Novel insight into the in-situ study of biodegradable microplastics in soil aggregates

Biodegradable plastic as an effective alternative to conventional plastic has been widely applied in recent years, but its incomplete degradation in soil has potentially led to microplastics pollution. Soil aggregates may have a remarkable influence on the degradation behavior of biodegradable microplastics (BMPs). In this study, a 12-month field in-situ incubation experiment was conducted to investigate the surface features and biodegradation behavior of BMPs in soil aggregates. It was found that soil particles cement into BMP surfaces, as evidenced by the appearance of Si-O peaks, and the soil cementation is an interfacial phenomenon and does not alter the chemical structure of BMPs. After 12-month, the secondary BMPs concentration in soil particles reached 836 ± 106 items g^-1, and that in soil aggregates was only 258 ± 72 items g^-1. Almost 80 % of the secondary BMPs were less than 0.5 mm in size. Furthermore, BMPs underwent slower biofragmentation within the soil aggregates. The occlusion in soil aggregates prevented the migration of smaller-sized BMPs, resulting in a high proportion of smaller-sized BMPs in soil aggregates. During BMPs biodegradation, changes in the molecular structure at the polymer level resulted in a persistent residue of highly cross-linking BMPs. This research highlights the dual role of soil aggregates in both limiting microplastics dispersal and influencing degradation pathways, offering actionable data for improving biodegradable plastic policies and environmental risk assessments.