Aging of biodegradable plastics alters soil aggregate stability and organic carbon through shifts in microbial...

The proliferation of drinking straw waste as a single-use plastic pollutant poses significant risks to the environment and, by extension, to human health. Polylactic acid (PLA) has shown notable advantages in the material of single-use plastic drinking straws owing to its biocompatibility and non-toxic properties. However, research on PLA straw-induced microplastic pollution entering natural ecosystems, along with the associated potential microbial degradation mechanisms, remains insufficient in both scope and depth. Therefore, this study systematically investigates the effects of PLA straws at 0, 0.1, 0.2, 0.3, and 0.4 wt% on soil aggregate stability, organic carbon, and microbial communities. Addition of PLA straw significantly influenced the stability of water-stable soil aggregates, which initially increased and then declined with increasing PLA straw concentrations. A similar trend was observed in the contribution of large macroaggregates to soil organic carbon. Bacterial community α-diversity also first increased, followed by a decline with an increased PLA concentration, whereas fungal communities displayed an opposite trend. Microbial communities were found to be pivotal in PLA straw aging and degradation. Bacterial communities significantly influenced soil aggregate stability, whereas fungal communities had a more substantial impact on the organic carbon content of aggregates. The most active degradation occurred at 0.2 wt% PLA, which coincided with increases in Acidibacter (bacteria) and Mortierella (fungus). Moreover, the degradation of PLA's functional groups (-CH₃, -CH₂-, C=O, and = C-H) was closely associated with significant enrichment of Botryotrichum atrogriseum (fungus), and Luedemannella and Pseudomonas (bacteria). Notably, PLA degradation in the soil appears to promote the proliferation of potentially pathogenic bacteria that could affect plants and animals. These microorganisms may compromise soil aggregate stability and organic carbon storage, raising potential food safety concerns.