Comprehensive Investigation of Microplastics size distribution in Marine Environment: Detection, Quantification, and Optical Analysis Using Static Light Scattering (SLS)

Microplastics are detected in the environment, particularly in oceanic waters, and have adverse effects on marine ecosystems, biota, climate dynamics, and human health, primarily through the induction of marine pollution. The microplastics are introduced into marine ecosystems either as primary particles through direct discharge or as secondary particles resulting from the weathering of macroplastics. For this, a new laboratory optical-based measurement technique using the static light scattering (SLS) instrument was proposed for the detection and quantification of the microplastics size distribution and to mitigate marine pollution. The SLS instrument relies on the Lorenz-Mie scattering and Fraunhofer diffraction theories and a single monochromatic laser beam is passed through the sample and measures the light scattered intensity in all the scattering angles and with one or many detectors. SLS analysis yields information about microplastic samples, including the volume fraction of each size class bin and the cumulative log-normal distribution of particles. The volume fraction calculation will give the microplastics mean diameter (Dµ) and standard deviation (σ). The microplastics considered in the present study, include polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC). The mean size and standard deviation for PE samples are 3 µm and 2 µm and similarly, the mean size and standard deviation for PP are 3.5 µm and 2 µm. In the case of PS samples, the mean size and standard deviation are 3.5 µm and 2 µm, whereas PVC samples demonstrate a mean size and standard deviation of 3 µm and 2 µm. The findings of the SLS data show the Dµ and σ values are in the range of 3-3.5 µm and 2 µm, respectively, for all the microplastic types. The results of the present study will be helpful for a comprehensive understanding of microplastic behavior, facilitating the development of targeted methodologies for detection using hyperspectral remote sensing data in marine environment.