Microplastic fluxes in a large and a small Mediterranean river catchments: The Têt and the Rhône, Northwestern Mediterranean Sea

Mel Constant; Wolfgang Ludwig; Philippe Kerhervé; Jennifer Sola; Bruno Charrière; Anna Sanchez-Vidal; Miquel Canals; Serge Heussner

doi:10.1016/j.scitotenv.2020.136984

Microplastic fluxes in a large and a small Mediterranean river catchments: The Têt and the Rhône, Northwestern Mediterranean Sea

Sci Total Environ. 2020 May 10:716:136984. doi: 10.1016/j.scitotenv.2020.136984. Epub 2020 Jan 28.

Authors

Mel Constant¹, Wolfgang Ludwig², Philippe Kerhervé², Jennifer Sola², Bruno Charrière², Anna Sanchez-Vidal³, Miquel Canals³, Serge Heussner²

Affiliations

¹ Université de Perpignan Via Domitia, Centre de Formation et de Recherche sur les Environnements Méditerranéens, UMR 5110, 52 Avenue Paul Alduy, F-66860 Perpignan cedex, France; CNRS, Centre de Formation et de Recherche sur les Environnements Méditerranéens, UMR 5110, 52 Avenue Paul Alduy, F-66860 Perpignan cedex, France. Electronic address: mel.constant@lilo.org.
² Université de Perpignan Via Domitia, Centre de Formation et de Recherche sur les Environnements Méditerranéens, UMR 5110, 52 Avenue Paul Alduy, F-66860 Perpignan cedex, France; CNRS, Centre de Formation et de Recherche sur les Environnements Méditerranéens, UMR 5110, 52 Avenue Paul Alduy, F-66860 Perpignan cedex, France.
³ GRC Geociències Marines, Departament de Dinàmica de la Terra i de l'Oceà, Facultat de Ciències de la Terra, Universitat de Barcelona, C/ Martí Franquès s/n, 08028 Barcelona, Spain.

PMID: 32059309
DOI: 10.1016/j.scitotenv.2020.136984

Abstract

This paper aims at quantifying current riverine fluxes of microplastics (MPs) in two Mediterranean river catchments, a large one and a small one, namely the Rhône and the Têt, which are discharging to the Gulf of Lion in the Northwestern Mediterranean Sea. MP fluxes change markedly through time and space in both river systems. However, no clear relationships between MP concentrations and hydroclimatic conditions have been observed. In the Rhône River a non-linear dilution pattern of MPs in total suspended matter (TSM) during flood conditions could be observed. Although dilution is important, samples during floods exert a strong control on average MP fluxes. Compared to the Rhône River, average MP concentrations in the Têt River were throughout greater and more variable in shape and polymer composition. However, as the study year was exceptionally dry, the average specific MP flux, 76 g km^-² y^-¹, is only slightly larger than the non-flooding value of the Rhône River. We further monitored MP concentrations in shoreline sediments at the mouth of the Têt River to test whether these sediments can represent MP transport in the river. Besides fibers, which probably are easily washed out and transported offshore, MP concentrations and compositions are in agreement with MP loads upstream the river. We also examined the potential role of atmospheric deposition as a source of MP to the Têt River. The average atmospheric MP deposition of 6 kg km^-² y^-¹ exceeds by far the river average specific MP flux. Moreover, all MPs in atmospheric deposits were fibers, which in terms of mass are of minor importance in the bulk river fluxes. Atmospheric MP deposits may either have been overestimated and/or may be removed from surface waters by efficient removal processes (such as waste water treatment plants).

Keywords: Atmospheric deposits; Microplastic shapes; Microplastics; Northwestern Mediterranean rivers; Polymer composition; River flux; River mouth shoreline sediments.