Effects of cobalt oxide nanoparticles and cobalt ions on gill histopathology of zebrafish (Danio rerio)

Headnote

Abstract. The purpose of this study was to determine acute toxicity of cobalt ions (as C°Cl₂.6H₂O) and cobalt oxide nanoparticles (as Co₂O₃ NPs) as well as their effects on histopathology of gills of zebrafish (Danio rerio) with average weight of 2-3 g. The results of this study showed that the 96-houre LC₅₀ values for both C°Cl₂.6H₂O and Co₂O₃ NPs were > 100 mg L^-1. On the other hand, the results of histopathological studies indicated that exposure of zebrafish to cobalt nanoparticles and cobalt ions caused several gill injuries such as aneurism, dilated and clubbed tips, hyperplasia, oedema, curvature, fusion of lamellae, increase of mucous secretion, hypertrophy, and necrosis. In conclusion, the results of this study showed that the zebrafish is sensitive to both cobalt oxide nanoparticles and cobalt (II) chloride hexahydrate.

Key Words: cobalt, toxicity, zebrafish, nanotoxicology, nanoparticle, ion.

Introduction. Since most of the metals have potentially toxic effects on organisms, contamination of aquatic ecosystems by metals has become a serious problem worldwide (Yilmaz 2009). Metals such as cobalt may present environmental risk when occurring at raised levels (Mansouri et al 2011, 2012), although cobalt is of relatively low abundance in the earth's crust and in natural waters. The concentration of cobalt in organs of fish is low and accumulation of this metal in fishes was not detected in places where levels of cobalt in water were near to the background values (Güner 2010). Results of acute toxicity tests on marine fish have shown that cobalt has a low toxicity, with 96-h LC50 ranging from 52.5 to more than 1000 mg L-1 (WHO 2006). The several studies reported the 96-h LC50 values of C°Cl2 on Pimephales prometas, and Carassius auratus, rainbow trout (Oncorhynchus mykiss) were 21.8 mg L-1 by Ewell et al (1986), and 333 mg L-1 by Das & Kaviraj (1994), and 1.4 mg L-1 by Marr et al (1998) respectively. On the other hand, metal oxides nanoparticles (NPs) such as cobalt oxide, play an important role as antimicrobial agents and can be used because of its effectiveness on resistant strains of microbial pathogens, less toxicity and heat resistance (Karvani & Chehrazi 2011). Moreover, cobalt oxide...