Differential effects of field-aged versus new LDPE and PLA/PBAT plastic film fragments on soil quality and crop productivity

Whilst complex interactions of plastic type, size, shape, and concentration have been established, most research to date has focused on new, uniform microplastics that fail to represent the heterogeneous mixture of weathered fragments resulting from natural aging of PMF in agricultural fields. To address this, we investigated the concentration-dependent effects (0.05 %, 0.5 %, 1.5 % w/w) of realistic size mixtures (1:1:1 w/w/w macro-, meso-, microplastic) of both conventional (LDPE) and biodegradable (PLA/PBAT) PMFs in their new and field-weathered forms on radish (Raphanus sativus L.) growth, soil physio-chemical properties, ¹⁵N fertiliser partitioning, N₂O emissions, and microbial activity. We showed that degradation plays a crucial role in how PMFs affect soil and crop functioning, emphasising the importance of utilising size mixtures and field-weathered materials when assessing plastic impacts in agricultural settings. Soil bulk density and moisture reduced with increasing PMF concentration regardless of PMF type or degradation, and aged PMFs increased cumulative ¹⁴CO₂ respiration similarly to organic straw amendment compared to new PMF. Additionally, biodegradable PMF, especially in its aged form, positively affected ¹⁵N plant uptake and plant biomass compared to conventional PMF. This study highlights that using uniform, new microplastics may misrepresent the complex effects on soil and plant properties under realistic conditions.