

approaches by the drinking water and

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66447

ambient surface water programs on

using lifetime excess risk values when

setting health-based criteria for

carcinogens. The surface water program

historically derived AWQC for

carcinogens that generally corresponded

to lifetime excess cancer risk levels of

10¥7 to 10¥5. The drinking water

program has set MCLGs for Group C

agents based on a slightly less stringent

risk range of 10¥6 to 10¥5, while

MCLGs for chemicals with strong

evidence of carcinogenicity (that is,

classified as Group A (known) or B

(probable) human carcinogen) are set at

zero. The drinking water program is

now following the 1999 draft revised

cancer guidelines to determine the type

of low-dose extrapolation based on

mode of action.

It is also important to note that under

the drinking water program, for those

substances having an MCLG of zero,

enforceable Maximum Contaminant

Levels (MCLs) have generally been

promulgated to correspond with cancer

risk levels ranging from 10¥6 to 10¥4.

Unlike AWQC and MCLGs which are

strictly health-based criteria, MCLs are

developed with consideration given to

the costs and technological feasibility of

reducing contaminant levels in water to

meet those standards.

The 2000 Human Health Methodology

states that EPA will publish its national

304(a) water quality criteria at a 10¥6

risk level, which we consider to be

appropriate for the general population.

Again, consistent with the 1999 draft

revised cancer guidelines, there are no

more alphanumeric categories. We will

only quantify those considered

‘‘carcinogenic to humans’’ or ‘‘likely to

be carcinogenic to humans.’’ We are

increasing the degree of consistency

between the drinking water and ambient

water programs, given somewhat

different requirements of the CWA and

SDWA. We will use the same hazard

characterizations of dose-response.

B. What Specific Scientific Advances

Have Occurred Since 1980?

Since 1980, EPA risk assessment

practices have evolved significantly in

all of the major Methodology areas:

cancer and noncancer risk assessments;

exposure assessments; and

bioaccumulation. EPA first published

guidelines on cancer risk assessment in

1986. EPA published Proposed

Guidelines for Carcinogen Risk

Assessment in 1996 (hereafter ‘‘1996

proposed cancer guidelines’’; USEPA,

1996a). These were recently revised

following review by the Agency’s

Science Advisory Board (SAB) and

receipt of their comments in May 1999.

The most recent document is the July

1999 draft revised cancer guidelines

(USEPA, 1999a). The 1999 draft revised

cancer guidelines discuss the use of

mode of action (MOA) information to

support both the identification of

carcinogens and the selection of

procedures to characterize risk at low,

environmentally relevant exposure

levels. They also address the

development of new procedures to

quantify cancer risks at low doses to

replace the current default use of the

linearized multistage (LMS) model. In

noncancer risk assessment, we are

moving toward the use of the

benchmark dose (BMD) and other doseresponse methodologies in place of the

traditional NOAEL approach to estimate

an RfD concentration or other point of

departure (POD) divided by an

uncertainty factor (UF). In addition,

several risk assessment guidelines have

been published. For example, in 1986

EPA published Guidelines for

Mutagenicity Risk Assessment (USEPA,

1986b). In 1991, EPA published the

Guidelines for Developmental Toxicity

Risk Assessment (USEPA, 1991a), and

in 1996, it published the Guidelines for

Reproductive Toxicity Risk Assessment

(USEPA, 1996b). In 1998, EPA also

published the Guidelines for

Neurotoxicity Risk Assessment (USEPA,

1998a). In May 1999, EPA published the

Draft Guidance for Conducting Health

Risk Assessment of Chemical Mixtures

(USEPA, 1999b). In addition, the

Agency is developing a framework for

cumulative risk assessment, and the

Office of Pesticide Programs has

developed draft guidance for assessing

cumulative risk of common mechanism

pesticides and other substances.

In 1986, EPA made available to the

public the Integrated Risk Information

System (IRIS). IRIS is a database that

contains risk information on the cancer

and noncancer effects of chemicals. The

IRIS assessments represent EPA

scientific consensus positions across the

Agency’s program offices and regional

offices.

In exposure analysis, several new

studies have addressed water

consumption and fish tissue

consumption. These exposure studies

provide a more current and

comprehensive description of national,

regional and special population

consumption patterns that we reflected

in the 1998 Draft Water Quality Criteria

Methodology: Human Health (hereafter

‘‘1998 draft Methodology revisions’’;

USEPA, 1998c). In addition, more

formalized procedures are available to

account for human exposure to multiple

sources when setting health goals such

as AWQC that have previously

addressed only one exposure source.

The Exposure Factors Handbook was

updated in 1997 (USEPA, 1997a). In

1992, we published the revised

Guidelines for Exposure Assessment

(USEPA, 1992a), which describe general

concepts of exposure assessment,

including definitions and associated

intake rate parameters, and provide

guidance on planning and conducting

an exposure assessment. In 1986, the

Agency published the Total Exposure

Assessment Methodology (TEAM)

Study: Summary and Analysis, Volume

I, Final Report (USEPA, 1986c), which

presents a process for conducting

comprehensive evaluation of human

exposures. The Agency has recently

developed a revised relative source

contribution (RSC) policy for assessing

total human exposure to a contaminant

and apportioning the RfD among the

media of concern for use in deriving or

revising AWQC. In 1997, we developed

Guiding Principles for Monte Carlo

Analysis (USEPA, 1997b). Also in 1997,

we published the Policy for Use of

Probabilistic Analysis in Risk

Assessment (USEPA, 1997c; see http://

www.epa.gov/ncea/mcpolicy.htm). The

Monte Carlo guidance document can be

applied to exposure assessments and

risk assessments. The Agency has

moved toward the use of a

bioaccumulation factor (BAF) to reflect

the uptake of a contaminant from all

sources (e.g., ingestion, sediment) by

fish and shellfish, rather than just from

the water column as reflected by the use

of a bioconcentration factor (BCF) in the

1980 Methodology. We have developed

detailed procedures and guidelines for

estimating BAF values for use in

deriving or revising AWQC.

C. What Process Did EPA Follow in

Revising the Methodology?

We began by developing (along with

other Federal agencies, State health

organizations, Canadian health agencies,

academies, environmental and industry

groups, and consulting organizations) an

issues paper that described the 1980

Methodology, discussed areas that

needed strengthening, and

recommended revisions. The paper was

distributed for review and comment and

was examined at a national workshop,

where more than 100 participants

discussed critical issues. Based on

individual expertise, attendees were

assigned to specific technical

workgroups. The workgroups’ topics

included cancer risk, noncancer risk,

exposure, microbiology, minimum data

and bioaccumulation in fish.

A summary document based on the

workshop recommendations was

submitted for review and comment by

the EPA SAB. Once final comments and

66448 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

revisions were received from the SAB,

the recommendations were again

reviewed at a meeting of the FederalState Toxicology and Risk Analysis

Committee, where state representatives

presented their opinions on the

preliminary draft recommendations. (A

more detailed chronology of this process

was provided with the 1998 draft

Methodology revisions.)

EPA subsequently developed the 1998

draft Methodology revisions (USEPA,

1998c) and the Ambient Water Quality

Criteria Derivation Methodology Human

Health Technical Support Document

(TSD) (USEPA, 1998d) that provides

greater detail on the Methodology

guidance—including case study

examples, data tables, and other

supporting information. These were

published in the Federal Register in

August 1998. A four-month public

comment period followed. In May of

1999, a fifteen-member independent

peer review workshop was held, and a

public stakeholder meeting followed.

The 2000 Human Health Methodology

reflects, in part, the input received from

the public and peer review experts, in

addition to more recent scientific

information and science policies since

the 1998 draft publication.

F. What Are the Major Revisions to the

Methodology?

The major revisions are in four

assessment areas: Noncancer, cancer,

exposure and bioaccumulation.

Equations have been developed for

deriving AWQC, which include

parameters relevant to those four

assessment areas. These parameters are

derived from scientific analysis, science

policy and risk management decisions.

For noncarcinogens, the process for

deriving a level of exposure considered

to be without appreciable risk of effect—

known as the Reference Dose (RfD)

value—has evolved over time.

• EPA has developed guidance on

assessing noncarcinogenic effects of

chemicals and for the RfD derivation.

• The Methodology revisions

recommend consideration of other

issues related to the RfD process

including integrating reproductive/

developmental, immunotoxicity, and

neurotoxicity data into the calculation.

• EPA is recommending the use of

quantitative dose-response modeling for

the derivation of RfDs.

• EPA has provided additional

guidance (in its Risk Assessment TSD)

to allow States and authorized Tribes

greater flexibility in conducting their

own risk assessments.

For carcinogen (cancer) risk

assessment, more sophisticated methods

for determining the likely mechanism

that causes human carcinogenicity are

being recommended, as well as

consideration of all biological

information (rather than just tumor

findings) and full risk characterization

for the general population as well as

sensitive groups such as children.

Changes in the area of exposure

assessment include the following.

• States and authorized Tribes are

encouraged to use local studies on fish

consumption that better reflect local

intake patterns and choices.

• EPA will recommend default fish

consumption values for the general

population, recreational fishers and

subsistence fishers.

• A factor to account for other sources

of exposure, such as food and air, is

included when deriving AWQC for

noncarcinogens and for carcinogens

based on a nonlinear low-dose

extrapolation (i.e., water and fish

consumption are not the only exposures

considered).

The 2000 Human Health Methodology

places greater emphasis on the use of

BAFs compared to the 1980

Methodology for estimating potential

human exposure to contaminants via

the consumption of contaminated fish

and shellfish.

• BAFs reflect the accumulation of

chemicals by aquatic organisms from all

surrounding media (water, food,

sediment). Compared with BCFs, which

reflect chemical accumulation by

aquatic organisms from water only,

BAFs are considered to be better

predictors of chemical accumulation by

fish and shellfish for chemicals where

exposure from food and sediment is

important (e.g., highly persistent,

hydrophobic chemicals).

• EPA gives preference to the use of

high quality field data over laboratory or

model-derived estimates of BAFs, since

field data best reflect factors that can

affect the extent of bioaccumlation (e.g.,

chemical metabolism, food web

structure).

G. How Will EPA Use the Human Health

Methodology?

Our future role in developing AWQC

for the protection of human health will

include the following.

• Further refinement of the

Methodology as the science and EPA’s

science policies evolve;

• Development of revised AWQC for

pollutants of high priority and national

importance (including, but not limited

to chemicals that bioaccumulate, such

as PCBs, dioxin, and mercury); and

• Development or revision of AWQC

for some additional priority pollutants.

We plan to fully update the most

environmentally important criteria

developed in 1980 (or those updated as

part of the 1992 National Toxics Rule

(NTR)). Partial updates of substantially

more criteria may be warranted. We

encourage States and authorized Tribes

to use the 2000 Human Health

Methodology to develop or revise

AWQC to reflect local conditions. EPA

believes that AWQC inherently require

several risk management decisions that

are, in many cases, better made at the

State or Tribal level (e.g., selection of

specific fish consumption rates or target

risk levels). We will continue to develop

and update necessary toxicology and

exposure data needed for the derivation

of AWQC that may not be practical for

the States or Tribes to obtain. More

information on implementation issues

and the effect of the 2000 Human Health

Methodology on States and authorized

Tribes is discussed below.

II. Implementation Issues

Water quality standards consist of

designated uses, water quality criteria to

protect those uses, a policy for

antidegradation, and general policies for

application and implementation. As

part of the water quality standards

triennial review process defined in

section 303(c)(1) of the CWA, States and

authorized Tribes are responsible for

maintaining and revising water quality

standards. Section 303(c)(1) requires

States and authorized Tribes to review,

and modify if appropriate, their water

quality standards at least once every

three years.

A. How Does EPA Use Its Recommended

304(a) Water Quality Criteria?

EPA’s recommended 304(a) water

quality criteria form the basis for

Agency decisions, both regulatory and

nonregulatory, until superseded by EPA

publication of new or revised 304(a)

water quality criteria. For example,

these criteria are used in the following

ways: (1) As guidance to States and

authorized Tribes in adopting water

quality standards; (2) as guidance to

EPA in promulgating Federal water

quality standards; (3) in establishing

National Pollutant Discharge

Elimination System (NPDES) water

quality-based permit limits, where the

criteria have been adopted by a State or

authorized Tribe or promulgated by

EPA; and (4) for all other purposes of

Section 304(a) criteria under the Act. It

is important to emphasize again two

distinct purposes which are served by

the 304(a) criteria. The first is as

guidance to the States and Tribes in the

development and adoption of water

quality criteria which will protect

designated uses. The second is as the

basis for promulgation of Federal water

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66449

quality standards for States or

authorized Tribes when such action is

necessary.

B. What Water Quality Criteria Must a

State or Authorized Tribe Adopt Into Its

Water Quality Standards?

States and authorized Tribes must

adopt water quality criteria that protect

designated uses. Such criteria must be

based on sound scientific rationale and

must contain sufficient parameters or

components to protect the designated

uses. Criteria may be expressed in either

narrative or numeric form. States and

authorized Tribes have four options

when adopting water quality criteria for

which EPA has published 304(a)

criteria. They can establish numerical

values based on 304(a) criteria, 304(a)

criteria modified to reflect site-specific

conditions, other scientifically

defensible methods, or establish

narrative criteria where numeric criteria

cannot be determined. (See 40 CFR

131.11.)

EPA’s recommended 304(a) water

quality criteria for States and authorized

Tribes to use as guidance in adopting

water quality standards consistent with

Section 303(c) of the Act and the

implementing Federal regulations at 40

CFR part 131 are contained in EPA’s last

compilation of National Recommended

Water Quality Criteria (USEPA, 1998e)

(corrected in USEPA, 1999c). In the

future, we will be publishing new and

revised 304(a) water quality criteria

based upon the 2000 Human Health

Methodology for pollutants of high

priority and national importance.

Because the revision of existing 304(a)

human health criteria to reflect the 2000

Human Health Methodology will take

time, EPA encourages States and

authorized Tribes to make appropriate

changes to their existing numerical,

pollutant-specific criteria in their water

quality standards to reflect this new

Methodology prior to publication of a

revised 304(a) criteria where they

determine that such actions are

necessary. For example, a pollutant of

concern in a particular State may not be

a high priority on the national level and

revision of the national 304(a) criteria

may not occur for several years. In this

case, the State or a group of States,

might choose to use this new

Methodology to revise their water

quality standards prior to EPA

publication of a revised 304(a) criteria

for that pollutant. EPA will recognize

criteria that are revised pursuant to the

2000 Human Health Methodology as

scientifically defensible and promptly

approve such revised criteria as

enforceable elements of State or Tribal

water quality standards.

Once a new or revised 304(a) criteria

reflecting this new Methodology is

published, EPA expects States and

authorized Tribes to reassess their water

quality standards and, where necessary,

establish new or revised water quality

criteria consistent with one of the four

options described above. Because of the

critical role that human health ambient

water quality criteria play in protecting

human health, EPA will work with

States and authorized Tribes to revise

existing water quality standards

promptly following EPA publication of

revised section 304(a) criteria.

C. May States and Authorized Tribes

Adopt Water Quality Criteria Based on

Local Conditions?

In keeping with their primary

responsibility in establishing water

quality standards, we encourage States

and authorized Tribes to develop and

adopt water quality criteria to reflect

local and regional conditions. States and

authorized Tribes will have access to

EPA regional, laboratory, and

headquarters staff when help is needed

to interpret today’s Human Health

Methodology and to make critical risk

assessment decisions. For the purpose

of deriving criteria based on the 2000

Human Health Methodology, EPA is

publishing default values for risk level,

fish intake, drinking water intake, and

body weight. Default BAF values and

RSC factor values will be published as

chemical-specific criteria are developed

or revised. (Other RSC estimates will be

made when data are adequate to make

them.) We believe these default values

result in water quality criteria protective

of the general population, and we will

use these values when deriving 304(a)

criteria. States and authorized Tribes

may use other values more

representative of local conditions if data

have been collected supporting the

alternative values. However, when

establishing a numerical value based on

a 304(a) criterion modified to reflect

site-specific conditions, or water quality

criteria based on other scientifically

defensible methods, we strongly caution

States and authorized Tribes not to

selectively apply data in order to ensure

water quality criteria less stringent than

EPA’s 304(a) criteria. Such an approach

would inaccurately characterize risk.

D. What Cancer Risk Level Should

States and Authorized Tribes Use When

Establishing Water Quality Criteria?

In deriving 304(a) criteria based on

the 2000 Human Health Methodology or

when promulgating Federal water

quality standards under section 303(c)

of the CWA, EPA intends to use a 10¥61

cancer risk level, which we believe

reflects an appropriate target risk level

for the general population. EPA

acknowledges that at any given cancer

risk level for the general population,

those segments of the population that

are more highly exposed face a higher

relative risk. For example, if fish are

contaminated at a level allowed by

criteria derived on the basis of a risk

level of 10¥6, individuals consuming up

to 10 times the assumed fish

consumption rate would still be

protected at a 10¥5 risk level. States and

authorized Tribes have the flexibility to

adopt water quality criteria that result in

a risk level higher than 10¥6, up to the

10¥5 level. EPA recommends adoption

of such criteria if the State or Tribe has

identified the most highly exposed

subpopulation within the State or Tribe,

has demonstrated that the chosen cancer

risk level is protective of the most

highly exposed subpopulations, and has

completed all necessary public

participation. EPA notes that special

scientific circumstances and assessment

of natural contaminants may lead to

numbers outside the 10¥6 to 10¥5 risk

range. (For additional discussion on this

issue, including restrictions on selection

of a cancer risk level, refer to the

response on the comment for cancer risk

ranges summarized in Section III of this

Notice, below.)

E. How Does the Review and Approval

of State and Tribal Water Quality

Standards Rule Affect Water Quality

Criteria Adopted by States and

Authorized Tribes?

Consistent with the Review and

Approval of State and Tribal Water

Quality Standards rule revision

(USEPA, 2000a), water quality criteria

adopted into law or regulation by States

and authorized Tribes prior to May 30,

2000, are in effect for CWA purposes

unless superseded by replacement

Federal water quality standards (see, for

example, the National Toxics Rule, 40

CFR 131.35; Water Quality Standards

for Idaho, 40 CFR 131.35). Water quality

criteria adopted into law or regulation

by States and authorized Tribes after

May 30, 2000, are in effect for CWA

purposes only after EPA approval of any

new or revised water quality standards.

F. While EPA is Re-Evaluating a 304(a)

Criterion, What Criterion Is in Effect?

Until such time as EPA reevaluates

the 304(a) criteria, subjects the criteria

to appropriate peer review, and

subsequently publishes revised 304(a)

criteria, the existing 304(a) criteria

remain in effect for the purposes of EPA

review of State and Tribal water quality

standards under section 303(c). Where

EPA has not published a revision of a

66450 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

1New criteria and criteria revised under this new

Methodology are published annually as the

‘‘Compilation of National Recommended Water

Quality Criteria and EPA’s Process for Deriving

New and Revised Criteria’’ at www.epa.gov/ost/

standards/.

304(a) criteria reflecting the 2000

Human Health Methodology, EPA will

not require the revision of State water

quality standards to reflect this new

Methodology. As noted above, however,

EPA will assist those States or Tribes

that choose to use the new Methodology

to revise their existing water quality

standards prior to publication of a

revised criteria under section 304(a).

G. What Design Stream Flow Should Be

Used to Implement Human Health

Criteria?

Human health criteria represent

ambient pollutant concentrations that

are acceptable based on a lifetime (70

years) of exposure. Accordingly,

discharges of pollutants should be

regulated such that criteria will not be

exceeded under stream conditions that

represent long-term average conditions.

Current EPA guidance recommends the

use of the long-term harmonic mean

flow to implement criteria for

carcinogens and the 30Q5 flow to

implement criteria for noncarcinogens

(USEPA, 1991b). The harmonic mean

flow is the sum of the reciprocals of

individual flow measurements divided

into the total number of individual flow

measurements, and the 30Q5 flow is

defined by the lowest 30-day average

that has an expected return frequency of

once every five years. With today’s

Human Health Methodology, EPA is

revising its guidance to recommend

harmonic mean flow be used to

implement both carcinogen and

noncarcinogen human health criteria.

Harmonic mean flow should be used to

implement human health criteria

because, by and large, human health

criteria are designed to protect an

individual over a lifetime of exposure.

As stated in the 1998 draft Methodology

revisions, we are not recommending the

development of additional water quality

criteria similar to the drinking water

health advisories that focus on acute or

short-term effects. These are not seen as

routinely having a meaningful role in

the water quality criteria and standards

program because the chronic health

effects associated with chemical

contaminants are usually the most

sensitive health endpoint. Human

health criteria based on cancer

potencies and risk levels are based on

models that extrapolate animal data to

a human lifetime. Similarly, a human

noncancer criterion is based on an RfD,

which is an acceptable daily exposure

over a lifetime. Therefore, we have

attempted to match the longest stream

flow averaging period (using harmonic

mean) with the criterion which is

protective over a human lifetime.

In rare instances where a human

health criterion or value is based on a

short-term toxicological effect (i.e., the

critical effect upon which the criterion/

value is based is significantly less than

lifetime and may be an acute effect), the

design flow should be adjusted

accordingly. This does not pertain to

RfDs in which a short-term study has

been used as the RfD basis and an

uncertainty factor has been used to

account for less than lifetime study

results; that is, the short-term study has

been used to estimate a lifetime RfD

value. This pertains only to those

situations where the critical effect is a

short-term effect (and where no

additional uncertainty factor has been

used to account for less than lifetime

exposure). A good example of this is

EPA’s RfD for nitrate. The critical effect,

upon which the RfD is based, is toxicity

to infants after a short-term exposure. In

this case, harmonic mean flow would be

an inappropriate design flow for such a

short-term effect. In this case, a 7Q10 or

a 4Q3 design flow may be more

appropriate.

H. What Is the Relationship Between the

Agency’s Recommended Section 304(a)

Water Quality Criteria and Drinking

Water Standards?

EPA recommends that States and

authorized Tribes use this 2000 Human

Health Methodology to develop their

own AWQC for all pollutants of concern

using the latest scientifically defensible

data and principles. Sources of

scientifically defensible data include

published toxicological literature or

recent EPA assessments, including those

that underlie IRIS values, the most

recently published recommended

Section 304(a) water quality criteria or

the most recently promulgated SDWA

MCLGs.

When adopting water quality criteria

to protect CWA Section 101(a) fishable

uses, States and authorized Tribes need

to ensure such criteria adequately

address fish consumption as an

exposure route.

When States and authorized Tribes do

not develop their own AWQC, EPA

recommends that States and authorized

Tribes use the most recently published

recommended Section 304(a) water

quality criteria for ‘‘water and

organisms’’ based on this new Human

Health Methodology to protect CWA

Section 101(a) fishable uses and waters

designated for drinking water. This

ensures that the water quality criteria

adequately address fish consumption,

bioaccumulation and drinking water

uses.

When EPA publishes the annual

compilation of new and revised national

recommended Section 304(a) water

quality criteria, those criteria represent

the Agency’s most current

recommended Section 304(a) water

quality criteria and should be used by

States and authorized Tribes when

reviewing their water quality standards.

When States and authorized Tribes do

not develop their own AWQC, and there

are no recommended Section 304(a)

water quality criteria for a pollutant of

concern, or the recommended Section

304(a) water quality criteria have not yet

been revised based on this new Human

Health Methodology 1:

1. For a pollutant for which EPA has

published a recommended Section

304(a) water quality criterion for ‘‘water

and organisms’’ based on the 1980

Methodology and for which EPA has not

promulgated an MCLG, EPA will

recognize the current Section 304(a)

water quality criterion, or a criterion

that is developed or revised pursuant to

the 2000 Human Health Methodology

and approved by EPA.

2. For a pollutant for which EPA has

published a recommended Section

304(a) water quality criterion for ‘‘water

and organisms’’ based on the 1980

Methodology and for which EPA has

more recently promulgated an MCLG,

EPA generally recommends the MCLG

for noncarcinogenic pollutants, or a

criterion derived by recalculating the

MCLG at an acceptable cancer risk level

(i.e., a level within the range of 10¥6 to

10¥5, as specifically discussed in

Section II.D, which notes that special

scientific circumstances and assessment

of natural contaminants may lead to

numbers outside the to 10¥6 to 10¥5

risk range).

3. For a pollutant for which EPA has

not published a recommended Section

304(a) water quality criterion for ‘‘water

and organisms’’ and for which EPA has

promulgated an MCLG, EPA generally

recommends the MCLG for

noncarcinogenic pollutants, or a

criterion derived by recalculating the

MCLG at an acceptable cancer risk level

(i.e., a level within the range of 10¥6 to

10¥5, as specifically discussed in

Section II.D, which notes that special

scientific circumstances and assessment

of natural contaminants may lead to

numbers outside the 10¥6 to 10¥5 risk

range).

EPA no longer recommends that an

MCL be used where consideration of

available treatment technology, costs, or

availability of analytical methodologies

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66451

has resulted in an MCL that is less

protective than an MCLG.

States and authorized Tribes continue

to have the flexibility to adopt water

quality criteria that are more protective

than EPA’s recommendations, as long as

such criteria are protective of the

designated uses and scientifically

defensible.

I. How Are Health Risks to Children

Considered in the Methodology?

In recognition that children have a

special vulnerability to many toxic

substances, EPA’s Administrator

directed the Agency in 1995 to

explicitly and consistently take into

account environmental health risks to

infants and children in all risk

assessments, risk characterizations and

public health standards set for the

United States. On April 21, 1997,

President Clinton signed Executive

Order 13045, ‘‘Protection of Children

From Environmental Health Risks and

Safety Risks,’’ which assigned a high

priority to addressing risks to children.

In May 1997, EPA established the Office

of Children’s Health Protection to

ensure the implementation of the

President’s Executive Order (E.O.).

Circumstances where risks to children

should be considered in the context of

the 2000 Human Health Methodology

are discussed in the Noncancer Section

(in terms of developmental and

reproductive toxicity) and in the

Exposure Section (for appropriate

exposure intake parameters).

All of EPA’s risk assessment

guidelines should be consulted when

conducting a risk assessment to ensure

that information from studies on

carcinogenesis and other health effects

are considered together in the overall

characterization of risk. This is

particularly important in the case in

which a precursor effect to tumor is also

a precursor or endpoint of other health

effects and is used in dose-response

assessment. The overall characterization

of risk will be the basis for carrying out

assessments of instances in which

fetuses, infants, or children are at risk.

