Validating Possible Effects of Eutrophication Using PCB Concentrations in Bivalves and Sediment of the US Musselwatch and Benthic Surveillance Programs

In order to examine the possible interactions of eutrophication and hydrophobic organic contaminants, data for polychlorinated biphenyl (PCB) concentrations (C-PCB) in three species of bivalves and in sediments were examined. These were correlated to total organic carbon content of sediments (TOCsed), which was assumed to represent the trophic status of the sampling sites. Almost all C-PCB on dry weight basis in the bivalves and in the sediments were positively linearly correlated to TOCsed. Regarding the sediments, this simply reflects the high affinity of these compounds for TOC, but for the bivalves the correlation was not explained. In the bivalves, the difference in PCB homologue concentration was positively linearly correlated to TOCsed. To understand these field data, a box model was used to simulate the fate of PCB in oligotrophic, mesotrophic, eutrophic, and hypertrophic marine environments. The calculated results qualitatively predicted the change in C-PCB for the sediment correctly. For increased trophic status of the water compartment, on a scale from oligo- to hypertrophic, the model predicted decreasing fugacities for the PCBs, and thus could not support the observations of increased bivalve C-PCB seen in the field data study. It was suggested that the PCB pattern change in the bivalves could be influenced by algae-growth dynamics in the watercolumn. This would selectively intensify the washout of the lighter chlorinated homologues from the water and, thereby, decrease their concentrations in the bivalves.