Historical Deposition of PCBs and Organochlorine Pesticides to Lake Winnipeg (Canada)

Abstract

Two dated sediment cores; one taken from the north basin and one from the south basin of Lake Winnipeg (Manitoba, Canada) were analyzed for PCBs and organochlorine insecticides in order to examine the depositional history of these persistent organic pollutants (POPs). No previous work had been conducted 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 dated to the late 1960s to early 1970s. Recent PCB fluxes were estimated to be 5 to 11 μg/m 2/y in Lake Winnipeg sediments, with burdens of 388 and 337 μg/m 2 in the north and south basins, respectively. Loadings in the north basin sediment indicated atmospheric sources; south basin sediment reflected inputs from agricultural, industrial, and urban activities. DDT inventories were 37 and 127 μg/m 2 in the north and south basin cores, respectively. DDD contributed the largest amount to DDT in sediments, corresponding to anaerobic degradation of the parent molecule. Maximum hexachlorocyclohexane (HCH) concentrations were observed in recent slices of both sediment cores and fluxes ranged from 177 to 914 ng/m 2/y. There was evidence for recent increases in lindane deposition. Subsurface maximum concentrations were observed for total chlordane (ΣCHL), pentachloroanisole (PCA), and total chlorobenzenes (ΣCBz) in the south basin. ΣCHL, PCA, and ΣCBz, however, were present at maximum concentrations in the surface slice in sediment from the north basin.