UNITED STATES £N V 1 PQNMENT AL
"WASHING 10% DC
July 31, 1989 EPA-SAB-&ETFC-89-027
The Honorable William Reilly
Administrator
U.S. Environmental Protection Agency
401 M. Street, S.W.
Washington, D.C. 20460
Dear Mr. Reilly:
The Sediment Criteria Subcommittee of the Science Advisory
Board has completed its review of the Apparent Effects Threshold
(AET) Approach to setting sediment criteria. This approach was
developed by EFA's Region 10, Office of Puget Sound. The review
was conducted at the request of Region 10's Administrator, Mr.
Robie Russell, and was conducted on October 27 and 28 in Seattle,
Washington.
The AET approach is designed to identify adverse effects .due
to chemical contamination in sediments by determining specific
chemical concentrations above which adverse effects will always
occur. The method has major strengths in its ability to
determine biological effects and assess interactive chemical
effects. The method is considered by the Subcommittee to contain
sufficient scientific merit that, with appropriate validation, it
could be used to .estimate sediment quality at specific sites.
In the Subcommittee's opinion, the AET approach should not
be used to develop general, broadly applicable sediment quality
criteria. Some major limitations drive this opinion, including
the site specific nature of the approach, its inability to
describe cause and effect relationships, its lack of independent
validation, and its inability to describe differences in
bioavailability of chemicals on different sediments.
The Subcommittee recognizes the Apparent Effects Threshold
Approach as a credible step towards development of a technically
defensible and publicly acceptable tool for managing contaminated
sediments. The approach provides a constructive beginning
towards assessing the impact of mixtures of chemicals as they
occur in actual situations. Such innovative empirical approaches
that assess actual contamination and concomitant effects are
encouraged and applauded by the Subcommittee. However, the
Subcommittee also recommends that neither the AET or any other
existing methodology be used as a stand-alone decision tool to
provide absolute pass/fail criteria to dictate regulatory action.
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The Subcommittee has several suggestions for strengthening
the AET approach. These include utilizing replicate sediment
samples for assessments, devising criteria for selection of
reference sites, including considerations of physical factors,
and developing measures of variance. In addition, the use of
both carbon normalization and benthic infaunal assays are
strongly supported by the Subcommittee.
The Subcommittee appreciates the opportunity to conduct this
scientific review. We request that the Agency formally respond
to the scientific advice transmitted in the attached report.
Sincerely
ENC
cci Rebecca
Martha Frothro
James M. Conlon
Robie Russell
Chris Zarba
Catherine Krueger
Donald Barnes
Dr '. 'Raymond Loehr, chairman
Executive Committee
Science Advisory Board
Dr. Kenneth Dickson, Chairman
Environmental Effects,
Transport and Fate
Committee
w./
L/
Dr. Robert^luggfet:
Sediment briteri
chairman
ubconunittee
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United States Office of the AdnMstrator SAB-EETFC-89-027
Environmental Protection Science Advisory Board July 1989
Agency Washington, D. C - 20460
4>EPA Report of the Sediment
Criteria Subcommittee
Evaluation of the Apparent
»
Effects Threshold (AET)
Approach for Assessing
Sediment Quality
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UN|TED STATES ENVIRONMENTAL PROTECTS AGENCY
I»V A ft H i ,\ r, t Q fj. o C 20460
July 31, 1989
EPA-SAE-EETFG-89-027
The Honorable William Reilly
Administrator
U.S. Environmental protection Agency ,L,t ^;,.:"' -
401 M. Street, s.w.
Washington, D.C. 20460
Dear Mr, Reilly:
The Sediment Criteria Subcommittee of the Science Advisory
Board has completed its review of the Apparent Effects Threshold
(AET) Approach to setting sediment criteria. This approach was
developed by EPA's Region 10, Office of Puget Sound. The review
was conducted at the request of Region 10'a Administrator, Mr.
Robie Russell, and was conducted on October 27 and 28 in Seattle,
Washington.
The AST approach is designed to identify adverse effects due
to chemical contamination in sediments by determining specific
chemical concentrations above which adverse effects will always
occur. The method has major strengths in its ability to
determine biological effects and assess interactive chemical
effects. The method is considered by the Subcommittee to contain
sufficient scientific merit that, with appropriate validation, it
could be used to estimate sediment quality at specific sites.
In the subcommittee's opinion, the AIT approach should not
be used to develop general, broadly applicable sediment quality
criteria. Some major limitations drive this opinion, including
the site specific nature of the approach, its inability to
describe cause and effect relationships, its lack of independent
validation, and its inability to describe differences in
bioavailability of chemicals on different sediments*
The Subcommittee recognizes the Apparent Effects Threshold
Approach as a credible step towards development of a technically
defensible and publicly acceptable tool for managing contaminated
sediments. The approach provides a constructive beginning
towards assessing the impact of mixtures of chemicals as they
occur in actual situations. Such innovative empirical approaches
that assess actual contamination and concomitant effects are
encouraged and applauded by the Subcommittee. However, from a
scientific standpoint, the Subcommittee recommends that multiple
approaches be used to estimate sediment quality, develop
criteria, and guide regulatory action, since the AET approach
alone provides insufficient certainty for broad-scale decision
making.
-------
The Subcommittee has several suggestions for strengthening
the AET approach. These include utilizing replicate sediment
samples for assessments, devising criteria for selection of
reference sites, including considerations of physical factors,
and developing measures of variance. in addition, the use of
both carbon normalization and benthic infaunal assays are
strongly supported by the Subcommittee.
The Subcommittee appreciates the opportunity to conduct this
scientific review. We request that the Agency formally respond
to the scientific advice transmitted in the attached report.
Sincerely
ENC
cc: Eebecca Manner
Martha Prothro
James M. Conlon
Mobie Russell
Chris Zarba
Catherine Krueger
Donald Barnes
Dr. 'Raymond Loehr, Chairman
Executive Committee
Science Advisory Board
L
Dr. Kenneth Dickson, Chairman
Environmental Effects,
Transport and Fate
Committee
Dr. .Robertyipigget,
Sediment criteri
Chairman
ubcowmittee
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ABSTRACT
This report presents the conclusions and recommendations of
the U.S, Environmental Protection Agency's Science Advisory Board
summarizing a review of EPA's Apparent Effects Threshold Approach
for setting sediment quality criteria. The AET approach
integrates data from bulk sediment chemistry, sediment bioassays
and infaunal species measurements to provide estimates of
sediment chemical concentrations above which adverse
environmental effects will occur. An objective of the AET
methodology is to identify adverse effects due to chemicals
occurring in mixtures in sediments by determining specific
chemical concentrations above which adverse effects will always
be found. The method has major strengths in its ability to
determine biological effects and assess interactive chemical
effects. The method is considered by the Subcommittee to contain
sufficient scientific merit that, with appropriate validation of
the AET values, it could be used to establish sediment quality
values for use at specific sites. In the Subcommittee's opinion,
the AIT approach should not be used to develop general, broadly
applicable sediment quality criteria. Some major limitations
drive this opinion, including the site specific nature of the
approach, its inability to describe cause and effect
relationships, its lack of independent validation, and its
inability to describe differences in bioavailability of chemicals
on different sediments. The Subcommittee has several suggestions
for strengthening the AiT approach including: building in
replicate sediment samples to assessments, devising criteria for
selection of reference sites, including considerations of
physical factors, and developing measures of variance.
