From raw to cooked: The impact of cooking on bioaccessibility and health risks of toxic elements in leafy vegetables

Abstract

Environmental policies in China have significantly reduced toxic element fluxes in soil and air, but slower declines in atmospheric toxic element flux have increased its relative contribution to crop contamination. Leafy vegetables, with their large surface area and high capacity for toxic element accumulation, may pose dietary health risks. Current health risk assessments are typically based on total toxic element concentrations or in vitro bioaccessibility. Although boiling can affect the PBET-derived in vitro bioaccessibility of toxic elements, studies incorporating these effects into leafy vegetable health risk assessments remain limited, potentially leading to dietary risk misestimations. To address this, concentrations of cadmium (Cd), lead (Pb), and the metalloid arsenic (As) were determined in 183 samples of six leafy vegetables from Guangzhou, China, while PBET-derived in vitro bioaccessibility before and after boiling was evaluated only for three representative vegetables: water spinach, choy sum, and Leek. Total concentration monitoring showed that As and Cd were generally within Chinese regulatory limits, whereas Pb exceeded the limit in lettuce, indicating light Pb pollution. Conventional and bioaccessibility-adjusted screening-level health risks were then compared for adults and children. After updating the As toxicity values according to the 2025 U.S. EPA IRIS assessment for inorganic As, total As dominated the screening-level non-carcinogenic and carcinogenic risk estimates. The bioaccessibility-adjusted assessment generally produced lower risk estimates than the conventional total-concentration-based method; however, children’s non-carcinogenic risk and adults’ screening-level carcinogenic risk still exceeded acceptable thresholds for some vegetables after boiling. For example, the BTTHQ for children consuming water spinach decreased from 13.09 before boiling to 7.22 after boiling, while the BTCR for adults consuming water spinach decreased from 0.00410 to 0.00222. Boiling reduced the PBET-derived in vitro bioaccessibility of Cd and Pb in the three representative vegetables, whereas As showed vegetable-specific responses, decreasing in water spinach and Leek but slightly increasing in choy sum. These results indicate that boiling modifies the gastrointestinal soluble fraction of toxic elements in a vegetable- and element-specific manner and should be considered in dietary exposure assessment and food-safety guidance.