The effect of contaminant desorption on assimilation of sediment-sorbed hydrophobic contaminants by deposit-feeders

The literature shows that assimilation efficiencies of lab-spiked nonpolar contaminants by deposit-feeders are generally much greater than the assimilation of the organic carbon sorbent matrix. Thus the rate and extent of contaminant desorption into the aqueous gut environment is likely to play a significant role in uptake from sediments. Contaminated New York Harbor sediments were examined in parallel desorption kinetic and bioaccumulation studies with the clam Yoldia limatula. A clear relationship was observed between the contaminant desorption rates over the first two days and organism/sediment bioaccumulation factors (BAF) determined across a wide range of individual PCBs, PAHs, and linear alkylbenzenes. Bioavailability was affected by hydrophobicity, shape of the contaminant, and contaminant class/source. Lower bioavailability of PAH may be the result of matrix associations with soot or fine coal particles. Interestingly, contaminant desorption/bioavailability were not influenced greatly by depth in the sediment core. The authors have initiated a study to determine the critical chemical and biological factors that control contaminant assimilation. They hope that it will become possible to replace expensive biological exposure studies with simple desorption tests when assessing the risk associated with contaminated sediments or dredge materials.