Historical contamination of Yukon Lake sediments by PCBs and organochlorine pesticides: influence of local sources and watershed characteristics

PCBs and other persistent organochlorine (OC) pesticides were analyzed in s ediment cores collected from six lakes in Yukon Territory and one in northe rn British Columbia, Canada, with the objective of establishing sources and historical trends of these contaminants. DDT was found to be the most prom inent CIC in the sediment profiles of most of the lakes. Maximum Sigma DDT levels (3.47-2680 ng g(-1) dw) were observed in sediment slices dated to th e 1950s from lakes near populated areas. In contrast, in more remote takes (Hanson, Kusawa and Lindeman), the maximum Sigma DDT concentrations were ob served in the sediments dated to the 1970s. Highest Sigma PCB and Sigma DDT concentrations were measured in sediments from Watson Lake, near a suspect ed PCB; waste disposal site and in a region where DDT was heavily applied i n the 1950s and 1960s. Elevated Sigma PCB concentrations [16.1-93.6 ng g(-1 ) dry weight (dw)] were also observed in sediments from lakes situated near populated areas, relative to Kusawa and Lindeman (11.1 and 12.7 ng g(-1) d w, respectively). Recent Sigma PCB fluxes ranged from 621 ng m(-2) y(-1) in Kusawa Lake to 16 400 ng m(-2) y(-1) in Little Atlin Lake. The extremely h igh sedimentation rate (2050 g m(-2) y(-1)) in glacial fed Lindeman Lake ga ve rise to elevated fluxes of Sigma PCB (2410 ng m(-2) y(-1)) and other OCs , despite much lower concentrations in the sediment. Levels of hexachlorocy clohexanes (Sigma HCH), chlordane-related compounds (Sigma CHL), and chloro benzenes (Sigma CBz) were in the low ng g(-1) (dw) range in all lake sedime nts, similar to concentrations previously reported for Arctic lakes in Cana da, indicating that their major source was long range atmospheric transport . Contamination of the lakes with PCBs and DDT near populated areas of the Yukon Territory appears to be a result of regional activities rather than l ong range transport and deposition. The results also point to glacial runof f as a significant source of OCs to small. high elevation lakes (Lindeman), but not to larger lakes within the Yukon River drainage basin that are als o affected by glacial sources (Kusawa, Laberge). (C) 2001 Elsevier Science B.V. All rights reserved.