Environmental risks of pollution of the Modonkul River bottom sediments, South-Western Transbaikalia

The planning of water management measures in the Modonkul River Basin require a comprehensive studying the heavy metal pollution of bottom sediments flowing through the drainage runoff area of ​​ore deposits and waste from their development. Aim. To determine the environmental risks of pollution of bottom sediments, which can be a source of secondary pollution of surface waters and toxicity to biota. Object. The bottom sediments of the Modonkul River. Method. X-ray fluorescence analysis. Results and conclusions. It was established that when compared the mouth with the upper reaches of the river, the environmental risks of pollution of bottom sediments increase downstream. The accumulation of Cd in bottom sediments increases by 6.3, Cu – 3.2, As – 2.0, Co – 1.5, Pb – 1.8, Mn – 1.5 times. According to the value of the geoaccumulation index, Cd accumulations vary from weak to strong pollution, Pb – from weak to moderate pollution, Cu – weak pollution. The indicators of total pollution and additional load of heavy metals in bottom sediments increase by 3.63 times. According to the classification of the degree of pollution by heavy metals, bottom sediments are characterized as objects of strong pollution. The ecological risk of toxicity of bottom sediments increases by 4.6–5.4 times. During the formation of bottom sediments, the lithogenic contribution decreases for Cd, Pb, Cu to 4–17%, for As, Ni, Zn, Mn to 40–67%. The lithogenic contribution of Co varies within 77–90%. For citation: Khazheeva Z.I., Doroshkevich S.G., Plyusnin A.M. Environmental risks of pollution of the Modonkul River bottom sediments, South-West Transbaikalia. Bulletin of the Tomsk Polytechnic University. Geo Assets Engineering, 2026, vol. 337, no. 7, pp. 49-57. https://doi.org/10.18799/24131830/2026/7/5203