Comprehensive exploration of heavy metal contamination and risk assessment at two common smelter sites

This study investigated the horizontal, vertical and fractional distribution of heavy metals in the soil and the pollution and risk assessment of two smelter sites in Daye (a Cu smelter) and Zhuzhou (a Zn oxide smelter). Nine sampling points were reasonably established at each site, and nine soil samples were collected in each soil profile, with a total of 81 samples at each site. The results indicated that only As concentration was exceeded in most of the samples from the Daye site, and several were contaminated with multiple heavy metals, i.e. As, Cd and Pb; the values exceeding the standard were significant. Most of the samples at the Zhuzhou site were contaminated with many heavy metals, i.e. As, Cd, Pb and Ni. With increasing depth, the proportion of the acid-soluble and reducible heavy metal fraction decreased, while the proportion of the oxidized and residual fraction increased. The pollution index (PI) indicated that As at all positions, and Cd and Pb at several positions at the Daye site, as well as Cd and Pb at all points of Zhuzhou should have received more attention. The Nemerow integrated pollution index (NIPI) showed that a few sampling points in Daye were severely polluted, i.e. the points D5 with the value of 77.49 and the point D7 with 62.33, were more than the threshold value with 3 of severe pollution. Almost all sampling points in Zhuzhou were severely polluted, but the pollution degree was slightly lower than at Daye. The hazard index (HI) indicated the potential non-carcinogenic risk at the Daye and Zhuzhou sites. These values were unacceptable for both adults and children. The carcinogenic risk (CR) index indicated that the potential carcinogen risk due to As and Ni contamination were unacceptable at both sites, especially for children with 9.27E-03 and 1.99E-03 of As and Ni at Daye site, while 4.55E-03 and 4.09E-03 at Zhuzhou site. Strict control of industrial waste residues and smelters emissions into the soil is necessary to avoid further aggravation of heavy metal pollution.