8.2.4 Tier I - Animal Bioaccumulation Decision

species and humans, where individuals are of concern. If a reasonable complete

exposure route to a ROC population outside the CDF exists, there is generally no

risk of an effect unless there is potential for a sufficient number of individual

organisms to be affected in a manner severe enough to threaten the long-term

sustainability of viable local populations of the ROC species outside the CDF.

The conceptual site model constructed from existing Tier I information is

examined. The site-specific COC and ROC for animal bioaccumulation are

identified. Any reasonable, potentially complete exposure routes to ROC outside

the CDF are described. Any incomplete exposure routes to ROC outside the

CDF, and any potentially complete routes that clearly involve such minimal

potential exposure as to pose negligible risk of unacceptable adverse effect, are

described.

8.2.4 Tier I - Animal Bioaccumulation Decision

After consideration of the Tier I animal bioaccumulation information in the

context of the conceptual site model, one of the following conclusions is reached

(Figure 8-1).

1. Information is sufficient to reach a decision without further evaluation.

This is the case if there are no reasonable, potentially complete exposure

routes, or all potentially complete routes clearly involve such minimal

potential exposure as to pose negligible risk of any effects, to ROC

populations outside the CDF. No further evaluation of animal

bioaccumulation is necessary.

2. Information is not sufficient to reach a decision regarding animal

bioaccumulation. This is the case if there are potentially complete

exposure routes that may pose a potential risk to ROC populations outside

the CDF.

8.3 Tier II Theoretical Bioaccumulation Potential

The Tier II animal bioaccumulation evaluation considers earthworms as the

primary animals for direct bioaccumulation of COC from dredged material in

terrestrial habitats in CDFs. If these organisms bioaccumulate COC, they may

provide a crucial link in a complete exposure route to off-site consumers that may

feed in the CDF. There is generally not a complete exposure route to off-site

consumers for those COC not taken up by earthworms. Theoretical

bioaccumulation potential (TBP) is used for Tier II evaluation of animal

bioaccumulation.

To date, the TBP calculation has been used only in relation to

bioaccumulation of nonpolar organic chemicals such as PCBs in aquatic

organisms. However, theoretical considerations indicate the procedure should

also be applicable to earthworms, and its utility for these organisms is being

confirmed. TBP is used for bioaccumulation of nonpolar organic chemicals by

8-10

Chapter 8

Animal Bioaccumulation