Evaluation of field-generated accumulation factors (AF) predicting the bioaccumulation potential of sediment-associated PAH compounds

Equilibrium partitioning of neutral organic chemicals between the organic carbon fraction of bedded sediments and the lipids of resident organisms provides the theoretical basis for one of the most popular approaches to the development of sediment quality criteria (SQC) by the USEPA. Proposed equilibrium partitioning-based SQC seek to relate estimated doses of sediment-associated chemicals to toxicity in exposed biota. Criteria documents for several polynuclear aromatic hydrocarbon (PAH) compounds, endrin, and dieldrin have been released by the USEPA for public review, and may soon be promulgated. A procedure recommended in the Implementation Manual (the "Green Book") for Public Law regulating ocean disposal of dredged sediments, (Section 103 of PL 92-532, MPR&SA, the "Ocean Dumping Act") has used equilibrium partitioning-based estimations to screen sediments for bioaccumulation potential for several years. The screening test, termed "theoretical bioaccumulation potential," (TBP), is also included in the draft manual for inland waters to implement dredged material testing requirements of the Clean Water Act. TBP employs an accumulation factor (AF), defined as the ratio at equilibrium of the organic carbon-normalized concentration of a neutral organic chemical in a sediment and the lipid-normalized concentration of the chemical in an exposed organism. The Green Book currently recommends using a universal AF = 4 for all neutral chemicals; the rationale being that this value is suitably protective and, based on field data, reasonably representative of all neutral chemicals provided certain caveats are recognized. This dissertation compared the predictive capability of PAH AFs derived from field data with that of the universal AF = 4 in making TBP estimations. Predicted bioaccumulation using the two methods was compared with PAH tissue concentrations measured in laboratory exposures of clams, Macoma nasuta and mussels, Mytilus edulis.