From macro to micro: The key parameters influencing the degradation mechanism and the toxicity of microplastics in the environment

Plastic cannot decompose entirely in natural ecosystems due to its persistent covalent bonds, hydrophobicity, and resistant functional groups. It disintegrates into micro or nano form due to certain physical, chemical, or biological factors. Plastic's micro and nano forms can readily enter the food chain, resulting in the bioaccumulation and biomagnification of harmful substances. In view of the facts concerning plastic degradation, this review article aims to provide a comprehensive understanding of microplastic degradation processes, degradation mechanism, uptake and translocation, and toxicity mechanism. A prominent search in Google Scholar used the keywords microplastics, degradation mechanisms, biotoxicity, and toxicity mechanism to strengthen and identify the concepts related to MPs and their effect on ecosystems. Plastics, with a lifespan of 100-1000 years, undergo degradation due to environmental weathering. Degradation processes include chemical, thermal, photochemical, and biological. Factors like composition, structure, and additives influence degradation. Advanced oxidation methods are popular for chemical degradation, showing UV radiation can degrade 7-22% of floating plastic. The eradication of microplastics from the ecosystem has become a significant challenge for protecting humans and other organisms. Future research should identify environmental parameters affecting plastic degradation, predict plastic fate, and develop technologies for pollution reduction, mainly focusing on microplastics and nanoplastics' formation and degradation.