Microplastics in Landfill Leachate: A Comprehensive Review on Characteristics, Detection, and Their Fates during Advanced Oxidation Processes

Microplastics are generated from plastic waste in landfills due to physical, chemical, and biological effects, and eventually enter into the leachate. Leachate is a potential source of environmental microplastics which has not been emphasized. Here, we summarized the investigation of microplastics in leachate in 9 countries from 28 papers, provided a comprehensive review of the sampling, detection, and separation of microplastics in leachate, and elaborated on the quality control in each process. There are more than forty types of microplastics in leachate, with diverse shapes, wide size distribution, and concentrations of 0–25 items/L. Commonly used techniques are FTIR, Raman, SEM, and py-GC–MS for characterizing microplastics, while standardization of micro- or nanoplastics for leachate with a complex composition should be further studied. We also discussed in depth the degradation mechanism of microplastics in advanced oxidation processes (AOPs). Microplastics can be decomposed into small molecules such as aldehydes and ketones, and some can even eventually be degraded into CO2 and H2O in AOPs, which may be further implemented in leachate treatment plants. This review provides the scientific fundamentals for understanding the microplastics in landfill leachate and proposes removal strategies for future research.