United States
             Environmental Protection
              Office of Saence and Tecnnology
              Health and Ecoiog,cal Catena division
              Washington. DC 20460
May 19S2
Interim Guidance on

Interpretation and Implementation
of Aquatic Life  Criteria for Metals


         Interim Guidance on
Interpretation and Impiementation  of
   Aquatic Life Criteria for Metals
                 May 1992
       Health and Ecological Criteria Division
        Office of Science and Technology
       U.S. Environmental Protection Agency
            Washington, DC 20460


*•  *


       TS at^pSl  ^dresses the ^ of EPA (and corresponding
       State) metals criteria m water quality standards intended to
  Hon nfPMPnpcq   '    e' ThlS Suidance also addresses the derive
  ion of NPDES permit limits from such criteria. The main body of
  the document presents recommendations on the best current ap-
  proaches for implementing aquatic life criteria for metals and
  measuring attainment of such criteria. This guidance supersedes
 aPnSL-CH   ? *?cumfts^e™^ expressing criteria in terms of
 an acid soluble analytical method. Appendix A presents a case
 study illustrating derivation of site-specific criteria (item 3 below)
 £PPe_n.dlx  B presents  recommendations on  the  derivation  of
 NPDES permit limits from ambient metals criteria. As  described in
 m^fm^-  ' k SUp6f6deS Part °f the Te<*nical Support Docu-
 ment [1] discussion of metals.

    The principal issue is the correlation between metals that are
 measured   and metals   that are  biologically  available.   The
 bioavaiability and toxicity of metals depend strongly on the exact
 physical and chemical form of the metal, and on  the species af-
 fected. The form of the metal, in turn, can vary depending on the
 chemical characteristics of the surrounding water matrix. Because
 of differences between various effluents and site waters, and be-
 tween laboratory  toxicity test waters  and many site waters
 establishment and  implementation of  metals  criteria  are  not
straight forward.  Consequently,  this guidance  presents three
reasonable approaches that differ in their complexity.

   (1)  The  simplest approach is to measure total recoverable
       metals in ambient waters, and to compare such meas-
       urements to national or state-wide criteria.
 A closer focus on biologically available metals can be
 obtained by measuring dissolved metals  in ambient
 waters, and comparing such measurements to criteria
 appropriate for dissolved metal. Since effluent limits
 for both technical and legal (40 CFR 122.45) reasons
 are generally expressed in terms of total recoverable
 metal, it  is necessary  to translate between the total
 recoverable concentration in the effluent and the dis-
 solved concentration in the ambient water.

 Because of the complexity of metal chemistry, there is
 no one chemical analytical method that can accurately
 determine the metals that are bioavailable and toxic
 For implementing metals  criteria established from
 laboratory toxicity tests, an adjustment of the criteria
value can address this constraint. It involves measur-

                                  ing a pollutant's water-effect ratio in the receiving
                                  water covered by the standard. The water-effect ratio
                                  compares the toxicity of a pollutant in the actual site
                                  water to its toxicity in laboratory water, for two or
                                  more aquatic species. Because the metal's toxicity in
                                  laboratory water is the' basis for the national criterion,
                                  the water-effect ratio is used in an adjustment to ob-
                                  tain a site-specific value. Implemented in conjunction
                                  with either of the first two alternatives, this adjust-
                                  ment may either increase  or decrease  the  numeric
                                  value of the criterion.
      The principal problem in relating discharges of toxic metals to
      environmental impacts is the different toxicities of various
      metal species in ambient waters, and the varying fractions of
such species with location and time. This results in the same metal
concentration exerting  different toxicity from place to place and
from time to time. The chemical species involved include metals
dissolved in a variety of forms, and metals sorbed to or within
particulate matter. Metals may differ markedly from each other
with respect to speciation and bioavailability.
   Although metal toxicity may vary depending on the chemical
characteristics of the water body, the national criteria have been
designed to protect all or almost all bodies of water. However, this .
does not mean that the national criteria will always be overprotec-
tive. For example, some untested locally important species might
be very sensitive to the material of concern, or the local aquatic or-
ganisms  might  have  increased sensitivity due  to  diseases,
parasites, other pollutants or water quality conditions, or extreme
flow or temperature conditions [2].
   Another problem involves metal speciation  in effluents, and
the potential transformations that may occur in moving from the
chemical environment of the effluent to the chemical environment
of the receiving water. Consequently, in contrast to  an ambient
measurement, which should respond predictably to metal that is
actually bioavailable, an effluent measurement needs to respond
also to metal that may not be bioavailable under effluent chemical
conditions, but would  possibly  become bioavailable under am-
bient chemical conditions.
   Because of the complexity of metal speciation and its effect on
toxicity, the relationship between measured concentrations and
toxicity is  not precise. Consequently, any chemical analytical
method that could be recommended would  not: guarantee precise
comparability between concentrations measured in the field and
concentrations employed in the toxicity  tests  underlying  the
criteria. However, the three approaches presented in this guidance
should provide acceptable approximations.

        EPA has recognized four methods of sample preparation for
        metals analysis. These lead to measurement of: (a) total me-
        tals, (b) total recoverable metals, (c) acid soluble metals, and
  (d) dissolved metals.  Ordinarily, the four methods measure all of
  the dissolved metal present at the time of sampling. They differ in
  the amount of particulate metal that they measure.

