GEOECOLOGICAL ASSESSMENT OF THE CONDITION OF SURFACE WATERS OF AVZYAN GOLD REGION IN THE REPUBLIC OF BASHKORTOSTAN

Abstract

The relevance. Monitoring the levels of chemicals in the surface waters of mining areas and environmental assessment of their condition are the most important measures to ensure the quality of drinking water and reduce risks to public health. At the same time, to date, there is no information on the concentrations of heavy metals and metalloids in the surface waters of the Avzyan gold region. The main aim is to determine the content of trace elements, including heavy metals and metalloids, to identify the reasons for their increase in the surface waters of Avzyan gold region, and to assess the environmental risk to public health. Objects: surface waters in the middle reaches of the Bolshoy Avzyan and Bolshoy Inzer rivers and their tributaries, draining both known deposits of indigenous and placer gold in the Avzyan gold region, and the proposed gold mining sites. Methods: inductively coupled plasma-atomic emission spectrometry. Results. The surface waters of the Avzyan gold region are characterized by an unfavorable ecological condition. The main contaminant element is antimony, exceeding the maximum allowable concentration by 1,2...7,6 times in all selected samples. The level of water contamination with this element in most samples is high and extremely high. Based on the results of the research, a map of the degree of contamination of surface waters with antimony was built. In many cases, there is an average of 1,6...5,0-fold excess of the maximum allowable concentration for iron, manganese, tungsten, copper, aluminum, vanadium, in single samples – for arsenic and molybdenum. Areas of extremely high contamination for aluminum, molybdenum, and a high level of contamination for tungsten were locally established. According to the values of the coefficients of complexity of pollution (8,7…30,4 %) and the values of the coefficients of complexity of high and extremely high levels of pollution (up to 4,3 %), the surface waters of Avzyan gold region are moderately toxic and belong to the I–II category of pollution. Based on the values of the total hazard coefficients, a non-carcinogenic risk to public health was determined, which consists in possible adverse consequences and is mainly associated with high concentrations of antimony in water. The increase in the concentrations of polluting elements in surface waters is due to natural (geogenic) factors – geochemical and mineralogical features of rocks involved in the geological structure of deposits and ore occurrences of the Avzyan gold region. Arsenic concentrations naturally increase in the tributaries of the Bolshoy Avzyan river, forming local scattering streams near gold deposits. The migration ability of antimony in comparison with arsenic is manifested to a greater extent. The predominant dissolved forms of arsenic are the oxyanions HAsO42– and H2AsO4–, antimony – Sb(OH)6–. An increase in the concentrations of these metalloids in the Bolshoy Avzyan river and its tributaries is associated with the dissolution of silicate minerals and iron hydroxides, as well as with the dissolution of pyrite-containing carbonate rocks of the Suran formation. The ongoing development of deposits of indigenous and placer gold currently does not have a great impact on the increase in the content of these elements in surface waters.

Keywords

• avzyan gold region
• gold
• surface waters
• bolshoy avzyan
• bolshoy inzer
• antimony
• arsenic