Szx10 research high class stereo microscope

The filters were observed under an Olympus SZX10 Research High-Class Stereo microscope (Olympus Corporation, Japan), and photographed with an Olympus UC30 digital camera. A visual assessment was conducted to identify particles according to the physical characteristics. MPs were classified as fibers, film, fragments or spheres using the descriptions from Tagg et al. (2015) . A number of commonly detected particles were selected and verified with a micro-FT-IR, iNicolet, Thermofisher Scientific) cooled with liquid nitrogen (Tagg et al. 2015) . Analysis was conducted in transmittance mode with MPs mounted on a diamond compression cell. Spectra were acquired and matched using a series of polymer library databases (Hummel), a hit index of at least 70% was considered acceptable.

Virgin PVC powder (Sigma-Aldrich, Gillingham, U.K.) was ground with a mortar and pestle. Distilled water was added to the mortar and stirred with a glass rod. The mixture was successively filtered with a steel mesh with a pore size of 75 μm and a filter paper (1 μm). Afterwards, the PVC particles ranging from 1 to 75 μm on the filter paper were transferred to a centrifuge tube and dyed with 500 μg/mL Nile red solution in acetone for half an hour. The dye liquor was filtered on a filter paper (1 μm) and distilled water was added to remove remaining dye. The dyed particles were transferred to a small amount of distilled water in a glass bottle. Three replicates of 2 μl mixture were pipetted to a hemocytometer (Agar Scientific, Stansted, U.K.) and the number of red particles counted under an Olympus SZX10 Research High-Class Stereo microscope (Olympus Corporation, Japan). The solution was stored below 4 °C in the dark.