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The contribution of plastic film mulch to microplastics in agricultural soils was highly overestimated
Summary
Farmers have long blamed plastic mulch film (the plastic sheeting used to cover crop rows) as the main source of microplastic pollution in farm soil, but this new study of Chinese farmland found that film only accounts for a small fraction—sometimes less than 1%—of the tiny plastic bits found in soil. Instead, things like compost, irrigation water, and even plastic particles falling from the air appear to be major contributors, meaning efforts to reduce microplastics in our food-growing soil need to target a much wider range of sources than just farm plastic.
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 × 10 5 items kg − 1 ), followed by Gansu (94.0 kg ha − 1 ; 6.1 × 10 5 items kg − 1 ) and Shandong (61.2 kg ha − 1 ; 4.0 × 10 5 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.