Integrated assessment of heavy metal contamination and ecological and human health risks in agricultural soils, groundwater and surface water of an industrialized arid region (Arak Plain, Iran)

Study region Arak Plain, central Iran. Study focus This study evaluated the concentrations and associated ecological and human health risks of Cd, Cu, Zn, Pb, Ni, Cr, and Hg in agricultural soils, groundwater, and surface water of an industrialized wheat-growing plain. Soil contamination was assessed using the geoaccumulation index, contamination factor, Pollution Load Index, and Potential Ecological Risk Index. Human health risks associated with soil and water exposure were evaluated using non-carcinogenic and carcinogenic risk models. The effects of soil texture, farming system, and their interaction on soil metal concentrations were also examined. New hydrological insights for the region Distinct concentration and risk profiles were observed among agricultural soils, groundwater, and surface water. Because soil and water represent different matrices and were reported in different units, these differences are interpreted as compartment-specific signatures rather than direct evidence of retention, attenuation, or transfer. Zn and Cu showed the highest concentrations in agricultural soils, whereas Cd dominated the toxicity-weighted ecological risk. Soil texture significantly affected only Zn concentrations, with a small effect size, while farming system and its interaction with soil texture were non-significant. Mean soil hazard quotients remained below 1, although some individual values for Cd and Cr approached or exceeded this threshold. Groundwater showed greater modeled non-carcinogenic concern than surface water, particularly for Cd, Pb, and Cu, while Pb made the largest contribution to groundwater carcinogenic risk. The results provide a regional screening-level assessment and identify groundwater as the principal water compartment requiring continued risk-based monitoring in the Arak Plain.