     The total metals procedure, the  total recoverable metals proce-
  dure [3], and the acid soluble metals procedure [4, 5] measure
  metals that are dissolved in water or become dissolved when
  treated with acid. They differ in the concentration of acid and in
  the  temperature used  during  the analytical procedure, both
  decreasing in the order cited above.

    The dissolved procedure  [3]  measures  metal that passes
  through a 0.45 urn filter at the time  of sample collection.  The
  results from this procedure are reported as "dissolved," although
  it may include metal that was.bouncl to micro-particles (<0.45 urn)
  at the time of sample collection. More recent dissolved procedures
  recommend  positive-pressure,  in-line  filtration  through poly-
 carbonate membrane filters having a uniform pore size selected
 from  a range  of 0.1-0.4 urn  [6],  and  emphasize  ultra-clean
 laboratories, labware,  and reagents [7, 13]. Measurements using
 different filter sizes may, however, give different result;;.

    Metals criteria documents issued in  1980  recommended the
 use of the total recoverable method.  Beginning in 1984, although a
 final  acid soluble method was not  available,  the  criteria  docu-
 ments have stated that an acid soluble method would be a better
 way  of measuring attainment of  the criteria. Noting  the  un-
 availability of a final method, they  recommended the  continued
 use of the total recoverable method, which they acknowledge may
 be overly protective.

    Because the acid soluble method  uses a less rigorous digestion,
 it was expected that it would generally measure less of the particu-
 late metal  than the total  recoverable method. It was therefore
 believed that the acid soluble method would more accurately
 measure bioavailable metal. Recently available ambient and ef-
 fluent data  suggest,  however,  that acid soluble results  are
 ordinarily nearly identical to total recoverable results, while being
 somewhat different from dissolved results. Because an increased
 understanding of  the complexity of metals bioavailability indi-
 cates  that the acid soluble method will not significantly improve
 the correlation between measured metal and bioavailable metal,
 this guidance is not recommending the use of this method.

      Bioavailability and toxicity vary with the form of the metal.
      Particulate  metal  is  generally  expected to  have  less
      bioavailability than  dissolved  metal.  Nevertheless, the
toxicity of ambient particulate metal is not necessarily zero. For
example, some metal that is in the particulate phase in the ambient
  on Analytical
and  Toxicity

and  Total
                           water environment may become  dissolved in the  chemical en-
                           vironment associated with the gill or the gut.
                              In natural waters, some metals may exist in a variety of dis-
                           solved species that differ significantly in toxicity. For copper, the
                           divalent free cation and some inorganic complexes have substan-
                           tial toxicity, whereas dissolved organic complexes generally have
                           significantly less toxicity. As a result, the same concentration of
                           dissolved copper may exert different toxicity in different waters.
                              Toxicity tests that form the basis for the criteria are usually per-
                           formed in an untreated or slightly treated natural water from an
                           uncontaminated source, or in water that has been  first purified
                           and then reconstituted by the addition of appropriate mineral
                           salts. Because such dilution water is generally lower in metal-
                           binding particulate matter and dissolved organic matter than most
                           ambient waters, these toxicity tests  may overstate the ambient
                           toxicity of non-biomagnified metals that interact with particulate
                           matter or dissolved organic matter.

                              In most but not all toxicity tests underlying the criteria, the
                           percentage of metal in the particulate phase is fairly low. For am-
                           bient waters, on the other hand, recent data suggest that typically
                           30-80 percent of the copper, nickel, and zinc, and 90-95 percent of
                           the lead may be in a particulate  phase  measured by the total
                           recoverable method but not by the dissolved method.
                              In freshwater laboratory tests, organic carbon concentrations
                           of a few mg/L are typical, with chronic tests having higher con-
                           centrations  than acute tests. In ambient waters, organic carbon
                           concentrations are  typically somewhat higher than this, and may
                           be substantially higher at the edge of small mixing zones.
                              Because of the  greater fraction of particulate metal in ambient
                           waters, as well as  the higher levels of dissolved organic binding
                           agents in ambient waters, the fraction of metal that is biologically
                           available may often be lower under ambient field conditions than
                           under laboratory conditions, particularly for freshwaters.
      Aquatic life criteria in ambient waters may be implemented
      either as total recoverable metal or as dissolved metal. Ef-
      fluent  limits  must  generally be  expressed  as  total
recoverable metal. For analyses of metals in the low ng/L range or
below, ultra-clean sample handling techniques [7, 13] should be

Ambient Waters

When used for expressing ambient water quality criteria, the total
recoverable  method provides  greater  safety  than does  the
dissolved method. Nevertheless,  when used for ambient  waters,

   total recoverable measurements may result in overestimating the
   toxicity. While toxicity testing has shown dissolved measurements
   to  be  better  predictors  of  toxicity  than  total  recoverable
   measurements, there  are also  some potential  concerns with this
   approach, as discussed below.

