Complex Degradation of PBAT and PLA in Estuarine and Coastal Waters

Abstract Understanding the environmental degradation of biodegradable plastics under realistic aquatic conditions is critical for assessing their contribution to microplastic pollution. Here, we report an 18-month in situ study of the degradation of poly(butylene adipate-co-terephthalate) (PBAT), poly(lactic acid) (PLA), and linear low-density polyethylene (LLDPE) sheets deployed in marine and estuarine environments under benthic and surface exposure conditions. PBAT showed highly variable degradation, with mass loss ranging from 5% in likely anaerobic or oxygen-limited benthic marine settings to 93% in estuarine conditions. After 10 months of exposure, mechanical property deterioration and molecular weight loss were evident, with fragmentation into macro- and mesoplastics at several sites. PLA also exhibited a decrease in molecular weight and mechanical properties over time, resulting in fragmentation at all sites to various extents after 18 months, but it showed minimal mass loss, indicating slow bulk degradation and likely persistence of both macro- and microplastics. LLDPE remained largely unchanged with no significant mechanical changes, supporting the probability of long-term persistence of polyethylene. Overall, the results highlight that degradation and microplastic formation of PBAT and PLA samples are nonlinear and highly dependent on aquatic environmental conditions.