Figure 5. Example of conceptual model for ecological exposure pathways

b. The physical accessibility of the contaminants to a receptor.

c. The chemical properties of a COC (e.g., solubility, partitioning coefficients)

which govern its partitioning among media and from physical media to

biota.

d. The physical attributes of a site which may govern movement of a

contaminant (e.g., advection, upwelling, sediment transport).

The risk assessor must consider these factors in deciding whether there is a

complete pathway at a specific site. When an exposure pathway is complete, the risk

assessor must decide whether there is potential for risk associated with that

pathway. A complete exposure pathway does not necessarily translate to risk. Risk

depends on the concentration or dose to the receptor relative to that receptor's toxic

response. Later sections of the risk assessment will address the dose or

concentration to which a receptor is exposed and will address the toxicity of the

chemical.

At most dredged aquatic material management sites, the potential links between

contaminants and potential ecological receptors are:

a. Sediment to benthic organisms.

b. Benthic organisms to pelagic or demersal organisms.

c. Water column to pelagic organisms.

Figure 5 shows a generalized conceptual model with the most likely complete

exposure pathways at dredged material management sites. Note that direct exposure

from sediments to pelagic organisms is possible (e.g., exposure to

Figure 5.

Example of conceptual model for ecological exposure pathways

Chapter 2 Problem Formulation