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Polymer–environment interplay drives microplastic degradation in a surface-flow wetland: New insights into bacterial assembly, network structure, and function across aquatic and sedimentary habitats
Original title: Polymer–environment interplay drives microplastic degradation in a surface-flow wetland: New insights into bacterial assembly, network structure, and function across aquatic and sedimentary habitats
Summary
Scientists tested how well five common plastics break down in wetland environments over four months, finding that surprisingly, some plastic-based materials (like polyurethane) degraded faster than "eco-friendly" bioplastics like PLA, while polypropylene barely broke down at all. The real drivers of breakdown were bacteria living on the plastic surfaces, and their activity depended more on their surroundings—water versus sediment—than on the type of plastic itself. This matters because wetlands are often used to filter water, and understanding which plastics linger longest helps identify which microplastics may accumulate in ecosystems and, eventually,
It remains unclear how polymer types (petroleum- vs. bio-based) and environmental media interact to affect microplastic (MP) biodegradation in wetlands. We conducted a 120-day in situ experiment, incubating five MPs (polylactic acid [PLA], polyurethane [PU], polyethylene terephthalate [PET], polyethylene [PE], and polypropylene [PP]) in a surface-flow wetland. A distinct degradation order was observed: PU (15.2 ± 3.2% in sediment; 12.0% ± 3.9% in water) > PE (11.9% ± 2.9%; 8.2% ± 4.0%) > PLA (4.4% ± 2.2%; 5.0% ± 3.1%) ≈ PET (2.4% ± 1.5%; 7.1% ± 3.5%) ≫ PP (0.0-0.3%), showing faster degradation of most petroleum-based MPs than bio-based PLA. Integrating 16S rRNA sequencing, co-occurrence network analysis, neutral and null model analyses, we demonstrated plastisphere community assembly was governed by deterministic habitat filtering (>85% contribution) over polymer type. Functional specialization diverged between habitats, with aquatic plastispheres being enriched in nitrate reducers and aromatic hydrocarbon degraders (Nitrospira, Methyloversatilis, and Hydrogenophaga), whereas sedimentary ones were dominated by plastic/polysaccharide degraders (Psychrobacter and Microbulbifer). Co-occurrence networks contrasted sharply, being high-modularity/low-connectivity structures in water but low-modularity/high-connectivity ones in sediment. Structural equation modeling identified the plastisphere microbiome as the direct degradation driver. This degradation is enhanced by light irradiation (loadings: 0.888) in water and but is inhibited by the contents of organic matter (-0.738), DGT-labile Fe (-0.876) and S (-0.876) in sediment. These findings underscore the critical interplay between habitat and polymer type in controlling MP fate in wetlands.