Kay words; Sediment•, AIT? Apparent Effects Threshold
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U.S. ENVIRONMENTAL PROTECTION AGENCY
NOTICE
This report has been written as a part of the activities of
the Science Advisory Board, a public advisory group providing
extramural scientific information and advice to the Administrator
and other officials of the Environmental Protection Agency. The
Board is structured to provide a balanced expert assessment of
scientific matters related to problems facing the Agency. This
report has not been reviewed for approval by the Agency; and,
hence, the contents of this report do not necessarily represent
the views and policies of the Environmental Protection Agency or
other agencies in Federal government. Mention of trade names or
commercial products does not constitute a recommendation for use.
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U.S. ENVIRONMENTAL PROTECTION AGENCY
SCIENCE ADVISORY BOARD
ENVIRONMENTAL EFFECTS, TRANSPORT AND FATE COMMITTEE
SEDIMENT CRITERIA SUBCOMMITTEE
ROSTER
CHAIRMAN
Dr. Robert Huggett
Professor of Marine Science
Virginia Institute of Marine Science
School of Marine Sciences
College of William and Mary
Gloucester Point, Virginia 23062
VICE CHAIRMAN
Dr. Rolf Hartung
Professor of Environmental Toxicology
University of Michigan
3125 Fernwood Avenue
Ann Arbor, Michigan 48108-1955
MEMBERS
Dr. William J. Adams
Monsanto Company (U4G)
800 N. Lindbergh Blvd.
St. Louis, Missouri 63167
*** Dr. Peter M. chapman
Partner
E.V.S. Consultants
195 pemberton Avenue
North Vancouver, B.C.
Canada V7P 2R4
Dr. Kenneth L. Dickson
University of North Texas
Institute of Applied Sciences
P.O. Box 13078
Denton, Texas 76203
Dr. Benjamin C. Dysart III
Professor of Environmental and Water
Resources Engineering
401 Rhodes Engineering Research Center
Clentson University
Clemson, South Carolina 29634-0919
Dr. Eugene Kenaga
Consultant (Ret*/Dow)
1584 E* Pine River Road
Midland, Michigan 48640
*** Dr. Chapman served on the Subcommittee until December 6, 1988,
iii
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Dr. Frederic K. Pfaender
Department of Environmental Sciences
and Engineering
University of North Carolina
Chapel Hill, ^North Carolina 27599-7400
Dr. Y. Peter Sheng
Professor, Department of coastal and
Qceanographic Engineering
336 Weil Hall
University of Florida
Gainesville, Florida 32611
SUBCOMMITTEE LIAISONS
Dr. Robert M. Engler
(CEWESEP-D)
Waterways Experiment Station
U.S. Army Corps of Engineers
P.O. Box 631
vicksburg, Mississippi 39180
Dr. Chris Ingersoll
National Fisheries contaminant
Research Center
U.S. Fish and Wildlife Service
Route 2
Columbia, Missouri 65201
Dr. H. Suzanne Bo1ton
NGAA-DOG
Office of Legislative Affairs
(LAX-2)
Herbert c. Hoover Building
loom 5222
Washington, D.C* 20230
SCIENCE ADVISORY BOARD STAFF
Ms. Janis C. Kurtz
Environmental Scientist & Executive Secretary
U.S. Environmental Protection Agency
Science Advisory Board
401 M Street, s.W.
Washington, D.C. 20460
iv
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TABLE OF CONTENTS
l.o Executive Summary- ................ l
2,0 introduction .................... 2
2.1 Request for Science Advisory Board Review . . , 2
2,1.1 Charge to the subcommittee 2
2.2 Subcommittee Review Procedures ........ 2
2.3 Expected Future Activities * . . 3
3.0 Evaluation of the Apparent Effects Threshold Approach 4
3,1 Quality of Data for AET Determination 4
3.2 Determining spatial Extent of Contamination . . 5
3.3 Field Applicability and Site Specificity ... 6
3.4 Cause-and-Effect Relationships ........ 6
3.5 Endpoint Considerations .,, .... 8
3.6 Complex Mixtures .......... 10
3.7 Physical Factors . . ........ 11
3.8 Carbon Normalization ............. 11
3.9 Uncertainties in the AIT 12
4.0 sumraary of Subcommittee Recommendations ..*.., 15
Appendix A - Briefing Report to the EPA Science Advisory Board:
The Apparent Effects Threshold Approach
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1.0 EXECUTIVE SUMMARY
The Apparent Effects Threshold (AET) approach for deriving
sediment quality values integrates data from bulk sediment
chemistry, sediment bioassays and infaunal species measurements
to provide estimates of sediment cheaical concentrations.
Concentrations above these estimates are thought to result in
adverse environmental effects. An objective of the AET
methodology is to identify adverse effects due to chemicals
occurring in mixtures in sediments by determining specific
chemical concentrations above which adverse effects will always
be found.
The major strengths of the approach are a) the fact that
both infaunal analyses and laboratory bioassays are incorporated
to determine biological effects and b) the fact that the approach
has the ability to incorporate interactive cheaical effects, such
as synergism and antagonism under the specific conditions
encountered in the environment where the AET is applied. The
method is considered by the Subcomnittee to contain sufficient
scientific merit that, with appropriate validation of the AET
values, it could be used to establish sediment quality values for
use at specific sites.
The major limitations of the AET method are a) its site-
specific nature b) its inability to describe cause and effect
relationships for specific chemicals c) its lack of independent
validation of the AIT values and 4) its inability to describe
differences in bioavailability of chemicals on different
sediments. These factors restrict the applicability of the
specific AEt values to the locality and conditions under which
they were developed. In the Subcommittee's opinion, the AET
approach should not be used to develop general, broadly
applicable sediment quality criteria.
The validity of the AET estimates can be improved by formal-
izing criteria, designating reference sites, and developing
measures of uncertainty for specific AET values. The
Subcommittee recommends that AET values be derived based on more
than one sediment bioassay, and that benthic infaunal analyses be
included in AET development. in addition, the accuracy of AET
values can toe assessed by comparison with endpoints and through
other experimental approaches that permit examination of the
major convergences and divergences in the values.
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2.0 INTRODUCTION
2.1 Request for Science Advisory Board Review
At the request of the Regional Administrator of EPA's Region
10, the Science Advisory Board (SAB) agreed to conduct a
scientific review of the Apparent Effects Threshold (AET)
approach. The* SAB's Environmental Effects, Transport and Fate
Committee authorized the formation of a Subcommittee to perform a
series of tasks related to the technical aspects of sediment
quality assessment and criteria development, with the approval of
the Board's Executive Committee.
