The contribution of plastic film mulch to microplastics in agricultural soils was highly overestimated

The extensive use of plastics in agriculture has resulted in the accumulation of macroplastics (MAPs, >5 mm) and microplastics (MPs, ≤5 mm) in agricultural soils, posing risks to soil functioning and food security. However, the relative contributions of different input pathways to soil MPs remain insufficiently quantified, particularly within intensively plastic-mulched systems. This study quantified and comparatively evaluated multiple MP input pathways within representative long-term plastic film mulch (PFM)-dominated farmlands in China. A large-scale field investigation (266 samples for MP analysis and 29 soil samples for MAP analysis, collected across 27 counties in Yunnan, Gansu, and Shandong Provinces) was integrated with a material flow analysis (MFA) modelling framework to assess source contributions under a defined system boundary. MAP and MP concentrations were highest in Yunnan (120.9 kg ha−1; 7.3 × 105 items kg−1), followed by Gansu (94.0 kg ha−1; 6.1 × 105 items kg−1) and Shandong (61.2 kg ha−1; 4.0 × 105 items kg−1). Model results showed that PFM contributed 19.0 ± 3.1%, 0.7 ± 0.1%, and 4.3 ± 0.9% of soil MPs in Yunnan, Gansu, and Shandong, respectively. Compost, irrigation water, and atmospheric deposition were also identified as relevant pathways. Within the defined study boundary and modelling assumptions, non-PFM pathways, particularly atmospheric deposition, may contribute substantially to soil MP inputs in plastic-mulched systems. These results highlight the importance of integrating multiple pathways for comparative source assessment and for developing more targeted agricultural plastic management strategies.