COMPARISON OF WHOLE-SEDIMENT, ELUTRIATE AND PORE-WATER EXPOSURES FOR USE IN ASSESSING SEDIMENT-ASSOCIATED ORGANIC CONTAMINANTS IN BIOASSAYS

Bioassays have frequently been used as tools to simulate exposure of b enthos to sediment-associated contaminants in hazard assessments. Due to the problems involved with estimating bioavailability in whole-sedi ment bioassays, aqueous fractions such as elutriates and pore water ha ve been substituted for whole-sediment exposures. The objective of thi s research was to compare and evaluate the bioavailability of represen tative neutral hydrophobic contaminants in whole sediments and in aque ous extracts of whole sediment (elutriate and pore water) in simultane ous bioassays, using three representative indicator species, Diporeia spp., Chironomus riparius larvae, and Lumbriculus variegatus. Aqueous extracts of whole sediment did not accurately represent the exposure o bserved in whole sediment. Generally, the aqueous extracts underexpose d organisms compared to whole sediment, even after adjusting accumulat ion to the fraction of organic carbon in the test media. Accumulation comparisons among whole-sediment, elutriate, and pore-water exposures depended on sampling time. At some sampling times for some contaminant s, differences in accumulation between a particular aqueous extract an d whole sediment were not significant; however, these similarities wer e not observed for all species at the particular sampling time. Bioacc umulation and contaminant clearance data suggest that a number of fact ors such as the indicator species, exposure media, and chemical/physic al properties of individual contaminants are responsible for the accum ulation differences observed among the tested media. Normalizing bioac cumulation to the amount of organic carbon in a source compartment adj usted for bioavailability differences of only some contaminants. We su ggest that the bioavailability of contaminants such as those tested ca nnot be accurately predicted in bioassays that expose organisms to aqu eous representations of whole sediment.