65FR31681 Water Quality Standards; Establishment of Numeric Criteria for Priority Toxic Pollutants for the State of California, Part 2/4
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Posting-number: Volume 65, Issue 97, Page 31681, Part 1
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criterion before finalizing the proposed criterion. Therefore, EPA is
not promulgating a final acute freshwater selenium criterion at this
time.
b. Dissolved Metals Criteria
In December of 1992, in the NTR, EPA promulgated water quality
criteria for several States that had failed to meet the requirements of
CWA section 303(c)(2)(B). Included among the water quality criteria
promulgated were numeric criteria for the protection of aquatic life
for 11 metals: arsenic, cadmium, chromium (III), chromium (VI), copper,
lead, mercury, nickel, selenium, silver and zinc. Criteria for two
metals applied to the State of California: chromium III and selenium.
The Agency received extensive public comment during the development
of the NTR regarding the most appropriate approach for expressing the
aquatic life metals criteria. The principal issue was the correlation
between metals that are measured and metals that are bioavailable and
toxic to aquatic life. It is now the Agency's policy that the use of
dissolved metal to set and measure compliance with aquatic life water
quality standards is the recommended approach, because dissolved metal
more closely approximates the bioavailable fraction of the metal in the
water column than does total recoverable metal.
Since EPA's previous aquatic life criteria guidance had been
expressed as total recoverable metal, to express the criteria as
dissolved, conversion factors were developed to account for the
possible presence of particulate metal in the laboratory toxicity tests
used to develop the total recoverable criteria. EPA included a set of
recommended freshwater conversion factors with its Metals Policy (see
Office of Water Policy and Technical Guidance on Interpretation and
Implementation of Aquatic Life Metals Criteria, Martha G. Prothro,
Acting Assistant Administrator for Water, October 1, 1993). Based on
additional laboratory evaluations that simulated the original toxicity
tests, EPA refined the procedures used to develop freshwater conversion
factors for aquatic life criteria. These new conversion factors were
made available for public review and comment in the amendments to the
NTR on May 4, 1995, at 60 FR 22229. They are also contained in today's
rule at 40 CFR 131.38(b)(2).
The preamble to the August 5, 1997, proposed rule provided a more
detailed discussion of EPA's metals policy concerning the aquatic life
water quality criteria for the State of California. See 62 FR 42160-
42208. EPA incorporates that discussion here as part of this rulemaking
record. Many commenters strongly supported the Agency's policy on
dissolved metals aquatic life criteria. A few commenters expressed an
opinion that the metals policy may not provide criteria that are
adequately protective of aquatic or other species. Responses to those
comments are contained in a memo to the CTR record entitled
``Discussion of the Use of Dissolved Metals in the CTR'' (February 1,
2000, Jeanette Wiltse) and EPA's response to comments document which
are both contained in the administrative record for the final rule.
Calculation of Aquatic Life Dissolved Metals Criteria: Metals
criteria values for aquatic life in today's rule in the matrix at
131.38(b)(1) are shown as dissolved metal. These criteria have been
calculated in one of two ways. For freshwater metals criteria that are
hardness-dependent, the metals criteria value is calculated separately
for each hardness using the table at 40 CFR 131.38(b)(2). (The
hardness-dependent freshwater values presented in the matrix at 40 CFR
131.38(b)(1) have been calculated using a hardness of 100 mg/l as CaCO3
for illustrative purposes only.) The hardness-dependent criteria are
then multiplied by the appropriate conversion factors in the table at
40 CFR 131.38(b)(2). Saltwater and freshwater metals criteria that are
not hardness-dependent are calculated by taking the total recoverable
criteria values (from EPA's national section 304(a) criteria guidance,
as updated and described in section F.2.a.) before rounding, and
multiplying them by the appropriate conversion factors. The final
dissolved metals criteria values, as they appear in the matrix at 40
CFR 131.38(b)(1), are rounded to two significant figures.
Translators for Dissolved to Total Recoverable Metals Limits: EPA's
National Pollutant Discharge Elimination System (NPDES) regulations
require that limits for metals in permits be stated as total
recoverable in most cases (see 40 CFR 122.45(c)) except when an
effluent guideline specifies the limitation in another form of the
metal, the approved analytical methods measure only dissolved metal, or
the permit writer expresses a metal's limit in another form (e.g.,
dissolved, specific valence, or total) when required to carry out
provisions of the CWA. This is because the chemical conditions in
ambient waters frequently differ substantially from those in the
effluent and these differences result in changes in the partitioning
between dissolved and absorbed forms of the metal. This means that if
effluent limits were expressed in the dissolved form, additional
particulate metal could dissolve in the receiving water causing the
criteria to be exceeded. Expressing criteria as dissolved metal
requires translation between different metal forms in the calculation
of the permit limit so that a total recoverable permit limit can be
established that will achieve water quality standards. Thus, it is
important that permitting authorities and other authorities have the
ability to translate between dissolved metal in ambient waters and
total recoverable metal in effluent.
EPA has completed guidance on the use of translators to convert
from dissolved metals criteria to total recoverable permit limits. The
document, The Metals Translator: Guidance for Calculating a Total
Recoverable Permit Limit From a Dissolved Criterion (EPA 823-B-96-007,
June 1996), is included in the administrative record for today's rule.
This technical guidance examines how to develop a metals translator
which is defined as the fraction of total recoverable metal in the
downstream water that is dissolved, i.e., the dissolved metal
concentration divided by the total recoverable metal concentration. A
translator may take one of three forms: (1) It may be assumed to be
equivalent to the criteria guidance conversion factors; (2) it may be
developed directly as the ratio of dissolved to total recoverable
metal; and (3) it may be developed through the use of a partition
coefficient that is functionally related to the number of metal binding
sites on the adsorbent in the water column (e.g., concentrations of
total suspended solids or TSS). This guidance document discusses these
three forms of translators, as well as field study designs, data
generation and analysis, and site-specific study plans to generate
site-specific translators.
California Regional Water Quality Control Boards may use any of
these methods in developing water quality-based permit limits to meet
water quality standards based on dissolved metals criteria. EPA
encourages the State to adopt a statewide policy on the use of
translators so that the most appropriate method or methods are used
consistently within California.
c. Application of Metals Criteria
In selecting an approach for implementing the metals criteria, the
principal issue is the correlation between metals that are measured and
metals that are biologically available and toxic. In order to assure
that the metals criteria are appropriate for the chemical conditions
under which they are applied, EPA is providing for the
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adjustment of the criteria through application of the ``water-effect
ratio'' procedure. EPA notes that performing the testing to use a site-
specific water-effect ratio is optional on the part of the State.