2.1.1 Charge to the Subcommittee
This review is the first to be completed in a series of SAB
reviews related to sediment quality criteria. Preliminary
reviews focus on approaches to examining non-ionic organic
contaminants. Specifically, the charge accepted by the
Subcommittee is to:
a) Evaluate individually the scientific and technical
foundations for the various methodologies available to the Agency
to estimate sediment toxicity and biological impact of contam-
inated sediments in situ.
b) Evaluate the feasibility of utilizing each methodology
to determine extent of contamination and risk posed to the envi-
ronment and human health,
c) Identify research directions that would provide informa-
tion to strengthen each methodology.
d) Conduct a technical review of documents provided by the
Agency that compare and contrast the scientific and technical
strengths and weaknesses of the methodologies available to the
Agency to estimate sediment toxicity and biological impact of
contaminated sediments insitu.
2.2
The Sediment Criteria Subcommittee met on August 8 and 9,
1988, in Denver, Colorado, to assess the Agency's activities
regarding contaminated sediment and to explore avenues for
providing oversight. A second meeting was held on October 27 and
28, 1988, in Seattle, Washington. Informative and well-prepared
briefings were provided on the objectives, historical perspective
and technical components of the AET. The briefings were supported
by extensive documentation provided to Subcommittee members prior
to the meeting. Both the briefings and the documentation were
considered by the Subcommittee to be very well done and relevant
to the issues under review. This preparation and support was
provided by Region 10 staff and associated contractors (PTI
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Environmental Service, Inc.). The Environmental protection Agency
is divided into 10 Regional Offices, and Region 10 serves the
states of Alaska, Washington, Oregon, and Idaho from its base in
Seattle, Washington.
The contamination present in Puget Sound was characterized.
Biological assays used in AET development were described.
Additional briefings highlighted the statistical procedures
utilized in the method, and procedures used to treat
uncertainties in both biological and chemical data. Comments
were heard from interested members of industry and the public,
and intended application of the nethod was described by the
Washington state Department of Ecology,
2,3 Expected Future Activities
The Sediment Criteria Subcommittee plans to review and re-
port on the technical appropriateness of the Equilibrium Parti-
tioning (IP) method in the near future. In addition, bioassay
procedures that are used as an integral part of the AET, EP and
other approaches will be subjected to review for scientific
adequacy. Other methods, including methods for assessing metal
contaminants, are expected to be developed and existing
approaches refined, and as this occurs, they will be transmitted
to the Subcommittee for review. The Contaminated Sediment
Technical Committee, established by EPA's Office of Water, is in
the process of preparing a manual which describes currently
available methods that may be applied to establishing sediment
criteria. The Subcommittee will comment on this manual in the
future.
During the course of these critical evaluation processes, it
is likely that areas for additional or future research will be
targeted. To facilitate the incorporation of these recommenda-
tions into EPA research planning, the Subcommittee may conduct a
review of the office of Research and Development's proposed Sedi-
ment Initiative. The time sequence of these proposed events is
contingent on their completion by Agency staff.
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3.0 EVALUATION OF THE APPARENT EPFBCT8 THRESHOLD APPROACH
The AET approach provides useful information for developing
the weight of evidence needed to make decision regarding
contaminants in sediment. The AET is a statistically-based
empirical approach which attempts to establish quantitative
relationships between sediment contaminants and resulting
biological effects. It has been developed using synoptic data on
chemical contaminants and biological effects (as assessed by
benthic infaunal analyses and sediment bioassays) at suspected
contaminated sites and reference sites. The AET represents a
credible step towards development of a technically defensible and
publicly acceptable tool for managing contaminated sediments.
The use of quantified data for the derivation of relation-
ships between exposure and effects is the only scientifically
justifiable basis for describing such relationships quantitative-
ly. Thus, the technical acceptability of the development of
sediment quality values depends upon the fidelity with which
measures of exposures and effects on the environment can reflect
"true" environmental conditions, and upon the characteristics of
the model that seeks to summarize these complex relationships in
the form of a descriptor of sediment quality.
The AET approach provides a constructive beginning toward
assessing the impact of mixtures of chemicals as they occur in
actual situations, as opposed to solely assessing the influence
of single chemicals under laboratory conditions. Its major
strength is its ability to assess impacts of contaminated
sediments on aquatic life. Innovative empirical approaches such
as the AET that assess actual contamination and concomitant
effects are encouraged and applauded by the Subcommittee.
3.1 Quality of Data for AET Determination
The subcommittee is concerned that several limitations of
the data sets used to develop the AET values have influenced the
interpretation of relationships between sediment contamination
levels and resulting biological effects. This concern steins in
part from the lack of true field replication of the chemistry and
bioassay data used in the development of the AET. The preponder-
ance of the chemical and bioassay data is based on single samples
from each site. While a sample may be divided into sub-samples
and chemical analyses and/or bioassays performed on sub-samples
(thus measuring the precision of the respective methods), there
is no estimate of the within-site variability of chemical
concentrations and sediment toxicity (as measured by sediment
bioassays}. Although in some cases {e.g., assessments of the
suitability of material for dredging) within-site variability is
less important than in other cases (e.g., determination of the
extent and significance of problem areas), some estimate of this
variability is considered necessary.
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On the other hand, the data base used to develop an AET does
contain an estimate of infaunal variability at each site, since
replicate field samples are independently analyzed. The
appropriate level of infaunal community structure analysis must
be carefully evaluated.and applied. Since there is no estimate
of the variance for any of the chemical concentrations, an
undefined uncertainty exists around the AET, The su*™™"***^*"*
recommends that future application of the AET include replicate
sediment samples for determination of chemical contaminantsand
for assessment of toxicitv. By so doing, the uncertainties can
be better defined and * stronger relationship between contaminant
levels and biological effects established. In addition, with
field replication data available on chemical contaminants, it may
be feasible to statistically estimate the variance of the
chemical data used in the development of the AET, a feature not
presently incorporated in this or most other field approaches*
3.2
One of the proposed uses of AET is to quantitatively define
the spatial extent of biological impacts associated with
contaminated sediments. Because the method depends on a
statistical comparison of test sites to reference sites, it is
critical that valid reference sites be determined. A crucial
factor in determining the location of the reference sites is that
they be physically similar to the test sites. Although several
sediment characteristics were considered in the selection of
reference sites (e.g. season, water depth, grain size, or organic
carbon content) and decisions were made using best professional
judgment, it does not appear that a formalized set of decision
criteria have been established. If inappropriate reference sites
are used, an assessment of whether or not a test site is impacted
is difficult. The Subcommittee recommends that criteria for
selecting reference sites be formalized. The
aeleetion/re-i action criteria need to be clearly defined and the
rationale for their choice explained.
Furthermore, it is important that the AET approach clearly
recognize and incorporate systematic temporal changes that may
impact both the materials present in the sediment and the effects
they may have. In reference areas there will be temporal as well
as spatial changes in the composition and functioning of the
resident faunal community. In impacted areas there will also be
temporal changes in the concentrations of chemicals as a result
of physical (burial, re-suspension, etc.), chemical (degradation,
sorption, etc.), and biological (biodegradation) processes.
Biologically, the community that is present at any site exists in
response to the matrix of chemical, biological and physical
factors that are present. Therefore, the presence of pollutants
represents a selective influence that may lead over time to a
community adapted to the conditions present, which may be
different than the reference area but not necessarily "impacted"
in a functional sense.
