Heavy Metal Accumulation and Health Risks in Selected Leafy Vegetables Irrigated with Mixed Potable and Wastewater-A Case Study: Southern Tehran, Iran.

The effect of mixed potable and wastewater (WW) irrigation on leafy vegetables cultivated in southern Tehran, Iran, was investigated in 2022. Eight species-spinach (Spinacia oleracea), scallion (Allium fistulosum), radish (Raphanus sativus), cress (Lepidium sativum), basil (Ocimum basilicum), purslane (Portulaca oleracea), cilantro (Coriandrum sativum), and savory (Satureja hortensis)-were grown in calcareous loamy soil under greenhouse conditions using five irrigation regimes (0%, 25%, 50%, 75%, and 100% WW) applied every 2 days. Soil salinity, DTPA-extractable Co, Cu, Ni, and Zn, plant growth traits, and health risk indices-transfer factor (TF), bioaccumulation factor (BAF), average daily dietary intake (ADD), hazard quotient (HQ), and cancer risk (CR)-were determined for children and adults. Heavy metal (HM) accumulation differed significantly among wastewater levels and plant species (p < 0.05). While low WW levels (≤ 50%) enhanced plant growth parameters, higher application rates sharply increased soil salinity (up to 6.5 dS m⁻1) and DTPA-extractable Co, Cu, Ni, and Zn. Zn and Cu were retained mainly in roots, whereas Ni and Co were more readily translocated to shoots, especially at 50-75% WW. Radish exhibited the highest TF, particularly for Zn and Ni. Children showed 2.8-3.1 times higher ADD and HQ values than adults, indicating greater vulnerability. The CR for Ni exceeded the 10⁻4 threshold, particularly in radish and scallion. BAF values exceeded 1 in all vegetables except radish, following the order Cu > Zn > Ni > Co. These findings suggest that strategic substitution of WW with potable water can sustain yields while limiting HM risks, guiding safe irrigation strategies in semi-arid urban agriculture.