Effects of sediment composition on the bioavailability of PAH and PCB congeners to Diporeia spp.

Organic carbon is generally considered the major variable affecting the bioavailability of nonpolar sediment-associated contaminants. However, even after carbon normalization, the variation in bioavailability can vary approximately a factor of ten when comparing some Great Lakes sediment to a reference material, Florissant soil. Because this soil might not truly represent sedimentary materials, sediments were gathered from several locations in the United States, Canada and Finland. The accumulation kinetics were measured for pyrene, benzo[a]pyrene (BaP), 2,4,2{prime},4{prime}-tetrachlorobiphenyl (TCBP), and 2,4,5,2{prime},4{prime},5{prime}-hexachlorobiphenyl. The organic carbon content of the sediments ranged from 0.45 to 21.2 percent and the biota-sediment accumulation factors ranged from 0.018 for BaP in the Savannah River sediment to 2.28 for TCBP in Pond 5 sediment. In general, the sediment collected from Pond 5 of the Savannah River Plant yielded the greatest bioavailability by a factor of 4 to 13 across the various compounds, although the organic carbon content was approximately 3 times greater than the lowest concentration. Thus, simple organic carbon normalization was not adequate to describe the bioavailability differences among the various sediments. Additional features including fraction of fines and particle size distribution of the contaminants were measured and may explain some of the remaining variation in bioavailability.