Microplastics in saltmarshes: developing extraction methods and examining past accumulation

Saltmarshes are complex, dynamic environments, which play a vital role in protecting both humans and wildlife, by acting as a natural barrier against coastal erosion and flooding, and providing habitats for a diverse range of biota. However, the sources and accumulation of microplastics on saltmarshes have not yet been subject to detailed research. These environments have the potential to resolve the temporal evolution of plastic pollution since production began, and improve understanding of their fate in the coastal environment. The aim of this study is to develop a suitable extraction methodology to investigate temporal trends in the concentration and type of microplastic pollution in saltmarsh sediments, from the mid-20th century to the present day. Two cores were taken from a radionuclide-dated saltmarsh in NW England, in an attempt to evaluate the relationship between microplastic concentrations and sedimentological parameters. A novel method has been developed to optimise the extraction of microplastics from organic rich, fine grained sediments based on sequential density separations with the added benefit of reducing the use of harmful chemicals. The majority of microplastics were separated at a density range of 1.6 - 1.4 g cm-3. Microplastics were found in both cores, with pellets being the most common type, making up 80 % of the total concentration. The record of accumulation observed in both cores taken from Biggar marsh does not follow the growing historical increase in global plastic production. There is no consistent relationship between mean grain size and microplastic concentrations. Future work should focus on improving chronological control to better constrain sedimentation rates to establish microplastic influx over time.