Assessing heavy metal pollution in paddy soil from coal mining area, Anhui, China

Heavy metal pollution in agricultural soil has negative impact on crop quality and eventually on human health. A total of 24 top soil samples were collected from paddy field near the Zhangji Coal Mine in Huainan City, Anhui Province. Seven heavy metals (Cu, Zn, As, Cr, Cd, Pb, and Ni) were selected to evaluate the pollution status through total content and chemical speciation, geo-accumulation index (I_geo), and risk assessment code (RAC) and investigate leaching behavior of heavy metals under simulated rainfall. The results of present study indicated that mining activities were responsible for elevated Cu and Cd in surrounding paddy soil. Based on the results of chemical speciation, most heavy metals were associated with the residual fraction, and the environmental risk of heavy metals in soil was sequenced as Pb > Cd > Ni > As > Zn > Cu > Cr. It revealed that Pb in soil would pose a higher environmental risk due to its higher reducible fraction, then followed by Cd, Ni, As, and Zn, which would pose a medium risk. The result of simulated rainfall leaching analysis showed that heavy metals could be categorized into two groups: concentrations of Cu, Ni, Cd, Zn, and Cr in the leachates displayed a continuous decrease tendency with the increase in accumulative simulated rain volume; whereas leachable tendency of As and Pb was enhanced with increasing leaching time and rain volume. Generally, the leaching percentage of heavy metals followed the sequence of As > Zn > Ni > Cd > Cr > Cu > Pb. More attention should be paid to the higher environmental risk of Pb and higher leaching percentage of As with regard to ecosystem safety and human health.