Environmental and ecological determinants of microplastic pollution and ingestion by freshwater organisms in the Garonne River (France)

, Carvalho Aline, Garcia Flavien, Riem-Galliano Louna, Tudesque Loic, Albignac Magali, Ter Halle Alexandra, Cucherousset Julien.

Microplastic (MP) pollution and the ingestion of MP by organisms is now considered as a ubiquitous phenomenon in freshwater ecosystems. However, our understanding of the dynamics of MP pollution and the drivers modulating MP ingestion by macroinvertebrates and fish is still limited. In this study, we first quantified the spatial and temporal variability of MP (700 μm – 5 mm) pollution in surface water in 14 sites located across the Garonne river catchment (France). We then quantified the level of MP contamination in macroinvertebrates and fish and used stable isotope analyses (δ13C and δ15N) to quantify trophic niches. Results revealed that spatial variation in MP concentration was high and driven by urbanisation. Temporal variation in MP concentration and size was driven by hydrological variations, with higher concentrations and smaller particles sizes observed in warm seasons with low discharge. The proportion of the main MP polymers (polyethylene, polystyrene, and polypropylene) did not significantly differ between sampled sites and MP colour differed between polymer types, with a high proportion of white polystyrene particles. Overall, fish had a significantly higher abundance of ingested microplastics than macroinvertebrates. MP ingestion by macroinvertebrates and fish was not significantly related to MP pollution in surface water and sediment. Interestingly, MP characteristics (shape, colour, size, and polymer composition) significantly differ between the abiotic (surface water and sediment) and biotic (macroinvertebrates and fish) compartments. The MP abundance increased with the size of organisms for macroinvertebrates and fish. Stable isotope analyses revealed that MP abundance tended to increase with trophic position in macroinvertebrates only. The origin of the resource consumed (allochthonous vs. autochthonous) significantly affected the abundance of microplastic ingested by fish. Altogether, these results highlight the complex dynamic of MP pollution in freshwater ecosystems and suggest the absence of microplastic bioaccumulation in freshwater food webs.

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