Historical deposition of PCBs and organochlorine pesticides to Lake Winnipeg (Canada)

Two dated sediment cores; one taken from the north basin and one from the s outh basin of Lake Winnipeg (Manitoba, Canada) were analyzed for PCBs and o rganochlorine insecticides in order to examine the depositional history of these persistent organic pollutants (POPs). No previous work had been condu cted on current or historical deposition of POPs in Lake Winnipeg sediments . Analysis by high resolution gas chromatography-electron capture detection showed elevated PCB concentrations in sediments dared to the late 1960s to early 1970s. Recent PCB fluxes were estimated to be 5 to 11 mu g/m(2)/y in Lake Winnipeg sediments, with burdens of 388 and 337 mu g/m(2) in the nort h and south basins, respectively. Loadings in the north basin sediment indi cated atmospheric sources; south basin sediment reflected inputs from agric ultural, industrial, and urban activities. DDT inventories were 37 and 127 mu g/m(2) in the north and south basin cores, respectively. DDD contributed the largest amount to DDT in sediments, corresponding to anaerobic degrada tion of the parent molecule. Maximum hexachlorocyclohexane (HCH) concentrat ions were observed in recent slices of both sediment cores and fluxes range d from 177 to 914 ng/m(2)/y. There was evidence for recent increases in lin dane deposition. Subsurface maximum concentrations were observed for total chlordane (Sigma CHL), pentachloroanisole (PCA), and total chlorobenzenes ( Sigma CBz) in the south basin. Sigma CHL, PCA, and Sigma CBz, however, were present at maximum concentrations in the surface slice in sediment from th e north basin.