A coupled Lagrangian-Eulerian model for microplastics as vectors of contaminants applied to the Mediterranean Sea

Abstract The pervasiveness of microplastics in global oceans is raising concern about their impacts on organisms. While quantifying their toxicity is still an open issue, sampling evidence has shown that rarely are marine microplastics found clean; rather, they are often contaminated by other types of chemical pollutants, some known to be harmful to biota and humans. To provide a first tool for assessing the role of microplastics as vectors of plastic-related organic pollutants (PROPs), we developed a data-informed simulation model that accounts for the intertwined dynamics of Lagrangian microplastic particles transported by surface currents and the Eulerian advection-diffusion of pollutants that partition on them through seawater-particle interaction. Focusing on the Mediterranean Sea and using simple, yet realistic forcings for the input of PROPs, our simulations highlight that microplastics can mediate the export of PROPs across different marine regions. Particle origin, in terms of both source type (either coastal, riverine, or fishing-derived) and geographical location, plays a major role in determining the amount of PROPs conveyed by microplastics during their journey at sea. We argue that quantitative numerical modelling approaches can be focal to shed some light on the vast spatiotemporal scales of microplastics-PROPs interaction, complementary to much-needed field investigation.