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In its development, the AET methodology has not clearly
addressed the influences of temporal factors on the distribution
of benthic biota and the bioavailability of sedimentary
contaminants. It would be useful to conduct repeated sampling
over some time period- at a few stations to establish whether
changes occur that would significantly alter the generated AET
value. Some Knowledge of how temporal changes impact the AST is
neededto characterize tie uncertainty thatmay be added by this
variable.
3,3 Fieia Applicability and Site Specificity
The AET values produced from the Puget Sound data appear to
work well in Puget Sound* The Subcommittee recognizes the merits
of the AET for identifying potential problem areas and potential
problem chemicals, since AET are currently being proposed for use
as part of a process that involves site-specific biological
testing in Puget Sound, as opposed to broader, more generic
application, this application seems to be consistent with the
Subcommittees recommendations.
However, application of Puget Sound AET to another location
or different physical setting must be done with extreme caution
because the effects of physical, chemical and biological factors
on AET are not well understood. For example, differences in
current and wave conditions from one site to another may lead to
very different bottom sediment compositions, even within the same
body of water. The density, size distribution, salinity and
degree of flocculation of sediments may be quite different at
different sites. Moreover, the AET's inability to address the
causality of biological response by a single chemical, although
not unique to the AET approach, must be taken into consideration.
Even though one can argue that an AET may be generically
protective, there is presently no evidence that AITs developed in
one place are protective in another environment.
High levels of chemical contamination may result in toxicity
to laboratory species, but may cause no alteration of the real
world benthos. This situation may indicate a potential problem
that is not yet realized due to such factors as adaptation,
hormesis (i.e., stimulation of growth and/or fecundity in the
presence of low levels of contamination or stress-induced vigor),
etc. such information is valuable and could be misinterpreted by
the AET as presently applied. Tha Subcommittee r«
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method does not provide a way of isolating biological effects
that are caused by one specific chemical when the same chemical
is present in a mixture of known and unknown chemicals sorbed to
sediment. Therefore the scientific defensibility of chenical-
specific AET values is .unknown. A logical conclusion is that the
AET method is not capable of demonstrating specific cause and
effect relationships for any one specific chemical. Furthermore,
the report provided to the Board ("Briefing Report to the EPA
Science Advisory Board" , page 15, see excerpt in Appendix A)
states that "... it cannot distinguish and quantify the
contributions of interactive effects, unmeasured chemicals or
matrix effects in environmental samples. M
The AET method can generate values for a wide variety of
chemicals. However, to assess th* general applicability of AETs.
the implied relationship between the chemical sediment
concentration and biological affect must be validated. The
following points are presented to support this contention;
1. The existing data set does not contain verification data
from experiments with spiked sediments or from toxicity identifi-
cation evaluations which would assess the accuracy of the AETs.
The work of Swartz with fluoranthene and amphipods is an example
of the type of study that could be done to assess AET
accuracy (Dr* Richard Swartz, EPA/QRD, Newport, Oregon; personal
communication) . Additionally, toxicity fractionation-
identification for specific chemicals from elutriate or liquid-
phase sediments at selected sites could be used.
2. The AET values for phthalates do not reflect the physi-
cal^chemical properties of this group of chemicals. it would be
expected that the AET values would increase for the more water
soluble, less toxic phthalates such as dimethyl and diethyl
phthalate. This is not the case. This may reflect an inadequate
data set for the phthalate class, which would improve with
additional sampling, but it also indicates a fundamental lack of
consistency with the existing literature on this class of
compounds. Belated comments can be made for some other chemicals.
It JLa y*«!ggHiiift^ttded that tha_-_data M|t__be ray4.«*a4_JEoy all tlia ABTs
in relation to their phsical-chemical roperties (e.g., Koc. Lo
P and water solubility) and feftair existing
properties (e.g., acut* versus chronic or genetic effects) for
tha wirot o^ •ftfc-l Jailin the sensitivit of 3UBT values to
parameters that are known to affect toxic! tv. These types of
data can be used as supportive evidence of cause-and-ef feet
relationships.
3, Several of the AETs are below existing acute and chronic
toxicity values for aquatic organisms based on aqueous exposure.
In water, most chemicals are assumed to be bioavailable, with
some exceptions. Bioavailability is generally considered to be
reduced when a chemical is sorbed to sediment. Therefore it does
not seem plausible that AET values for protecting aquatic life
from chemicals sorbed to sediments can be lower than chronic
water exposure values. It— is recommended tftat tha 2US*E.. values
-------
compared to existing toxioity values for aquatic organisms for
the purpose of identifying those AET values vhieft arc
inconsistent vith the existingbody of toxicoloaical data.
4. The sediment Jaioassay and field infaunal biological
effects measurements do not show a strong dose-response relation-
ship above the AET values* A basic premise of toxicology is that
effects intensify with increasing dose. Inability to demonstrate
this relationship argues against a causal relationship between
exposure and effect for these chemicals near the AET concentra-
tion. It therefore diminishes the weight of evidence of the
accuracy of the AET values as they relate to specific chemicals
and indicates that the toxieity may be due to more than one
chemical or that bioavailability or population resistance is
changing from station to station. Both factors detract from the
method's ability to relate observed effects to a specific
chemical or chemical concentration. it la recommended that
additional researchbe conducted to evaluate AETs relative to the
applicable, available data for dose-response relationships.
Additionally, most of the existing AETs have only a limited
number of stations that fall above the AET value. This suggests
that additional sampling and analysis could be beneficial to the
AET method if the samples were collected from sites with high
chemical concentrations.
5, Several of the AET values are for chemicals which do not
show acute toxicity in laboratory aqueous toxicity tests. This
is generally due to the limited solubility of the test chemical.
Since the AET values are derived primarily from acute toxicity
tests, one would expect a priori that these same chemicals would
not be acutely toxic when sorbed to sediments. since the bio-
availability of chemicals sorbed to sediments is usually less
than that in the aqueous phase, the trend is for chemicals to
become less toxic on sediments, not more toxic. These data
suggest that the effects are due, in part, to the presence of
other chemicals, the physical properties of the sediment,
or some other unknown factor(s). Inconsistency with known
toxicological principles raises questions about the accuracy of
AET values and, therefore, the scientific validity of the method.
The AET has clear utility for assessing contaminated
sediments. Points such as those raised above., once addressed
through additional research or comparison with existing
literature, can go a long way towards improving confidence in the
method and in demonstrating its consistency with established
scientific principles.
3.5 Endpoint Considerations
The ability of the AET to effectively assess impacts at
contaminated sites is related to the choice of the biological
effect endpoint(s) used. The application of the AIT to Puget
Sound utilizes data on benthic infaunal assessments, amphipod
sediment bioassays, oyster larvae bioassays and Microtox«-RJ bio-
8
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assays. The AET can theoretically incorporate any biological
effect(s) endpoint. In the generation of the AET, a battery of
biological effects endpoints should be used, in the selection of
biological effects endpoints one should considers
1. The range of organismal responses to the contaminated
sediments.
