Exposure effects of iron oxide nanoparticles and iron salts in blackfish (Capoeta fusca): Acute toxicity, bioaccumulation, depuration, and tissue histopathology.

We assessed the toxicity of iron oxide nanoparticles compared with iron salts in the blackfish (Capoeta fusca). After an acute toxicity assessment, we conducted a chronic exposure to a sub-lethal concentration of FeO NPs, and iron salts (ferric nitrate (Fe(NO)), ferric chloride (FeCl), ferrous sulfate (FeSO)) to measure iron uptake over a period of 28 days and then subsequent clearance of the iron uptake in the exposed fish that were transferred to clean water for 28 days. Fe(NO) was the most acutely toxic compound followed by FeCl, FeSO, and FeO NPs. Exposure to FeO NPs and iron salts induced histopathology anomalies in both gills and intestine that included aneurism, hyperplasia, oedema, fusion of lamellae, lamellar synechiae, and clear signs of necrosis (in the gills) and increases in the number of goblet cells, blood cell counts, and higher numbers of lymphocyte (in the intestine). FeO NPs showed a higher level of uptake in the body tissues compared with iron salts (p < 0.05) with levels of Fe in the gill > intestine > liver > kidney. Fe was shown to be eliminated most efficiently from the gills, followed by the kidney, then liver and finally the intestine. The highest tissue bioconcentration factors (BCF) occurred in the liver for FeCl, FeO NPs, and FeSO and in the gills for Fe(NO). We thus show differences in the patterns of tissue accumulation, clearance and toxicological responses for exposures to FeO NPs and iron salts in blackfish with implications for different susceptibilities for biological effects.