title: A critical assessment of visual identification of marine microplastic using Raman spectroscopy for analysis improvement.
abstract: Identification and characterisation of microplastic (MP) is a necessary step to evaluate their concentrations, chemical composition and interactions with biota. MP ≥10μm diameter filtered from below the sea surface in the European and subtropical North Atlantic were simultaneously identified by visual microscopy and Raman micro-spectroscopy. Visually identified particles below 100μm had a significantly lower percentage confirmed by Raman than larger ones indicating that visual identification alone is inappropriate for studies on small microplastics. Sixty-eight percent of visually counted MP (n=1279) were spectroscopically confirmed being plastic. The percentage varied with type, colour and size of the MP. Fibres had a higher success rate (75%) than particles (64%). We tested Raman micro-spectroscopy applicability for MP identification with respect to varying chemical composition (additives), degradation state and organic matter coating. Partially UV-degraded post-consumer plastics provided identifiable Raman spectra for polymers most common among marine MP, i.e. polyethylene and polypropylene.
authors.affiliation: National Institute of Aquatic Resources, Technical University of Denmark, DTU, Kavalergården 6, 2920 Charlottenlund, Denmark. Electronic address: roble@aqua.dtu.dk.
authors.forename: Robin
authors.initials: R
authors.lastname: Lenz
authors.affiliation: National Institute of Aquatic Resources, Technical University of Denmark, DTU, Kavalergården 6, 2920 Charlottenlund, Denmark.
authors.forename: Kristina
authors.initials: K
authors.lastname: Enders
authors.affiliation: National Institute of Aquatic Resources, Technical University of Denmark, DTU, Kavalergården 6, 2920 Charlottenlund, Denmark.
authors.forename: Colin A
authors.initials: CA
authors.lastname: Stedmon
authors.affiliation: Department of Micro- and Nanotechnology, Technical University of Denmark, DTU, Ørsteds Plads, 2800 Lyngby, Denmark.
authors.forename: David M A
authors.initials: DMA
authors.lastname: Mackenzie
authors.affiliation: National Institute of Aquatic Resources, Technical University of Denmark, DTU, Kavalergården 6, 2920 Charlottenlund, Denmark.
authors.forename: Torkel Gissel
authors.initials: TG
authors.lastname: Nielsen
mesh_terms: D001267:Atlantic Ocean; D004784:Environmental Monitoring / Q000379:methods*; D010969:Plastics / Q000032:analysis* / Q000737:chemistry; D020959:Polyethylene / Q000032:analysis / Q000737:chemistry; D011108:Polymers / Q000032:analysis / Q000737:chemistry; D011126:Polypropylenes / Q000032:analysis / Q000737:chemistry; D013059:Spectrum Analysis, Raman; D014873:Water Pollutants / Q000032:analysis* / Q000737:chemistry
chemical_list: D010969:Plastics; D011108:Polymers; D011126:Polypropylenes; D014873:Water Pollutants; D020959:Polyethylene
keywords: Photodegradation; RAMAN; Small microplastics; Spectroscopy