Histopathology of Chironomus riparius (Diptera, Chironomidae) exposed to metal oxide nanoparticles

As the production of metal-based nanomaterials increases, it is inevitable that nano-scale products and byproducts will enter the aquatic environment. In terms of global production, the most abundant nano-oxides are TiO2, CeO2 and Fe3O4 nanoparticles. Chironomus riparius is commonly used for ecotoxicological assessment and defining its histopathological biomarkers that showcase the toxic effect of tested nanoparticles should lead to a better understanding of the consequences of nanomaterial accumulation in aquatic ecosystems. In this study, a histological description of the digestive and excretory systems as well as the fat body structure of C. riparius larvae is provided. In addition, potential histological biomarkers of nano-oxide toxicity were determined based on the obtained histopathological alterations in organs. Vacuolization was observed in epithelial cells of midgut region I that were treated with nano-Fe3O4 as well as in Malpighian tubules treated with nano-Fe3O4 and nano-CeO2. Larvae exposed to nano-TiO2 showed alterations in the fat body and midgut region II tissue architecture. Additionally, shortening of the intestinal brush border was determined in groups exposed to nano-Fe3O4. These results reveal the high sensitivity of these organs, which can be used as biomarkers in histopathological assessment and therefore lead to further improvement of existing methodology in ecotoxicological studies.