[Sources Identification, Ecological Risk Assessment, and Controlling Factors of Potentially Toxic Elements in Typical...

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.