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UV Aging Strengthens the Effects of Polyvinyl Chloride Microplastics on Soil Bacterial Community Structure and Predicted Functional Profiles
Summary
Sunlight breaks down plastic bits (like those from PVC pipes and packaging) that end up in soil, and this study found that "sun-aged" microplastics change soil bacteria communities more than fresh, unweathered plastic does—including a possible increase in bacteria linked to antibiotic resistance. Since soil bacteria play a key role in growing our food and keeping ecosystems healthy, this matters because most real-world plastic pollution has already been weathered by sunlight, so studying only "fresh" plastic may underestimate its true impact on the soil that feeds us.
Soil microplastics undergo aging, but how aging modifies their effects on soil bacterial communities remains unclear. Here, we conducted a 180-day incubation experiment with no PVC (CK), pristine PVC microplastics (IP), and UV-aged PVC microplastics (AP, 0.5%, w/w). UV aging markedly altered PVC surface properties: roughness increased from approximately 12.9 to 21.8 nm, water contact angle decreased from 91.44° to 82.38°, and the O/C ratio increased from 0.37 to 0.43. Bacterial richness indices were largely unchanged, whereas Shannon diversity decreased under AP, indicating reduced community evenness. Bray–Curtis analysis showed significant community separation among treatments (PERMANOVA: R2 = 0.364, p = 0.003), with UV aging further altering the trajectory of PVC-induced community reorganization. At the genus level, AP was associated with enrichment of Methylobacillus and lower robustness in exploratory co-occurrence network analysis, suggesting a distinct bulk-soil bacterial response compared with IP. Functional prediction further suggested that AP and IP were associated with different predicted pathway profiles, with AP showing higher predicted representation of pathways related to carbon metabolism, respiratory energy metabolism, potential prokaryotic carbon fixation, environmental sensing, cellular maintenance, and antimicrobial-resistance-associated categories, whereas IP was mainly associated with transport- and communication-related predicted functions. These predicted functional patterns require further validation using metagenomic, qPCR, transcriptomic, biochemical, or chemical approaches. Overall, these findings highlight the need to consider the UV aging status of PVC microplastics when evaluating their effects on soil bacterial communities.