PARTICLE-ASSOCIATED PCBS IN LAKE-ONTARIO

A study was carried out to evaluate the role of the nepheloid layer in the transport and cycling of PCBs in Lake Ontario in 1987-89 and 1991 . Water, suspended matter, and bottom sediment samples were collected at eleven stations in Lake Ontario. The concentrations of t-PCBs in th e suspended matter in the nepheloid layer ranged from 151 to 728 ng/g (dry wt) in 1987-1989, and were greater than those in most of the top 3-cm sediments (<1-405 ng/g dry wt). The suspended matter in the nephe loid layer contained more lower chlorinated biphenyls, particularly te tra- and pentachlorobiphenyls, than the bottom sediments. The greatest concentrations (up to 4100 ng/g dry wt) existed in the suspended matt er at 15 m above the lake bottom after the development of the nepheloi d layer. The results of the study indicated the association of t-PCBs with allochthonous particles originating mainly during the summer mont hs in the surface water which were sinking through the water column an d accumulated in the nepheloid layer in late August and September.