United States        Office of Science and Technology and
         Environmental Protection   Office of Research and Development
         Agency          Washington, DC 20460
         Methods for the Derivation of
         Site-Specific Equilibrium
         Partitioning Sediment Guidelines
         (ESGs) for the Protection
         of Benthic Organisms:
         Nonionic Organics
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Foreword
                Under the Clean Water Act (CWA), the U.S. Environmental Protection Agency (EPA) and the
                States develop programs for protecting the chemical, physical, and biological integrity of the
                nation's waters. To meet the objectives of the CWA, EPA has periodically issued ambient water
                quality criteria (WQC) beginning with the publication of "Water Quality Criteria, 1972" (NAS,
                1973), The development of WQC is authorized by Section 304(a)(l) of the CWA, which directs
                the Administrator to develop and publish "criteria" reflecting the latest scientific knowledge on
                (1) the kind and extent of effects on human health and welfare, including effects on plankton, fish,
                shellfish, and wildlife, that may be expected from the presence of pollutants in any body of water,
                including ground water; and (2) the concentration and dispersal of pollutants on biological
                community diversity, productivity, and stability, All criteria guidance through late 1986 was
                summarized in an EPA document entitled "Quality Criteria for Water, 1986" (U.S. EPA, 1987).
                Updates on WQC documents for selected chemicals and new criteria recommendations for other
                pollutants have been more recently published as "National Recommended Water Quality Criteria-
                Correction"  {U.S. EPA, 1999). EPA will continue to update the nationally recommended WQC
                as needed in the future.

                In addition to the development of WQC and to continue to meet the objectives of the CWA, EPA
                has conducted efforts to develop and publish equilibrium partitioning sediment guidelines (ESGs)
                for some of the 65 toxic pollutants or toxic pollutant categories.  Toxic contaminants in bottom
                sediments of the nation's lakes, rivers, wetlands, and coastal waters create the potential for
                continued environmental degradation even where water column contaminant levels meet
                applicable water quality standards.  In addition, contaminated sediments can lead to water quality
                impacts, even when direct discharges to the receiving water have ceased.  These guidelines are
                authorized under Section 304(a)(2) of the CWA, which directs the Administrator to develop and
                publish information on, among other things,  the factors necessary to restore and maintain the
                chemical, physical, and biological integrity of all navigable waters.

               The ESGs and associated methodology presented in this document are EPA's best recommendation
                as to the concentrations of a substance that may be present in sediment while still protecting
                benthic organisms from the effects of that substance.  These guidelines are applicable to a variety
               of freshwater and marine sediments because  they are based on the biologically available
               concentration of the substance in the sediments.  These ESGs are intended to provide protection to
               benthic organisms from direct toxicity due to this substance.  In some cases, the additive toxicity
               for specific classes of toxicants (e.g., metal mixtures or polycyclic aromatic hydrocarbon
               mixtures) is addressed. The ESGs do not protect against synergistic or antagonistic effects of
               contaminants or bioaccumulative effects to benthos. They are not protective of wildlife or human
               health endpoints.

               EPA recommends that ESGs be used as a complement to existing sediment assessment tools, to
               help assess the extent of sediment contamination, to help identify chemicals causing toxicity, and
               to serve as targets for pollutant loading control measures.  EPA is developing guidance to assist in
               the application of these guidelines in water-related programs of the States and this Agency.

               This document provides guidance to EPA Regions, States, the regulated community,  and the
               public.  It is designed to implement  national policy concerning the matters addressed. It does not,
               however, substitute for the CWA or EPA's regulations,  nor is it a regulation itself. Thus, it
               cannot impose legally binding requirements on EPA, States, or the regulated community. EPA
               and State deeisi onmakers retain the discretion to adopt approaches on a case-by-case basis that
               differ from this guidance where appropriate.  EPA  may change this guidance in the future.
                                                                                                   Hi

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             This document has been reviewed by EPA's Office of Science and Technology (Heal* and
             Ecological Criteria Division, Washington, DC) and Office of Research and Development (Mid-
             Continent Ecology Division, Duluth, MN; Atlantic Ecology Division, Narragansett, HI; Western
             Ecology Division, Corvallis, OR), and approved for publication.

             Mention of trade names or commercial products does not constitute endorsement or
             recommendation of use.

             Front cover image provided by Wayne R. Davis and Virginia Lee.
IV

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Contents
                  Acknowledgments	vu


                  Executive Summary	k


                  Glossary of Abbreviations	xi


                  Section 1
                  Purpose and Application	1-1
                  1.1    General Information	1-1
                  1.2    Rationale for Procedures Used to Develop Site-Specific Guidelines	1-1
                  13    Definition of Site of Concern and Resident Species at a Site	1-3

                  Section 2
                  Procedures for Conducting Site-Specific ESG Modifications	2-1
                  Zl    Resident Species Deletion/Substitution Procedure	,	2-1
                       2.1.1   Rationale for Use of the Resident Species Deletion/
                             Substitution Procedure	2-1
                       2.12   Details of the Resident Species Deletion/Substitution Procedure	2-2
                       2.13   Derivation of the Site-Specific ESG....	2-3
                  22    Bioavailability Procedure	2-4
                       22.1   Rationale for Use of the Bioavailability Procedure	2-4
                       222   Details of the Bioavailability Procedure	~	2-5
                             2.2.2.1   Sampling Interstitial Water	2-5
                             2222  Quantification of Dissolved and DOC-Associated
                                     Phases	2-5
                             222.3   Calculating the Freely-Dissolved, B ioavai 1 able Concentration	2-6
                       223   Derivation of the Site-Specific ESG	2-7

                  Section 3
                  References..                                                        , 3-1
                 Tables
                 Table 2-1.    Computed organic carbon-normalized partition coefficients	2-7

                 Table 2-2.    Solutions to Equation 2-3 using XDQC values computed from
                             Equation 2-4	2-7

