Assessment of Microplastics Present in Mussels Collected From the Scottish Coast

The presence of small (5 mm–1 µm) plastic debris, microplastics (MPs), in aquatic environments is recognized as among the highest international issues for environmental science and policy. MPs can be found in aquatic environments in suspension and/or associated with sediments and marine organisms can ingest MPs. Documentation of their presence and abundance in marine environments is an important initial step towards assessment of MPs effects on organisms. Particles have been found in most coastal areas where their presence has been investigated, but little is known about the abundance and types of MPs present on the Scottish coast. Our goal was to develop a standardized procedure to extract and quantify MPs in marine mussels, and then apply this method to assess MPs presence at specific locations along the Scottish coast. Complete Mytilus edulis soft tissue digestion was achieved with 1 M NaOH, 35% HNO3 and by 0.1 UHb/mL protease, but use of HNO3 caused destruction of nylon particles. The recovery of MPs spiked into mussels was similar (93±10%) for NaOH and enzyme digestions. We recommend the use of industrial enzymes for soft tissue digestion since it is relatively easy, reproducible, provides good recovery rate of MPs from spiked tissue samples, and avoids the use of caustic chemicals that can damage polymers. This extraction method was applied to assess abundance of MPs (1) in mussels collected from various field sites on the coast of Scotland, and (2) in M. edulis deployed in purpose built cages together with passive samplers in an Edinburgh port (Port Edgar). Preliminary results of M. edulis individuals (n=18) placed in cages in Port Edgar show a load of 2.0±0.42 fibers, 0.2±0.21 round shaped particles and 0.3±0.59 films/g (wet weight of soft tissue), which are within the range of previous reports for Mytilus spp. from various European locations.