Heavy metal pollution of soils from coal mines in China

Mining activities are among the main sources of heavy metal contamination in the environment. To analyze heavy metal pollution of soils from coal mines in China, we assessed pollution and potential ecological risk, compared heavy metal concentrations between soils from coal mines and soils from metal mines and identified the relationship between heavy metals on the nationwide scale. The data of heavy metal concentrations for 50 coal mines and 35 metal mines were collected from the published literature. Coal mines referred in this paper are distributed in 18 provinces and 4 climatic zones in China. Methods including Index of geoaccumulation (Igeo), Nemerow pollution index (P), potential ecological risk index and other statistics (Pearson correlation method and ANOVA variance analysis) were utilized. Compared with soils influenced by metal mining, heavy metal concentrations in soils from coal mines were much lower. For heavy metals, higher Igeo for Cd, Pb and Ni was observed. Soils were contaminated or slightly contaminated when calculated based on Chinese soil guidelines (grade I and grade II) but slightly contaminated or severely contaminated when calculated based on province backgrounds. Most heavy metals (i.e., As, Cr, Cu, Ni and Zn) showed a low potential ecological risk, whereas Cd, Pb and Hg showed slightly higher ecological risk potential. Statistically significant and positive correlations were found in pairs of As/Cr, As/Ni, As/Pb, As/Hg, Ni/Cr and Ni/Cu (P < 0.01) and Cu/Pb (P < 0.05).