Xiaoshan Zhu

Comparative toxicity of several metal oxide nanoparticle aqueous suspensions to Zebrafish (Danio rerio) early developmental stage

With the emergence of manufactured nanomaterials, it is urgent to carry out researches on their potential environmental impacts and biological effects. To better understand the potential ecotoxicological impacts of metal oxide nanoparticles released to aquatic environments, the zebrafish 96-h embryo-larval bioassay was used to assess and compare the developmental toxicities of nanoscale zinc oxide (nZnO), titanium dioxide (nTiO2) and alumina (nAl2O3) aqueous suspensions. Toxicological endpoints such as zebrafish embryos or larvae survival, hatching rate and malformation were noted and described within 96 h of exposure. Meanwhile, a comparative experiment with their bulk counterparts (i.e., ZnO/bulk, TiO2/bulk and Al2O3/bulk) was conducted to understand the effect of particle size on their toxicities. The results showed that: (i) both nZnO and ZnO/bulk aqueous suspensions delayed zebrafish embryo and larva development, decreased their survival and hatching rates, and caused tissue damage. The 96-h LC50 of nZnO and ZnO/bulk aqueous suspensions on the zebrafish survival are 1.793 mg/L and 1.550 mg/L respectively; and the 84-h EC50 on the zebrafish embryo hatching rate are 2.065 mg/L and 2.066 mg/L respectively. Serious tissue ulceration was found on zebrafish larvae exposed to nZnO and ZnO/bulk aqueous suspensions. (ii) In contrast, neither nTiO2 and TiO2/bulk nor nAl2O3 and Al2O3/bulk showed any toxicity to zebrafish embryos and larvae under the same experimental condition. It revealed that the metal oxide nanoparticles with different chemical composition have different zebrafish developmental toxicities. (iii) Exposures of nTiO2, nZnO and nAl2O3 produced toxic effects on zebrafish embryos and larvae, which was not different from the effects caused by exposing to their bulk counterparts. This is the first study about the developmental toxicity of metal oxide nanoparticles, and the results demonstrate that nZnO is very toxic to zebrafish embryos and larvae, which highlights the need to evaluate the potential eco-toxicity of these manufactured nanomaterials (MNMs).

Toxicity and bioaccumulation of TiO2 nanoparticle aggregates in Daphnia magna.

Little is known about the potential ecotoxicity of engineered nanoparticles (NPs) to aquatic organisms. To carefully address this issue, we conducted a comprehensive toxicity assessment, including modified acute (72h) and chronic (21d) toxicity tests as well as nTiO(2) accumulation analysis using Daphnia magna as a model organism. We found that nTiO(2) exerted minimal toxicity to daphnia within the traditional 48h exposure time, but caused high toxicity when the exposure time was extended to 72h. This demonstrated that exposure duration may be a contributing factor in NP-mediated toxicity. Moreover, upon chronic exposure to nTiO(2) for 21d, daphnia displayed severe growth retardation and mortality, as well as reproductive defects. Interestingly, a significant amount of nTiO(2) was found accumulated in daphnia. However, these daphnia displayed difficulty in eliminating nTiO(2) from their body, presenting increased bioconcentration factor (BCF) values. This high level of bioaccumulation may interfere with food intake and ultimately affect growth and reproduction. In summary, long-term exposure of aquatic organisms to nTiO(2) may alter the growing status of these organisms at both individual and population levels, posing risks to aquatic ecosystems.

The impact of ZnO nanoparticle aggregates on the embryonic development of zebrafish (Danio rerio)

With extensive use of metal oxide nanoparticles (NPs) in a variety of applications comes a higher potential of release into aquatic environments. NPs tend to form much larger aggregates in water, which are expected to settle down to the bottom of the water column and possibly get mixed with the sediments. However, little is known about the environmental impacts and biological effects of these aggregated NPs in the sediment column. In this study, we examined the sedimentation of nanoscale ZnO particles (nZnO) in zebrafish culture medium, and assessed the toxicity of settled nZnO aggregates on developing zebrafish embryos and larvae. Given the known dissolution of nZnO particles to release Zn(2+), we also assessed the toxic effect of soluble Zn(2+) in this organism. We demonstrated that within 48 h, micron-sized nZnO aggregates were formed and settled out of the culture medium. These aggregates were found to exert dose-dependent toxicity to zebrafish embryos and larvae, reducing the hatching rate and causing pericardial edema. The observed toxicity of the nZnO aggregates was not likely a result solely of particle dissolution, as soluble Zn(2+) alone caused much less toxicity to zebrafish embryos than nZnO. Instead, the combination of both nZnO and Zn(2+) may contribute to the embryonic toxicity, possibly by increasing reactive oxidative species (ROS) and/or compromising the cellular oxidative stress response. Interestingly, we demonstrated that one type of formulated sediments could mitigate the toxicity of nZnO aggregates, highlighting a possible countermeasure to reduce the adverse impact of nZnO aggregates on the environment.

