Microplastic
pollution and ingestion are ubiquitous phenomena in
freshwater ecosystems. However, our understanding of the role of trophic
niche in microplastic ingestion is still limited. Here, we quantified
the level of microplastic (700 μm to 5 mm) contamination for
macroinvertebrates and fish within the Garonne river. We then used
stable isotope analyses (δ13C and δ15N) to quantify trophic niches. We first demonstrated that the abundance
of ingested microplastics differed between macroinvertebrates and
fish and was not significantly related to microplastic pollution.
We then found that microplastic characteristics (shape, color, size,
and polymer composition) differ between the abiotic (surface waters
and sediments) and biotic (ingested by macroinvertebrates and fish)
compartments. The abundance of ingested microplastics increased with
the size of organisms in both fish and macroinvertebrates and tended
to increase with trophic position in macroinvertebrates only. Finally,
the origin of the resources consumed by fish significantly affected
the abundance of microplastics ingested. Altogether, these results
suggest the absence of microplastic bioaccumulation in freshwater
food webs and the dominance of direct consumption, most likely accidentally.
The use of stable isotope analyses is therefore crucial to improve
our understanding of microplastic ingestion by wild organisms.
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