      First, EPA water quality criteria are generally based on  the
   reported total recoverable concentrations  in the toxicity tests If
   used  for  dissolved  standards,  the criteria values need  to be
  downwardly adjusted to account for the  typical dissolved fraction
  in test dilution water. For copper, approximately 86 percent of the
  reported total concentration was dissolved during freshwater
  acute toxicity tests with the more sensitive species. Consequently
  the copper freshwater acute criterion should be adjusted to 86 per-
  cent of  its  total  recoverable  criterion  in  order  to  serve  as a
  dissolved criterion, particularly in waters having  low concentra-
  tions of  dissolved organic binding agents. While  the adjustment
  may be small for most metals, a few metals, such as aluminum
  may require much larger adjustments to account for the  much
  lower  percentage dissolved typically  occurring  during toxicity
  tests. Chronic criteria may require larger adjustments than acute
  criteria, due to the higher particulate concentrations caused by the
  addition of food during chronic tests.

    Except for copper in freshwater, the factors are not yet avail-
 able  for converting EPA's published criteria into dissolved criteria
 A re-examination of data underlying the metals criteria is now un-
 derway to compile the dissolved concentrations measured during
 toxicity tests. While  preliminary analysis does not indicate that
 these dissolved adjustment factors are of sufficient magnitude to
 be of great concern, they should be considered in any adoption of
 dissolved metal standards subsequent to distribution of this infor-

    Second, by measuring comparatively little of the particulate
 fraction, it may be possible that the dissolved method could oc-
 casionally understate the toxicologically  effective  concentration
 Although toxicity data  suggest that this is not ordinarily a prob-
 lem, it is more likely to be a concern if the  dissolved concentration
 is only  a  very small percentage of the particulate concentration,
 such as may occur with aluminum.

    In some situations  the dissolved  method may overstate the
 toxicologically effective concentration. When certain metals (such
 as copper) become complexed with elevated concentrations of dis-
 solved organic matter, a reduction in toxicity may occur, compared
 to toxicity in  laboratory water,  which is  low in organic matter.
 Where dissolved organic matter is likely  to interact with  the
 toxicant, the water-effect ratio approach is likely to be more ac-
 curate and is currently the recommended solution.

    A  review  of the  limited number of available site-specific
studies found that the water-effect ratio (site water LC50 versus

                           lab  water  LC50) was generally significantly  larger than  the
                           measured total recoverable  versus dissolved  ratio [10]. These
                           limited freshwater data thus suggest that use of properly formu-
                           lated dissolved criteria would be at least as protective as criteria
                           derived from careful measurements of water-effect ratios.

                           The dissolved method is  generally not applied to effluents to
                           determine achievement of effluent quality  goals. Such use is
                           generally barred  by regulation (40 CFR 122.45). Because  the
                           chemical conditions in ambient surface waters may differ sub-
                           stantially from those in the effluent, there is no assurance that
                           effluent particulate metal would not  dissolve after  discharge.
                           A common method of removing metals from  wastewaters is to
                           chemically precipitate the metal and settle the resulting particles.
                           Expressing a metals limitation in terms  of dissolved metal would
                           imply little concern about the effectiveness of the settling process
                           or the fate of the discharged particulate metal.
                              Determining  the total  recoverable  effluent limitation cor-
                           responding to a dissolved criterion would involve specifying the
                           fraction of effluent total recoverable metal that would exist as dis-
                           solved metal under the  chemical conditions of the receiving water.
                           In the absence of site information, any values assumed for this
                           fraction should be environmentally conservative.
                              Where greater  accuracy is  desired, the dissolved fraction of
                           total recoverable metal  could be evaluated by direct measurement
                           of dissolved and total  recoverable metal  in the affected ambient
                           waters,  or possibly by geochemical model  calculations (as  dis-
                           cussed in Appendix B).  All of the techniques involve approx-
      Due to the complexity of metals speciation, and due to the
      varying degrees of bioavailability and toxicity of the many
      forms and complexes, there is no chemical method that can
assure that a unit of concentration measured in the field would al-
ways be lexicologically  equivalent  to  a unit  of  concentration
employed in the laboratory toxicity tests underlying the criteria.
   For metals criteria derived from laboratory toxicity tests, one
approach is to use a biological method to compare bioavailability
and toxicity in receiving waters versus laboratory test waters. This
involves running toxicity tests with at least two species, measur-
ing acute (and possibly chronic) toxicity values for the pollutant
using (a) the local receiving water, and (b) laboratory toxicity test-
ing  water, as  the sources of toxicity  test dilution water.  A
water-effect  ratio  is the  acute (or chronic) value in site water

 divided by the acute (or chronic) value in laboratory waters. An
 acute  value is an LC50 or EC50 from a  48-96 hour test, as ap-
 propriate  for the species.  A chronic value  is a  concentration
 resulting from hypothesis  testing or regression analysis of meas-
 urements of survival, growth, or reproduction in life cycle, partial
 life cycle, or early life stage tests with aquatic species.

