Characteristics of wastewater from the industrial zone of Usolye-Sibirskoe and its impact on hydrochemical composition of the Angara river during periods with different technogenic load

Abstract

Relevance. Tense ecological situation in the impact zone of the large industrial complex of Usolye-Sibirskoe on the Angara river, search for sources and ways of pollutants inflow during different periods of technogenic load, necessary to assess and forecast the current changes in the aquatic ecosystem. Aim. To study chemical composition of wastewater from the industrial zone of Usolye-Sibirskoe during different periods of technogenic load and assess their impact on hydrochemical parameters of the Angara river water. Objects. Wastewater from the industrial zone of Usolye-Sibirskoe and Angara river waters in the impact area during the period of high technogenic load (2010) and the period of its reduction (2020). Methods. Chemical composition of wastewater and natural water was determined in the Center of Collective Use «Isotope-Geochemical Investigations» of Vinogradov Institute of Geochemistry SB RAS (Irkutsk, Russia). Concentrations of major ions in waters were measured using a set of methods generally accepted in hydrochemistry (atomic absorption and atomic emission flame spectrometry, spectrophotometry, potentiometry, titrimetry), Hg concentration was measured using atomic absorption spectrometry, concentrations of other trace elements – using mass spectrometry method (ISP MS). Results. The authors have revealed significant changes in chemical composition of wastewater of the industrial zone in different periods of technogenic load, reflecting the transformation of pollution sources during the liquidation of technogenic objects of the area. Over the ten-year period particularly important changes are expressed in a significant decrease of Hg, Al, Cs, Ti, Cr, Cl– and Na+ concentrations and increase of Mn concentrations in the wastewater of the industrial zone. This is reflected, in its turn, in the dynamics of hydrochemical composition of Angara river water in the impact area. In 2010 a regular consecutive decrease of most of elements concentrations was observed with distance of Angara river waters from technogenic sources. Where as in 2020 their spatial distribution is opposite: with a significant decrease in concentrations of most of the studied elements at the river site 50 m downstream of industrial discharges, their increase was detected at more distant monitoring stations (1.5 and 5 km) where Mn, Cu, Cd and Tl concentrations were the highest. Despite significant changes in wastewater chemical composition in different periods of technogenic load, the Angara river waters at all monitoring stations in the impact zone of the industrial complex of Usolye-Sibirskoe are polluted.

Keywords

• pollution
• major ions
• , trace elements
• Angara river
• wastewater