Assessment of water pollution near the deep oil seep in Lake Baikal

Water purity was assessed at the site of a deep oil seepage near Cape Gorevoy Utes (Central Baikal). Polycyclic aromatic hydrocarbons (PAHs) and n-alkanes were determined in different types of oil-containing samples collected at this section of Lake Baikal. The set of studied samples included: (i) samples of water from the surface water layer; (ii) samples of water from different depths; (iii) oil on the water surface; (iv) oil from a sediment core. In the surface water layer and the water column, the total concentration of n-alkanes ranged from 0.2 to 5.3 µg/L and did not exceed the 0.1 maximum permissible concentration (MPCfish = 50 µg/L) established for hydrocarbons in water bodies of fishery importance. PAHs with carcinogenic properties were less than 0.1 ng/L. The total concentration of PAHs found in the water column did not exceed 110 ng/L; toxic equivalent (TEQ) values ranged from 0.001 to 0.110 ng/L. The distribution of petroleum hydrocarbons from the seepage site was limited, and water pollution was localised. The low level of water pollution is associated with natural mechanisms in the Baikal ecosystem. Microbiological community and phytoplankton make a decisive contribution to the purity of Baikal water, and oil fractionation during deep discharge contributes to the bioavailability of petroleum hydrocarbons.