In the NTR, as amended, EPA identified the water-effect ratio (WER)
procedure as a method for optional site-specific criteria development
for certain metals. The WER approach compares bioavailability and
toxicity of a specific pollutant in receiving waters and in laboratory
waters. A WER is an appropriate measure of the toxicity of a material
obtained in a site water divided by the same measure of the toxicity of
the same material obtained simultaneously in a laboratory dilution
water.
On February 22, 1994, EPA issued Interim Guidance on the
Determination and Use of the Water-Effect Ratios for Metals (EPA 823-B-
94-001) now incorporated into the updated Second Edition of the Water
Quality Standards Handbook, Appendix L. A copy of the Handbook is
contained in the administrative record for today's rule. In accordance
with the WER guidance and where application of the WER is deemed
appropriate, EPA strongly encourages the application of the WER on a
watershed or water body basis as part of a water quality criteria in
California as opposed to the application on a discharger-by-discharger
basis through individual NPDES permits. This approach is technically
sound and an efficient use of resources. However, discharger specific
WERs for individual NPDES permit limits are possible and potentially
efficient where the NPDES discharger is the only point source
discharger to a specific water body.
The rule requires a default WER value of 1.0 which will be assumed,
if no site-specific WER is determined. To use a WER other than the
default of 1.0, the rule requires that the WER must be determined as
set forth in EPA's WER guidance or by another scientifically defensible
method that has been adopted by the State as part of its water quality
standards program and approved by EPA.
The WER is a more comprehensive mechanism for addressing
bioavailability issues than simply expressing the criteria in terms of
dissolved metal. Consequently, expressing the criteria in terms of
dissolved metal, as done in today's rule for California, does not
completely eliminate the utility of the WER. This is particularly true
for copper, a metal that forms reduced-toxicity complexes with
dissolved organic matter.
The Interim Guidance on Determination and Use of Water-Effect
Ratios for Metals explains the relationship between WERs for dissolved
criteria and WERs for total recoverable criteria. Dissolved
measurements are to be used in the site-specific toxicity testing
underlying the WERs for dissolved criteria. Because WERs for dissolved
criteria generally are little affected by elevated particulate
concentrations, EPA expects those WERs to be somewhat less than WERs
for total recoverable criteria in such situations. Nevertheless, after
the site-specific ratio of dissolved to total metal has been taken into
account, EPA expects a permit limit derived using a WER for a dissolved
criterion to be similar to the permit limit that would be derived from
the WER for the corresponding total recoverable criterion.
d. Saltwater Copper Criteria
The saltwater copper criteria for aquatic life in today's rule are
4.8 <greek-m>g/l (CMC) and 3.1 <greek-m>g/l (CCC) in the dissolved
form. These criteria reflect new data including data collected from
studies for the New York/New Jersey Harbor and the San Francisco Bay
indicating a need to revise the former copper 304(a) criteria guidance
document to reflect a change in the saltwater CMC and CCC aquatic life
values. These data also reflect a comprehensive literature search
resulting in added toxicity test data for seven new species to the
database for the saltwater copper criteria. EPA believes these new data
have national implications and the national criteria guidance now
contains a CMC of 4.8 <greek-m>g/l dissolved and a CCC of 3.1
<greek-m>g/l dissolved. In the amendments to the NTR, EPA noticed the
availability of data to support these changes to the NTR, and solicited
comments. The data can be found in the draft document entitled, Ambient
Water Quality Criteria--Copper, Addendum 1995. This document is
available from the Office of Water Resource Center and is available for
review in the administrative record for today's rule.
e. Chronic Averaging Period
In establishing water quality criteria, EPA generally recommends an
``averaging period'' which reflects the duration of exposure required
to elicit effects in individual organisms (TSD, Appendix D-2). The
criteria continuous concentration, or CCC, is intended to be the
highest concentration that could be maintained indefinitely in a water
body without causing an unacceptable effect on the aquatic community or
its uses (TSD, Appendix D-1). As aquatic organisms do not generally
experience steady exposure, but rather fluctuating exposures to
pollutants, and because aquatic organisms can generally tolerate higher
concentrations of pollutants over a shorter periods of time, EPA
expects that the concentration of a pollutant can exceed the CCC
without causing an unacceptable effect if (a) the magnitude and
duration of exceedences are appropriately limited and (b) there are
compensating periods of time during which the concentration is below
the CCC. This is done by specifying a duration of an ``averaging
period'' over which the average concentration should not exceed the CCC
more often than specified by the frequency (TSD, Appendix D-1).
EPA is promulgating a 4-day averaging period for chronic criteria,
which means that measured or predicted ambient pollutant concentrations
should be averaged over a 4-day period to determine attainment of
chronic criteria. The State may apply to EPA for approval of an
alternative averaging period. To do so, the State must submit to EPA
the basis for such alternative averaging period.
The most important consideration for setting an appropriate
averaging period is the length of time that sensitive organisms can
tolerate exposure to a pollutant at levels exceeding a criterion
without showing adverse effects on survival, growth, or reproduction.
EPA believes that the chronic averaging period must be shorter than the
duration of the chronic tests on which the CCC is based, since, in some
cases, effects are elicited before exposure of the entire duration.
Most of the toxicity tests used to establish the chronic criteria are
conducted using steady exposure to toxicants for a least 28 days (TSD,
page 35). Some chronic tests, however, are much shorter than this (TSD,
Appendix D-2). EPA selected the 4-day averaging period based on the
shortest duration in which chronic test effects are sometimes observed
for certain species and toxicants. In addition, EPA believes that the
results of some chronic tests are due to an acute effect on a sensitive
life stage that occurs some time during the test, rather than being
caused by long-term stress or long-term accumulation of the test
material in the organisms.
Additional discussion of the rationale for the 4-day averaging
period is contained in Appendix D of the TSD. Balancing all of the
above factors and data, EPA believes that the 4-day averaging period
falls within the scientifically reasonable range of values for choice
of the averaging period, and is an appropriate length of time of
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pollutant exposure to ensure protection of sensitive organisms.
