Quantification of Microplastics in North-Western Mediterranean Harbors: Seasonality and Biofilm-related Metallic Contaminants

Abstract

The Mediterranean Sea is one of the most impacted basin in terms of microplastics pollution. Land-based activities are the major sources of plastic litter to the ocean, with harbors probably representing significant hotspots. In the framework of the SPlasH! project (Stop alle Plastiche in H2O, Interreg Marittimo project), microplastics were sampled in three north-western Mediterranean harbors during summer and winter. In this study, the areal concentrations of microplastics ranged from 5,576 to 379,965 items.km-2. A decreasing gradient was observed from the inner to the outer zones of the studied harbors, pointing out these enclosed systems as hotspots regarding microplastic pollution. During the summer, because of an enhancement of port activities, the areal concentrations of microplastics were higher than in winter. The investigation microplastics size classes distribution in the surface waters revealed that microplastic within a size range between 300 µm and 500 µm were depleted. During this study, we assessed trace metal partitioning (Pb, Fe, Cu, V, Cd and As) between the dissolved phase and biofilm, thus highlighting concentrations within the biofilm two and six orders higher than those in the dissolved phase. This result strongly suggest trace metal bioaccumulation within the biofilm. When trace metal concentrations are normalized over the corresponding surface of microplastics and microplastics, higher values were obtained for microplastics evidencing their enhanced capacities to bioaccumulate contaminants with respect to macroplastics.

Seawater copper content controls biofilm bioaccumulation and microbial community on microplastics

“…Along this gradient, bacterioplankton composition is shaped, including shifting the autotrophic community from picoeukaryote dominated community in the most contaminated parts to cyanobacteria (more representative of the open ocean) in less impacted areas (Coclet et al, 2018(Coclet et al, , 2019(Coclet et al, , 2020. Alongside TMs pollution, an important amount of MPs can be found in the surface water of Toulon bay, with an average of 32 800 MPs/km-2 (Tesan- Onrubia et al;2021). Potential bioaccumulation of TMs on MPs may also influence microbial biofilm diversity.…”