Polyethylene microplastics mineralize slowly in soil but integrate into soil structures and organic matter

Polyethylene is the most abundant microplastic in agricultural soils and can alter soil properties and plant health. However, microbial mineralization rates and the fate of polymer-derived carbon in soil remain poorly understood. We incubated UV-aged 13 C-labeled polyethylene in agricultural soil for 22 months and monitored microbial mineralization by measuring 13 CO 2 production. After incubation, the spatial distribution of micro- and nanoplastics within individual soil aggregates and the incorporation of polyethylene-derived carbon into soil organic matter and soil microbial biomass were investigated. The results showed low mineralization of polyethylene (0.12% in 22 months), with decreasing mineralization over time. Microplastics and nanoplastics were found in pores inside 1–2 mm soil aggregates, and minor amounts of polyethylene-derived carbon were found incorporated into soil organic matter and microbial biomass. Overall, these results demonstrate the high persistence of polyethylene in agricultural soils and its gradual physical integration into soil structures.