UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON. D.C. 20460
Honorable Lee M* Thomas
Administrator
tl. S» Environmental Protection Agency
401 M Street, S. W. OFFICE OF
Washington, D. C, 20460 THE ADMINISTRATOR
Dear Mr* Thomas:
The Science Advisory Board has completed its review of the Agency's
revised Guidelines for Water Quality Criteria. The Board's review was
carried out by its Environmental Effects, Transport and Fate Committee.
The Committee concludes that the Agency has made great progress in
developing a more scientifically sophisticated and realistic set of
Guidelines. It has identified additional areas of research to further
Improve the scientific data base in future years. These areas include;
o Organisms used for future studies should be selected for the
role they play in ecosystems, if ecosystem impact is to be
reasonably approximated.
o The family within which species are assumed to react similarly
to toxicants should be abandoned as a unit of study in favor
of the ecologically more relevant units of trophic levels or
functional groups,
o The Agency should reconsider the use of the acute/chronic ratios
or its validity should be examined within a range of exposure
conditions normally found in field situations.
o EPA should acknowledge that interactions are a reality that
should be considered in criteria setting and should begin to
examine the problem of mechanises of toxlcity.
The Board appreciates the opportunity to present its advice on these
revised Guidelines and hopes that its review proves helpful to the Agency's
criteria development efforts. We request that the Agency provide a formal
response to our report.
John M. Neuhold, Chairman
Water Quality Criteria Subcommittee
Environmental Effects, Transport
and Fate Committee
Norton Nelsons Chairman
Executive Committee
Science Advisory Board
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If.
WATER QUALITY CRITERIA
A Report of the Water Quality Criteria Subcommittee
Environmental Effects, Transport and Fate Committee
Science Advisory Board
Environmental Protection Agency
April 1985
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EPA NOTICE
This report has been written as a part of the activities
of the Environmental Effects, Transport and Fate Committee of
the Science Advisory Board, a public advisory group providing
external scientific advice to the Administrator and other
officials of the Environmental Protection Agency* The Board is
structured to provide a balanced expert assessment of the
scientific matters related to problems facing the Agency, This
report has not been reviewed for approval by the Agency and,
hence, its contents do not represent the views and policies of
the Environmental Protection Agency, nor does mention of trade
names or commercial products constitute endorsement or recom— *
niendations for use.
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TABLE OF CONTENTS
I. Introduction.».,,*. .............,......,.*.. 1
II. Conclusions and Recommendations» ,*.........»,, 3
III. Philosophical and Operational Bases 5
IV, Biological Considerations.*.......... ...*,.. 8
A. Laboratory to Field Relationships ..........8
B. The Role of Organisms in the Ecosystem...........9
C. The Family Concept in Toxicity Testing......,«..10
D. Acute/Chronic Ratios.»»*.,...............**.....11
V. Chemical Considerations.., 12
A. Metal Speciation ,,. »» 12
B. Organic Matter and Dynamics ...»........*,..13
C. Contaminant Interactions».....»***.......»4.....14
VI. Exposure Considerations....«44«......*44...... 4.4... 15
A, Level of Protection.4.......4 *». .......*.15
B. Statistical Issues «,........».. .15
1. Statement of Scientific Assumptions.........16
2. Achievement of Protection ....*......17
3. Verification.. — ,,.,»... .18
4. Implications for Statistical Analysis....4..19
VII. Literature Cited...,. *** *........»... 21
VIII. Appendix
A. Members of the Subcommittee on Water Quality
Criteria 22
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I. INTRODUCTION
The Executive Committee of the Science Advisory Board
agreed to review, beginning in the Spring, 1984, the Environ-
mental Protection Agency's revised Guidelines for Water
Quality Criteria as proposed by the Criteria and Standards
Division in the Office of Water* The Executive Committee
referred this issue to its Environmental Effects, Transport &
Pate Committee (EETPC). The latter Committee carried out the
review and developed a scientific report by creating a Subcom-
mittee on Water Quality Criteria. (See Appendix A for a
roster of Subcommittee members.) The specific assignment
issued to the subcommittee was to prepare a critique of the
scientific rationale of and proposed modifications to EPA'S
Guidelines.
The initial presentation to the Environmental Effects,
Transport and Fate Committee occurred in February, 1984 at a
meeting at EpA's Gulf Breeze Environmental Research Laboratory.
At that time, the Committee also formulated the charge of the
Subcommittee on Water Quality Criteria. The Subcommitte held
its first meeting at the Environmental Research Laboratory in
Duluth, Minnesota where it was briefed by laboratory personnel
responsible for providing scientific input to the Guidelines.
The Subcommittee held subsequent meetings in July, 1984 in
Corvallis, Oregon, where it received from EPA staff an update
on the public comments submitted on the document, and that same
month in Monterey, California where the EEFTC received a status
briefing of the Subcommittee's review and preparation of a
scientific report. The Subcommittee met in December 1984, in
New Orleans, Louisiana to continue writing its report. The
report was submitted to the SAB Executive Committee for its
April 25-26, 1985 meeting at which time it was officially
approved for transmittal to EPA.
The Science Advisory Board has followed the development
of water quality criteria by the Agency since the Board's
creation in 1974. The process of developing criteria has
undergone considerable evolution since the Agency's initial
efforts, which resulted in the "Blue Book" followed shortly
by the "Red Book", that placed sole emphasis for the setting
of criteria on the results of individual species* toxicity
tests, subsequent iterations of the Guidelines included
consideration of such issues as mode of exposuret level of
protectiveness and ecosystem protection. Each update has
resulted in a more sophisticated and realistic set of Guide-
lines. To the credit of the scientists at the EPA
laboratories and within the Office of Water, the latest
edition of the Guidelines takes advantage of advances in
research made over the past few years. The Subcommittee
has identified some additional areas where the Guidelines
can be improved, and this report presents those recom-
mendations.