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                   Site-Specific Equilibrium Partitioning Sediment Guidelines (ESGs): Nonionic Organic*
Acknowledgments
             Coauthors
             David J. Hansen           HydroQual, Inc., Mahwah, NJ; Great Lakes Environmental
                                     Center, Traverse City, MI (formerly with U.S. EPA)
             Christopher S. Zarba        U.S. EPA, Office of Research and Development, Washington, DC
             Robert J. Ozretich*         U.S. EPA, NHEERL, Western Ecology Division, Corvallis, OR
             Dominic M. Di Toro        Manhattan College, Riverdale, NY; HydroQual, Inc.,
                                     Mahwah, NJ
             Significant Contributors to the Development of the Approach and Supporting Science
             David J. Hansen           HydroQual, Inc., Mahwah, NJ; Great Lakes Environmental
                                     Center, Traverse City, MI (formerly with U.S. EPA)
             Robert J. Ozretich*         U.S. EPA, NHEERL, Western Ecology Division, Corvallis, OR
             Dominic M. Di Toro        Manhattan College, Riverdale, NY; HydroQual, Inc.,
                                     Mahwah, NJ
             Technical Support and Document Review
             Maria R. Paruta           U.S. EPA, NHEERL, Atlantic Ecology Division,
                                     Narragansett, RI
             Heidi E. Bell*             U.S. EPA, Office of Water, Washington, DC
             Robert L. Spehar           U.S. EPA, NHEERL, Mid-Continent Division, Duluth, MN
             Robert M. Burgess         U. S. EPA, NHEERL, Atlantic Ecology Division,
                                     Narragansett, RI
             Mary C. Reiley           U.S. EPA, Office of Water, Washington, DC
             D. Scott Ireland           U.S. EPA, Office of Water, Washington, DC
             *Principal U.S. EPA contact
                                                                                     vii

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Executive  Summary
               The purpose of this document is to provide guidance on procedures that can be used to modify
               national equilibrium partitioning sediment guidelines (ESGs) for nonionic organic chemicals to
               reflect specific local conditions. This methodology is issued in support of the published ESGs for
               endrin and dieldrin (U.S. EPA, 2000a,b) and is intended to supplement the procedures described
               for calculating ESGs for nonionic organic chemicals based on the equilibrium partitioning (EqP)
               theory as described in the ESG Technical Basis Document (U.S. EPA, 2000c).

               According to the EqP theory, a nonionic chemical in sediment partitions between sediment
               organic carbon, interstitial (pore) water, and benthic organisms. At equilibrium, if the
               concentration in any one phase is known, then the concentration in the others can be predicted.
               The ratio of the concentration in water to the concentration in sediment organic carbon is termed
               the organic carbon partition coefficient (A^-,), which is a constant for each chemical. It has been
               demonstrated that if the effect concentration in water is known, for example, a water quality
               criteria final chronic value (WQC FCV), die effect concentration in sediments on an organic
               carbon basis (ESG^) can be accurately  predicted by multiplying the effect concentration in water
               by the chemical's K^ (U.S. EPA, 2000c).
               The U.S. Environmental Protection Agency (EPA) currently recognizes that the national ESGs
               may be under- or overprotecti ve when (1) pertinent differences occur between the sensitivities of
               benthic organisms at a site and the organisms used to derive the WQC FCV, or (2) differences
               occur in the bioavailability of the chemical in the sediment from the site because of alternate
               partitioning phases or the presence in the sediment of undissolved chemical. The two procedures
               recommended to correct for such site-specific differences are the Resident Species Deletion/
               Substitution Procedure (U.S. EPA, 1994) and the Bioavailability Procedure. The basic principle
               of the Resident Species Deletion/Substitution Procedure is to permit deletion of all acute values
               for nonresident benthic species/life-stages and water column species/life-stages when acute values
               for all benthic resident species/life-stages in a family have been tested.  The Bioavailability
               Procedure assumes that the true concentration of bioavailable chemical can be reasonably
               measured or estimated as freely-dissolved chemical in interstitial water, which can men be
               compared with the WQC FCV.  For the latter value, sediments in which the freely-dissolved
               interstitial water concentration is less than the WQC FCV are acceptable for maintaining the
               presence of benthic organisms. If bioassays demonstrate that a sediment is toxic, EPA
               recommends sediment-specific risk assessments.  These risk assessments should utilize a tiered
               approach prior to conducting the site-specific ESG modification procedures to identify chemicals
               causing the observed effects (such as a Toxicity Identification Evaluation [TIE]) (e.g., Ankley et
               al., 1991; Ho etal., 1997).
                                                                                                ix

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                    Site-Specific Equilibrium Partitioning Sediment Guidelines (ESGs): NonionicO
Glossary of Abbreviations
              ACR
              ASTM
              CWA
              DOC
              EPA
              EqP
              ESA
              ESG(s)
              ESG,
                 oc
              per;
              EOU
              FACR
              FAV
              FAV
                  ss
              FCV
              GC/MS
              GMAV
              HECD
              V
              •^
              L-L
              NAS
              NTIS
Acute-chronic ratio
American Society for Testing and Materials
Freely-dissolved interstitial water chemical concentration
Total interstitial water chemical concentration
Clean Water Act
Dissolved organic carbon
United States Environmental Protection Agency
Equilibrium partitioning
Endangered Species Act
Equilibrium partitioning sediment guideline! s)
Organic carbon-normalized equilibrium partitioning sediment guideline
Site-specific organic carbon-normalized equilibrium partitioning sediment
guideline
Final acute-chronic ratio
Site-specific final acute-water chronic ratio
Final acute value
Site-specific final acute value
Final chronic value
Site-specific final chronic value
Gas chromatograph/mass spectrophotometer
Genus mean acute value
U.S. EPA, Health and Ecological Criteria Division
Dissolved organic carbon-water partition coefficient
Organic carbon-water partition coefficient
Oc (a no! -water partition coefficient
Liquid-liquid extraction
National Academy of Sciences
National Technical Information Service
                                                                                         XI

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                      Site-Specific Equilibrium Partitioning Sediment Guidelines (ESGs): Nonionic O
 Section  1
 Purpose and  Application
 1.1  General Information

    The purpose of this document is to provide
 guidance on procedures thai can be used to modify
 national equilibrium partitioning sediment guidelines
 (ESGs) for nomonic organic chemicals to reflect local
 environmental conditions. These procedures may be
 utilized as part of the basis for establishing site-
 specific sediment quality standards to protect the uses
 of a specific water body. The procedures are intended
 to apply to the sediment guidelines for endrin and
 dieldrin (U.S. EPA, 2QOOa,b) and ESGs published for
 other substances including, but not limited to, mixtures
 of metals (cadmium, copper, lead, nickel, silver, and
 zinc) (U.S. EPA, 2000f) and mixtures of polycyclic
 aromatic hydrocarbons (PAHs) (U.S. EPA, 2000g).

