Non-carcinogenic and carcinogenic health risk assessment of selected metals in soil around a natural water reservoir, Pakistan

Contaminants in surface soil can directly pose significant human health risks through oral ingestion, dermal contact and particle inhalation, especially for children. Both non-cancer and cancer risks associated with selected metal levels (Cd, Cr, Cu, Fe, Mn, Pb and Zn) were evaluated in surface soil around Mangla Lake during summer and winter. The results based on average pseudo-total metal concentrations followed the decreasing order: Fe (4038 mg/kg)>Mn (394 mg/kg)>Zn (40 mg/kg)>Pb (17 mg/kg)>Cr (21 mg/kg)>Cu (15 mg/kg)>Cd (1.3 mg/kg) during summer and Fe (3673 mg/kg)>Mn (407 mg/kg)>Zn (30 mg/kg)>Cr (26 mg/kg)>Pb (26 mg/kg)>Cu (14 mg/kg)>Cd (1.8 mg/kg) during winter. Present metal levels in the soil were also compared with other studies and guideline values which showed significant increase in the metal concentrations in this study. The metal levels also showed considerable spatial variations around the lake. The correlation study and multivariate principal component analysis revealed significant anthropogenic contributions of the metals in soils. Aqua-regia extractable (pseudo-total) contents were used as the reference to establish the percentage of bioavailability. After considering the bioavailability (Cd>Pb>Cr>Zn>Cu>Fe>Mn during both seasons), the non-cancer and cancer risks posed by Cd, Pb and Cr was relatively higher than rest of the metals, though the overall hazard index (HI) and cancer risk levels were within the safe limits (1.0 and 1.0E-06, respectively). The overall cancer risk to the adults based on pseudo-total metal concentrations exceeded the target value (1.0E-06), mainly contributed by Cr. A method considering bioavailability is suggested to produce a more realistic estimation for human health risks of trace metals contamination in soil.