2. The methods used for assessment of acute and chronic
toxicity.
The AET incorporates the first consideration by requiring
multiple biological effects enuSpoints. In the Puget Sound data
base, the latter concern was also addressed by including benthic
infaunal assessments. However, if infaunal data are not
available, the AET fails to consider any estimate of chronic
toxicity. This conclusion is based on recognizing that the
infaunal analyses are integrated measurements of chronic and
acute toxieities while the bioassays chosen and available to date
reflect acute toxicities only.
It ia the conclusion of the subcommittea that; properly
designed and applied infaunal analyses ar» extremely valuable to
the development and validation of the AET and that they should be
Includedin future activities. Research should be initiated to
develop improved toxicitv assay methods that can be used to
assess long-term impacts of sediment tOKJcity.
The AET approach factors in both in situ biological effects
through the benthic infaunal analysis and laboratory toxicity
tests through bioassays. The former measures alteration, but is
prone to all the problems inherent in field data. These include
natural variability from biotic (predation, competition) as well
as abiotic factors (grain-size, salinity). As the method is
presently being used, few ecological endpoints are being
measured* A 50% reduction in major taxa is a gross change
indicative of major adverse effects. The use of major taxa rather
than species changes may be correct, but it is heavily weighted
to serious acute effects. It may incorporate chronic and more
subtle changes, but these may be masked by the overriding lethal
effects, even though chronic effects can also result in
lethality.
Regarding bioassays, both acute and chronic tests should be
used. The later is defined as a test that encompasses at least
one full life-cycle of an organism. The more tests the better,
given the value of a preponderance of evidence approach, but it
is recognized that there are always going to be limitations to
resources. It ia recommended that not only different organisms
be used but also that different oxpoaure routes and life-stages
bo used. It is important that those using AET clearly and
precisely specify what each biological parameter measured is
assumed to mean. For instance, it is very difficult from the
data presented to determine what MicrotoxW is supposed to
indicate. If the test is intended to indicate impacts on the
procaryotic level of the community, then its use in sediment is
-------
probably inappropriate since it is based on photoluminescence by
aerobic organisms that are not normally inhabitants of sedinents,
which are usually anaerobic. If it is used as an empirically
derived indicator of toxicity, then the choice is more
reasonable. The need . for clearly defining the assumptions is
most important for the potential users of both the AET value and
the methodology.
The biological indicators used in Puget Sound for the
development of AET values are some of the best tools presently
available, but this is a rapidly evolving field. At present
there is a need for better sediment bioassays, in particular
chronic bioassays. We are now using first generation (water
bioassays adapted for sediment, usually through the use of
elutriates) and second generation bioassays (acute bioassays
specifically adapted for use with whole sediments), The
developers of the AET approach in Puget Sound are to be
complimented for incorporating a range of biological evaluation
teata_. in their approach. The fact that there may be other
methods or even better ones does not detract from the effort. As
stated above, there is a definite need to incorporate more than
one assay and the concordance of the results provides reassuring
evidence for effects.
3.6 ComplexMixtures
In some circumstances, the AET method has the potential to
assess the impact of complex chemical mixtures on indigenous
benthic infauna. This is because organisms utilized in the bio-
assays and organisms enumerated in the environment are exposed to
the array of chemicals incorporated in the sediment of question.
If the composition of the complex mixture responsible for the
measured biological effects remains relatively constant in sedi-
ments throughout the area of interest (i.e., that portion of a
water body to which an AET value is to be applied), then the
•predictive potential of the AET is increased. It is also neces-
sary that the chemicals measured be those responsible for the
biological effects or else that they act as surrogates for those
that are the causative agents. In some situations, such as im-
pacts from PAH, these criteria may be met, but in situations
where the complex mixture changes in composition rather than
concentration or where the chemicals measured do not vary propor-
tionally with the concentrations of the substances responsible
for the effects, AETs will be faulty predictors of biological
impacts of complex nixtures.
Cause/effect relationships, as pointed out in section 3.4
and in the briefing document provided to the SAB, are not well
defined by the AET approach. This is because there is no
certainty that the chemical substances measured are, in fact,
those responsible for the noted biological effect. A chemical(s)
which appears to be the causative agent may only co-exist and" co-
vary with the toxicants rather than be involved in the toxicity.
10
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In such cases, one may regulate surrogates rather than the
toxicants.
Even with these limitations, there are definite advantages
associated with this or similar iwiltivariate methodologies over
univariate methodologies which consider only single chemicals.
These advantages are that additive, synergistic or antagonistic
effects can be taken into account, as long as the composition of
the contaminants remains constant.
3.7
Factors
Attention should be given to the effects of physical factors
on biological response (s) to chemicals since many areas of con-
cern are in environments that are highly dynamic. It should be
noted, however, that many other areas are relatively placid and
physical factors are less important. The currents , turbulent
mixing, and dispersion of sediments generally vary significantly
with time and space according to the tides, winds, waves, and
freshwater discharges. All of these factors can have significant
impacts on biological response (s) to chemicals. For example,
variation in currents, salinity, turbulence level, sediment char-
acteristics (mineralogical composition, size distribution) , and
dissolved oxygen levels can all affect the biota.
The Puget Sound study concentrated on the chemical and bio-
logical data and used little or no physical data (currents, sal-
inity, turbulence, and sediment characteristics) in the develop-
ment of AIT. Until the effect of physical factors on AET is
adequately studied, the present AET values could contain signif-
icant errors and the AET cannot be applied generically with
confidence .
H comprehensive study ghould be conducted to determine the
of feet of physical factors on biological response to chemicals.
It ia yjtftammflnneg that hydyegynMii e »|id. sedinenfcary information
(via monitoring or modeling effort) be collected and used to
lide
i« select ion of &BT ^^mplincf stations and reference sites.
Such effort will not only provide a scientifically more defens-
ible basis for site selection, but may also lead to a reduction
in the number of required sampling sites*
3.8 Carbon normalization
A large amount of data exists in the literature, from both
laboratory and field studies, demonstrating the utility of carbon
normalization for relating the bioavailability of non-ionic
organic chemicals sorbed to sediments. These data indicate that
the free form of the chemical which is available for organism
uptake, whether by ingestion or by transport across respiratory
and external membranes, can best be approximated by carbon
normalization of the measured sediment chemical concentrations.
This also tends to reduce variability in the data.
11
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The information presented on the AET approach indicates that
no improvement in the sensitivity of the method was achieved, by
carbon normalization of the data for the individual stations with
subsequent recalculation of the AET values. Several reasons may
exist for this lack of change in sensitivity*
a) Most of the sediment chemical concentration data have
organic carbon values in the range of 1-3%. This is not a wide
range, and therefore one would not expect major changes in the
normalized values.
b) Chemical concentrations on sediments do not always cor-
relate well with organic carbon in areas impacted by massive dis-
charges of chemicals above their water solubilities, i.e., due to
spills. In such situations it is possible to find high concen-
trations of chemicals on sediments which are very low in carbon.