EPA established a 4-day averaging period in the NTR. In settlement
of litigation on the NTR, EPA stated that it was ``in the midst of
conducting, sponsoring, or planning research related to the basis for
and application of'' water quality criteria and mentioned the issue of
averaging period. See Partial Settlement Agreement in American Forest
and Paper Ass'n, Inc. et al. v. U.S. EPA (Consolidated Case No. 93-0694
(RMU), D.D.C.). EPA is re-evaluating issues raised about averaging
periods and will, if appropriate, revise the 1985 Guidelines.
EPA received public comment relevant to the averaging period during
the comment period for the 1995 Amendments to the NTR (60 FR 22228, May
4, 1995), although these public comments did not address the chronic
averaging period separately from the allowable excursion frequency and
the design flow. Comments recommended that EPA use the 30Q5 design flow
for chronic criteria.
While EPA is undertaking analysis of the chronic design conditions
as part of the revisions to the 1985 Guidelines, EPA has not yet
completed this work. Until this work is complete, for the reasons set
forth in the TSD, EPA continues to believe that the 4-day chronic
averaging period represents a reasonable, defensible value for this
parameter.
EPA added language to the final rule which will enable the State to
adopt alternative averaging periods and frequencies and associated
design flows where appropriate. The State may apply to EPA for approval
of alternative averaging periods and frequencies and related design
flows; the State must submit the bases for any changes. Before
approving any change, EPA will publish for public comment, a notice
proposing the changes.
f. Hardness
Freshwater aquatic life criteria for certain metals are expressed
as a function of hardness because hardness and/or water quality
characteristics that are usually correlated with hardness can reduce or
increase the toxicities of some metals. Hardness is used as a surrogate
for a number of water quality characteristics which affect the toxicity
of metals in a variety of ways. Increasing hardness has the effect of
decreasing the toxicity of metals. Water quality criteria to protect
aquatic life may be calculated at different concentrations of
hardnesses measured in milligrams per liter (mg/l) as calcium carbonate
(CaCO<INF>3</INF>).
Section 131.38(b)(2) of the final rule presents the hardness-
dependent equations for freshwater metals criteria. For example, using
the equation for zinc, the total recoverable CMCs at a hardness of 10,
50, 100 or 200 mg/l as CaCO<INF>3</INF> are 17, 67, 120 and 220
micrograms per liter (<greek-m>g/l), respectively. Thus, the specific
value in the table in the regulatory text is for illustrative purposes
only. Most of the data used to develop these hardness equations for
deriving aquatic life criteria for metals were in the range of 25 mg/l
to 400 mg/l as CaCO<INF>3</INF>, and the formulas are therefore most
accurate in this range. The majority of surface waters nationwide and
in California have a hardness of less than 400 mg/l as
CaCO<INF>3</INF>.
In the past, EPA generally recommended that 25 mg/l as
CaCO<INF>3</INF> be used as a default hardness value in deriving
freshwater aquatic life criteria for metals when the ambient (or
actual) hardness value is below 25 mg/l as CaCO<INF>3</INF>. However,
use of the approach results in criteria that may not be fully
protective. Therefore, for waters with a hardness of less than 25 mg/l
as CaCO<INF>3</INF>, criteria should be calculated using the actual
ambient hardness of the surface water.
In the past, EPA generally recommended that if the hardness was
over 400 mg/l, two options were available: (1) Calculate the criterion
using a default WER of 1.0 and using a hardness of 400 mg/l in the
hardness equation; or (2) calculate the criterion using a WER and the
actual ambient hardness of the surface water in the equation. Use of
the second option is expected to result in the level of protection
intended in the 1985 Guidelines whereas use of the first option is
thought to result in an even more protective aquatic life criterion. At
high hardness there is an indication that hardness and related
inorganic water quality characteristics do not have as much of an
effect on toxicity of metals as they do at lower hardnesses. Related
water quality characteristics do not correlate as well at higher
hardnesses as they do at lower hardnesses. Therefore, if hardness is
over 400 mg/l as CaCO<INF>3</INF>, a hardness of 400 mg/l as
CaCO<INF>3</INF> should be used with a default WER of 1.0;
alternatively, the WER and actual hardness of the surface water may be
used.
EPA requested comments in the NTR amendments on the use of actual
ambient hardness for calculating criteria when the hardness is below 25
mg/l as CaCO<INF>3</INF>, and when hardness is greater than 400 mg/l as
CaCO<INF>3</INF>. Most of the comments received were in favor of using
the actual hardness with the use of the water-effect ratio (1.0 unless
otherwise specified by the permitting authority) when the hardness is
greater than 400 mg/l as CaCO<INF>3</INF>. A few commenters did not
want the water-effect ratio to be mandatory in calculating hardness,
and other commenters had concerns about being responsible for deriving
an appropriate water-effect ratio. Overall, the commenters were in
favor of using the actual hardness when calculating hardness-dependent
freshwater metals criteria for hardness between 0-400 mg/l as
CaCO<INF>3</INF>. EPA took those comments into account in promulgating
today's rule.
A hardness equation is most accurate when the relationships between
hardness and the other important inorganic constituents, notably
alkalinity and pH, are nearly identical in all of the dilution waters
used in the toxicity tests and in the surface waters to which the
equation is to be applied. If an effluent raises hardness but not
alkalinity and/or pH, using the hardness of the downstream water might
provide a lower level of protection than intended by the 1985
guidelines. If it appears that an effluent causes hardness to be
inconsistent with alkalinity and/or pH, the intended level of
protection will usually be maintained or exceeded if either (1) data
are available to demonstrate that alkalinity and/or pH do not affect
the toxicity of the metal, or (2) the hardness used in the hardness
equation is the hardness of upstream water that does not contain the
effluent. The level of protection intended by the 1985 guidelines can
also be provided by using the WER procedure.
In some cases, capping hardness at 400 mg/l might result in a level
of protection that is higher than that intended by the 1985 guidelines,
but any such increase in the level of protection can be overcome by use
of the WER procedure. For metals whose criteria are expressed as
hardness equations, use of the WER procedure will generally be intended
to account for effects of such water quality characteristics as total
organic carbon on the toxicities of metals. The WER procedure is
equally useful for accounting for any deviation from a hardness
equation in a site water.
3. Human Health Criteria
EPA's CWA section 304(a) human health criteria guidance provides
criteria recommendations to minimize adverse human effects due to
substances in ambient water. EPA's CWA section 304(a) criteria guidance
for human health are based on two types of
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toxicological endpoints: (1) carcinogenicity and (2) systemic toxicity
(i.e., all other adverse effects other than cancer). Thus, there are
two procedures for assessing these health effects: one for carcinogens
and one for non-carcinogens.
