Distribution, fractionation, and contamination assessment of heavy metals in paddy soil related to acid mine drainage

Soil heavy metal contamination is a major environmental concern, especially soil affected by acid mine drainage (AMD), and attention about potential ecological risk associated with heavy metals is increasing. Heavy metal contents of soil samples collected from 6 sites alongside Hengshi River were analyzed to investigate the contamination degree of heavy metal in paddy soil irrigated with AMD. Fractional distribution of heavy metal and the potential ecological risks (E (r)) of the polluted soil were discussed as well. The results showed that Cu, Zn, and Cd in topsoil were 2.5-7.5, 1-2.1, and 2.2-5.5 times, respectively, exceeding the maximum allowable concentrations for Chinese agricultural soil. The single (P) and the comprehensive (P (N) ) factor pollution index revealed that the contamination degree followed the sequence of Cd > Cu > Zn > Pb. Furthermore, Pb, Cu, and Zn in vertical soil profiles reduced as soil depth increased, while Ni and Cd increased with the depth increasing slightly. Results of European Community Bureau of Reference (BCR) sequential extraction procedure indicated that the non-residual form of Pb, Cu, and Cd were pretty high in spatial variation, suggesting they were potentially mobilizable and bioavailable. Results implied that the order of the E-r of heavy metals was Cd > Pb > Cu > Ni > Zn > Cr; the E-r in Wengcheng (S9) and Xuwu (S10) were 353.30 and 327.60, which were considered as very high ecological risk. Thus, some effective measures should be taken to prevent heavy metal from polluting paddy soil and to reduce metal translocation from soil to edible crops. [GRAPHICS] .