Comparative toxicity of nano-ZnO and bulk ZnO suspensions to zebrafish and the effects of sedimentation, ˙OH production and particle dissolution in distilled water.

With the common application of nanoscale zinc oxide (nZnO) and significant potential for its release directly into aquatic environments, it is urgent to carry out research on ecotoxicological impact of nZnO. The characterization of nZnO, the amount of ˙OH in suspensions in the presence of light and the acute toxicity of nZnO and its bulk counterpart suspensions, as well as the acute toxicity of Zn(2+) solution to zebrafish (Danio rerio) at 96 h were studied. It was found that nZnO aggregated into irregular shapes in suspensions, and showed a relationship between its size distribution and concentration. In the presence of light, nZnO suspensions could generate ˙OH, the concentration of which increased with time. Although it was generally thought that ˙OH played a role in the biotoxicity to zebrafish, similar toxicity was observed for the nZnO and bulk ZnO suspensions (96 h LC(50) 3.969 mg L(-1), 2.525 mg L(-1), respectively). Furthermore, the sedimentation of nZnO and bulk ZnO in suspensions, and the accumulation of Zn in zebrafish were studied. The results showed that dissolved Zn(2+), from nZnO and bulk ZnO in suspensions, were toxic to zebrafish, while the aggregation and sedimentation of nZnO suspensions reduced the toxicity of nZnO. However, Zn(2+) may not be the main source of acute toxicity of nZnO and bulk ZnO to zebrafish. The experimental results highlight the importance of a systematic assessment of toxicity mechanisms of metal oxide nanoparticles (NPs) to determine definitively whether their toxicity is caused by nano-effects.

[Oxidative stress effects and damage of nanoscale TiO2 and ZnO on zebrafish].

The oxidative stress effects and damage of nanoscale zinc oxide (nZnO), titanium dioxide (nTiO2) and their bulk counterparts (i.e., ZnO/bulk, TiO2/bulk) suspension on gill, intestine and liver of zebrafish (Danio rerio) were studied, as well as the characterization of nZnO, nTiO2 ZnO/bulk and TiO2/bulk and the amount of .OH in suspension in the presence of light were studied. The results show that the size distribution of nanoparticle and bulky particle are similar in suspension, while the amount of SOH in 50 mg/L nTiO2, nZnO suspension are 2.17 mmol/L, 0.72 mmol/L respectively in the presence of 96 h illumination, which is much higher than that of 50 mg/L bulky particle suspension (not detected). As exposed to 50 mg/L nTiO2 suspension, in contrast to control, the superoxide dismutase (SOD), catalase(CAT) and reduced glutathione (GSH), protein carbonyl content in liver tissue of zebrafish are 70.2%, 65.4%, 53%, 178.1% respectively, and the SOD activity and GSH, malondialdehyde (MDA) content in digestive tract are 149.6%, 212.9% and 217.2% respectively. The MDA content in gill is 160.9% than that of control as exposed to 50 mg/L nTiO2 suspension. However, there are no toxic effects on zebrafish after 96 h exposure to 50 mg/L TiO2/bulk suspension. The strongest oxidative damage is found in liver tissue of zebrafish as exposed to 5 mg/L nZnO and ZnO/bulk suspension for 96 h. In contrast to control, the SOD, CAT activity and GSH, MDA content are 62.9%, 53.1%, 45.2% and 204.2% after 96 h exposure to 5 mg/L nZnO suspension, and 48.3%, 51.8%, 34.6%, 289.6% after 96 h exposure to 5 mg/L ZnO/bulk suspension. Significant oxidative stress is also found both in gill and intestine. However, there is no oxidative damage on gill and intestine. The experiment results indicated that the effects of agglomeration on nanoparticle of different chemical composition are various. The oxidative stress and damages induced by reactive oxygen species (ROS) which generated through different way by nanoparticle of different chemical composition might play a role in the bio-toxicity of nanoparticle.