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An accumulation of heavy metals in soil poses a risk to the ecological environment and human health. In this study, the concentrations of heavy metals in soil and crops were examined in a lead-zinc mining area in Guizhou Province, China. The distribution and sources of heavy metals were analyzed using GIS spatial mapping. The potential ecological risks of heavy metals were assessed using the potential ecological risk index (RI), and the human health risk assessment method recommended by the United States Environmental Protection Agency (USEPA) was used to quantify the health risk of residents exposed to heavy metals in the soil around lead-zinc mines. According to the results, the average of concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in the soil were 58, 7.9, 175, 64, 0.461, 65, 1539, and 2513 mg·kg -1 , respectively, which were significantly higher than the background values in Guizhou Province. It was found that the As, Cd, Cu, Hg, Pb, and Zn concentrations were extremely irregular in the soil and that the concentrations decreased significantly with the distance to the smelters, which were greatly disturbed by human activities. Comprehensive evaluation of soil heavy metals using the potential ecological risk index revealed that the risks of soil heavy metals were pole-strength and strong levels, and Cd constituted the primary ecological risk factor. A total of 22% and 10% of the corn samples contained Pb and As above the heavy metal pollution thresholds in the national food safety standards. According to human health risk assessments, heavy metals in the soil present potential non-carcinogenic risks to adults or children, and pose a potential carcinogenic risk to children. Soil pH was an important controlling factor affecting the bioavailability, migration, and accumulation of Cd in soil-crop systems. This study provides data and theoretical support for the prevention and control of soil pollution in lead-zine mining areas.

Taking a typical lead-zinc mining area in Yangshuo county, Guangxi as the research object, the contents of 10 metal elements (Cr, Mn, Ni, Cu, Zn, As, Cd, Sb, Hg, and Pb) in the surface soil of Sidihe River basin in Yangshuo were analyzed and determined. Pearson correlation analysis, principal component analysis (PCA), positive definite matrix factorization (PMF), and other methods were comprehensively used to quantitatively analyze their contributions and identify pollution sources. In total, 168 surface soil samples were collected across the study area. The mean concentrations of Zn, Cd, Hg, and Pb in the soils were higher than the National Environmental Quality Standards for Soils in China. The mean contents of Sb, Cd, Cu, Pb, and Zn were higher than their corresponding local background values by approximately 1.01, 5.50, 3.29, 9.11, and 10.67 times, respectively, indicating that heavy metals have been enriched in topsoil. The I geo showed that the major pollutant element in the soils was Hg, followed by Pb, Zn, and Mn. Correlation analysis and principal component analysis showed that the sources of metal pollution in surface soil in the study area were complex and mainly from human activities. Cu, Zn, Cd, Sb, As, and Pb were mainly derived from mining activities; Hg, Cr, and Ni were controlled by soil parent material sources; and Mn and Cd were mainly derived from mining activities and agricultural activities. PMF model analysis results showed that the metal pollution sources in the surface soil were jointly affected by these three sources. Mining activities, natural sources, and a mixed source of mining activities and agricultural activities were the main sources of heavy metal pollution in the soils, accounting for 58.0%, 13.5%, and 28.6% of the total heavy metal accumulation, respectively. Ni, Cu, Zn, As, Sb, Hg, and Pb were derived mainly from mining activities. Cr, Ni, and Hg were mainly attributed to natural sources, such as soil parent materials and rainfall erosion (44.6%, 23.2%, and 21.0%, respectively), and Mn and Cd were associated with a mixed source of mining activities and agricultural activities (75.4% and 70.4%).

Carbonatite and basalt are widely distributed in southwest China, and potentially toxic elements (PTEs) are associated with the naturally high background properties. It is important to carry out ecological risk assessments and identify potential sources of PTEs. A total of 3180 soil samples (0-20 cm) were collected in Hezhang county, a typical high background area of PTEs with the parent lithology of carbonatite and basalt. Samples were obtained from 18 large lead-zinc mines, which belong to a multi-ecological risk superimposed area with high ecological risk. The concentration of PTEs (Cd, Cr, As, Hg, Pb, Cu, Zn, and Ni) in the topsoil were analyzed, and statistical analysis (SA), geographic information system (GIS), enrichment factor (EF), potential ecological risk index (RI), and positive matrix factorization (PMF) methods were used to assess the ecological risk and quantify sources of PTEs. The mean values of PTEs concentrations in topsoil were 24.55, 2.25, 176.40, 89.60, 0.19, 64.20, 102.00, and 257.00 mg·kg -1 for As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, respectively, which were remarkably higher than the average background value (ABV) of soils in Guizhou Province. The average concentrations of Cd, Cr, Cu, Ni, Pb, and Zn exceeded the screening values specified for the soil contamination risk in agricultural land (GB 15618-2018) by 7.50, 1.18, 1.79, 1.07, 1.40, and 1.29 times, respectively. The EF showed that Cd had a large area of moderate pollution; Pb, Zn, and Cu had a small area of slight pollution; the EFs values of Hg, Cr, Ni, and As were near the baseline value (EF≈1), and contaminations were slight or nonexistent. The PMF indicated that there were five sources, namely pyrite mines, lead-zinc mines, natural sources of basalt and carbonatite, and agricultural activities; the risk contribution ratios were 5.25%, 27.37%, 28.94%, 17.91%, and 20.53%, respectively. The most toxic coefficients of Hg and Cd were mainly natural sources, with contribution ratios of 86.3% and 72.7%, respectively. The soil samples in the mining areas expectedly contained high ratios of Zn/Cd and Pb/Cd, which confirmed that PTEs in the soil were mainly derived from the smelting wastes. The contents of metal oxides such as Fe, Mn, and Si were the influencing factors of PTEs enrichment. On the contrary, soil samples exhibited much lower Zn/Cd and Pb/Cd ratios in non-mining areas, indicating that the main origin of these metals in soil was the smelting flue gas dusts and geological background.

The farmland soil around a Pb-Zn mine in southwestern China was studied. One hundred forty-nine surface soil samples were taken from 0-20 cm depth, and the contents of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn were tested. The correlations among these heavy metals were studied with multivariate analysis, and the potential sources of the metals were identified. The environmental risk of the metals was evaluated with the Potential Ecological Risk Index method. The results showed that the amounts of Cd, Pb, and Zn were at relatively high level, with average concentrations of 15.56, 419.4, and 933.4mg·kg -1 respectively, indicating the soil was heavily polluted. The average concentrations of Hg and As were 0.13 and 37.3mg·kg -1 , suggesting moderate soil pollution. The average concentrations of Cu, Ni, and Cr were lower than Yunnan soil background values. The multivariate analysis suggested that the sources of Cd, Pb, Zn, Hg, and As were similar and came mainly from smelting activities in the mining area. The sources of Cu, Ni, and Cr were similar and can be attributed to natural sources. The comprehensive potential ecological risk index was 2294.8, which suggested a high potential ecological risk. In general, the farmland soils in the research area were polluted seriously by the mining and industrial activities.