    Because the metal's toxicity in laboratory water is the basis for
 EPA's  criterion, this water-effect ratio is used to adjust the national
 criterion (or corresponding State criterion) to a site-specific value.
 This adjustment may either increase or decrease the criterion. Be-
 cause the water-effect ratio reflects differences in water chemistry,
 it is acceptable to assume that a ratio derived from acute LGSOs or
 ECSOs may be applied to both acute and chronic criteria, provided
 that the water-effect ratio is determined with an acutely sensitive
 species. Nevertheless,  performing chronic tests is an option that
 could  produce a different water-effect ratio,  due  to changes in
 water  chemistry caused by the addition of food during chronic
 tests. While this may  somewhat improve the  accuracy  of the
 resulting criteria, it will substantially increase the testing costs.
   The principle of criteria adjustment using  a water-effect ratio
 was set forth in previous guidance [8, 9]. The procedure applies to
 criteria derived from laboratory toxicity data. As such, it does not
apply to the residue-based mercury chronic criteria, or the field-
based  selenium freshwater criterion. The basic features  of the
procedure  as recommended herein are  described below.  Dis-
chargers or private entities wishing to perform such testing should
consult with the appropriate regulatory agency before proceeding.
   (1)  At least two sensitive species, including at least one in-
       vertebrate, should be tested through standard toxicity
       testing protocols, using site dilution water and using
       laboratory dilution water. Test organisms  should be
       drawn from the same population and tested under
       identical conditions  (except for water source). Test
       species should ordinarily be  selected from those
       species that were used for national criteria develop-
       ment in order  to be able to ascertain whether the
       laboratory water results are comparable to the those in
       the criteria document.

   (2)  Site water samples used  for testing are to  be repre-
       sentative  of  the receiving water  to which the site-
       specific criteria value is to apply. For flowing waters, it
       is generally recommended that at least one sample
       correspond to a condition in which point or nonpoint
       pollutant  contributions are reasonably  well mixed
       with the flow of the receiving water. For other types of
       waters, it is generally recommended that a sample cor-
       respond  to  a  dilution situation  well outside any
       regulatory mixing zone. These recommendations are

          intended to yield a water-effect ratio appropriate for
          the affected receiving water as a whole. These recom-
          mendations supersede  those  of  the  previous  site-
          specific guidance  [8, 9],  which recommended  that
          pristine waters always be used.

      (3)  The laboratory  dilution water should  be comparable
          to what was used in  tests  underlying the national
          criteria. For any pollutant with a national or State
          criterion  calculated,  from   site-specific   hardness,
          laboratory-water and site-water toxicity results should
          be computationally normalized to the same hardness,
          using the specified hardness slope.

      (4)  The toxic metal should be added in the form of an in-
          organic salt having relatively high solubility. Nitrate
          ?-ilts are generally acceptable; chloride  and sulfate
            its of  many  metals are also acceptable.  Results
          snould be based on measured  or nominal initial  con-
          centrations  if static tests  are performed, and on
          average measured concentrations if flow-through  tests
          are performed.

      (5)  Water quality characteristics affecting bioavailability
          and toxicity should be monitored. Measurements or-
          dinarily  snould include both dissolved  and  total
          recoverable  metal  concentrations,  hardness,  pH,
          alkalinity, suspended solids,  conductivity,  dissolved
          solids or salinity, total organic carbon, dissolved or-
          ganic carbon, temperature, and specific metal binding
          ligands (where known to be important).

      (6)  The number of site water samples to be tested  may
          vary with the size  of the affected water body (or the
          size of the metal loading).  Except in the smallest sys-
          tems, a minimum of two site water samples  should be
          collected in different seasons during times of relatively
          low flow or low dilution. In  moderately sized  and
          larger  systems  (e.g., multiple m3/sec or double to
          triple digit cfs low flow), additional samples should be
          collected during other times in the year and possibly
          at additional locations appropriate  for  the segment
          under study.

      (7)  In studies involving continuous discharges, samples
          ordinarily should  not be taken from  storm affected
          waters,  which  may  contain  particulate matter not
          present during  design flow conditions. On the other
          hand, in effluent dominated  situations, at least one
          sample should  represent a higher dilution  condition
          (less than 50 percent  effluent) in order to portray am-
          bient conditions. In all situations, it  should be recog-

          uized that the water-effect ratio may be affected by
          constituents  contributed  by  point  and  nonpoint
          sources. Consequently, new measurements should be
          undertaken if newly implemented controls or other
          changes  substantially  affect  ambient  levels  of
          suspended solids, organic carbon, or pH.

      (8)  Additional testing should be performed before accept-
          ing  unusually or inexplicably  high values for the
          water-effect ratio, based on experience with the par-
          ticular pollutant, and based on  the chemical charac-
          teristics  of the  water.  Retesting should also  be
         performed for ratios having wide uncertainty ranges.
         EPA intends to compile additional information to as-
         sist in judging water-effect ratios  in this manner. These
         recommendations, which focus concern on large and
         uncertain water-effect ratios, supersede the previous
         guidance  [8,  9]  recommendations  that encourage
         retesting or rejection of small water-effect ratios.

     (9)  Ordinarily, the acute and  chronic criteria for the site
         are  calculated by multiplying the national or  State
         criteria by the geometric mean water-effect ratio for
         the  two or more tested species. The  previous site-
         specific guidance [8, 9] provides some additional sug-
         gestions for situations  where the  measured  ratios
         differ significantly, and provides other alternatives for
         setting the chronic criterion.

    (10) As with other types of water quality-based control ac-
         tions for toxic pollutants, it is recommended that the
         chemical-specific approach be  implemented in  con-
         junction  with assessments of whole effluent toxicity
         and field ecology ("bioassessment") [1]. Nevertheless,
         m light of the stated limitations of these latter techni-
         ques with regard to identifying causative agents and
        predicting future changes [I], considerable caution is
        warranted  in using  such information (particularly
        ecological data) to make inferences about  the ade-
        quacy of particular numeric criteria.

