PREVIOUS FIELD VALIDATION 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