Occurrence of microplastics in surface waters of the Gulf of Lion (NW Mediterranean Sea)
Introduction
Plastic and its chemical compounds have played an important role in the Anthropocene and might threaten human health (Kobrosly et al., 2014, Tranfo et al., 2012, Sathyanarayana, 2008, Heudorf et al., 2007) and both terrestrial (Zhao et al., 2016, Lwanga et al., 2016, Oehlmann et al., 2009) and marine environments (Przybylinska and Wyszkowski, 2016, Van Franeker and Law, 2015, Sigler, 2014). In 2014, 311 million tons of plastic were produced worldwide, 15% of which were consumed in Europe (PlasticsEurope, 2015). The degradation of large plastic items into microplastics (≤5 mm) in the ocean is a slow and heterogeneous process, varying with respect to the quality, shape and size of the plastic. This process is driven by mechanical forcing (e.g., waves), salt water, and UV radiation (Ter Halle et al., 2016). Because of its small size, micro debris can easily be ingested (e.g., Desforges et al., 2015, Neves et al., 2015). Approximately 270 · 103 tons of plastic are suspected to float in the world’s oceans (Eriksen et al., 2014). Estimates for floating microplastic loads range from 7 · 103 to 35 · 103 tons for global open-ocean surface waters (Cózar et al., 2014) or from 93 · 103 to 236 · 103 tons depending on the model used (Van Sebille et al., 2015). Plastic accounts for 60 to 80% of all marine litter, followed in quantity by glass and metal (UNEP, 2009). About 370 · 109 plastic particles or 1455 tons have been estimated to be floating on the surface of the Mediterranean Sea (Ruiz-Orejón et al., 2016). Other estimates range from 756 to 2969 tons (Cózar et al., 2015) and from 874 to 2576 tons (Suaria et al., 2016).
The Mediterranean Sea is a semi-enclosed basin subject to significant anthropogenic pressures (e.g., The MerMex Group, 2011, Blanfuné et al., 2016, Hassoun et al., 2015, Casale et al., 2015). Marine debris, including microplastics, are a particularly important concern in this region (Deudero and Alomar, 2015, Cózar et al., 2015, Ioakeimidis et al., 2014, Faure et al., 2015, Pedrotti et al., 2016). Concerns about marine litter in the Mediterranean Sea were first expressed in 1976 when the Barcelona Convention was signed with the goal of preventing and abating marine and coastal pollution (UNEP, 2009). In subsequent years, studies have been undertaken to better understand pollution sources and trajectories, through approaches as modeling the transport of floating marine debris (Mansui et al., 2014). However, knowledges on the spatial and temporal microplastic distribution remain limited (Ruiz-Orejón et al., 2016, Suaria et al., 2016, Cózar et al., 2015). Their contents are highly variable, although the sea surface circulation seems to be the main driver on the distribution of floating marine litter whatever their sizes. Currents affect time-dependent movements that remain difficult to predict, and cause several non-trivial Lagrangian mechanisms (Zambianchi et al., 2014). In semi-enclosed seas, such as the Mediterranean Sea, aggregation patterns are not permanent and high variability is observed at a small scale (Suaria et al., 2016). Wind-induced effects on floating material and Stokes drift velocities require further investigation, such as refinement of regional models. Nevertheless, some available scenarios could be hypothesized with possible retention areas in the northwestern Mediterranean and the Tyrrhenian sub-basins (Poullain et al., 2012, Mansui et al., 2014). The Gulf of Lion is in the northwestern sector of the Mediterranean Sea, and its hydrodynamics are influenced by shallow water depths of the shelf, wind regimes (Mistral and Marin), the Northern Current (NC), and freshwater inputs from the Rhône River (Gatti et al., 2006, Fraysse et al., 2014). The NC has a high seasonal variability: while a decrease in intensity is observed in summer, it becomes faster, deeper and narrower in winter (Millot, 1991). Intrusion of the NC onto the shelf of the Gulf of Lion has been observed (Ross et al., 2016, Barrier et al., 2016 and references therein). This productive shelf is also highly exploited for commercial fishing (Bănaru et al., 2013) and the coastal area is strongly influenced by tourism activities. Given this areas great economic, touristic and environmental significance, monitoring threats, such as pollution sources, is essential. Therefore, the primary goal of this study was to provide insight into the temporal and spatial distribution of microplastics in the eastern sector of the Gulf of Lion. Furthermore, we wanted to examine relationships between microplastic size distributions and possible pollution sources and transportation routes.
Section snippets
Materials and methods
Following the framework of the Particule-MERMEX and PLASTOX projects, microplastic debris were collected at different times between February 2014 and April 2016 (Table S1) in three distinct areas with specific hydrodynamic characteristics (Fig. 1) within the eastern sector of the Gulf of Lion (northwestern Mediterranean Sea). The first area is located 40 km offshore at the eastern part (station #1, also called ‘Antares site’) and is within the direct influence of the Northern Current, which
Microplastic abundance
Microplastic abundance ranged from 6 · 103 to 1 · 106 (mean 96 · 103) items km−2 in the Marseille Bay area, from 33 · 103 to 400 · 103 (mean 113 · 103) items km−2 in the Rhône River plume, from 7 · 103 to 69 · 103 (mean 34 · 103) items km−2 in the river itself and from 9 · 103 to 916 · 103 (mean 212 · 103) items km−2 off-shore (Fig. 2, top). The highest microplastic concentration (1 · 106 items km−2) was observed at station #2 (Marseille Bay area). The day this sample was collected was
Conclusions
This study provides additional data on microplastic occurrence in the eastern Gulf of Lion. Our results revealed that surface water microplastic concentrations and size distributions in this area affected by anthropogenic impacts are consistent with those already published for the western Mediterranean Sea. Significant temporal and spatial heterogeneity was observed for microplastic abundances. Our results confirm that the Rhône River, large cities, such as Marseille, and the Northern Current
Acknowledgments
This study was conducted as part of MERMEX/MISTRALS, the JPI Oceans PLASTOX and PARTICULE-region PACA and is a contribution to the international LOICZ program. We acknowledge the technical support provided by the Service Atmosphere Mer (SAM), the Microscopie et Imagerie (MIM)-M I O platforms. We sincerely thank the captain and crew of N. O. Antedon II and Thethys, as well as Sandrine Ruitton, who kindly allowed sampling time during her diving trips. We thank Maryvonne Henry and Anne Delmont for
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