III. Summary of Comments Received on

the 1998 Draft Methodology Revisions

and EPA’s Responses

A. Implementation

1. Application of Human Health Water

Criteria Within Mixing Zones

Comments—Commenters stated that

human health criteria should start with

the local relevant fish consumption

rates and then make adjustments to

reflect the actual relevant fish

consumption rate related to the

discharge and the mixing zone. It was

also suggested that implementation in

the NPDES program inherently needs a

translator mechanism to adjust the

standards to reflect actual consumption

associated with allowed mixing zones.

Response—Application of human

health water criteria within a mixing

zone is not within the scope of this

Methodology. At this time, EPA’s

current recommendations regarding the

application of human health criteria

within mixing zones are contained in

the Technical Support Document for

Water Quality-Based Toxics Control

(USEPA, 1991b) and the Water Quality

Standards Handbook (USEPA, 1994).

We also note that mixing zones are an

optional policy that not every State and

authorized Tribe has adopted into their

water quality standards. For States and

Tribes that have authorized mixing

zones, the designated uses of a

waterbody as a whole must be

maintained and protected.

2. Application of Human Health Water

Quality Criteria to Marine Waters

Comment—A question was raised as

to whether human health water quality

criteria are applicable to marine waters,

given the vastness of most marine

waters.

Response—EPA believes human

health water quality criteria should be

applied to near-shore waters

(specifically within a three-mile limit)

wherever dischargers are located to

protect aquatic food organisms, but not

to include the drinking water

consumption parameter. These water

quality criteria are then used to derive

permit limits that will ensure water

quality criteria are not exceeded within

the vicinity of an outfall. This protects

organisms that are sessile and other

organisms that may be attracted to the

effluent and that are food sources. In the

absence of data specific to the coastal

site indicating that particular marine

species are impacted by those

discharges, we recommend our human

health criteria to protect coastal waters.

[Note: EPA’s recommended national

default fish intake value, which

excludes marine species, supports this

position. Estuarine species that are more

likely to be found in near-shore waters

are included in the default intake value.

Potential exposure from open-ocean

marine species are not ignored; the

marine species exposure pathway can

be accounted for as part of the RSC

factor.]

3. Cancer Risk Range

Comments—Many comments were

received on the appropriateness of the

cancer risk range. Numerous

commenters stated that the permissible

range and recommended default of 10¥6

are appropriate and approved of the

range’s consistency with other Agency

programs. EPA was asked to reconcile

the statements that both 10¥6 and 10¥5

are acceptable for the general

population, that 10¥6 is appropriate for

promulgation of Federal water quality

standards under Section 303(c) given

that we have said 10¥5 is appropriate

for the Great Lakes, and that a 10¥5 risk

level along with a 17.8 g/day fish intake

assumption will protect the highest

consumers at a 10¥4 risk level. Other

comments are listed as follows.

• The Methodology should use a

10¥5 risk level.

• 10¥6 represents a change in the

acceptable risk level.

• The 10¥6 risk level represents a

binding regulatory constraint that will

provide no State flexibility.

• 10¥5 is used by most States, and

EPA should retain this default because

the Agency has not determined that it is

inadequate.

• A range of 10¥4 to 10¥5 is

advocated.

In addition, we received comments

that allowing highly exposed groups to

potentially experience cancer risks an

order of magnitude higher than the

general population is unjust and

disregards Native American treaty

rights. A commenter supported the idea

that a 10¥4 risk level can be protective

and believed highly exposed

populations are few in number. Another

stated that the cancer risk range should

apply to total contaminants (i.e., a

cumulative cancer risk ceiling). It was

cautioned that the concept of relative

risk could result in selection of

inappropriate target populations and

intake rates. Others agreed that States

and authorized Tribes should have the

flexibility to select cancer risk levels as

risk management decisions and

requested that EPA explicitly state that

it will support risk levels chosen by a

Tribal authority, while another

requested the flexibility without

requiring involved demonstrations

specific to the subpopulation at issue. A

commenter recommended changes in

EPA’s Methodology to ensure that the

resulting water quality criteria are more

applicable to exposed populations.

Others asked EPA to indicate the

percentile of the exposed population

that would meet the 10¥6 risk level.

Response—With the 1980

Methodology, EPA presented three

separate 304(a) criteria for carcinogens

at risk levels corresponding to 10¥7,

10¥6, and 10¥5 for States and

authorized Tribes to choose from.

However, the 10¥7 risk level has not

been used by any State or authorized

66452 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

Tribe when adopting water quality

standards. Furthermore, since that time,

EPA’s guidance and regulatory actions

have utilized a 10¥6 risk level as an

appropriate target risk for the general

population.

With the 2000 Human Health

Methodology, our position is that both

10¥6 and 10¥5 are appropriate targets

for health protection of the general

population and that highly exposed

populations should not exceed a 10¥4

risk level. We also note that special

scientific circumstances and assessment

of natural contaminants may lead to

numbers outside the 10¥6 to 10¥5

range. However, we are not

automatically assuming that 10¥5 will

protect ‘‘the highest consumers’’ at the

10¥4 risk level. One commenter referred

to specific data indicating high intake

levels that would not satisfy such an

assumption. Nor are we advocating that

States and authorized Tribes

automatically establish criteria based on

assumptions for highly exposed

population groups at the 10¥4 risk level.

We acknowledge that fish consumption

rates vary considerably, especially

among subsistence populations, as is

evident from the studies summarized in

the Exposure TSD. Indeed, it is the

variation of fish consumption among

these population groups that could

make either 10¥5 or 10¥6 protective of

those groups at a 10¥4 risk level.

Specifically, if a State adopted a

criterion based on a 10¥5 risk level and

a 17.5 g/day consumption rate, a highend subsistence consumption of 1,750

g/day would exceed a 10¥4 risk level.

It is important to understand that

criteria for carcinogens are based on

chosen risk levels that inherently

reflect, in part, the exposure parameters

used to derive those values. Therefore,

changing the exposure parameters will

also change the risk. Specifically, the

incremental cancer risk levels are

relative, meaning that any given

criterion associated with a particular

cancer risk level is also associated with

specific exposure parameter

assumptions (i.e., intake rates, body

weights). When these exposure values

change, so does the relative risk. As we

have previously indicated for a criterion

derived on the basis of a cancer risk

level of 10¥6, individuals consuming up

to 10 times the assumed fish intake rate

would not exceed a 10¥5 risk level.

Similarly, individuals consuming up to

100 times the assumed rate would not

exceed a 10¥4 risk level. Thus, for a

criterion based on EPA’s default fish

intake rate (now 17.5 g/day, based on

the most recent survey data) and a risk

level of 10¥6, those consuming a pound

of fish per day would potentially

experience between a 10¥5 and a 10¥4

risk level (closer to a 10¥5 risk level).

Even if a criterion were based on highend intake rates and the relative risk of

10¥6, then an average fish consumer

would not exceed a cancer risk level of

approximately 10¥8. The point here is

that the risks for different population

groups are not the same.

EPA believes that the adoption of a

10¥6 or 10¥5 target risk level, both of

which States and authorized Tribes

have historically chosen, represents a

generally acceptable health protection

decision, noting again that special

scientific circumstances or assessments

of natural contaminants may necessitate

additional considerations. EPA

recommends adoption of water quality

standards that include water quality

criteria based on either the 10¥5 or 10¥6

risk level if the State or authorized Tribe

has identified the most highly exposed

subpopulation, has demonstrated that

the chosen risk level is adequately

protective of the most highly exposed

subpopulation, and has completed all

necessary public participation. States

and authorized Tribes also have

flexibility in how they demonstrate this

protectiveness and obtain such

information. A State or authorized Tribe

may use existing information as well as

collect new information in making its

determination as to an appropriate level

of protection. In addition, if a State or

authorized Tribe does not believe that

the 10¥6 risk level adequately protects

highly exposed subpopulations, water

quality criteria based on a more

stringent risk level may be adopted.

However, we are now adding that a

generally specific analysis should be

made and presented to ensure that

highly exposed groups do not exceed a

target 10¥4 risk level. In cases where

fish consumption among highly exposed

population groups is of a magnitude that

such a 10¥4 risk level would be

exceeded, a more protective risk level

should be chosen. These determinations

should be made by the State or

authorized Tribe and are subject to

EPA’s review under Section 303 of the

CWA. Guidance on choosing

appropriate exposure parameters is

discussed in both the 2000 Human

Health Methodology and the Exposure

Assessment TSD.

Given the relatively significant

variation in fish consumption rates, EPA

intends to derive Section 304(a) criteria

at the 10¥6 risk level, based on an

intake rate of 17.5 g/day. We believe

that basing our 304(a) criteria on general

U.S. population exposures is most

appropriate, given their use as a default

value for the nation as a whole. Most

States have, in fact, already adopted a

10¥6 risk level with their criteria for

carcinogens, not the 10¥5 risk level

claimed by one commenter. This default

would, in turn, be protective for fish

intakes of up to 1,750 g/day at the 10¥4

risk level. However, in the Exposure

Assessment TSD, EPA has

recommended that States and

authorized Tribes give priority to

identifying and adequately protecting

the most highly exposed population by

adopting more stringent criteria, if the

State or authorized Tribe determines

that the highly exposed population

would not be adequately protected by

criteria based on protecting the general

population. States and authorized

Tribes have the option to derive their

criteria at a 10¥6 risk level, as EPA will

do with its 304(a) criteria. They also

have the flexibility to combine the 10¥6

risk level with fish consumption rates

for highly exposed population groups.

Thus, States and authorized Tribes may

choose to adopt criteria that are more

protective than EPA’s 304(a) criteria. We

intend to support the health protection

decisions made by States and

authorized Tribes as long as they use the

risk range that EPA has stated here and

in the 2000 Human Health

Methodology. EPA has made reasonable

and conservative assumptions in

choosing exposure parameters with the

goal of protecting the majority of the

population. However, we do not believe

it is possible to calculate the exact

percentile of the population that would

be protected at a given risk level in

terms of the overall combination of

exposure parameters. We emphasize

that the criteria are derived to be

protective, not predictive of an exact

percentile of the total population that is

protected.

Regarding the use of a 10¥5 risk level

in the Great Lakes Water Quality

Initiative (GLI), the criteria values were

based on fish consumption estimates

that reflected intake data among

sportfishers, a group that consumes

more fish than the general population.

Again, we recommend that States and

authorized Tribes base their criteria on

more highly exposed population groups,

if they would not be adequately

protected by criteria based on intake

rate estimates for the general

population. Regarding the application of

a cumulative cancer ceiling, the

commenter has misunderstood EPA’s

policy when setting 304(a) criteria for

carcinogenic effects based on linear lowdose extrapolation. With these

carcinogens, the AWQC are set with

respect to the incremental lifetime risk

posed by the substance in water and are

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66453

not being set on an individual’s total

cancer risk from all sources of exposure.

4. Coordinating the Human Health

Methodology With Other EPA Programs

Comments—Numerous commenters

recommended that the Methodology

revisions be coordinated with the

drinking water program (specifically,

MCLs/MCLGs required under the

SDWA) and believed that the drinking

water portion of AWQC and MCLGs

should be equivalent. Several

commenters stated that the burden of

achieving health goals should be borne

by dischargers and other polluters, not

by water users or the environment.

Commenters also recommended that

EPA use MCLs when AWQC are less

protective or for chemicals when AWQC

do not exist. Another recommended that

an additional margin of safety be

included if the MCL were used, in

particular for chemicals not effectively

removed by conventional drinking

water treatment, and also stated that

neither the availability of MCLs or

MCLGs should deter development of

AWQC. Some commenters believed that

the use of an MCLG is an acceptable

alternative for chemicals of drinking

water concern because, like the AWQC,

it is a health-based value. However,

others recommended that MCLGs not be

used when they are more stringent than

AWQC because they are not regulatory

standards. Two commenters stated that

EPA should not abandon its policy of

setting AWQC for carcinogens at zero

for ‘‘maximum protection of human

health’’ and recommended that the

‘‘Group C’’ chemicals also have AWQC

set at zero (referring to non-zero MCLs

as inconsistent with the intent of a zero

MCLG). However, other commenters

recommended that AWQC be set at onehalf of the MCL when the MCLG is zero,

at a 10¥6 risk level, or by calculating

both and choosing the lower of the two.

Two commenters urged EPA to unify

the national Human Health

Methodology with the GLI guidance.

Another discussed microbial pathogens

and, in addition to recommending

development of criteria for specific

microbial contaminants, recommended

coordination with the drinking water

program [i.e., the SDWA’s Candidate

Chemical List (CCL)] and stated that

microbial criteria need to be set for more

than recreational waters.

Response—EPA intends to continue

deriving AWQC that include a drinking

water pathway, applicable to waters that

are potential sources of drinking water,

and agrees that the drinking water

component of AWQC should be

consistent with the MCLG (if one has

been established). Therefore, we intend

to use a similar methodology for

deriving AWQC and MCLGs. We also

intend to coordinate with the Agency’s

safe drinking water program when

prioritizing chemicals for AWQC

derivation/revision (see also response to

Comment A.11, Proposed Chemical

List). Regarding the relationship

between AWQC and the drinking water

MCLs and MCLGs, we have clearly

stated our position in the Federal

Register Notice for the 1998 draft

Methodology revisions (USEPA, 1998c)

on this relationship and our approach to

considering when an MCL or MCLG

may be appropriate to use in lieu of

AWQC. That discussion is excerpted in

the 2000 Human Health Methodology

document, along with clarification of

our policy on the circumstances and

limitations under which either should

be used. We do not necessarily assume

that a chemical’s concentrations in

ambient waters and drinking water are

equivalent but are aware that chemicals

may not be effectively removed by

conventional drinking water treatment.

Commenters who referred to EPA’s

abandonment of its policy of setting

AWQC for carcinogens at zero have

substantively misstated our policy based

on both the 1980 Methodology for

deriving AWQC and our 1998 draft

Methodology revisions, and are directed

to the Federal Register Notice cited

above. We did state in our 1980

Methodology that for the maximum

protection of human health from

potential carcinogenic effects, the

ambient water concentration should be

zero, based on an assumption of a linear

dose-response relationship at low doses.

The 1980 Methodology also indicated

that zero levels may not have been

attainable at that time. This remains the

case at present. The combination of

background levels of carcinogens from

natural sources and global background

levels from anthropogenic sources make

attainment of zero levels for many

potential carcinogens impossible. In

addition, more recent and sophisticated

toxicological information on

carcinogenicity suggests modes of action

for carcinogens that would lead to

nonlinear low-dose extrapolation. Note

that the 1980 Methodology preceded the

Agency’s original 1986 cancer

guidelines, which are now being

revised. We are maintaining our policy

to derive AWQC for carcinogens to

correspond to incremental lifetime

cancer risk levels, applying a risk

management policy that ensures a

reasonable level of protection for the

general population.

When EPA developed the

methodology to derive human health

criteria for the waters of the Great Lakes

System, the Agency was mindful of the

need for consistency with the planned

changes in the Human Health

Methodology presented today for

deriving national AWQC for the

protection of human health. Throughout

the 1998 draft Methodology revisions,

references were made to comparisons of

the two methodologies, especially

whenever differences occur due to

regional exposure assumptions made for

the Great Lakes System. The GLI

guidance consisted of water quality

criteria, detailed methodologies to

develop criteria for additional

pollutants, implementation procedures,

and antidegradation policies and

procedures tailored to the Great Lakes

system; these reflected the unique

nature of the Great Lakes ecosystem.

Those States and authorized Tribes are

to use the GLI methodology to establish

criteria for the waters of the Great Lakes

system, which allows appropriate

flexibility to States and authorized

Tribes to develop equitable strategies to

control pollution sources and to

promote pollution prevention practices.

The 2000 Human Health Methodology is

undertaken pursuant to Section 304 of

the CWA, and is independent of, and

does not supersede, the GLI. Although

consistency in State water quality

standards programs is an important goal

for EPA, we also recognize that it is

necessary to provide appropriate

flexibility to States and Tribes, both

Great Lakes States and non-Great Lakes

States, in the development and

implementation of place-based water

quality programs. Recognition of a

general need for flexibility is not

incompatible with the requirements for

the Great Lakes States and Tribes

established in Section 118(c)(2) of the

CWA. We have harmonized the two,

where appropriate, while maintaining

parameters and provisions that are

appropriate for Great Lakes-specific

criteria.

EPA has identified development of

microbial water quality criteria as part

of its strategy to control waterborne

microbial disease, by controlling

pathogens in waterbodies and by

protecting designated uses, such as

recreation and public water supplies.

The program fosters an integrated

approach in order to protect both

ground-water and surface water sources.

EPA plans to conduct additional

monitoring for Cryptosporidium parvum

and Escherichia coli, and determine

action plans in accordance with the

results of this monitoring.

5. Designated Uses

Comments—Commenters indicated

that designated uses for waterbodies

66454 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

that cross State boundaries and that fail

to take into account downstream uses

may effectively prohibit downstream

waters from being used as a water

supply; the AWQC should reflect the

use of a waterbody as a drinking water

source unless the use patterns of the

entire waterbody indicate that this is not

a current or future possibility.

Response—EPA regulations at 40 CFR

131.10(b) state:

In designating uses of a water body and the

appropriate criteria for those uses, the State

shall take into consideration the water

quality standards of downstream waters and

shall ensure that its water quality standards

provide for the attainment and maintenance

of the water quality standards of downstream

waters.

We believe this requirement is sufficient

to address the concerns raised by the

commenter and to ensure downstream

uses are maintained and protected.

6. Developing National 304(a) Criteria

Comments—Commenters stated that

EPA should not derive national 304(a)

AWQC and stated their preference for

regional measurements, and that

national 304(a) criteria could be overly

stringent or underprotective from State

to State. Instead, they recommended

that EPA simply provide specific

‘‘algorithms’’ to force States to develop

their own criteria. However, they also

said that EPA should develop a single

criterion for each chemical based on the

most relevant toxic endpoint and

appropriate target population. A

commenter recommended that EPA

develop criteria for both cancer and

noncancer endpoints because their

comparative protectiveness may not be

clear until permit limit design flows are

determined. Another commenter stated

that relying on default parameter values

would inhibit the process for

developing criteria/implementing

standards because the regulated

community will not accept such criteria.

Two commenters stated that the amount

of information on adverse impacts to

water quality, fish, birds, wildlife, and

human health warrants regulatory

action to eliminate those toxicants. They

recommended that EPA include all

biotic pathways using the water source,

including wildlife and plant life, and

advocated protecting cultural and

religious uses. A commenter stated that

limited information exists for

development of criteria in arid regions

and that resources would be better spent

gaining knowledge on the impacts of

chemicals in regional watersheds.

Another questioned how AWQC can be

derived when ambient levels are below

analytical detection limits. Several

commenters supported the derivation of

fish tissue criteria.

Response—Section 304(a) of the CWA

requires EPA to develop national water

quality criteria recommendations for

States and authorized Tribes to use as

guidance in adopting water quality

standards. It is not an option for EPA to

ignore this requirement. As such, the

national 304(a) criteria that EPA

periodically publishes are generally

applicable to the nation’s waters.

Although we encourage States and

authorized Tribes to use the

Methodology to develop criteria based

on local/regional information and

believe that water quality criteria

reflecting such local conditions are

desirable, we have not abandoned our

obligations under the CWA. The

commenter should be aware that States

have adopted EPA’s recommended

304(a) criteria. Furthermore, in contrast

to another commenter’s suggestion,

under the CWA, 304(a) criteria are not

enforceable regulations; these criteria

are guidance and do not impose legally

binding requirements.

States and Tribes always have the

option to undertake their own

evaluations to develop water quality

criteria, as long as such criteria are

consistent with the CWA and the

implementing Federal regulations.

States have derived water quality

criteria for their waters in the absence

of EPA guidance and may continue to

do so. However, the recommended

criteria serve as guidance to States and

authorized Tribes, and EPA cannot force

States or Tribes to conduct their own

evaluations. We are well aware that the

resources and expertise within States

and Tribal authorities vary greatly and,

while encouraging them to pursue their

own criteria development programs, we

anticipate that many will continue to

rely on our expertise and recommended

304(a) criteria. We included guidance

on site-specific modifications for States

and authorized Tribes to derive their

own water quality criteria and will

expand this information as part of the

TSD volumes for the 2000 Human

Health Methodology.

Although we have provided

numerous default parameter values for

different population groups, we intend

to derive or revise AWQC based on the

most sensitive health endpoint and the

population group most relevant for that

endpoint. Regarding measurable levels

of chemicals in the water column, the

CWA clearly states that limitations in

analytical methods will not be

considered when deriving AWQC.

Rather, the AWQC represent healthbased considerations only. However,

analytical method limitations are taken

into account in the implementation of

water quality standards. We believe that

deriving AWQC based on fish tissue

concentrations may be appropriate in

some instances to overcome this

problem when there is a health concern

for that chemical (for greater discussion

of fish tissue criteria, see response to

Comment F.7). Regarding cancer versus

noncancer endpoints, it is EPA policy to

develop criteria for the most sensitive

endpoint in order to be protective of

both potentially relevant cancer and

noncancer effects. EPA intends to

continue this practice. Regarding design

flows, see the response on this issue

under Comment A.9. Finally, these

Methodology revisions apply to the

protection of human health only. Other

EPA efforts to develop methods and

criteria for the protection of birds or

other wildlife are not part of this

guidance and will not be addressed

here. Considerations such as religious or

cultural uses cannot be quantitatively

factored into the AWQC equation for

setting pollutant criteria values.

7. Developing Organoleptic Criteria

Comments—Commenters suggested

that EPA should provide guidance for

States to develop organoleptic criteria

for ambient waters that are sources of

drinking water, and develop specific

organoleptic criteria. Taste and odor are

strongly associated with consumer

perceptions and confidence in water

quality. They suggested that EPA should

provide organoleptic criteria and allow

States to make decisions about their use.

Others stated that organoleptic criteria

should not be developed because they

are not relevant to protection of human

health and because they should only be

considered for drinking water standards.

Response—The 2000 Human Health

Methodology is focused on deriving

toxicity-based criteria because they, not

organoleptic criteria, are directly related

to potential adverse human health

effects. We have received much support

for our position on this issue since

initiating the Methodology revisions.

EPA acknowledges that if organoleptic

effects (i.e., objectionable taste and

odor) cause people to reject the water

and its designated uses, then the public

is effectively deprived of the natural

resource. EPA encourages the

development of organoleptic criteria

when States and Tribes believe they are

needed to protect designated uses and

have indicated this in the 2000 Human

Health Methodology.

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66455

8. Establishing EPA’s Most Recent

Federally Recommended Water Quality

Criteria

Comment—A commenter stated that

the proposed California Toxics Rule

(CTR) established EPA’s most recent

federally recommended water quality

criteria, and because EPA did not

propose to promulgate arsenic in the

CTR, there is no federally recommended

water quality criterion for arsenic.

Response—With regard to arsenic and

the Agency’s policy on applicable 304(a)

criteria, EPA clearly stated in the 1998

draft Methodology revisions that until

such time as the Agency re-evaluates a

chemical and subsequently publishes

revised chemical-specific 304(a) criteria,

the existing criteria remain in effect.

Although the 2000 Human Health

Methodology represents improvements

to the 1980 Methodology, EPA believes

that the existing 304(a) criteria are

fundamentally sound from a scientific

standpoint. We have long supported this

position. Our recommended water

quality criterion for arsenic remains the

value published in EPA’s Goldbook in

1986 (USEPA, 1986d) and promulgated

in 1992 as part of the NTR. Federal

promulgations for individual States take

into account the needs of the individual

State and site-specific conditions of

waterbodies within the State. Federally

promulgated water quality standards for

a State may not always result in water

quality criteria that are nationally

applicable. We understand there has

been some confusion regarding the

current recommended water quality

criteria in light of State-specific

promulgations, and as a result, in 1998,

we published National Recommended

Water Quality Criteria (USEPA, 1998b)

to clarify our national

recommendations. This list will be

updated approximately on an annual

basis to contain our most current

recommended water quality criteria for

States and authorized Tribes to use as

guidance in adopting water quality

standards.

9. Flows

Comment—Comments received

suggested that EPA should adequately

consider and account for regional

differences, such as highly variable

flows, lower exposures, and lack of fish

habitat due to no-flow conditions in

many Southwestern washes (i.e.,

waterbody flow only following a storm

event).

Response—EPA believes there is

sufficient flexibility in the current

regulatory program for States to modify

designated uses and water quality

criteria to protect those uses to address

the conditions that exist in waterbodies

such as intermittent streams and

washes. Modifications to the water

quality standards program are

unwarranted at this time.

10. Implementation on a Waterbody

Basis

Comment—Commenters stated that

human health criteria should be met

within the waterbody on a long-term

average basis instead of short-term

maximums never to be exceeded. It was

recommended that States be able and

even encouraged to develop site-specific

standards for waterbodies to reflect

relevant fish consumption rates.

Response—The 2000 Human Health

Methodology incorporates long-term

exposure into the development of water

quality criteria. Determination of when

human health criteria are met within the

waterbody is beyond the scope of this

document. However, EPA guidance

addresses this issue (USEPA, 1991b).

We recommend harmonic mean flow to

calculate permit limits and taking the

geometric mean of ambient water

samples to determine attainment. Both

of these recommendations account for

the long-term exposure effects of

chemical water quality criteria.

EPA recommends that States develop

site-specific water quality criteria to

reflect relevant fish consumption rates.

We have published default fish

consumption rates in the Methodology

as recommendations to States and

Tribes in adopting water quality

standards when a State or Tribe lacks

information on local fish consumption

rates. EPA’s preference, however, is that

States and Tribes adopt human health

criteria reflecting local fish

consumption rates.

11. Proposed Chemical List

Comments—Commenters suggested

that EPA integrate the AWQC

prioritization process with the drinking

water program (i.e., with the Candidate

Contaminant List). Other comments

suggested that EPA’s short list of

pollutants (for revision) would result in

a greater burden for States that will need

to develop more criteria. EPA was asked

to strengthen efforts to develop criteria

for persistent chemicals and to add

endocrine disruptors. It was pointed out

that the short priority list published in

the 1998 draft Methodology revisions

includes numerous banned pesticides.

Additional chemicals and microbial

contaminants for EPA to consider in its

prioritization of criteria to revise/

develop are suggested, as follows:

Atrazine

Benzo(a)pyrene

Chlordane

Cryptosporidium parvum strains

Cyanazine

Endrin

Giardia lamblia

Heptachlor

Heptachlor epoxide

Hexachlorobenzene

Methyl-tertiary-butyl-ether (MTBE)

Lead

Other PAHs (specifically advocated use

of Relative Potency Factors)

Total Organic Carbon (TOC)

Toxaphene

Response—We will evaluate all

suggested pollutants based on the

following factors: relative toxicity;

occurrence in fish tissue, water, and

sediments (frequency as well as

concentration levels); and for chemicals,

information on the chemical’s

bioaccumulation. This strategy,

previously published in the 1998 draft

Methodology revisions, received general

support, and we will consider these

suggestions along with priorities

identified by both the Office of Pesticide

Programs and the Office of Ground

Water and Drinking Water, and other

input received from States and Tribes.