    A thorough understanding of the 'Technical Basis
 for the Derivation of Equilibrium Partitioning Sediment
 Guidelines (ESGs) for the Protection of Benthic
 Organisms: Nonionic Organics" (U.S. EPA, 2000c), the
 ESG documents for endrin and dieldrin (U.S. EPA,
 2000a,b), "Implementation Framework for Use of
 Equilibrium Partitioning Sediment Guidelines (ESGs)"
 (U.S. EPA, 2000d), "Interim Guidance on Determination
 and Use of Water-Effect Ratios for Metals" (U.S. EPA,
 1994)," Water Quality Standards Handbook" (U.S. EPA,
 1983), "Guidelines for Deriving Numerical National
 Water Quality Criteria for the Protection of Aquatic
 Organisms and their Uses" (Stephan et al., 1985),
 response to public comment on the "Guidelines for
 Deriving Numerical National Water Quality Criteria for
 the Protection of Aquatic Organisms and their Uses"
 (U.S. EPA, 1985), and the response to public comment
 on the proposed ESGs (U.S. EPA, 2000e) is
 recommended. Importantly, these procedures for  site-
 specific modification of national ESGs should be used
 only after expanded chemical monitoring of chemical
concentrations in sediments and interstitial water;
 biological monitoring including toxicity  tests, TIEs, and
 faunal surveys; and other risk assessment procedures
that have been conducted at the specific site.
preferably using a tiered approach.

    The national ESGs have been developed
specifically for use in the 304(a) criteria program.
These guidelines are EPA's best estimate of the highest
concentration of a substance in sediments that will
protect benthic (infaunal and epibenthic) organisms
including macro in vertebrates and fishes.

    The U.S. EPA, Office of Science and Technology
(OST), recognizes and has encouraged the potential use
of sediment guidelines by other EPA programs.
Appropriate use of the site-specific ESG in these
programs should be obtained from the implementation
guidance developed by that program for inclusion in
the "Implementation Framework for Use of Equilibrium
Partitioning Sediment Guidelines (ESGs)" (U.S. EPA,
2000d).

1.2   Rationale for Procedures Used to
      Develop Site-Specific Guidelines
    National ESGs may be under- or overprotective if
(1) the benthic (infaunal and epibenthic) species at the
site are more or less sensitive than the benthic and
water column species included in the national criteria
dataset or (2) the sediment or chemical quality
characteristics at the site alter the bioavaitability and,
consequently, the toxicity of the sediment-bound
chemical relative to that predicted by the equilibrium
partitioning (EqP) theory. Therefore, it is appropriate
that site-specific guidelines procedures address each of
these conditions.

    This document recommends the use of the
Resident Species Deletion/Substitution Procedure to
adjust the national ESG for the sensitivity of species
found at the site. It is similar to the Recalculation
Procedure published for use as a  means to modify
national water quality criteria (WQC) values (U.S. EPA,
1983,1994).  This approach permits deletion of certain
toxicological data on (1) water column species, (2)
nonresident benthic species, and (3) water column life-
stages of a resident species having both benthic and
water column life-stages. For example, although water
column species have sensitivities similar to those of
benthic species overall (Di Tore et a)., 1991),
sensitivities of water column species at a site may differ
from those of benthic species found there. The
toxicological data on these species may not be
applicable to the derivation of a site-specific guideline;
                                                                                                1-1

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  Purpose and Application
 therefore, these data can be deleted. Furthermore, the
 national criteria dataset may contain data for benthic
 fauna that are particularly sensitive (e.g., certain
 amphipods, penaeid shrimp, or mysids) or insensitive
 (e.g., certain adult polychaetes or molluscs) to some
 chemicals. If they do not occur at a particular site, their
 sensitivities may nof be representative of those species
 expected to be found there, and lexicological data on
 them can be deleted.  When resident organisms such as
 echinoderms, molluscs, or crustaceans have both
 benthic and water column life-stages, and both have
 been tested, data from tests with the benthic life-stage
 are most relevant to the site-specific ESG, and data on
 water column life-stages can be deleted. When
 nonresident benthic species or water column life-stages
 of resident species having a benthic life-stage are likely
 to be toxicologically related  to untested resident
 benthic species because of their taxonomic
 relationship, deletion of acute toxicity data on them is
 prohibited. However, it should be noted that deletion
 of toxicological data may result in loss of taxonomic
 representation required to meet the minimum database
 for deriving WQC(Stephanetal., 1985). These WQC
 are used to derive the national ESG.  For this reason,
 additional testing may be required. Furthermore, given
 the rules of this procedure, EPA strongly encourages
 that  additional tests be conducted with resident
 benthic species to permit replacement of data on
 surrogate species or life-stages.

     This document recommends the use of die
 Bioa vail ability Procedure as  a means to replace the
 national ESG when there are  differences in the
 bioavailability of the chemical in unique sediments.
 These, unique sediments can  be identified by measuring
 the chemical both in sediment and dissolved in
 interstitial water, then comparing the resultant partition
 coefficient with the organic carbon partition coefficient
 (KOC) in the sediment guidelines document.  Through
 use of this procedure, the bioavailability concentration
 of the chemical in interstitial  water can be quantified for
 comparison to the WQC final chronic value (FCV)
 found in the chemical-specific ESG documents for
 nonionic organic chemicals.

    The reason for using the Bioavailability Procedure
 is that, although a variety of sediments have been
 tested that demonstrate the applicability of the EqP
 approach to a wide array of sediments (U.S. EPA,
 2000c), at certain unique sites sediments do exist where
EqP  theory does not accurately predict  partitioning.
 Unique sediment characteristics, chemical speciation,
or chemical form may make the guidelines chemical
 more or less bioavailable, thereby altering the toxicity
of the sediment (for further detail, see Section 4.1.3 in
the Technical Basis Document [U.S. EPA, 2000c]). For
example, in some sediments the partitioning of PAHs
cannot be explained by standard models of equilibrium
partitioning to organic carbon (Maruya et al., 1996;
McGroddy etal., 1996).  Instead, accurate predictions
of partitioning behavior may require the use of both a
KQC and a soot carbon partition coefficient (Gustafson
et al., 1997).  Quantification of partitioning at these sites
requires measurement of the concentration of the
nonionic organic chemical in interstitial  water and
sediment.

