Identification of microplastics in landfill leachate: An underestimated tiny microplastics using Focal Plane Array (FPA)-based Fourier Transform Infrared (FTIR) imaging

Landfills are significant contributors to the generation of microplastics (MPs) in the environment. However, how to accurately identify and quantify tiny MPs (10-100 µm) in landfill leachate remains an ongoing challenge. The identification of MPs in the leachate of operating and closed landfills was comparatively investigated using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and focal plane array-based micro-Fourier-transform infrared (FPA-FTIR) imaging. The abundance of MPs detected by FPA-FTIR (70-235 items/L) was two-order magnitude higher than that by ATR-FTIR (2-7 items/L), indicating that FPA-FTIR was more efficient in detecting tiny MPs than ATR-FTIR. Furthermore, the MPs in landfill leachate from 13 different landfills in China, comprising both operating and closed landfills, were determined by FPA-FTIR. The morphology of MPs mainly consists of white fragments, and they are predominantly high-density engineering plastics, which make up 90 % of the total MPs. In operating landfills, the abundance of MPs ranged from 175 to 5320 items/L. The abundance initially increased to a maximum peak at around 15 years of landfill age, and then declined as the landfill continued to operate. In closed landfills, the abundance of MPs showed a decreasing trend with the increasing of landfill closure age. The operational conditions and landfill age significantly affect the quantity of MPs in leachate; however, they do not exert a notable influence on the morphological characteristics of MPs in leachate. This study provided valuable insights for evaluating the transportation and migration behavior of MPs from landfill cells into leachate.