Toxicities of nano zinc oxide to five marine organisms: influences of aggregate size and ion solubility

Abstract

Nano zinc oxide (nZnO) is increasingly used in sunscreen products, with high potential of being released directly into marine environments. This study primarily aimed to characterize the aggregate size and solubility of nZnO and bulk ZnO, and to assess their toxicities towards five selected marine organisms. Chemical characterization showed that nZnO formed larger aggregates in seawater than ZnO, while nZnO had a higher solubility in seawater (3.7 mg L(-1)) than that of ZnO (1.6 mg L(-1)). Acute tests were conducted using the marine diatoms Skeletonema costatum and Thalassiosia pseudonana, the crustaceans Tigriopus japonicus and Elasmopus rapax, and the medaka fish Oryzias melastigma. In general, nZnO was more toxic towards algae than ZnO, but relatively less toxic towards crustaceans and fish. The toxicity of nZnO could be mainly attributed to dissolved Zn(2+) ions. Furthermore, molecular biomarkers including superoxide dismutase (SOD), metallothionein (MT) and heat shock protein 70 (HSP70) were employed to assess the sublethal toxicities of the test chemicals to O. melastigma. Although SOD and MT expressions were not significantly increased in nZnO-treated medaka compared to the controls, exposure to ZnO caused a significant up-regulation of SOD and MT. HSP70 was increased two to fourfold in all treatments indicating that there were probably other forms of stress in additional to oxidative stress such as cellular injury.

Comparative cytotoxicity induced by bulk and nanoparticulated ZnO in the fish and human hepatoma cell lines PLHC-1 and Hep G2

“…The size of the aggregates of the bulk material was lower (859-1564 nm). Our results are in close agreement with those of Wong et al (2010) who found that ZnO NPs tended to form aggregates in the micrometre range (2.3 ± 1.6 mm) in seawater, and these aggregates were bigger than those formed by its bulk counterpart (1.7 ± 1.2 mm). By contrast, in the study of Hsiao and Huang (2011) using ZnO NPs prepared by a precipitation or a solvothermal method, the smaller-sized ZnO particles aggregated to smaller secondary sizes than the larger NPs.…”

“…It has also been described that ZnO NPs can dissolve into Zn ions. The solubility of ZnO in aqueous media can show important variations ranging from 3.7 mg/ml in seawater (Wong et al 2010) to 5.8-7.2 mg/ml in serum-free DMEM medium (Hsiao et al 2011) and up to 15 mg/ml in complete DMEM medium (Xia et al 2008). Since some Zn ions can be released into solution from the particles, a controversy surrounding the role played by these ions on toxicity remains.…”

“…Among NPs, ZnO is frequently used in personal care products such as sunscreens, ceramics, rubber processing, waste water treatment and even as a fungicide (Wong et al 2010). Due to the increasing volumes of consumer products containing ZnO NPs, the probability that they will enter the environment and particularly the aquatic ecosystems is heightened.…”

“…Due to the increasing volumes of consumer products containing ZnO NPs, the probability that they will enter the environment and particularly the aquatic ecosystems is heightened. It has been suggested that the use of TiO 2 , ZnO and Fe 2 O 3 in sunscreens represents, by itself, a potential discharge of 250 tonnes/year into the marine environment (Wong et al 2010). Moreover, the potential risks towards occupational workers and consumers are not clearly established.…”

“…It has been reported that ZnO NPs are toxic to isolated trout hepatocytes (Scown et al 2010), Daphnia magna (Adams et al 2006, Heinlaan et al 2008) as well as zebrafish embryos and larvae (Zhu et al 2008(Zhu et al , 2009. Acute toxicity studies of ZnO NPs and bulk ZnO in different marine organisms such as algae, crustaceans and medaka fish, concluded that the toxicity of ZnO NPs could be mainly attributed to dissolved Zn ions (Franklin et al 2007;Wong et al 2010). However, other authors ascribed the toxicity also to ZnO NPs and the bulk ZnO themselves.…”