Pollution sources, characteristics and environmental risk assessment of heavy metals in surface water and sediments of typical pyrite mine in Southwest China

Abstract

Abandoned mines, especially pyrite-rich ones, release acid mine drainage (AMD) with high acidity and excessive amounts of heavy metals, threatening regional ecosystems. Six samples of mine drainage, nine samples of surface water, and twelve samples of sediment were analyzed in this case study of the Dashu pyrite mine in southwest China. A comprehensive analysis of the pollution levels, pollution sources, and potential hazards of eight metals (Ni, Cd, Cu, Zn, Fe, Al, Pb, and Mn) that exceeded regulatory standards was conducted by monitoring 24 conventional and characteristic indicators. Ultimately, this research evaluated the environmental hazards associated with abandoned mine water using the "pressure-response" model, thereby providing valuable insights for the effective protection of the environment in mining regions. The primary pollutants in mine water were determined to be SO₄²⁻, Fe, and Mn, with concentrations of 7700, 1450, and 6.78 mg/L, respectively. A clear "source-sink" dynamic was observed between the mine water and the surrounding water system. surface water was primarily polluted by Ni and Mn, while water system sediments were primarily polluted by Cu and Hg. Ion ratio and Pearson correlation analyses indicated heavy metals in surface water and sediments originated from the same AMD source. The "pressure-response" model was used to assess the environmental hazards of water from abandoned mines. Mines W1, W2, W5, and W6 were classified as high-risk, while W3 and W4 were medium-risk. This study offers a novel approach and valuable reference for identifying and classifying environmental risks in abandoned mines and targeting AMD treatment.