Regarding a State’s need to revise more

criteria, see the response to Comment

A.13, Revising Existing 304(a) Criteria.

12. Publishing Existing 304(a) Criteria

Information

Comments—EPA received support for

its proposal to occasionally publish a

list of its criteria and information on

revisions or new criteria in progress.

Some commenters stated that EPA

should publish a list in the Federal

Register annually, and one suggested

that EPA post any changes during the

interim on the Agency’s website. It was

also suggested that EPA should identify

which criteria were changed and why.

One commenter stated that a timeframe

of 3 to 5 years is more appropriate

because little is likely to change in just

one year. Another commenter expressed

support for publishing an annual list of

EPA drinking water regulations and

health advisories.

Response—EPA believes that regular

updates on its website are the most

efficient way to make accurate

information available to the public. We

hope this will be helpful for States and

authorized Tribes in reviewing and

revising their water quality standards

during the triennial reviews required

under 40 CFR 131. We will consider

further the circumstances and frequency

with which Federal Register

publications may be used. The

commenter who referred to drinking

water standards and health advisories

misunderstood EPA’s intention, which

is to publish a list annually on the

66456 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

304(a) water quality criteria similar to

that done for the drinking water

program.

13. Revising Existing 304(a) Criteria

Comments—EPA received support for

revising its Methodology and for

providing clear indication of the

scientific components versus the

science policy components.

Commenters supported the idea of EPA

revising criteria based on partially

updated components of the criteria

equations. One expressed a preference

for comprehensive revisions but also

stated that partial updates should be

done as soon as possible, referring to

components such as fish consumption

rates and ‘‘interspecies conversion of

doses’’ as those that can automatically

be inserted, thereby enabling revision of

all criteria within a week of effort.

[Note: It is unclear whether the

commenter is referring to the new body

weight/surface area scaling factor or

something else by the term ‘‘interspecies

conversion of doses,’’ because it is not

specified.] A commenter stated that as

any component is updated, so should

the criteria. Another suggested that EPA

partially revise all criteria for the

components that current information

would allow. On the other hand, a

commenter stated that EPA should not

revise criteria based on the new scaling

factor or other pieces of data, but should

conduct literature searches for new

available data applicable to the

Methodology. Other comments were

that priority should be given to

chemicals with significant new toxicity

information; the use of partial updates

is not scientifically sound, will produce

overly conservative criteria, and

restricts the public’s right to comment;

and all revision actions should be

subject to public review and comment.

Response—EPA ideally seeks to

conduct re-evaluations of every

component used in the derivation of

304(a) criteria before revising any

criteria. However, we have discussed

updating a limited number of 304(a)

criteria over the course of the next

several years based on one or more

components of the criteria equation (a

‘‘partial update’’) rather than a complete

set of components, realizing that

updating some of these (e.g., the BAF,

the exposure parameters) is not as timeor resource-intensive as completing a

toxicological evaluation. Recent actions

taken by EPA represent this option; both

the NTR and the GLI were partial

updates. We intend to focus our limited

resources on revising (either partially or

completely) those pollutants that we

consider highest priority in terms of

both toxicological concern and

frequency of occurrence.

EPA has indicated that it does not

believe it is desirable to revise criteria

based on piecemeal information, such as

the interspecies scaling factor, when

there may be other information (e.g.,

new toxicity studies) that could also

change the risk assessment and, thus,

the criteria. We have also cautioned the

States and Tribes not to selectively

apply data or methods that would

inaccurately characterize risk (e.g., in

order to ensure a water quality criterion

that is less stringent than an EPA 304(a)

criterion). For a water quality criterion

revision based on a partial update to be

considered acceptable to EPA, a

component of the criterion (e.g., the

toxicological risk assessment) would

need to be comprehensive (e.g., a new

or revised RfD or cancer dose-response

assessment, as opposed to simply a new

scaling factor), should stand alone and

be based on new national or local data.

A toxicological update should be on a

weight-of-all-of-the-evidence basis, as

called for under EPA’s risk assessment

guidelines. This should incorporate the

latest published toxicological literature

and risk assessment approaches. States

or authorized Tribes seeking to establish

ambient water quality criteria are urged

to continue using the IRIS noncancer

and cancer risk assessments if they

cannot conduct a complete evaluation to

update toxicological values.

The Agency has developed an

improved process that it intends to use

when deriving new criteria or

conducting a major reassessment of

existing criteria. The process is intended

to provide expanded opportunities for

public input and to make the process

more efficient. When deriving new

criteria or when initiating a major

reassessment of existing criteria, we will

publish a notice in the Federal Register

and on the EPA website announcing our

assessment or reassessment of the

pollutant. References relied on will be

provided, and we will solicit additional

data or information useful in deriving

new or revised criteria. After input is

received and evaluated, we will develop

draft recommended water quality

criteria. Next, EPA will initiate an

independent external peer review of the

draft criteria. The public will also be

able to submit views on issues of

science pertaining to the information

used in deriving the draft criteria. We

will then revise the draft criteria as

necessary, incorporating peer review

and public input, and announce the

availability of the final water quality

criteria in the Federal Register and on

the EPA website. In addition to

developing new criteria and conducting

major reassessments of existing criteria,

EPA also from time to time will partially

revise criteria based on new information

pertaining to individual, stand-alone

components of the criteria. Because

such recalculations normally result only

in changes to single parameters of the

criteria (not in the underlying scientific

methodologies) and reflect peerreviewed data, EPA will typically

publish such recalculated criteria

directly as the Agency’s recommended

water quality criteria. If substantial

revision is done, we will follow the

process of peer review and public input

outlined above. Further discussion of

this process can be found in the Federal

Register Notice compilation of

recommended water quality criteria and

notice of process for new and revised

criteria (USEPA, 1998e).

14. State Evaluation of Data Supporting

Criteria

Comment—One commenter asserted

that ‘‘states should be allowed to

critically evaluate all data and disregard

data that, for one reason or another, are

unrepresentative or unreliable’’ and

further asserted that States should be

allowed to critically review EPA’s

published 304(a) criteria and to decline

to adopt any criteria they feel are

inappropriate.

Response—EPA disagrees with

underlying assumptions of the

comment. EPA’s 304(a) criteria are

guidance. States and authorized Tribes

may develop their own scientifically

defensible, peer-reviewed criteria.

Moreover, States and any other

interested parties have the opportunity

to participate in development of water

quality criteria published under Section

304(a) of the Act. Prior to publishing

any new or revised 304(a) criteria, EPA

provides stakeholders with an

opportunity to review and provide

scientific views. EPA maintains that at

the time of publishing of new or revised

304(a) criteria, the criteria are

scientifically defensible and establish

guidance to States for adopting water

quality standards under section 303(c)

of the Act. Under 40 CFR 131.11, States

continue to have the option of adopting

water quality criteria based on 304(a)

criteria modified to reflect site-specific

conditions, or other scientifically

defensible methods.

15. Streamlined Approach to

Developing Criteria Documents

Comment—EPA received support for

the streamlined format used in the

example criteria documents published

in 1998.

Response—We acknowledge this

support.

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66457

16. Treaty Rights and Trust Obligations/

Government-to-Government Relations

Comments—Commenters recommend

EPA fully incorporate treaty rights and

Federal trust obligations to Indian tribes

in its national AWQC guidelines. It was

reiterated that EPA has an obligation to

maintain government-to-government

relations with Tribal Governments.

Response—As stated in the 1998 draft

Methodology revisions, ‘‘risk levels and

criteria need to be protective of tribal

rights under federal law (e.g., fishing,

hunting, or gathering rights) that are

related to water quality.’’ We believe the

best way to ensure that Tribal treaty and

other rights under Federal law are met,

consistent with Federal trust

responsibility, is to address these issues

at the time EPA reviews water quality

standards submissions.

B. General Policy

1. AWQC Derivation Equation Errors

Comments—Commenters pointed out

that the term ‘‘RSC’’ (relative source

contribution) in the Linear Cancer

Effects equation of the 1998 draft

Methodology revisions was incorrect

and should have been ‘‘RSD’’ (riskspecific dose).

Response—The commenters are

correct; this was a misprint and should

have been RSD for the linear equation.

2. Chronic Human Health Effects

Assumption

Comments—EPA received support for

its assumption that, by and large,

AWQC are set to protect against longterm (chronic) human health effects.

Response—We acknowledge the

commenter’s support.

3. Protectiveness of the Methodology

Comments—A commenter stated that

inherent uncertainties in EPA’s risk

assessments make them useless and that

EPA must adopt the most conservative

methodologies in order to protect

human health, while also

acknowledging the presence of

uncertainties in assessing adverse health

impacts. They suggested that EPA

should tighten regulations for chemicals

of national priority, develop criteria for

additional priority chemicals, and take

the most conservative approach

regarding reproductive and

developmental effects. Other

commenters advocated that EPA

incorporate pollution prevention

policies into its risk assessment

methodologies. One commenter asked

EPA to provide guidance to States for

developing AWQC less restrictive than

AWQC for the general public, and

suggested that engineering and

administrative controls could reduce

exposures. Another stated that the

population groups identified represent

appropriate categories and that the

corresponding default parameter values

are reasonable. The same commenter

advocated use of the same percentile

value for each default parameter (‘‘e.g.,

95th percentile’’). Another commenter

recommended that EPA determine

distributions of exposure in order to

assess whether a significant subgroup is

more highly exposed than the general

population, especially in the context of

the chosen exposure parameter values.

Others stated that the general

population should not be targeted and

that EPA should instead target the

population group most at risk, or that

protection of health should apply to all

humans. Commenters also expressed

uncertainty over the segment of the

population that the AWQC are designed

to protect, and questioned whether EPA

would evaluate all subpopulations for

all chemicals. Two commenters

requested an analysis of the overall

impact that each parameter has on the

criteria and how that relates to the

conservativeness of the estimated risk,

with one criticizing EPA for not

conducting probabilistic analyses of

exposures or other methods to evaluate

the interaction of exposure parameters.

This commenter stated that the Agency

has used ‘‘high confidence-level’’ values

for all parameter values and, therefore,

the AWQC are ‘‘inordinately

conservative.’’ Furthermore, EPA should

specify the level of protection within

the high-end proportion of the general

population (e.g., ‘‘the 95% level’’) and

adjust the exposure parameter values

within ‘‘their defined distributions.’’

Concern was expressed that the

flexibility regarding infants and

children (i.e., for developmental effects)

conflicted with the fact that chronic

lifetime effects cover persons when they

are children and adults. A commenter

recommended consideration of tissue

effects, as well as organ-level effects.

Another stated that increasingly strict

criteria/discharge limits represent

regulatory environmental injustice, and

that discharges in effluent-dependent

streams are necessary for trees,

vegetation, and wildlife.

Response—EPA believes that it has

made appropriately conservative

assumptions in conducting risk

assessments where uncertainties exist.

Furthermore, for this effort we will rely

on the Agency’s peer-reviewed,

published risk assessment

methodologies, which incorporate

procedures to address uncertainties in

the risk assessments. We will continue

to make the most appropriate risk

management decisions when developing

or revising criteria, including

determining pollutants of high priority.

EPA does consider tissue-level effects in

addition to organ-level effects when

conducting its risk assessments. We

acknowledge the comment regarding

integrating pollution prevention policies

with our risk assessment methodologies

and specifically discuss this in the

context of CWA goals in the 2000

Human Health Methodology. We also

believe that we have selected

appropriate default parameter values.

Regarding the idea of criteria that are

less restrictive than EPA’s 304(a)

criteria, a State or authorized Tribe

would have such flexibility as long as it

could clearly demonstrate that the

criteria it calculated would be protective

of its population. Such alternate

assessments and the resulting proposed

State or Tribal standard would be

subject to EPA’s triennial review

process. Furthermore, the AWQC are

health-based criteria, and therefore

potential effects of engineering and

administrative controls are not part of

criteria.

By and large, the AWQC are derived

to protect most of the overall population

from chronic adverse health effects.

However, States and authorized Tribes

also need to understand that there are

RfD’s based on developmental or other

short-term adverse health effects,

perhaps where an exposure of one day

could result in the effect. Long-term

averaging of exposure would not be

appropriate in such circumstances.

States and authorized Tribes are also

encouraged to consider protecting

population groups that they determine

are at greater risk and, thus, would be

more protected using alternative

exposure assumptions. We do not

intend to derive multiple criteria for all

subpopulation groups for every

chemical. The commenter who

discussed probabilistic analyses has

misunderstood EPA procedures. We

have used median and mean values, and

percentile estimates, not high

confidence-level values, as suggested by

the commenter. We also disagree that

the resulting criteria represent

inordinately high levels of

conservativeness. In general, we are

doing what the commenter

recommended about targeting the

overall protection at the high end of the

general population, even though the

criteria have not been subjected to an

assessment of whether a 95% level has

been achieved (as recommended by the

commenter). Although we have not

subjected the parameter values chosen

66458 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

to a rigorous analysis, we have not used

high-end percentiles for all parameters.

The assumed body weight value used is

an arithmetic mean, as are the RSC

intake estimates of other exposures,

when data are available. The BAF

component data values are based on

median (i.e., 50th percentile) values.

The drinking water and fish intake

values are 90th percentile estimates. We

believe this will result in water quality

criteria that will be protective of a

majority of the population. That is our

goal. The commenter has not provided

a method that would allow us to

determine the overall percentile

associated with the criteria calculations.

EPA has provided additional language

in the 2000 Human Health Methodology

to clarify the population the AWQC are

intended to protect.

Finally, if EPA determined that

pregnant mothers/fetuses or young

children are the population basis of a

chemical’s RfD or POD/UF, then we

would derive our 304(a) criteria using

exposure parameter values for that

subgroup. This would be relevant only

for less-than-lifetime exposure

situations and, therefore, does not

conflict with the fact that chronic health

effects potentially reflect a person’s

exposure during both childhood and

adult years.

4. Setting Criteria to Protect Both Fish

and Drinking Water Versus Fish Only

Comments—EPA received strong

support for deriving one AWQC value to

protect both drinking water and fish

intakes and another to protect for fish

intakes only, given that the designated

uses of waterbodies vary and drinking

water may not be a designated use. One

commenter stated that in addition to

these two types of criteria, EPA should

also develop criteria for water ingestion

only. They indicated that waters may

exist where fishing and consumption of

fish are not relevant but water ingestion

is relevant. Furthermore, they pointed

out that EPA’s Advanced Notice of

Proposed Rulemaking for Water Quality

Standards discussed protection for

aquatic life and, therefore, stated that

flexibility is needed so that fish

consumption is not inappropriately

applied to all waters. A commenter

questioned whether ambient waters that

are fished are also sources of drinking

water, and whether contaminant levels

in the two water types could be

equivalent. Others stated that the

drinking water pathway should not be

included in the AWQC, given the way

AWQC are implemented (e.g., AWQC

apply to waste water discharges and

MCLs apply to public drinking water

system exposures) and that MCLs may

consider affordability and treatability. A

commenter stated that AWQC to protect

fish/shellfish are not justified and

should be dealt with under other

regulatory programs (e.g., the Food

Quality Protection Act).

Response—EPA believes that AWQC

should include a drinking water

pathway to protect waters designated as

potable water sources. (Also see EPA’s

response to Comment A.4 regarding the

relationship between MCLs/MCLGs and

AWQC, Coordinating the Human Health

Methodology With Other EPA

Programs.) EPA strongly disagrees that

AWQC to protect humans exposed

through consumption of fish/shellfish

should not be developed. Ensuring the

protection of human health from

consumption of contaminated fish and

shellfish is clearly within the

requirements of the CWA. We do not

believe that 304(a) criteria to protect

drinking water uses only are

particularly useful, because by and

large, State and Tribal standards for

human health are set to protect waters

with multiple designated uses, not

merely drinking water use. The water

quality standards program also protects

aquatic life. The 2000 Human Health

Methodology will not change our

requirement to apply aquatic life criteria

to protect aquatic species where they are

more sensitive (i.e., when human health

criteria would not be protective enough)

or where human health via fish or water

ingestion is not an issue.

5. Setting Criteria to Protect Against

Multiple Exposures From Multiple

Chemicals

Comments—Several commenters

thought EPA should consider multiple

chemical exposures when setting

AWQC and consider these exposures

additive, at a minimum, while using

information on synergistic impacts from

the combination of chemicals.

Commenters also suggested that certain

Native American Tribes may have

significant confounding factors (not

specified) to be considered with any

synergistic assessment. A commenter

suggested that the cancer risk range

apply to total contaminants or that a

cumulative cancer ceiling be

established. Another stated that the

suggested alternate approach to account

for inhalation and ingestion exposures

(via the RfD and RfC equation)

regardless of the target organ/endpoint

was inconsistent with EPA’s guidance

on the use of hazard indices (HIs) and

hazard quotients (HQs) to evaluate

multiple noncarcinogenic toxicants.

Commenters also questioned whether

all exposure routes exhibit the same

toxicity or stated that inhalation

exposures should be disregarded if the

pollutant in question does not affect the

same endpoint.

Response—Assuming that all multiple

exposures from multiple chemicals are

additive, as the commenters suggest, is

not scientifically sound unless they

exhibit the same toxic endpoints and

modes of action. We are aware of the

complex issues and implications of

cumulative risk and are developing an

overall approach at the Agency-wide

level. In particular, the Agency’s

program offices are engaged in ongoing

discussions on how to address the great

complexities, methodological

challenges, data adequacy needs, and

other information gaps, as well as the

science policy and risk management

decisions that will need to be made, as

we pursue developing a sound strategy

and, eventually, specific guidance for

addressing cumulative risks. As

previously indicated, the Agency is

developing a framework for cumulative

risk assessment, and the Office of

Pesticide Programs has developed draft

guidance for assessing cumulative risk

of common mechanism pesticides and

other substances. We have added

discussion about the concept of

cumulative risk and the state of the

science in the 2000 Human Health

Methodology and its TSDs. As a matter

of internal policy, we are committed to

refining the Methodology as advances in

relevant aspects of the science improve.

Regarding the alternate approach to use

the HI/HQ equation (combining RfDs

and RfCs), we do not intend to use this

approach to combine chemicals when

deriving criteria at this time. We

requested comment on this as an

alternate method to consider inhalation

exposures for a given chemical, but

would not consider its use in situations

where existing information indicates

that ingestion exposures and inhalation

exposures affect different target organs.

EPA intends to consider the

comparative toxicity between exposure

routes for Section 304(a) water quality

criteria and has encouraged States and

Tribes to do so. For the recommended

national 304(a) criteria, cumulative risk

approaches will not work since the

mixture of pollutants present in water is

inherently site-specific.

6. Uncertainty with the Derivation of

304(a) Criteria

Comment—Comments suggested that

cumulative uncertainty guidance should

be included in the Methodology,

including a maximum acceptable

uncertainty level.

Response—Establishing a maximum

level of acceptable uncertainty is not

part of the Methodology and will not be

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66459

factored into the decision of whether to

develop or revise 304(a) criteria.

However, issues regarding uncertainties

with the risk assessments, exposure

assessments, and bioaccumulation

assessments will be addressed in the

risk characterization sections of future

criteria documents.

7. Toxicity Equivalency Factors (TEFs)

for Dioxin-like Compounds

Comments—Several commenters

addressed the use of TEFs for dioxinlike and other mixtures and classes of

compounds. They believed the TEF

approach has only limited application

in risk assessment. Commenters

indicated that complexities of the

biology argue strongly against any more

than limited and very cautious use of

the TEF approach for assessment of

human health from exposure to dioxinlike compounds.

Response—EPA agrees that there is a

limitation to TEF use and that caution

should be exercised when using it. More

guidance can be found in the Guidance

for Conducting Health Risk Assessment

of Chemical Mixtures (USEPA, 1999b)

and the Health Assessment for 2,3,7,8–

Tetrachlorodibenzo-p-dioxin (TCDD)

and Related Compounds, Internal

Review Draft, February 14, 2000; Part II,

Chapter 9: Toxicity Equivalency Factors

(TEFs) for Dioxin and Related

Compounds (USEPA, 2000b).

C. Cancer

1. Acceptable Risk Level for

Carcinogens

Comments—Comments were received

suggesting that regulations should be

tightened or that AWQC for all

carcinogens including the Groups C

compounds (possible human

carcinogens) should be set at zero, while

others believed that cancer potency

factors may overestimate actual risk.

Some suggested the actual risk may be

much lower, perhaps as low as zero,

particularly for chemicals for which

human carcinogenicity information is

lacking. Comments also addressed the

EPA cancer risk range for deriving

AWQC.

Response—Regarding the permissible

cancer risk range, see response to

Comment A.3, Cancer Risk Range.

2. ED10 (central estimate) versus LED10

(lower bound on dose)

Comments—Several commenters

preferred the use of ED10 over LED10 as

the POD or BMD.

Response—The 1999 draft revised

cancer guidelines provided a rationale

for the selection of PODs. EPA’s 1999

draft revisions provide for the use of the

LED10. The EPA Science Advisory

Board (SAB) suggests harmonization of

the LED10 between the BMD approach

for noncancer assessments and cancer

assessments. The SAB also recommends

reporting both the LED and ED (see

USEPA, 1999d).

3. Group C Contaminants

Comments—One commenter stated

that Group C compounds are treated

differently under the SDWA and the

CWA and wanted clarification on

development of AWQC for Group C

contaminants. Also, an ‘‘integrated

approach’’ was suggested in evaluating

nonlinear carcinogen and

noncarcinogen assessments. However,

the commenter’s approach was to

determine tentative AWQC for the

contaminant as both a noncarcinogen

and a carcinogen at 10¥6 risk, and then

choose the lower of the two values (i.e.,

RfD vs. 10¥6 risk) for setting the AWQC.

Another commenter stated that

integrating nonlinear and

noncarcinogen assessments proposed by

EPA is reasonable and it may be

possible to replace this in the future

with the categorical regression

approach.

Response—The 1999 draft revised

cancer guidelines require risk assessors

to use the best science and consider

mode of action in selecting an

appropriate model to use. Under the

1999 draft revised cancer guidelines,

Group C will no longer exist. The linear

approach is used when there is

insufficient information on mode of

action, or the mode-of-action

information indicates that the doseresponse curve at the low dose is or is

expected to be linear. The default

approach for nonlinearity is to use a

margin of exposure analysis. However,

when the mode of action suggests both

linear and nonlinear approaches, then

both methods will be applied and

considered. As for the integrated

approach, EPA currently is working to

increase the harmonization of both

cancer and noncancer risk assessments.

In the 2000 Human Health

Methodology, we will only quantify

cancer risks for those chemicals

considered ‘‘carcinogenic to humans’’ or

‘‘likely to be carcinogenic to humans.’’

4. Guidance on Carcinogen Risk

Assessment

Comments—Several commenters

supported EPA’s 1996 proposed cancer

guidelines. They endorsed the proposed

guidelines for considering all scientific

data and using the latest information,

including weight of evidence, mode of

action, margin of exposure, and a

nonlinear approach for certain

contaminants. They thought the new

approach is more in line with recent

advances in understanding

carcinogenesis. However, they requested

more guidance on how and when to

apply the cancer guidelines.

Response—We will provide more

guidance when the guidelines are

finalized.

5. Hexachlorobutadiene (HCBD)

Comments—Comments stated that

EPA should not propose AWQC for

HCBD before the 1999 draft revised

cancer guidelines are final.

Furthermore, for HCBD, there is

inconsistency between the statement in

the 1998 Federal Register (Appendix

VI) and that in the example HCBD

criteria document.

Response—The Agency is considering

the comment and will postpone

completion of the AWQC for HCBD

until more recent data can be

incorporated. In reference to the risk

assessment of the chemical, the

discrepancy is minor. The 1998

Methodology states that both linear and

nonlinear approaches will be used by

EPA. The criteria document presents

both approaches.

Note: EPA also will postpone completion

of the criteria for 1,3-dichloropropene.

Because of the large volume of new scientific

information available for acrylonitrile,

additional effort will be necessary to review

the material. Therefore, EPA will not

complete the criterion for acrylonitrile at this

time. For the same reason, we are not

addressing the comments on this chemical at

the present time.

6. Integration of Analyses for Cancer

and Noncancer Effects

Comments—Commenters supported

integration and harmonizing procedures

for risk assessment of cancer and

noncancer effects in ambient water and

drinking water programs.

Response—EPA agrees that it is a

good idea to use an integrated approach

to assess both cancer and noncancer

effects. Currently, EPA has Agency-wide

efforts to investigate harmonization of

cancer and noncancer risk assessments.

7. Margin of Exposure (MOE) Analysis

Comments—Commenters requested

that EPA provide more guidance on how

to do MOE analysis and how to select

the MOE. They also requested a

comparison of the BMD with the LED10.

Response—Guidance will be provided

either in the final Guidelines for

Carcinogen Risk Assessment or in a

separate document from the Agency’s

Risk Assessment Forum in the future.

66460 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

8. MOE Approach to Applying

Uncertainty Factors (UFs)

Comments—A commenter disagreed

with the proposal to apply a UF to

account for the severity of a precursor

effect. Another commenter opposed

applying a UF of no less than 0.1 when

humans are less sensitive than animals.

Response—The Agency will develop

more specific guidance on the MOE

approach, as recommended by the SAB

in 1999. The guidance will be peer

reviewed and published separately as

part of the Agency’s implementation

activity for these guidelines.

9. MOE and MOP

Comments—Commenters seemed

confused regarding MOE and MOP

(‘‘margin of protection,’’ as defined by a

commenter). They defined MOE = MOP

= POD/RfD and claimed that the

calculated MOEs for chemicals based on

nonlinear low-dose extrapolation are

100 times higher than those for

carcinogens based on linear low-dose

extrapolation, and claimed that the

MOE is implicitly linear and, thus, is an

inadequate approach to dealing with

‘‘nonlinear’’ carcinogens.

Response—There is a significant

misunderstanding on the part of the

commenters. The MOE is defined as the

POD (i.e., NOAEL or LOAEL or LED10)

divided by the environmental level of

interest (actual exposure or possible

criterion). The MOE approach is

recommended for chemicals that have a

nonlinear low-dose response. For

carcinogens with a linear low-dose

response, we estimate the slope of the

line drawn between zero and the LED10,

and use the equation presented in the

Methodology to estimate the

concentration in water for human heath

protection (10¥6 is the recommended

risk level). EPA does not recommend

using any formula such as the one

presented [i.e., MOE = (POD) /(RfD)] to

estimate MOE for carcinogens with a

linear low-dose response.

