Bioaccumulation of organochlorines through a remote freshwater food web in the Canadian Arctic

Abstract

Persistent organochlorines (OCs) were measured in water, sediment and biota from a remote lake in the Canadian Arctic to examine the bioaccumulation of atmospherically deposited OCs through a high-latitude freshwater food web. All major OC groups (polychlorinated biphenyls [PCBs], dichlorodiphenyl trichloroethane and metabolites [DDT], chlordane [CHL]-related compounds, and hexachlorocyclohexane [HCH] isomers) were detectable at sub-ng liter −1 concentrations in lake water and at low ng g −1 levels (dry wt) in surface sediments. Estimates of air–water exchange using a two-film model suggested that lake waters were close to equilibrium with the atmosphere for αHCH, trans-nonachlor and p,p′-DDE but that PCB congeners 52 and 153 were undergoing volatilization. Despite the relatively short open water season, gas absorption was found to be a major input pathway into the lake, when compared to estimated inputs from precipitation. Mean concentrations of ΣHCH, ΣDDT, ΣCHL and ΣPCB ranged from 1 to 10 ng g −1 wet wt in arctic char and from 2 to 82 ng g −1 in lake trout and were comparable to results from other lakes in the Canadian Arctic. Exceptionally high concentrations (six- to 10-fold higher than mean values) of these OCs were observed in a few lake trout and were explained by the larger size, longer lifespans and higher lipid contents of these individuals. Trophic interrelationships of food-web organisms were characterized using their tissue stable carbon and nitrogen isotope ratios. Through the food web, lipid-adjusted concentrations of αHCH, trans-nonachlor, p,p′-DDE, and PCB congeners 52 and 153 in biota were significantly related to their trophic position as determined by measurements of tissue stable nitrogen isotope ratios. In addition, the slopes and coefficients of determination for these relations increased with the lipophilicity and recalcitrance of the OCs, demonstrating that the more lipophilic OCs bioaccumulated to a greater degree through this food web even after accounting for the effects of lipid.