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This report is organized into five sections. These
include; 1) conclusions and recommendations; 2) a discussion
of the philosophical arid operational bases for water quality
criteria; 3) a discussion and critique of the application
of biological principles to such issues as the relationship
of laboratory derived toxicity data to field realities, the
role of organisms in ecosystems, the taxonomic family as a
discriminant unit and acute/chronic ratios? 4) a review of
chemical considerations, particularly the question of metal
speciation; and 5) an evaluation of exposure considerations
involving the concept of level of protection as well as a
discussion of the validity of statistical approaches.
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II. CONCLUSIONS AND RECOMMENDATIONS
1. The Subcommittee understands that the Congressional
intent in adopting the concept of physical, chemical and
biological integrity in amendments to the Clean Water Act
was to lessen the Nation's dependence on water use specification
criteria and to incorporate ecosystem principles into the promul-
gation of water quality criteria. To make_ _th_is_ concept operation-
ally possible, it is necessary to view the ecosystem i_n__its
^ ° cu s Attention on measures of stability.
2, Laboratory toxicity studies are useful in examining
dose-response relationships and mechanisms of toxicity. Their
applicability to predicting responses in the field, however, is
limited. Thus, any criteria based on these studies, even with
the application of safety factors, may not be protective. For
the present, we are limited to using laboratory studies for
the establishment of water quality criteria. In future revi$lg_ns_
of the Guidelines^ EPA should direct emphasis toward; a) laboratory
examination of the effects of toxicants on the sensitivity o_f_
organisms; b) mesoscale ecosystem studies of the effects ,of__
toxicants on organisms and ecosystems; and c) demonstration of
the impact o£ field variables_in_the laboratory^
3. Scientists have carried out toxicity studies, to a large
extent, on organisms of utility (those that have value to society)
or facility (those that easily adapt to laboratory conditions),
but such studies provide little insight into ecosystem impacts.
Organisms used for future studies should be selected for the role
they play in ecosystems r if_ecosystem impact is to be reasonably
app r ox irnate_d._
4. The taxonomic family is not a unit within which species
can be expected to react similarly to pollution insults. Classes
of functional units within ecosystems would constitute a more
suitable framework for analysis. The Subcommittee^ believes that
EPA should abandon the family (withTn y_h_ich'"sp"ec"i'e"s are assumed
to react similarly to toxica_nts) as the unit _for _testing in favor
of the ecologically more relevant units of trophic levels or i .
functional groups.
5* The Subcommittee challenges the assumption that a simple
relationship exists between acute and chronic toxicities on the
basis that the mechanisms for, and behavior of, acute and chronic
toxicities differ under a variety of environmental conditions.
The Agency should_re_CQns icier the use of the acute/chronic ratio,.
or its validity should_be examined within__a range of exposure
conditions normally found in field situations*
6. The proposed criteria for metal toxicity derive from
empirical laboratory toxicity studies which take into account some
environmental interaction effects, notably water hardness. They
do not, however, consider the effects of pH on complexing or,
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generally, metal ligand interactions on the toxicity of the metal.
Also, the standard approach to determining metal concentrations
has no bearing on the bioavailability of metals* The Agency
should consider the proposed metad ^criteria as temporaryf and it__
should _deyelop. riew criteria based on methods that^consider the
mechanisms which dictate metal speculation^ bioavailabi_lity_f.
accumulation_and_toxicity»
7. Dissolved and particulate organic matter loadings of the
aquatic ecosystem can have a pronounced effect on the toxicity of
metals and xenobiotie organic 'compounds. EPA__shoul<3 initiate
studies to establish the .effect of organic matter on_the toxicity
o_£ jtte_talis and .xenpb_io_t_ic_s_._
8, The Guidelines' revisions address only individual
toxicants. Organisms in the environment are exposed to complex
pollutant mixtures including those that interact and produce
results different from those expected from exposures to single
compounds» The Agency should acknowledge that .interactions are
a reality to be CQnsidere_d_in__criteria setting and, _sho_uld begin_
to__exami_ne_the_problem of mechanisms of toxicity.
9. An apparent assumption in the Guidelines that EPA needs
to assess further for its validity is that the 5th percentile
based criterion protects 95% of the organisms or species or
families in an ecosystem, and that this level of protection for
organisms also protects both ecosystem function and integrity.
The EPA studies conducted at the Monticello Research Field Station
are developing a data base addressing the relative sensitivities
of structural and functional properties of aquatic ecosystems,
but they represent only a beginning.
10. The Guidelines generate criteria in two ways by: a) the
application of formal procedures based on distributional concepts,
and 2} the utilization of scientific judgment as to the reason-
ableness of the formal procedures. Mien distributional .gonc_epts_
are applied, EPA should include a measure of variability with
each criterion to prQvide_a_b_a_s_i_s_L_u_pon__whi_ch to decide whether
more data_points_need_ tp_ be c_ollected or tjie methodology revised.
When judgmental methodology is .employed, the Agency should c_arefully_
articulate and document the scientific rationale for the judgment.
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Ill, PHILOSOPHICAL AND OPERATIONAL BASES
The Congressional intent of the phrase "physical, chemical
and biological integrity" in the 1972 amendments to the Federal
water Pollution Control Act was to incorporate the ecological
concept of biochemical/geochemical cycling into the enforcement
of the Act or, more specifically, to recycle anthropogenically
generated substances to their places of origin (Jorling 1975}*
By implementing the concept, the land application of domestic
sewage, for example, would return organic material and nutrients
to the land for society's future use. Similarly, the reduction
of synthetic organics to carbon dioxide and water, and the
transformation of heavy metal products to parent metals for
reuse, embody this concept of biochemical/geoehemial recycling.