10. Oral Scaling Factor for Dose

Adjustment

Comments—Several commenters

endorsed EPA’s use of the body weight

raised to the three-quarters power as the

scaling factor. It was also suggested that,

if available, chemical-specific data

should take precedence over the generic

default scaling factor.

Response—EPA agrees.

11. Toxic Endpoints

Comments—A commenter stated that

EPA should make clear in its

Methodology that it intends to take into

consideration the toxic actions of the

individual chemicals for which criteria

are being established so that an

appropriate target population and

consumption rate can be selected. The

commenter suggested that if the critical

toxic endpoint of a chemical is cancer

or other chronic disease, then use of the

adult population and long-term

consumption rates are appropriate to

develop the AWQC. However, if the

most sensitive toxic endpoint of a

chemical of interest is acute

reproductive effects, it may be more

appropriate to use short-term

consumption rates and exposure

parameters that are relevant for women

of childbearing age in developing the

AWQC.

Response—EPA agrees.

12. Weight-of-Evidence Narrative and

Classification System

Comments—A commenter expressed

support for the use of narrative

statements, but found the guidance on

the weight-of-evidence narrative to be

overly general and confusing. They

suggested that some sort of classification

system such as the alphanumeric should

be retained. They also stated that

without such a system, practical use of

the weight-of-evidence approach will be

more difficult, particularly for States

that do not have strong expertise and

sufficient resources in the application of

health-based risk assessment.

Response—Current revisions to the

cancer guidelines and the use of

descriptors and narratives have been

endorsed by the SAB and other

commenters and will be included in

assessments and final guidelines

because they provide important

information to the risk manager that a

number or letter cannot convey.

D. Noncancer

1. Benchmark Dose Methodology

Comments—Commenters supported

the flexibility of having the NOAEL/

LOAEL/UF, categorical regression, and

benchmark options for derivation of an

RfD but pointed out a variety of

concerns or factors for EPA to consider

as it revises the BMD guidance.

Commenters suggested that the BMD

methodology will eventually have a

prominent role in risk assessment, but

checks and balances need to be set to

ensure that it is applied intelligently

and with a healthy scepticism for its

results, especially those that vary

significantly from the results of the

conventional NOAEL/LOAEL approach.

The following specific

recommendations were presented for

EPA’s consideration:

• Prohibit extrapolations without

some mechanistic foundation. Permit

interpolation only within the

experimental dose range, for example,

between NOAELS and LOAELS.

• Present a range of BMD estimates

from the use of multiple-dose models,

including models with thresholds just

below LOAELS; estimates with the highdose results dropped sequentially from

the analysis; and multiple response

rates (i.e., 1%, 5%, and 10% response

rates as well as the response rate

associated with the experimental

detection limit).

• Estimate the BMD using several

confidence bounds.

• Compare the results of the

alternative modeling approaches and

reconcile discrepancies.

Other comments are summarized in

the following paragraphs.

The BMD methodology lacks a

mechanistic basis. There is no

connection between the mechanisms of

action that underlie the observed

responses. Because the methodology is

devoid of a mechanistic basis, its use

needs to be restricted to the observable

range. Extrapolations below the lowest

nonzero dose of a study have no

scientific foundation. However, it is

acknowledged that some extrapolation

of the data below the observable range

is inevitable.

An additional critique was that highdose effects influence low-dose

estimates. The curve fitting involved in

estimation of the mathematical doseresponse relationship permits the

responses at the high end of the dose

range to influence the estimated

responses at the low end of that range.

This will occur whether or not the highdose observations are mechanistically

related to the responses at low doses.

Furthermore, response and dose

estimates are model dependent. In some

cases, both central estimates and lowerbound estimates of doses associated

with various response rates are known

to be highly unstable and fluctuate

significantly in response to minor data

manipulations or assumptions.

More research is needed on

implementation of the benchmark

model. Guidelines for selecting

appropriate models/benchmark

responses, handling lack of fit, or

selecting a single benchmark dose when

more than one is calculated should be

developed by EPA to assist States and

other users in implementing this

methodology.

The central estimate rather than the

lower bound on dose should be used as

the POD for benchmark modeling. Such

an approach provides greater

opportunity to compare effect doses

among chemicals. Uncertainty

associated with wide confidence limits

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66461

can be accommodated in other portions

of the risk assessment process.

Furthermore, the most recent peer

review of the BMD methodology

(USEPA, 1996c) recommended use of

the ED10 rather than the LED10.

Use of the benchmark model could

introduce additional conservatism into

the derivation of an RfD. Certain

benchmark models as applied to

developmental toxicity endpoints are

substantially more conservative, on

average, than the corresponding

NOAELs. Using the benchmark

approach in such a circumstance will

introduce additional unjustified

conservatism in the standard-setting

process.

Caution should be taken when using

different methods for RfD

determination; that is, the degree of

human health protection should be

comparable from different methods.

Because the BMD and categorical

regression are relatively new methods,

more studies are needed to compare the

RfDs derived using the typical NOAEL/

UF approach and those derived using

the BMD and categorical regression

methods.

EPA should closely coordinate

adopting BMDs for noncancer endpoints

under the Human Health Methodology

with other Agency programs so that the

policy is implemented identically

throughout the Agency. However,

because the benchmark approach makes

better use of all data, the Agency should

continue to work on its development.

Response—EPA agrees with the

concerns regarding widespread

application of the benchmark approach

without consideration of the many

factors addressed by commenters. The

AWQC guidelines do not prescribe use

of the benchmark approach in the

derivation of an RfD. The guidelines

allow the use of either the NOAEL/UF,

benchmark, or categorical regression

approaches. The risk assessor can select

the approach most suitable to the

available data. Accordingly, if the data

do not support derivation of a BMD,

then the NOAEL/UF approach can be

selected for the RfD derivation rather

than the benchmark approach. In

addition, when selecting the appropriate

equation for derivation of the BMD, one

should consider goodness-of-fit along

with the impact of high doses on the

model results, confidence interval

domains, and consistency of the doseresponse pattern with the mode of

action.

We do not anticipate that either of the

new approaches, benchmark or

categorical regression, will soon

completely replace the NOAEL/UF

approach. Both of the new approaches

require more extensive data than the

NOAEL/UF approach, and in many

cases the data required to apply the

methodology will not be available.

EPA is developing technical guidance

that will assist in determining whether

or not a particular data set is compatible

with the BMD approach. Use of BMD

methods involves fitting mathematical

models to dose-response data obtained

primarily from toxicology studies. When

considering available models to use for

a BMD analysis, it is important to select

the model that best fits the data and is

the most biologically appropriate. EPA

has developed software following

several years of research and

development, expert peer review, public

comment, subsequent revision and

quality assurance testing. The software

(BMDS, Version 1.2) can be downloaded

from http://www.epa.gov/ncea/

bmds.htm. BMDS facilitates these

operations by providing simple datamanagement tools, a comprehensive

help manual and online help system,

and an easy-to-use interface to run

multiple models on the same doseresponse data.

As part of this software package, EPA

has endorsed sixteen (16) different

models that are appropriate for the

analysis of dichotomous (quantal) data

(Gamma, Logistic, Log-Logistic,

Multistage, Probit, Log-Probit, QuantalLinear, Quantal-Quadratic, Weibull),

continuous data (Linear, Polynomial,

Power, Hill) and nested developmental

toxicology data (NLogistic, NCTR, Rai &

Van Ryzin). Results from all models

include a reiteration of the model

formula and model run options chosen

by the user, goodness-of-fit information,

the BMD, and the estimate of the lowerbound confidence limit on the

benchmark dose (BMDL). Model results

are presented in textual and graphical

output files which can be printed or

saved and incorporated into other

documents.

2. Categorical Regression

Comments—Commenters expressed

reservations regarding use of the

categorical regression methodology.

They stated that the methodology

presents difficulties in that it requires

distinction of diverse endpoints and

definition of severity categories, not as

they apply to the animal studies, but as

they apply to human health effects.

Commenters also stated that categorical

regression would allow the Agency to

consider several endpoints

simultaneously rather than use data for

only the most sensitive endpoint. Some

commenters believed that the major

limitation of the approach is the need

for classifying effects into categories

(mild, moderate, frank).

Other commenters believed regression

analysis offers attractive advantages but

does not seem well enough developed at

the present time to be incorporated into

the Methodology. They suggested that

because the approach makes better use

of all data, the Agency should continue

to work on its development. They also

stated that when the data indicate that

one of the new methodologies is clearly

superior to the NOAEL/LOAEL/UF

approach, it should be utilized.

Response—As stated in the response

on BMD above, EPA does not anticipate

that either of the new approaches,

benchmark or categorical regression,

will soon replace the NOAEL/UF

approach. Both new approaches require

more extensive data than the NOAEL/

UF approach, and in many cases the

data required by the methodology will

not be available. We agree that the

categorical regression methodology is

less well developed than the benchmark

method. However, we also anticipate

that the number of chemicals evaluated

with this approach will grow over time.

Including the categorical regression

methodology among the available

options in the 2000 Human Health

Methodology provides an opportunity

for its application in appropriate

situations.

3. Integrated Approach

Comments—Commenters stated that

an integrated approach to assessing both

cancer and noncancer effects for

substances that are carcinogenic has

merit, particularly when the systemic

effects of concern occur at very low

doses. However, they believed it is

unclear how the nonlinear cancer

assessment and the noncancer

assessment would differ if the tumors

were considered secondary to the

systemic toxicity upon which the RfD is

based. They stated that such

considerations become more important

when the systemic toxicity is unrelated

to tumor formation, as in the case of

lead and mercury. Some indicated that

because EPA recommends different

design flows to account for exposure

scenarios that are appropriate for

carcinogenic and systemic effects, the

Methodology should develop and adopt

similar criteria for both carcinogenic

and systemic effects when appropriate.

Some further stated that for some waters

and pollutants, it will not become clear

whether the systemic or carcinogenic

criterion is more protective until the

limits are developed using the different

design flows. This was not previously a

concern because a single human health

design flow was used in most locales.

66462 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

Response—The 2000 Human Health

Methodology is not a stand-alone

methodology. It depends on established

or proposed Agency risk assessment

guidelines for cancer and noncancer

endpoints. We do not have the latitude

to change Agency-wide risk assessment

guidelines through the AWQC

Methodology. Any changes must first be

made to the supporting documents (e.g.,

1999 draft revised cancer guidelines,

RfD methodology).

4. Integrated Risk Information System

(IRIS)

Comments—Concern was expressed

that EPA does not update the IRIS files

in a timely manner. States use these

assessments for their risk assessment

work and do not have the resources to

perform the types of detailed consensus

risk assessment done under the IRIS

process, according to comments

received. They additionally pointed out

that many IRIS assessments are more

than 10 years old and suggested that

EPA should update these assessments

on a 3- to 5-year cycle.

Response—We realize the importance

of the IRIS program and dedicate a

portion of our resources to preparation

of IRIS documentation for regulated

chemicals. However, competing

priorities throughout the Agency limit

the effort that can be expended on IRIS

by program offices and by the IRIS

program.

5. NOAEL/LOAEL Approach

Comment—A commenter called

attention to the facts that the NOAEL/

LOAEL/UF approach is the current

approach for establishing an RfD and

that many present regulatory values are

based on this approach. They stated that

use of newer techniques that account for

severity of effects and sample size seems

reasonable, as long as the new

techniques have been extensively

reviewed and have wide acceptability

among practitioners. However, the

commenter also said that in some cases,

the data needed to use the newer

techniques may not be available, in

which case it seems entirely appropriate

to use the NOAEL/LOAEL approach as

a default.

Response—See our responses to

Comments D.1 and D.2, the benchmark

dose and categorical regression

comments, respectively.

6. Nonthreshold Approach for

Noncarcinogens

Comments—The Agency requested

comments on the suitability of using a

nonthreshold approach for noncancer

endpoints. Although open to the

concept, commenters stated that a

threshold should be considered the

norm and a nonthreshold approach

should be applied only if there are

substantial scientific data supportive of

a nonthreshold mechanism of toxicity.

They stated that when receptor

interactions are a component of the

response, it is important that EPA

differentiate between the receptor

binding that might be without a

threshold and subsequent biological

responses such as enzyme induction or

frank toxicity that would be expected to

exhibit threshold dose-response

relationships.

An additional concern was the use of

nickel as an example of a chemical

without a threshold. It was pointed out

that double-blind studies indicate that

there is a threshold for dermatological

responses to nickel even in sensitized

individuals.

Response—The Agency made

modifications to the recommendations

regarding a threshold approach for

noncarcinogens, most specifically using

lead as an example rather than nickel.

We incorporated the commenters’

suggestions in making the revisions.

7. RfD Range

Comments—The concept of

establishing a range around the

calculated RfD from which an

alternative RfD might be selected in

certain circumstances received

considerable comment from the public.

The primary criticism was the lack of a

scientific basis for the breadth of the

range and its correlation to the net

uncertainty factor/modifying factor (UF/

MF) product. The comments are

summarized below.

The span of the range as described by

EPA seems to be arbitrary and without

any scientific support. It would be

useful for the Agency to analyze a

substantial number of past RfD

determinations using the ranges the

Agency has proposed to see whether

they make practical sense. The Agency

should provide more examples on how

the factors that are to be considered in

selecting a point within the range (i.e.,

bioavailability differences, sensitive

populations, and slope of the doseresponse curve) are related to the

magnitude of the proposed range.

Scientific data should be gathered and

presented to support the use of these

factors in influencing the range.

The Agency should give serious

consideration to the possibility that the

ranges of uncertainty surrounding the

point estimate are not symmetrical. In

particular cases, it may well be that

most of the RfD uncertainty is on the

high side of the point estimate.

The proposal to use a range is

inconsistent with the purpose of the

RfD. The proposal to use a range rather

than a point value for the RfD would

lead to the potential for double counting

uncertainty. The UFs and MFs presently

applied in calculation of the RfD allow

for many of the factors that are

presented as justifying selection of a

point within a range as an alternative to

the calculated RfD.

The range for the RfD would create

more problems than it would prevent.

The RfD, by nature, cannot be used to

calculate the risk at a given level of

exposure and is essentially a safety

estimate that should be expressed as a

single point estimate. The definition of

the RfD recognizes the uncertainty in

this assessment. The proposed approach

would be difficult to implement, create

unnecessary confusion and controversy

regarding the RfD, and could result in

prolonged unproductive debates

between parties with differing interests.

If EPA chooses to define a range, the

range should be developed by the

scientists undertaking the RfD

development. If a range is used, it is also

strongly recommended that it be

accompanied by detailed guidance on

the factors for choosing a point estimate

within the range. The uncertainty

surrounding the point estimate of an

RfD will be different for each chemical

and study and should be clearly stated

in any revised RfD.

An advantage of the range is that it

would make more apparent to States the

uncertainty in the RfD and the

flexibility that now exists surrounding

its use in the regulatory context.

However, it is preferable to retain the

presentation as a single point value but

provide in accompanying text

substance-specific information such as

steepness of the dose-response curve

that States can use in deriving standards

based on other than the default single

point RfD.

A range is useful to a risk manager or

other decision-maker because actions

can be taken with greater confidence in

how likely it is that adverse health

effects will be manifest at a particular

point concentration. For example,

slightly exceeding the MCL of 1 mg/L

for nitrite with a UF of 1 is more likely

to result in adverse health effects upon

exposure than slightly exceeding a

guideline of 70 μg/L for MTBE with a

UF of 10,000.

Some of the factors EPA recommends

in selecting a point within an RfD range

should be used in determining the RfD

itself rather than for deviating from it

after it is derived. These include the

seriousness and reversibility of the

effect, whether it is based on a LOAEL,

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66463

and bioavailability within humans. The

issue of considering the presence or

absence of sensitive segments of the

population is impractical and

inappropriate in deriving an ambient

water quality standard. EPA should

delete this option and understand that

States generally set water quality

standards on a statewide level. It is

impractical to ascertain whether infants

or pregnant women live near and

consume fish or water from a particular

waterbody. It is not practical from an

administrative standpoint to set

different, separate standards for each

waterbody.

The Agency should provide guidance

regarding the development of scientific

rationales for departure from the default

RfD. The Agency should provide a

methodology for deriving the range,

along with supporting examples, and

subject that methodology to peer review

before using the concept in developing

AWQC.

Response—EPA agrees that the

method used to quantify the range from

which an alternative to the calculated

RfD can be chosen is not based on

specific scientific or statistical data. It is

purely an equal partitioning of a default,

10-fold uncertainty factor into four

equal quarter log segments.

It is important to note that the range

around the calculated RfD only

establishes a domain from which a risk

assessor can select a single point to use

as an alternative to the RfD for a specific

circumstance. The 2000 Human Health

Methodology criteria for using a point

within the range other than the

calculated RfD when calculating AWQC

clearly require the State to provide a

detailed justification for that decision.

One example of a situation where a

point other than the calculated RfD

might be applied would be where there

is a difference in the bioavailability of

the contaminant in the water

component of the AWQC as opposed to

the fish component. In such an instance,

the decreased bioavailability from fish

tissues could be used to support

selection of an alternative value greater

than the calculated RfD if the critical

study were one where the contaminant

had been administered through drinking

water. Most inorganic contaminants,

particularly divalent cations, have

bioavailability values of 20 percent or

less from a food matrix, but are much

more available (about 80 percent or

higher) from drinking water.

Accordingly, the external dose

necessary to produce a toxic internal

dose would likely be higher for a study

where the exposure occurred through

the diet rather than the drinking water.

As a result, the RfD from a dietary study

would likely be higher than that for the

drinking water study if equivalent

external doses were used.

The exposures considered in deriving

AWQC include fish (food) and water.

Thus, one might be able to justify an

alternative value to the RfD point

estimate that was slightly higher than

the RfD estimate in cases where the

NOAEL that was the basis for the RfD

came from a drinking water study, but

slightly lower than the RfD estimate if

the NOAEL came from a dietary study.

Several commenters suggested that

there would be value in applying the

range concept to several relevant RfD

values and then to evaluate the results.

The range concept was considered in

the peer review of the 1998 draft

Methodology revisions, and the peer

reviewers had many of the same

concerns regarding the range. The

revised Risk Assessment TSD gives

examples of how one could justify an

alternate RfD value that was lower or

higher than the RfD estimate.

8. Severity of Effects

Comments—Several commenters

supported consideration of severity of

effects in determining AWQC, although

there was considerable diversity in the

opinions expressed, as follows.

Some believed that there was no

science behind use of different UFs (i.e.,

3, 10) in making intraspecies decisions

based on severity of effect. Some stated

that EPA should provide a methodology

that will define a severity scale prior to

adopting use of severity in deriving

RfDs and associated AWQC. Others

commented that the severity scale could

be alphanumeric, similar to that used

for carcinogens under the EPA 1986

cancer guidelines, and the severity

rating could be presented along with the

RfD value. However, any severity scale

must also consider whether it is

consistent with the definition of an RfD

as a dose below which no adverse

effects are anticipated to occur in

exposed populations.

Other commenters believed that

making adjustments in the RfD value for

severity of effects only confounds

regulatory policy with toxicological

science, and the Agency should explore

alternative approaches to the problem of

differences in severity of various

toxicological endpoints. The Agency

should not have considered severity in

calculating an RfD because this practice

could result in double counting of

uncertainty. Severity should be

considered in selection of a UF only

when the RfD is based on a LOAEL. If

the NOAEL were used, concerns for

severity should be reflected in the MF.

Response—There are several

situations in which EPA has considered

the severity of effect in selection of the

UF. The Risk Assessment TSD cites zinc

as an example. The LOAEL used in

establishing the RfD for zinc was a

change in the activity of the enzyme

superoxide dismutase. This effect

compromises the ability of the

individual to avoid damage to

macromolecules, such as proteins and

polynucleotides, in the presence of free

radical oxygen. Although clearly

adverse, this effect is not as severe as

tissue necrosis or impaired organ

function. Thus, a UF of 3 was used

rather than the default of 10 for the

adjustment of a LOAEL to a NOAEL.

The nutritional requirements for zinc

relative to the RfD supported the use of

a UF of less than 10 in this instance.

As monitoring of molecular

biomarkers of toxicity increases, the

number of situations will most likely

increase in which a LOAEL is early

enough in the progression toward

overtly adverse effects that factors of

less than 10 can be used for the RfD

calculation and will be supported by

mode of action data. Past EPA practice

is consistent with the suggestion that

severity be considered where the RfD is

based on a LOAEL and that an MF be

used, if the data warrant, when

calculating from a NOAEL.

We do not believe that establishing a

scale for severity is necessary at this

time. It would be extremely difficult to

establish a scale for rating toxicological

endpoints that could be easily applied

to the spectrum of endpoints monitored

in more recent toxicological studies.

The present flexibility in UFs and MFs

provides ample opportunity for severity

adjustment.

9. Stochastic Modeling

Comments—Commenters encouraged

EPA to use a stochastic approach

(Monte Carlo and/or Latin square

modeling) for setting RfDs. The

commenters stated that this would

allow EPA to better ‘‘quantify the

uncertainties and separate them from

the variability in the data.’’ They

believed such methods would provide a

sounder, more quantitative approach to

determining whether a range of RfD

values is needed.

Response—The guidelines for

determination of the RfD are based on

previously published, Agency-wide

guidelines. The suggestion to use a

stochastic approach has been noted and

will be considered in the context of the

Agency revisions to its risk assessment

guidelines. Revisions to fundamental

Agency guidelines are beyond the scope

of the AWQC Methodology.

66464 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

10. Synergistic Effects

Comment—Several commenters

encouraged the Agency to consider

multiple exposures to various chemicals

and persistent bioaccumulative

toxicants when establishing AWQC. For

substances that do not persist or

bioaccumulate in the environment, or

do not cause reproductive,

developmental, or neurological effects,

EPA’s risk assessment methodologies

were deemed in need of

reconsideration. However, as part of the

reconsideration, EPA was asked to

apply best science on synergistic

impacts from exposures to a

combination of chemicals. Other

comments suggested sensitive

subpopulations, such as Native

American Tribes and other susceptible

populations, may have significant

confounding, underlying health

problems that must be recognized with

any synergistic assessment.

Commenters also stated that EPA

should give specific attention to certain

categories of contaminants: persistent

organic pollutants and endocrine

disruptors. The commenters identified

two aspects to consider in applying this

recommendation: (1) Individual

contaminants with a similar mode of

action whose cumulative effects may

reach an unacceptable level; and (2)

selection of specific biologic endpoints

to use as the basis of an RfD. They also

believed that tissue effects are valid

measures of injury and should be used

in addition to organ-level effects in

people and biota. It was also considered

important to include immunological,

reproductive/developmental, and

neurological effects to derive RfDs.

Response—The Risk Assessment TSD

encourages States to consider

synergistic and additive effects of

individual chemicals in mixtures when

establishing AWQC. The HI approach is

suggested and described for situations

where the chemicals have the same

effect by similar modes of action. The

Risk Assessment TSD also

acknowledges that methods are not

presently available for evaluating risk

from mixtures where the individual

chemicals have dissimilar health effects

and recommends that chemicals in such

mixtures be evaluated individually.

Specific recommendations are found in

EPA’s Draft Guidance for Conducting

Health Risk Assessment of Chemical

Mixtures published in May 1999

(USEPA, 1999b).

The 2000 Human Health Methodology

accommodates concerns regarding

persistent bioaccumulative toxicants

primarily through use of

bioaccumulation factors in the

calculation. Situations in which

ambient waters may contain a group of

chemicals that are persistent and

bioaccumulative and have additive or

synergistic effects can in some cases be

factored into the HI approach. The

description of the treatment of mixtures

in the TSD was expanded to encourage

States to consider persistence,

bioaccumulation, and mixtures

concerns in their risk assessments. The

references to Agency mixtures

guidelines were updated to include the

most recent draft of the mixtures

guidelines.

11. Target Population Adjustments

Comments—EPA was asked to

consider the characteristics of the target

population when determining AWQC.

Commenters suggested that when the

chemical is a carcinogen, it is

appropriate that the target population

consist only of residents of the United

States. In cases where the effect is an

acute reproductive effect, the

commenters believed it is appropriate to

specify adult women as the target

population and to use short-term

consumption rates and exposure

parameters.

Response—The default input

parameters for determining AWQC for

human health apply to lifetime

exposures and the adult population of

the United States. However, the

equations used for the calculation

provide the flexibility to use body

weight, water intake, and fish intake

parameter values that are specific to

other target populations.

12. Uncertainty and Modifying Factors

Comment—Additional guidance was

requested on factors to consider in

selecting UFs, particularly a UF for an

incomplete database.

Response—In revisions to the Risk

Assessment TSD for the 2000 Human

Health Methodology, we increased the

number of examples given to illustrate

how UFs were selected in establishing

RfDs included in the IRIS.

Comment—The suggestion was made

to replace the interspecies UFs with a

body weight to the three-quarters power

and thereby harmonize the cancer and

noncancer approaches.

Response—The peer reviewers of the

1998 draft Methodology revisions also

suggested harmonizing the cancer and

noncancer approaches with regard to

the use of the body weight to the threequarters power. This can be

accomplished only through changes to

the Agency documents on which the

methodologies presented in the 2000

Human Health Methodology are based.

The Agency currently is working on

harmonizing the cancer and noncancer

methodologies.

In addition, as pointed out by the peer

reviewers, a body weight to the threequarters power conversion adjusts for

allometric differences between

laboratory animals and humans. It does

not reflect toxicodynamic differences

between species that must still be

included when adjusting for

interspecies differences. The use of the

scaling factor cannot totally replace the

interspecies UF.

Comment—Another comment

requested EPA to adopt more rigorous

quantitatively supportable methods

such as PBPK models to replace the

more arbitrary and less well founded

use of numerical scaling factors

identified in UFs and MFs.

Response—The revisions to the

Methodology clearly support use of

toxicokinetic modeling when the data

are available and use of the modeled

data in lieu of the toxicokinetic portion

of the interspecies UF.

13. Use of Less-Than-90-Day Studies in

Determining an RfD

Comments—In general, commenters

agreed with the scientific review board

that false-negatives might result from

use of less-than-90-day studies to

develop an RfD. It was suggested that

EPA evaluate data sets for groups of

chemicals for which there are both

chronic and less-than-90-day studies

and compare RfDs. Any comparison of

chronic and less-than-90-day studies

should consider the purpose for which

the less-than-90-day studies were

conducted and whether they provide

evidence relevant to the results of longer

term experiments. A commenter agreed

with the scientific review board that any

RfD based on a less-than-90-day study

should be used only temporarily.