If there are no data on how a chemical agent causes cancer, EPA's
existing human health guidelines assume that carcinogenicity is a
``non-threshold phenomenon,'' that is, there are no ``safe'' or ``no-
effect levels'' because even extremely small doses are assumed to cause
a finite increase in the incidence of the effect (i.e., cancer).
Therefore, EPA's water quality criteria guidance for carcinogens are
presented as pollutant concentrations corresponding to increases in the
risk of developing cancer. See Human Health Guidelines at 45 FR 79347.
With existing criteria, pollutants that do not manifest any
apparent carcinogenic effect in animal studies (i.e., systemic
toxicants), EPA assumes that the pollutant has a threshold below which
no effect will be observed. This assumption is based on the premise
that a physiological mechanism exists within living organisms to avoid
or overcome the adverse effect of the pollutant below the threshold
concentration.
Note: Recent changes in the Agency's cancer guidelines
addressing these assumptions are described in the Draft Water
Quality Criteria Methodology: Human Health, 63 FR 43756, August 14,
1998.
The human health risks of a substance cannot be determined with any
degree of confidence unless dose-response relationships are quantified.
Therefore, a dose-response assessment is required before a criterion
can be calculated. The dose-response assessment determines the
quantitative relationships between the amount of exposure to a
substance and the onset of toxic injury or disease. Data for
determining dose-response relationships are typically derived from
animal studies, or less frequently, from epidemiological studies in
exposed populations.
The dose-response information needed for carcinogens is an estimate
of the carcinogenic potency of the compound. Carcinogenic potency is
defined here as a general term for a chemical's human cancer-causing
potential. This term is often used loosely to refer to the more
specific carcinogenic or cancer slope factor which is defined as an
estimate of carcinogenic potency derived from animal studies or
epidemiological data of human exposure. It is based on extrapolation
from test exposures of high doses over relatively short periods of time
to more realistic low doses over a lifetime exposure period by use of
linear extrapolation models. The cancer slope factor, q1*, is EPA's
estimate of carcinogenic potency and is intended to be a conservative
upper bound estimate (e.g. 95% upper bound confidence limit).
For non-carcinogens, EPA uses the reference dose (RfD) as the dose-
response parameter in calculating the criteria. For non-carcinogens,
oral RfD assessments (hereinafter simply ``RfDs'') are developed based
on pollutant concentrations that cause threshold effects. The RfD is an
estimate (with uncertainty spanning perhaps an order of magnitude) of a
daily exposure to the human population (including sensitive subgroups)
that is likely to be without appreciable risk of deleterious effects
during a lifetime. See Human Health Guidelines. The RfD was formerly
referred to as an ``Acceptable Daily Intake'' or ADI. The RfD is useful
as a reference point for gauging the potential effect of other doses.
Doses that are less than the RfD are not likely to be associated with
any health risks, and are therefore less likely to be of regulatory
concern. As the frequency of exposures exceeding the RfD increases and
as the size of the excess increases, the probability increases that
adverse effect may be observed in a human population. Nonetheless, a
clear conclusion cannot be categorically drawn that all doses below the
RfD are ``acceptable'' and that all doses in excess of the RfD are
``unacceptable.'' In extrapolating non-carcinogen animal test data to
humans to derive an RfD, EPA divides either a No Observed-Adverse
Effect Level (NOAEL), Lowest Observed Adverse Effect Level (LOAEL), or
other benchmark dose observed in animal studies by an ``uncertainty
factor'' which is based on professional judgment of toxicologists and
typically ranges from 10 to 10,000.
For CWA section 304(a) human health criteria development, EPA
typically considers only exposures to a pollutant that occur through
the ingestion of water and contaminated fish and shellfish. Thus, the
criteria are based on an assessment of risks related to the surface
water exposure route only where designated uses are drinking water and
fish and shellfish consumption.
The assumed exposure pathways in calculating the criteria are the
consumption of 2 liters per day of water at the criteria concentration
and the consumption of 6.5 grams per day of fish and shellfish
contaminated at a level equal to the criteria concentration but
multiplied by a ``bioconcentration factor.'' The use of fish and
shellfish consumption as an exposure factor requires the quantification
of pollutant residues in the edible portions of the ingested species.
Bioconcentration factors (BCFs) are used to relate pollutant
residues in aquatic organisms to the pollutant concentration in ambient
waters. BCFs are quantified by various procedures depending on the
lipid solubility of the pollutant. For lipid soluble pollutants, the
average BCF is calculated from the weighted average percent lipids in
the edible portions of fish and shellfish, which is about 3%; or it is
calculated from theoretical considerations using the octanol/water
partition coefficient. For non-lipid soluble compounds, the BCF is
determined empirically. The assumed water consumption is taken from the
National Academy of Sciences publication Drinking Water and Health
(1977). (Referenced in the Human Health Guidelines.) This value is
appropriate as it includes a margin of safety so that the general
population is protected. See also EPA's discussion of the 2.0 liters/
day assumption at 61 FR 65183 (Dec. 11, 1996). The 6.5 grams per day
contaminated fish and shellfish consumption value was equivalent to the
average per-capita consumption rate of all (contaminated and non-
contaminated) freshwater and estuarine fish and shellfish for the U.S.
population. See Human Health Guidelines.
EPA assumes in calculating water quality criteria that the exposed
individual is an average adult with body weight of 70 kilograms. EPA
assumes 6.5 grams per day of contaminated fish and shellfish
consumption and 2.0 liters per day of contaminated drinking water
consumption for a 70 kilogram person in calculating the criteria.
Regarding issues concerning criteria development and differences in
dose per kilogram of body weight, RfDs are always derived based on the
most sensitive health effect endpoint. Therefore, when that basis is
due to a chronic or lifetime health effect, the exposure parameters
assume the exposed individual to be the average adult, as indicated
above.