    In cases where it is necessary to identify causative
chemicals when toxicity is indicated by  bioassays or
other tools, EPA recommends sediment-specific risk
assessments be conducted using a tiered approach.
This assessment may include expanded monitoring of
chemical concentrations in sediments and interstitial
water; biological monitoring including toxicity tests and
faunal surveys (Swartz et al., 1994), and  TlEs (Ankley et
al., 1991; Hoet al., 1997); and other risk  assessment
procedures conducted at the specific site.  These
studies are recommended prior to conducting the site-
specific ESG modification procedures to identify
chemicals causing observed effects and partitioning
not predicted by EqP theory. In the context of the tests
used in this risk assessment, it is important to recognize
that national ESGs are derived to provide estimates of
the sediment concentrations of specific substances
that are expected to protect communities of benthic
organisms from chronic effects mat are applicable
across sediments—a goal that cannot be attained using
other assessment methods.

    Studies conducted to modify site-specific WQC
have demonstrated that, if up-front planning with all
stake-holders had occurred before beginning each site-
specific study, the results of these studies could have
been significantly improved (Brungs, 1992). Therefore,
we strongly recommend that users of these guidelines
for developing site-specific ESGs consult early, and
closely, with the appropriate EPA Regional Office,
Office of Science and Technology, and Office of
Research and Development concerning  the design and
conduct of these procedures. In addition, experience
with the use of the initial guidance for conducting site-
specific WQC adjustments {U.S. EPA, 1983) has
identified improvements in the procedures required to
make the resultant site-specific criteria more appropriate
and less costly to derive (U.S. EPA, 1994). EPA
believes that application of these site-specific ESG
procedures will identify improvements that will require
modification over time. Because these procedures are
1-2

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                        Site-Specific Equilibrium Partitioning Scd intent Guidelines (ESGs}: NonionJc Organks
scientifically complex, it is important that they be
conducted only by those who are well qualified and
experienced.


1,3  Definition of Site of Concern and
      Resident Species at a Site

    The aerial distribution of sediments that exhibit
toxicity to benthic organisms, or exceed the national
ESG, defines the site of concern.  In the context of site-
specific ESG derivation, the concept of site must be
consistent with the requirements of the Resident
Species Deletion/Substitution Procedure or the
Bioa vailabilily Procedure.

    Derivation of a site-specific ESG based on species
sensitivity differences requires identification of
resident species expected to occur at the site. To
identify the species expected to occur at the site where
sediments exceed the ESG, a spatially larger area, as
well as temporal changes in fauna, must be considered.
The reason for this is that species may occur
permanently, seasonally, or intermittently at  the site and
may be excluded from the site because of existing
temporary conditions, including pollution. Therefore,
the creation of a list of resident species might possibly
require knowledge of those species occurring in
adjacent water bodies or even in the entire ecological
province. Species not occurring at the site, due for
example to anthropogenic causes, must be included in a
list of resident species because they would likely return
if the pollutants or other conditions causing impacts
were removed. Therefore, identification of resident
species must include consideration of species found at
the immediate site of concern over time, at other similar
sites, and so on, and may include entire biogeographic
provinces.  If the sediment is to be moved, the species
resident at the site where sediments will be placed
should be included as resident species.

    The spatial extent of the site, as applied to the
Bioavaliability Procedure, includes only the area
containing sediments that exceed the ESG. Of
particular concern are those sediments from the site
that exceed the ESG and are believed to be unique
because of sediment characteristics or chemical form
that may violate partitioning assumptions that are
fundamental to the sediment guidelines.

    In case site-specific ESGs are deemed necessary
for purposes such as deriving permit limits and
identifying causative chemicals for toxicity, EPA
recommends preliminary site-specific evaluations prior
to initiation of these site-specific modification
procedures.  For example, these procedures should not
be used until the horizontal and vertical extent of
sediments exceeding the ESG  and the  magnitude of the
exceedance is determined.  These monitoring studies
can also be used to (1) determine if the partitioning of
the chemical to sediments is as predicted by EqP (e.g.,
for nonionic organic chemicals) by comparing the ratio
of the sediment concentration  and the interstitial water
concentration with the K^ in the ESG document, (2)
identify the chemical cause of the observed toxicity, or
(3) determine if the toxicity of the sediment to the
tested species is predicted by EqP theory.  All of these
can help determine if application of these site-specific
ESG procedures will likely decrease or increase the
national ESG.
                                                                                                     1-3

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                      Site-Specific Equilibrium Partitioning Sed iineut Guidelines (ESGs): Noiuonic Organic*
Section 2
Procedures  for  Conducting
Site-Specific  ESG  Modifications
2.1   Resident Species Deletion/Substitution
      Procedure

    The Resident Species Deletion/Substitution
Procedure is intended to result in a site-specific ESG
that appropriately adjusts the national ESG when there
are pertinent differences in the sensitivities of benihic
organisms that occur at the site from those organisms
used to derive the national ESG concentration. This
procedure follows that found in "Appendix B
Recalculation Procedure" of "Interim Guidance on Use
of Water-Effect Ratios for Metals" (U.S. EPA, 1994).


2.1.1   Rationale for Use of the Resident
        Species Deletion/Substitution Procedure

    This procedure is relevant for site-specific
modification of national ESGs because (1) sensitive or
insensitive benthic or water column species used to
derive the national ESG may not occur at the site, (2)
water column species or water column life-stages of
species that also have benthic life-stages that do occur
at the site may not be relevant to the ESG derivation, or
(3) water column species and nonresident benthic
species may be toxicological surrogates for
taxonomically related but untested resident benthic
species or benthic life-stages of water column species.
The procedure considers the need to retain acute
values for nonresident benthic species or resident and
nonresident water column life-stages of benthic
species as toxicological surrogates for taxonomically
related but untested resident benthic species.  The
rules that permit deletion of data are intentionally
restrictive because national databases often contain
data for only a relatively small number of genera and
deletion of data on nonresident species expected to
represent the sensitivities of untested resident species
must be avoided. Toxicity testing with resident benthic
species may be needed to complete minimum database
requirements for deriving guidelines. EPA encourages
testing of resident benthic species to permit deletion of
acute values for water column or nonresident benthic
species that serve as surrogates for untested resident
benthic species. In addition, it is important to obtain
data on recreationally important, commercially
important, and endangered or threatened species found
at the site.