Other comments pointed out that the

Great Lakes methodology allowed use of

less-than-90-day studies for determining

an RfD but required a duration UF of 30

rather than 10. This factor when

combined with a 10 for intraspecies

variability and a 10 for interspecies

variability would yield a total UF of

3,000, the maximum that is said to

support RfD derivation. The commenter

believed very few situations would

qualify to use less-than-90-day studies,

but their use should be allowed as long

as the total UF is 3,000 or less.

Additional comments stated that

reproductive, developmental,

immunotoxicological, and neurotoxicity

data provide an appropriate basis for

determining an RfD even if they come

from studies of less-than-90-day

duration. However, one commenter also

urged that data must be collected using

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66465

methods of sufficient accuracy and

validity. It was also emphasized that

evaluations should be conducted to

determine how dose-response

relationships developed for these toxic

effects, particularly immunotoxicity, are

related to modifications in function and

evidence of overt pathology. Response—In several instances, the

Agency has developed an RfD based on

data from studies of less-than-90-day

duration (e.g., nitrite, zinc), particularly

where the data were from humans and

evaluated endpoints of chronic as well

as acute significance. Data from lessthan-90-day studies of reproductive,

developmental, immunotoxicological,

and neurotoxicity data are also

considered appropriate for an RfD if

they identify the critical effect.

However, such data are used for RfD

determination only when supported by

a rather complete database and a good

understanding of the mode of action.

The Agency does not use data from lessthan-90-day studies purely because they

are the only available data. When the

database is inadequate to support an

RfD determination, no RfD is calculated.

E. Exposure Assessment

Default Intakes

1. Assumption That All of the Drinking

Water Consumed Is Contaminated at the

Criteria Level

Comment—A commenter questioned

the assumption that all drinking water

consumed has been contaminated to the

maximum extent allowed by the criteria. Response—Refer to response on this

same issue for Comment E.2,

Assumption That All Fish Consumed Is

Contaminated at the Criteria Level.

2. Assumption That All Fish Consumed

Is Contaminated at the Criteria Level

and All Fish May Come from One

Waterbody

Comments—Commenters questioned

the assumption that all fish consumed

have been contaminated to the

maximum extent allowed by the criteria.

They state the assumption that all of the

17.8 g/day (now 17.5 g/day) could come

from one source is unrealistic, and that

EPA should specify ways to adjust the

fish intake rates to reflect a

contaminated fish consumption rate. Response—As required under Section

304(a) of the CWA, EPA develops water

quality criteria that reflect the latest

scientific knowledge on effects of

pollutants on human health. The

Agency’s recommended 304(a) water

quality criteria are used by States and

authorized Tribes to adopt enforceable

water quality standards including

designated uses of a waterbody

consistent with Section 101(a) of the

CWA (e.g., fishing, swimming,

propagation of aquatic life, recreation).

In developing the 2000 Human Health

Methodology, we have made

assumptions about exposure to

contamination from eating fish taken

from surface waters of the United States.

The purpose of the assumptions is to

ensure that if criteria are met in a

waterbody designated with the uses

specified in Section 101(a) of the CWA,

fish consumers can safely eat fish from

that waterbody. In addition to the

assumption that 17.5 g of fish are

consumed per day based on the most

recent U.S. Department of Agriculture

(USDA) survey data (a value reflecting

the 90th percentile of the general

population), EPA also assumes that fish

and shellfish are taken from water with

pollutants present at the criteria level.

In order to ensure that people can safely

eat fish from waters designated with

Section 101(a) uses, it is necessary to

assume that all of the consumed fish is

taken from waterbodies at the criteria

level (i.e., contaminated to the

maximum safe level).

We recognize that fishing patterns

(i.e., extent and location of fishing) and

the degree to which fish and shellfish

bioaccumulate contaminants from

waters across the United States may

differ from the exposure assumptions

used to calculate national 304(a) water

quality criteria. However, the degree

and frequency of such variation are not

clearly known, and these potential

differences do not relieve EPA from its

CWA obligations to develop national

water quality criteria (which States and

authorized Tribes may modify) that are

protective for the general population.

Furthermore, we note that not all of

these differences would lead to less

restrictive (higher) AWQC. For example,

some subpopulations may consume fish

at a higher rate than the 17.5 g/day

assumed in the national 304(a) criteria,

and bioaccumulation might occur to a

higher degree than the central tendency

assumptions used in calculating the

national default BAF. As indicated

above, EPA believes that the data do not

exist to enable us to account reliably for

the myriad of spatial and temporal

differences in fishing patterns and

bioaccumulation and subsequent

differences in exposure to fish

contaminants at the national level. In

addition, we have not received

information from any stakeholder that

would allow us to make such fine

distinctions. Our goal is to ensure that

populations who rely on a particular

waterbody as the predominant source of

their fish and shellfish are adequately

protected, thus protecting the

designated use of that waterbody. For

these reasons, we believe that these

assumptions are appropriate for the

development of 304(a) criteria. Where

States and Tribes have concerns

regarding the level of protection

afforded by EPA’s national 304(a)

criteria, we encourage States and

authorized Tribes to make appropriate

adjustments to reflect local conditions

affecting fish consumption and

bioaccumulation. Guidance for making

such modifications is provided in the

2000 Human Health Methodology.

3. Body Weight Assumptions

Comments—Numerous comments

were submitted on issues regarding the

adequacy of the body weight default

values recommended in the 1998 draft

Methodology revisions and what agebased body weight categories are

appropriate. Several commenters stated

the proposed default body weights were

appropriate and that the 70 kg default

for adults is appropriate. One

commenter stated that the difference

between 70 kg and the 65 kg value for

women of childbearing age is so small

that to distinguish between the two is

unimportant. Another believed that the

recommended children’s body weights

are sufficient and that finer age

categories would not be useful at this

time. However, other commenters

addressed the potential need to use finer

age-category body weights if it is known

that the adverse health endpoint affects

a particular age group sensitive at that

developmental stage, and one

commenter stated that the broad-age

default (i.e., for 0- to 14-year-olds)

would be inappropriate for an infant.

Another commenter pointed out that the

default assumption for children ages 1

to 3 (i.e., 10 kg) is too low compared

with data from EPA’s Exposure Factors

Handbook. Other comments advocated

that EPA specifically define the

percentile value associated with the

defaults or recommended that EPA not

specify default body weights for

children.

Response—We believe it is useful to

provide default parameters for various

population groups of concern, where

possible, and have received support for

this from States and from the recent

peer review workshop panel. The

difference between the general adult

default body weight and the weight for

women of childbearing age is

statistically significant and, therefore,

we are providing this value for

situations where the critical health

endpoint is an in utero developmental

effect. All parameters used for an

exposure evaluation should reflect the

specific population group of concern.

66466 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

As stated in the 1998 draft Methodology

revisions, EPA has not provided finer

age group defaults for children because

the fish intake data do not permit

breakouts other than the broader age

category. However, in spite of this

limitation, we have included finer age

group body weights for State and Tribal

use (when they have local or regional

fish intake data that allow for their use)

in the Exposure Assessment TSD. In

most cases, we have indicated the

specific percentile from each data

source for the default value chosen

(based on the surveys used and not in

the context of the total population

because data are not available to

conclusively describe the entire

population), but we have clarified this

in the 2000 Human Health

Methodology. Associating a derived

criterion with a specific percentile is not

possible because such a quantitative

descriptor would require more detailed

distributional exposure and dose

information than is available.

EPA acknowledges that the proposed

value of 10 kg for a child ages 1 to 3 is

lower than the values reported in the

Exposure Factors Handbook (USEPA,

1997a). The 2000 Human Health

Methodology uses default body weight

values based on the more recent

NHANES III data. Contrary to the one

commenter’s suggestion, the data were

not chosen to overestimate exposures;

we intended to choose the average body

weight as a default. In all cases (i.e., for

the adult, childbearing woman, children

aged one to ten, and infant/toddler

categories), we chose average (mean)

body weight values as defaults and do

not believe these are overly

conservative.

4. Combining Consumption Intakes and

Body Weights

Comments—Several commenters

stated that when possible or where

appropriate, the intake values and body

weight data should be combined to

generate a ratio/correlation of

consumption to body weight, in order to

provide better estimates. One

commenter requested that EPA consider

deriving a 95th percentile value of the

water consumption to body weight ratio

as the basis for the national 304(a)

criteria. However, the opposite opinion

was also expressed; that is, several

commenters supported the use of

separate parameters in the derivation

equation. One commenter stated that,

based on mean intake and body weight

rates in EPA’s Exposure Factors

Handbook, differences in fish and water

intakes between pregnant women and

adults in general are so insignificant

that they are not worth distinguishing.

Opinion was also expressed that

differences in intake rates per unit body

weight can be more significant for

children. EPA was cautioned to make

sure that if differences in body weight

are considered for different age groups,

then the variation of intake by each

specific group also needs to be

considered.

Response—EPA agrees that the intake

rates and body weights for the specific

population groups should match (e.g., a

body weight for women of childbearing

age should be matched with a drinking

water intake assumption for women of

childbearing age). However, we believe

that the exposure parameter choices

should be based on the population of

concern, regardless of how small the

change in the resulting criterion might

be compared with a general adult

population default. We also believe that

there is not always a direct relationship

between consumption and body weight.

When EPA presented the issue for

review by the Agency’s SAB, they

provided the following advice:

In theory it would be better to develop

standards on a per kilogram body weight

basis. However, in practice the results are not

different enough to make much difference in

the magnitude of AWQCs. In particular, data

should not be rejected because individual

body weights are not available, and funds

should not be allocated for collecting such

data since no conceivable benefit would

accrue.

EPA has also received input from its

State stakeholders regarding potential

confusion over combining the two

parameters. Most believe that the

difference in accuracy is negligible but

that the difficulty in associating the

units of mg/kg-BW/day with a meal size,

especially for public communication

and understanding, is great and,

therefore, not particularly useful.

Several stakeholders believed that if the

data were combined as part of a study,

or if a strong, demonstrated correlation

between intake and body weight exists,

the combined parameter should be used.

We have evaluated recent information

on both drinking water intake and fish

intake from the 1994 to 1996 CSFII data

and have assessed the differences

between the two units of measure—

including an emphasis on the

differences that result with smaller age

categories and drinking water

consumption rates for children when

mL/kg-BW/day are used (USEPA

2000c,d). [Note: SAB’s comment on the

unavailability of individual body

weights is not an issue with the CSFII;

that is, this information is available.]

EPA intends to base its national 304(a)

criteria on the separate intake values

and body weights because of the strong

input received from its State

stakeholders. However, we have also

provided tables in the final Exposure

Assessment TSD of all fish/population

categories for both g/day and mg/kgBW/day, if States or Tribes prefer their

use. The TSD will also provide

examples on deriving criteria using

either, including identifying situations

where the latter estimate may provide

substantively more accurate estimates.

Additionally, the TSD will provide

tables listing comparable values in mg/

kg-BW/day (fish) or mL/kg-BW/day

(drinking water).

5. Combining Fish Intake and Body

Weights

Comments—Several commenters

recommended the use of separate fish

intake and body weight assumptions

because of clarity, familiarity among the

States, and data availability.

Specifically, the option of combining

these values was not considered

practical because most studies do not

provide such information, even if

potentially more accurate. Furthermore,

it was suggested that this complicates

the derivation process or introduces

error (an example was cited), and States

and Tribes have the flexibility to use

intake values other than the default

values provided. Another commenter

stated that there is a direct proportional

relationship between fish consumption

and body weight and that selection of

the 90th to 95th percentile value of fish

consumption per unit body weight is an

appropriate basis for deriving the

criteria.

Response—EPA agrees that the use of

separate fish intakes and body weights

is more easily understood and provides

reasonable and protective default

estimates. For additional discussion, see

our response to Comment E.4,

Combining Consumption Intakes and

Body Weights. We do not agree that

there is necessarily a direct relationship

between fish intake and body weight,

especially in the context of intake on a

per-unit-body-weight basis.

6. Default Drinking Water Intake Rates

Comments—One commenter stated

that EPA has overestimated the amount

of untreated surface water consumed by

the population. However, another

commenter believed that the 2 L/day

rate is reasonable. A commenter stated

that drinking water intake rates in hot,

arid climates may be higher than the

recommended default rate. Numerous

commenters stated that incidental water

ingestion should not be considered in

deriving AWQC or that it is

unimportant. One called for empirical

data to support its use and believed that

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66467

EPA has implied that incidental

ingestion occurs every day. However,

other commenters believed that this

route should be considered for waters

not designated as drinking water

sources. One of these requested that

EPA provide additional guidance on

incidental ingestion relevant to acute

toxicity and exposures. Another

recommended that EPA evaluate the

circumstances to determine whether the

incidental ingestion rate would make a

difference. A commenter recommended

that EPA use a 30 mL/hour assumption

in cases where short-term effects may be

considered in criteria derivation. One

commenter stated that the 10 mL/day

value would be too restrictive for use in

all nonpotable waterbodies and would

conflict with existing State guidance on

incidental ingestion.

Response—EPA acknowledges that

much of the population consumes water

from public water supplies that receive

treatment. However, we intend to

continue including the drinking water

exposure pathway in deriving AWQC

for the reasons clearly stated in the 1998

draft Methodology revisions. Refer to

that discussion for clarification on this

issue [see Federal Register Notice,

August 14, 1998; Appendix III, C.1.(b)].

We encourage States and Tribes to use

alternative intake rates if they believe

that water consumption is higher in arid

climates than the recommended default

rate. We have not assumed that

incidental ingestion occurs every day.

We have estimated an averaged rate

based on available study information.

When initiating the process to revise the

methodology, several stakeholders

identified recreational or accidental

water ingestion as a potential health

concern. A couple of States have

indicated that they already have

established incidental ingestion rates for

use in developing water quality criteria.

EPA agrees that the averaged amount is

negligible and will not have any impact

on the chemical criteria values

representative of both water and fish

ingestion. The lack of impact would

likely also be true for chemical criteria

based on fish consumption only, unless

the chemical exhibits no

bioaccumulation potential. However, we

believe that the issue could be

important for the development of

microbial contaminant water quality

criteria, and for either chemical or

microbial criteria for States where

recreational uses such as swimming and

boating are substantially higher than a

national average would indicate.

Although we will not use the incidental

ingestion intake parameter when

deriving our 304(a) national chemical

criteria, we will leave the guidance

language in the final Exposure

Assessment TSD in order to assist States

and authorized Tribes that face

situations where this intake parameter

would be of significance.

7. Default Fish Intake Rates

Comments—EPA received strong

support for its hierarchy of preferences

regarding fish intake values; that is, use

of local or regional studies, and studies

characterizing similar populations and/

or geography, over default values. EPA

also received support for encouraging

decisions on intake rates to be made at

the State or Tribal level. EPA generally

received support for its default fish

consumption rates, including the

national 304(a) criteria value of 17.8 g/

day (now 17.5 g/day based on the 1994–

96 CSFII data). There was support for

the new default rates as more accurately

representing current levels of fish

consumption among the general

population than the old assumption of

6.5 g/day. Support was also received for

providing the variety of default values

to protect highly sensitive or highly

exposed population groups. One

commenter advocated that EPA clearly

state that using the 90th percentile value

is a risk management decision.

However, others stated that EPA has

overestimated fish consumption for the

population at large. A commenter stated

that EPA should use the intake value

that its Superfund program utilizes (i.e.,

54 g/day). EPA also received support for

the default of 86.3 g/day for subsistence

fishers (now 142.4 g/day based on the

most recent USDA survey data). Some

commenters disagreed with the use of a

subsistence default as contrary to the

purpose of AWQC (while conceding its

use for site- or region-specific criteria)

or recommended that EPA caution

against the use of subsistence values

without risk management decisions

balancing risk benefits and costs. One

commenter stated that subsistence

populations are very rare and cannot

generally be defined by socioeconomic

factors and, thus, EPA’s assumption of

86.3 g/day may be over-or

underprotective. Several commenters

stated their support for the subsistence

default but also advocated that EPA

should require States to consult with

Tribes in order to select an adequate fish

consumption rate. Other comments

expressed the opinion that a Tribe

would be obligated to use EPA’s default

value if the Tribe could not conduct its

own survey or expressed concern over

the extrapolation of data from the

general population to subsistence

populations. Several commenters

questioned EPA’s choice in selecting a

value to represent the 90th percentile of

the general population, in contrast to

selecting average values for sportfishers

and subsistence fishers. A commenter

stated that the assumption of 17.8 g/day

as a default for sport anglers was not

supported by peer-reviewed studies and

contradicts the EPA’s Exposure Factors

Handbook. Another commented that

because 17.8 g/day is recommended to

represent the general population, it

should not be used to represent

sportfishers and indicated that 39 g/day

may be more appropriate. Other

comments advocated the use of actual

sportfisher/subsistence population data

or making sure that the defaults chosen

appropriately correspond to these

groups.

Two commenters stated that the

recommended values for children and

women of childbearing age were overly

conservative and inappropriate because

developmental effects would not result

from short-term exposures. However,

another commenter stated that evidence

on reproductive/developmental effects

should make EPA take the most

conservative approach to protect

pregnant women, fetuses, and young

children. Other commenters found these

values acceptable and believed that the

approach is consistent with EPA

developmental toxicity guidelines. One

commenter noted that single meal or

short-term consumption for these

groups could easily exceed the EPA

defaults. Other comments cautioned

EPA to make sure that the exposure

assumptions to protect against

developmental health effects be used

only with chemicals causing acute

toxicity, or believed the defaults are

unrealistically high and favored an

averaged daily equivalent (mean or

median value). Two commenters

believed that basing both national and

regional criteria on a fish consumption

rate in the 90th to 95th percentile would

be most appropriate, and one stated that

the high-end percentile should be used

with rates for children and women of

childbearing age to protect against

reproductive or developmental effects.

Another commented that criteria to

protect subsistence fishers or pregnant

women should be left to the States and

Tribes to consider. Still another

suggested that EPA develop special fish

consumption rates for populations that

consume much higher amounts than

average and, thus, not be overly

conservative in its default assumptions.

Two commenters questioned EPA’s

assumption that children consume more

fish on a body weight basis than adults,

and one commenter advocated use of

childhood fish consumption rates.

Concern was also expressed that all of

66468 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

the default rates assume that consumers

eat from a single source only, and that

the RSC factor results in a doublecounting of fish intake rates. One

commenter said that EPA should not

establish default values. Finally, one

commenter advocated using mean

consumption rates (not the 90th

percentile) if the Agency intends on

retaining its RSC factor.

Response—EPA acknowledges the

support for the default fish intake rates.

Our national 304(a) water quality

criteria serve as guidance to States and

authorized Tribes, who must in turn

adopt legally enforceable water quality

criteria into water quality standards.

States and authorized Tribes have the

option to develop their own criteria and

the flexibility to base those criteria on

population groups that they determine

to be at potentially greater risk because

of higher exposures, yet, EPA cannot

oblige the States to specific consulting

agreements because, again, criteria are

guidance, not enforceable regulations,

and do not impose legally binding

requirements. Therefore, we recommend

that States and Tribes give priority to

identifying and adequately protecting

their most highly exposed population by

adopting more stringent criteria, if the

State or Tribe determines that the highly

exposed populations would not be

adequately protected by criteria based

on the general population. In all cases,

States and authorized Tribes have the

flexibility to use local or regional data

that they believe to be more indicative

of the population’s fish consumption—

instead of EPA’s default rates—and we

strongly encourage the use of these data.

In most instances, using alternate fish

intake rates should not be difficult, once

the value has been determined, in that

the criteria calculation is performed by

substituting the State/Tribal intake rate

in place of EPA’s default rate. We

believe that the assumption of 17.5 g/

day (again, based on the recent 1994–96

CSFII data) will protect a majority of the

population of consumers of fresh/

estuarine finfish and shellfish,

especially population groups who rely

on a particular waterbody for most or all

of their fresh/estuarine intake. It is our

goal to utilize an intake rate that

represents more of the population than

would a central tendency value. Thus,

we intend to derive our national 304(a)

criteria using this 90th percentile

assumption, based on the updated

analysis of the 1994–96 CSFII data. EPA

also acknowledges that other Agency

programs may utilize different default

assumptions. In the case of the

Superfund program, the value used (54

g/day) represents a default used for

recreational fishers. It reflects total fish

consumption from both marine and

fresh/estuarine sources; however, it

includes only finfish, not shellfish. As

such, it cannot be directly compared to

our default based on the general

population for finfish and shellfish from

fresh/estuarine sources only. [Note: The

comparable 90th percentile CSFII value

from the 1994–96 data, if marine species

were included, would be 74.87 g/day.]

For the AWQC program, EPA believes it

has selected an appropriate, not overly

conservative default value, given the

goals of the CWA and the criteria

program.

For the rationale stated above, we

strongly believe that providing a default

rate for subsistence fishers is important

for States and Tribes, if they choose to

use it in lieu of their own study data.

We disagree with the commenter that

the concept is contrary to the purpose

of AWQC. Moreover, the commenter

appears to have incorrectly assumed

that EPA would base its national 304(a)

water quality criteria on the subsistence

fishers intake value. We intend to base

our national criteria on the

recommended value for the general

population. We emphasized in our 1998

draft Methodology revisions that States

and Tribes should consider developing

criteria based on highly exposed

populations when those populations

would not be adequately protected by

criteria based on the general population.

This is, in fact, consistent with the

purpose of AWQC. We also

acknowledge that there is variation in

fish consumption patterns, especially

among subsistence fishers. For the

purpose of providing one national

intake rate for subsistence fishers, we

believe that the value of 142.4 g/day (an

estimated national average value based

on comparing the CSFII 1994–96 data

with subsistence fisher studies) is

appropriate. Although the exact

percentile represented by the arithmetic

mean varies from survey to survey, we

believe this value is more appropriate

and protective than a median or central

tendency value—which we cautioned

against using in the 1998 draft

Methodology revisions, because median

values in the available short-duration

surveys may be zero. However, as

indicated above, EPA strongly

encourages the use of site or regionalspecific studies instead of this default

value, and the State’s/Tribe’s discretion

in considering higher intake rates than

an arithmetic mean. We reemphasize

here our four-preference hierarchy,

which is designed to give States and

Tribes more options than simply

conducting a survey or using our

default. EPA’s national 304(a) criteria

are health-based values only and are not

intended to account for cost/benefit

analyses. As indicated in our 1998 draft

Methodology revisions, risk

management decisions regarding

balancing risk benefits should be made

at the State or Tribal level.

EPA believes it is appropriate to offer

default fish intake rates for children and

women of childbearing age for States

and authorized Tribes to consider if

exposures resulting in health effects in

children or developmental effects in

fetuses are of primary concern. We have

recommended a 90th percentile from

the 1994–96 CSFII for this potential

situation, in order to protect a majority

of these population groups. As stated in

the 1998 draft Methodology revisions,

EPA is not recommending the

development of additional water quality

criteria, similar to the drinking water

health advisories, which focus on acute

or short-term effects because these are

not seen routinely as having a

meaningful role in the water quality

standards program. However, we

disagree with the commenter that

developmental effects cannot result

from short-term exposures. To the

contrary, we believe there may be

instances where the consideration of

acute or subchronic toxicity and

exposure in the derivation of AWQC is

warranted—specifically when such

toxicity and exposure are the basis of an

RfD, not a chronic effect. Only in this

situation would EPA consider such a

basis for its national 304(a) criteria.

Using long-term consumption rates to

evaluate potential developmental effects

would not accurately reflect meal size

and would be inappropriate for use in

such assessments. The separate

distribution of short-term (i.e.,

consumers-only) consumption estimates

represents the amount of fish an

individual consumes in a day, or

multiple days in a short time period, if

the person eats fish on that day. The

consumers-only consumption estimate

approximates a serving size for women

of childbearing age or for children. The

intent is to characterize consumption

over a very short period of time, not as

an average or per capita value over a

longer period of time. We recommend

the use of the short-term (consumersonly) consumption values in assessing

developmental risks to children or

women of childbearing age. However,

we intend to routinely base our national

304(a) criteria on the recommended fish

intake rate for the general population.

One commenter appears to have

incorrectly assumed that EPA would

normally base its national criteria on

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66469

acute toxicity scenarios. EPA

acknowledges that it may have

overstated the likelihood that children

are more highly exposed in terms of the

frequency of their consumption of

freshwater and estuarine fish, although

this may certainly be true for various

subpopulation groups. However, the

CSFII data clearly show that children do

consume more fish per unit body weight

than do adults. Therefore, as stated

above, we believe it is useful to provide

intake defaults to States and authorized

Tribes for children, and we have

specifically used childhood fish

consumption rates (to the extent

allowable by the CSFII data) as

advocated by the commenter.

EPA disagrees with the comment that

the sportfisher default assumption (i.e.,

that 17.5 g/day based on the 1994–96

CSFII data represents average

consumption rates for this population

group) is not supported by available

studies or by the Exposure Factors

Handbook. The value of 17.5 g/day falls

within the range of mean values from

sportfisher/angler studies reviewed by

EPA. The Exposure Factors Handbook

indicates that mean intakes from

recreational freshwater studies ranged

from 5 to 17 g/day, with mean values

from the key West et al. studies used in

the GLI between 12.1 and 16.7 g/day

(USEPA, 1997a). Furthermore, the

default rate recommended here for the

AWQC is representative of consumption

of both freshwater and estuarine fish

species, not freshwater species only. We

are also aware that some of the

sportfisher studies that support higher

estimates (e.g., 39 g/day) include marine

species.

EPA’s fish intake assumption is that

all of the consumed fish is taken from

one particular waterbody. This is to

ensure that any population can safely

eat fish from waters designated for

fishing, including those who may rely

on a single source for their fish (for

additional discussion on this issue, see

response to Comment E.2, Assumption

That All Fish Consumed Is

Contaminated at the Criteria Level).

EPA disagrees with the idea that using

a 90th percentile value as a default is

inappropriate because of the RSC factor.

The RSC is used to account for other

sources of exposure and, thus, is

independent of potential exposures

from fresh/estuarine fish. The fresh/

estuarine species are not doublecounted, as the commenter suggests.

(For additional discussion on RSC, refer

to the responses in the RSC section

below.)

8. Effect of Cooking on the Contaminant

Concentration

Comments—Commenters stated that

the concept of changes in contaminant

level caused by cooking is important to

recognize. They recommended that a

loss from cooking should be accounted

for and that EPA should provide factors

in order to calculate this loss into

criteria. However, one commenter did

not believe that increases caused by

cooking should be factored into criteria.

One commenter stated that it is not

appropriate to assume no loss as a

default when no data exist to account

for it. Another recommended that the

chemical structure be assumed as

constant before and after cooking. One

commenter stated that the relevance of

cooking methods is not clear.

