Bonk A., Dąbrowska A., Skawina A.
The presence of diverse plastic particles in aquatic environments and their influence on the ecosystems became a world-scale fact. Although the impact of plastics of different sizes on marine environments is under investigation for several years now, little is known about the presence and influence of these materials in freshwaters even if they are considered as likely places of original plastics’ load to the oceans. Several freshwater bivalve species were observed to be contaminated with microplastic fibres and spheres, however, there are currently no data on the presumable impact of this contact on plastic properties.
We treated adult Unio tumidus and Sphaerium sp. with the 20 μm polystyrene microspheres suspended in Scenedesmus algae for 2 hours. After this, bivalves were sacrificed, histological frozen sections were prepared and confocal microscopy used for analysis. Microspheres were detected in the intestine of both species, together with algae. Raman spectroscopy was used for acquiring spectra of both polystyrene spheres - suspended in algae and spheres from intestine content. Furthermore, we treated adult Unio tumidus with polystyrene nanoparticles (<20 nm). Although preliminary test on variants of sole polystyrene resulted in obtaining clear spectra, both bivalves’ induced samples: pre- and post- intestinal passage occurred as inaccessible for this method, but presumably for different reasons. The spectrum of spheres suspended in algae was presumably hidden in algae spectra, while particles from the intestine were likely precisely covered by the intestine content, which made access to the plastic and its measurement impossible. Nevertheless having in mind these difficulties we look for future methods of removal of biological contaminations to open the possibilities for testing the composition of the plastic particle in different moments of their passage through organisms and ecosystems.
Keywords: microplastic, freshwater, Unio tumidus, Sphaerium sp, Raman spectroscopy.
Acknowledgements: We are grateful to Barbara Pałys for the access to Raman spectroscopy, Piotr Maszczyk for sharing the microplastic sample, and to Piotr Bernatowicz for providing Scenedesmus algae suspension for these tests.