Tracing Sources and Bioaccumulation of Mercury in Fish of Lake Baikal- Angara River Using Hg Isotopic Composition

This study presents the determination and comparison of isotopic compositions of Hg in sediments, plankton, roach, and perch of two freshwater systems in the Lake Baikal-Angara River aquatic ecosystem: the man-made Bratsk Water Reservoir contaminated by Hg from a chlor-alkali factory and the noncontaminated Lake Baikal. Isotopic ratios of biota exhibit both significant mass-independent fractionation (MIF) (Delta Hg-199 from 0.20 to 1.877 parts per thousand) and mass-dependent fractionation (MDF) (delta Hg-202 from -0.97 to -0.16 parts per thousand), whereas sediments exhibit high MDF (delta Hg-202 from -1.99 to -0.83 parts per thousand) but no MIF. delta N-15 and delta C-13 are correlated with methylmercury in organisms from both sites, indicating bioaccumulation and biomagnification through food webs of both regions. Combining this with isotopic composition of samples shows that (delta Hg-202 increases with the trophic level of organisms and also with methylmercury in fish from Lake Baikal. This study demonstrates that MIF in fish samples from Bratsk Water Reservoir allow to trace anthropogenic Hg, since fish with the highest levels of Hg in muscle have the same isotopic composition as the sediment in which anthropogenic Hg was deposited. Less contaminated fish do not exhibit this anthropogenic signature accumulating relatively lower Hg amount from the contaminated sediments. This work reveals that Hg isotopic composition can be used to track the contribution of anthropogenic sources in fish from a contaminated lake.