Response—EPA has stated its

intention to assume no loss from

cooking unless there are adequate data

to characterize such a loss. We are

aware of some studies on cooking loss

and provide reference to quantified

information in the 2000 Human Health

Methodology. However, we believe it is

important to consider both losses and

gains in the chemical contaminant from

cooking. EPA has also received input

from several States regarding the

difficulty in making such adjustments

on a routine basis. We continue to

evaluate this issue in the context of the

national 304(a) criteria. We believe that

providing guidance on making such

adjustments may be useful in the

Exposure Assessment TSD volume for

States or Tribes that wish to modify

their criteria accordingly. However, EPA

does not intend to provide specific

cooking loss default factors.

9. Inclusion of Marine Species in the

Default Rate

Comments—A commenter stated that

coastal States have a need to derive

water quality criteria for saline waters

under their jurisdiction and, therefore,

requested additional consideration of

marine fish consumption. Another

commenter requested that EPA provide

greater clarification on its policy not to

include marine species, again believing

that States and Tribes need to include

this in their criteria development.

Response—In the 1998 draft

Methodology revisions, EPA

recommended inclusion of fresh/

estuarine species only for the intake

parameter, and accounting for the intake

of marine species as part of the RSC. We

consider this appropriate because the

304(a) water quality criteria are

applicable to discharges from fresh and

estuarine waters, not deep marine

waters. EPA’s 304(a) water quality

criteria apply to navigable waters of the

United States up the three miles offshore. However, EPA also says that

coastal States and authorized Tribes

could consider total fish consumption

(fresh/estuarine and marine species)

when appropriate for protecting the

population of concern. It is important

that the marine intake component not be

double-counted with the RSC estimate.

We maintain our default policy decision

and the flexibility afforded to a State or

authorized Tribe to base its criteria on

alternative assumptions.

10. Precision of the Drinking Water

Parameter

Comments—A commenter interpreted

EPA’s discussion on significant figures

as indicating that the drinking water

intake should not be factored into that

determination because the number

represents a science policy value. The

commenter also requested that EPA

specify a level of protection represented

by the AWQC.

Response—The commenter has

misunderstood EPA’s discussion in the

1998 draft Methodology revisions on

significant figures; they have extended

the discussion to an evaluation of

overall criteria conservativeness via

statistical analysis. We stated that the

AWQC should not necessarily always be

limited to one significant figure because

the 2 L/day drinking water value,

although supported by data, represents

a science policy decision. The

discussion only addresses the issue of

significant figures, not characterization

of criteria protectiveness. For discussion

of the issue regarding the population

protected by the criteria level, refer to

the response for Comment B.3,

Protectiveness of the Methodology.

11. Redesignation of Salmon as a Marine

Species

Comments—Some commenters

disagreed with EPA’s reclassification of

salmon to the marine category. They

stated that EPA has ignored salmon

biology and life history, that salmon is

an anadromous species, and that salmon

eggs, fry, and juveniles take up

chemicals. Commenters specifically

criticized EPA for ignoring steelhead

salmon’s life history. Three commenters

thought the redesignation is reasonable.

One had no objection to the

redesignation for threshold toxicants but

did object for carcinogenic effects based

on a linear low-dose extrapolation,

because it would not account for

exposures of salmon to ubiquitous

chemicals (e.g., PCBs) contributing a

substantial portion to total exposure.

Another commenter who supported the

redesignation advocated flexibility

66470 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

regarding coastal sportfisher

consumption.

Response—EPA has not ignored the

life history of salmon. We provided

information on the known biology and

life history of the species consumed that

were included in the CSFII survey, the

basis of the default values, in our 1998

draft Methodology revisions. The term

anadromous generally refers to a species

that spawns in fresh water or near-fresh

water and then migrates into the ocean

to grow to maturity. It can also refer to

an ocean species that spawns in fresh/

near-fresh waters. The life cycles of

anadromous species vary as to whether

they remain in fresh/near-fresh waters

until they die or whether they return to

ocean waters after spawning. As such,

the description provided by EPA in the

1998 draft Methodology revisions is

correct and does not conflict with the

term anadromous. The CSFII food codes

for salmon do not indicate the source of

the salmon (e.g., land-locked freshwater,

farm-raised, or wild). We based our

allocation of salmon between freshwater

and marine habitats on commercial

landings data provided by the National

Marine Fisheries Service for the period

1989–1991. All landings of Pacific

salmon, including chum, coho, king,

pink, or sockeye, were assigned to the

marine habitat. All land-locked Great

Lakes salmon and farmed salmon

received the classification of fresh

water. The resulting apportionment for

salmon was 1.18% to the fresh-water

habitat and 98.82% to the marine

habitat. We believe this is appropriate

for our national default intake rates.

EPA understands that steelhead

salmon, also known as steelhead trout

(Oncorhynchus mykiss), is an

oceangoing version of rainbow trout

with a complicated life history, and may

spend a significant portion of its

lifetime in fresh waters. States and

authorized Tribes have the flexibility to

use different assumptions in deriving

their water quality criteria, as we stated

in the 1998 draft Methodology revisions.

That is, States and authorized Tribes

could make alternative assumptions to

specifically account for steelhead

salmon intake. We strongly encourage

States and authorized Tribes to do so, as

reflected by the recommended fish

intake hierarchy of preferences.

However, we do not intend to ignore the

contribution from salmon in the

calculation of our 304(a) criteria. We

recommended accounting for this as

part of the RSC, thereby ensuring that

the criteria would account for the

contribution of a contaminant from

marine salmon.

12. Studies on Sportfishers and

Subsistence Fishers

Comments—Two commenters stated

that in summarizing various sportfisher

and subsistence fisher studies, EPA

failed to provide direction on how

States or Tribes can use and interpret

the information. One commenter

requested additional guidance on the

use of local data, while cautioning about

such data’s reliability. Commenters also

listed errors, discrepancies, or missing

information from numerous studies that

appear in the 1998 draft TSD. One

commenter recommended separating

studies by type, population, and basis

for consumption rate (presumably

referring to habitat designations of fish),

along with providing comments on the

studies. Another stated that many angler

studies are biased because the

respondents are more ‘‘avid’’ in their

fishing habits, and a study of freshwater anglers from Maine might serve

better as the basis of EPA’s default for

sportfishers.

Response—It is EPA’s intention to

provide summaries of various studies

for States and Tribes to consider using

and, as such, the Agency is merely

providing information, not critiquing or

endorsing particular studies. We do not

intend to rank the studies because there

are significant differences in the

purposes and limitations of each study,

in addition to the fact that consumption

rates vary significantly throughout the

country. Therefore, any particular study

may be most appropriate to the State or

Tribe’s particular circumstances.

However, we are committed to

providing accurate information and

intend to correct errors or missing

information that would make the

summaries of greater use to States and

Tribes. We have reviewed the

commenters’ listed errors or omissions

and made appropriate changes. EPA

disagrees that any of the sportfisher

studies are biased from ‘‘avidity’’ among

recreational anglers. Although the rates

may vary significantly from study to

study, the studies specifically sample

fishing patterns of these groups and are

the most appropriate data for

prospective use by States and Tribes.

We considered the Maine angler study

along with the others presented in the

1998 draft TSD to evaluate the range of

mean values before recommending the

default value. However, we do not

believe this particular study is

necessarily best suited for deriving a

national default value. Just as with

EPA’s national 304(a) criteria, States

and Tribes always have the flexibility to

use other local- or regional-specific

studies. We have provided additional

guidance on how to consider the studies

included in the Exposure Assessment

TSD.

13. USDA Continuing Survey of Food

Intake by Individuals (CSFII)

Comments—Some commenters

believed that the CSFII data are

appropriate for deriving AWQC and

supported their use in the hierarchy of

choices. Others stated that the CSFII

data are not appropriate because they

include marine species, and combine

recreationally and commercially

acquired species. One commenter

suggested that a significant fraction of

the default rate would include farmraised fish, which would not

bioaccumulate the same as wild fish.

One commenter stated that the default

inappropriately assumes consumption

from a single waterbody. Two

commenters stated that the CSFII data

are biased toward individuals

consuming large quantities of fish

(assuming constant consumption every

day and failing to consider those people

who consume less frequently). One of

these stated that the CSFII assumes that

participants who did not eat fish during

the study period are not fish eaters.

Several commenters recommended that

longer term studies be used, one

specifically stating the difficulty in

estimating the upper end of the

distribution. Comments also referred to

or recommended data from NPD

Research Inc. or the Tuna Research

Institute, presumably referring to the

National Purchase Diary (NPD). One

commenter assumed that the CSFII

default estimates exclude individuals

who consume fish but did not report

consumption during the sampling

period. Another questioned dividing

reported consumption by the days of the

survey and incorporating

nonconsumption. Instead, this

commenter recommended using the

positive values only (‘‘acute

consumers’’) for determining default

intake rates, which it believed to be

consistent with the concept of

identifying the population to be

protected. One commenter also

indicated that intake rates do not vary

significantly for fish obtained from

different sources—that is, fresh or

marine waters. Another stated that the

CSFII data assume short-term

consumption is representative of longterm consumption. One commenter

advocated that EPA use probabilistic

methods to derive AWQC.

Response—The comments are

incorrect about the exclusion of

respondents who did not report fish

consumption during the CSFII sampling

period. The general population,

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66471

recreational fisher, and subsistence

fisher default values all include both

CSFII respondents who reported eating

fish during the sampling period and

respondents who reported zero

consumption (what the commenter

referred to as ‘‘non-consumers’’). The

CSFII mean values are not biased.

Specifically, the intraindividual

variation does not bias estimates of the

mean intake of the population. The

estimates of the upper percentiles of per

capita fish consumption based on the

short sampling period data may be

biased upward, thereby resulting in a

conservative estimate of risk. However,

the extent to which this is overestimated

is not knowable. We note that we did

not rely exclusively on the CSFII data;

rather, the data were analyzed with

those from other studies (especially for

recreational fisher and subsistence

fisher estimates) to evaluate and

corroborate our decision. We believe the

CSFII data are representative of fish

intake rates among the general

population. As part of the CSFII

analysis, sampling weights were

adjusted to account for nonresponse and

were subsequently reweighted using

regression techniques that calibrated the

sample to match characteristics

correlated with eating behavior.

EPA generated mean and percentile

estimates of daily average per capita fish

consumption based on the USDA 1994–

96 CSFII. The strengths of this survey

for supporting estimates of per capita

food consumption are twofold. First, the

survey design is structured to obtain a

statistically representative sample of the

U.S. population. Second, the survey is

designed to record daily intakes of foods

and nutrients and to support estimation

of food consumption. These features are

in direct alignment with the objective of

producing current, per capita fish

consumption estimates for the U.S.

population. The 1994–96 CSFII

collected two non-consecutive days of

food consumption data from a sample of

11,912 individuals in the 50 states and

the District of Columbia. The method

employed to collect dietary intake data

also strengthened the CSFII design for

supporting per capita consumption

estimates. For example, the survey was

administered by an interviewer on both

days of data collection. For these

reasons, we believe that the 1994–96

CSFII is the best source of data on a

nationwide basis for estimating fish

consumption by the U.S. population.

The NPD study was conducted over

25 years ago. The NPD is the basis of the

6.5 g/day default value that EPA has

historically used for fresh/estuarine fish

consumption. We have received

consistently strong input from many of

our stakeholders (including States and

Tribes) who consider the 6.5 g/day

value inadequate and advocate the use

of much more recent data. The Agency

also believes that such an update is

needed. We are not aware of any

subsequent major survey conducted

during a 30-day period as was done by

the NPD. The Agency does not believe

that the year-long study of 29 people

mentioned by one commenter is

appropriate to use for a national default

value. The use of probabilistic methods

was discussed earlier in our response to

Comment B.3, Protectiveness of the

Methodology.

EPA also believes that its discussion

of identifying population groups to

protect is not contradicted by its

combining positive and zero values to

estimate long-term or average

consumption. We reiterate here that we

believe the summation of the amounts

of fish consumed by each individual

across the 2-day reporting period for the

CSFII 1994–96 data (formerly a 3-day

reporting period), followed by dividing

that total individual consumption by 2,

is a reasonable approach to estimating

average consumption. The CSFII did not

specifically ask questions on whether

respondents consume fish or how often

and, therefore, it is not possible to

distinguish fish consumers from fish

nonconsumers. EPA is aware from other

major surveys that most people

consume fish—at least episodically—

and, therefore, believes that using the

positive and zero values from the CSFII

is a reasonable method of estimating

average intake. We contrast this to using

only the subset of survey responses

where fish was actually consumed as a

method to estimate an ‘‘acute

consumer,’’ that is, to provide an

estimate of the amount of fish consumed

in the context of acute or short-term

exposures (not in the context of average

or long-term exposures).

The commenters are also incorrect

about the inclusion of marine species.

The proposed default rates for the

general population, as well as for

children and women of childbearing

age, are based on freshwater and

estuarine species only. The CSFII study

does include marine species and EPA

has additionally provided States and

Tribes with these data in the Exposure

Assessment TSD; however, they are not

included in the default estimates of

national freshwater and estuarine fish

consumption. According to the CSFII

data, most persons in the general

population appear to consume more

marine species than fresh/estuarine

species. However, EPA supports State/

Tribal use of local or regional data that

indicate otherwise. We have not made

any specific assumptions regarding

farm-raised fish and their contribution

to the default intake rate, nor have we

received any information that would

allow us to characterize (or discount)

the amount that farm-raised fish

contributes to the national default value

or to differentiate bioaccumulation

levels.

14. Use of Uncooked or As Consumed

Fish Weight for Default Intake Rates

Comments—One commenter stated

that either raw weight or cooked weight

can be appropriate as long as the effect

of cooking on the contaminant is

accounted for. Some commenters stated

that the cooked weights are the most

technically defensible, because they are

the basis for the consumption estimates.

However, others believed the default

intakes should be adjusted to reflect

uncooked weights, with one commenter

concerned that a cooked weight would

result in incomplete accounting of

exposure to threshold toxicants. One

commenter also pointed out the

difficulty of making appropriate

adjustments to the BAF because of

uncertainties in concentration levels of

contaminant due to cooking and that

many cooking techniques result in

retention of fish fluids. Another

commenter stressed the need to use

uncooked weights in order to be

consistent with fish tissue studies and

BAF values. One commenter expressed

concern that use of cooked weights

would produce an inadequately

protective criterion for mercury, while

another believed that cooked values

introduce a source of uncontrolled

variability.

Response—We have considered the

pros and cons of using uncooked/as

consumed weights on several levels.

First, the intake parameters of the

criteria derivation equation are intended

to capture ingestion—that is, what

people actually consume and are

exposed to. By and large, people

consume cooked fish, and if raw

shellfish or sushi was consumed by the

CSFII respondents, those intakes were

included in the as consumed weights.

This assumption is also consistent with

the dietary estimates based on prepared

foods (not raw commodities) that are

made by both EPA’s pesticide program

and the Food and Drug Administration

(FDA) Total Diet Study program. We

also considered the ‘‘consistency’’ issue

in the context of the fact that the CSFII

survey respondents estimated the

weight of fish that they consumed.

Similar to the CSFII, EPA’s GLI was

based on a consumption survey of fish

intakes for prepared meals. EPA

additionally considered the effect of the

66472 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

cooking process. There are

comparatively few chemicals for which

measurements are available, and the

process is complicated further by the

different parts of a fish where the

chemical may accumulate, the method

of preparation, and how the cooking

process may transform the chemical.

What is certain is that the mass of the

contaminant will either remain constant

or be reduced. The resulting

concentration is harder to predict. In the

1998 draft Methodology revisions, we

recommended the use of as consumed

weights and an adjustment of the

bioaccumulation factor for cooking loss,

if information was available. Otherwise,

we recommended using the as

consumed weight along with the full

bioaccumulation factor (unadjusted for

cooking loss), which would produce

slightly more stringent AWQC. We have

also received input from stakeholders

regarding potential confusion over the

fact that uncooked weights are used in

the Agency’s fish advisory program and

that having two sets of values may prove

confusing to States and Tribes, as well

as the general public. Furthermore, the

measures of a contaminant in fish tissue

samples that would be applicable to

either compliance monitoring or the

permitting program are related to the

uncooked fish weights.

Therefore, EPA has reconsidered its

position based on these facts and

despite the fact that the as consumed

values more accurately represent actual

intake, we will derive our national

304(a) criteria on the uncooked weight

fish intakes. The approach of using an

uncooked weight in the calculation will

result in somewhat more stringent

AWQC (studies indicate that, typically,

the weight loss in cooking is about

20%). We will also provide guidance on

site-specific modifications in the

Exposure Assessment TSD. Specifically,

we will describe an alternative approach

for calculating the AWQC using the as

consumed weight (again, more directly

associated with exposure and risk)

which is subsequently adjusted by the

approximate 20% cooking loss to a

resultant uncooked equivalent. Thus,

the AWQC conversion to an uncooked

equivalent can be consistently used

between State/Tribal standards

programs and still represent the same

relative risk as the as consumed value.

It is important to understand that the

two approaches will not result in the

same AWQC value. Whereas the as

consumed approach is more

scientifically rigorous and represents a

more direct translation of the as

consumed risk to the uncooked

equivalent, it may be too intensive a

process to expect of State and Tribal

organizations whose resources are

already constrained.

Relative Source Contribution (RSC)

15. Default Percentages and RSC Floor

of 20% and Ceiling of 80%

Comments—A commenter criticized

EPA’s recommended RSC default rate in

the face of uncertainty about other

routes of exposure. Another commenter

considered the ceiling of 80% to be a

redundant uncertainty factor. Other

comments suggested the use of an 80%

RSC for bioaccumulative chemicals so

that the contribution from fish

consumption would not be

underestimated, did not support the

range of 20% to 80%, or requested

additional justification for the

assignments of 20%, 50%, or 80%.

Response—EPA has recommended

using the 20% RSC default when routes

of water exposure other than oral or

sources of exposure other than fish and

water are anticipated, but adequate data

are lacking to quantify those exposures.

When data are adequate, they should be

used instead of the default. If it can be

demonstrated that other sources and

routes of exposure are not anticipated

for the chemical in question (based on

information about its known/anticipated

uses and chemical/physical properties),

then the 80% ceiling is recommended.

The ceiling is intended to provide

adequate protection for those who

experience exposures (from any or

several sources) higher than available

data indicate. For many of the chemical

contaminants that EPA evaluates, data

are not available on multipathway

exposures. It is possible that as we

progress with our development of a

cumulative risk policy, we may find an

80% RSC to be underprotective. This

concern was expressed during the

scientific peer review workshop on the

Methodology. One commenter

misunderstood the application of lower

ceilings (i.e., 50%, 20%) when existing

information indicates no other mediaspecific uses or sources. Also, some

chemicals that bioaccumulate in fish

also bioaccumulate in other meat and

dairy products (e.g., dioxins). Therefore,

to simply assume an 80% default in all

cases would not be appropriate. The

RSC approach allows for an

apportionment of 80% when

information indicates that other

exposures are not relevant for the

chemical being evaluated. EPA has

added discussion in the final

Methodology to address these situations

and to better explain the application of

the lower ceilings.

16. Duplication of Fish Intake

Assumptions

Comments—Commenters stated that

applying an RSC factor results in a

double-counting of fish from other

sources.

Response—The commenters are

incorrect. The fish intake default used

in the equation accounts for fresh and

estuarine species only. The RSC factor

potentially applies to nonfish dietary

intake, air exposures, and marine fish

species. To protect humans who

additionally consume marine species of

fish, the marine portion should be

considered as part of the ‘‘other sources

of exposure,’’ that is, part of the RSC or

dietary value. EPA specifically

emphasized in the 1998 draft

Methodology revisions that States and

authorized Tribes need to ensure, when

evaluating overall exposure to a

contaminant, that the marine fish intake

is not double-counted with the dietary

intake estimate used. This applies if the

State or authorized Tribe chooses to

account for total fish consumption (i.e.,

fresh/estuarine and marine species) in

the fish intake parameter used in the

AWQC equation.

17. Exposure Route Differences

Comments—EPA received support for

its rationale on accounting for

differences in bioavailability and

absorption between exposure routes

when data are available, and assuming

equal rates when data are absent.

Response—We acknowledge this

support.

18. Need for an RSC Factor/Considering

Multiple Routes of Exposure

Comments—Commenters supported

the greater emphasis on RSC, including

the use of empirical data. Some stated

that EPA should give full consideration

to multiple routes of exposure (i.e.,

ingestion, inhalation, dermal), with

emphasis on the variety of water-related

activities, cultural practices, and

lifestyles. Several commenters pointed

to published studies on assessing

inhalation and dermal exposures, and

two commenters advocated that EPA

determine when there is a need to factor

in these exposures, based on available

information on the chemical. One

commenter stated that there are

circumstances where inhalation

exposures can be a significant portion of

total exposure (e.g., for some chemicals

during showering). However, another

suggested that consideration of

inhalation and dermal exposures is

premature. Two commenters stated that

uncertainty factors, severity of effects,

essentiality, and additive/synergistic

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66473

effects should be factored into the RfD

apportionment, with one believing that

this should also include the option of

developing less stringent criteria when

there is great uncertainty in the data.

Five commenters stated that they

believe the RSC/Exposure Decision Tree

concepts represent an unnecessary

safety factor or should not be

considered. One suggested that the

water quality criterion should relate

only to water exposures. Two

commenters suggested that factoring in

other exposures is ‘‘penalizing’’ the

AWQC and makes them overall

environmental exposure criteria.

Another questioned the need to

apportion the RfD, but focused on

drinking water regulations, stating that

accounting for other sources of exposure

would likely have no benefit,

presumably due to conservatism in the

RfD derivation (yet acknowledging that

those uncertainty factors are

independent of the exposure

assessment). Several commenters

recommended that EPA reconsider the

SAB’s advice not to routinely apportion

the RfD. Others believed that the RSC

should be used only for site-specific

criteria, or that States should have the

flexibility to make adjustments for local

conditions. Two commenters also stated

that the Exposure Decision Tree is

unclear, is overly complicated, or has

unrealistic data requirements. Another

stated that the approach is generally

desirable but that EPA needs to provide

a greater and more easy-to-follow

explanation of the rationale, indicating

policy judgments where they occur.

However, other commenters supported

the Decision Tree approach for its

facilitation of identifying the decisions

necessary to select the most appropriate

RSC value and considered it

scientifically valid. One commenter

cautioned that if probabilistic analysis

techniques are used, their application

must be valid and underlying

assumptions clearly indicated.

Commenters expressed the need for data

to avoid the 20% default, others stated

that defaults should be avoided

altogether, and one recommended a

100% RSC for highly bioaccumulative

chemicals. One of the supporters

believed that the approach is a

reasonable compromise between

avoiding problematic increases in

exposures to substances and not setting

unduly restrictive requirements. A

commenter questioned how new data

would be considered in the context of

RSCs based on older data. Another

recommended that non-zero values for

other exposure sources not be assumed

unless a significant number of samples

are positive. It was also recommended

that EPA coordinate the RSC policy

with other Agency programs.

Response—EPA disagrees that the

RSC represents an excessive or

unnecessary safety factor. The purpose

of the RSC is to ensure that the level of

a chemical allowed by a criterion or

multiple criteria, when combined with

other identified sources of exposure

common to the population of concern,

will not result in exposures that exceed

the RfD or POD/UF. The policy of

considering multiple sources of

exposure when deriving health-based

criteria has become common in EPA’s

program office risk characterizations

and criteria and standard-setting

actions. Since the SAB expressed

concerns in 1993, numerous Agency

workgroups have evaluated the

appropriateness of factoring in such

exposures and concluded that it is

important for adequately protecting

human health. Consequently, Agency

policy has evolved significantly over the

last 6 years. Various EPA program

initiatives and policy documents

regarding aggregate exposure and

cumulative risk have been developed,

and include consideration of inhalation

and dermal exposures. Additionally,

accounting for other exposures has been

discussed in recent mandates (e.g., the

Food Quality Protection Act) and, thus,

is becoming a requirement for the

Agency. The RSC approach has been

shared with other EPA offices, and

efforts to coordinate policies on

aggregate exposure, where appropriate,

have begun. EPA intends to continue

developing guidance on the RSC issue

and guidance to address the concern

that human health may not be

adequately protected if criteria allow for

higher levels of exposure that,

combined, may exceed the RfD or POD/

UF. We also intend to refine the 2000

Human Health Methodology in the near

future to incorporate guidance on

inhalation and dermal exposures. As

stated previously, we are required to

derive water quality criteria under

Section 304(a) of the CWA and do not

intend to derive site-specific criteria for

individual waterbodies. However, States

and authorized Tribes do have the

flexibility to make different exposure

and RSC estimates based on local data.

Uncertainty factors used in the

derivation of the RfD to account for

intra-and interspecies variability and

the incompleteness of the toxicity

dataset(s)/animal studies are specifically

relevant to the chemical’s internal

toxicological action, irrespective of the

sources of exposure to humans. The

Agency’s policy is to consider and

account for other sources of exposure in

order to set protective health criteria.

We disagree that uncertainty in the data

should result in less stringent criteria.

However, we have provided additional

clarification on the guidance allowing

less stringent assumptions when

multiple sources of exposure are not

anticipated.

The adequacy requirements for the

Exposure Decision Tree are not unduly

restrictive. The ideas of

representativeness, quality assurance,

and sampling size are fundamental to

properly conducted monitoring studies.

Furthermore, the minimal requirement

of samples to make an (at least,

nominally) acceptable estimate of

average and high-end exposure from

that relative source (i.e., 45 samples) is

not unreasonable guidance. EPA also

believes that the number of decision

points in the Decision Tree for any

particular chemical are not excessive.

We have provided additional discussion

in the 2000 Human Health Methodology

in order to clarify numerous issues on

the Decision Tree approach, including

the discussion on the use of defaults.

We believe that probabilistic techniques

are potentially appropriate for use and

agree that they must be valid,

appropriately applied, and clearly

presented.

Regarding changes in ambient

chemical concentrations that would

affect the RSC calculation, States and

authorized Tribes have the opportunity

to make changes in their water quality

standards during triennial reviews, and

EPA would evaluate those changes

based on information submitted with

the proposed changes. Similarly, EPA

would consider changes to AWQC when

significant changes in sources of

exposure occur that affect the default

values.

19. Use of RSC With Carcinogenic

Effects Based on Linear Low-Dose

Extrapolation

Comments—A commenter advocated

the use of an RSC factor with

carcinogenic effects based on linear lowdose extrapolation in order to account

for other sources of exposure.

Response—EPA does not apply the

RSC to carcinogenic effects based on

linear low-dose extrapolation because

the AWQC are being determined with

respect to the incremental lifetime

cancer risk posed by a substance’s

presence in the exposure sources

relevant to the specific criterion, not in

terms of an individual’s total cancer risk

from all sources of exposure. In the case

of carcinogens based on nonlinear lowdose response extrapolation or a

noncancer endpoint where a threshold

is assumed to exist, non-water

66474 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

exposures (i.e., non-drinking water and

non-fish ingestion exposures, and

inhalation or dermal exposures) are

considered when deriving the AWQC.

