Ecological risk assessment of heavy metals in soils of lignite mining area of Kutch district of Gujarat, India.

Toxic element concentrations including As, Hg, Pb, Zn, Cr, Co, Cu, Cd, and Mn were assessed in lignite mining areas of the Kutch district of Gujarat. It was assessed mainly in land uses like reclaimed mine soil, core zone soil, roadside soil, and reference agricultural soil along the soil layer of different depths. Roadside soil has the highest concentration of mercury (5.36 mg/kg), arsenic (18.2 mg/kg), lead (34.5 mg/kg), and manganese (464 mg/kg). In comparison, the core zone soil has the highest concentration of zinc (93.4 mg/kg), chromium (52.3 mg/kg), cobalt (19.2 mg/kg), and cadmium (5.65 mg/kg), respectively. Numerous soil indices including contamination factor, geo-accumulation index, ecological risk factor (ERF), and ecological risk index (ERI) showed that the study area lies within the moderate contamination to very high contamination zone and moderately polluted to the unpolluted range. The (E) (Hg) for roadside soil and core zone soil indicated high potential ecological risk category, while reclaimed mine site indicated considerable potential ecological risk. The E (Cd) in all sites in the mining area (121-327) can be put under high potential ecological risk, and the rest of the metals (As, Pb, Zn, Co, Cu, Cr, and Mn) can be put under low ecological risk category. In the three sites (i.e., reclaimed mine site, roadside soil, and core zone soil), core zone soil of (10-20 cm) showed the highest ERI value of 660.48 (10-20 cm), indicating high ecological risk. Cd and Hg contribute to 48% and 38% of ERI value. Hierarchical cluster analysis (HCA) suggested that the Cu and Mn were closely linked with each other and derived from similar origin and geo-chemical composition. The results of this study interpreted that the soil near the lignite mining area was contaminated with toxic elements. It is, therefore, recommended that the routine toxic element monitoring in the soil sample of the examined area should be done, and remediation action should be advised to prevent the accumulation of toxic elements in the soil and further into the food chain.