    For the purposes of this site-specific guidelines
document, resident organisms that "occur at the site"
are defined as those benthic species, genera, families,
orders, classes, or phyla of organisms that would be
expected to occur periodically or commonly at the
location where sediments contain chemicals in excess
of the ESG.  However, note that determining the species
expected to occur at the site will require expanding the
definition of site. This includes organisms that would
be expected to occur continually, seasonally, or
intermittently; those now absent because of
anthropogenic causes; and those that will be used as
toxicological surrogates. Organisms absent because of
physical changes,  such as the impoundment of rivers,
are not considered resident.  Creation of a list of
resident species will require the use of historical
species lists for the site and, possibly, biological
assessment databases from nearby reference sites.
Enlisting the help of experts on local aquatic fauna is
suggested to create the resident species list.

    Use of this procedure may increase, decrease, or
fail to change the national guideline value. If highly
sensitive species are not present at the site, an increase
in the guideline value is likely. If the number of acute
values is decreased, the guideline value will likely
decrease.  Additional testing may reveal uniquely
sensitive or resistant species that could lower or raise
the guideline value. Because water column and benthic
species have similar sensitivities (Di Toro et al., 1991;
U.S. EPA, 2000c), deletion of acute values for certain
water column species or life-stages, and replacement
with newly obtained data on benthic organisms would,
on the average, not be expected to markedly alter the
guideline value.
                                                                                             2-1

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  Cond
nducting Site-Specific ESG Modifications
 2.1.2   Details of the Resident Species
         Deletion/Substitution Procedure
     The basic principle of the Resident Species
 Deletion/Substitution Procedure is to permit deletion of
 all acute values for nonresident benthic species/life-
 stages and water column species/life-stages when
 acute values for all resident benthic species/life-stages
 in a family have been tested. While implementing this
 procedure, EPA encourages additional testing to
 overcome conservatism in rules that prohibit deletion
 of acute values that may be surrogates for acute values
 of untested resident benthic species in a family.  Ten
 rules MUST be followed:

 1.   Literature search: A search MUST be conducted
     of the scientific literature and unpublished reports
     available since the date of the literature search for
     the ESG document to obtain all acceptable acute,
     chronic, and other toxic it y data from water-only
     and sediment toxicity tests. Of particular interest
     are data such as those in Section 3, Section 4, or
     Appendix A of the chemical-specific ESG
     documents. The toxicity test results MUST be
     subject to rules for data acceptability found in
     Stephan et al. (198S), or subsequent guidance.  The
     most important component of the review process is
     that a qualified reviewer MUST use good judgment
     in the review of data, experimental designs, and
     methods used. This process MUST include both
     published and unpublished data. Discarding good
     data needs to be avoided. Rejection of bad data is
     REQUIRED. The resultant acute toxicity daiaset is
     the new "national database." The deletion process
     that follows pertains only to acute toxicity values,
     and the resultant database is termed the "site-
     specific database."  (In the future, EPA intends to
     develop a database of toxicity test results that
     have been screened for applicability to sediment
     guidelines derivation. Until  this database becomes
     available, those wishing to derive site-specific
    ESGs MUST conduct the literature search to obtain
     the new national database.)

2.   Applies to ALL data: In all cases, deletion and
    substitution decisions MUST apply to the entire
    national database, not just to the data for  sensitive
    species.

3.   Resident benthic species in a class, order, or
    phylum have not been tested, but acute values for
    nonresident species in that class, order, or phylum
    are available:  If the national database contains
    acute values for benthic or water column life-
    stages of species in a class, order, or phylum from
                                                       which resident benthic species have not been
                                                       tested, the site-specific database MUST contain all
                                                       data for species in that class, order, or phylum
                                                       found in the national database.

                                                   4.   All resident benthic species in a family tested: If a
                                                      'family contains one or more benthic genera that
                                                       occur at the site, and if the national database
                                                       contains every one of the resident species in these
                                                       genera, the site-specific database MUST contain
                                                       every one of these species that occur both at the
                                                       site and in the national database, but MUST NOT
                                                       contain  any nonresident species in the genus or
                                                       nonresident genera in the family.

                                                   5.   Not all resident benthic species in a family tested:
                                                       If a family contains one or more benthic genera that
                                                       occur at the site, but the national database does
                                                       NOT contain every one of the resident benthic
                                                       species in each genus, the site-specific database
                                                       MUST contain al) of the species in the national
                                                       database that are in that family.

                                                   6.   Benthic  life-stages of all resident species in a
                                                      family tested and water column life-stages of one
                                                       or more of these resident species tested: If a family
                                                       that occurs at the site contains one or more genera
                                                       with species having both benthic and water
                                                       column  life-stages, and if the national database
                                                       contains acute values on the benthic life-stages for
                                                       every one of the resident species and acute values
                                                       for water column life-stages for one or more of
                                                       these species, the site-specific database MUST
                                                       contain every one of these acute  values for the
                                                       benthic life-stages of the species that occur at the
                                                       site, but MUST NOT contain any acute values for
                                                       nonresident benthic species or life-stages or acute
                                                       values for the water column life-stages of any
                                                       species in the family.

                                                   7.   Not all benthic life-stages of resident species in a
                                                      family tested and nonresident benthic life-stages
                                                       or water column life-stages of resident or
                                                       nonresident species have been tested: If one or
                                                       more genera in a family that occurs at the site
                                                       contain species with  both benthic and water
                                                       column  life-stages, but the national database does
                                                       NOT contain acute values on the benthic life-
                                                       stages for every one of the resident species in all
                                                       resident genera, the site-specific  database MUST
                                                       contain acute values  for all benthic and water
                                                       column  life-stages for resident and nonresident
                                                       species in all genera that are in the national
                                                       database,
2-2

-------
                        Site-Specific Equilibrium Pnrtltioning Sediment Guidelines (ESGs): Non
 8.   Minimum data requirements: If the site-specific
     database does not meet the minimum database
     requirements in the "Guidelines for Deriving
     Numerical National Water Quality Criteria for the
     Protection of Aquatic Organisms and Their Uses"
     (Stephan et al., 1985), a site-specific sediment
     guideline value "can not be derived and the national
     sediment quality guideline value applies to the site
     until additional acceptable toxicity tests are
     completed that meet the minimum data
     requirements.

 9.   Required and optional toxicity testing: Toxicity
     tests MUST be conducted to complete minimum
     data requirements for deriving the WQC FCV or to
     ensure that data are available on at least one
     benthic species in each animal or plant class critical
     to the site and each resident benthic species, or an
     acceptable surrogate species, listed as threatened
     or endangered under Section 4 of the Endangered
     Species Act (ESA). Toxicity tests can be
     conducted on resident benthic species or benthic
     life-stages of resident species for which only water
     column life-stages have been tested to complete
     data requirements that permit deletion of data on
     nonresident benthic species and water column life-
     stages of either resident or nonresident species
     (see rules 3 to 7 above). It may  be most helpful to
     repeat toxicity tests on four or more of the most
     sensitive resident genera in the  national or site-
     specific databases using measured chemical
     concentrations and improved testing methodology
     to permit replacement of acute values from
     previously published  tests.

