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SPECTROSCOPY


AIDS RESEARCH M


icroplastics (MPs) are tiny pieces of plastics ranging from 5mm down to 100nm in diameter. T ey represent a global


anthropogenic pollution that is expected to last for many generations and become a geological marker of our time. Scientists have found MPs in the air, on mountain summits, on polar ice caps, at the bottom of the deepest abyssal trenches, as well as in virtually all marine lifeforms – from zooplankton to whales. Now, the attention of the community has turned towards the impact of MPs on human health as recent studies revealed their presence in bottled water and even in human stools and placenta. Since regulation and standardisation agencies only recently started to look at the problem, much eff ort is required to improve existing methodologies, ensure reproducibility, comparability and representativeness of the analysis, and put in place validated standard operating


42 www.scientistlive.com


RAMAN ANALYSIS


protocols (SOPs). In the end, the quality of the data produced should meet predefi ned performance criteria for wide acceptance. While MPs sorting and counting is still often done by visual inspection or under a dissection microscope, chemical characterisation is becoming essential to diff erentiate MP-like polymers from other organic and inorganic materials and avoid misidentifi cation when analysing samples. Another key aspect is the need for developing faster procedures and imaging technologies, as mapping large surfaces of fi lters used to collect MPs can be extremely time consuming, especially when a spatial resolution of the order of micrometres is wanted. T e French Research Institute for


Exploitation of the Sea (Ifremer) is currently working on an effi cient and time-eff ective method for MPs monitoring in marine environment, by using a Horiba LabRam Raman microspectrometer in conjunction with the ParticleFinder module


Catalina David & Emmanuel Rinnert discuss morphological and chemical characterisation of microplastics using particle image analysis combined with Raman spectroscopy


proposed with the LabSpec 6 software suite.[1] Particles collected at sea with a Manta


trawl are fi rst deposited on a gold-coated microscope slide to avoid parasitic signal from the borosilicate glass. A large, high-resolution, centimetre-scale optical image of the sample is recorded by the microscope camera, using the integrated video montage/mosaic tool. Image analysis algorithms are applied to perform a binary segmentation based on the optical contrast and to quickly locate all the particles, highlighting their positions. T e analysis of this binary image provides at the same time various morphological descriptors (diameter, area, perimeter, major/minor axis, circularity, as well as brightness). T e particles can then be fi ltered according to the statistics results, allowing only particles that correspond to a specifi c size/shape to be analysed. In the present study, MPs were classifi ed into three groups: 0.335 -1mm (335 µm is the mesh size of the Manta


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