Assessment of microplastics in the sediments around Hywind Scotland Offshore Wind Farm

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Abstract Leading edge erosion of turbine blades is hypothesized to be a source of microplastic (MP; 1-5000 µm) emissions from offshore wind farms (OWFs) to the marine environment. Given the higher density of rotor blade coating and leading-edge protection (LEP) materials than seawater, released MP are expected to enter the surrounding waters and sink to the sediments, where the highest concentrations may be expected in the sediments in and around the OWF infrastructure. Here, we present a methodological approach for the quantification and characterisation of coating and LEP MPs (>300 µm) in sediments, applied to samples collected from 15 locations around the Hywind Scotland floating OWF. To validate the approach, reference materials were produced from the different coating layers and LEP material and used to generate library IR spectra and mass spectra so that such particles could be robustly identified if present in the sediment samples. The reference materials were also used to evaluate particle integrity and recovery across the sample preparation applied to real samples (ZnCl2 density separation, filtration). Results suggested the LEP material was unaffected by the sample processing, but fragmentation was observed for the two coating layers studied, leading to an increase in the number of particles and a decrease in weight due to loss of particles <300 µm. After isolation, particles were evaluated using microscopy and suspected MP particles were identified and subjected to a detailed chemical characterisation by Fourier transform infrared spectroscopy (FTIR). In the field samples, twenty particles were confirmed as MP, but none had polymer compositions matching the coatings and LEP materials, instead representing common thermoplastics in the form of flakes, films, fragments, and filaments.

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