 10.  Critical species testing: If data are not available
     for a critical resident benthic species that is
     threatened, endangered, commercially important,
     recreationally important, or ecologically important,
     data should be generated for that species or an
     acceptable surrogate species (see Stephan et al.
     [ 1985] for details on test requirements).

     Step-by-step examples of the deletion procedure
used to modify national WQC, a procedure not
substantively different from this Deletion/Substitution
Procedure for modifying national ESGs, are illustrated
in Appendix B of the "Interim Guidance on
Determination and Use of Water-Effect Ratios for
Metals" (U.S. EPA, 1994).  This deletion process is
designed to ensure the following:

a.   Each benthic species, or benthic life-stage of a
    species that  has both benthic and water column
    life-stages, that occurs both in the national dataset
     and at the site also occurs in the site-specific
     dataset.

 b.   Each species having a benthic life-stage that
     occurs at the site, but does not occur in the
     national dataset, is represented in the site-specific
     dataset by ALL species in the site-specific dataset
     that are in the same genus.

 c.   Each genus having species with a benthic life-
     stage that occurs at the site, but does not occur in
     the national dataset, is represented in the site-
     specific dataset by ALL genera in the national
     dataset that are in the same family.

 d.   Each order, class, and phylum that occurs both  in
     the national dataset and at the site is represented
     in the site-specific dataset by  one or more benthic
     or water column species in the national dataset that
     are closely related to a species that occurs at the
     site.

 e.   Testing is encouraged or required to add new acute
     toxicity data to the site-specific dataset on critical
     resident benthic species that are threatened,
     endangered, commercially important, recreationally
     important, or ecologically important, or to permit
     deletion of data on nonresident benthic species,


 2.1.3   Derivation of the Site-Specific ESG

     Following the Deletion/Substitution Procedure
 above, the guidelines for the derivation of a FCV
 (Stephan et al., 1985) must be applied to the site-
 specific database. Species mean acute values (SMAVs)
 and genus mean acute values (GMAVs) must be
 calculated. If minimum database requirements are met,
 except those that require water column species, a site-
 specific final acute value (FAVSS) is calculated. If an
 acute value for a critical resident benthic species that is
 threatened, endangered, commercially important,
recreationally important, or ecologically important is
lower than the FAV, this value becomes the FAV.
Finally, the FAV is divided by the final acute-chronic
ratio (FACR) from the ESG document, or the new site-
specific FACR (FACRSS) derived using new chronic
data from the literature search, to derive the site-
specific FCV (FCVSS). Acute-chronic ratios (ACRs) for
sensitive benthic species do not differ from those of
the entire WQC database of acute-chronic ratios (U.S.
EPA, 2000c,e); therefore, the deletion procedure does
not apply to the chronic toxicity database for a
substance for which an ESG is available.
                                                                                                      2-3

-------
  Conducting Site-Specific ESG Modifications
     The site-specific ESG, on an organic carbon basis,
 is the product of the /^ from the ESG document and
 theFCVc
       'ss
                   ss
                                              (2-1)
 This ESG0C gj and the procedures in Section 5 of the
 relevant ESG document should be used to derive the
 95% confidence intervals.

    All steps in the derivation of a site-specific ESG
 must be documented in a report that includes a table
 listing (1) all species and their life-stages used to derive
 SMAVs, (2) all species and life-stages deleted, (3) test
 conditions of the SMAV and GMAV data used for
 calculation, and (4) references for the source of the
 acute values. This table should be similar to Appendix
 A in the ESG documents. The new calculated FAVSS,
 FACRSS, FCVSS, and ESG,-^ ss should appear after the
 tabular presentation of toxic j ty data. All toxicity data
 on all aquatic resident animal and  plant species,
 especially critical resident benthic species that are
 threatened, endangered, commercially important,
 recreational!y important, or ecologically important, must
 be listed to permit comparisons between their
 sensitivities and the FAV orFCV, All other species
 known to be resident to the site and the source of this
 information must also be listed.
2.2   Bioa vail ability Procedure

    The Unavailability Procedure is intended to result
in a site-specific ESG that appropriately replaces the
national ESG when there are pertinent differences in the
bioavailability of the chemical in the sediment from the
site, due to partitioning phases in the sediment, in
addition to organic carbon, or the presence in the
sediment of undissolved chemical. These alternate
partitioning phases may include, but not be limited to,
interstitial dissolved organic carbon (DOC), pure
chemical, or soot carbon. This approach assumes that
the "true" bioavailable concentration can be
reasonably measured or estimated as "freely-dissolved"
chemical in the interstitial water, which can then be
compared with the WQC FCV. Sediments in which the
freely-dissolved interstitial water concentration is less
than the WQC FCV would not be expected to cause
toxicity to benthic organisms and are acceptable for
maintaining the presence of the benthic community.
2.2.1  Rationale for Use of the Bwavailability
        Procedure

    EPA's sediment guidelines for nonionic organic
chemicals are based on the EqP model. This model
uses a two-phase approach:  particulate-associated
chemical and dissolved interstitial chemical, where the
total concentration in sediment equals the
concentration in the paniculate phase plus the
concentration freely-dissolved in interstitial water. If
alternate phases exist in a sediment, it is possible that
the EqP model for sediment guidelines may not directly
apply. In  these cases, the toxicity of the sediment
cannot be predicted from the two-phase carbon-
normalized sediment concentrations and the KQC
because, in addition to organic carbon, combustion
particles, pure chemical, or other properties of the
sediments at the site may alter bioavailability. For these
sediments, site-specific criteria modification using the
Bioavailability Procedure is warranted.

