Sediment characteristics influencing the bioavailability of nonpolar organic contaminants to Diporeia spp.

Organic carbon is considered the major variable affecting the bioavailability of non-polar, sediment-associated contaminants. Previously, variation in bioavailability for some Great Lakes sediments compared to a soil material was nearly a factor of 10 after carbon normalization. Because a soil might not truly represent sedimentary materials, sediments and soils were gathered from several locations in the United States, Canada, and Finland. The accumulation kinetics of the amphipod Diporeia spp, were measured for pyrene, benzo[a]pyrene (BaP), 2,4,2',4'-tetrachlorobiphenyl (TCBP), and 2,4,5,2',4',5'-hexachlorobiphenyl (HCBP) sorbed to sediments and soils. The organic carbon content of the sediments ranged from 0.45-21.2% and 32.2-45.0% for soils. The bioavailability, measured as the uptake clearance (amount of source compartment cleared of contaminant per mass of organism per hour), was controlled by the amount of organic carbon, particularly for the chlorinated biphenyls. However, for polycyclic aromatic hydrocarbons (PAH), bioavailability was controlled more by the organic carbon polarity represented by the carbon/nitrogen ratio of the sediment. PAH bioavailability increased as the ratio increased; thus, the more nonpolar the organic matter, the more available the compound. This polarity did not account for any of the chlorinated biphenyl bioavailability. The amount and type of mineral matrix of the sediment did not influence the bioavailability for either compound class. In addition, the amount of oxygen in the sediment was correlated with the bioavailability for BaP after carbon normalization.