Health Risk of Mercury and Cadmium and Their Migrations in a Soil- Maize System of the Karst Mining Area

Abstract

Mining activities have caused serious heavy metal and metalloids contamination in agricultural soils, while the differences in contamination characteristics and ecological impacts of metalloid within soil-crop systems between mining and non-mining areas in karst regions remain poorly understood. Therefore, this study investigated the contents, speciation, and ecological risks of mercury (Hg) and cadmium (Cd), and explored their occurrence characteristics and risk levels in soils and maize from mining and non-mining areas in the karst environment of Guizhou Province, China. Results showed that Cd concentrations in soils from mining areas were significantly higher than those in control areas (p < 0.01), while Hg concentrations showed no significant difference. Medium contamination and ecological risk were identified in 44.44% of mining-area soils, primarily driven by Hg contamination. However, the risk assessment code indicated a higher bioavailability risk for Cd compared to Hg, with 22.22% of soils in the mining area exhibiting medium risk. In maize, the concentrations of Cd and Hg followed the order: roots > leaves > stems > corns. The enrichment and translocation capacities of Cd and Hg in mining-area maize were significantly greater than that of in controls. Hg and Cd speciation in soil significantly influenced their content in maize. Potential carcinogenic health risks from Cd and Hg exposure were found in mining-area maize and control areas, especially in children. Our results suggested that there was a relatively higher potential health risk caused by Cd and Hg in soil and maize, and it was necessary to pay attention to the effect of exposure by the more hazardous substances on the other local crops. Our suggestion is that several measures, including phytoremediation, biochar, advanced nanomaterial technologies, etc., are urgently needed to alleviate the heavy metal and metalloid pollution in soil and some crops according to local environmental conditions. This study provides important insights and basic data to inform strategies for mitigating heavy metal pollution of agricultural soils in karst mining areas.