Taken to its ultimate level of philosophical application to
water quality issues, this approach would allow for no degra-
dation Of water quality.
This concept has a number of operational difficulties.
Short of declaring a nondegradation policy, EPA must develop an
operational definition of biochemical/geochemical recycling
before establishing a philosophical basis for the promulgation
of water quality criteria. An examination of what physical,
chemical and biological integrity means in an ecosystem offers
a start for such efforts.
One interpretation of ecosystem integrity relates to the
role that society assigns to the system. This may be a very
functional role such as a highly managed sewage treatment
lagoon, a power generation facility, an irrigation project, a
shipping channel or a drinking water supply. The ecosystem might
be valued in some completely natural or wild state for its
aesthetic qualities such as a refuge for endangered species or as
a recreational fishery. Whether these systems retain integrity
depends upon how well they are managed to fulfill their role and
function as assigned by society.
This interpretation of ecological integrity was applied in
environmental policies, prior to passage of the 1972 amendments,
in the form of specifying the use of water bodies. As Jorling
(1975) pointed out, this application has a tendency toward a
single user dominated policy which inevitably reduces the options
available to decision makers. In this context, ecosystems are
but an incidental consideration, while overall societal use is
the primary concern.
The term "integrity" conveys the concept of wholeness.
Within this concept, the terms physical, chemical and biological,
taken in the context of water quality, encompasses the totality
of the aquatic environment or the ecosystem. Thus, physical,
chemical and biological integrity taken together mean ecosystem
integrity.
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Ecosystem/water characteristics are dynamic, that is, they
change with time, whether in seasonal, geological or catastrophic
senses. An ecosystem comprises states (species composition,
biomass) and processes which act on those states through rate of
movement or loss of energy and materials among the trophic
levels which respond to seasonal forces (temperature, sunlight),
geological forces (erosion of parent materials, gradients) or
catastrophic forces (hurricanes, floods)* In the strictest
sense, an ecosystem never loses integrity but merely changes
states. Given such an interpretation, any physical, chemical and
biological quality of water is possible in a system which maintains
its integrity. Therefore, basing water quality criteria on this
concept is problematical, particularly if use is the dominant
concern.
Most ecosystems are not static but develop along some tra-
jectory to higher or lower levels of complexity and productivity.
Loss of ecosystem integrity might be described as a greater than
normal divergence from the natural path or trajectory in a new
direction. In most cases, information does not exist to adequately
define pathways, trajectories or normal divergence.
Ecosystem stability relates to its capability to withstand
perturbations either through inertia, or high resilience and
rapid return to equilibrium. Whether a perturbed ecosystem returns
to the original trajectory or to some new pathway is related to
the maintenance of ecosystem integrity.
Community composition indicates the state of ecosystem
stability. The community evolved as a cohesive, compensating and
regenerating unit. The loss or replacement of species from a
community occurs frequently, but the ecosystem continues to
function. Thus, a measure of how species work and function
together through time becomes, an important consideration. The
presence of keystone species (species"that play a critical role
in the function of ecosystems) may be an important measure of
ecosystem stability. Community respiration, productivity, nutrient
turnover and nutrient loss are also measures of ecosystem stability
and can be employed profitably in determining pollution effects on
ecosystems.
Considerable knowledge of an ecosystem is necessary if its
integrity is to be specified. The more knowledge of its component
parts and functions, the better scientists are able to determine
when impacts occur and if an ecosystem has lost integrity.
Only in the simplest systems does the capability exist to
understand these issues. As additional knowledge is obtained
and synthesized, the definition of ecosystem integrity will
become more sophisticated and more useful in the protection of
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our environment for current and future generations. Until such
time, scientists must work with relatively crude measures of
ecosystem stability.
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IV. BIOLOGICAL CONSIDERATIONS
A. Laboratory to Fiel^ Relationships
Virtually all of the toxicity data available on aquatic
organisms derive from laboratory studies although some minor
"incident" data exist. The key scientific question is whether
the data on organism sensitivities to toxicants gained from
laboratory experiments accurately reflect the sensitivities that
organisms experience in the environment, and whether the results
of such experiments relate to the integrity of the ecosystem.
Laboratory toxicity studies of chemical compounds or
mixtures are usually conducted on single species under closely
controlled conditions. Such studies are designed to examine the
responses to administered doses, over fixed periods of time,
and to measure such factors as mortality, growth, reproduction,
histopathological or biochemical changes. Such studies are
particularly suitable for establishing cause and effect relation-
ships between exposure to particular anthropogenic compounds
and pathological or physiological alterations. The ability to
control environmental and exposure variables represent the
primary strengths of laboratory studies. Even though the
design of laboratory studies can vary, the number of variables
remains relatively small,
The applicability of laboratory studies to predicting the
fate of individual organisms or populations exposed to pollutants
in the environment is more difficult to establish because such
organisms contend with more forms and degrees of stress under
real world environmental conditions. These are presented in
Table 1.
VARIABLE
Table 1
LABORATORY
ENVIRONMENT
Type of toxicant
Toxicant
concentration
Exposure
Interspecific
competition
Disease/parasites
Population density
Space
Temperature
Structure
Single/known
Constant
Single toxicant
Absent
Absent
Extreme/controlled
Constrained
Constant
Glass/impoverished
Multiple/unknown
Variable/intermittent
Multiple toxicants
Present
Present
Variable
Adequate/unconstrained
Fluctuating
Plants/stones/cover
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The stresses organisms experience in the laboratory and the
environment also differ and, because stresses affect the response
of organisms, the responses examined in the laboratory may not
directly translate to the environment. Studies such as those
conducted by EPA at the Monticello Research Field Station can
provide useful information on the relationships between laboratory
data and the field. The experimental streams utilised provide an
opportunity to assess the effects of chemicals on structural and
functional relationships* Information presented to the Subcom-
mittee by EPA regarding research at the Monticello Research Field
Station demonstrated ecosystem responses not predicted by laboratory
toxicity test data, such studies are especially valuable in
developing a better understanding of how to translate laboratory
studies to the field setting, and EPA should continue its work in
this area.
