Risk assessment and sources identification of soil heavy metals in a typical county of Chongqing Municipality, Southwest China

Eight heavy metals (HMs: As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) were measured from 337 top and 80 deep soil samples in Tongliang District (Chongqing, SW China), and consequently multiple statistics and indices (PI - pollution index; Igeo - geoaccumulation index; EF - enrichment factor, and RI potential ecological risk index) were employed for risk evaluation of HMs in soils. The concentrations of Cd and Hg in top soils exceeded threshold values for China's State Environmental Quality Standards for soils. PI suggested the contamination of HMs in top soils was ranked as: Cr < As < Cu < Ni < Pb < Zn < Hg < Cd, while deep soil showed a different order as: Cr < As < Cu < Hg < Cd < Pb < Zn < Ni. EF showed moderate enrichment of Cd in top soils, and top soils were unpolluted to moderately polluted by Cd and Hg, as indicated by Igeo. However, minimal enrichments of HMs in deep soils were found. It should be noticeable that several sites in top soils showed As, Cd and Hg with Igeo > 1, indicating moderate pollution. RI showed that 59% of top soils and 8% of deep soils were moderate risk, while 3% and 1% of top soils were considerable and high risk, respectively. PCA (principal component analysis) identified two possible sources for HMs, which explained 69% and 71% of total variances in top and deep soils, respectively. The sources for Ni, Zn, Cu, Cd, and Pb could be fertilizers, pesticides, and domestic wastes. The sources for Hg and As enrichment could be industrial activities. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.