    The Bioavailability Procedure compares the
bioavailable, freely-dissolved interstitial water
concentration with the WQC FCV found in the
sediment guideline document, or the site-specific final
chronic value derived using the Resident Species
Deletion/Substitution Procedure above. If the
interstitial water concentrations are below the WQC
FCV, the concentration of the chemical is below the
site-specific ESG. The three approaches EPA
recommends for estimating or measuring the freely-
dissolved chemical concentration in interstitial water
require procedures appropriate for obtaining and
chemically analyzing interstitial water. The approaches
assume that the chemical is distributed into three
phases: freely-dissolved, DOC-associated, and
paniculate. The Bioavailability Approach assumes that
the use of the two-phase based K(l(: in calculating the
freely-dissolved concentration from sediment
concentrations is  not appropriate for this sediment, and
furthermore, that the bioavailable concentrations can
be determined directly from an interstitial water sample.
The analytical procedures presented below employ the
best presently available technology for obtaining
interstitial water, chemically analyzing interstitial water
chemical concentrations, and estimating or measuring
the freely-dissolved concentration of the chemical.
2-4

-------
                                      uilibrium Partitioning Sediment 1; uwielines (ESGs): Noniemk Organic*
 2.2.2   Details of the Bioavailability Procedure

     The problem of adequately collecting and
 processing interstitial water samples is well
 documented (Adams, 1991; Schullset al., 1992; Ankley
 and Schubauer-Berigan, 1994; ASTM, 1994; Ozretich
 and Schults, 1998). Artifacts from the procedures can
 preclude accurate determination of interstitial water
 contaminant concentrations. The following procedures
 are recommended to minimize effects of interstitial water
 sample collection and processing for nonionic
 organics.


 2.2.2.1  Sampling Interstitial  Water

     In general, centrifugation without subsequent
 filtration results in the highest concentrations of metals
 and nonionic organic compounds in interstitial water
 from fine-grained, high water content sediment.
 Because the objective of centrifugation is to obtain
 interstitial water containing material smaller in diameter
 than that which would pass through a 0.45/^m filter (i.e.,
 only the "soluble fraction"), any combination of
 gravitational force (speed with effective radius) and
 time that would settle the particles of greater effective
 diameter to the sediment-interstitial water interface
 would be acceptable. For example, the following
 recommended procedure resulted in 25 to 60 mL of clear
 interstitial water from several industrialized waterways
 including the Lauritzen Channel in northern San
 Francisco Bay (Lee et al., 1994; Swarte et al., 1994). A
 150 g portion of wet sediment in a 150 mL glass
 centrifuge bottle (Corex, Corning®) is spun at 5,000 rpm
 (2,590-4.080 x |) in a fixed angle rotor (GSA, Sorvall®)
 for 90 min at 4°C to obtain maximum volumes. When
 completed, the centrifuge bottle is back-lighted and the
 interstitial water is gently aspirated through Teflon®
 tubing (drawn to a fine  point) and placed deep into the
 bottle next to the sediment/water interface. The
 interstitial water passes through a stainless steel needle
 directly into a glass  vial. This procedure has been
 shown to reduce losses of organic constituents
 (Ozretich and Schults, 1998). At this point, subsamples
 can be taken for measurement of DOC (-3 mL). The
 DOC-associated components (12-40 mL) (Landrum et
 a!., 1984; Ozretich et al., 1995) and the remaining
 interstitial water (12-40 mL) can be extracted in the
 receiving vial for the determination of the total chemical
 concentration (freely-dissolved fraction plus the
 fraction bound to dissolved DOC material). Collecting
 and subsampling the interstitial water must be done
 within 2 hours to avoid complications from the
potential formation of de novo particles from oxidation
of reduced iron. It is clear that cleanly sampled
 interstitial water is important, as the presence of a
 particle of sediment could result in erroneously high
 concentrations; on the other hand, if the time periods
 before extractions are long or filtering and excessive
 sample handling has occurred, erroneously low
 concentrations would result as the chemicals are
 sorbed to surfaces.


 2.2.2.2  Quantification of Dissolved and DOC-
         Associated Phases

    Once an adequate interstitial water sample has
 been obtained, the quantity of contaminant present
 must be accurately determined. Liquid-liquid (L-L)
 extraction methods are routinely used to extract total
 water samples and  the DOC-associated fraction.
 Commonly used L-L procedures (U.S. EPA, 1986) for
 total water samples include the use of separately
 funnels (Method 35 IOC) and, when emulsions are
 encountered, continuous extraction (Method 3520C).
 PAHs and chlorinated pesticide compounds are
 typically quantified in 1 mL extracts from 1L samples
 by GC/MS (Method 8270C) in the scan mode with
 quanlitation limits of 10 fJ.g/L (PAHs), which exceeds
 the solubility of many of the higher molecular weight
 compounds for  which these combined methods were
 developed. Clearly, the recommended volumes and
 mass spectrometer operational conditions of these
 standard procedures are not adequate to quantify the
 same compounds in easily obtained volumes of
 interstitial water at concentrations near their WQC
 FC Vs. Alternatively, the gentle L-L extraction
 procedure used for small volumes of interstitial water is
 recommended (Ozretich et a)., 1995), because it is
 conceptually similar to continuous extraction in
 providing long solvent-sample contact time while
 eliminating emulsions. In addition, it uses fewer
 extraction solvents and no elaborate, hard-to-clean
 glassware. Because the need to do a site-specific
 determination of freely-dissolved interstitial water
 concentrations is related to concerns regarding the
 applicability of carbon-normalized concentrations of a
 specific compound, the mass spectrometer need not be
operated in the scanning mode, but may be optimized
only for the mass fragmentation ions of the compound
of concern by operating in the selected ion mode, and
limiting the ions to 2-5 with maximum dwell times, as is
used for chlorinated dioxins and furans (Method 8280)
(U,S. EPA, 1992). By combining these mass
spectrometer modifications with smaller sample sizes
reduced to smaller volumes (50-250 fiL) but larger
injection volumes (2-5 /*L\ instrument dependent),
sample quantitaiion limits on the order of 10-50 ng/L
can be achieved (Ozretich et al., 1995).
                                                                                                    2-5

-------
  Conducting Site-Specific ESG Modifications
 2.2.2.3  Calculating the Freely-Dissolved,
         Bioavailable Concentration

     The bioavailable interstitial water concentration of
 a chemical can be determined in the following three
 ways:

 1.   It can be assumed that the total interstitial water
     concentration (Cw) for a nonionic organic
     chemical with a low to intermediate octanol-water
     partition coefficient (KQW) value is equivalent to
     the dissolved concentration; that is,  the freely-
     dissolved interstitial water concentration equals
     the total dissolved interstitial water concentration.
     However, this approach may be problematic
     because high concentration of DOC  can be present
     in interstitial water. Nonionic organics are known to
     bind to this material, causing a reduction in their
     bioavailability. Therefore, a L-L extraction of
     interstitial water would contain the freely-dissolved
     and the DOC-associated chemical, overestimating
     the true bioavailable concentration.  The
     magnitude of the overestimate would depend on
     the affinity of the DOC for the chemical of interest.
     This affinity is represented by the partition
     coefficient K^^, which  is the ratio of the chemical
     concentration bound to the DOC to the freely-
     dissolved  interstitial water concentration.

