9.2.2 Tier I - Evaluation Procedure

organized and used in a risk assessment framework. The information is compiled

and used as described for evaluation of animal bioaccumulation in Section 8.2.1.

The project-specific conceptual site model developed for animal bioaccumulation

is also used for plant bioaccumulation, with the obvious modifications to identify

COC for plant bioaccumulation (which may be different from animal

bioaccumulation COC) and reasonable potentially complete exposure routes

involving plant bioaccumulation to ROC populations outside the CDF. The ROC

populations outside the CDF for plant bioaccumulation will be the same as the

ROC populations for animal bioaccumulation. The Tier I plant bioaccumulation

evaluation emphasizes identification of complete exposure routes in the context of

the conceptual site model. There can be no risk unless there is a complete

exposure route by which a ROC can come into direct physiological contact with a

COC.

9.2.2 Tier I - Evaluation Procedure

A fundamental emphasis of the Tier I evaluation is on identification of

complete exposure routes to ROC outside the CDF. Complete exposure routes are

evaluated in Tier I if the available information is sufficient to make a decision,

and if there is not sufficient information to support a decision, they are carried to

subsequent tiers for more detailed evaluation. Incomplete exposure routes to

ROC outside the CDF, and complete routes that are clearly involve such minimal

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

documented and eliminated from further consideration.

A key to the evaluation of ecological impacts of plant bioaccumulation in Tier

I, as well as in subsequent tiers, is the concept of effect as discussed in Section

2.2.4. Effects are generally evaluated at the population or higher level rather than

at the level of individual organisms, except in the case of endangered species and

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

route to an 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 plant 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.

9.2.3 Tier I - Plant Bioaccumulation Decision

After consideration of the Tier I plant bioaccumulation information in the

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

(Figure 9-1).

9-5

Chapter 9

Plant Bioaccumulation