In spite of the shortcomings of laboratory testing for
predicting environmental effects, such studies have advantages in
defining the problem, in their ease of execution, in the potential
clarity of interpretation and in verification. If the full
potential of laboratory studies for environmental assessments is
to be realized, EpA should address several major research needs.
These include: 1) examination of the effects of some environmental
components in the laboratory (e.g., the influence of multiple
biological species interactions); 2) extension of these studies to
mesoscale ecosystem studies which, to a degree, duplicate field
conditions? and 3) an examination of the effects of multiple
contaminants as is most often encountered in the environment.
B, The Role of Organisms in the Ecosystem
Most toxicity tests utilize organisms that either easily adapt
to laboratory conditions (organisms of facility) or those that have
value to society (organisms Of utility). A few species, such as the
bluegill (Lepomis macrochirus) and the fathead minnow (pimephales
promelas), represent a relatively wide geographic distribution.
seldom, if ever, have test organisms been selected for the role
they play in the environment. Yet, ecosystems change states
depending upon the organisms most affected by the intrusion of a
toxicant.
The Agency should consider the different concentrations at
which community perturbation(s) affects various organisms and which
different organisms discriminate toxicant concentrations. This is
particularly important for "keystone" species which perform roles
that determine the makeup of the community of which they are a
part. The alewife (Alosa pseudoharengu_s), for example, controls
the quality of the plankton population upon which it feeds in
northeastern ponds {Brooks and Dodson, 1965). A starfish (Pisaster
sp_p_._) of the intertidal shores in the Pacific Northwest controls
the makeup of the intertidal community in which it exists (Paine,
1969). A pollutant that affects either the alewife or the star-
fish will have marked effects on ecosystem composition. The
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Guidelines should reflect recognition of the role of keystone
species 'in communities and of the effect on communities in their
absence.
C. The Family Concept in_Toxicity Testing
The Guidelines assume that, as a unit, the taxonomic family
contains species whose sensitivites to pollutants are essentially
interchangeable. In other words, EPA believes that the species
within families can serve as surrogates for one another in their
response to pollutant insults. The Agency has not documented
this contention and sound reasons, discussed below, exist suggest-
ing that it might not be true.
TaxOnomic designations of orders, families, genera and species
represent constructs which attempt to relate organisms phylogenet-
ically. They do not delineate how organisms are organized in
ecosystemsr the functional role they play or their potential
response to pollutant exposures. Scientists constantly analyze
new species and reorganize taxonomic relationships an<3, in some
instances, rename species and genera or recognize new families.
Although the system of nomenclature conveniently describes plants
and animals, it is not useful for presenting the terms of ecosystem
relationships and has limited utility for testing toxicants.
The number of subfamilies, genera and species comprising a
given taxonomic family varies considerably. Family designation
does not assure a broad spectrum of function or role of an organ-
ism in an ecosytem. A salient issue is whether any given number
of families from which test species are drawn will assure a cross
section of oganisms important to the continued function, stability
and productivity of ecosystems.
Trophic levels (reducer,,producer and consumer) and feeding.
strategies perform a more important role in determining the
transfer, accumulation and concentration of toxic substances in
ecosystems. All species in a single family, however, raay not act
as reducers, herbivores or predators or have similar feeding
strategies. Certain widely distributed families, such as members
of the family Cyprinidae (minnows) have diverged into many species
representing all trophic levels and an abundance of feeding
strategies.
Detailed knowledge of how organisms are exposed to pollutants,
given their role in the ecosystem, and how organisms defend
against intrusion of environmental insults (e.g., regulation of
uptake, excretion and detoxification), might provide the basis for
selecting species for toxicity testing.
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Exposure of aquatic organisms occurs in two major waysi 1}
ingestion with food or water, and 2) active or passive absorption
through epithelial membranes, The role an organism plays in the
ecosystem determines, to a large extent, the level of exposure it
receives through the food it ingests. For toxic substances that
biomagnify, predators will receive greater exposures than herbiv-
ores. Predators, herbivores and reducers also have differing
behavioral, anatomic and, most likely, physiological characteris-
tics that relate to exposure, metabolism and, consequently,
their sensitivity to toxicants.
The Subcommittee recommends that the Agency abandon use of
the family as a unit for testing in favor of ecologically more
tractable units such as trophic levels or functional roles.
D. Ac u t e/Ch ron ic_Rat iqs
The proposed revisions of the Guidelines allow for the use of
acute/chronic ratios to estimate chronic toxicity of a compound
from acute toxicity data. The Agency adopted this approach
apparently because of the difficulties and expense associated with
conducting chronic toxicity studies. This underlying assumption
derives from the belief that a precise and predictable relationship
exists between the acute and chronic toxicities of a compound.
As the Subcommittee's understanding of the toxicity of metals
and organic compounds has developed, however, it has become clearer
that physiological mechanisms differ by which acute and chronic
'exposures affect organisms. For example, acute metal exposures
in fish will primarily affect the gills. The rate limiting steps
appear to be the availability of metal ligands in the blood that
serve to clear the gill epithelia and ability of the gill to
detoxify or transport accumulated metals. Chronic exposures,
however, have their greatest impact on the kidney, with the rate
limiting steps being the ability of the liver to detoxify circulating
metals and to detoxify any accumulated metals.
