Distribution and factors of accumulation of heavy metals and metaloids in river bottom sediments in the territory of the Ulan-Ude city

The distribution and accumulation factors of heavy metals and metalloids (HMMs) in the bottom sediments of the Selenga river and its tributary Uda have been studied on the territory of Ulan-Ude. Their ecological and geochemical condition can influence the state of the lower reaches of the Selenga river and Baikal lake. We selected 3 background, 12 urban and 1 sample of bottom sediments downstream of the city. The main physical-chemical properties (pH, content of organic matter, iron oxides, granulometric composition) and the total content of HMMs in the samples were determined. The sediments of the Selenga and Udarivers are characterized by sandy and sandy-loamy granulometric composition, neutral reaction, low content of organic matter and Fe2O3. Upstream Ulan-Ude the rivershave a similar chemical composition of the sediments and are characterized by the dispersion and near-clark concentrations of the HMMs. Within the city and downstream, microelemental composition of the sediments has not significantly differ from the background one, this is due to their low sorption capacity and insignificant contamination of the precipitating suspended matter. Low-contrast geochemical anomalies were formed near the motorways (Mo, Cd, Bi), the oil storage facilities “BuryatTerminal” (W, Cu, Mo, As, Sb, Pb, Bi, Cd, Co, Ni), treatment plant (As, W, Bi), upstream of the aircraft plant (Cd) and below TPP-1 (W, V, Cd, Cu, Sb). The presence of correlations between the HMM content and the physico-chemical properties of the deposits indicates that the geochemical anomalies were formed also due to the sorption-sedimentation, chemisorption and biogeochemical barriers. The acid barrier is of great importance for the accumulation of an anionic Mo. The total HMM contamination of sediments within the city and downstream refers to the permissible level. The MPC in the sediments of the Selengariver was exceeded for As(in 1,5-3,4 times). Thus, in the UlanUde city and downstream, there are a weak man-made transformation and a low ecological danger of pollution of river sediments. The maximum contents of HMMs are localized on geochemical barriers near industrial enterprises and highways.