IMIS

Fish gastro-intestinal tract (GIT) and fillet samples were dissected onboard scientific fisheries survey vessels, before lab digestion, density separation and analysis. Samples were processed individually or GIT contents from 3 fish were pooled prior to a two-step digestion. The size of each particle was measured along its maximum Feret diameter using the scale bar function of the Leica Application Suite (LAS) microscope software, while fibre length was measured as the shortest distance between the two fibre tips. Microplastics were classified by colour and shape according to MSFD Technical Subgroup on Marine Litter (2013). A micro-Fourier Transform Infrared Spectroscopy (µFTIR) analysis was performed using a Spotlight 200i FT-IR microscope (Perkin Elmer) to distinguish between synthetic (i.e., plastic) and natural (i.e., non-plastic) particles, and to further identify the polymers of selected 52 particles (size > 50 µm), 36 potential plastic and 16 non-plastic particles. To identify the spectra, a search was performed in a spectra commercial library (Perkin Elmer), excluding the range 1,250 - 1,100 cm-1, and polymers identification was accepted when a match was over 60% (with one exception for a Fluorocarbon particle, where the match was 55%).