A meta-analysis of microplastic accumulation dynamics in agricultural soils under long-term plastic film mulching

Background Plastic film mulching enhances water conservation and crop productivity in arid regions, yet microplastic (MP) accumulation from film degradation threatens long-term soil health and food security. Objective This meta-analysis quantified the temporal dynamics of MP accumulation under continuous plastic film mulching and evaluated modulating factors across agricultural systems and geographic regions (8 countries, 268 observations). Methods A systematic review following PRISMA guidelines was conducted across Web of Science, Scopus, PubMed, Google Scholar, and China National Knowledge Infrastructure. From 47 studies (2000–2025) reporting mulching duration–MP relationships, 12 primary studies met the inclusion criteria. Mixed-effects meta-regression and subgroup analyses were employed. Results A significant positive correlation was observed between mulching duration and MP abundance (pooled correlation coefficient = 0.82, 95% confidence interval (CI): 0.76–0.87, p < 0.001). The weighted mean accumulation rate was 47.3 items kg⁻¹ year⁻¹ (95% CI: 38.6–56.0), with substantial heterogeneity (I² = 94.3%). Accumulation followed a non-linear quadratic trajectory (R² = 0.89), driven by photo-oxidative fragmentation and positive feedback from residual film accumulation. Polyethylene systems exhibited 2.3-fold higher rates than biodegradable films (p < 0.001). Arid climates showed 3.1-fold higher rates than humid regions (p < 0.001), with ultraviolet (UV) intensity explaining 67% of the variance. Sandy soils accumulated MPs 2.7-fold faster than clay soils (p < 0.001). Mulching duration (β = 38.2), UV intensity (β = 0.54), and soil sand content (β = 0.38) emerged as the strongest predictors. Conclusion Plastic film mulching drives progressive, non-linear MP accumulation in agricultural soils, accelerated by environmental factors. Without intervention, 76% of long-term mulched fields are projected to exceed 10,000 items kg⁻¹ by 2050. This framework supports urgent policy interventions.