Tracing the sources of PCDD/Fs and PCBs to Lake Baikal

Lake Baikal is a unique freshwater ecosystem that has been declared a UNESC O World Heritage Site. It contains high levels of PCBs, and Baikal seal wer e recently found to have PCDD/F concentrations comparable to those in the B altic Sea. In this work fish and soil were analyzed to trace the sources of these compounds to the lake. The fish samples indicated that the PCDD/F an d PCB contamination of Lake Baikal does not originate from background input s and that the contamination increases from north to south. The soil invent ory (quantity of chemical per m(2) ground) was determined at 34 sites aroun d Lake Baikal and in the Angara River valley. For the PCDD/Fs and most PCBs , the soil inventory is a good approximation of the cumulative atmospheric deposition. It varied over a factor of 1000, with the highest levels in Uso l'ye Sibirskoe, a city 110 km north of the southwestern tip of the lake in the highly industrialized Angara River valley, and the lowest values in the pristine areas to the northeast of the lake. A continuous decrease in the soil inventory was observed moving from Usol'ye S. up the Angara River vall ey to Lake Baikal and from there northeastward along the lake. This indicat es that there was a major atmospheric source of these compounds in the Usol 'ye area. The cumulative deposition to the lake was estimated to be 1.2 kg of TEQ (PCDD/F + PCB). The cumulative deposition of Sigma PCB to Lake Baika l was comparable to the Sigma PCB inventory in Lake Superior in 1986, indic ating that the atmospheric emissions in the Usol'ye S, area have been a maj or source to Lake Baikal. The soil inventories of the PCDD/Fs and PCBs were highly correlated, and the PCDD/F pattern in the soils was similar to the PCDD/F pattern in technical PCB mixtures. There is a large chloralkali chem ical complex in Usol'ye Sibirskoe, and the chloralkali industry has caused environmental contamination with PCBs elsewhere. This chemical complex is s uspected to have been the source of the PCB and PCDD/F contamination, but d ue to the paucity of information about this facility it has not yet been po ssible to confirm this hypothesis. This study illustrates the utility of so il contaminant inventories to trace sources of persistent hydrophobic organ ic contaminants.