Modelling the Uptake and Exchange of Microplastics in Marine Ecosystems using a Novel, Integrated System of High-Resolution Numerical Models

<p>Microplastics (mPs), defined as plastic particles that are less in 5mm in size, are ubiquitous within the marine environment. They are difficult to remove from natural water streams and persist for long periods of time, breaking down into continually smaller particles. Since the diversity of organisms that can ingest plastic particles increases as the particle size decreases, microplastics have been identified as an emerging contaminant of concern in the marine environment and the determination of the potential ecological harm caused by mPs is a key objective of the EU Marine Strategy Framework Directive (MSFD 2008/56/EC). However, the completion of a comprehensive risk assessment of this marine pollutant is prevented by the current lack of consensus on the processes influencing mP transport, uptake and exchange in the marine environment. For example, the processes driving the transport of mPs with buoyant polymers to the deepest part of the ocean are surrounded in uncertainty. The potential for mPs to accumulate within organisms and consequently the significance of trophic transfer as an uptake route for mPs is also unclear, particularly at lower trophic levels where contrasting arguments have formed on the risk of trophic transfer of mPs via zooplankton.</p> <p>In this study, an integrated system of numerical models has been proposed to improve our understanding of mP processes in the marine environment by simulating the transport and ecosystem uptake and exchange of mPs at lower trophic levels in the northwest European continental shelf region. The continued refinement of the mathematical models will be presented, including the results of tests undertaken to evaluate the efficacy of empirical models for the calculation of the vertical settling velocity of irregularly-shaped particles from the perspective of mP transport modelling. Based on the current availability of data on mP distribution and uptake by lower trophic level organisms in the study area, the feasibility of model implementation will be examined as well as the significance of this research in providing information required by policy makers to complete risk assessment and implement suitable management strategies for marine mP pollution.</p>