Because of these differences in underlying mechanisms, the
relationship between acute and chronic toxicity might be constant
only under carefully controlled laboratory-conditions. Extrapola-
tions to field situations in which numerous uncontrolled variables
exist are highly questionable.
The Agency should reconsider the use of acute/chronic ratios
as a substitute for performing chronic toxicity tests. If it
retains this approach, however, EPA should examine its validity
with a range of exposure conditions that more accurately reflect
the variables encountered in actual field situtations.
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V. CHEMICAL CONSIDERATIONS
A. Metajl gjgeciation
The Guidelines do not effectively address the problem of
metal speciation in aqueous systems. Metals in solution exist
as a variety of chemical species including free ions and a number
of inorganic and organic complexes. They may also adsorb to
participates such as fine clays and detritus (Stunott and Morgan,
1981). Not all of these species are available or toxic to the
organism (Sunda and Guillard, 1976? Sundaf et.al., 1978? Cross
and Sunda, 1978).
For metals such as Cd, Cu and Zn, bioaccuraulation and
toxicity relate to free ion activity rather than the total
concentration of dissolved metals. This relationship appears
to result from thermodynamic and biochemical considerations
(Cross and Sunda, 1978). Free metal ion activity is a measure
Of the free energy of the system and reflects the potential
for interactions between the metal and available ligands* The
various complexes of metals, such as Cd, have very low perme-
ability coefficients for lipid bilayers and do not enter cells
at a significant rate {Gutkneeht, 1983). As a consequence,
transport of these metals may be mediated by membrane-bound
transport proteins. Uptake of these metals is a function of
the interaction taeween the metal and the transport protein,
and the potential for this interaction is reflected in the
free metal ion activity.
Metals sugh as Hg and Ag, however, form complexes (e.g.,
HgClj and AgCl ) that pass rapidly across membranes (Gutkneeht,
1981J, For these metals, the membrane-permeable complexes
dictate bioavailability and toxicity, not free ion activity
(Engel, et.al. , 1981),
Regardless of mode of uptake, any attempt to define the
toxicity of a metal in an aqueous environment should take into
account the metal speciation which, in turn, determines bio-
availability. The revised criteria do not address these
mechanisms.
The Guidelines do attempt to account for alterations in the
toxicity of metals (e.g., Cd, Cu and Pb) due to variations in
water hardness defined as the concentration of CaCC^. Changes in
CaC03, however, can alter metal speciation via a number of mech-
anisms including increased complexation, competition with Ca^+
for available ligands or modification of complexation due to
changes in pH. Any extrapolation from laboratory toxicity
studies to actual field situations requires an understanding of
these mechanisms and other potential metal-ligand interactions
that could modify availability and toxicity. The proposed Guide-
lines, however, utilize empirical data while largely ignoring
the basic mechanisms, AS a consequence, they can only be
expected to provide useful information for a limited number of
metals and under carefully controlled conditions.
12
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The Guidelines also attempt to distinguish between total
recoverable metal concentrations and "active" metal concentra-
tions. Active metal concentrations are operationally defined as
the concentration of metals that passes through a 0.45 um filter
after the sample is acidified to pH 4.0 with nitric acid. This
approach does provide a standard method for determining metal con-
centrations, but it has no bearing on the actual concentrations of
bioavailable metals* Because it has no mechanistic basis, it does
not allow useful quantitative comparisons of metal toxicity
between different water samples. Thus, it has limited predictive
potential.
The Subcommittee believes that Agency staff have worked
diligently to refine the existing Guidelines to their logical
limits. However, this approach does not consider the underlying
metal chemistry, and any further refinements are unwarranted.
The Subcommittee recommends that the Agency regard its proposed
metal criteria and the methods used in their development as
temporary. Future revisions of the Guidelines should rely on new
methods that take advantage of increased understanding of the
mechanisms that dictate metal speciation, accumulation and toxicity.
The Subcommittee recognizes that adoption would require a basic
reevaluation of EPA's current approach to determining metal
toxicity and developing metal criteria, but it considers these
changes essential.
B. Organic Matter and Dynamics
The need for site-specific criteria in considering limiting
concentrations of heavy metals and xenobiotic organic chemicals
that a given body of water can carry without degrading the intended
uses of that water, or the well being of the indigenous biota,
can be substantiated. One of the variables that influences the
effects of xenobiotics in various bodies of water is the con-
centration of dissolved,and particulate organic matter. Prime
activities of dissolved .organic matter (humic acids, particulate
organic matter) affecting the bioavailability of toxic heavy
metals to aquatic organsims include chelation, sulfhydryl binding
and other complexation mechanisms. As considered in the above
discussion of metal speciation, the toxicity of a heavy metal
in the aqueous environment is less a function of its total
concentration than its bioavailability. Heavy metal ions may
be complexed by other inorganic ions, primarily sulfates,
chlorides and bicarbonates. These inorganic anions vary from
one water mass to another and should be considered in establishing
site-specific criteria for heavy metal concentrations. The
concentration of these inorganic anions will, however, remain
relatively constant for a given body of water. The total
concentration of organic matter may also remain fairly constant,
but various components exist in a dynamic state since both
13
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terrestrial sources and biota continuously add fresh organic
materials. The complexation of heavy metals by organic matter
undergoes constant flux as organic matter is degraded by bacteria.
Because microbial metabolism is temperature sensitive, the rate
of this flux will vary diumally and seasonally.
In contrast to the direct effect of dissolved organic
matter on the bioavailability of heavy metals, little is known
of the effects of naturally dissolved organic matter on the
bioavailability and toxicity of xenobiotics. While it might be
expected that xenobiotics partition onto particulate organic
matter, this effect is probably minor in comparison to their
partition onto inorganic clay suspensoids. Differences in the
load of dissolved and particulate organic matter between various
bodies of water may have a greater indirect effect on the fate
of xenobiotics. A heavy input of organic matter into a body of
water may sustain an abundant and diverse microbial population,
This condition would be reflected in a faster rate of microbial
detoxification of many xenobiotics in organically rich waters.
