PROBABILISTIC RISK ASSESSMENT APPROACH IN METAL CONTAMINATED SOIL AND GROUNDWATER

Abstract

Rapid industrial expansion along with urbanization and intensive agriculture without adequate environmental management strategies leads to a significant enrichment of contaminants in the ecological system. Heavy metal contamination in natural matrixes (soil or groundwater), whether through natural weathering, anthropogenic activities, or both, had been the concern of many researchers because of their potential toxicity, persistence, and high bioaccumulative tendency. The soil is the ultimate and the crucial sink of trace elements in the terrestrial environment. Soil has a great capacity for absorbing, decomposing and remediating wastes and pollutants of different kinds. Unmanaged disposal of industrial and domestic wastes, long span wastewater irrigation, atmospheric decompositions, leaching from landfills etc. leads to a substantially high buildup of heavy metal concentration in the soil and further percolation in the groundwater plume. Plants are the major carriers of heavy metal from soil to human. Therefore, the presence of metals in the soil is important in the chemistry of plants and in human health as well. High buildup of heavy metals in environmental system has important repercussions for the environment and human health, thus it is essential to identify the potential of a source to introduce risk associated with metal contamination into the environment, estimated amount of risk agents that have come to contact with the human-environmental boundaries and quantifies the health impact of the exposure. Heavy metal distribution was analyzed in the soil of three industrial zones of Saharanpur district of India, viz. Pilakhni, Nanauta and Railway Road. The mean concentration (mgkg-1) of As, Cu, and Pb were observed to be maximum (22.10±9.68, 88.4±21.68 and 40.50±14.90 respectively) in Pilakhni industrial area; Cd (1.98±0.79), Cr (92.10±42.39) and Zn (97.04±33.07) in Nanauta; whereas, Ni (95.38±48.13) was observed maximum at Railway Road industrial area. Geo-accumulation index (Igeo) reflects moderate to high contamination of Cu, Pb, Cr, Ni, and Zn, whereas, high enrichment and contamination factor were observed in As and Cd in all three industrial areas. Health risk due to exposure of metal was potentially high in the children in comparison to adults in the study area. High metal contamination was observed in the groundwater sample collected from Pilakhni followed by Nanauta and Railway Road industrial zones. Maximum groundwater contamination of As (84.4 μgL-1), Cr (123.3 μgL-1), Mn (703.5 μgL-1), Pb (44.1 μgL-1), Zn (288.8 μgL-1) were observed in Pilakhni; Cd (7.2 μgL-1) and Cu (88.7 μgL-1) in Nanauta and Ni ii (88.2 μgL-1) was observed in the Railway Road area. Health risk via oral pathway was assessed in both adult and children population. Non-carcinogenic risk (HQ) value was observed to be > 1.00E+00 for As and Cr contamination in both adult and children population in Pilakhni and Nanauta area indicating high non-carcinogenic risk. Cancer risk associated As contamination observed to be potentially high (> 1.00E-03) in all three industrial zones in both adult and children population in the study area. The present study also indicates the status of metal contamination in the vegetables/crops grown in the uppermost Ganga-Yamuna doab region of India and associated health risk. Commonly grown vegetables and crops were sampled and analyzed for metal contamination. Maximum concentration (mg/kg) of Cd and Cr, was observed in Radish (7.6) and Cabbage (56.24) respectively, whereas the maximum concentration of Pb, Ni and Zn were observed in the edible parts of Mustard plant (95.4, 58.6, 756.43 respectively). Bioconcentration factor (BCF) value indicated the transfer level of metal from soil to crop; indicated high transfer value of Cd in Radish followed by cabbage and spinach. Considerably high BCF value was observed in the Mustard (8.13), Cabbage (4.18) and radish (3.07) for Zn contamination. Estimated daily intake (EDI) and Hazard quotient (HQ) or Non-carcinogenic health risk was calculated using the USEPA method. The result revealed that the metal intake and associated health risk was considerably high in the children population in comparison to the adult population. The fuzzy-based aggregate risk assessment revealed a high risk of cadmium and arsenic toxicity in the study area with the risk score of 0.751 and 0.698, respectively. The fuzzy-based risk assessment is a conceptual methodology that restricts the vagueness in the estimation of risk for better decision-making approach. Probabilistic risk estimation by Monte Carlo simulation on iterating the Risk assessment expression for 10,000 trials inferred high risk in children population for Cr and As contamination.