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Phototoxicity of TiO2 nanoparticles to zebrafish (Danio rerio) is dependent on life stage
Citation:
Ma, H. AND S. Diamond. Phototoxicity of TiO2 nanoparticles to zebrafish (Danio rerio) is dependent on life stage. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 32(9):2139-2143, (2013).
Impact/Purpose:
: Nanotechnology is an emerging field that will produce hundreds of new and novel substances that have the potential for biological activity not typical of their bulk forms. One concern with many of these materials is their nano scale facilitates the conversion of photon energy to electron energy, leading to production of reactive oxygen species. Based on that knowledge and important question is how life stage effects the sensitivity of small fish species, in particular those that undergo embryonic development within a protective egg chorion. The work presented here indicates that newly-hatched larvae are the most susceptible life stage, the chorion reduces sensitivity, and sensitivity decreases rapidly over about 24 days of development. The work will be of significant value to regulators of nanomaterials and many standard tests involve embryo exposures, and thus may underestimate hazard for these materials.
Description:
The zebrafish (Danio rerio) embryo has been increasingly used as a model to evaluate toxicity of manufactured nanomaterials. Many studies indicate that the embryo chorion may protect animals from toxic effects of nanomaterials, suggesting that post-hatch life stages may be more susceptible to nanomaterial toxicity and should be tested to fully discern the potential hazard and risk of nanomaterials. The objective of this study was to compare TiO2 nanoparticle phototoxicity to zebrafish at different life stages under environmentally relevant UV radiation and to identify the most sensitive life stage. Standard 96-h toxicity assays were conducted to zebrafish at four different life stages, namely, embryos (< 2-h post fertilization), “yolk-sac” larvae (< 48-h post hatch), “free-swimming” larvae (21-d post hatch), and juvenile (50-d post hatch) under simulated solar radiation (SSR) or ambient laboratory light. Toxicity endpoints included hatching rate, incidence of malformation, and mortality. Under SSR, 96-h LC50s for embryo, “yolk-sac” larvae, and “free-swimming” larvae were 34.4 mg/l (95% CI: 24.5, 48.4), 20.3 mg/l (95% CI: 18.9-21.8), and 134.6 mg/l (95% CI: 103.7, 174.7), respectively. TiO2 at concentrations up to 300 mg/l caused < 25% mortality in juvenile fish. In the embryo test, mortality occurred only after hatching. Furthermore, introducing SSR to the exposure system before embryo hatching induced no toxicity, confirming the protective role of the embryo chorion. These findings suggest that the widely used 96-h zebrafish embryo test may not fully or accurately predict hazard and risk of TiO2 nanoparticles to small fish, and multiple life stage testing may be necessary. More broadly, the importance of the chorion in mediating embryo exposure to engineered nanomaterials indicates that results of embryo-larval testing should be considered carefully when applied to risk assessment for these materials.