The Subcommittee recommends that EPA initiate studies to establish
the effect of organic matter on the toxicity of pollutants.
C. Contaminant Ijitjsr act ions
The proposed Guidelines' revisions, like all previous water
quality criteria development efforts, deal only with individual
contaminants. This approach, while simplifying the analytical
task of the regulator, ignores the complex realities that organisms
must routinely face in their environments. These include non^
additive or synergistic effects on toxicity. Different metals
compete for organic and inorganic ligands as well as membrane
transport proteins that regulate their bioaecumulation. AS a
consequence, alterations in the concentration of one metal may
change the speciation and toxicity of another. Scientists have
documented changes for phytoplankton where 2n, Cw and Mn all
compete for common transport sites (Jenkins, et. al», 1983).
Reduced concentrations of zn or Mn dramatically increase the
apparent toxicity of Cu because this substance effectively competes
with these essential metals, and. organisms quickly become deficient
in Zn and Mn. Similar interactions occur between organic hydro-
carbons, and recent data suggest that metals and hydrocarbons may
also interact and modify each other's availability and toxicity
in precise ways (Jenkins, 1985).
In short, the Subcommittee believes it is important for EPA
tot 1) begin to examine the impact of mechanisms upon contaminant
interactions in a thorough manner, and 2} point out the potential
for interactions between contaminants and their relationship to
criteria development.
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VI. EXPOSURE CONSIDERATIONS
A. Level o£ protection
The Guidelines for deriving National Water Quality Criteria
for the protection of aquatic life an<3 its uses assume that
criteria based on the 5th percentile of the distribution of the
geometric mean, species geometric mean, or EC50 or LC50 values
will result in protection of the biological integrity of aquatic
resources. Implicit in this assumption is the belief that water
quality criteria derived from toxicity data for fish, inverte-
brates, and plants protect the myriad of other aquatic organisms
in aquatic ecosystems, and that protection of the structure
(i.e., organisms) of the ecosystem will protect the functional
properties of the ecosystem.
The approach taken in the Guidelines represents a positive
step toward protecting the integrity of aquatic resources, but
it is incomplete because the above assumptions have not been
totally validated. In addition, EPA has not demonstrated what
current level of protection adequately protects the integrity
of aquatic ecosystems. If one of the unprotected species is a
keystone species in the ecosystem, collapse of the structure
of the aquatic community may occur. In their present form, the
Guidelines do not address the keystone species concept nor did
the Agency staff present data to the Science Advisory Board
demonstrating, through field validation experiments, that they
could address the keystone species issue. An example of a
keystone species is smooth cordgrass (Spartina alterniflora) in
a salt marsh. Elimination of cordgrass would cause collapse of
the salt marsh ecosystem. ¥et cordgrass is not a routine test
species, and its sensitivities to chemicals are largely unknown.
An apparent assumption in the Guidelines that EPA needs to
assess furthur for its validity is that the 5th percentile based
criterion protects 95% of the organisms or species or families
in an ecosystem, and that this level of protection for organisms
also protects both ecosystem function and integrity. Data
supporting this assumption are scarce, in part due to the diffi-
culties in assessing ecosystem functional responses to stresses
caused by chemicals. The EPA studies conducted at the Monticello
Research Field Station are developing a data base addressing the
relative sensitivities of structural and functional properites
of aquatic ecosystems, but they represent only a beginning. If,
in fact, essential ecosystem functions exhibit more sensitivity
to chemical stresses than the fish, invertebrates, and plants
used to develop the water quality criteria data bases, then it
is possible that the criteria will underprotect the integrity of
aquatic ecosystems. Inclusion of test results that evaluate
responses of functional processes to chemicals should be included
in the approach advanced by EPA for establishing water quality
criteria.
B. Statistical Issues
From 1976 to the present, the Agency developed and revised
*
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technical guidance for calculating water quality criteria. This
guidance has taken the form of methodologies using laboratory
studies of the toxicity of pollutants. The Agency has also
generated new data from laboratory experiments, field studies
and field experiments. As new data became available, the Agency
periodically modifies the Guidelines so that they reflect current
scientific judgment on the factors that protect designated uses.
Among the important developments in the Agency's evolutionary
development of Guidelines include efforts to: 1) correctly state
the scientific assumptions of its criteria development methods?
2) demonstrate how these assumptions will achieve the degree of
protection sought; and 3) verify that the predicted result and
protection do occur.
Each of these three areas has a statistical component to
the extent that analyses supporting the methodology are based on
distributional descriptions of relevant data. The current
Guidelines (Federal Register, February 7, 1984, p. 4553) rely
heavily on the distribution of species' ECSQ's and LCSO's in
setting criteria. In the following sections, the Subcommittee
reviews the statistical basis of the current Guidelines in terms
of the three preceding points.
1. Statementof Scientific Assumptions
The Guidelines for deriving water quality criteria consist
of a formal procedure using laboratory data to calculate numerical
criteria and less formal techniques on the use of professional
judgment in applying the calculations. The formal proceduret
which uses laboratory data from many areas of aquatic toxicology,
is designed to provide criteria that are comparable among labor-
atories and for different pollutants. These data represent
primarily ECSO's and LCBO's for acute tests and no observable
effect levels for chronic tests. The assumptions that underlie
the formal method are limited by the capabilities of low cost
field monitoring and by the uncertainties of extrapolating observed
effects in laboratory tests to effects that may occur in the same
species in field situations.
