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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