Compare Visual and Spectroscopic Identification of Microplastics in Municipal Solid Waste Samples

Dumpsites and landfills contain huge amounts of spatially concentrated waste plastics for an infinite period. Waste plastics are susceptible to weathering and fragmentation which result in microplastics (MPs) that remain in the environment and almost impossible to clean up. Prior to land disposal, most waste plastics have been exposed to sunlight ultraviolet (UV) radiation, moisture intrusion, elevated temperature, mechanical stress, and may be stained by organic solvent and corrosive liquid. These exposures initiate and accelerate the weathering and fragmentation processes of waste plastics. However, the detection methods and available measurements on MPs occurrences in landfills are lacking. In this study, we separate and characterize MPs in environmental solid samples by density-based extraction and filtration followed by selective fluorescent staining using Nile Red. The dried solid samples were mixed with saturated sodium chloride solution, and the supernatant was subsequently filtered by cellulose acetate membrane filters with a pore size of 0.45μm and digested with 30% hydrogen peroxide. The recovered particles were combined, filtered again, photographed and visually counted. The particles were confirmed by Fourier-Transform Infrared Spectroscopy (FT-IR). The best concentration of Nile Red is 10 μg/L, the microscopic fluorescent images can be further analyzed by software. There is no significant difference between the visual and spectroscopic results of the MPs. The composition of MPs in different waste fractions of solid waste samples were detected.