In the absence of this final rule, there may be particular risks to
children. EPA believes that children are protected by the human health
criteria contained in this final rule. Children are protected against
other less sensitive adverse health endpoints due to the conservative
way that the RfDs are derived. An RfD is a public health protective
endpoint. It is an amount of a chemical that can be consumed on a daily
basis for a lifetime without expecting an adverse effect. RfDs are
based on sensitive health endpoints and
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are calculated to be protective for sensitive human sub-populations
including children. If the basis of the RfD was due to an acute or
shorter-term developmental effect, EPA uses exposure parameters other
than those indicated above. Specifically, EPA uses parameters most
representative of the population of concern (e.g., the health criteria
for nitrates based on infant exposure parameters). For carcinogens, the
risk assessments are upper bound one in a million (10<SUP>-6</SUP>)
lifetime risk numbers. The risk to children is not likely to exceed
these upper bounds estimates and may be zero at low doses. The exposure
assumptions for drinking water and fish protect children because they
are conservative for infants and children. EPA assumes 2 liters of
untreated surface water and 6.5 grams of freshwater and estuarine fish
are consumed each day. EPA believes the adult fish consumption
assumption is conservative for children because children generally
consume marine fish not freshwater and estuarine.
EPA has a process to develop a scientific consensus on oral
reference dose assessments and carcinogenicity assessments (hereinafter
simply cancer slope factors or slope factors or q1*s). Through this
process, EPA develops a consensus of Agency opinion which is then used
throughout EPA in risk management decision-making. EPA maintains an
electronic data base which contains the official Agency consensus for
oral RfD assessments and carcinogenicity assessments which is known as
the Integrated Risk Information System (IRIS). It is available for use
by the public on the National Institutes of Health's National Library
of Medicine's TOXNET system, and through diskettes from the National
Technical Information Service (NTIS). (NTIS access number is PB 90-
591330.)
Section 304(a)(1) of the CWA requires EPA to periodically revise
its criteria guidance to reflect the latest scientific knowledge: ``(A)
On the kind and extent of all identifiable effects on health and
welfare * * *; (B) on the concentration and dispersal of pollutants, or
their byproducts, through biological, physical, and chemical processes;
and (C) on the effects of pollutants on the biological community
diversity, productivity, and stability, including information on the
factors affecting eutrophication rates of organic and inorganic
sedimentation for varying types of receiving waters.'' In developing
up-to-date water quality criteria for the protection of human health,
EPA uses the most recent IRIS values (RfDs and q1*s) as the
toxicological basis in the criterion calculation. IRIS reflects EPA's
most current consensus on the toxicological assessment for a chemical.
In developing the criteria in today's rule, the IRIS values as of
October 1996 were used together with currently accepted exposure
parameters for bioconcentration, fish and shellfish and water
consumption, and body weight. The IRIS cover sheet for each pollutant
criteria included in today's rule is contained in the administrative
record.
For the human health criteria included in today's rule, EPA used
the Human Health Guidelines on which criteria recommendations from the
appropriate CWA section 304(a) criteria guidance document were based.
(These documents are also placed in the administrative record for
today's rule.) Where EPA has changed any parameters in IRIS used in
criteria derivation since issuance of the criteria guidance document,
EPA recalculated the criteria recommendation with the latest IRIS
information. Thus, there are differences between the original 1980
criteria guidance document recommendations, and those in this rule, but
this rule presents EPA's most current CWA section 304(a) criteria
recommendation. The basis (q1* or RfD) and BCF for each pollutant
criterion in today's rule is contained in the rule's Administrative
Record Matrix which is included in the administrative record for the
rule. In addition, all recalculated human health numbers are denoted by
an ``a'' in the criteria matrix in 40 CFR 131.38(b)(1) of the rule. The
pollutants for which a revised human health criterion has been
calculated since the December 1992 NTR include:
mercury
dichlorobromomethane
1,2-dichloropropane
1,2-trans-dichloroethylene
2,4-dimethylphenol
acenaphthene
benzo(a)anthracene
benzo(a)pyrene
benzo(b)flouranthene
benzo(k)flouranthene
2-chloronaphthalene
chrysene
dibenzo(a,h)anthracene
indeno(1,2,3-cd)pyrene
N-nitrosodi-n-propylamine
alpha-endosulfan
beta-endosulfan
endosulfan sulfate
2-chlorophenol
butylbenzyl phthalate
polychlorinated biphenyls.
In November of 1991, the proposed NTR presented criteria for
several pollutants in parentheses. These were pollutants for which, in
1980, insufficient information existed to develop human health water
quality criteria, but for which, in 1991, sufficient information
existed. Since these criteria did not undergo the public review and
comment in a manner similar to the other water quality criteria
presented in the NTR (for which sufficient information was available in
1980 to develop a criterion, as presented in the 1980 criteria guidance
documents), they were not proposed for adoption into the water quality
criteria, but were presented to serve as notice for inclusion in future
State triennial reviews. Today's rule promulgates criteria for these
nine pollutants:
copper
1, 2-dichloropropane
1,2-trans-dichloroethylene
2,4-dimethylphenol
acenaphthene
2-chloronaphthalene
N-nitrosodi-n-propylamine
2-chlorophenol
butylbenzene phthalate
All the criteria are based on IRIS values--either an RfD or q1*--
which were listed on IRIS as of November 1991, the date of the proposed
NTR. These values have not changed since the final NTR was published in
December of 1992. The rule's Administrative Record Matrix in the
administrative record of today's rule contains the specific RfDs, q1*s,
and BCFs used in calculating these criteria.
Proposed Changes to the Human Health Criteria Methodology: EPA
recently proposed revisions to the 1980 ambient water quality criteria
derivation guidelines (the Human Health Guidelines). See Draft Water
Quality Criteria Methodology: Human Health, 63 FR 43756, August 14,
1998; see also Draft Water Quality Criteria Methodology: Human Health,
U.S. EPA Office of Water, EPA 822-Z-98-001. The EPA revisions consist
of five documents: Draft Water Quality Criteria Methodology: Human
Health, EPA 822-Z-98-001; Ambient Water Quality Criteria Derivation
Methodology Human Health, Technical Support Document, Final Draft, EPA-
822-B-98-005; and three Ambient Water Quality Criteria for the
Protection of Human Health, Drafts--one each for Acrylonitrile, 1,3-
Dichloropropene (1,3-DCP), and Hexachlorobutadiene (HCBD),
respectively, EPA-822-R-98-006, -005, and -004. All five documents are
contained in the administrative record for today's rule.
The proposed methodology revisions reflect significant scientific
advances that have occurred during the past nineteen years in such key
areas as cancer and noncancer risk assessments, exposure assessments
and bioaccumulation. For specific details on
[[Page 31695]]
these proposed changes and others, please refer to the Federal Register
notice or the EPA document.
