Toxic metal-adsorbed microplastics threaten human digestive system: A bioaccessibility-based risk assessment

Microplastics (MPs) serve as carriers of toxic metals in aquatic environments, facilitating co-contamination and raising concerns about the potential negative effects on human exposure through dietary ingestion. As MPs undergo environmental aging, changes in surface properties and functional groups enhance their adsorption capacity for toxic metals. Meanwhile, toxic metal-adsorbed MPs are widely present, yet mechanistic dietary risk assessment based on age/gender and human health thresholds is still lacking. Here, by integrating adsorption experimental data and oral bioaccessibility-based human digestive kinetics, exposure levels of Cr(VI)-/Pb(II)-adsorbed virgin/aged MPs in seafood, bivalves, crustaceans, sea salt, and drinking water were estimated. The age-/gender-specific average daily dose was assessed across different digestive phases, whereas non-carcinogenic risks were undertaking hazard quotient- and margin of exposure-based assessment. Results showed that aging increased adsorption of Cr(VI)-/Pb(II)-adsorbed MPs by ∼9-fold, with the highest risk observed in 0-3 age group, particularly in stomach phase. Among dietary sources, toxic metal-adsorbed MPs ingestion through fish, bivalves, and crustaceans contributed most significantly to non-carcinogenic risk, with ingestion rate and food-specific MPs identified as key sensitivity factors. The findings reveal potential trends of toxic metal-adsorbed MPs accumulating in foods and being transferred to human digestive system. This work highlights a plausible yet understudied pathway of MPs-associated toxic metals exposure that has human health implications. Although there are no immediate health risks found in this study, the observed age-related trends and the influence of MP aging are deserving further research to confirm their application to public policy.