The Subcommittee ree**"""«>"*3 that carbon normalization be
used to develop the proposed AET values. The use of this
approach is consistent with theory and it provides an AET which
is based on mass of chemical per mass of carbon. In practice,
converting a carbon-normalized AST for a specific chemical into
non-normalized concentrations results in a range of (AET) values
depending upon the value of carbon that is used to make the
conversion. For example, the carbon-normalised Microtox^J AET
for hexachlorobenzene is listed as 2.3 mg/Kg C (USEPA, Briefing
Report to the EPA Science Advisory Board, page 35, Table 4,
September, 1988) To interpret environmental sediment chemical
concentrations in relation to this normalized AET (2,3 mg/Kg C),
the non-normalized sediment chemical concentration would have to
be divided by its respective sediment total organic carbon (TOC)
content. This means that a non-normalized sediment
concentration, which is what is usually determined analytically,
would exceed the normalized AET value (2.3 mg/Kg C) if it
contained 0.02 mg/Kg hexachlorobenzene and a TOC of 1.0% (0.20
mg/Kg/1% TOC =20 mg/Kg C). However, if the same sediment sample
had a TOC of 10%, it would not exceed the carbon normalized AET
(0.20 mg/Kg/10% =2.0 mg/Kg C).
Carbon normalization does not assume that all sediments are
equal. The same sediment chemical concentration detected in a
range of different sediments may or may not exceed the AET
depending on the TOC of the sediment. The use of TOC-normalized
values in the above manner should eliminate the criticism that
the AET approach is insensitive to differences in sediment types
and differences in bioavailability.
3*9 Uncertainties in the RET
The AET approach relies on the use of a single AST value for
each chemical and each biological indicator/endpoint* The choice
of such single value(s) is necessarily somewhat subjective. Any
12
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uncertainty and variability of the actual data are not adequately
incorporated into single-valued AET.
Uncertainties in the data used for the AET process are based
in part upon the variabilities inherent in sampling, naturally
occurring patchiness in the distribution of organisms, and
similar patchiness in the spatial distribution of chemicals. It
may be possible to display these kinds of uncertainties through
the use of appropriate sampling strategies.
Uncertainties that nay be due to inadvertent biases or due
to uncontrolled variables are much more difficult to uncover.
The inclusion of such uncertainty may lead to artificially
elevated AET values. This factor is of concern since AET values
(by definition) can only be elevated as more data is generated.
Examples of factors that may give rise to biased relationships
between the exposure and response variables are;
a. Measurement of total metals, rather than of indicators
of bio-available metals.
b. Failure to consider the strength of sorption of con-
taminants to the sediment matrix.
c. Estimation of effects based on responses of higher taxa,-
changes in lower taxa would be expected to be
more sensitive.
d. Bioassays conducted with homogenized sediments or with
supernatants derived from agitated sediments as opposed
to undisturbed sediments,
e. Use of acute bioassays and consequent lack of considera-
tion for chronic and genotoxic response.
Environmental significant parameters that have not been
measured may influence uncertainties and biases in unpredictable
ways. The authors of the AET methodology clearly were aware of
some of the major categories of important variables that have not
been measured. Among such neglected variables that may influence
effects are:
a. Interactions between chemicals in the production of
effects,
b. Matrix effects that influence bioavailability.
c. Physical parameters that influence the distribution of
chemicals and benthic organisms.
The AET method correctly assumes that, as the exposure vari-
able is increased, the response or effects variable will even-
tually become resolvable. In the method, the exposure variables
are maintained throughout as individual chemical concentration
measurements* Although the list of chemicals tested for is rela-
13
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tively small, the list contains those substances that are of cur-
rent regulatory concern, and it can be increased to a broader
list of chemicals in the future.
The effects variables are treated in a more simplistic
fashion. Indicators of effects are limited to an in situ assess-
ment of four major benthic taxa, which should provide information
on chronic and interactive effects. In addition, the sediment
samples are subjected to one to three short-term laboratory
bioassays. The observed deviations from "reference" conditions
are then converted into quantal or affected/non-affected
categories. This process collapses the continuous data of the
effects variable into two categories, losing most of the
information related to the variability of effects in the process.
A further problem associated with the categorization into
affected vs. non-affected (non-impacted) conditions is based on
the selection of "reference" conditions. The exact
categorization criteria are not rigorous or self-evident, but are
based upon best professional judgment. Use of the term
"inconclusive" rather than non-affected or non-impacted may
better indicate the subjective nature of this determination.
The categorization process into affected/non-affected has
the advantage of providing a starting point for the development
of single-value delimiters for the AIT Methodology. Such single-
value delimiters have obvious attractiveness as administrative
tools for setting criteria, standards, or other limits. However,
these values are dependent on the available data, their central
tendency, and more importantly on the range and variability of
the available data. This makes it very important to investigate
the variabilities associated with the development of the exposure
and effect functions, to examine the relationships critically,
and to incorporate indicators or measures of the degree of
variability as part of any apparent effects threshold.
If no categorization step is undertaken initially, and if
the effects function is expressed in terms of the exposure func-
tion, then the relationship and its associated variability can be
described directly, leaving the need for professional judgment as
the final step. It should also be possible to substitute a form-
alized decision process for a portion of the professional judg-
ment required in the last step. Another alternative would be to
display the variability inherent in the process as outlined above
as an adjunct to the development of the AST along lines similar
to those suggested in the present methodology. The subcommittee
•j-oaiimm^nagtthat a measure of variance for AST values ba developed
in addition to tha ainala-valued statistical mean AET.
14
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committee
a. The Subcommittee recommends that future application of the A£T
include replicate sediment samples for determination of chemical
contaminants and for assessment of toxic ity*
b. The Subcommittee recommends that criteria for selecting
reference sites be formalized. The selection/rejection criteria
need to be clearly defined and the rationale for their choice
explained.
c. Some knowledge of how temporal changes impact the AET is
needed to characterize the uncertainty that may be added by this
variable.
d. The Subcommittee recommends that multiple approaches be used
to estimate sediment quality, determine criteria and guide
regulatory actions since the AET approach alone provides
insufficient certainty for broad-scale decision making.
e. It is recommended that the data set be reviewed for all the
AETs in relation to their physical-chemical properties (e.g. KQC,
Log P and water solubility) and their existing toxicological
properties (e.g., acute versus chronic or genetic effects) for
the purpose of establishing the sensitivity of AET values to
parameters that are known to affect toxicity.
f . It is recommended that the AET values be compared to existing
toxicity values for aquatic organisms for the purpose of
identifying those AET values which are inconsistent with the
existing body of toxicological data.
g, It is recommended that additional research be conducted to
evaluate AETs relative to the applicable, available data for
dose-response relationships*
h. it is the conclusion of the Subcommittee that properly
designed and applied infaunal analyses are extremely valuable to
the development and validation of the AET and that they should be
included in future activities. Research should be initiated to
develop improved toxicity assay methods that can be used to
assess long-term impacts of sediment toxicity.
i. It is recommended that not only different organisms be used
but also that different exposure routes and life-stages be used.
j . A comprehensive study should be conducted to determine the
effect of physical factors on biological response to chemicals.