It should be noted that some of the proposed changes may result in
significant numeric changes in the ambient water quality criteria.
However, EPA will continue to rely on existing criteria as the basis
for regulatory and non-regulatory decisions, until EPA revises and
reissues a 304(a) criteria guidance using the revised final human
health criteria methodology. The existing criteria are still viewed as
scientifically acceptable by EPA. The intention of the proposed
methodology revisions is to present the latest scientific advancements
in the areas of risk and exposure assessment in order to incrementally
improve the already sound toxicological and exposure bases for these
criteria. As EPA's current human health criteria are the product of
many years worth of development and peer review, it is reasonable to
assume that revisiting all existing criteria, and incorporating peer
review into such review, could require comparable amounts of time and
resources. Given these circumstances, EPA proposed a process for
revisiting these criteria as part of the overall revisions to the
methodology for deriving human health criteria. This process is
discussed in the Implementation Section of the Notice of Draft
Revisions to the Methodology for Deriving Ambient Water Quality
Criteria for the Protection of Human Health (see 63 FR 43771-43776,
August 14, 1998).
The State of California in its Ocean Plan, adopted in 1990 and
approved by EPA in 1991, established numeric water quality criteria
using an average fish and shellfish consumption rate of 23 grams per
day. This value is based on an earlier California Department of Health
Services estimate. The State is currently in the process of readopting
its water quality control plans for inland surface waters, enclosed
bays, and estuaries. The State intends to consider information on fish
and shellfish consumption rates evaluated and summarized in a report
prepared by the State's Pesticide and Environmental Toxicology Section
of the Office of Environmental Health Hazard Assessment of the
California Environmental Protection Agency. The report, entitled,
Chemicals in Fish Report No. 1: Consumption of Fish and Shellfish in
California and the United States, was published in final draft form in
July of 1997, and released to the public on September 16, 1997. The
report is currently undergoing final evaluation, and is expected to
published in final form in the near future. This final draft report is
contained in the administrative record for today's rule. Although EPA
has not used this fish consumption value here because this information
has not yet been finalized, the State may use any appropriate higher
state-specific fish and shellfish consumption rates in its readoption
of criteria in its statewide plans.
a. 2,3,7,8-TCDD (Dioxin) Criteria
In today's action, EPA is promulgating human health water quality
criteria for 2,3,7,8-tetrachlorodibenzo-p-dioxin (``dioxin'') at the
same levels as promulgated in the NTR, as amended. These criteria are
derived from EPA's 1984 CWA section 304(a) criteria guidance document
for dioxin.
For National Pollutant Discharge Elimination System (NPDES)
purposes, EPA supports the regulation of other dioxin and dioxin-like
compounds through the use of toxicity equivalencies or TEQs in NPDES
permits (see discussion below). For California waters, if the discharge
of dioxin or dioxin-like compounds has reasonable potential to cause or
contribute to a violation of a narrative criterion, numeric water
quality-based effluent limits for dioxin or dioxin-like compounds
should be included in NPDES permits and should be expressed using a TEQ
scheme.
EPA has been evaluating the health threat posed by dioxin nearly
continuously for over two decades. Following issuance of the 1984
criteria guidance document, evaluating the health effects of dioxin and
recommending human health criteria for dioxin, EPA prepared draft
reassessments reviewing new scientific information relating to dioxin
in 1985 and 1988. EPA's Science Advisory Board (SAB), reviewing the
1988 draft reassessment, concluded that while the risk assessment
approach used in 1984 criteria guidance document had inadequacies, a
better alternative was unavailable (see SAB's Dioxin Panel Review of
Documents from the Office or Research and Development relating to the
Risk and Exposure Assessment of 2,3,7,8-TCDD (EPA-SAB-EC-90-003,
November 28, 1989) included in the administrative record for today's
rule). Between 1988 and 1990, EPA issued numerous reports and guidances
relating to the control of dioxin discharges from pulp and paper mills.
See e.g., EPA Memorandum, ``Strategy for the Regulation of Discharges
of PHDDs & PHDFs from Pulp and Paper Mills to the Waters of the United
States,'' from Assistant Administrator for Water to Regional Water
Management Division Directors and NPDES State Directors, dated May 21,
1990 (AR NL-16); EPA Memorandum, ``State Policies, Water Quality
Standards, and Permit Limitations Related to 2,3,7,8-TCDD in Surface
Water,'' from the Assistant Administrator for Water to Regional Water
Management Division Directors, dated January 5, 1990 (AR VA-66). These
documents are available in the administrative record for today's rule.
In 1991, EPA's Administrator announced another scientific
reassessment of the risks of exposure to dioxin (see Memorandum from
Administrator William K. Reilly to Erich W. Bretthauer, Assistant
Administrator for Research and Development and E. Donald Elliott,
General Counsel, entitled Dioxin: Follow-Up to Briefing on Scientific
Developments, April 8, 1991, included in the administrative record for
today's rule). At that time, the Administrator made clear that while
the reassessment was underway, EPA would continue to regulate dioxin in
accordance with existing Agency policy. Thereafter, the Agency
proceeded to regulate dioxin in a number of environmental programs,
including standards under the Safe Drinking Water Act and the CWA.
The Administrator's promulgation of the dioxin human health
criteria in the 1992 NTR affirmed the Agency's decision that the
ongoing reassessment should not defer or delay regulating this potent
contaminant, and further, that the risk assessment in the 1984 criteria
guidance document for dioxin continued to be scientifically defensible.
Until the reassessment process was completed, the Agency could not
``say with any certainty what the degree or directions of any changes
in the risk estimates might be'' (57 FR 60863-64).
The basis for the dioxin criteria as well as the decision to
include the dioxin criteria in the 1992 NTR pending the results of the
reassessment were challenged. See American Forest and Paper Ass'n, Inc.
et al. v. U.S. EPA (Consolidated Case No. 93-0694 (RMU) D.D.C.). By
order dated September 4, 1996, the Court upheld EPA's decision. EPA's
brief and the Court's decision are included in the administrative
record for today's rule.
