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Designed to Guide, Destined to Pollute: The Overlooked Microplastic Source in Agricultural Mulch Films
Summary
Farmers often use plastic mulch (woven sheets with green stripes) to help crops grow, but a 12-year study found this practice leaves behind thousands of microplastic particles per kilogram of soil—and surprisingly, the thin green marking lines break down much faster than the black plastic, making them the biggest source of contamination despite being a tiny fraction of the material. The study also found that a plasticizer chemical (DEHP), linked to hormone disruption in humans, leached out of the plastic into the soil over time. Since these microplastics and chemicals can end up in the food we grow, the findings suggest simple design changes—
Mulching is a common agricultural practice that improves crop quality and yield. However, it also contributes to soil contamination with microplastics, raising environmental concerns. To develop sustainable agricultural policies, quantifying microplastic pollution in soils caused by mulching is essential. Despite their design for perennial use and widespread application, woven polypropylene films have not yet been investigated as a potential microplastic source. Here, we examined microplastic contamination in an agricultural field mulched for twelve years with a black woven polypropylene film with green marking lines. About 4000±1700 polypropylene particles per kilogram of dry soil were detected, with mulch film fragments making up ~60% of the total microplastic load. Although the green marking lines only constitute 2.5 wt% of the applied mulch film, they account for the majority (62%) of these fragments. We show that the significantly faster degradation of the marking lines is caused by enhanced photooxidation due to covalent grafting of the green dye using maleic anhydride and a lack of efficient UV protection. In contrast, the black woven fabric is protected against photooxidation by the addition of carbon black, causing less microplastic contamination (38%). In the pristine films, the environmentally problematic plasticizer DEHP (~0.1 mol%) was identified. However, after twelve years in the field, the DEHP content fell below the detection limit, indicating leaching. Our work highlights the marking lines as a major source of microplastic pollution in the investigated field, which can be easily avoided by alternative film design. Our results further urge a critical reassessment of problematic additives in mulch films.