Application of <i>in vitro</i> digestion and dialysability procedure for bioavailability evaluation of toxic elements in green leafy vegetables: a realistic health risk assessment by Monte Carlo simulation

Green leafy vegetables (GLVs), which are vital and widely consumed worldwide, require monitoring for contaminants, including toxic elements (TEs). This study measured total concentrations (TC) and bioavailable concentrations (BC) of arsenic (As), cadmium (Cd), lead (Pb), chromium (Cr), and nickel (Ni) in 15 GLV types in Riyadh, Saudi Arabia. Then, a health risk assessment (HRA) was conducted for TEs based on their BC and TC using the Monte Carlo simulation (MCS) method. The BC of TEs in GLV samples was estimated using an in vitro gastrointestinal digestion model combined with a dialysis step. The procedure simulated gastric and intestinal phases to reflect human digestion conditions. The TC of TEs was determined after acid digestion using inductively coupled plasma–optical emission spectroscopy (ICP-OES), and in vitro dialysability was used to estimate the BC of TEs. The Maximum Permissible Limits (PLs) (mg/kg) based on FAO/WHO standards are 0.15 for As, 0.30 for Pb, 0.20 for Cd, 2.30 for Cr, and 67.9 for Ni. The results indicated that levels of As, Cd, and Pb frequently exceeded these WHO/FAO limits. Across all GLV types, the bioavailability (BAV) percentages for As, Pb, Cd, Cr, and Ni were 6.8–10.5, 10.2–17.7, 16.2–22.1, 14.7–19.7, and 14.5–22.3, respectively. The average BAV percentages of TEs in all GLVs were 9.0, 14.4, 16.6, 18.2, and 18.5 for As, Pb, Cr, Cd, and Ni, respectively. The hazard index (HI) based on TC was 2.25 (unacceptable risk), whereas the HI based on BC was 0.26 (acceptable risk). Total cancer risk (TCR) was significantly different between TC and BC, with values of 3.8E-03 and 7.1E-04, respectively. Even at BC levels, carcinogenic risks for Cd, Cr, and TCR were significant and unacceptable for some GLVs. Therefore, monitoring, environmental assessment, and control of pollution sources are essential to ensure the safety of GLVs consumed in Riyadh.