Concentrations and health risks of heavy metals in soils and crops around the Pingle manganese (Mn) mine area in Guangxi Province, China

Abstract

Heavy metal concentrations in agricultural fields and their ecological risks are a source of extensive concern worldwide. A field survey was conducted to investigate the present situation and health risks of heavy metals (Mn, Pb, Zn, Cu, and Cd) and crops (corn, green soybean, sweet potato, persimmon, cassava, and Chinese chestnut) around the Pingle manganese (Mn) mine site in Guangxi Province, China, which was abandoned 20 years ago. The results showed that the ranges of Mn, Pb, Zn, Cu, and Cd were 2706.54–6760.16, 229.37–275.84, 160.39–215.48, 58.11–75.30, and 5.78–6.98 mg kg⁻¹, respectively, which were approximately 15.38–38.41, 11.76–14.15, 2.12–2.85, 2.09–2.71, and 21.64–28.75 times greater than their respective background values. Most of these concentrations exceeded the national standard for soil quality (grade 2) developed by the Ministry of Environmental Protection of China (1995). Contamination assessments based on the single contamination index (P_i), Nemerow multi-factor index (P_com), and potential ecological risk index (RI) showed that the sampled soils were severely polluted with these heavy metals, especially Pb and Cd. Similarly, the crops were enriched with Pb and Cd, with concentrations of 10.22–41.78 and 2.33–5.37 mg kg⁻¹, respectively, which were much higher than the threshold values of the national food standards. Contamination assessments with P_i and P_com also showed that the crops were severely polluted with Pb and Cd. The bioaccumulation factor values for Cd were highest among the heavy metals, with an average mean of 0.66 in these six crops, demonstrating that Cd readily accumulates in these crops. An assessment showed that the health risk for adults living in the mining-impacted areas was significant. Our study strongly recommends that heavy metal contamination in agricultural soils and crops grown around the Pingle Mn mining-affected areas should be treated to mitigate the health risks.