Trophic transfer of TiO2 nanoparticles from daphnia to zebrafish in a simplified freshwater food chain

The rapid development of nanotechnology and the corresponding increase in the use of manufactured nanomaterials (MNMs) in commercial products have led to concerns about the health risks and environmental impacts of such nanosized materials. One of the most significant and currently not well-understood risks is their potential transfer and magnification in food webs. To address this concern, a simplified model of a freshwater food chain including a low trophic level organism (daphnia, Daphnia magna) and a high trophic level organism (zebrafish, Danio rerio) was established. Our results provide the first direct evidence that nanoscale TiO(2) particles (nTiO(2)) can transfer from D. magna to D. rerio by dietary exposure. However, no biomagnifications of nTiO(2) was observed in this simplified food chain because the values of the biomagnification factors (BMF) in this study (0.024 and 0.009) were all less than one. Compared to the dietary intake, D. rerio could accumulate nTiO(2) by aqueous exposure with high bioaccumulation factors (BCFs) of 25.38 and 181.38 for 0.1 and 1.0mgL(-1) exposure groups, respectively. Nevertheless, higher body burden of nTiO(2) in the dietary exposure groups than that in the aqueous exposure groups demonstrated that dietary intake may constitute a major route of potential nanomaterial exposure for a higher trophic level of aquatic organisms. This study represents the first examination of the potential food chain transfer and biomagnification of nTiO(2) in an aquatic ecosystem.

Developmental toxicity in zebrafish (Danio rerio) embryos after exposure to manufactured nanomaterials: Buckminsterfullerene aggregates (nC60) and fullerol

The present paper summarizes, to our knowledge, the first study regarding the developmental toxicity of stable buckminsterfullerene aggregates suspended in water (nC60) using zebrafish (Danio rerio) as a vertebrate model. Zebrafish embryo survival, hatching rate, heartbeat, and pericardial edema were noted and described within 96 h of exposure. Fullerol (a hydroxylated C60 derivative, C60(OH)16-18) at 50 mg/L did not exert toxicity to zebrafish embryos. In contrast, nC60 at 1.5 mg/L delayed zebrafish embryo and larval development, decreased survival and hatching rates, and caused pericardial edema. Toxicity was mitigated by adding an antioxidant (glutathione), which suggests that a free radical-induced mechanism or another form of oxidative stress played a role in developmental toxicity.

Toxicity Assessment of Iron Oxide Nanoparticles in Zebrafish (Danio rerio) Early Life Stages

Iron oxide nanoparticles have been explored recently for their beneficial applications in many biomedical areas, in environmental remediation, and in various industrial applications. However, potential risks have also been identified with the release of nanoparticles into the environment. To study the ecological effects of iron oxide nanoparticles on aquatic organisms, we used early life stages of the zebrafish (Danio rerio) to examine such effects on embryonic development in this species. The results showed that ≥10 mg/L of iron oxide nanoparticles instigated developmental toxicity in these embryos, causing mortality, hatching delay, and malformation. Moreover, an early life stage test using zebrafish embryos/larvae is also discussed and recommended in this study as an effective protocol for assessing the potential toxicity of nanoparticles. This study is one of the first on developmental toxicity in fish caused by iron oxide nanoparticles in aquatic environments. The results will contribute to the current understanding of the potential ecotoxicological effects of nanoparticles and support the sustainable development of nanotechnology.

