Abstract
Mining and smelting activities are the primary sources of toxic metal pollution in China. The purpose of this study was to investigate the pollution risk and identify sources of metals in the arable soil of a Zn/Pb mining and smelting district located in Huize, in Southwest China. Topsoil (346) and profile (three) samples were collected and analyzed to determine the total concentrations of eight toxic elements (Cd, Hg, As, Pb, Cr, Cu, Zn and Ni). The results showed that the mean Cd, Hg, As, Pb, Cr, Cu, Zn and Ni concentrations were 9.07, 0.37, 25.0, 512, 88.7, 239, 1761 and 90.3 mg/kg, respectively, all of which exceeded both the Huize and Yunnan soil background levels. Overall the topsoil was quite acidic, with a mean pH of 5.51. The mean geoaccumulation index (Igeo) revealed that the pollution level was in the order of Pb > Zn > Cd > Hg > As > Ni > Cu > Cr. The ecological risk index (Ei) indicated that there were serious contamination risks for Cd and Hg, high risk for Pb, moderate risk for As, and Cd and Hg were the dominant contributors to the high combined ecological risk index (Er) with a mean parameter of 699 meaning a serious ecological risk. The Nemerow pollution index (Pn) showed that 99.1% of soil samples were highly polluted or worse. Horizontally, high concentrations of Cd, Hg, As, Pb and Zn appeared in the north and middle of the study area, while Cr, Cu and Ni showed an opposite trend. Vertically, as the depth increased, Cd, Hg, As, Pb and Zn contents declined, but Cr, Cu and Ni exhibited an increasing trend. The mobilities of the metals were in the order of Zn > Cd > Hg > As > Pb. Horizontal and vertical distribution, coupled with correlation analysis, PCA and CA suggested that Cd, Hg, As, Pb and Zn mainly came from the anthropogenic sources, whereas Cr and Ni had a lithogenic origin. The source of Cu was a combination of the presence of parent materials as well as human activities. This study provides a base for the local government to control the toxic metal pollution and restore the soil environment system and an effective method to identify the sources of the studied pollutants.
Highlights
Mining and smelting activities greatly promote employment and considerably benefit the domestic economy
Horizontal and vertical distribution, coupled with correlation analysis, principal component analysis (PCA) and cluster analysis (CA) suggested that Cd, Hg, As, Pb and Zn mainly came from the anthropogenic sources, whereas Cr and Ni had a lithogenic origin
This study provides a base for the local government to control the toxic metal pollution and restore the soil environment system and an effective method to identify the sources of the studied pollutants
Summary
Mining and smelting activities greatly promote employment and considerably benefit the domestic economy. B Background value of Yunnan, c Background value of Huize [26,34]; d Chinese Soil. Environmental Quality (Screening Values), e Chinese Soil Environmental Quality (Intervention Values) [35]; f Canadian. Soil Quality Guidelines [45]; g Dutch Pollutant Limit (Target Value), h Dutch Pollutant Limit (Intervention Value) [46]. The metals were Pb, Zn, Hg, As and Ni with levels 17, 14, 6, 3 and 1 times higher than the background values of Huize, respectively. Metals’ mean concentrations excluding As and Cr exceeded the DPL target values, whereas only the average concentrations of Cu and Zn were higher than the intervention values recommended in the DPL [46]. According to the related pH values of soil samples and scanning values of the CSEQ [35], the over-limit rate of Cd reached 100%, and Cu, Zn, Pb and Ni followed with the rate of 99.7, 99.4, 98.6 and 91.9%, and the over-limit rates of As, Hg and
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