It is recommended that hydrodynamic and sedimentary information
(via monitoring or modeling effort) be collected and used to
guide the selection of AET sampling stations and reference sites.
k. The Subcommittee recommends that carbon normalization be used
to develop the proposed AIT values.
15
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1. The Subcommittee recoawnends that a measure of variance for AET
values be developed in addition to the single-valued statistical
mean AET.
16
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APPENDIX
Briefing Report.to the EPA Science Advisory Board;
The Apparent Effects Threshold
17
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BRIEFING REPORT TO THE
EPA SCIENCE ADVISORY BOARD:
THE APPARENT EFFECTS THRESHOLD APPROACH
Submitted by
Office of Puget Sound
Puget Sound Estuary Program
U.S. Environment!! Protection Agency, Region 10
1200 6th Avenue
Seattle, Washington 9SIOI
Prepared by
PTI Environmental Services
3625 132nd Avenue SE
Suite 301
Beilevue, Washington 98006
under Battelle Columbus Division
EPA Contract No. 68-03-3534
PTI Contract No, C714-01
September 1988
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.2. THE CONCEPT OF AET
An AET is defined as the sediment concentration of a given chemical above which
statistically significant (P
-------
otherwise the AET is only a preliminary minimum estimate (or may not
exist).
5, Repeat Steps I -4 for «ach biological indicator.
A pictorial representation of the AET approach for two example chemicals is
presented in Figure 2 based on results for a toxicity bioassay. Two subpopulations of
all sediments analyzed for chemistry and subjected to a bioassay are represented by
bars in the figure and include:
• Sediments that did not exhibit statistically significant (P>0.05) toxicity
relative to reference conditions ("nonimpacted" stations)
• Sediments that exhibited statistically significant (P
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LEAD
NO SEDIMENT TOXIC1TY
SEDIMENT TQXICITY QBSEBVE0
S(M5
6300 pprn
r
to
too
T
tooo
APPARENT
CONCENTRATION (mg/Kg DW) TOX!CrfY
THRESHOLD
MAXIMUM
OBSERVED
LEVELATA
BIOLOGICAL
STATION
J
10,000
4-METHYL PHENOL
NO SEDIMENT TOXICITY
OH
-SEDIMENT
./:/• •/.. /////////
U10
APPARENT
CONCENTRATION (pi/Kg DW) TQXOTY
U * undetected at detection limit shown
W.OOO
MAXIMUM
OBSERVED
LEVEL AT A
BtOtOGICAL
STATION
Figure 2. The AET approach applied to sediments tested for lead and 4-methyl phenol
concentrations and toxicity response (Jnriflg tuoassays.
-------
other sites without associated biological effects). Based on the results for lead and 4-
raethylphenol, effects at 4 of the 28 impacted sites shown in the figures may be associated
with elevated concentrations of 4-methylphenol, and effects at 7 other sites may be
associated with elevated concentrations of lead (or similarly distributed contaminants).
These results illustrate that the occurrence of biologically impacted stations at
concentrations below the AET of a single chemical does not imply that AET in general
are not protective against biological effects, only that single chemicals may not account
for all stations with biological effects. By developing AET for multiple chemicals, a
high percentage of all stations with biological effects are accounted for with the AET
approach (reliability results are presented in Section 3 of this briefing document).
AET can be expected to be more predictive when developed from a large, diverse
database with wide ranges of chemical concentrations and a wide diversity of measured
chemicals. Data sets that have large concentration gaps between stations and/or do
not cover a wide range Of concentrations must be scrutinized carefully (e.g., to discern
whether chemical concentrations in the data set exceed reference concentrations)
before generation of AET is appropriate.
Dose-Response Relationships and AET
The AET concept is consistent with empirical observations in the laboratory of
dose-response relationships between increasing concentrations of individual toxic chemicals
and increasing biological effects. A simple hypothetical example of such single-chemical
relationships is shown for chemicals X and Y in Figure 3. In the example, data rare
shown for laboratory exposures of a test organism to sediment containing only increasing
concentrations of chemical X, and independently, for exposures to sediment containing
only increasing concentrations of chemical Y. The magnitude of toxic response in the
example differs for the two chemicals and occurs over two different concentration
ranges. It is assumed that at some level of response, for example >25 percent, the two
different responses can be distinguished from reference conditions (le., responses
resulting from exposure to sediments containing very low or undetectable concentrations
of any toxic chemicals).
These single-chemical relationships cannot be proven in the field because organisms
are exposed to complex mixtures of chemicals ia environmental samples. In addition,
unrelated discharges from different sources can result in uncorrelated distributions of
chemicals in environmental samples. To demonstrate the potential effects of these
distributions, response data are shown in Figure 4 for a random association of chemicals
X and Y using the same concentration data as in Figure 3. The data have been plotted
according to increasing concentrations of chemical X, and the same dose-response
relationship observed independently for the two chemicals in the laboratory has been
assumed. The contributions of chemicals X and Y to the toxic response shown for
these simple mixtures is intended only for illustration purposes to enable direct comparison
to the relationships shown in Figure 3, but are analogous to an additive toxic response,
Other interactive effects are not considered in this example.
In Figure 4, a significant response relative to reference conditions would result
whenever elevated concentrations of either chemical X or chemical Y occurred in a
sample. Because of the random association of Y with X in these samples, the significant
responses would appear to occur randomly over the lower concentration range of
12
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Bioassay Response
100
Chemical X
Chemical Y
0
Significant
Toxiclty / *~~~'T p
Increasing X or Y >
Figure 3. Hypothetical example of dose-response relationship resuliing from laboratory
exposure to sin&te chemicals X and Y,
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Bioassay Response
100
0
Chemical X Q
Chemical Y
Significant Toxicity -f- +O"
i
4
+ +
Increasing
Figure ^f. Hypothetical example of toxic response resulting from exposure lo environmental
samples of sedimeni contaminntetl with chemicals X ami Y.
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chemical X. The classification of the responses shown in Figure 4 into significant and
nonsignificant groups (i.e., >25 percent response for either chemical) results in generation
of Figure 5. .
Figure 5 represents the appearance of the environmental results when ranked
according 'to concentration of chemical X using these data. Below the AET for chemical
X, significant toxicity is produced by elevated concentrations of chemical Y, which is
randomly associated with the distribution of chemical X. Above the AET for chemical
X, significant toxicity is always produced by elevated concentrations of chemical X,
although in some samples, elevated concentrations of chemical Y also contribute to the
overall toxicity. The AET for chemical X corresponds conceptually, in this simple
example, to the concentration in Figure 3 at which a significant difference in response
was observed in the laboratory for chemical X,
In environmental samples that contain complex mixtures of chemicals, a mono tonic
dose -response relationship such as in this simple two-chemical example may not always
apply. For example, a consistently increasing biological response may not always occur
at increasing concentrations of a chemical above Its AET, Such observations could
indicate that the AET is coincidental (i.e., that the observed toxicky in some or all
samples above the AET is unrelated to the presence of that chemical), or that changing
environmental factors in samples exceeding an AET obscure a monotonic dose-response
relationship. Such factors are discussed in the following section.
