Climate and soil properties drive microplastic enrichment patterns in agricultural soils across a multi-country survey

Microplastics (MPs) are ubiquitous contaminants in terrestrial ecosystems, yet the environmental drivers governing their accumulation and composition in soils remain poorly understood. Here we present a multi-country survey of agricultural soils from farming systems using plastic mulch film across a global climatic gradient to investigate drivers of MP enrichment and polymer composition. To account for inter-laboratory analytical variability, MP abundances were analysed using robust Z-transformed enrichment values. Linear mixed-effects modelling showed that soil physical properties and climate were the primary regulators of relative MP enrichment, with soil properties explaining more variation than agricultural and plastic management practices. Higher precipitation was associated with lower MP enrichment, whereas higher temperatures were linked to increased enrichment, suggesting climate-driven modulation of MP production and accumulation processes. Polymer composition exhibited strong geographic variability but only weak vertical structuring within the upper 30 cm soil profile. Site-level heterogeneity frequently exceeded depth-related variation, indicating that localised inputs and soil processes dominate polymer distributions. However, while environmental surveys provide valuable insights into contamination patterns, comparisons across regions remain challenging and require improved standardisation of spectroscopic workflows and reference libraries, and the inclusion of environmentally weathered polymer spectra. Consequently, polymer identifications in environmental MP datasets should be interpreted cautiously and viewed as indicative rather than definitive. Our findings emphasise that environmental MP datasets are shaped by both natural heterogeneity and analytical uncertainty, and that improvements of analytical standardisation and environmental sampling frameworks are required to generate reliable, comparable global datasets capable of supporting environmental risk assessments and policy development.