The ideal National Water Quality Criteria for a compound or
element is the highest concentration of the toxicant which, when
placed into a wide variety of unpolluted bodies of waterf results
in no adverse effects. Field testing represents the ideal method
for establishing these concentrations. Since scientists experience
technical difficulties in conducting such studies, one of the
implied advantages of the current Guidelines is their reliance on
better understood laboratory results.
The major distributional feature of the Guidelines stems from
the use of the fifth percentile of the distribution of family
geometric mean, species geometric mean, or EC50 or LC50 values in
setting the criteria. These means are calculated from a data
base that provides a range of family mean values by taxonoroic and
functional groups which SPA assumes represents the range of
sensitivities seen in a field situation,
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Because no statistical sampling of individuals within
species, or of species within families or of families has occurred,
the assumption of representativeness is not supported by sampling
theory but relies instead upon the scientific judgment of the Guide-
lines' authors. Since all types of generalization do not require
random sampling, this feature of the Guidelines should not be
criticized. Because EPA provides no factual basis for the claim of
representativeness, however, the use of a distributional approach
might be misread as implying that the distribution of BCSO's and
LCSO's was representative on statistical, rather than some other
basis.
One reason why EPA cites no field data to establish representa-
tive results is the difficulty of relating the fifth percentile Of
the distribution of the geometric mean ECSO's and LCSO's to protec-
tiveness in the field. The Guidelines state that the fifth
percentile number should not be used to decide, in a field situation,
whether the criteria determines protectiveness. This point is
discussed further in the next section,
2. Achievement of Protection
one of the important provisions of the Guidelines is the argu-
ment, however idealized, that the numeric criteria achieve protection
of aquatic life. Based on the ideal criteria proposed in the Guide-
lines one might conceive of an idealized study, discussed below, to
verify protectiveness.
A toxic compound, for which criteria exist, is introduced into
a nonpolluted lake. A field study is performed before and after
introduction of the compound. Based on the field study, the pro-
portion of individuals affected is calculated for each species, and
from these data scientists estimate the LCSQ's and ECSQ's, Finally,
EPA determines that, as predicted from the laboratory data, 5% of
the family geometric mean LC50*s and ECSO's are less than the
criteria. (This assumes that at least 100 families inhabit the lake.)
Should EpA conclude that the criteria protect the lake for its
intended uses? The Guidelines, as noted above, state that this .
inference should not be made. Attainment of the criteria is neither
necessary nor sufficient for protection but is believed to be
positively associated with protection. The Guidelines explain that
this situation occurs because aquatic organisms do not interact in
the laboratory but, rather, in the field, and in the latter they are
influenced by factors typically absent in the laboratory. Such
factors are predator-prey relationships, disease, contamination of
food, an<3 extreme environmental conditions like high temperatures
and unusual conditions of water flow. In addition, some community
functions and species" interactions may be adversely affected at
concentrations lower than indicated by standard toxicity tests.
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The Guidelines state that attainment of the criteria will
probably result in a reasonable level of protection in the
field. The protectiveness is an anticipated consequence of
setting the criteria such that, in the laboratory data, only a
small fraction of families tested would have LCSO's or SCSO's
less than the criteria. The small fraction was set at 5%
because using other fractions resulted in criteria that "seemed
too high or too low in comparison to the data from which they were
calculated." It is apparent that the distributional nature of the
criteria is not intended as a consequence of an operational defi-
nition of protection appropriate to field situations. it is,
rather, a means of quantifying the authors* judgments of what
numerical criteria would be associated with protection, based on
laboratory data that are judged as representative of the taxo-
nomic and functional groups of aquatic organisms found in the
United States.
The only basis for criticizing this method of quantifying
the authors' judgment would be that the fifth percentile criterion
does not reflect the authors' concepts,, in the absence of an
effective method, to test not only the fifth percentile criterion
but any other criterion that might be proposed.
3. Ve r i f ic_ation
The Guidelines recognize that field verification of national
criteria should be based on an operational definition of protection
of aquatic life and its uses that takes into account the practi-
calities of field monitoring and public concerns. The Guidelines
also state that the amount of decrease in the number of taxa and
of individuals defined as unacceptable should take into account
the features of the body of water and its aquatic community.
The Guidelines do not state how this definition would he
developed or utilized in practice. They express the opinion that
moderate cost field studies are not sensitive enough to detect
unacceptable changes and that only highly reliable, extensive
testing could show that the criteria do not allow unacceptable
effects. These arguments suggest that, except for extreme cases,
the protectiveness of the numerical criteria is unverifiable,
In the absence of methods to effectively verify the criteria,
it is difficult to rely on the usual procedure for establishing
scientific truths. This procedure invariably involves prediction
and rejection (or confirmation) as a means for establishing the
factual basis for decision making.
Based on these considerations and on the informal guidance on
the use of professional judgment, the Subcommittee infers that the
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criteria resulting from this guidance are intended to be used
pragmatically, not dogmatically. The implications of this state-
ment for the statistical approach are discussed next,
4. Implications for Statistical Analysis
It is often easier to evaluate a pragmatic calculating
procedure than one that depends exclusively on theory for its
justification, This is because a pragmatic procedure is evaluated
by its success at achieving measurable objectives. The present
Guidelines are actually predicated on the assumption that, except
in extreme cases, cost-effective efforts to establish the criteria's
protectiveness will fail. Assuming the truth of this, the validity
of the Guidelines has to be assessed primarily on its biological
reasonableness as discussed in the previous sections.
A major issue is the use of the distributional approach. As
discussed above, this method reflects the Guidelines authors'
judgment of what would constitute an effective statistical pro-
cedure. As such, it cannot be criticized from the point of view
of sampling theory? if not misinterpreted, this use of distri-
butional concepts is acceptable.
