ORGANOCHLORINE DYNAMICS IN THE PELAGIC FOOD-WEB OF LAKE BAIKAL

In July and August 1993, samples were collected from Lake Baikal both to document organochlorine concentrations and to relate the contaminan t levels to trophic position and lipid concentration. High-volume wate r samples and representatives of the major organisms in the food web, including zooplankton, fish, and seals, were collected. Dissolved and particulate water samples were analyzed for polychlorinated biphenyls (PCBs; 74 congeners) and hexachlorobenzene. Biota samples were analyze d for PCBs, hexachlorocyclohexanes, chlordane and related compounds, d ieldrin, dichlorodiphenyltrichloroethane (plus metabolites), and toxap hene. Specific lipid classes were measured in fish since these were po stulated to affect organochlorine concentrations. Stable nitrogen (del ta(15)N) and carbon (delta(13)C) isotopic compositions were determined in all samples except seal blubber as a measure of trophic position. Total PCBs in surface water ranged from 130 pg/L in the lake's norther n basin to 1,900 pg/L in the southern basin. Total PCBs in fish ranged from 60 to 710 ng/g (wet weight), with differences mostly attributed to total lipid content rather than to specific lipid classes. The PCB bioaccumulation factor was significantly correlated with log K-ow, whe reas the PCB bioconcentration factor was not. The transfer of contamin ants through the food web was likely al steady state, whereas the upta ke of PCBs from the water was not. This indicates recent PCB contamina tion.