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Zinc-containing PVC microplastics reduce soil microbial activity and alter community structure in the plastisphere following UV-induced weathering
Summary
Researchers studied how zinc-containing PVC microplastics affect soil health before and after UV weathering and found that UV aging dramatically increased zinc release into soil. The weathered microplastics with high zinc content inhibited soil microbial activity, reduced bacterial diversity, and shifted community structure, highlighting how plastic additives can amplify the environmental impact of microplastic pollution in agricultural soils.
Plastic pollution poses a significant threat to agricultural ecosystems, yet the effects of metal additives in these plastics on soil health remain understudied. We investigated how new and UV-weathered PVC plastic film with realistic nano-ZnO addition rates (0, 1, and 5 % wt.) affected soil properties and microbial communities. UV aging significantly enhanced Zn release from nano-ZnO PVC plastics, substantially increasing both the total and bioavailable Zn concentrations in soil. UV-aging of PVC containing 1 % ZnO increased total soil Zn by ca. 2-fold and available Zn by ca. 6-fold, while in the 5 % ZnO treatment, total Zn increased 6-fold (reaching 649 mg kg-1) and available Zn ca. 25-fold (reaching 159 mg kg-1). FTIR analysis revealed formation of new functional groups after UV aging, including -OH groups and unsaturated C=C bonds due to PVC dehydrochlorination. Using 14C-isotope tracing, we demonstrated that UV-aged 5 % wt. ZnO microplastics inhibited soil microbial activity, induced shifts in microbial community structure, reduced bacterial diversity, and resulted in changes in microbial carbon use efficiency (CUE). Conversely, Zn-containing macroplastics showed negligible effects compared to their microplastic counterparts. Relative abundances of Actinomycetota, Planctomycetota, and Verrucomicrobiota increased with higher ZnO additive rates, while Pseudomonadota, Myxococcota, and Gemmatimonadota decreased. This research highlights the need to define critical thresholds for metal additives in plastics used within agriculture and emphasizes the importance of considering both physical fragmentation, UV aging, and chemical additive release when assessing the impact of plastics on soil health and ecosystem functioning.
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