BIOACCUMULATION OF ORGANOCHLORINES THROUGH A REMOTE FRESH-WATER FOOD-WEB IN THE CANADIAN ARCTIC

Persistent organochlorines (OCs) were measured in water, sediment and biota from a remote lake in the Canadian Arctic to examine the bioaccu mulation of atmospherically deposited OCs through a high-latitude fres hwater food web. All major OC groups (polychlorinated biphenyls [PCBs] , dichlorodiphenyl trichloroethane and metabolites [DDT], chlordane [C HL]-related compounds, and hexachlorocyclohexane [HCH] isomers) were d etectable 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 alpha HCH, trans-nonachlor and p,p'-DDE but that PCB congeners 52 and 153 were undergoing volatilizat ion. Despite the relatively short open water season, gas absorption wa s found to be a major input pathway into the lake, when compared to es timated inputs from precipitation. Mean concentrations of Sigma HCH, S igma DDT, Sigma CHL and Sigma PCB 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 compar able to results from other lakes in the Canadian Arctic. Exceptionally high concentrations (six- to 10-fold higher than mean values) of thes e OCs were observed in a few lake trout and were explained by the larg er size, longer lifespans and higher lipid contents of these individua ls. Trophic interrelationships of food-web organisms were characterize d using their tissue stable carbon and nitrogen isotope ratios. Throug h the food web, lipid-adjusted concentrations of aHCH, trans-nonachlor , p,p'-DDE, and PCB congeners 52 and 153 in biota were significantly r elated to their trophic position as determined by measurements of tiss ue stable nitrogen isotope ratios. In addition, the slopes and coeffic ients of determination for these relations increased with the lipophil icity and recalcitrance of the OCs, demonstrating that the more lipoph ilic OCs bioaccumulated to a greater degree through this food web even after accounting for the effects of lipid. Crown Copyright (C) 1998 P ublished by Elsevier Science Ltd. All rights reserved.