Geochemical baseline values determination and evaluation of heavy metal contamination in soils of lanping mining valley (Yunnan province, China)

Abstract

The largest lead/zinc mine in China is located in Lanping mining valley. The real impact of mining activity on the Lanping mining valley has not been studied to date. This study aims to characterize the geochemical baseline values and risk assessment of heavy metal contamination in soils of a study area located in the Lanping mining valley including upstream, mining and downstream areas. The results showed that the mean soil pH value was 6.8, and organic matter was 34.3%, in surface layer of the mining area. The mean soil pH value in the upstream and downstream areas was less than 5.5. The concentrations of Pb and Zn in the mining area were 56 and 47 times above the world average, the concentrations of Pb, Zn and Cd in the upstream area were six, seven, and six times above the world average, and the concentrations of Pb, Zn and Cd in the downstream area were eight, eight, and 18 times above the world average, respectively. The proposed geochemical baseline values of Pb, Cu, Zn and Cd were 169.93, 31.81, 569.06 and 4.13 mg•kg−1, respectively. The pseudo total and ethylene diamine tetraacetic acid (EDTA)-extractable concentrations of Pb, Zn and Cd showed similar tendency as follows: Mining area > downstream area > upstream area. The contamination degree with the geoaccumulation index (Igeo) and the improved Nemerow index (IIN) in the upstream and mining areas was non-contamination or slight contamination with low or moderate risk with the individual ecological risk index (Er) and the comprehensive potential ecological risk index (RI), although moderate or heavy contamination with pollution factor (Pi) and the Nemerow index (IN). The contamination degree with Igeo and IIN in the downstream area was non-contamination or extreme contamination with low or extreme risk with Er and RI. The results suggest that the IIN should be recommended to assess the soil contamination of heavy metals and the geochemical baseline values would be important for the environmental management and remediation of soils contaminated by heavy metals.