1    It can be determined that the freely-dissolved
     interstitial water concentration is the difference
     between the total interstitial water concentration
     and the DOC-associated concentration. This
     method depends on the DOC-associated
     concentration being operationally defined and
     limited by the methodology (e.g., the separation of
     total and bound fractions by CIS columns)
     (Landrum et al., 1984; Ozretich etal, 1995).
     However,  use of this procedure doubles the
     number of samples that need to be taken and
     analyzed, and may require monitoring of DOC
     retention (Ozretich et al., 1995). When using a
     similar procedure to separate the DOC-associated
    chemical, the freely-dissolved concentration can be
    directly measured (Burgess eta!., 1996). This
    approach should be used only if acceptable
    concentration mass balances (approximately 90%)
    of the DOC, dissolved, and total chemical are
    available (R.M. Burgess, U.S. EPA, Narragansett,
    RJ, personal  communication).

3.   It can be calculated from the total concentration
    using the DOC concentration and the K    of the
    compound from Equations 2-2 and 2-3, where the
    freely-dissolved (bioavailable) interstitial water
    chemical concentration is
    and the percentage of the total compound that is
    freely-dissolved is
%Cd =
                       + I) x 100
(2-3)
    This method depends on determination of DOC
    (kg/L) and K^^. Determining the concentration of
    DOC in water is routine.  However, identifying valid
         va'ues 's problematic at this time.
    Generally, it would be inappropriate to use K^ to
represent the partition coefficient of a chemical to DOC
material in calculating freely-dissolved concentrations
because paniculate organic matter, represented by K^,
is generally described as very nonpolar and insoluble
in interstitial water. Conversely, dissolved or DOC,
represented by K^^, is relatively more polar and
soluble in interstitial water (Chiou et al., 1986).
Fundamental differences in solubility of these types of
organic carbon in sediments will most likely also cause
differences in the magnitude of their respective
partition coefficients for a given chemical. Therefore,
they should not be used interchangeably.

    When available, K^^ values have been plotted
versus Kovf values for chemicals with log,0ATow values
<6.5, and a generally linear relationship is observed
(Ozretich et al., 1995; Burgess et al., 1996).  For example,
Ozretich et al. (1995), using the C-18 separation
technique, found the following relationship (Equation
2-4) between published ATOW and measured ^DOC
values of multiple PAHs and chlorinated hydrocarbons
that were placed in interstitial water and allowed to
equilibrate with unfractionated DOC.
                    io
                                              (2-4)
    Using this equation, computed KQQC values from
the endrin and dieldrin ESG documents were compared
with KQC values (Table 2-1), and the percentage of the
total compound that is freely-dissolved, calculated
using Equation 2-3, was determined for a range of DOC
concentrations that are likely to be encountered in
interstitial water (Table 2-2). The greatest percentage of
a guideline chemical that would be bound to DOC
material using K^^ is approximately 50% for dieldrin
2-6

-------
                       Site-Specific Equilibrium Partitioning Sediment Guidelines (ESGs): Nonionic Organics
(logmA:ow =5.37) at70rngDOC/L. Using K^in
Equation 2-4, approximately 93% of dieldrin would be
computed to be bound at this DOC level. Therefore,
using the total concentrations as bioavailable would
overestimate the freely-dissolved concentration by a
factor of 14 if partitioning were assumed to be more
soil-like using K^ in Equation 2-2 or by a factor of 2
using K^.

    For the purposes of this document, it is
recommended that Equation 2-4 be used with Equation
2-2 to calculate the Cd, because KDQC is more
representative of binding to dissolved DOC material
than ^.
                                                      2.2.3  Derivation of the Site-Specific ESG
                                                          This calculated or measured Cd is compared with
                                                      the WQC FCV from the individual ESG documents.  If
                                                      the freely-dissolved interstitial water concentration is
                                                      less than the FCV, toxicity would not be expected and
                                                      the sediment would be acceptable for maintaining me
                                                      presence of benthic organisms. Alternatively, the
                                                      interstitial water concentration can be compared with
                                                      the FCV derived using the Resident Species Deletion/
                                                      Substitution Approach.
Table 2-1. Computed organic carbon-normalized partition coefficients
   Compound
                                    Logi
                                                                                         Logi
   Endrin

   Dieldrin
                                       5.06

                                       5.37
3.84

4.12
4.97

5.28
aFrom corresponding ESG documents.
 Derived using Equation 2-4.
cFrom corresponding ESG documents using:
                                           = 0.983 x
                                                           + 0.00028.
Table 2-2.  Solutions to Equation 2-3 using A"l)Or values computed from Equation 2*4
DOC
(rng/L)
0
5
10
15
20
25
30
40
50
60
70
Endrin
(%free)
100
97
94
91
88
85
83
78
74
71
67
Dieldrin
(% free)
100
94
88
83
79
75
72
65
60
56
52
                                                                                                     2-7

-------

-------
 Section 3
 References
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 Mudroch A, MacKnight SD, eds. Handbook of
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 American Society for Testing and Materials (ASTM).
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 AnkleyGT.Schubauer-BeriganMK. 1994. Comparison
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 Ankley GT, Schubauer-Berigan MK, Dierkes JR,
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 DC

 Brungs WA. 1992. Synopsis of water-effect ratios for
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 DC

 Burgess RM, McKinney RA, Brown WA, Quinn JG.
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 Cniou CT, Malcolm RL, Brinton TI, Kile DE. 1986.
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 Di Toro DM, Zarba CS, Hansen DJ, Berry WJ, Swartz
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 Ho KT, McKinney RA, Kuhn A, Pelletier MC, Burgess
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 Maruya KA, Risebrough RW, Home AJ. 1996.
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 McGroddy SE, Farrington JW, Gschwend PM. 1996.
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Ozretich RJ, Schults DW. 1998. A comparison of
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centrifugation with aspiration yields reduced losses of
organic constituents.  Chemosphere 36:603-615.
                                                                                                3-1

-------
Ozretich RJ, Smith LM. Roberts FA. 1995. Reverse-
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Schults DW, Ferraro SP, Smith LM, Roberts FA,
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