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Polyamide microplastics outperform polylactic acid in reducing cadmium health risks in arsenic-cadmium co-contaminated water: Insights from experimental and theoretical analysis
Summary
Researchers compared how polyamide and polylactic acid microplastics interact with arsenic and cadmium in contaminated water and assessed resulting health risks. The study found that while PLA microplastics absorbed more cadmium, they also released it more readily during digestion due to surface degradation by gut enzymes, making polyamide microplastics paradoxically less hazardous as cadmium carriers despite being a conventional plastic.
Microplastics (MPs), arsenic (As) and cadmium (Cd) ubiquitously co-exist in aquatic systems, establishing interactions and posing potential health risk due to their pivotal roles in the co-transportation processes of contaminants, yet available information still remains limited. This study investigated the adsorption patterns of As(V) and Cd(II) on polyamide (PA-MPs) and polylactic acid (PLA-MPs), as well as assessed their bioaccessibility and human health risks using batch experiments, spectroscopic characterizations and density functional theory (DFT) calculations. The results demonstrated that PLA-MPs had higher adsorption affinity towards Cd(II) than PA-MPs, and As-Cd could be co-sorbed on MPs in their coexisting systems probably due to ternary MP-Cd-As complexes formation, reaching 530.17 and 192.55 µg/g, respectively. Cd(II) bioaccessibility in co-sorbed PA-MPs (3.22-14.65 %) was significantly lower than that in co-sorbed PLA-MPs (15.46-82.38 %). This phenomenon was facilitated by the formation of more stable molecular structure (PA-Cd-As) with a higher binding energy (-1.54 Ha) as calculated by DFT simulations. Besides, the extensive erosion and degradation on PLA-MPs surface affected by digestive enzymes and gut microbiota also accelerated Cd(II) release, thereby posing greater health risks. Overall, this study emphasized the significance of understanding the MP-metal(loid) interactions when handling with the health risk assessment in co-contaminated water.