Biodegradable plastics in soil: a significant gap from microplastics to nanoplastics and oligomers

Abstract

Biodegradable plastics (BPs) have been increasingly used as alternatives to conventional plastics to alleviate soil pollution caused by conventional (micro) plastics. However, BPs in soils can degrade into microplastics (MPs), nanoplastics (NPs), oligomers and monomers, which may pose risks to ecosystems. In comparison to the extensive studies on conventional MPs and NPs, much less is known about the behavior and risks of biodegradable MPs (BMPs), particularly biodegradable NPs (BNPs) and oligomers in soils, due to the lack of reliable methodologies. Despite previously published reviews in this field, the gap between BMPs, BNPs and oligomers has largely been overlooked. This review systematically and critically summarizes the latest advances and future research priorities of BPs in soil. In contrast to the well-studied aging of BPs, the fragmentation process, release of intermediates, and their interactions with each other and other pollutants in soils are poorly known. Despite the relatively well-explored effects of BPs on soil physicochemical properties, the ecotoxicological impacts on microbes, plants, and animals of BPs and BMPs, as well as the behavior and ecological risks of BNPs and oligomers, have been largely neglected. Significant knowledge gaps and future research priorities in the identification and quantification methodologies, as well as the behavior and risks of BNPs and oligomers in complex soil environments, are highlighted. These include the unique challenges of BMP and BNP experiments, particularly the dynamic changes in particle size and composition due to hydrolysis in the short term. This review underscores the need for further research on the formation, environmental behavior, and toxic effects of BNPs, oligomers, and monomers in soil. It improves the understanding of the potential risks posed by BNPs and oligomers and provides a reference for future BP management strategies.