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The degradation and greenhouse gas emissions of microplastic-derived dissolved organic matter: Role of mineral and polymer types
Summary
As plastic waste breaks down in soil, it releases dissolved carbon that soil particles (minerals) interact with, and this study found those minerals can reduce carbon dioxide emissions but actually increase nitrous oxide emissions—both potent greenhouse gases. This matters because it shows soil isn't just passively storing microplastic pollution; it's actively shaping how much these plastics contribute to climate change, with the effects depending on the type of soil mineral and plastic involved, meaning some regions may need more urgent plastic waste control than others.
Microplastic (MP) weathering releases MP-derived dissolved organic matter (MP-DOM) into soils, altering terrestrial carbon and nitrogen cycles and contributing to the emissions of greenhouse gases such as carbon dioxide (CO) and nitrous oxide (NO). However, how specific soil minerals regulate the degradation of MP-DOM and subsequently affect these emissions remains unclear. Here, we investigated these interaction mechanisms using a 56-day incubation experiment with different minerals as artificial soil and MP-DOM derived from different polymer types as the sole carbon source. We found that soil minerals generally reduced MP-DOM decomposition as reflected by the 2.7%-113.7% reduction in CO emissions, but generally enhanced NO emissions by 21%-2878%. This protective effect on MP-DOM decomposition was driven by surface adsorption, physical isolation, downregulation of carbon-degrading enzymes, and upregulation of carbon-fixation genes. The increased NO emissions was driven by restructuring microbial communities to shift inorganic nitrogen transformations. These emission patterns were jointly regulated by the types of soil minerals and MP polymers. Specifically, montmorillonite resulted in greatest NO emissions by providing heterogeneous microhabitats that favored K-strategists and enriched denitrifying bacteria such as Pseudomonas. Redox-active polyethylene-derived DOM interacted with goethite to accelerate decomposition and increase CO emissions, whereas polyvinyl chloride-derived DOM released cytotoxic chloride ions that impaired microbial metabolic functions and inhibited enzyme activities, reducing CO emissions. Scaling these mineral-specific rates with global plastic debris and soil mineralogy data, our spatial estimation shows that soil minerals reduce net MP-DOM-derived CO emissions by 2996 Mg C yr globally under the high-leaching scenario. Our findings demonstrate the potential of soil minerals to mitigate MP-DOM-derived CO emissions, while emphasizing the regulatory roles of mineral and polymer types, and highlighting the priority of plastic control in NO high-emission areas.