EPA has undertaken significant effort toward completion of the
dioxin reassessment. On September 13, 1994, EPA released for public
review and comment a draft reassessment of toxicity and exposure to
dioxin. See Health Assessment Document for 2,3,7,8-Tetrachlorobenzo-p-
Dioxin (TCDD) and Related Compounds, U.S. EPA, 1994. EPA is currently
addressing comments made by the public and the SAB and anticipates that
the final
[[Page 31696]]
revised reassessment will go to the SAB in the near future. With
today's rule, the Agency reaffirms that, notwithstanding the on-going
risk reassessment, EPA intends to continue to regulate dioxin to avoid
further harm to public health, and the basis for the dioxin criteria,
both in terms of the cancer potency and the exposure estimates, remains
scientifically defensible. The fact that EPA is reassessing the risk of
dioxin, virtually a continuous process to evaluate new scientific
information, does not mean that the current risk assessment is
``wrong''. It continues to be EPA's position that until the risk
assessment for dioxin is revised, EPA supports and will continue to use
the existing risk assessment for the regulation of dioxin in the
environment. Accordingly, EPA today promulgates dioxin criteria based
on the 1984 criteria guidance document for dioxin and promulgated in
the NTR in 1992.
Toxicity Equivalency: The State of California, in its 1991 water
quality control plans, adopted human health criteria for dioxin and
dioxin-like compounds based on the concept of toxicity equivalency
(TEQ) using toxicity equivalency factors (TEFs). EPA Region 9 reviewed
and approved the State's use of the TEQ concept and TEFs in setting the
State's human health water quality criteria for dioxin and dioxin-like
compounds.
In 1987, EPA formally embraced the TEQ concept as an interim
procedure to estimate the risks associated with exposures to 210
chlorinated dibenzo-p-dioxin and chlorinated dibenzofuran (CDD/CDF)
congeners, including 2,3,7,8-TCDD. This procedure uses a set of derived
TEFs to convert the concentration of any CDD/CDF congener into an
equivalent concentration of 2,3,7,8-TCDD. In 1989, EPA updated its TEFs
based on an examination of relevant scientific evidence and a
recognition of the value of international consistency. This updated
information can be found in EPA's 1989 Update to the Interim Procedures
for Estimating Risks Associated with Exposures to Mixtures of
Chlorinated Dibenzo-p-dioxins and -dibenzofurans (CDDs and CDFs) (EPA/
625/3-89/016, March 1989). EPA had been active in an international
effort aimed at adopting a common set of TEFs (International TEFs/89 or
I-TEFs/89), to facilitate information exchange on environmental
contamination of CDD/CDF. This document reflects EPA's support of an
internationally consistent set of TEFs, the I-TEFs/89. EPA uses I-TEFs/
89 in many of its regulatory programs.
In 1994, the World Health Organization (WHO) revised the TEF scheme
for dioxins and furans to include toxicity from dioxin-like compounds
(Ahlborg et al., 1994). However, no changes were made to the TEFs for
dioxins and furans. In 1998, the WHO re-evaluated and revised the
previously established TEFs for dioxins (Ds), furans (Fs) and dioxin-
like compounds (Vanden Bers, 1998). The nomenclature for this TEF
scheme is TEQDFP-WHO98, where TEQ represents the 2,3,7,8-TCDD Toxic
Equivalence of the mixture, and the subscript DFP indicates that
dioxins (Ds) furans (Fs) and dioxin-like compounds (P) are included in
the TEF scheme. The subscript 98 following WHO displays the year
changes were made to the TEF scheme.
EPA intends to use the 1998 WHO TEF scheme in the near future. At
this point however, EPA will support the use of either the 1989 interim
procedures or the 1998 WHO TEF scheme but encourages the use of the
1998 WHO TEF scheme in State programs. EPA expects California to use a
TEF scheme in implementing the 2,3,7,8-TCDD water quality criteria
contained in today's rule. The TEQ and TEF approach provide a
methodology for setting NPDES water quality-based permit limits that
are protective of human health for dioxin and dioxin-like compounds.
Several commenters requested EPA to promulgate criteria for other
forms of dioxin, in addition to 2,3,7,8-TCDD. EPA's draft reassessment
for dioxin examines toxicity based on the TEQ concept and I-TEFs/89.
When EPA completes the dioxin reassessment, the Agency intends to adopt
revised 304(a) water quality criteria guidance based on the
reassessment for dioxin. If necessary, EPA will then act to amend the
NTR and CTR to reflect the revised 304(a) water quality criteria
guidance.
b. Arsenic Criteria
EPA is not promulgating human health criteria for arsenic in
today's rule. EPA recognizes that it promulgated human health water
quality criteria for arsenic for a number of States in 1992, in the
NTR, based on EPA's 1980 section 304(a) criteria guidance for arsenic
established, in part, from IRIS values current at that time. However, a
number of issues and uncertainties existed at the time of the CTR
proposal concerning the health effects of arsenic. These issues and
uncertainties were summarized in ``Issues Related to Health Risk of
Arsenic'' which is contained in the administrative record for today's
rule. During the period of this rulemaking action, EPA commissioned a
study of arsenic health effects by the National Research Council (NRC)
arm of the National Academy of Sciences. EPA received the NRC report in
March of 1999. EPA scientists reviewed the report, which recommended
that EPA lower the Safe Drinking Water Act arsenic maximum contaminant
level (MCL) as soon as possible (The arsenic MCL is currently 50
<greek-m>g/l.) The bladder cancer analysis in the NRC report will
provide part of the basis for the risk assessment of a proposed revised
arsenic MCL in the near future. After promulgating a revised MCL for
drinking water, the Agency plans to revise the CWA 304(a) human health
criteria for arsenic in order to harmonize the two standards. Today's
rule defers promulgating arsenic criteria based on the Agency's
previous risk assessment of skin cancer. In the meantime, permitting
authorities in California should rely on existing narrative water
quality criteria to establish effluent limitations as necessary for
arsenic. California has previously expressed its science and policy
position by establishing a criterion level of 5 <greek-m>g/l for
arsenic. Permitting authorities may, among other considerations,
consider that value when evaluating and interpreting narrative water
quality criteria.
c. Mercury Criteria
The human health criteria promulgated here use the latest RfD in
EPA's Integrated Risk Information System (IRIS) and the weighted
average practical bioconcentration factor (PBCF) from the 1980 section
304(a) criteria guidance document for mercury. EPA considered the
approach used in the Great Lakes Water Quality Guidance (``Guidance'')
incorporating Bioaccumulation Factors (BAFs), but rejected this
approach for reasons outlined below. The equation used here to derive
an ambient water quality criterion for mercury from exposure to
organisms and water is:
[GRAPHIC] [TIFF OMITTED] TR18MY00.011
Where:
RfD = Reference Dose
BW = Body Weight
WC = Water Consumption
FC = Total Fish and Shellfish Consumption per Day
PBCF = Practical Bioconcentration Factor (weighted average)
For mercury, the most current RfD from IRIS is 1 x 10<SUP>-4</SUP>
mg/kg/day. The RfD used a benchmark dose as an estimate of a No
Observed Adverse Effect Level (NOAEL). The benchmark dose was
calculated by applying a Weibel model
[[Page 31697]]
for extra risk to all neurological effects observed in 81 Iraqi
children exposed in utero as reported in Marsh, et. al. (1987).
