Degradation of microplastics in the natural environment: A comprehensive review on process, mechanism, influencing factor and leaching behavior

In recent years, the pollution of microplastics (MPs) has attracted global attention because of their extensive distribution and significant impact on biota. Once MPs enter the ecosystem, the complex degradation process that MPs undergo will alter their surface properties and toxic effects. In order to address the global pollution issue caused by MPs, a range of technologies have been developed to degrade MPs. This study systematically summarizes the degradation methods of MPs reported recently, including physical, chemical and biological degradation processes. Dissolved organic matter (DOM), some reducing agents and sulfides are found to cause MPs aging and degradation. The roles of reactive oxygen species and biological enzymes in MPs degradation are elucidated. The chemical and biological degradation of various types of MPs are discussed and their degradation pathways are clarified. A number of factors affect the rates of MPs degradation in natural environment. Specifically, the influences of external factors and the intrinsic properties of MPs on their degradation are revealed. Furthermore, the potential environmental toxicity of MPs is investigated in greater depth, with particular attention paid to the release of plastic additives and DOM during the degradation process. This review article will assist in the comprehension of environmental degradation process and ecological risks of MPs and provide guidance for controlling the environmental pollution caused by MPs.