Are biodegradable mulch films a sustainable solution to microplastic mulch film pollution? A biogeochemical perspective

Mulch film residue contributes significantly to global plastic pollution, and consequently biodegradable mulch films (BDMs) are being adopted as a solution. BDMs decompose relatively quickly, but their complete biodegradation requires suitable conditions that are difficult to achieve in nature, causing biodegradable microplastics (bio-MPs) to be more likely to accumulate in soil than traditional microplastics (MPs). If BDMs are to be considered as a sustainable solution, long-term and in-depth studies to investigate the impact of bio-MPs on the biogeochemical processes are vital to agroecosystems operation and ecosystem services supply. Although bio-MP-derived carbon can potentially convert into biomass during decomposition, its contribution to soil carbon stocks is insignificant. Instead, given their biodegradability, bio-MPs can result in greater alterations of soil biodiversity and community composition. Their high carbon-nitrogen ratios may also significantly regulate various processes involved in the natural decomposition and transformation of soil organic matter, including the reduction of nutrient availability and increase in greenhouse gas emissions. Soil ecosystems are complex organic entities interconnected by disturbance-feedback mechanisms. Given the prevailing knowledge gaps regarding the impact of bio-MPs on soil biogeochemical cycles and ecosystem balance, this study emphasized the safety and sustainability assessment of bio-MPs and the prevailing comprehensive challenges.