Maternal hair mercury was the measure of exposure. Extra risk refers to
an adjustment for background incidence of a given health effect.
Specifically, the extra risk is the added incidence of observing an
effect above the background rate relative to the proportion of the
population of interest that is not expected to exhibit such as effect.
The resulting estimate was the lower 95% statistical bound on the 10%
extra risk; this was 11 ppm mercury in maternal hair. This dose in hair
was converted to an equivalent ingested amount by applying a model
based on data from human studies; the resulting benchmark dose was 1 x
10<SUP>-3</SUP> mg/kg body weight /day. The RfD was calculated by
dividing the benchmark dose by a composite uncertainty factor of 10.
The uncertainty factor was used to account for variability in the human
population, in particular the wide variation in biological half-life of
methylmercury and the variation that is observed in the ration of hair
mercury to mercury in the blood. In addition the uncertainty factor
accounts for lack of a two-generation reproductive study and the lack
of data on long term effects of childhood mercury exposures. The RfD
thus calculated is 1 x 10<SUP>-4</SUP> mg/kg body weight/day or 0.1
<greek-m>g/kg/day. The body weight used in the equation for the mercury
criteria, as discussed in the Human Health Guidelines, is a mean adult
human body weight of 70 kg. The drinking water consumption rate, as
discussed in the Human Health Guidelines, is 2.0 liters per day.
The bioconcentration factor or BCF is defined as the ratio of
chemical concentration in the organism to that in surrounding water.
Bioconcentration occurs through uptake and retention of a substance
from water only, through gill membranes or other external body
surfaces. In the context of setting exposure criteria it is generally
understood that the terms ``BCF'' and ``steady-state BCF'' are
synonymous. A steady-state condition occurs when the organism is
exposed for a sufficient length of time that the ratio does not change
substantially.
The BCFs that were used herein are the ``Practical Bioconcentration
Factors (PBCFs)'' that were derived in 1980: 5500 for fresh water, 3765
for estuarine coastal waters, and 9000 for open oceans. See pages C-
100-1 of Ambient Water Quality Criteria for Mercury (EPA 440/5-80-058)
for a complete discussion on the PBCF. Because of the way they were
derived, these PBCFs take into account uptake from food as well as
uptake from water. A weighted average PBCF was calculated to take into
account the average consumption from the three waters using the
following equation:
[GRAPHIC] [TIFF OMITTED] TR18MY00.012
Given the large value for the weighted average PBCF, the contribution
of drinking water to total daily intake is negligible so that
assumptions concerning the chemical form of mercury in drinking water
become less important. The human health mercury criteria promulgated
for this rule are based on the latest RfD as listed in IRIS and a
weighted PBCF from the 1980 Sec. 304(a) criteria guidance document for
mercury.
On March 23, 1995 (60 FR 15366), EPA promulgated the Great Lakes
Water Quality Guidance (``Guidance''). The Guidance incorporated
bioaccumulation factors (BAFs) in the derivation of criteria to protect
human health because it is believed that BAFs are a better predictor
than BCFs of the concentration of a chemical within fish tissue since
BAFs include consideration of the uptake of contaminants from all
routes of exposure. A bioaccumulation factor is defined as the ratio
(in L/kg) of a substance's concentration in tissue to the concentration
in the ambient water, in situations where both the organism and its
food are exposed and the ratio does not change substantially over time.
The final Great Lakes Guidance establishes a hierarchy of four methods
for deriving BAFs for non-polar organic chemicals: (1) Field-measured
BAFs; (2) predicted BAFs derived using a field-measured biota-sediment
accumulation factor; (3) predicted BAFs derived by multiplying a
laboratory-measured BCF by a food chain multiplier; and (4) predicted
BAFs derived by multiplying a BCF calculated from the log Kow by a
food-chain multiplier. The final Great Lakes Guidance developed BAFs
for trophic levels three and four fish of the Great Lakes Basin.
Respectively, the BAFs for mercury for trophic level 3 and 4 fish were:
27,900 and 140,000.
The BAF promulgated in the GLI was developed specifically for the
Great Lakes System. It is uncertain whether the BAFs of 27,900 and
140,000 are appropriate for use in California at this time; therefore,
today's final rule does not use the GLI BAF in establishing human
health criteria for mercury in California. The magnitude of the BAF for
mercury in a given system depends on how much of the total mercury is
present in the methylated form. Methylation rates vary widely from one
water body to another for reasons that are not fully understood.
Lacking the data, it is difficult to determine if the BAF used in the
GLI represents the true potential for mercury to bioaccumulate in
California surface waters. The true, average BAF for California could
be higher or lower. For more information see EPA's Response to Comments
document in the administrative record for this rule (specifically
comments CTR-002-007(b) and CTR-016-007).
EPA is developing a national BAF for mercury as part of revisions
to its 304(a) criteria for human health; however, the BAF methodology
that will be used is currently under evaluation as part of EPA's
revisions to its National Human Health Methodology (see section F.3
above). EPA applied a similar methodology in its Mercury Study Report
to Congress (MSRC) to derive a BAF for methylmercury. The MSRC is
available through NTIS (EPA-452/R-97-003). Although a BAF was derived
in the MSRC, EPA does not intend to use this BAF for National
application. EPA is engaged in a separate effort to incorporate
additional mercury bioaccumulation data that was not considered in the
MSRC, and to assess uncertainties with using a National BAF approach
for mercury. Once the proposed revised human health methodology,
including the BAF component, is finalized, EPA will revise its 304(a)
criteria for mercury to reflect changes in the underlying methodology,
recommendations contained in the MSRC, and recommendations in a
National Academy of Science report on human health assessment of
methylmercury. When EPA changes its 304(a) criteria recommendation for
mercury, States and Tribes will be expected to review their water
quality standards for mercury and make any revisions necessary to
ensure their standards are scientifically defensible.
New information may become available regarding the bioaccumulation