Chemical speciation, vertical profile and human health risk assessment of heavy metals in soils from coal-mine brownfield, Beijing, China

The characterization of the concentration and chemical speciation of heavy metals in surface and vertical profile soils is a necessary for pollution monitoring and the potential risk assessment of the heavy metals (HMs) to animal and human health. Surface soil samples (n = 14) and vertical profile soil samples (n = 36) from selected sites (n = 6) were collected from coal-mine brownfield in the Qingshui River Basin, in which the concentrations and chemical speciation of HMs (Cd, Cr, Cu, Mn, Ni, Pb, Zn) in surface soils and HM concentrations in vertical profile soils were determined by ICP-OES and analyzed using methods of geo-accumulation index (Igeo), Tucker 3 model and health risk assessment. The chemical fractions of HMs were extracted by BCR-sequential extraction procedure. Results show that HMs in surface soils accumulate in descending order of Cd > Pb > Cu > Ni > Mn > Zn > Cr. All HMs are associated with residue fraction to different degrees. Manganese and Ni are closely related to extractable BCR fractions and turn to be the severer pollutants in some sites. The Igeo values of HMs in vertical profile soils indicate ‘uncontaminated’. Whereas coal mining activities with long history increase HM concentrations in subsurface soils at the coal mine former site. The non-carcinogenic risk posed by HM extractable fractions to children and adults fall below the safe level of 1. Lead extractable fraction exhibits the highest risk value in the case of children. The levels of carcinogenic risk posed by Cr and Ni extractable fractions are above that of the United States Environmental Protection Agency (USEPA) acceptable level (1 × 10− 6). Nickel extractable fraction exhibits the highest carcinogenic risk values for children with exceeding that of the maximum USEPA acceptable level (1 × 10− 4).