Weathered plastic bits change how wetland soils handle nitrogen
Ruan S, Chen R, Liu C, Chen F, Zhang Y
Soil Health
The nitrogen cycling happening in the mudflats and marsh edges near any coastal garden or park depends on soil chemistry that aged plastic fragments are quietly rewriting, with knock-on effects for the plants and shellfish that rely on that nitrogen balance.
Scientists buried bits of plastic (some fresh, some weathered by sun and salt water like plastic litter really experiences) in coastal wetland soil for three months. The weathered plastic pushed soil microbes to convert more nitrate into ammonium, a nitrogen form plants can use directly, while fresh plastic barely changed anything. Oddly, a little weathered plastic had a bigger effect than a lot of it, showing that how plastic pollution behaves depends heavily on its age, not just how much is there.
Key Findings
Aged polypropylene microplastics at 0.5% concentration increased DNRA (nitrate-to-ammonium conversion) rates by 60% after 90 days, while virgin polypropylene had negligible effect.
The effect was non-linear: the higher 1.0% concentration of aged microplastics was less stimulatory than the lower 0.5% concentration.
Sulfide, total organic carbon, and nitrate levels, rather than the abundance of nitrogen-cycling functional genes, were the main drivers of the DNRA response.
chevron_right Technical Summary
Microplastic pollution that has weathered in the environment for years affects soil nitrogen cycling very differently than fresh plastic, boosting a process that keeps nitrogen in wetland soils rather than letting it wash away or convert to greenhouse gases.
Abstract Preview
Original paper
Environmental aging alters microplastic effects on soil DNRA in estuarine and coastal wetlands.
Increased microplastic pollution in estuarine and coastal wetlands threatens the balance of the global nitrogen cycle. As microplastics (MPs) inevitably undergo environmental aging, their impacts o...
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