Sources of Uncertainty in Effects Assessment

Some members of the group suggested that the applicant be given the

opportunity to accept a "failure" due to exceedance of numerical criteria and avoid

the expense of biological testing, if there is no reasonable expectation of a

biological test passing the material. The PSDDA Program has implemented such

provisions in its dredging program. Other participants stated that numerical

criteria should never be used alone to fail a sediment and exclude it from open

water disposal. However, exceedance of the criteria could be considered as

additional justification for the need for biological testing.

Sources of Uncertainty in Effects Assessment

The workgroup identified several important areas of uncertainty:

a. Lack of phylogenetic diversity in toxicity testing.

b. Uncertainty in extrapolating from effects measured in one test species to

effects in a species of local concern.

c. Lack of standard approach for extrapolating from results of toxicity tests

to population-level impacts.

d. Identification of appropriate species of concern.

e. Consideration of natural variability.

Lack of information about potential for chronic or sublethal toxicity.

g. Interpretation of bioaccumulation data.

Research Needs

The workgroup discussed and suggested the following research to further refine

the manner of estimating the environmental effects associated with dredging:

a. Compilation and interpretation of existing data. Participants of the

Effects Workgroup agreed that existing data and tools should be organized

and made accessible to managers and applicants. Data from past dredging

and monitoring projects should be analyzed, and the correlations between

sediment chemistry (concentration of contaminants), toxicity in bioassays,

and bioavailability of contaminants in bioaccumulation tests should be

examined. Members of the regulated community noted that it might be

useful for the applicant to have some ability to predict, on the basis of

sediment chemistry, whether a particular sediment might exhibit significant

toxicity and bioaccumulation in the standard tests and therefore be

unsuitable for open water disposal. In that case, the applicant might

Chapter 3 Effects Assessment Workgroup Summary