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Effects of microplastics on nitrogen and phosphorus cycles and microbial communities in sediments
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Researchers found that PVC, PLA, and polypropylene microplastics altered nitrogen and phosphorus cycling in freshwater sediments by shifting microbial community composition, with effects varying by polymer type and biodegradability.
Sediments are the long-term sinks of microplastics (MPs) and nutrients in freshwater ecosystems. Therefore, understanding the effect of MPs on sediment nutrients is crucial. However, few studies have discussed the effects of MPs on nitrogen and phosphorus cycles in freshwater sediments. Herein, 0.5% (w/w) polyvinyl chloride (PVC), polylactic acid (PLA), and polypropylene (PP) MPs were added to freshwater sediments to evaluate their effects on microbial communities and nitrogen and phosphorus release. The potential biochemical functions of the bacterial communities in the sediments were predicted and assessed via 16S rRNA gene sequencing. The results showed that MPs significantly affected the microbial community composition and nutrient cycling in the sediments. PVC and PP MPs can promote microbial nitrification and nitrite oxidation, while PP can significantly promote alkaline phosphatase (ALP) activity and the abundance of the phosphorus-regulation (phoR) gene. PLA MPs had the potential to promote the abundance of microbial phosphorus transporter (ugpB), nitrogen fixation (nifD, nifH, and nifX), and denitrification (nirS, napA, and norB) genes and inhibit nitrification, resulting in massive accumulation and release of ammonia nitrogen. Although PLA MPs inhibited the activity of ALP and the abundance of the organophosphorus mineralization (phoD) gene, it could enhance dissimilatory iron and sulfite reduction, which may promote the release of sedimentary phosphorus. Our findings may help understand the mechanisms of nitrogen and phosphorus cycles and microbial communities driven by MPs in sediments and provide a basis for future assessments of the environmental behavior of MPs in freshwater ecosystems.
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Unveiling the impact of microplastics with distinct polymer types and concentrations on tidal sediment microbiome and nitrogen cycling
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Researchers tested how five different types of microplastics at varying concentrations affect microbial communities and nitrogen cycling in tidal sediments over 30 days. They found that microplastics generally reduced microbial diversity and enhanced nitrogen fixation, with biodegradable PLA plastic showing concentration-dependent effects. The study suggests that microplastic contamination in coastal sediments can disrupt important nutrient cycling processes driven by microorganisms.
Varied influence of aged microplastics and related leachates on phosphorus transformation and release from the sediments
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Researchers investigated how aged microplastics and their chemical leachates affect phosphorus cycling in freshwater sediments, a process linked to harmful algal blooms. They found that different types of weathered plastics and their leachates altered microbial communities and shifted the forms of phosphorus present in sediments. The study suggests that microplastic pollution in lake and river sediments may contribute to nutrient imbalances that worsen water quality problems.
Biodegradability of microplastics reshapes surface biofilm microbial community structure and nitrogen cycling functions in aquatic environments
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Researchers compared how biodegradable (PLA) and non-biodegradable (polyethylene and PVC) microplastics affect the microbial communities that form on their surfaces in aquatic environments, finding substantial differences in which bacteria colonized each plastic type and how they processed nitrogen. PLA supported communities rich in nitrogen-cycling bacteria, while PVC and polyethylene enriched different microbial groups associated with pollutant degradation. The study suggests that the push toward biodegradable plastics will change — not just reduce — the ecological effects of microplastics in rivers and lakes.
Impacts of microplastics on the nitrogen transformation in hyporheic zones with different grain sizes
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A lab experiment simulated riverbed sediment zones to test how two types of microplastics, PVC and biodegradable PLA, affect nitrogen processing. PLA reduced nitrate levels, especially in fine-grained sediment, and altered oxygen levels, microbial communities, and nitrogen-related genes, while PVC had smaller effects overall.
Impact of Microplastic on Freshwater Sediment Biogeochemistry and Microbial Communities Is Polymer Specific
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Researchers used a microcosm approach to test how three common plastic types found in Great Lakes sediments affect freshwater benthic biogeochemistry and microbial communities. They found that each polymer had distinct effects: PET fibers decreased ecosystem metabolism, PVC particles increased nutrient uptake, and tire-derived rubber most substantially altered microbial community function. The study highlights that the environmental impact of microplastics in freshwater sediments depends heavily on the specific polymer type involved.
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