    The water-effect ratio is affected not only by speciafrion among
the various dissolved and particulate forms, but also by additive
synergistic, and antagonistic  effects of other materials in  the af-
fected site waters. As such, the water-effect ratio is a much more
comprehensive measure than a ratio of total recoverable metal to
dissolved metal.  Because  the basic technique  involves  adding
soluble metal salts to site water samples, it is most accurate where
rapid sorption or complexation processes are involved.

   Because effluent  limits  are generally expressed as  total
recoverable metal, simplicity would suggest deriving water-effect
ratios in terms of total recoverable measurements. Derivation in

 with  Sediment
Support and
                          terms of dissolved measurements is also acceptable, and may be
                          preferred in situations involving highly variable suspended solids

                              Data available from a limited number of site-specific studies
                          performed  in rather clean freshwater suggest that copper, lead,
                          and cadmium often  have substantial water-effect ratios, while
                          zinc, in situations where it is preponderantly dissolved, often does
                          not [10]. Much less information is available for such ratios in salt
      For national or state-wide criteria expressed as dissolved or
      total recoverable metal, and for site-specific criteria derived
      from water-effect ratios, questions may be raised about the
adequacy of water column criteria for protecting sediment. The
issue is whether particulate metal settling from the water column
could contribute to sediment quality problems,  even  where no
toxicity is manifested in the water column.

   Because  sediment  toxicity is considered  to  be  determined
primarily by the concentrations of pollutant dissolved in the sedi-
ment interstitial  water,  the question becomes whether the
pollutant would have a greater propensity to become dissolved or
bioavailable  in the  sediment than in the water column.  While
available information does not suggest that this is ordinarily the
case, the ongoing development of sediment criteria should resolve
this issue. Nevertheless, in those cases where the beneficial uses of
a receiving water are known to be impaired by the toxicity of me-
tals  in  sediments,  water quality-based  control requirements
should be designed to abate  any sources that would continue to
cause sediment toxicity.
     The Environmental Research Laboratories in Duluth and m
     Narragansett will continue to  answer technical questions
     about the possible problems in applying the above methods
to criteria for specific metals. The contact for freshwater is Charles
Stephan (Duluth, Minnesota telephone (218) 720-5510). The con-
tact for salt water is Gary Chapman (Newport, Oregon telephone
(503) 867-4027).
   EPA intends to undertake further work to facilitate the im-
plementation  of   metals   criteria  in  terms   of   dissolved
measurements. For metals such as copper, silver, zinc, lead, and
cadmium, the dependency of toxicity on factors other than hard-
ness will be considered for  inclusion.  Where appropriate and
feasible, EPA may develop equations  relating dissolved metal
criteria to hardness and organic matter concentration, and possib-
ly pH and other water quality  characteristics. EPA might also
consider other biological or chemical techniques for ascertaining
the effective concentration of bioavailable metals.

           APPENDIX A
            CASE STUDY:
Determination of the Water-Effect Ratio
       Using Indicator Species
             Norwalk River
         Georgetown, Connecticut*


         Connecticut's Upper Norwalk watershed, where this study   |M+^ j    A.
         was conducted, covers an area of 18.5 square miles and in- ,  ln»OdUCtlOn
         eludes the region  extending from the  headwaters of the '
  Norwalk River to its confluence with Comstock Brook.            ]
      Two  secondary treatment plants discharge  a total of 0 44 mgd l
  of municipal wastewater to a reach 9-14 stream miles upstream of i'
  the study site.  An  area  of  failed  septic systems  in the  same i
  upstream vicinity also contributes to the pollutant loading of the  i

      Although water quality is degraded somewhat in the immedi-  '
  ate vicinity of these municipal pollutant sources, as the river flows
  southward towards Long  Island Sound, it recovers to support a
  valuable  recreational trout fishery. There are no industrial point
  source discharges of metals upstream of the study area.

     Within the study area itself, the Gilbert and Bennett Manufac-
  turing Company discharges treated process water to the Norwalk
  River at a point below Factory Pond  in Georgetown, Connecticut
  Gilbert and Bennett cleans, draws, and coats metal wire Waste-
  water is primarily generated during the wire cleaning process The
  wastewater treatment system of the facility consists  of  pH
  neutralization and equalization followed  by'precipitation and
  clarification of the effluent before discharge  to the river The
  treated wastewater is discharged intermittently to the river.

     The Connecticut Department of Environmental  Protection un-
  dertook the study of the Norwalk River site because  the Gilbert
 and Bennett metal loadings were calculated to result in excursions
 of national water quality criteria for  lead and zinc under design
 flow conditions. In order to evaluate the effect of site water on the
 toxicity of lead and zinc, EPA and the State used the indicator
 species (water-effect ratio) protocol.

