Ecological and human health risk assessment of heavy metal accumulation in soil and vegetables under 60 years of sewage water irrigation

Long-term irrigation of agricultural soils with sewage water poses serious threats to soil quality, vegetable safety, and human health through the progressive accumulation of heavy metals. This study assessed the accumulation of eight heavy metals Fe, Cu, Mn, Zn, Cd, Pb, Ni, and Cr in sewage-irrigated soils and thirteen cultivated vegetable species in the Patna Bypass area, Bihar, India, a peri-urban zone with over six decades of continuous sewage water use. Pollution indices revealed that the potential ecological risk index (PERI = 484.81) fell within the considerable risk category, dominated by Cd’s individual ecological risk factor (ER = 368.22), which exceeded the very high risk threshold (ER ≥ 320) by approximately 15%. Among vegetables, coriander recorded the highest metal pollution index (MPI = 36.66), followed by spinach (29.16) and amaranth (27.20) values approximately 2.7, 2.1, and 2.0-fold higher than cauliflower (13.61), the least contaminated species. Non-carcinogenic hazard index (HI) exceeded the safe threshold of 1.0 for all vegetables in both demographic groups, ranging from 2.83 to 9.11 in adults and 3.58 to 11.52 in children representing a 26.5% greater cumulative burden in children (CMHI = 92.67) versus adults (CMHI = 73.27). Carcinogenic risk was equally alarming, with cumulative multi-metal total carcinogenic risk (CMTCR) values of 1.20 × 10 − 1 (adults) and 1.52 × 10 − 1 (children) exceeding the USEPA acceptable limit of 1 × 10 − 4 by three orders of magnitude. These findings underscore the urgent need for regulatory interventions, phytoremediation strategies, and vegetable-specific dietary advisories for communities dependent on sewage-irrigated produce in the Indo-Gangetic Plains.