Zinc-containing PVC microplastics reduce soil microbial activity and alter community structure in the plastisphere following UV-induced weathering

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.