Soil pollution characteristics and systemic environmental risk assessment of a large-scale arsenic slag contaminated site

Soil arsenic (As) pollution around large-scale As mine contaminated sites is of great concern, but there have been no detailed reports about them in China. A comprehensive study was conducted to determine the soil pollution characteristics and the multiple potential risks to the environment and the ecosystem of a large-scale arsenic slag contaminated site in southwest China. A total of 2,816 samples from three soil layers were collected and the As concentration was determined. The results showed that the As concentrations in the soil samples were highly variable and ranged from not detectable (N.D.) to 76,400.00 mg/kg, with a mean concentration of 1,205.97 mg/kg. The estimation of the mean value for the potential ecological risk index (Eᵣ) was 606, which indicated that there was a potential severe ecological risk, and over 39% of the samples were in the high ecological risk category (Eᵣ ≥ 80). The geoaccumulation index (Igₑₒ) results showed that the As levels ranged from uncontaminated (Igₑₒ < 0) to very strongly polluted (Igₑₒ = 11.3), and the proportion of samples that were strongly polluted and above (Igₑₒ ≥ 3) was 30.8%. The As content in the surface water may have increased due to the migration of pollutants in the site soil, especially within a migration distance of 200 m. The migration prediction results showed that the As residue and contaminated soil at the site posed a considerable risk of contaminating a downstream drinking water reservoir that is about to be built because it will be the main receptor for the site. The groundwater beneath the site had little effect on the As content in the surface water after its migration and posed a low risk to the receptor. The results from this study can help prevent potential cumulative risk and improve the implementation of effective environmental risk controls at large-scale As mine contaminated sites.