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Heavy metals trigger distinct molecular transformations in microplastic-versus natural-derived dissolved organic matter
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This study compared how heavy metals interact with organic matter that comes from natural sources versus organic matter released by degrading microplastics in water. Natural organic matter formed stable complexes that kept heavy metals in check, while microplastic-derived organic matter formed weaker bonds and was more vulnerable to chemical reactions that could release metals back into the water. This means that as plastic pollution increases, heavy metals in waterways may become more mobile and more available to enter the food chain.
Dissolved organic matter (DOM) is a key determinant of heavy metal fate in aquatic environments, influencing their mobility, toxicity, and bioavailability. Derived from natural sources such as soil and vegetation decomposition, natural DOM (N-DOM) typically features humic-like substances with abundant oxygen-containing functional groups that stabilize heavy metals through complexation. However, microplastic-derived DOM (MP-DOM), increasingly prevalent due to plastic degradation, may interact differently with heavy metals, potentially exacerbating environmental risks amid rising plastic pollution. Yet, how heavy metals drive molecular transformations in MP-DOM versus N-DOM remains unclear, hindering accurate pollution assessments. Here, we compare interactions between N-DOM and MP-DOM with cadmium, chromium (Cr), copper, and lead from both fluorescence and molecular perspectives. Our results show that N-DOM, dominated by humic-like substances (46.0-57.3 %), lignin-like (55.0-64.9 %), and tannin-like (10.1-17.6 %) compounds, forms more stable heavy metal complexes via carboxyl, phenolic hydroxyl, and ether groups than MP-DOM. By contrast, MP-DOM-enriched in protein/phenolic-like substances (13.8-24.0 %), condensed aromatic (12.1-28.5 %), and protein/aliphatic-like (8.6-12.4 %) compounds-yields less stable complexes and is highly susceptible to Cr-induced oxidation. Mass-difference network analysis and density functional theory calculations further reveal that both DOM types undergo heavy-metal-triggered decarboxylation and dealkylation, but N-DOM retains complex structures, whereas MP-DOM degrades into smaller, hazardous molecules such as phenol and benzene. This study underscores the potential for heavy metals to exacerbate the ecological risks associated with the transformation of MP-DOM, providing crucial insights to inform global risk assessment and management strategies in contaminated waters where plastic and metal pollution co-occur.
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This review examines how microplastics and heavy metals interact in water environments, finding that microplastics can attract and concentrate toxic metals on their surfaces through various chemical forces. This combination effect is a concern for human health because contaminated microplastics carrying heavy metals can be consumed through seafood, delivering a double dose of pollutants.
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Researchers compared how microplastics made of PVC, polyethylene, and polyamide break down under UV light, natural sunlight, and real-world water body conditions, finding that natural environments cause more complex degradation involving both biofilm growth and heavy metal interactions. Importantly, microplastics in natural water can both release and re-absorb heavy metals over time, complicating their environmental risk profile.
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