Unio crassus and Unio tumidus mussels were collected at four sampling sites in the
Tisza River (Hungary) to investigate their applicability as sentinel species for the
biomonitoring of microplastic contamination. Since mussels, as filter feeders, are
able to ingest particles only below a physically defined size, it was expected that
their sentinel role in rivers is restricted to small particles, including fibers or
microfibers. This assumption was confirmed by our results, as fibers were detected
as the dominant particles in all the 80 mussel samples investigated. The length and
diameter of the fibers changed in the size range of 20–1000 μm and 10–75 μm, respectively.
The number of fibers in the individuals originating from the same sampling site was
nearly two times higher in Unio tumidus than in Unio crassus and amounted to 2.7–4.9
and 5.2–8.3 items/individual. The fiber/g soft tissue ratio between these species
could be characterized by a factor of three. After applying Raman spectrometry, mostly
indigo-dyed polyethylene terephthalate and cellulose-based fibers, as well as a few
larger (200 um) polyamide fragments, were identified. The microplastic particles stored
temporarily by mussels provide only restricted qualitative information on the microplastic
load of the Tisza River, and as our observations confirmed, the sampling efficiency
of these ‘living sampling devices’ is highly species-specific.