A second issue is that of the uniqueness of a criteria for a
given pollutant. There are many combinations of acute and chronic
species data satisfying the required minimum data base. For each
data base there is a possibly different criteria because it is not
required that, if more than the minimum data is available, all data
must be used. Thus, for a given pollutant, the Guidelines can be
thought of as leading to a distribution of the criterion for the
pollutant, with one point in the distribution for each combination
of data that satisfies the minimum data base. Where sufficient
data exist, this distribution should be evaluated. If it happens
that the Guidelines lead to distributions of criteria that are not
concentrated around a single reasonable value, the cause should
be investigated and, if necessry, EPA should alter the Guidelines.
A simple approach to this could be based on jack-knifing (Hosteller
and Tukey, 1977), which is one way of estimating the sampling error
of complex statistics. , '
In evaluating the distribution of a criteria, EPA should
ensure that all sources of variability, such as those associated
with acute/chronic ratios, are reflected. Since the basic acute
and chronic data represent point estimates, their variability
should be reflected in the final distribution.
The-Guidelines propose that the ideal criteria should derive
from field tests although they argue that obtaining truly infor-
mative results is difficult with such tests. Based on this
argument, the Subcommittee recommends that as field test methodology
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becomes raore refined, EPA should modify the Guidelines to include
such methods and their results. This will help incorporate prag-
matic methods of criteria development in terms of measurable
environmental outcomes.
A useful step in achieving the integration of the Guidelines'
criteria and the ideal criteria would be to use data generated by
the Monticello test streams. This would provide a means to validate
the criteria in situations that more closely approximate those
existing in the field.
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V VII. LITERATURE CITED
Brooks, Jchn L. and S. I. Dodson, "Predation, Body Size and Composition
of Plankton," Science 150 (1965), 28-35.
Cross, P. A., and W. G. Sunda, "Relationship Between Bioavailability of
Trace Metals and Geoehernical Processes in Estuaries," in M* L. Wiley/
ed., EstuarineInteractions, International Estuarine Research Con-
ference, Mount Pocono, Pa,, (New York* Academic Presst 1978).
Engel, D. W., W. G. Sunda and B. A. Fowler, "Factors Affecting Trace
Metal Uptake and Toxicity to Istuarine Organisms," in P. J, Vernberg,
A. Calabrese, P. P. Thurberg and W. B. Vernberg, eds., Biological
Monitoring of Marine Pollutants, (New York; Academic Press, 1981).
Gutknecht, J.f "Inorganic Mercury (Hg2-s-) Transport Through Lipid Bilayer
Membranes," J. Membrane Biol. 61 (1981), 61-66,
Gutknecht, J,, "Cadmium and Thallous Ion Permeabilities Through Lipid
Bilayer Membranes," Biochem.B_iophys* Acta._ 735 (1983), 185-188.
Jenkins, K. D*, "Tolerance Limits in Aquatic Organisms: A Mechanistic
Basis," in Envirorroental Protection Agency, &ew Approaches to Water
Quality Criteria (in press).
Jenkins, K» D,, B. M. Sanders and W. G. Sunda» "Metal Regulation and
Tojdcity in Aquatic Organisms," in T. P. Singer, T. E. Mansour and R.
N. Ondarza, eds., Mechanisms of Drug Action (New ¥orks Academic Press,
1983), pp. 277-288.
Jorling, Thomas, "Incorporating Ecological Interpretation Into Statutes/'
Proceedings of an Environmental Protection Agency Synf>osium The Integ-
rity of Water, March 10-12, 1975 (u. S. Government Printing Office,
Washington, D. C., 19770-227-466), pp. 9-14.
Hosteller and Tukey, Data Analysis and Regression (Reading, Mass., Addison-
Weslesy Publishing^ 1977),
Paine, R, T., "A note on Complexity and Ccramunity Stability," Jtoier. Nat. 103
(1969), 91-93.
Sturam, wt, and J, J. Morgan, Aquatic Chemistry (New York; John Wiley and Sons,'
Inc., 1981).
Sunda, W,, D. W. Engel and R. M, Thuotte, "Effects of Chemical Speciation
on Toxicity of Cadmium to Grass Shrimp? Palaemonetes pugio? Importance of
Free Cadmium Ion," Environ. Sci_._ and Technol._ 12 (1978), 409-413.
Sunda, W. / and R* R. L» Guillard, "The Relationship Between Cupric ion Activ-
ity and the Ttoxicity of Copper to Phytoplankton," J.Mar. Res. 34 (1976),
511-529.
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Appendix A
U.S. ENVIRDNMENTAL PROT3CTIQN AGENCY
SCIENCE ADVISORY BOARD
SUBCOMMITTEE ON WKTER QUALITY CRITERIA
Dr, John M» Neuhold, Chairman
College of Natural Resources
Utah State University
Logan, Utah 84322
Dr. Kenneth L. Dickson, Co-chairman
North Texas State University
Denton, Texas 76203
Dr. Douglas Seba
Executive Secretary, SAB
401 M Street, SW
Washington, D*C* 20460
Melbourne Carriker
College of Marine Studies
University of Delaware
Lewes, Delaware 19958
Dr. Rolf Hartung
School of Public Health
University of Michigan
Ann Arbor, Michigan 48109
Dr. E. Allison Kay
University of Hawaii at Manoa
Honolulu, Hawaii 96822
Dr. Charles Norwood
4985 Escobedo Drive
Wfoodland Hill/ California
91364
Dr. Tony J. Peterle
College of Biological Sciences
Chio State University
Columbus, Ohio 43210
Dr, Leonard Greenfield
1221 Columbus Blvd.
Coral Gables, Florida 33134
Dr* Kenneth Jenkins
California State University
at Long Beach
Long Beach, California 90804
Dr. James Kittredge
1140 w. 17th Street
San Pedro, California 90731
Dr. Bernard Patten
Department of Zoology
University of Georgia
Athens, Georgia 30602
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