Microplastic contamination in agricultural soils from mulch films and organic amendments: Transformation mechanism, soil-Biota toxicity, and future perspectives

Microplastic contamination has emerged as one of the most pressing environmental challenges of our time. While extensive research has been conducted on microplastics in aquatic ecosystems, there remains a significant knowledge gap regarding their presence and impact in terrestrial environments, particularly in agricultural soils, despite microplastic contamination on land being 4 to 23 times higher than in aquatic systems. These soils are increasingly polluted with microplastics from various sources, including plastic mulch films, organic amendments, irrigation, and atmospheric deposition. Among these, the extensive use of plastic mulch film is the primary contributor to microplastics pollution, with China accounting for the highest regional consumption. The degradation rate of microplastics in soil varies significantly, ranging from several months to years depending upon the type of microplastic and environmental conditions. Microplastic accumulation disrupts soil properties, such as soil structure, bulk density, water holding capacity, and nutrient availability. Moreover, soil organisms that ingest these microplastics face severe health issues, often leading to mortality, while these particles enter the food chain posing potential risks to human health. The general objective of this review is to provide a comprehensive understanding of microplastics contamination in agricultural soils by exploring their sources, available techniques for their identification, and mechanisms of their physical, chemical, and biological transformation. It also examines the harmful effects on soil properties, microbial communities, and crop growth. Finally, the review highlights the key strategic directions for future research aimed at bridging the existing knowledge gaps and advancing our understanding of microplastic contamination in agricultural soils.