    By testing a sensitive  invertebrate and a fish in both site and
 reconstituted laboratory dilution water, the water-effect ratio pro-
 cedure  accounts for differences  in bioavailability  and effective
 toxicity of a pollutant in the two waters. The procedure responds
 to the summation of all synergistic and antagonistic effects of site
 water quality  characteristics (including pH, hardness, particulate
 matter,  dissolved organic matter, and other contaminants).  The
 procedure  does not, however,  elucidate factors causing the dif-
 ference  in toxicity.                                   6

    A water-effect ratio is the ratio of a species LC50 in site water
 versus  its  LC50  in  laboratory dilution water.  The 1983 Water
 Quality Standards Handbook recommends that two relatively sen-
 sitive indicator species be tested, and that the geometric mean of
 the two results be used. The  site-specific criterion would be calcu-
 lated as the product of the national criterion and the water-effect

     The results from the testing of metals toxicity in laboratory
     and site water forms the primary basis for the site-specific
     criteria. To provide additional information, the monitoring
of ambient water chemistry, surveying of macroinvertebrates, and
testing of whole effluent toxicity were also performed.
                          Chemical and Ecological Monitoring

                          Concentrations of  several metals  were measured in  composite
                          samples  taken at  each  of four ambient stations and  in  grab
                          samples of the Gilbert and Bennett main effluent. One  ambient
                          station was in the upstream control zone, two in the impact zone,
                          and one in the recovery zone.
                             Benthic populations were sampled at five locations to assess
                          .the impact of the discharge on the stream community. One refer-
                          ence station  was located  in the upstream control zone. Three
                          stations were in the Bennett and Gilbert impact: zone, and one was
                          in the recovery zone. Physical substrate,  stream velocity, and
                          water depth were  similar at each  location. Four Surber  samples
                          were collected at each of the five locations. Organisms were sorted
                          in the field, preserved in 70 percent ethanol, and returned to the
                          laboratory for identification and enumeration.
                          Toxicity Testing

                          Norwalk River water was withdrawn from a station upstream of
                          Gilbert  and Bennett and  transported (along with the effluent
                          samples) back to the laboratory. Toxicity tests were conducted in
                          the sampled river water and in reconstituted water, with differing
                          amounts of either lead or zinc added, in order to determine the
                          LC50. Whole toxicity  testing  of one of the Gilbert and Bennett
                          effluents was also performed, using both upstream Norwalk River
                          water and reconstituted water for dilution.
                              Because the  lead  and  zinc  toxicity  tests were  run  using
                          upstream water, they do not indicate the effects of synergism, an-
                          tagonism, or toxicant  additivity with constituents of the Gilbert
                          and Bennett effluent. Although this guidance recommends  use of
                          downstream water for at least one sample, the case study predates
                          the guidance and does not follow this recommendation.
                              Ninety-six  hour acute toxicity tests (static with measured con-
                          centrations of  toxicant) were conducted with laboratory  reared
                          rainbow trout  (Oncorhynchus mykiss, formerly Salmo gairdneri) and
                          48-hour acute  toxicity tests (static with measured concentrations)
                          were conducted with laboratory-reared Daphnia magna.

   Water Chemistry and Ecological Quality

  Mean instream concentrations of lead, zinc, and cadmium were
  higher in the impact and recovery zones than in the control zone  :
  Levels of cadmium and copper appeared to exceed  national acute !
  criteria at all sampling locations both upstream and downstream '
  of Gilbert and Bennett.                                        !

     It should be noted that the metals data were generated using '
  the sample  handling and analytical protocols of the early  1980s  '
  rather than more recent protocols emphasizing ultra-clean tech-
  niques. While the link between chemical quality and ecological
  quality is of great interest, it is not clear that these ambient metals
  data are sufficiently reliable to be used in such comparisons. If the
  ambient metals  concentrations were  reliably known, such  infor-
  mation would be most useful  for comparing concentrations in the
  control, impact, and recovery  zones with the criteria derived from
  the water-effect ratio.

    At the upstream reference location, 889 organisms from 44 taxa
  were collected. Most of the species collected could be classified as
  sensitive or facultative with respect to pollution tolerance Species
 diversity was high (Shannon Diversity index of 3.4), indicating ac-
 ceptable water quality and aquatic habitat.

    At  the three near  downstream locations, the number  of or-
 ganisms, number of taxa, and diversity were reduced significantly
 At some of the impact zone stations, the number of organisms was
 less than one-fourth, and number of taxa one-third that of the ref-
 erence site. The Shannon index registered as low as 1.0.
    At the recovery zone station (500 m downstream  from the dis-
 charge), a larger number of organisms were found-than at any of
 the other stations, including the upstream reference site. Diversity
 and numbers of taxa, however, remained at levels more charac-
 teristic of the impacted stations.

    The ecological assessment  demonstrated that the ecology of
 the Norwalk  River was  impaired, and strongly suggested that
 some type of  pollutant release from Gilbert and Bennett was in-
 volved  m  the impairment. However,  as noted in the Technical
 Support Document [1], ecological assessments cannot identify the
 causative agents, and  generally  do not predict the  ecological
 quality  as a function of chemical-specific concentrations. Conse-
 quently, these ecological data do not indicate the appropriateness
 of particular values for the water-effect ratio.

 Toxiclty Testing with Lead and Zinc

Table A-l shows the results of  static toxicity tests with daphnids
and rainbow trout exposed to lead and zinc, in river water and in
laboratory water.

 Table A-1.—Toxicity of lead and zinc in Norwalk River and in laboratory water.

