Pollution, sources and environmental risk assessment of heavy metals in the surface AMD water, sediments and surface soils around unexploited Rona Cu deposit, Tibet, China

Abstract

The pollution by heavy metals (HMs) of mining is a widespread problem in the world. However, the pollution by HMs around unexploited deposits (virgin fields) has been studied rarely, especially in Tibet, China. Water, sediments and surface soils were collected to investigate the concentrations of HMs around unexploited Rona Cu deposit in Tibet, China. Furthermore, geochemical fractions of these elements were also analyzed. Pollution and environmental risk introduced by HMs accumulation were assessed using pollution indices, geo-accumulation (Igeo), potential ecological risk index and risk assessment code (RAC). Results indicated that the pH values of Rona tributary river ranged from 2.70 to 3.08, and the average concentrations of Cu and Zn were 2114.00 ± 65.89 and 1402.14 ± 27.36 μg L−1, respectively, exceeding their standard limits. The concentrations (mg kg−1) of Cu, Zn and As ranged in 19.01–1763.10, 62.00–543.06 and 11.12–61.78 for sediments, respectively, and 154.60–1489.35, 55.38–344.74 and 10.05–404.03 for surface soils, respectively, exceeding their standard limits. According to RAC, almost all Cu, Zn and As near low risk status. However, Cd ranged from medium to very high risk in sediments, and low to high risk in surface soils. Statistical analysis suggested that Cu, Pb, Zn, As and Cd in sediments and surface soils may mainly derive from Rona deposit, whereas Cr and Hg may primarily originate from lithogenic sources. The results indicated that very high concentrations of HMs could be occurred in surface water, sediments and surface soils around unexploited deposits. Especially at high-altitude Tibet, the high environmental risk of HMs deserves more attention.