Bioaccumulation of COCs (Cont.)

Note, however, that the findings of Burkhard (1998) are based on

the analysis of a Great Lakes food web in which benthic organisms

are an important food source for higher trophic level organisms. In

food webs where the benthic component is less important, the

importance of the input parameters on the uncertainties associated

with predicted output parameters will be different.

Iannuzzi et al., (1996) developed probabilistic distributions for

several important parameters that are typically used in mechanistic

bioaccumulation models to predict the uptake of organic

contaminants in aquatic food webs. The ranges, central tendencies,

and distributions of key parameters of the models were derived

from a critical evaluation of the literature on the physiology and

ecology of three common estuarine organisms. Distributions of the

physical/chemical characteristics (i.e., the octanol-water partition

coefficient Kow) for several congeners of PCBs were also compiled

from the literature.

The model used by Iannuzzi et al. (1996) is based on a Monte Carlo

version of the equations developed by Thomann, Connolly, and

Parkerton (1992), and Gobas (1993). This model was used to

estimate the concentrations of five coplanar PCB congeners in adult

mummichog fish, blue crab, and striped bass, using distributions of

available data on PCB and total organic carbon (TOC)

concentrations that were measured in surface sediments from the

Passaic River in northern New Jersey. A model sensitivity analysis

was performed in order to measure and rank the sensitivity of the

bioaccumulation model output (i.e., concentration of contaminant in

fish and crabs) to each of the input parameters.

Results of the sensitivity analysis suggest that the following input

parameters most influence the model (not listed in order of

importance):

(a) BSAF (biota-sediment accumulation factor) for infaunal

organisms.

(b) Lipid content.

(d) TOC content of sediments.

(e) The chemical assimilation efficiency (CAE).

(f)

Residence time in the river for striped bass.

(g) log Kow.

In summary, both Burkhard (1998) and Ianuzzi et al. (1996)

concluded that the lipid content of the exposed organisms and the

Chapter 5 Uncertainty in Tier IV Risk Assessments