The rationale for this approach has been

that for pollutants with effect

thresholds, the objective of the AWQC

is to ensure that an individual’s total

exposure does not exceed that threshold

level. Health-based and mediumspecific criteria values for carcinogens

based on a linear low-dose extrapolation

typically vary from other mediumspecific criteria values in terms of the

concentration value, and often the

associated risk level. Therefore, the RSC

concept could not apply unless all risk

assessments for a particular carcinogen

based on a linear low-dose extrapolation

used the same concentration value and

same risk level; that is, an

apportionment would need to be based

on a single risk concentration value and

level.

20. Use of Subtraction or Percentage

Methods in RSC Apportionment

Comments—One commenter

advocated the subtraction method

instead of the percentage method for

RfD apportionment, and advocated the

use of central tendency values. This

commenter criticized the percentage

method as irrational and likely to

produce overly stringent criteria. In

addition, it was stated that the

percentage method would allow criteria

that could result in exposure levels that

exceed the RfD when combined

exposures are high. Other commenters

expressed concern over basing the RSC

on current levels of contamination.

However, one believed that the

percentage apportionment was

reasonable given the difficulty in

alternative apportionment methods (for

example, an apportionment that would

minimize the costs of reducing total

exposure to/below a certain amount).

One commenter suggested using a

multiple default system.

Response—The first commenter has

significantly misunderstood EPA’s

policy goals. The argument against use

of the percentage approach is based on

the idea that the maximum possible

amount of chemical concentration, after

subtracting other sources, should be

allocated to drinking water criteria or

standards. This is not EPA’s goal nor is

it stated in any relevant mandate. The

rationale of deliberately removing the

entire cushion between precriteria

levels (i.e., actual levels) and the RfD,

and thereby setting criteria at the

highest levels short of exceeding the

RfD, is counter to the goals of the CWA

for maintaining and restoring the

nation’s waters. It is also directly

counter to Agency policies, explicitly

stated in numerous programs, regarding

pollution prevention. EPA has

advocated that it is good health policy

to set criteria such that exposures are

kept low when current levels are

already low. The subtraction method

generally results in prospective criteria

values for a contaminant in a particular

medium at significantly higher levels

than the percentage method and, in this

respect, is contradictory to these Agency

goals. In fact, many chemicals have

existing levels in environmental media,

based on available monitoring data,

substantially lower (compared with the

RfD) than the resulting criteria allow.

This is the case with most of the

theoretical examples that one

commenter provided to refute the

method.

The Agency has modified its policy

with the Exposure Decision Tree

approach to allow use of the subtraction

method when multiple media criteria

are not relevant. The Agency RSC

Workgroup recommended that, although

combined exposures above the RfD may

or may not present an actual health risk,

a combination of health standards

exceeding the RfD may not be

sufficiently protective. Therefore: (1)

Maintaining total exposure below the

RfD is a reasonable health goal; (2) there

are circumstances where health-based

criteria for a chemical should not

exceed the RfD (either alone or in

combination); and (3) the best way to

prevent exceedance of the RfD is to

apportion it when multiple health

criteria are relevant to a given chemical.

We believe that the percentage method

is rational in the context of the above

goals when multiple media criteria are

at issue. However, as a commenter

suggested, the percentage method does

not simply depend only on the amount

of the contaminant in the prospective

criterion source. It is not a set amount.

It is intended to reflect health

considerations, the relative contribution

of other sources, and the likelihood for

ever-changing levels in each of those

multiple sources (due to ever-changing

sources of emissions and discharges).

The percentage method does not break

any ‘‘logical link,’’ as a commenter

suggested (the commenter referenced an

unpublished report from discussions

prior to the development of the

Exposure Decision Tree approach). EPA

is interested in knowing the amounts of

current exposures, including water, and

is always cognizant of their relationship

to the RfD (one commenter suggested

that EPA does not compare actual

exposures to the RfD; this comparison is

always known). We have historically

evaluated chemicals in the context of

their current levels (i.e., ambient levels

prior to either criteria development or

regulatory activity). Evaluating these

levels, along with the hazard

identification, has historically formed

the basis for prioritization and whether

the Agency would pursue criteria or

standards development. We disagree

with the comment that criteria should

be set without regard to the actual level

of the contaminant. Actual levels are

advocated by a commenter for use with

the subtraction method. In the case of

multiple criteria for a given chemical,

the commenter’s claim that the

subtraction method will ensure that ‘‘an

individual’s exposure to a chemical

does not exceed the RfD’’ is not

necessarily guaranteed if criteria for

other media allow for concentrations in

environmental media that, combined,

may result in exposures greater than the

RfD. EPA acknowledges that the

percentage approach outcome varies

depending on the magnitude of current

exposures, and we have sought to

provide greater clarification on this

policy issue in the 2000 Human Health

Methodology. Of course, depending on

the levels from each source, the

subtraction method can also produce

unstable values—that is, they could vary

from very high, to moderate, to very

low, even to a negative number.

As previously indicated, probabilistic

analyses are appropriate when they are

validated techniques that are applied

correctly and supported by adequate

data. However, much of the time, the

amount of data available to describe

distributions of exposure from various

known sources to the U.S. population—

for use in setting nationwide criteria—

is inadequate to support meaningful

probabilistic analyses. Nevertheless,

rather than simply using a default value

in every instance, the Agency attempts

to compare exposure intakes based on

available data to estimate their relative

contribution to the total—given that

understanding the degree to which their

concentrations vary, or making any

distributional analysis, is not possible.

When multiple criteria are at issue, the

criteria values are based on the best

available information, with an

assumption that there may be enough

relative variability such that an

apportionment (relating that percentage

to the RfD) is a reasonable way of

accounting for the uncertainty regarding

that variability. Again, in the context of

making an estimate of potential national

exposures, there is great uncertainty in

the range of exposures, and as

previously stated, the goal is not to

allow a water criterion to use up the

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66475

‘‘space’’ between the total exposure and

the RfD. An example of the percentage

apportionment’s potential use is when

pesticides are at issue. It does not make

sense to allow the water criterion to use

up that space when (in terms of the

chemical’s intended uses) the dietary

route is obviously the ‘‘direct’’ source of

exposure. When the course of pesticide

tolerance-setting activities may, over

time, vary the exact amount of the RfD

taken up, an apportionment may also be

best for pesticide program planning. The

Exposure Decision Tree has allowed for

the use of the subtraction approach

when only one criterion is relevant.

Also, given the future need to develop

cumulative risk policies, the subtraction

method in these cases could be a shortlived option.

Finally, one commenter incorrectly

assumed that the percentage method

would allow criteria that could result in

exposure levels that exceed the RfD

when combined exposures are high.

Again, this commenter incorrectly

assumed that EPA is not aware of the

relationship of the estimated exposures

to the RfD. The Exposure Decision Tree

approach states that, in these situations,

a risk management decision would be

made in order to reduce exposures to

levels that would prevent exceedance of

the RfD. We have provided greater

clarification on this issue in the 2000

Human Health Methodology. We have

also provided clarification on the use of

central tendency values when

estimating exposures, which we do not

believe to be fully adequate for

protection of human health when

setting national 304(a) criteria.

F. Bioaccumulation

1. Use of Bioaccumulation Factors

(BAFs) in General

Comments—Overall, commenters

were not adverse to incorporating

bioaccumulation into criteria derivation,

but were concerned with the

methodology EPA proposed to use. Most

comments received were focused on the

general use of BAFs. Because of the sitespecific nature that BAFs can take,

several commenters are concerned with

applying national BAFs developed from

a limited set of data and array of aquatic

systems, or from a model, to all

waterbodies in the United States. Some

commenters did not agree with EPA’s

proposed BAF tiered hierarchy. These

commenters stated that EPA should not

derive single national BAFs because

there is substantial variation among

waterbodies in factors that influence

bioaccumulation (e.g., food chain,

metabolism, bioavailability, loading

history). They recommended that BAFs

be calculated on a site-specific basis, or

that field-derived BAFs be used in

conjunction with modeled BAFs in a

weight-of-evidence approach to select a

final BAF. Some commenters also

wanted the BAF guidance to more

clearly state how it applies to different

groups of compounds (e.g., nonionic

organics, ionic organics, metals,

organometallics). Several commenters

did agree with EPA that field-derived

BAFs better reflect potential exposure to

chemicals from all sources than BCFs

and incorporate factors in the field (e.g.,

food chain, metabolism, chemical

loading history, temperature) that can

affect bioaccumulation.

Response—Although EPA

acknowledges there are site-specific

factors that affect bioaccumulation, we

disagree that national BAFs should not

be derived. For some pollutants (e.g.,

PCBs, methylmercury), biomagnification

through the food chain can be

substantial. Using a BCF, which only

accounts for exposure from the ambient

water, could substantially

underestimate the potential exposure to

humans for some chemicals and result

in criteria that are underprotective of

the designated uses. Since publishing

the 1980 Methodology, there has been a

growing body of scientific knowledge

that clearly supports the observation

that bioaccumulation and

biomagnification occur and are

important exposure issues to consider

for many highly hydrophobic organic

compounds and certain organometallics

(Russell et al., 1999; Fisk et al., 1998;

USEPA, 1998d; Watras and Bloom,

1992; Oliver and Niimi, 1988;

Swackhammer and Hites, 1988; Niimi,

1985; Oliver and Niimi, 1983). For

highly persistent and bioaccumulative

chemicals that are not easily

metabolized, BCFs do not reflect what

the science indicates. For this group of

chemicals, bioaccumulation (i.e.,

accumulation of a chemical in aquatic

biota from all routes of exposure) should

be accounted for in the derivation of

water quality criteria in order to protect

against unacceptable risks from

contaminated biota. The use of properly

derived BAFs will enable chemical

exposure from all sources to be

accounted for in water quality criteria.

The lack of national BAFs would greatly

hinder the development of water quality

criteria because many States and

authorized Tribes may not have the

resources to develop site-specific BAFs.

We continue to believe that using

national BAFs is the most scientifically

valid approach to deriving national

AWQC.

EPA acknowledges that data available

to derive national BAFs and to validate

the overall bioaccumulation

methodology are primarily limited to

persistent, hydrophobic chemicals from

selected locations (e.g., Lake Ontario,

Green Bay, Bayou d’Inde, Hudson

River). However, we believe these

chemicals and sites encompass a

reasonable range of chemicals,

locations, and ecosystems from which to

evaluate the appropriateness of the

bioaccumulation methodology. To

obtain better representation of lotic (e.g.,

river) systems, we also performed

evaluation of the predictive BAF

methods with PCB, pesticide, and

chlorinated benzene data from the

Hudson River and Fox River/Green Bay.

In the vast majority of comparisons

between the predicted BAFs and fieldmeasured BAFs using all four methods,

the predicted BAFs were in very good

agreement with the field-measured

BAFs. We further acknowledge

commenters’ concerns that certain

portions of the methodology may not be

applicable to some types of chemicals.

As a result, we have developed

additional guidance that restricts some

aspects of the methodology to certain

types of chemicals. For example, we

have revised the 1998 draft

Methodology revisions to remove the

use of Kow×FCM to estimate BAFs for

chemicals that have been consistently

shown to be metabolized substantially

in aquatic biota (e.g., certain PAHs) and

have clearly differentiated which

methods apply to ionizable chemicals

and which do not.

We also recognize that there were

some uncertainties in the 1998 draft

Methodology revisions on how the BAF

methodology would be applied both

nationally and on a site-specific basis.

In response to this, we made substantial

revisions to the 1998 draft

bioaccumulation methodology which

we believe makes the revised

methodology applicable on a national

basis. First, we improved the readability

and guidance presented in the

bioaccumulation methodology based on

public and peer reviewers’ comments.

Specifically, we separated guidance for

developing national BAFs from

guidance for developing site- or regionspecific BAFs and revised the

Methodology document to make it more

clear to the reader on how EPA will

derive national BAFs. Second, EPA

expanded the guidance for deriving siteor region-specific BAFs to better enable

such adjustments to be made by States

and authorized Tribes. For example, we

updated, expanded, and made more

accessible the databases used to develop

national values for lipid content in

aquatic biota and organic carbon content

66476 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

in water. Third, we plan to develop

detailed guidance to assist States and

authorized Tribes in designing and

conducting field studies to measure sitespecific BAFs and BSAFs (biotasediment accumulation factors). This

guidance will specify our

recommendations for how, when,

where, and how often one should

sample water, biota, and sediment for

producing reliable measurements of

BAFs and BSAFs.

In addition to improved clarity and

expanded guidance, EPA believes the

changes we made to the national BAF

methodology address concern indicated

by some public commenters about

uncertainty in various aspects of the

methodology. We believe the changes

we have made reduce the uncertainty in

several components of the national BAF

methodology. For example,

development of separate procedures for

deriving BAFs for different chemical

classes (e.g., high vs. low

hydrophobicity, high vs. low

metabolism in biota, ionic vs. nonionic

organics) will reduce uncertainty in

national BAFs and simplify procedures.

As part of these revisions, we

recommended that Kow-based estimates

of BAFs and food chain multipliers

(FCMs) not be used for nonionic

organics that are known to be

metabolized substantially in targeted

biota (e.g., some PAHs). Restrictions

have also been placed on the use of the

BSAF methodology so that the method

is used for the chemicals for which it is

most appropriate.

We clearly recognize that even with

these revisions incorporated into the

national BAF methodology, significant

uncertainty might exist in the

assessment and application of national

BAFs at some sites throughout the

United States because of the influence

of site-specific factors. Therefore, we

have more clearly indicated that

development of site-specific BAFs is

encouraged and supported when it can

be shown that a national BAF is

inappropriate, or when a State or

authorized Tribe prefers to derive a sitespecific BAF.

EPA agrees with commenters that in

some cases it may be appropriate to

derive a BAF using several of the

recommended methods (Methods 1–4),

with the final BAF chosen using a

weight-of-evidence approach. We have

provided general guidance on the

assessment of uncertainty in using fieldmeasured BAFs (and BAFs derived

using the other methods) when deriving

national BAFs. However, we do not

believe that the mere existence of

uncertainty means that national BAFs

(and resulting national 304(a) water

quality criteria) cannot be implemented

effectively throughout the United States.

For more than two decades, we have

developed and implemented our

national 304(a) water quality criteria

(aquatic life and human health) through

State, Tribal, and on occasion, Federal

water quality standards programs.

Implementation of this program has

relied on the use of national 304(a)

criteria as a cornerstone but has evolved

to allow the use of procedures to modify

national criteria by States and

authorized Tribes where appropriate.

EPA’s national bioaccumulation

methodology is consistent with this

programmatic practice, by enabling

States and authorized Tribes to readily

adopt national 304(a) water quality

criteria into standards (based on

National BAFs) that achieve the CWA

goals of protecting public health while

also allowing site- or State-specific

adjustments in situations where

national AWQC may be considered

overprotective or in some cases,

underprotective.

Comments—Some commenters

questioned the application of the BAF

prediction approaches (Tiers 2–4;

referred to as Methods 2–4 in the

revised Methodology) on a national

scale because the data used to validate

the approaches and develop predicted

BAFs come primarily from chemical

partitioning relationships observed from

a limited set of studies (e.g., Great Lakes

region).

Response—EPA agrees that the

locations for which the BAF

methodology has been fully applied are

limited in number (e.g., Lake Ontario,

Green Bay). To address this concern, we

have conducted additional assessments

and comparisons among the

bioaccumulation approaches (Methods

1–4) to further validate their usefulness

and have validated the methods using

other locations (e.g. Bayou d’Inde, LA,

Fox River/Green Bay, Hudson River,

NY). We acknowledge that a model

prediction is not a perfect simulation of

what occurs in a natural aquatic

ecosystem and that uncertainty exists in

the BAFs. However, this does not

invalidate the usefulness of models

validated using data from the Great

Lakes and Hudson River in predicting

bioaccumulation in other ecosystems.

Results of analyses that support using a

predictive bioaccumulation approach

for a variety of chemicals and aquatic

ecosystems can be found in Burkhard et

al. (1997), Burkhard (1998), Oliver and

Niimi (1988), Swackhammer and Hites

(1988), and Oliver and Niimi (1983).

Data from these studies clearly indicate

that the food web is a dominate

exposure route for many highly

hydrophobic chemicals and that use of

BCFs only underestimates exposure.

EPA’s proposed BAF methodology does

account for some site-specific

differences in bioaccumulation (an issue

expressed by commenters) by

considering factors such as percent lipid

in the fish consumed and the freely

dissolved concentration of the chemical

in the ambient water (i.e., a baseline

BAF). This allows a BAF developed

from one set of data and location(s) to

be ‘‘normalized’’ and applied to another

location. We believe the approach in the

2000 Human Health Methodology

appropriately balances protectiveness

with the uncertainties surrounding the

science currently available to predict

bioaccumulation. Comparisons of fieldmeasured and predicted BAFs

demonstrate agreement within an order

of magnitude in the vast majority of

cases, and often within a factor of two

to five. Burkhard (1998) observed good

agreement between measured and

predicted BAFs for the Lake Ontario

food web using the Gobas and Thomann

food web models. For individual

commonly detected PCBs and

chlorinated pesticides, the BAFs

estimated using the two Gobas and

Thomann models were on average

within a factor of 1.2 and 2.5 of the

observed (i.e. field-measured) BAFs,

respectively (Burkhard 1998). The

overall uncertainties in each of these

two bioaccumulation models (expressed

as the ratio of the 90th to 10th percentile

predicted BAF for each model) were a

factor 3.6 and 4.0 for the Gobas and

Thomann models, respectively

(Burkhard 1998). Furthermore,

Burkhard et al. (1997) reported that

predicted BAFs (using EPA’s national

BAF methodology) were within a factor

of 5 for 94% (n=32, using laboratory

measured BCFs and FCMs) and 90%

(n=48, using predicted Kows and FCMs)

in Bayou d’Inde (Lake Charles, LA).

These data comparisons show the good

predictability of the methods used in

the national BAF methodology. Should

States or authorized Tribes have

information to suggest that a national

BAF is inappropriate for their situation,

the 2000 Human Health Methodology

specifically allows and encourages

development of site-specific BAFs. With

this in mind, we will be developing

guidance on how to collect and interpret

field data for the purpose of deriving

site-specific field BAFs. This guidance

will specifically address major sources

of variability, including spacial and

temporal factors and species life history.

Finally, to further address concerns

that the predictive approaches used to

derive BAFs may not be applicable at a

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66477

national scale, we revised the 1998 draft

Methodology to clarify and limit for

which chemicals and under what

conditions BAFs based on Methods 2 to

4 are most applicable. For example,

chemicals were grouped into broad

categories based on their persistence

and bioaccumulation potential (e.g.,

high vs. low hydrophobicity, high vs.

low biota metabolism, ionic vs.

nonionic), and we have limited the use

of predicted BAF approaches to selected

groups of chemicals for which the data

reasonably support their use (i.e., highly

hydrophobic chemicals that are not

expected to be metabolized

appreciably). The national BAF

methodology was also changed to

indicate that for those chemicals with

sufficient data to indicate they are

metabolized, model-predicted BAFs are

not recommended; rather, field BAFs or

laboratory BCFs are recommended. The

use of the BSAF methodology has been

restricted to chemicals that are highly

hydrophobic (e.g., log Kow≥4).

EPA believes these revisions to the

1998 draft Methodology have improved

the Methodology and have addressed

many of the commenters’ concerns and

questions about uncertainty in applying

the various approaches and BAFs on a

national scale.

Comments—One commenter

suggested that it is ‘‘scientifically

indefensible to use the field-measured

BAF procedure to derive BAFs for

benthic systems.’’ They commented that

in a benthic-based aquatic food web, the

water column concentration of a

chemical is not directly related to

aquatic organism exposure potential for

that chemical. Therefore, their view is

that a field-measured BAF may over- or

underestimate bioaccumulation in

benthic-based systems.

Response—EPA acknowledges that

the concentration of a chemical in the

water column is not directly related to

what pelagic organisms (i.e., fish) are

exposed to in a benthic-based system.

However, the concentrations of a

chemical in water, sediment, and fish

are interconnected, although they may

not be equally partitioned into each

compartment, and residues in fish can

be predicted equally well using either a

sediment or water concentration as the

starting basis. In the revised TSD on

Bioaccumulation, the relationships

between BAFs and BSAFs have been

shown more clearly in order to

demonstrate this interconnectedness. In

the BAF methodology, we are assessing

exposure through all routes (i.e., from

water, sediment, and contaminated

food) in the aquatic ecosystem. By

including all routes of exposure, the

BAFs do not assume simple water-fish

partitioning; rather they are an overall

expression of the total bioaccumulation

using the concentration of the chemical

in water column as a reference point.

Thus, a field-measured BAF or BASF at

any given time is reflective of historic

chemical loadings and bioaccumulation

that has occurred. EPA does agree that

a BAF may change over time because of

differential chemical loadings; however,

some frame of reference has to be

chosen as the starting point to assess

bioaccumulation. EPA has chosen to use

the water concentration as that reference

point. Science has shown that

bioaccumulation occurs and is an

important exposure pathway to humans

for many chemicals, and EPA cannot

ignore bioaccumulation in development

of its AWQC simply because variability

and uncertainty exist. In situations

where chemical loadings are highly

variable or are reduced substantially,

EPA believes that a field-measured BAF

will still be predictive of what will

bioaccumulate in fish until the

concentrations in sediments and benthic

organisms are reduced enough to lead to

reduced bioaccumulation. In situations

such as this, a revised site-specific field

BAF can be developed to reflect the

change in chemical loading and

partitioning.

This issue of field-measured BAFs

and benthic-based food webs was also

brought up in public comments made at

the stakeholders meeting held in May

1999. At that time, we asked

commenters if they could recommend

another approach to assess

bioaccumulation in benthic-based

systems. No other approaches were

suggested. We have concluded that in

the absence of any other approaches,

field-derived BAFs are good predictors

of bioaccumulation because they

integrate biological, chemical, and

physical factors that influence

bioaccumulation.

2. Guidance for Deriving Field

Bioaccumulation Factors (BAFs)

Comments—Several commenters

agreed with EPA that field-derived

BAFs should take precedence over

modeled BAFs. However, many

commenters discussed the need for

guidance on how to collect and review

field data so that high-quality, fieldbased BAFs can be derived.

Commenters noted that there are

numerous site-specific biological,

chemical, and physical factors that

affect bioaccumulation, which should

be considered during design of field

sampling programs.

Response—We agree that properly

derived field BAFs should take

precedence over modeled BAFs; we

have clearly indicated in the 2000

Human Health Methodology that this is

our preferred approach for deriving a

BAF. We also acknowledge that, as with

any field measurement, there can be

errors in determining field-measured

BAFs. In the development of national

BAFs, EPA will attempt to minimize

potential errors or uncertainties by

carefully screening the data based on

the criteria outlined in the

Bioaccumulation TSD. Furthermore, an

additional validation of national BAFs

will be conducted as part of the external

peer review process that occurs for all

published 304(a) water quality criteria.

We continue to assert that for many

chemicals, a field-measured BAF is a

better gauge of what is occurring in

nature than a laboratory-measured or

predicted BCF; the BAF measures the

actual effects of bioavailability,

concentration in the water or sediment,

growth dilution, metabolism, and

biomagnification rather than predicting

them through use of a model. We do

agree with commenters concerned about

the difficulty of collecting and

interpreting field-measured BAFs;

however, we believe that States and

Tribes can adequately design and

interpret field studies. To assist them in

this task, we will be developing

guidance concerning field data

collection and interpretation for sitespecific field-measured BAFs and

BSAFs.

3. Use of Biota-Sediment Accumulation

Factors (BSAFs)

Comments—Several commenters

stated that the use of the BSAF

approach for deriving a BAF is

inappropriate. Some comments centered

around the perceived lack of validation

and peer review of the BSAF approach,

and others focused on the relationship

between the water column

concentration of a chemical and its

sediment concentration, represented by

the factor Πsocw. One commenter noted

that the BSAF method is simply a

means to predict a water concentration

of a chemical of interest from the

sediment concentration of that

chemical, the water and sediment

concentration of a reference chemical(s),

and the ratio of Kow for the chemical of

interest and the reference chemical(s). A

commenter indicated that loading

history of a given chemical directly

affects what the value of Πsocw would be

at any given time, and that Πsocw/Kow

(disequilibrium ratio) for the chemical

in question and the reference chemical

has to be constant under the

assumptions of the BSAF approach. The

commenter stated, however, that Πsocw/

Kow will not be constant because of

66478 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

differential loading histories, and that

because the concentration of the

chemical of interest cannot be measured

in water, the assumptions about Πsocw/

Kow cannot be verified. In their view this

made the use of BSAFs invalid.

Response—The method of predicting

BAFs from BSAFs has been evaluated

for certain pesticides, PCBs, chlorinated

benzenes, and dioxins using two data

sets from Lake Ontario (Oliver and

Niimi,1988;USEPA, 1990) and one from

Green Bay (USEPA, 1992b). EPA has

also recently completed further

evaluation of this method for certain

PCB congeners, pesticides, and

chlorinated benzenes in Lakes Ontario,

Green Bay, and the Hudson River. This

additional evaluation and validation

work is included in the

Bioaccumulation TSD. The evaluations

show that in the vast majority of

situations, the BSAFs predict fieldmeasured BAFs very well.

EPA agrees with the commenter who

noted that the BSAF method is

structured to predict water

concentrations for chemicals that cannot

be measured for the purpose of directly

measuring a field BAF. However, the

BSAF method is more important for its

ability to capture the net effect of

biomagnification, food web structure,

hydrophobicity, bioavailability factors,

and metabolism on a specific chemical’s

net potential for bioaccumulation. The

BSAF method is needed to predict BAFs

for chemicals with nondetectable and

difficult-to-predict concentrations in

water (e.g., dioxins). No alternative

methods to predict BAFs for such

chemicals were identified by either

public commenters or peer reviewers.

The BSAF method equation has been

modified (see below) in the

Bioaccumulation TSD to clarify the

essential data components of the

method. The revised BSAF equation

shows that measured concentrations in

water and surface sediment, not a

complete BSAF, are needed for the

reference chemical. The equation also

shows that a measured BSAF for the

chemical of interest is the most

important component for determination

of a BAF when the concentration in

water cannot be measured.

EPA agrees with commenters that the

BSAF method should not be used for all

organic chemicals that may be

addressed through the 2000 Human

Health Methodology, and accordingly

have restricted application of the

method to nonionic organic chemicals

with log Kows ≥ 4.0. We have also

provided more specific guidance on

selection of reference chemicals and use

of multiple reference chemicals to

secure the most accurate estimate of a

chemical’s BAF.

