Microplastics in the Bay of Marseille

Influence of the Rhone River intrusion on microplastic distribution in the Bay of Marseille, Alcaïno et al, 2024, Regional Studies in Marine Science

La contamination ubiquiste des matrices environnementales par les microplastiques (MP) a récemment émergé comme une problématique sociétale majeure. Malgré un nombre croissant d’études, leurs dynamiques de dispersion et d’accumulation restent largement sous-documentées. Le besoin en données quantitatives, avec un suivi récurrent, est particulièrement crucial en domaine marin, pour mieux estimer les stocks et les flux ainsi que l’impact de la courantologie sur la dispersion des MP.

In this work, we studied PM contamination in surface water and sediments in the Bay of Marseille on a bi-annual basis from 2020 to 2022. Average concentrations of (5.79±12.71 MP.m^-3) (9.13.10⁵ MP.km^–² ) were observed at the surface. No spatiotemporal trend was statistically demonstrated, except in February 2020 with an abnormally high PM concentration (22.47±8.85 MP.m^-3 on average). These data indicate an average level of contamination comparable to those observed in surface waters over the last 10 years in the Bay of Marseille. Concentrations in sediments averaged 865±63 MP.kg^-1 dry sediment.

The particles sampled in the water and sediments are mainly fibres (>65%) and are small in size (75% between 250µm and 1mm). The most abundant polymers are polypropylene (PP) and polyethylene (PE).

The data obtained in surface waters were combined with modelling results (MARS3D-ROHMA model) and Ichthyop software to study the Lagrangian transport of PM. We were able to show the influence of intrusions from the Rhône into the Bay of Marseille (linked to specific hydrometeorological conditions) and its impact on concentration levels in February 2020.