Human health risk assessment of potentially toxic elements in the soil and groundwater resources in arid areas: a case study of the Mojen Plain, Northeast Iran

Mojen Plain is an important agricultural and horticultural region in northeastern Iran. The main objective of this study was to evaluate the advert impacts of agricultural practices on the soil and groundwater resources of the Mojen Plain. The results of the study revealed that Cd, As, Cu, Zn, Ni, Cr, and Mn accumulations (with average concentrations of 0.6, 9.3. 16.4, 61.9, 22.1, 25.5, and 305.4, respectively) in the soils are due to agricultural practices which may result in the non-carcinogenic risk of As, Mn, and Cr through ingestion and dermal contact. In the groundwater of the study area, the average hazard quotient of As, Cd, Cr, Ni, Mo, Pb, and Cu through dermal contact route is higher than 1, indicating the probable non-carcinogenic risks of these elements. The average incremental lifetime cancer risk (ILCR) of dissolved As, Cd, and Pb through dermal contact exposure route was found to be higher than 1 × 10 −4 , implying a carcinogenic risk of these elements in the study area. While the water quality for irrigation purposes ranges from excellent to permissible, As and Cr content of water samples exceeds the WHO standards for drinking water. Nickel, Fe, Al, Pb, Zn, Cu, and Cd concentration in groundwater samples falls within the acceptable range of the WHO standard. Except for Ni and Co, a negative correlation exists between the concentration of toxic elements and the tube well depths, pointing to the anthropogenic origin of the toxic elements. The concentration of nitrate and phosphate, as the two major agricultural pollutants of groundwater, is generally higher in tube wells deeper than 175 m, reaffirming the impact of agricultural practice on groundwater quality.