Assessment of Soil Heavy Metal Pollution, Non-Carcinogenic and Carcinogenic Human Health Risk in Raniganj Coalfield, Eastern India

Heavy metal accumulation in soil is increasing due to opencast coal mining. This research analyzed the heavy metal pollution and associated ecological and human health risk taking 50 soil samples from four overburden dumps (0-year, 4-year, 7-year and 26-year old) at Bansra opencast project (OCP) of Raniganj Coalfield (RCF) and adjacent forest Gurjungle as background values. Six heavy metals (Cd, Cr, Zn, Pb, Ni, and Fe) were tested by inductively coupled plasma optical emission spectrometry (ICP-OES). Heavy metals, except Fe, in overburden dumps exceeded background values displaying high coefficient of variation. Cr, Ni and Fe decreased from 0-year to 26-year dumps, while Pb, Zn and Cd increased. Positive correlations among Cr-Ni-Fe and Pb-Zn metal pairs, principal component analysis (PCA) and agglomerative hierarchical clustering (AHC) identified mainly geogenic and anthropogenic sources. Single element pollution indices (Contamination factor (CF), geoaccumulation index (I_geo) and enrichment factor (EF)) showed extremely high contamination (CF > 6), moderate to extreme pollution and significant to high enrichment. Multi-element indices (degree of contamination (C_deg) and modified degree of contamination (mC_deg)) indicated very high to extreme contamination while pollution load index (PLI 12 to 16) indicated significantly worst soil quality. Ecological risk factor (ER_i) varied from low to high for different metals, with contamination higher in 26-year old dump than in running dump, while potential ecological risk (RI > 600) was high in all the dumps. Pb and Cd gave the highest contamination and ecological risk in all the dumps, respectively. The hazard index (HI > 1) and total carcinogenic risk (TCR >10⁻⁴) assessed through total exposure of metals exceeded the tolerable risk values indicating high non-carcinogenic and carcinogenic health risks, mainly through inhalation followed by ingestion and dermal contact. Children were more susceptible compared to adults. Pb and Cr posed the highest non-carcinogenic risk, while Ni gave the highest carcinogenic risk.