Heavy metal contamination in wastewater-irrigated leafy vegetables: implications for food safety

The limited availability of fresh water sources across many developing countries necessitates the intake of wastewater as an alternative option for irrigation, raising worries about heavy metal contamination. The present study evaluated the accumulation of chromium (Cr), lead (Pb), cadmium (Cd), copper (Cu), and nickel (Ni) in easily available and highly consumed leafy vegetables (fenugreek, spinach, and mustard) irrigated with industrial effluents (post-primary, secondary, and tertiary treatments), drain water, and groundwater in a controlled pot experiment. The concentrations of Cr, Pb, Cd, and Cu in all irrigation water sources remained within the permissible limits, whereas Ni exceeded the recommended limit in drain water. Heavy metal concentrations in soils were within safety thresholds; the concentration of Cr (5-20 mg/kg), Pb (2.5-12.5 mg/kg), and Cd (0.5-1.5 mg/kg) levels in vegetables occasionally surpassed FAO/WHO limits (Codex Alimentarius Commission,  1984), WHO, 2007), indicating potential health risks. The bioconcentration factor (BCF) indicated notable uptake of Pb and Cu (exceeding the limit of 1) in spinach. Furthermore, the daily intake of metals was higher in children than adults, with the highest intake of Ni (0.04 mg/kg in children and 0.03 mg/kg in adults) and Cu (0.015 mg/kg in children; 0.013 mg/kg in adults) in spinach. The hazard index (HI) for Ni in spinach and for Pb in mustard and fenugreek indicated a heightened risk of non-carcinogenic health effects. The novelty of the study lies in its comparative evaluation of primary, secondary and tertiary-treated wastewater, drain water, and groundwater for vegetable cultivation under controlled pot conditions. The study highlights the health implications associated with heavy metal accumulation.