Risk assessment of hazardous elements in wastewater irrigated soil and cultivated vegetables in Pakistan

Wastewater irrigation leads to the deposition of hazardous elements (HE) in irrigated soils which could be accumulated in cultivated vegetables, contaminating the food chain and pose threat to the human population. HE concentrations could be varied in the wastewater-irrigated and background soil and cultivated vegetables with season depending on temperature, humidity, and quantity of irrigation water. For this purpose, soil and vegetable samples were collected in the summer and winter seasons of Peshawar, Pakistan, and analyzed for HE including Cu, Cr, Cd, Co, Zn, Pb, Mn, and Ni. Results revealed that HE contaminations except for Ni in wastewater-irrigated soil and vegetables of both seasons were multifold higher than reference. Between seasons, summer had higher HE contamination in soil and vegetables compared to the winter season. The Cd and Ni concentrations in soil and Pb, Cd, and Cr in vegetables of both seasons exceeded their respective threshold limits set by the Food and Agriculture Organization/World Health Organization. Soil enrichment factors for HE contamination were observed greater than one that could be attributed to wastewater irrigation. Higher values of bioaccumulation factors were found for Cd (1.4), Co (1.8), and Cu (4.0). HE concentrations of vegetables were used for the risk assessment using average daily intake (ADI) and target hazard quotient (THQ). The ADI values of Cd and Pb were observed higher than their respective referenced dose. The THQ values ranged from 0.002–3.86 and 0.02–3.46 for adults and children. Higher THQ values could result in various health problems for the exposed human community.