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Microplastic contamination enhances benthic dissolved organic carbon fluxes and molecular transformations in sediments
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Scientists found that microplastics buried in lake and river sediments don't just sit there, they leach out dissolved carbon compounds into the water, in some cases increasing this "dissolved organic carbon" by up to 27-fold. This matters because it shows plastics can actively reshape the chemistry of aquatic ecosystems, potentially affecting water quality and the natural processes that break down pollutants, even though this study focused on lab conditions rather than direct human health effects.
Microplastics (MPs) are pervasive in aquatic environments and ultimately accumulate in sediments, yet their role in regulating benthic carbon cycling remains poorly constrained, particularly with respect to dissolved organic matter (DOM) exchange across the sediment-water interface. In this study, we conducted 28-day laboratory sediment-column incubations under controlled oxic and hypoxic conditions to quantify MP-associated changes in DOM quantity and composition in porewater and overlying water. Polyethylene (PE; petroleum-based) and polylactic acid (PLA; bio-based) MPs were added at 5% (w/w) as a high-end (hotspot) loading scenario. MP contamination increased porewater dissolved organic carbon (DOC) concentrations by up to 27-fold relative to controls, resulting in 1.6-18-fold higher cumulative benthic DOC fluxes across the sediment-water interface. Optical and size-fraction analyses revealed polymer-specific shifts in exported DOM quality. PLA treatments were characterized by strong enrichment of low-molecular-weight neutral fractions, consistent with MP-associated DOM inputs, whereas PE treatments were associated with enhanced mobilization and redistribution of sediment-derived DOM. Molecular-level analyses further showed that MP-associated formulas accounted for up to one-third of all detected molecular features, despite MPs comprising only ∼5% of sediment mass. This disproportionate molecular representation suggests that MPs may influence DOM composition beyond their direct mass contribution. Oxygen availability further modulated these molecular patterns, with oxic conditions characterized by higher proportions of formulas classified as metabolically active within the operational reactivity-activity framework, whereas hypoxic conditions favored the accumulation of relatively inactive and more persistent molecular fractions. Overall, these results suggest that sediment-associated MPs may alter both the quantity and molecular characteristics of DOM exchange across the sediment-water interface, highlighting their potential role in modifying benthic carbon exchange processes in MP-impacted aquatic systems.
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Researchers investigated how dissolved organic matter released by microplastics affects the way soil microbes process carbon. They found that compounds leaching from both new and aged microplastics stimulated soil carbon release, with aged microplastics having a larger effect by altering microbial community structure. The findings suggest that microplastic pollution may influence soil carbon cycling and potentially affect how effectively soils store carbon.
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Researchers discovered that ocean plastics continuously leach dissolved organic carbon into seawater — an estimated 23,600 metric tons per year globally — fueling the growth of bacteria at the base of the marine food web. Because plastic pollution is projected to increase tenfold in the coming decade, this plastic-derived carbon input could significantly alter microbial communities and ocean chemistry in ways not yet fully understood.
Divergent Shifts in Sediment Dissolved Organic Matter Stability and Microbial Carbon Metabolic Potential Induced by Biodegradable and Conventional Microplastics
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"Biodegradable" plastics are often marketed as eco-friendly, but this study found they still disrupt sediment ecosystems, changing the chemistry of organic matter and shifting microbial communities much like conventional plastics do. This matters because these microbial and chemical changes could affect water quality and nutrient cycling, showing that swapping to biodegradable plastics isn't automatically safer for the environment.
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