Refining health risk assessment of heavy metals in vegetables from high geochemical background areas: Role of bioaccessibility and cytotoxicity

A systematic study of heavy metal levels, bioaccessibilities, and gastrointestinal cytotoxicity in two popular consumed vegetables mint (Mentha spicata Linn.) and pea sprouts (Pisum sativum Linn.) from three major producing cities in Yunnan, Southwest China were conducted for evaluating potential health risk to local inhabitants. The mean concentrations of As, Cd, Cr, and Pb were 0.34, 0.06, 1.04, and 0.79 mg/kg, respectively, with Cr and Pb exceeding 1.86–2.63 folds greater than the limit of Chinese National Standards and WHO/FAO. Their average gastric and intestinal bioaccessibilities varied within 12.1–59.4% and 9–53.3%, 0–93.3% and 0–82%, 41.8–71.1% and 19.1–62.9%, 16.1–93.6% and 9.5–81.7%, respectively. Cd in mint was the highest (86.8% and 39%, in the gastric phase and intestinal phase), while Pb had the highest bioaccessibility of 69.9% and 48.7% in pea sprouts. The bioaccessible target hazard quotient (BTHQ) of As, Cr, and Pb from vegetables reflected no potential health risks. However, toxicity assays showed intestinal digesta induced significant cytotoxicity in human intestinal Caco-2 cells, indicating the existing models based on total or bioaccessible heavy metals may be not accurate enough to assess their human health risk, especially for adverse effects evaluation. Taken together, the human risk assessment should be modified by taking their gastrointestinal cytotoxicity into account.