Microplastic as a vector of chemical contamination in the marine environment: A coupled Lagrangian-Eulerian approach

Contamination by microplastics has become common in many environments, and particularly dangerous in marine ecosystems. During their journey at sea, floating microplastic particles affect both the biotic and the abiotic components of the seascape through ingestion by (or other physical interactions with) the marine biota. They also provide support for microbial growth (often resulting in reduced particle buoyancy and sinking), and exchange primary hydrophobic pollutants with seawater. These two latter processes, in particular, regulate the balance on the sea surface layers of both microplastics and the pollutants carried by them. Here we propose a novel modeling framework to account for the interactions between microplastics and hydrophobic chemicals in the marine environment. Our approach couples Lagrangian particle tracking with Eulerian advection-diffusion modeling of pollutants. Focusing on the Mediterranean Sea, we simulate two years of plastic particle motion and the concurrent pollutant exchanges occurring between plastic debris and the surrounding environment. As these interactions are found to significantly affect the concentration patterns of chemical pollution over the simulated period, we argue that further modeling research should account for coupled microplastics-pollutants dynamics towards a comprehensive assessment of the risks caused by plastic pollution on marine ecosystems.