Technogenic impact of wastewater on the hydrochemical composition of the Angara River
The Angara River is a source of drinking water supply for the population of Irkutsk Oblast (Russia). The ecosystem of the river has been under anthropogenic impact from the large Usolie-Sibirsky industrial zone for several decades. The aim of the present study was to analyze the concentrations of trace elements in the wastewater entering the Angara River and to determine their impact on the river’s hydrochemical composition. For this purpose, concentrations of 21 trace elements were measured in the wastewater and waters of Angara River at different distances from the technogenic sources. The results obtained show that wastewater contains high concentrations of a large range of trace elements. The intensity of anthropogenic impact was determined using a contamination factor (CF), which allowed to identify four groups of trace elements depending on their concentration exceeding the background level. The largest factors are determined for Sb (CF up to 123), B (CF up to 345), Ti (CF up to 651), Br (CF up to 913), Ge (CF up to 1093), Hg (CF up to 1991). The inflow of elements of anthropogenic origin is reflected in a negative change in the hydro-chemical composition of the Angara River at sites where waste- and river water are mixed. However, due to intensive dilution of wastewater by the Angara River, concentration of most trace elements in the river water at a distance of 5 km downstream of contamination sources are reduced to background levels. At the same time, elements (Li, As, V, Mo, B, Br, Ge, Hg) have been identified, whose concentrations in the water of the Angara River in this section remain above the background values. Increased concentrations of the observed trace elements can lead to negative consequences for hydrobionts, which are vulnerable even to minor changes in the chemical composition of the Angara River.