One commenter contended that the

BSAF approach for deriving BAFs is

seriously flawed. The concern is that the

approach is valid only if a reference

chemical (chemical r) can be found with

a sediment-water fugacity ratio (which

represents the differential partitioning

of a chemical between water and

sediment) equal to that of the chemical

for which the BAF is being determined

(chemical of interest). The commenter

contends that the BSAF approach could

validly be used only if it could be

shown that the fugacity ratio is a

constant for the chemical of interest and

the reference chemical. The commenter

submitted figures to demonstrate

conceptually that two chemicals with

radically different loading histories will

have dissimilar fugacity ratios. EPA

disagrees that in order for the BSAF to

work, the fugacity ratio has to be

constant, but does agree that in order to

best use the BSAF approach, a general

knowledge of chemical loading histories

to an ecosystem is needed to help

provide a basis for choosing appropriate

reference chemicals. Such information

may be obtained from chemical

production records, historical fish

residue monitoring data, or dated

sediment core analysis. We recognize

that due to various factors (loading

histories, microbial degradation, etc.)

fugacity ratios for both chemical (i) and

(r) may shift over time, leading to the

potential for temporal variability of

sediment-water distributions of

nonpolar organic chemicals. Although it

was not shown explicitly in the 1998

draft TSD, an important benefit of the

BSAF approach is that it can account

precisely for such differences in

sediment-water distributions of

nonpolar organic chemicals. The BSAF

method is robust to the extent that the

choice of reference chemicals is based

on meeting the sediment-to-water

fugacity ratio condition: That the ratios

be similar—they do not have to be

constant. The extent that these ratios for

chemicals with log Kows ≥ 4 may change

with chemical loading over long periods

of time after sediments become

contaminated, and thereby contribute to

small shifts in BSAFs and larger shifts

in BAFs, is an issue of possible concern

that EPA recognized in the 1998 draft

TSD. EPA noted on page 188 of the TSD

(USEPA, 1998d) that ‘‘BSAFs measured

for systems with new chemical loadings

or rapid increases in loadings may be

unreliable due to underestimation of

steady-state Csocs.’’

To better address the water-tosediment relationship issue, EPA has

revised the equations that serve as the

basis for deriving a BSAF. In the revised

equations, a factor Di/rhas been added,

which is defined as the ratio of the

fugacity gradient (modeled as Πsocw/Kow)

between sediment and water for

chemical (i) in comparison to that of a

reference chemical (r). The revised

equations are as follows:

socw i

ow i

i r

socw r

ow r

socw i

i r socw r ow i

ow r

K

D

K

thus

D K

K

∏ ∏

∏ ∏

( )

( ) = ( ) ( )( )

( ) = ( )( ) ( )

( )

/

/

( )

,

1

By definition, Πsocw can be used to

relate chemical i’s BSAF to its BAFƒfd:

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66479

socw i

soc i

w

fd

i

fd

i

i

fd

i i socw i

C

C

BAF

BSAF

thus BAF BSAF

∏

∏

( ) = ( )

( ) =

( )

( )

( ) = ( ) ( )

l

l

( )

,

2

By substituting rearranged Equation 1

into rearranged Equation 2:

BAF BSAF

D K

K

fd

i i

i r socw r ow i

ow r

( ) l = ( ) ( )( ) ( )

( )

/ ∏ ( ) 3

where:

(BAFƒfd)i = BAF expressed on a freely

dissolved and lipid-normalized

basis for chemical of interest ‘‘i’’.

(BSAF)i = Biota-sediment accumulation

factor for chemical of interest ‘‘i’’.

(Csoc)i = Concentration of chemical of

interest ‘‘i’’ in sediment normalized

to sediment organic carbon.

(Csoc)r = Concentration of a reference

chemical in sediment normalized to

sediment organic carbon.

(Cwfd)i = Concentration of chemical of

interest ‘‘i’’ freely dissolved in

water.

(Cwfd)r = Concentration of the reference

chemical freely dissolved in water.

Di/r = ratio between Πsocw/Kow for

chemicals ‘‘i’’ and ‘‘r’’ (normally

chosen so Di/r = 1).

(Kow)i = octanol-water partition

coefficient for chemical of interest

‘‘i’’.

(Kow)r = octanol-water partition

coefficient for the reference

chemical ‘‘r’’.

(Πsocw)i = sediment organic carbon to

water freely dissolved

concentration ratio of chemical of

interest ‘‘i’’.

(Πsocw)r = sediment organic carbon to

water freely dissolved

concentration ratio of reference

chemical ‘‘r’’.

Equation 3 is intended to provide an

improved representation of how the

BSAF method/model works. By using

Di/r, the new equation accounts for

differences in sediment to water column

concentrations that might exist between

the chemical of interest and the

reference chemical because of factors

such as loading histories or degradation.

Unlike one commenter’s analysis, in

which an equation was derived without

the BAF or BSAF, equation 3 shows

these quantities as central to the model;

that is, the BSAF is measured and then

transformed into a BAF by estimating

the chemical’s Πsocw/Kow. This model

could alternatively be described as a

determination of (Cwfd)i from a measured

value of (Csoc)i combined with a

measured value of (Cƒ)i to give an

accurate measure of (BAFƒfd)i. However,

we believe that equation 3 best

describes the BSAF method as allowing

measured BSAFs to be transformed into

BAFƒfds for the specific purpose of

developing either national or a sitespecific water quality criteria when

directly measured BAFƒfds cannot be

obtained.

When good-quality data are available

for reference chemicals (r) that should

have equal or similar sediment-water

fugacity ratios as a chemical (i) whose

(BAFƒfd)S cannot be measured directly,

then Di/r = 1. When Di/r ≤ 1, it may be

estimated based on properties of the

chemicals and knowledge of their

loading histories to the ecosystem.

Equation 3 provides a greater degree of

flexibility for use of the BSAF method

than the original equation. This

flexibility highlights a logical stepwise

transition from measured to fully

modeled site-specific BAFs that can

incorporate estimates of Di/r through fate

modeling, should interested parties

choose to do so. In such a situation, if

the uncertainty associated with choice

of Di/r is perceived to be too great, a

determination of a site-specific

(BAFƒfd)i, which still takes advantage of

measured values of (Cƒ)i and (Csoc)i,

could be accomplished if a mass balance

model, specifically calibrated with (Cƒ)i

and (Csoc)i, is used to predict (Cwfd)i.

Such an approach would be time

consuming and expensive but would

allow prediction of (BAFƒfd)i over time

as a function of changes in (Πsocw)i

associated with anticipated changes in

mass loading of the chemical into an

ecosystem. In cases where the intended

use of the site-specific criterion is to

determine permit conditions or

establish a TMDL, a mass balance model

presumably would have to be

developed, and thus use of the model

for providing a (BAFƒfd)i would not

require an extraordinary effort.

However, as with the BSAF method, it

should be noted that mass balance

model predictions of Cwfdi also cannot

be directly validated through

measurements. EPA’s appreciation for

the value of hybrid models comes from

recognition that incorporation of

measured bioaccumulation potentials,

including those provided by the BSAF

method, are especially advantageous for

those chemicals with transformation

rates, such as metabolism throughout

the food chain, that are presently not

accurately known or incorporated into

mechanistic bioaccumulation models.

Finally, we disagree with the circular

argument that the BSAF approach has

‘‘extremely limited utility’’ because ‘‘it

will not be possible to demonstrate that

Πsocw/Kow is a constant’’ because Πsocw/

Kow cannot be measured directly for one

chemical. The inherent limitation for

validation of a predicted BAF because of

the inability to measure the

concentration of freely dissolved

chemical in water (Cwfd) applies to any

approach/model available and is not a

just criterion for rejection of a BAF

method. Validation may be based on the

ability of the BAF to predict

concentrations in fish from predicted

values of Cwfd. Data from the Great Lakes

clearly show that such predictions are

possible, and accurate (USEPA, 1998d).

It should also be noted that during the

external peer review of the BSAF

approach, the peer reviewers stated ‘‘for

the chemicals examined (persistent and

bioaccumulative), extrapolation to other

circumstances may be reasonable,’’

thereby disagreeing with public

commenters. EPA believes that

restricting the use of the BSAF method

to highly hydrophobic chemicals,

clarifying the use of reference

chemicals, elaborating on the primacy of

the sediment-water fugacity equivalence

66480 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

condition for use of the method, and

validation with additional data sets

alleviates concerns about using this new

method.

4. Dissolved Organic Carbon (DOC) and

Particulate Organic Carbon (POC)

Comments—Two comments were

received on the DOC/POC approach

used to determine the bioavailable

fraction of organic chemicals in surface

water and sediments. Rather than solely

use default organic carbon values,

commenters wanted to the ability to

select DOC/POC values they believe are

more representative of their waterbody

type or site-specific conditions.

Response—In the 2000 Human Health

Methodology, EPA allows use of sitespecific DOC and POC data when

normalizing the BAF to organic carbon

content. One can either conduct studies

to generate the necessary site-specific

data or modify the national organic

carbon database to their particular site

and conditions. To facilitate the latter,

we have updated and expanded the

organic carbon database used to develop

the national default POC/DOC values to

enable the regulated community to

choose which values best represent their

site conditions and will provide

defensible site-specific DOC and POC

estimates. The national DOC/POC

database will be made available for use

by all States, Tribes, and other members

of the regulated community.

5. Fish Lipid Content

Comments—A commenter stated that

lipid content can affect the results of the

Gobas model used to derive national

default FCMs. The commenter noted

that the model is relatively insensitive

to fish lipid content but more sensitive

to benthic invertebrate lipid content.

They believed this should be considered

in the development of FCMs.

Response—EPA agrees that lipid

content can affect the results of the

Gobas model and is only using the

Gobas model with default lipid values

to derive national BAFs when there are

no data to derive a field-measured BAF.

In cases where a State or authorized

Tribe has site-specific data on fish lipid

content, the revised methodology allows

input of those site-specific data to

estimate bioaccumulation. Furthermore,

to facilitate the generation of sitespecific lipid values, we have updated

and expanded the lipid database used to

develop the national default values

based on a whole range of organisms

commonly consumed by persons in the

United States. We will include

additional guidance for States and

authorized Tribes on how to adapt the

national default lipid values to reflect

State and local consumption patterns.

To enable such adaptions, EPA will

make the raw data available to States

and authorized Tribes.

6. Use of Food Chain Multipliers (FCMs)

Comments—Several commenters

stated that the use of model-derived

FCMs (Gobas 1993) to calculate a BAF

from either a BCF or a Kow (Methods 3

and 4) is inappropriate. The

commenters noted issues with several of

the default input parameters (e.g., food

web, lipid, Πsocw, temperature). The

primary concern of commentors is that

Gobas model-based national default

FCMs do not account for site-specific

factors that influence bioaccumulation,

such as food web structure, nor does the

current use of the model account for

metabolism. Commenters expressed

concern that use of default FCMs in

predictive approaches may lead to

overestimates of bioaccumulation. Some

commenters preferred the use of fieldbased FCMs or direct use of the Gobas

model, which allows for input of sitespecific data and metabolism rates if

available, rather than uses of modelderived default FCMs.

Response—EPA is using a state-of-theart food web model for deriving FCMs,

which incorporates the latest thinking

and knowledge on the processes

occurring in aquatic food webs.

Commenters suggested that the

assumptions used in constructing these

models are not appropriate. We

recognize that any modeling

formulation of contaminant behavior in

aquatic food webs requires

simplification of a very complex

biological system in order to assemble a

tractable model. These simplifications

do not imply or mean that our scientific

understanding of all processes occurring

in food webs is complete. As

documented in the scientific literature,

these simplifications provide reasonable

model formulations with good

predictive power. The suggestion that

every modeling assumption has to be

completely understood and validated

under all circumstances before using or

constructing a useful modeling tool is

unreasonable. EPA has performed a

detailed analysis of the importance and

sensitivities of individual input

parameters for food web models and of

the overall uncertainties associated with

predictions from food web models

(Burkhard 1998). We have provided a

discussion in the Bioaccumulation TSD

of the Gobas model and implications

that uncertainties in their respective

input parameters have on derived

FCMs. EPA has retained the use of

Gobas model to derive default FCMs.

To address national versus sitespecific concerns expressed by some

commenters, the methodology has been

revised to separate the BAF

methodology into national and sitespecific guidance. The national

methodology for deriving national BAFs

retains the use of default FCMs based on

a mixed benthic/pelagic food web and

national averages of various model

input values. We believe this food web

is the most broadly applicable food web

encountered in nature; its use results in

FCMs that are midway between pure

benthic and pure pelagic structures. The

revised guidance includes a brief

discussion of the uncertainties

associated with our selection of the

mixed benthic/pelagic food web. In the

site-specific guidance, the 2000 Human

Health Methodology provides guidance

on which of EPA’s recommended FCMs

to use depending on the situation. In

addition, we encourage direct use of the

Gobas model by stakeholders so that

changes could be made to the default

food web inputs to reflect site-specific

factors that influence bioaccumulation,

and also encourage derivation of fieldbased FCMs. States and authorized

Tribes have the option to generate sitespecific FCMs by conducting sitespecific field studies, reviewing

published literature, or using other

scientifically defensible models.

Although several commenters

criticized the national application of the

Gobas model because metabolism rate is

set equal to zero, the peer review panel

acknowledged EPA’s position that there

are currently no acceptable methods

available to adequately determine

species and chemical-specific

metabolism rates for use in the Gobas

model. Because EPA agrees that for

certain chemicals metabolism can be an

important factor in bioaccumulation, the

revised methodology does not use FCMbased predictions for chemicals that are

expected to be metabolized

substantially. To assist users of the 2000

Human Health Methodology in

determining for which chemicals or

groups of chemicals metabolism should

be of little concern, we have developed

a table of chemicals that are not

substantially metabolized or are likely

very slowly metabolized. This table has

been put in the Bioaccumulation TSD.

The table is not all inclusive because

there are numerous chemicals (e.g.,

hundreds of thousands in use

commercially today) for which few or

no metabolism data exist, but is

representative of chemicals or groups of

chemicals that are likely to be

commonly encountered in aquatic

systems. When metabolism is suspected,

Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices 66481

users of the 2000 Human Health

Methodology might be more inclined to

use or develop field data and/or

measure a BCF in the laboratory in these

situations. It should also be noted that

in the future, should appropriate

chemical and species-specific

metabolism data become available, the

Gobas model can incorporate it with

little effort.

Finally, EPA partially agrees with

commenters that certain procedures of

the 1998 draft Methodology revisions

(e.g., Kow and FCM-predicted BAFs)

might lead to overestimates of BAFs for

certain types of pollutants, such as those

that are metabolized substantially to

chemical forms not addressed by the

AWQC. In response to this issue, and as

discussed previously, additional

guidance and limitations have been

placed on several of the procedures in

the revised methodology. However, EPA

does not agree with the notion that our

methodology would lead to a general

over prediction for all BAFs. We use

central tendencies where possible for all

inputs in the Gobas model, and a

geometric mean BCF for chemicals that

have more than one BCF for a given

trophic level. Thus, we know of no

reason why laboratory-measured BCFs

multiplied by a FCM would always

result in overestimates of BAFs, or why

the BSAF and Kow * FCM-predicted

BAFs applied to highly hydrophobic

contaminants that do not metabolize

substantially would be biased a priori

toward overestimating BAFs. These

views are supported by information in

the 1998 TSD (Exhibits 2.4.1, 2.4.3, and

2.4.6 for BSAFs), Burkhard et al. (1997)

for the Kow*FCM method, and

information presented in the

Bioaccumulation TSD.

7. Fish Tissue Criteria

Comments—A few commenters

suggested that for selected highly

bioaccumulative chemicals that are

difficult to measure in water, criteria

based on fish tissue concentration may

be more appropriate than ambient water

column concentration criteria.

Response—Regarding fish tissue

criteria, EPA agrees that the

development of human health criteria

for highly bioaccumulative chemicals

which are expressed in terms of tissue

residues in aquatic organisms is worthy

of consideration. However, such tissue

residue criteria would still require a

mechanism to relate chemical loads and

concentrations in water and sediments

to concentrations in tissues of

appropriate aquatic organisms (i.e.,

bioaccumulation factors or

bioaccumulation models). EPA is

presently exploring the feasibility of

developing tissue-based criteria and is

evaluating numerous issues associated

with implementation of tissue-based

criteria. At an appropriate in the future,

EPA will consider development of

additional guidance on tissue residue

criteria pending the outcome of this

evaluation.

G. Literature Cited

Burkhard LP. 1998. Comparison of two

models for predicting bioaccumulation

of hydrophobic organic chemicals in a

Great Lakes food web. Environ. Toxicol.

Chem. 17(3):383–393.

Burkhard LP, Sheedy BR, McCauley DJ,

DeGraeve GM. 1997. Bioaccumulation

factors for chlorinated benzene,

chlorinated butadienes and

hexachloroethane. Environ. Toxicol.

Chem. 16(8):1677–1686.

Fisk AT, Norstrom RJ, Cymbalisty CC, Muir

DCB. 1998. Dietary accumulation and

depuration of hydrophobic

organochlorines: bioaccumulation

parameters and their relationship with

the octanol/water partition coefficient.

Environ. Toxicol. Chem. 17(5):951–961.

Gobas FAPC. 1993. A model for predicting

the bioaccumulation of hydrophobic

organic chemicals in aquatic food-webs:

application to Lake Ontario. Ecol. Model.

69:1–17.

Niimi AJ. 1985. Use of laboratory studies in

assessing the behavior of contaminants

in fish inhabiting natural ecosystems.

Water Poll. Res. J. Can. 20:79–88.

Oliver BG, Niimi AJ. 1983. Bioconcentration

of chlorobenzenes from water by

rainbow trout: correlations with partition

coefficients and environmental residues.

Environ. Sci. Technol. 17:287–291.

Oliver BG, Niimi AJ. 1988. Trophodynamic

analysis of polychlorinated biphenyl

congeners and other chlorinated

hydrocarbons in the Lake Ontario

ecosystem. Environ. Sci. Technol.

22:388–397.

Russell RW, Gobas FAPC, Haffner GD. 1999.

Role of chemical and ecological factors

in trophic transfer of organic chemicals

in aquatic food webs. Environ Toxicol

Chem. 18:1250–1257.

Swackhamer, DL, Hites RA. 1988.

Occurrence and bioaccumulation of

organochlorine compounds in fishes

from Siskiwit Lake, Isle Royale, Lake

Superior. Environ Sci. Technol. 22:543–

548.

USEPA (U.S. Environmental Protection

Agency). 1980. Guidelines and

methodology used in the preparation of

health effect assessment chapters of the

consent decree water criteria documents.

Federal Register 45:79347, Appendix 3.

USEPA (U.S. Environmental Protection

Agency). 1984. Proposed guidelines for

carcinogen risk assessment. Federal

Register 49:46294.

USEPA (U.S. Environmental Protection

Agency). 1986a. Guidelines for

carcinogen risk assessment. Federal

Register 51:33992–34003.

USEPA (U.S. Environmental Protection

Agency). 1986b. Guidelines for

mutagenicity risk assessment. Federal

Register 51:34006–34012.

USEPA (U.S. Environmental Protection

Agency). 1986c. Total Exposure

Assessment Model (TEAM) Study:

Summary and Analysis, Volume I, Final

Report. EPA/600/6–87/002a.

USEPA (U.S. Environmental Protection

Agency). 1986d. Quality Criteria for

Water—1986. Office of Water

Regulations and Standards, Office of

Water. Washington, DC. EPA/440/5–86/

001.

USEPA (U.S. Environmental Protection

Agency). 1990. Lake Ontario TCDD

Bioaccumulation Study—Final Report.

USEPA, Region II. New York, NY. EPA/

822/R–94/002.

USEPA (U.S. Environmental Protection

Agency). 1991a. Guidelines for

developmental toxicity risk assessment.

Federal Register 56:63798–63826.

USEPA (U.S. Environmental Protection

Agency). 1991b. Technical Support

Document for Water Quality-Based

Toxics Control. Office of Water.

Washington, DC. EPA/505/2–90/001.

USEPA (U.S. Environmental Protection

Agency). 1992a. Guidelines for exposure

assessment. Federal Register 57:22888–

22938.

USEPA (U.S. Environmental Protection

Agency). 1992b. Development and

Application of a Model of PCBs in the

Green Bay, Lake Michigan Walleye and

Brown Trout and Their Food Webs.

Prepared by Manhattan College,

Riverdale, NY.

USEPA (U.S. Environmental Protection

Agency). 1994. Water Quality Standards

Handbook and Appendices. Second

edition. Office of Water. Washington,

DC. EPA/823/B–94/005a.

USEPA (U.S. Environmental Protection

Agency). 1996a. Proposed guidelines for

carcinogen risk assessment. Federal

Register 61:17960.

USEPA (U.S. Environmental Protection

Agency). 1996b. Guidelines for

reproductive toxicity risk assessment.

Federal Register 61:56274–56322.

USEPA (U.S. Environmental Protection

Agency). 1996c. Report on the

Benchmark Dose Peer Consultation

Workshop. Office of Research and

Development. Washington, DC. EPA/

630/R–96/011. November.

USEPA (U.S. Environmental Protection

Agency). 1997a. Exposure Factors

Handbook. Office of Research and

Development. Washington, DC. EPA/

600/P–95/002Fa.

USEPA (U.S. Environmental Protection

Agency). 1997b. Guiding Principles for

Monte Carlo Analysis. Risk Assessment

Forum. Washington, DC. EPA/630/R–97/

001.

USEPA (U.S. Environmental Protection

Agency). 1997c. Policy for Use of

Probabilistic Analysis in Risk

Assessment at the U.S. Environmental

Protection Agency. Risk Assessment

Forum. Washington, DC. Web site: http:/

/www.epa.gov/ncea/mcpolicy.htm.

USEPA (U.S. Environmental Protection

Agency). 1998a. Guidelines for

66482 Federal Register / Vol. 65, No. 214 / Friday, November 3, 2000 / Notices

neurotoxicity risk assessment. Federal

Register 63:26926.

USEPA (U.S. Environmental Protection

Agency). 1998b. National recommended

water quality criteria. Federal Register

64:19781.

USEPA (U.S. Environmental Protection

Agency). 1998c. Draft water quality

criteria methodology: Human health.

Federal Register 63:43756.

USEPA (U.S. Environmental Protection

Agency). 1998d. Ambient Water Quality

Criteria Derivation Methodology: Human

Health. Technical Support Document

(TSD). Office of Water. Washington, DC.

EPA–822–B–98–005.

USEPA (U.S. Environmental Protection

Agency). 1998e. National recommended

water quality criteria; republication.

Federal Register 63:68354–68364.

USEPA (U.S. Environmental Protection

Agency). 1999a. 1999 Guidelines for

Carcinogen Risk Assessment—Review

Draft. Office of Research and

Development. Washington, DC. NCEA–

F–0644. July.

USEPA (U.S. Environmental Protection

Agency). 1999b. Guidance for

Conducting Health Risk Assessment of

Chemical Mixtures—External Peer

Review Draft. Risk Assessment Forum.

Washington, DC. NCEA–C–0148. April.

USEPA (U.S. Environmental Protection

Agency). 1999c. National Recommended

Water Quality Criteria—Correction.

Office of Water. Washington, DC. EPA–

822–Z–99–001. April.

USEPA (U.S. Environmental Protection

Agency). 1999d. Review of Revised

Sections of the Proposed Guidelines for

Carcinogen Risk Assessment. Science

Advisory Board (1400). Washington, DC.

EPA–SAB–EC–99–015. July.

USEPA (U.S. Environmental Protection

Agency). 2000a. Review and approval of

state and tribal water quality standards.

Federal Register 65:24641.

USEPA (U.S. Environmental Protection

Agency). 2000b. Health Assessment for

2,3,7,8-Tetrachlorodibenzo-p-dioxin

(TCDD) and Related Compounds,

Internal Review Draft. Office of Research

and Development. Washington, DC.

EPA–600–P–001Af. February 14.

USEPA (U.S. Environmental Protection

Agency). 2000c. Estimated Per Capita

Water Ingestion in the United States:

Based on Data Collected by the United

States Department of Agriculture’s 1994–

96 Continuing Survey of Food Intakes by

Individuals. Office of Science and

Technology, Office of Water.

Washington, DC. EPA–822–00–008.

April.

USEPA (U.S. Environmental Protection

Agency). 2000d. Estimated Per Capita

Fish Consumption in the United States:

Based on Data Collected by the United

States Department of Agriculture’s 1994–

1996 Continuing Survey of Food Intake

by Individuals. Office of Science and

Technology, Office of Water.

Washington, DC. March.

Watras CJ, Bloom NS. 1992. Mercury and

methylmercury in individual

zooplankton: Implications for

bioaccumulation. Limnol. Oceanogr.

37(6):1313–1318.

This Notice finalizes revisions to

EPA’s 1980 Methodology for the

development of water quality criteria to

protect human health. The revisions

reflect scientific advancements since

1980 in a number of areas, including

cancer and noncancer risk assessments,

exposure assessments and

bioaccumulation. The revised

Methodology provides guidance to

States, Tribes, and the public on the

approach that EPA expects to take in

developing recommended human health

criteria. The revised Methodology also

provides guidance to States and Tribes

that they may use in developing human

health criteria as part of their water

quality standards; States and Tribes use

such standards in implementing a

number of environmental programs,

including setting discharge limits in

NPDES permits. The revised

Methodology does not substitute for the

Clean Water Act or EPA’s regulations;

nor is it a regulation itself. Thus, the

revised Methodology cannot impose

legally-binding requirements on EPA,

States, Tribes or the regulated

community, and may not apply to a

particular situation based upon the

circumstances. EPA and State/Tribal

decision-makers retain the discretion to

use different, scientifically defensible,

methodologies to develop human health

criteria on a case-by-case basis that

differ from this guidance where

appropriate. EPA may change the

Methodology in the future through

intermittent refinements as advances in

science or changes in Agency policy

occur.

This criteria Methodology

incorporates scientific advancements

made over the past two decades. The

use of this Methodology is an important

component of the Agency’s efforts to

improve the quality of the Nation’s

waters. EPA believes the Methodology

will enhance the overall scientific basis

of water quality criteria. Further, the

Methodology should help States and

Tribes address their unique water

quality issues and risk management

decisions, and afford them greater

flexibility in developing their water

quality programs.

Dated: October 24, 2000.

J. Charles Fox,

Assistant Administrator for Water.

[FR Doc. 00–27924 Filed 11–2–00; 8:45 am]

BILLING CODE 6560–50–P