United States                    Office of Water
               Environmental Protection Agency      4304
                    EPA-822-F-98-004
                    July 1998
              FACT SHEET
              Draft Revisions to the Methodology for Deriving
              Ambient Water Quality Criteria for the
              Protection of Human  Health
Abstract
The U.S. Environmental Protection Agency is proposing to revise the methodology used to
develop human health water quality criteria published in accordance with the Clean Water
Act. These revisions, once finalized, will replace the existing 1980 National guidelines and
methodology. These revisions are being made at this time to incorporate the many
significant scientific advances that have occurred during the past 18 years in such key
areas as cancer and  noncancer risk assessments, exposure assessments, and
bioaccumulation in fish.
Human Health Water Quality Criteria

Human health water quality criteria are numeric
values limiting chemical concentrations in
ambient waters. The criteria are developed under
Section 304(a) of the Clean Water Act of 1972
(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 exposure intakes that humans
may experience. These criteria do not reflect
consideration of economic impacts or the
technological feasibility of meeting the chemical
concentrations in ambient water. The criteria are
used by states and regions to establish water
quality standards and ultimately provide a basis
for controlling discharges or releases of
pollutants.

EPA Methodology for Deriving Criteria

States and authorized Indian tribes must develop
water quality standards that include designated
uses and water quality criteria necessary to
support those uses.  The Methodology is the
guidance for states  and tribes to help them
establish water quality criteria and standards to
protect human health. 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.
EPA Methodology Revisions

EPA periodically revises water quality criteria to
ensure that they accurately reflect the latest
scientific knowledge on the kind and extent of all
identifiable effects on health and welfare which
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 necessitate the revisions.
Specifically, advances in such key areas as
cancer and noncancer risk assessments, exposure
assessments, and bioaccumulation make the
revisions critical at this time. Therefore, EPA is
updating its Ambient Water Quality Criteria
(AWQC) Methodology to provide states and
tribes with the most current procedures to reflect
these changes in risk and exposure assessment.
States and tribes will need to modify their water
quality criteria to be consistent with current
Agency practices.

General Background of the Revision Process

To begin developing a "state-of-the-science"
approach revising the 1980 AWQC National
Guidelines, EPA (along with other federal
agencies, state health organizations, Canadian
health agencies, academies, environmental and
industry groups, and consulting organizations)
prepared an issues paper that described the 1980
methodology, discussed areas that needed
strengthening, and recommended revisions. The
paper was distributed for review and comment

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and was examined at a 1992 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.

After reviewing the draft of the recommended
revisions to the methodology developed by EPA
and the workshop participants, a summary
document was submitted for review and
comment by the EPA Science Advisory Board
(SAB). Once final comments and revisions had
been received from the board, the
recommendations were again reviewed at a
meeting of the Federal State Toxicology and Risk
Analysis Committee, where state representatives
presented their opinions on the preliminary draft
recommendations.

Major Methodology Revisions

The major revisions are in four assessment areas:
noncancer, cancer, exposure, and
bioaccumulation. Equations have been developed
for deriving AWQC, including parameters
relevant to these four assessment areas, which are
derived from scientific analysis, science policy
and risk management decisions.

For noncarcinogens, the process for deriving an
acceptable level of exposure—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 neurotoxiciry data into
    the calculation.

•   EPA intends to allow the use of a range
    around the RfD point estimate to reflect the
    inherent imprecision of the RfD. EPA would
    select the midpoint of the range as a default
    when calculating a 304(a) criteria value for
    use in state, tribal, or regional water quality
    standards and require justification if a state
    or tribe proposes a different value within the
    range.

•   EPA is recommending the use of
    quantitative dose-response modelling for the
    derivation of RfDs.

For carcinogen (cancer) risk assessment, more
sophisticated methods to comprehensively
determine the likely mechanism that causes
human carcinogenicity are being recommended.

•   EPA is recommending a mode of action
    (MoA) approach to determine the most
    appropriate low-dose extrapolation for
    carcinogenic agents.

•   The MoA  approach follows EPA's 1996
    proposal of revised cancer guidelines and
    considers all biological information (rather
    than just tumor findings).

Changes in the area of exposure assessment
include the following.

•   States and 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 nonlinear carcinogens (i.e., the dose is
    not allocated to drinking water and fish
    consumption alone).

The new National AWQC Guidelines place
greater emphasis on the use of bioaccumulation
factors (BAFs) compared to the 1980  Guidelines
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 to
    Bioconcentration Factors (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

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sediment is important (e.g., highly persistent,
hydrophobia chemicals).

•   EPA gives preference to the use of high
    quality field data over laboratory or model-
    derived estimates for deriving BAFs, since
    field data best reflect factors which can
    affect the extent of bioaccumlation (e.g.,
    chemical metabolism, food web structure).

Methodology Revisions Implementation by
EPA/States

EPA's future role in developing AWQC for the
protection of human health will include:

•   The refinement of the revised methodology
    based on public comments received,

•   The development of revised criteria for
    chemicals of high priority and national
    importance (including, but not limited to
    chemicals that bioaccumulate, such as
    PCBs, dioxin, and mercury), and

•   The development or revision of AWQC for
    some additional priority chemicals.

EPA does not plan to completely revise all of the
criteria developed in 1980 or those updated as
part of the 1992 National Toxics Rule (NTR).
Partial updates of all criteria may bejplausible.
EPA encourages states, tribes and EPA Regional
Offices to use the revised methodology to
develop or revise AWQC to appropriately reflect
local conditions. EPA believes that AWQC
inherently require several risk management
decisions that are, in many cases, better made at
the state and regional level (e.g., fish
consumption rates, target risk levels). EPA will
continue to develop and update necessary
toxicology and exposure data needed in the
derivation of AWQC that may  not be practical
for the states and regions to obtain.

Affect on State and EPA Regional Offices

The revised methodology will provide more
flexibility for decision-making at the state, tribal
and EPA regional level. EPA believes the
AWQC inherently require several risk
management decisions that are, in many cases,
better made at the state, tribal and regional level.
It is most likely that the methodology will result
in more stringent criteria for bioaccumulatives
(due to the use of BAFs instead of BCFs) and
generally similar, or less stringent, values of
nonbioaccumulatives.

Affect on Existing Criteria

Existing criteria will continue to be used in the
following ways:

•    As guidance to states, tribes and regions for
     use in establishing water quality standards;

•    As the basis for EPA promulgation of water
     quality standards; and

•    In establishing water quality-based permit
     limits for industrial effluent discharges (i.e.,
     NPDES limits), where the criteria have been
     adopted by a state, tribe or region or
     promulgated by EPA.

Until such time as EPA re-evaluates a chemical,
subjects the criteria to appropriate peer review,
and subsequently publishes a revised chemical-
specific 304(a) criteria, the existing criteria
remain in effect.

Information

For additional information concerning these
recommended methodology revisions, contact
Denis Borum, Health and Ecological Criteria
Division (4304), 401 M Street, S.W.,
Washington, D.C., 20460 (telephone: 202- 260-
8996).
You may view the Federal Register notice that
describes these recommended methodology
revisions on the Internet at:
http://www.epa.gov/OST/. The notice gives
complete information on how to obtain additional
information, how to review the complete
administrative record for these recommended
methodology revisions, and how to solicit public
comment.

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