River water
Lab water
River water
Lab water
48-hr LC50, iig/L
(95% confld llm)
320 (290-360)
900 (740-1100)
400 (380-480)
96-hr LCSO, ng/U
(95% confld lim)
1500 (1200-1800)
     The toxicity of both lead and zinc was lower in Norwalk River
  water than in laboratory water. For both metals, the more sensitive
  species, Daphnia magna, had the higher water-effect ratio. This is
  consistent with general tendencies observed in other studies [10].
  Whole Effluent Toxicity for One Effluent

  In  unspiked, static toxicity  tests  in  which rainbow trout were
  exposed to one of the Gilbert and Bennett effluents, the effluent
  was rendered nontoxic by relatively little dilution of the effluent.
  As effluent constituted the bulk (60-68 percent) of the test water at
  dilutions toxic to half the organisms, it was not surprising that the
  whole effluent toxicity tests could not discern differences between
  toxicity in laboratory and river water. That is, toxicity was much
  reduced before enough laboratory or river water could added to
  the effluent to discern differences between the added water.
     The monitored effluent was not sufficiently toxic to  daphnids
  to  allow calculation of the dilution  lethal  to half the organisms,
  However,  to eliminate toxicity to all the tested individuals, sig-
  nificantly more dilution was required with laboratory water than
  with river water. This suggests that this effluent may be less toxic
  in Norwalk River water than in laboratory water.
     If the lead and zinc concentrations had been measured during
  the whole effluent toxicity tests, it would be possible to compare
  effect concentrations with the lead and zinc LCSO values shown in
  the previous section. In making  such comparisons, however, it
  must be recognized that the cause of toxicity of the effluent is not
     Finally, it should be noted that the tested effluent is only one of
  Gilbert and Bennett's releases to the Norwalk River. There is no
  disparity between the observed significant instream impacts and
  the relatively  low toxicity of the one  monitored effluent. The
  ecological assessment suggested that the unmonitored release was
  more toxic than the monitored one.

  Calculation of the Site-Specific Criteria

  The water-effect ratios for lead and zinc differed relatively little
  between species. If the overall water-effect ratio for each metal
  were  calculated  from  the  geometric  mean  of  the  species
  water-effect ratios, then the water-effect ratio for lead would be
  3.9, and that for zinc would be 1.9.

     It is assumed that the water-effect ratio would apply to both
 the acute and the chronic criteria. As the national criteria for lead
 and zinc are hardness dependent, for purposes of determining the
 value of the site-specific criteria during the survey period, it is ap-
 propriate to calculate the national criteria  at the hardness of the
 laboratory reconstituted water, if different from the site water The
 site-specific acute and chronic criteria for each metal would equal
 the national (or state-wide) criteria multiplied by the water-effect
 ratio for each  metal.

    Because all of the above toxicity tests and  water-effect ratios
 were based on total recoverable metal, the resulting site-specific
 criteria would also be expressed as total recoverable metal.

    When the  site-specific criteria were used to calculate effluent
limits, it was  found that large reductions in current  metals  load-
ings would  be required. This result is not surprising, considering
the ecological  effects observed downstream


Derivation of Effluent Limits
from Ambient Metals Criteria


  -T-he determination of the waste loads and effluent limits that

      basis for calculating effluent limits All of the
            to the ambient dissolved metal
age dzssolved metal from a geochemical moddsuch as
   f^gardlfs of which alternative is used, it must be recognized
                       requirements for technology-based
                      antibacksliding is necessary.
      Site-Specific Measurements

Metal Criteria

Metal Criteria

      Samples on which measurements are made should be repre-
   sentative of the bulk of the receiving water. It is recommended that
   sampling be performed over a period of time,  with samples repre-
   senting  the  usual range of effluent and ambient  quality, while
   emphasizing the season corresponding to the critical water quality
   conditions. Because the control strategy  assumes that the  dis-
   solved  concentration  is  related  to  the   total  recoverable
   concentration, it would be appropriate to verify that the dissolved
   and total recoverable concentrations are in fact correlated.
      In freshwaters, an alternative approach to downstream sam-
   pling is  to sample the effluent and the upstream waters and mix
   samples at an appropriate dilution. The dilution and the seasons
   for sampling should be related to the critical conditions, although
   it may be appropriate to reduce the dilution if necessary to detect
   and quantify the metal.

      The  most important constraint  on  the feasibility of carrying
   out  site-specific measurements is  the capability of  analytical
   laboratories to  detect and accurately quantify both the dissolved
   and total recoverable metal. Graphite furnace (flameless) atomic
   absorption AA techniques are usually needed. Furthermore, great
   care is needed to prevent external contamination of samples. The
   EPA- and  USGS-recommended sample handling methods, com-
   monly used, may produce inaccurate results when judged against
   newer techniques that emphasize highly purified reagents, Teflon
   and polyethylene labware, and clean laboratory environments [7,

     The high degree of imprecision of metals measurements tends
   to result in overstatement of the true variability of the dissolved-
   total ratio. As a result, unless a mean or median observed ratio is
   used, it may be necessary to compensate for the effect of measure-
   ment  imprecision  (by  subtracting   out   the  measurement
   imprecision variance).

