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Review of Field Validation Studies of Sediment Bioassays for the Regulatory Evaluation of Dredged Material
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Experimental/Manipulative Studies
ERDC TN-DOER-C23
September 2001
and Gibson 1993; Dillon, Moore, and Reish 1994; Dillon, Moore, and Gibson 1994; Bridges and
Farrar 1997).
A key element in the development of these tests has been the inclusion of technically sound
interpretive guidance. While simple acute survival effects are considered relatively straightforward
to interpret, more subtle sublethal effects on growth and reproduction require a higher level of
understanding to distinguish statistical significance from biological significance. For example, when
does a statistically significant reduction in growth or reproduction become biologically important
in maintaining a viable population in the environment? Equally important is an understanding of
the potential confounding factors (e.g., grain size, ammonia, etc.) that can affect organism responses
and interpretation of test results. Consequently, a great deal of effort has been expended in
developing tests with consistent and interpretable end points (Ankley et al. 1994; Bridges et al.
1996; Bridges, Farrar, and Duke 1997; Bridges and Farrar 1997; DeWitt, Ditsworth, and Swartz
1988; Gray et al. 1998; Moore and Dillon 1993; Moore and Farrar 1996).
Once implemented within the regulatory testing program, chronic sublethal tests will be used to
determine the suitability of dredged material for open-water disposal. Because of the higher costs
of alternative disposal options (confined aquatic or upland) and the role these new tests will have
in affecting disposal decisions, it is incumbent upon the regulatory authorities (USACE and USEPA)
to ensure the consistency and quality of the predictions these tests provide prior to their regulatory
implementation. Developing confidence in the quality of the prediction will require experimental
validation that the effects measured in the laboratory tests are predictive of measurable effects in
the field. The design of a meaningful field validation study requires extensive understanding of the
dredged material disposal process, the impacts to be predicted (e.g., impacts to the benthic
community related to sediment-associated contaminants), and careful consideration of factors that
may impinge on the interpretation of the results (e.g., natural temporal fluctuations in benthic
community structure). This technical note provides a review of field validation efforts for sediment
toxicity tests conducted to date as well as recommendations for the design and implementation of
future field validation efforts.
PREVIOUS FIELD VALIDATION STUDIES: Field validation studies conducted to date have
generally used one of two approaches. There are experimental/manipulative investigations where
contaminated material is tested in laboratory-based bioassays and then the same material is placed
in the field and subsequent effects on recruitment and benthic community dynamics are tracked
over time. There are also correlative/observational studies where the relationship between
laboratory-based sediment toxicity test results and benthic community indices are compared over
an existing contamination gradient in the field. In these more typical field validation efforts, samples
are collected along a pollution gradient and examined for alterations in benthic community structure
and/or function. Sediment toxicity is then evaluated in laboratory-based toxicity tests to determine
whether laboratory toxicity correlates with observed differences in the benthic community. A
statistically significant correlation is taken as evidence that the laboratory bioassay is predictive of
differences in the benthic community and therefore provides a useful predictive tool for such effects
in field-exposed communities.
Experimental/Manipulative Studies. While a number of other studies have used experimental/
manipulative approaches for comparing laboratory and field data, most of these were not designed
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