Ni10 ThermoFisher microFT-IR was used for the chemical characterization of particles suspected to be microplastic. Reflectance was used as the mode of analysis since the size of particles was highly variable (100-5,000µm). A modified coning and quartering method was used to randomize and reduce the size of samples that contained large amounts of particles before analysis. Selected particles were mounted onto a gold slide on which three 15 x 15 mm areas were demarcated using tape of known composition. For each sample, several mosaics were taken using OMNIC Picta software, and maps were produced for multipoint spectra collection to increase time efficiency. Collected maps were then split into individual spectra for analysis using the OMNIC Specta suite of libraries (See Supplementary Information Table ). The number of particles selected for analysis was varied between > 10% or 100% per sample according to the volume of each sample. Analysed spectra were compiled into an Excel Sheet and used for statistical analyses.