Wastewater irrigation elevates chromium uptake in cereal crops: Bioaccumulation dynamics and carcinogenic risk assessment in a semi-arid agroecosystems

Chromium (Cr) contamination in agricultural systems poses serious risks to human health and the environment. This study evaluated Cr accumulation in irrigation water, soils, and four cereal crops—corn, sorghum, millet, and wheat—under wastewater (WW), canal water (CW), and tubewell water (TW) irrigation across three sites. Water and soil samples were collected, and crop grains were analyzed at maturity using atomic absorption spectrophotometry (AAS) with strict quality control procedures. Results showed significantly higher Cr concentrations in WW compared to CW and TW. Chromium in WW ranged from 0.054 to 0.066 mg/L, exceeding CW (∼0.015 mg/L) and TW (∼0.012 mg/L). Soils irrigated with WW accumulated the highest Cr levels, averaging up to 2.00 mg/kg, while CW and TW soils contained much lower concentrations. Among crops, millet showed the highest Cr uptake under WW irrigation (2.18 mg/kg), followed by corn (2.00 mg/kg) and sorghum (1.93 mg/kg). Wheat displayed the lowest accumulation (0.28–1.68 mg/kg), particularly under CW and TW. Health risk assessment revealed that WW irrigation consistently produced the highest cancer risk values for both adults and children, followed by CW, while TW posed the least risk. Crop responses indicated that corn and millet effectively reflected environmental Cr levels, making them reliable bioindicators. Sorghum demonstrated moderate accumulation, suggesting partial exclusion mechanisms, whereas wheat exhibited natural resistance to Cr uptake, especially under CW and TW, marking it as the safest cereal for cultivation in contaminated regions. The study confirms wastewater irrigation as the primary source of Cr contamination in agroecosystems and emphasizes the urgent need for regulations governing its use. Adoption of cleaner irrigation sources, combined with cultivation of resistant crops such as wheat and monitoring through bioindicators like corn and millet, can reduce dietary Cr exposure and promote safer food production.