Impact of mechanical abrasion as a main driver for (micro)plastic fragmentation in the near shore environment – Methods and first results of experiments combining wave-breaking, sediment-particle-, and particle-particle collision

, Born Maximilian P., Brüll Catrina, Schüttrumpf Holger.

Several studies have shown that the prevailing forces at a shore environment, UV-irradiation and mechanical abrasion, are largely responsible for the fragmentation of plastic waste into particles smaller than five millimetres, so-called microplastic. However, UV-irradiation varies throughout the seasons and can be neglected during winter in northern latitudes. Thus, newly littered plastic is then barely degraded but rather abraded by wave action and sediment. Since only very few studies considered wave energy in their plastic-fragmentation experiments and mostly in short termed tests, this study focuses on long term tests with low intensity wave action, sediment-plastic-particle-, and particle-particle-collision regarding the fragmentation rate of PE-HD, PET, and EPS. For the realisation of a proper testing environment a “Slosh-Box” was used consisting of three boxes with 450x300x200 mm³ (L/W/H). The boxes are filled with a sediment layer of approximately ten millimetres of different grain sizes (0.25-0.5; 0.5-1.0; 1.0-2.0 [mm]) and 1.5 litres of saltwater. They are mounted onto a swivel table powered by a motor causing an oscillation of ±12° and up to 26 whole movements (angular work of 48° per movement) of the swivel table per minute, resulting in waves and wave breaking, respectively. The tests are then run up to 90 days. First results have shown that especially EPS spherules fragment to a great extent already after 30 days. Up to 25% of the spherules' weight and 0.64 mm³ in volume per square centimetres surface and day was abraded in this time into smaller microplastics. PE-HD and PET on the other hand are quite resistant against this mechanical influence, resulting in a weight loss of only 0.1% per 30 days for PE-HD and 0.4% per 30 days for PET. Further analytics such as MSQ and SEM will be conducted to classify the impacts more detailed once the tests are completed.

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