     In  order  to provide some sense of the general  magnitude of
   typically observed dissolved-total metals ratios, data from several
   sources have been compiled in Table B-l. The ambient data under-
   lying the tabulated values are considered to be reasonably reliable.

   Using Environmentally Conservative Default Values

   This option is best applied as the first tier of a tiered approach,
   where the second tier involves site-specific measurements. In this
   type of  framework, the default (first-tier) percentage  dissolved
   might be set at a reasonable worst-case value.

     One possible worst-case assumption is that 100 percent of the
   effluent  total recoverable metal will become dissolved in the
   receiving water. Such an assumption may be  particularly ap-
   propriate for a metal, such as mercury,  for which  there are
   substantial uncertainties regarding long-term processes convert-

                         *««*»"• °< «taM.vd meta.s in ambient
                             SALT WATER
                          NY-NJ HARBOR AREA [13)

                              ' a""Ult YMiucs uiay aiSO
 differ in diffeVnT^rSofZ3016 ^for?lation- Such values may
 quality characteristics       ^^ dU6 tO variatto™ ^ water
 Using a Geochemlcal Model
MIWEQ may be particuLfv   f, f«™mental  conditions.
                               ass -»
solubility.                S contro"ed by factors  such as

1.  U.S.  Environmental Protection Agency. 1991. Technical Support Docu
    ment of Water Quality-based Toxics Control. Office of Water, Washington,
    DC. EPA/505/2-90-001. PB91-127415.

2.  Stephan, C.E., D.I. Mount, D.J. Hansen, J.H. Gentile, G.A. Chapman, and
    W.A. Brungs. 1985. Guidelines for Deriving Numerical National Water
    Quality Criteria for the Protection of Aquatic Organisms and Their Uses.
    U.S.  EPA, Office  of Research and Development. PB85-227049. NTIS,
    Springfield, VA.

3.  U.S.  Environmental  Protection Agency. 1983.  Methods  for Chemical
    Analysis of Water and Wastes. Environmental Monitoring and Support
    Laboratory, Cincinnati, OH. EPA-60074-79-020. Sections 4.1.1, 4.1.3, and

4.  Martin, T.D., J.W. O'Dell, E.R. Martin, and G.D. McKee. 1986. Evaluation
    of Method 200.1 Determination of Acid Soluble Metals. U.S. EPA, Env.
    Monitoring and Support Lab, Cincinnati, OH.

5.  U.S. Environmental Protection Agency. 1991. Methods for the Determina-
    tion  of Metals in Environmental Samples. Environmental Monitoring
    Systems Laboratory, Cincinnati, OH 45268. EPA-600/4-91-010.

6.  Puls, R.W., and M.J. Barcelona. 1989. Ground Water^Sampling for Metals
    Analyses. EPA Superfund Ground Water Issue. U.S.  EPA, Office of Re-
    search and Development. EPA/540/4-89/001.

7.  Windom, H.L., J.T. Byrd, R.G. Smith,  and F. Huan. 1991.  Inadequacy of
    NASQAN Data for Assessing Metals  Trends in the Nation's Rivers. En-
    viron. Sci. Technol. 25, 1137. (Also see Comment and Response, Vol. 25, p.
8.  U.S.  Environmental Protection Agency. 1983. Water  Quality Standards
    Handbook. Office of Water Regulations and Standards, Washington, DC.

9.  Carlson, A.R., W.A. Brungs, G.A. Chapman, and D.J.  Hansen.  1984.
    Guidelines for Deriving Numerical Aquatic Site-s _peciric  Water Quality
    Criteria by Modifying National Criteria. U.S. EPA, Environmental Re-
    search Laboratory - Duluth. EPA-600/3-84-099. PB85-121101.

10.  Brungs, W.A., T.S. Holderman, and M.T. Southerland. 1992. Synopsis of
    Water-Effect Ratios for Heavy  Metals as Derived for Site-Specific Water
    Quality Criteria. Draft. U.S. EPA Contract 68-CO-0070.

11.  Delos, C.G., W.L. Richardson, J.V.  DePinto,  R.B. Ambrose, P.W.  Rodgers,
    K. Rygwelski, J.P. St. John, WJ. Shaughnessy, T.A. Faha, and W.N. Chris-
    tie.  1984.  Technical  Guidance Manual for Performing Waste  Load
    Allocations. Book II Streams and Rivers. Chapter 3 Toxic S.ubstances. U.S.
    EPA, OWRS, Washington, DC. EPA-440/4-84-022.

12.  HydroQual, Inc. 1986. Technical Guidance Manual for Performing Waste
    Load Allocations.  Book IV Lakes, Reservoirs, and Impoundments. Chap-
    ter   3  Toxic  Substances.   U.S.  EPA,  OWRS,   Washington,  DC.

13.  Battelle Ocean Sciences. 1992. Evaluation of Trace-Metal  Levels in Am-
    bient Waters and Tributaries to New York/New Jersey Harbor for Waste
    Load Allocation.. U.S.  EPA, Office  of Wetlands, Oceans, and Watersheds,
    and Region II. Contract No. 68-C8-0105.

14.  Brown, D.S., and J.D.  Allison.  1987. MINTEQA1, An Equilibrium Metal
    Speciation Model: User's Manual. U.S. EPA, Environmental  Research
    Laboratory, Athens, GA. EPA/600/3-87/012.