Influence of Environmental Factors on AET Interpretation
" '
Although the AET concept is simple, the generation of AET values based on
environmental data incorporates many complex biological-chemical interrelationships.
For example, the AET approach incorporates the net effects of the following factors
that may be important in field-collected sediments:
• Interactive effects of chemicals (e.g., synergism, antagonism, and additivity)
ii Unmeasured chemicals and other unmeasured, potentially adverse variables
• Matrix effects and bioavailability [Le., phase associations between
contaminants and sediments that affect bioavailability of the contaminants,
such as the incorporation of polycydic aromatic hydrocarbons (PAH) in
soot particles].
The AET approach cannot distinguish and quantify the contributions of interactive
effects, unmeasured chemicals, or matrix effects in environmental samples, but AET
values may be influenced by these factors. To the extent that the samples used to
generate AET are representative of samples for which AET are used to predict effects,
the above environmental factors may not detract from the predictive reliability of AET.
Alternatively, the infrequent occurrence of the above environmental factors in a data
set used to generate AET could detract from the predictive reliability of those AET
values. If confounding environmental factors render the AET approach unreliable, this
should be evident from validation tests in which biological effects are predicted in
environmental samples. Tests of AET values generated from Puget Sound data (see
Section 3) indicate that the approach is relatively reliable in predicting biological
effects despite the potential uncertainties of confounding environmental factors.
15
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Bioassay Response
100
0
Increasing X or Y
Significant Toxicity 1 **
No Toxicity
Bioassay Response
100
0
Increasing X
AET
>
* * * ****tt
I
oo o ooo o o
Increasing X
Figure 5. Hypothetical example of AET calculation for chemical X bused on classified ion
of significant and nonsignificant responses for environmental samples con-
taminated with both chemicals X and Y. [Previous Figures 3 ami A are also
shown for comparison; dashed line indicates level of significant toxiehyj
-------
Although the above environmental factors can influence the generation of field-
based sediment quality values such as AET, they also may influence the application of
all sediment quality value approaches for the prediction of adverse biological effects.
For example, sediment quality values based on laboratory sediment bioassays spiked with
single chemicals would not be susceptible to the effects of the environmental factors
listed above. However, in applying such values to field-collected samples, predictions of
biological effects could be less successful to the extent that interactive effects, unmeasured
chemicals, and matrix effects occur in the environment.
The nature of the relationships between AET values and confounding environmental
factors is discussed in the remainder of this section.
Interactive Effects and AET—AET uncertainty is increased by the possibility of
interactive effects; the increase in uncertainty 5s expected to be less pronounced when
large data sets collected from diverse areas are used to generate AET, Additivity and
synergism can produce a comparatively low AET for a given chemical by causing impacis
at concentrations that would not cause impacts in the absence of these interactive
effects. This would effectively reduce the pool of nonirnpacted stations used to generate
AET. This effect should be reduced if a diverse database is used such that chemicals
occur over a wide range of concentrations at stations where additivity and synergism
are not operative. For chemicals that covary regularly in the environment (e,g., fluor-
anthene and pyrene), even a large, diverse database will not reduce the effects of
additivity and/or synergism on AET generation. The resulting AET values for such
chemicals may be reliable in predicting biological effects in environmental samples
although not representative of the toxidties of the chemicals acting independently.
Antagonism will produce comparatively high AET values if (and only if) the AET is
established at a station where antagonism occurs, A large, diverse database could not
rectify this elevation of AET if the station at which antagonism occurred was the
nonimpacted station with the highest concentration (i.e., the station setting an AET),
An AET set by a station at which antagonism occurred would not be representative of
the toxieity of the chemical acting independently. Hence, if antagonism did not occur
widely, such antagonistic effects would cause the AET to be less sensitive in predicting
adverse effects in the environment.
Empirical approaches such as the AET do not provide a means for characterizing
interactive effects. Only laboratory-spiked sediment bioassays offer a systematic anci
reliable method for identifying and quantifying additivity, synergism, and antagonism.
A great deal of research effort would be required to test the range of chemicals
potentially occurring in the environment (both individually and in combination), a
sufficiently wide range of organisms, and a wide range of sediment matrices to establish
criteria. In addition, the applicability of bioassays conducted with laboratory-spiked
sediments to environmentally-contaminated sediments requires further testing.
Unmeasured Chemicals and AET—Another source of uncertainty for AET and other
field-based approaches is the possibility of effects being caused by unmeasured, covarying
chemicals. Such chemicals would not be expected to substantially decrease the ability
of AET to predict biologically impacted stations (excluding interactive effects discussed
above). If an unmeasured chemical (or group of chemicals) varies consistently in the
17
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environment with a measured chemical, then the AET established for the measured
contaminant will indirectly apply to, or result in the management of, the unmeasured
contaminant. Jn such cases, a measured contaminant would act as a surrogate for an
unmeasured contaminant (or group of unmeasured contaminants). Because all potential
contaminants cannot be, measured routinely, management strategies must rely to some
extent on "surrogate" chemicals.
If an unmeasured toxic chemical (or group of chemicals) does not always covary
with t measured chemical (e.g., if a certain industry releases an unusual mixture of
contaminants), the effect should be mitigated if a sufficiently large and diverse dara
set is used to establish AET, Use of a large data set comprising samples from a
variety of areas with wide-ranging chemical concentrations would decrease the likelihood
that an unrealistically low AET would be set Because AET are set by the highest
concentration of a given chemical in samples without observed biological effects. AET
will not be affected by less contaminated samples in which unmeasured contaminants
cause biological effects.
If an unmeasured toxic chemical does not covary with any of the measured chemicals,
it is unlikely that the AET (or any other chemical-specific approach) could predict
impacts at stations where the chemical is inducing toxic effects. The frequency of
occurrence of stations with biological effects but no chemicals exceeding AET is the
subject of validation tests (see Section 3 of this briefing document),
Matrix Effects and BioaYailabiIity~-Geochtmical associations of contaminants with
sediments that reduce bioavailabiUty of those contaminants would affect AET analogously
to antagonistic effects (i.e.,, they would increase AET relative to sediments in which
this factor was not operative). Sediment matrices observed in Puget Sound thai may
reduce bioavailabiUty of certain contaminants include slag material (containing high
concentrations of various metals and metalloids, such as copper and arsenic) and coal
or soot (which may contain high concentrations of largely unavailable PAH, as opposed
to oil or creosote, in which PAH would be expected to be far more bioavailable; e.g.,
Farrington and Teal 1982). Many kinds of matrices may occur in the environment and
a large proportion may be difficult to classify based upon appearance or routinely
measured sediment variables. Hence, the use of matrix-specific data sets to generate
AET, although desirable, would be difficult to implement.
To address this concern from a technical perspective (Le,, representativeness of
data used in AET generation), the AET database could be screened for sediment with
chemical concentrations that are anomalously high relative to those in other nonimpacted
sediments from different geographic areas.- From a management perspective, this
guideline would generate more protective (sensitive) sediment quality standards that
may also be less efficient in only identifying problem sediments. These sediments
would be considered nonrepresentative and not used in AET generation unless and until
additional data could substantiate that they are representative. Such data treatment
methods are discussed in the following section.
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