Potentially toxic elements in the Gusinoye Lake (Republic of Buryatia, Russia)

Abstract

Enterprises of fuel and energy complex are the main sources of carcinogenic and mutagenic potentially toxic elements (PTEs). Their particulate and gaseous emissions, wastes, and effluents enforce migration processes of PTEs in atmosphere, soil, and then in water bodies, creating a danger to the functioning of aquatic ecosystems. Vulnerable objects include water bodies with slow water exchange, due to the accumulation of PTEs in the bottom sediments and the threat of secondary contamination. Among them it is necessary to note cooling ponds of thermal power plants (TPP). In this study, the ecological and geochemical state of components of "water-suspended sediments-bottom sediments" aquatic system is assessed on the example of the Gusinoye Lake (the Republic of Buryatia), which is used as cooling pond for the largest in the region TPP, burning brown coal from local deposits. The Gusinoye Lake is the second largest lake in Buryatia after the Baikal Lake and a valuable source of water supply, place of recreation, and fish breeding. To study the distribution of PTEs in the waters of the lake, a network of 19 monitoring stations was deployed in the summer of 2019. In contrast to the previous researches, detailed studies of the central deep-water part of the lake were carried out. As a result, data on the concentration of PTEs in the dissolved and suspended forms and also in bottom sediments was obtained. To study the balance of chemicals in the lake, its main tributaries were surveyed, as well as the drainage channel of TPP. For the first time, for the Lake Gusinoye, bulk concentrations of As, Cd, Pb, Zn, Co, Mo, Cu, Sb, Cr, V, Mn, Sr, and Ag were determined using the inductively coupled plasma mass spectrometry. The highest concentrations of dissolved PTEs in the lake water are confined to the mouths of tributaries in the northern part of the lake. Dissolved Sr, Mo, and Cu in the lake exceed maximum permissible concentrations (MPCs) for fishery. The maximum concentrations of Sr and Cu are almost 3 MPCs and that of Mo is 22 MPCs near the TPP. The suspended sediments of the Gusinoye Lake are depleted of all studied PTEs as compared to the regional clarkes (natural abundances) of the lithosphere. Mn has the highest concentrations in the suspension, and its maximum concentration was due to the surface runoff from the solid waste landfill and an abandoned coal mine. Concentrations of Cu, Zn, Sr, Mo, and Pb in bottom sediments are higher than in suspended sediments, thus indicating the accumulation of pollutants. The maximum intensity of accumulation is characteristic of the deep central basin of the lake and its eastern part, where Sr, Ag, and Mo accumulate most intensively near the coal field. The main sources of PTE pollution are concentrated in the northern and northeastern parts of the lake catchment area. Significant amount of dissolved Mo, Sr, and As enter the lake with the waters of quarries and mines of the coal fields, the solid waste landfill of the town of Gusinoozyorsk, and northern rivers-tributaries, draining the dumps of the large Zagustaj coal field.

Keywords: Bottom sediments; Cooling pond; Fuel and energy complex; Potentially toxic elements; Slow water exchange; Suspended sediments; Water solution.