Investigating the seasonal importance on the composition and concentration of microplastics in coastal seawater, beach sediments and the wild mussel (Mytilus edulis)

, Paradinas Lola, James Neil, Quinn Brian, Dale Andrew, Narayanaswamy Bhavani E.

Microplastics are particles ranging in size from 1µm to 5mm, observed in natural ecosystems globally. While a better understanding of their distribution and effects on biota are increasing, the dynamic of microplastics in an active environment have not yet been extensively studied. It is hypothesised that the coastline is a transitional area where plastic particles are accumulating on the shore, in biota or released into the ocean and atmosphere. Microplastics have been studied temporally in seawater, fauna and sediments but the outputs have not proved to be convincing; some studies have highlighted a seasonal change whilst others the opposite. Here we present a quantification and characterisation of microplastics within mussels, seawater, and sediment in six sites located along the North and West coasts of Scotland. The combined effect of sites and seasons was investigated to explain the microplastics fluctuations along the shore. Despite the variations between sites, microplastics were recorded at all seasons. Of the digested mussels (n=240), 1030 particles were analysed with 15% of them being microplastics. Concentrations ranged from 0.19 ± 0.05 to 1.38 ± 0.64 particles per g.wwt flesh (mean± SE). Fragments and fibres were the prevalent shapes observed, covering the main plastic families such as polyester, polystyrene, polyethylene and polyamide. In water samples, ¿70 microplastics were identified from 60L collected with concentrations ranging from 0.60 ± 0.24 to 1.75 ± 0.48 particles per L (mean + SE). Fibres, fragments and films were observed comprising mainly polyester and polypropylene. Over 36 glass jars (10 g each) of sediment were analysed, containing 19 microplastics. Concentrations were ranging from 0.02 ± 0.02 to 0.16 ± 0.04 particles per gram of dry sand. Future work will examine microplastics found within seawater and sediment during a lunar cycle to assess the effect of tides on the accumulation on the shore.

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