Risk assessment of heavy metals in soil and simultaneous monitoring in wheat irrigated with groundwater and treated wastewater and its long-term effects for residents of adjacent regions

Abstract

The purpose of this study was to evaluate the health risks posed by heavy metals in irrigation water, soil, and wheat in areas of Iran that are either groundwater-irrigated (Gerdkhoon) or wastewater-irrigated (Shorghan). Concentrations of metals including Fe, Zn, Cu, Mn, and As were higher in effluent than groundwater; however, all heavy metal concentrations were below the irrigation water standard in both Shorghan and Gerdkhoon. The effluent-irrigated area had elevated soil concentrations of Fe, Mn, Ni, Cr, Cu, Co, and As, which exceeded WHO safety limits for Fe. Moreover, the concentrations of As, Cr, Ni, Fe, Mn, and Zn were higher in effluent-irrigated wheat by, respectively, 0.25, 3.4, 3.75, 370.85, 3.08, and 242.18 mg kg⁻¹ than in groundwater-irrigated wheat. Ingestion was the primary source of exposure for both carcinogenic and noncarcinogenic risk assessments. Besides, the HQ of exposure to soil was less than the threshold adopted by EPA, while the HQ of exposure to wheat was more than the EPA's threshold in both study areas. These findings demonstrate propagation of metals through the water-soil-crop continuum, indicating the need for better wastewater treatment and crop monitoring to reduce health risks. The integrated exposure and risk analysis provides an exemplar methodology for comprehensive assessment of a ubiquitous pollutant.