Lake Baikal is a unique freshwater ecosystem that has been declared a UNESCO World Heritage Site. It contains high levels of PCBs, and Baikal seal were recently found to have PCDD/F concentrations comparable to those in the Baltic 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 and PCB contamination of Lake Baikal does not originate from background inputs and that the contamination increases from north to south. The soil inventory (quantity of chemical per m2 ground) was determined at 34 sites around 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 Usol'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 valley to Lake Baikal and from there northeastward along the lake. This indicates 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 ΣPCB to Lake Baikal was comparable to the ΣPCB inventory in Lake Superior in 1986, indicating that the atmospheric emissions in the Usol'ye S. area have been a major 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 chemical complex in Usol'ye Sibirskoe, and the chloralkali industry has caused environmental contamination with PCBs elsewhere. This chemical complex is suspected to have been the source of the PCB and PCDD/F contamination, but due to the paucity of information about this facility it has not yet been possible to confirm this hypothesis. This study illustrates the utility of soil contaminant inventories to trace sources of persistent hydrophobic organic contaminants.

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This study evaluated the spatial and long-term variations of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in the snow at 55 industrial, urban, rural, and remote stations in Eastern Siberia, Russia, in 2021 in comparison to data obtained from the 1990s to the 2010s. In 2021, the mean levels of the organochlorine compounds in snow amounted to 76 ng/L ∑PCB36, 5.8 ng/L hexachlorobenzene (HCB), 0.02 ng/L α-hexachlorocyclohexane (HCH), and 1.01 ng/L dichlorodiphenyltrichloroethane (DDT) and its metabolites. The spatial distribution of organochlorines was shown to result from the presence of industrial and urban sources, as well as atmospheric transport. The PCB and HCB temporal distributions from the 1990s to the 2020s were represented as V-shaped curves. The PCB homological patterns show that, in some of the samples, the abundance of lower chlorinated homologues in 2021 is greater than in previous years. Over the last three decades, the HCH and DDT levels have significantly decreased. The relationship between PCBs and suspended particulate matter became stronger with the increase in PCB chlorination levels from lighter to heavier chlorinated congeners. Deposition with wet precipitation in the wintertime provided 3–8% of the annual deposition flux. Massive POP deposition with wet precipitation occurred in May (about 12–18%) and from July to September (60–65%).

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