TiO2 Nanoparticles in the Marine Environment: Impact on the Toxicity of Tributyltin to Abalone (Haliotis diversicolor supertexta) Embryos

Little information is available on the potential ecotoxicity of manufactured nanomaterials (MNMs) in the marine environment. To carefully address this issue, the toxicity of nanosized titanium dioxide (nTiO(2)) aggregates in the marine environment was evaluated using abalone (Haliotis diversicolor supertexta) embryonic development as a model. The effect of nTiO(2) aggregates on the toxicity of the highly toxic marine antifouling compound tributyltin (TBT) to abalone embryos was also investigated. No developmental effects of nTiO(2) were observed at 2 mg/L but concentrations ≥10 mg/L caused hatching inhibition and malformations. The presence of 2 mg/L nTiO(2) increased the toxicity of TBT up to 20-fold compared with TBT alone. This enhancement of TBT may be due to the combined effects of TBT adsorption onto nTiO(2) aggregates and the internalization of nTiO(2) aggregates by abalone embryos. These observations indicate that MNMs may have important indirect impacts on aquatic organisms by varying the toxicity of coexisting pollutants. Thus, risk assessments for MNMs should consider both their direct effects and possible indirect effects of interactions with other environmental contaminants.

Oxidative stress and growth inhibition in the freshwater fish Carassius auratus induced by chronic exposure to sublethal fullerene aggregates

The rapid growth of nanotechnology is stimulating research concerning the potential environmental impacts of manufactured nanomaterials. The present study summarizes, to our knowledge, the first examination regarding the potential effects of chronic exposure (32 d) of aquatic organisms (juvenile carp [Carassius auratus]) to sublethal concentrations (0.04-1.0 mg/L) of fullerene aggregates (nC60/aq; i.e., C60 suspended in water after long-term stirring) with average diameters of approximately 349 and/or 1,394 nm. The results demonstrated that the antioxidant enzymes superoxide dismutase and catalase were induced significantly in the gills and liver of C. auratus exposed to nC60/aq for 32 d, whereas a nonenzymatic antioxidant, glutathione, decreased in all tested tissues. In addition, lipid peroxidation (LPO) levels decreased in most cases, especially in the gills and brain, but exposure to 1.0 mg/L of nC60/aq led to a significant (p < 0.01) increase in the LPO level in the liver. This increase in LPO level in combination with the observed oxidative stress suggested that the liver might be the target of or most susceptible organ to nC60/ aq exposure. Furthermore, the body weight and total length of juvenile carp exposed to 1.0 mg/L of nC60/aq for 32 d decreased significantly (p < 0.05), indicating that nC60/aq had an inhibitory effect on fish growth. The present findings imply that the oxidative stress induced by long-term exposure could be the main mechanism of the toxicity of nC60/aq to juvenile carp. This important work contributes to a better understanding of the potential health effects of exposure to manufactured nanomaterials on species in aquatic ecosystems.

Disruption of zebrafish (Danio rerio) reproduction upon chronic exposure to TiO2 nanoparticles

As common engineered nanomaterials, TiO(2) nanoparticles (nTiO(2)) are usually perceived as non-toxic, and have already been widely used in many products and applications. Such a perception might have been shaped by some short-term studies that revealed no/low toxicity of nTiO(2) to cells and eco-relevant organisms. However, given the ultimate release of nTiO(2) into the aquatic environment, which can act as a sink for engineered nanoparticles, their long-term impact on the environment and human health is still a concern and deserves more research efforts. Here, for the first time, we demonstrate that chronic exposure of zebrafish to 0.1 mg L(-1) nTiO(2), can significantly impair zebrafish reproduction. For instance, there was a 29.5% reduction in the cumulative number of zebrafish eggs after 13 weeks of nTiO(2) exposure. Thus, we provided timely information on indicating a serious risk of reproductive impairment of environments contaminated with low levels of nTiO(2) on aquatic organisms, leading to alterations in population dynamics and aquatic ecosystem balance, and thus warrants a careful scrutiny on toxicity assessment of nTiO(2), especially their long-term impact.

Individual and joint toxic effects of pentachlorophenol and bisphenol A on the development of zebrafish (Danio rerio) embryo

Investigation of the toxicological effects of pentachlorophenol (PCP) and bisphenol A (BPA) alone and in combination was carried out following the method of the early life stage (ELS) test on zebrafish embryos. Both chemicals revealed lethal and sub-lethal effects, such as no blood flow, cardiac edema, delayed hatching, and tail malformations. According to their median effective concentrations (EC(50) values) in the single exposure, the toxic level of PCP was about two orders of magnitude higher than that of BPA. Result of the joint action modes varied depending on different endpoints. Synergistic action was observed based on the endpoint of 24h mortality and antagonistic effect displayed based on the endpoint of 72 h cardiac edema. It was also found that the toxicity of PCP would be enhanced with the addition of BPA even below its no observed effect concentration (NOEC) level at the endpoint of 32 h with no blood flow, and the level of the increase was influenced by the toxic unit (TU) ratio.