Conventional and biodegradable agricultural microplastics: effects on soil properties and microbial functions across a European pedoclimatic gradient

Agricultural plastics like mulching films may become a major source of microplastic (MP) soil contamination during their degradation and fragmentation. This study investigates the effects of agricultural MPs from conventional (linear low-density polyethylene, PE) and biodegradable (starch-blended polybutylene adipate co-terephthalate, PBAT-BD) mulching films on soil physicochemical properties, aggregation, microbial diversity and functions, litter decomposition, and greenhouse gases emissions (GHG). For this purpose, MPs were mixed into soils at realistic MP concentrations of 0.005% and 0.05% (w/w) in 2022 on experimental plots in three EU countries representing different pedoclimatic conditions (Finland, Germany and Spain), followed by monitoring of the above-mentioned variables in the subsequent growing seasons 2022 and 2023. We found several significant MP-induced effects for soil properties, aggregation, microbial diversity, litter decomposition, and GHG, but the effect endpoints were less pronounced or varied considerably. Contrarily, microbial activity, contributing to soil functions such as nitrogen cycling, was consistently reduced by both conventional and biodegradable MPs. The reductions were more pronounced after the second season and for the higher MP treatment. As the higher MP concentration (i.e., 0.05% w/w) is environmentally relevant in Europe, our findings emphasize the potential effects of environmentally relevant MP concentrations on soil health. Furthermore, the effects increased from north to south, probably modulated by varying pedoclimatic conditions, inducing reflection of a need for regionally tailored risk assessment to protect soil from plastic pollution.