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) (Δ(199)Hg from 0.20 to 1.87‰) and mass-dependent fractionation (MDF) (δ(202)Hg from -0.97 to -0.16‰), whereas sediments exhibit high MDF (δ(202)Hg from -1.99 to -0.83‰) but no MIF. δ(15)N and δ(13)C 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 δ(202)Hg 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.

The gold distribution in 32 pyrite samples and some samples of other ore minerals is studied using the method of statistical samplings of analytical data for single crystals. The samples were recovered from deposits of different genetic types within the largest gold provinces of Russia and Uzbekistan. The contents of uniformly distributed gold and the ratios of its structurally to superficially bound forms have been determined. According to the Au–As diagram for the chemical states of gold, uniformly distributed gold in pyrite is chemically bound in the overwhelming majority of cases. The previous experimental data suggest that it is partly incorporated into pyrite and partly into the structures of nanosized nonautonomous phases on the surface of the pyrite crystals. Micro- and nanoparticles of native gold might appear during postgrowth transformations of these phases. Data on the other ore minerals suggest that the dependence of the content of uniformly distributed gold on the size or specific surface area of the crystal and the superficial position of its considerable part are common to the ore minerals. It is shown for pyrite that the observed features are commonly found at deposits of different genetic types, only with differences in the slope and determination coefficients of the dependences. The size dependences of the contents of gold and other elements in pyrite are genetically significant, because they give an insight into the ore-forming processes. The data on structurally bound gold permit comparative evaluation of gold concentrations in ore fluids forming gold deposits of different genetic types.