Revealing the toxicity of monovalent and trivalent thallium to medaka fish in controlled exposure conditions.

Thallium (Tl) is a rare earth element increasingly being used in high-technology manufacturing. It is also an emerging pollutant with high exposure and toxicity risks to aquatic ecosystems. Tl exists in the environment in a monovalent [thallous, Tl(I)] or trivalent [thallic, Tl(III)] state. Currently, the stability of the two Tl species in natural water is uncertain and the toxicity in algae and daphnia are inconsistent due to lack of robust characterization of Tl species and matrix effects, while studies with fish are sparse. In this study, larvae of medaka fish (Oryzias latipes) were dosed with environmentally relevant concentrations of Tl(I) or Tl(III) spiked into synthetic and natural river water for 7 days to observe the toxic effects of two Tl species on fish. The transformation of Tl(I) and Tl(III) in water was analyzed by high performance liquid chromatography coupled with inductively coupled plasma and mass spectrometry. Analytical and toxicity results showed that Tl(I) is more stable presenting higher mortality and bioconcentration in medaka than Tl(III) in different water matrices. Tl(I)-induced LC50 and body burden in treated fish were highly correlated with its competitive ion, potassium (K), especially in waters containing medium K levels. This study provides reliable evidence regarding the stability and toxicity of Tl(I) and Tl(III) as well as the interaction of aqueous K versus Tl(I) in fish. Such information is useful for justifying water-quality guidelines and ecological risks of Tl pollution in natural water ecosystems.

Establishing a quick screening method by using a microfluidic chip to evaluate cytotoxicity of metal contaminants.

Due to rapid industrialization and urbanization, the environment is exposed to many chemicals from natural or anthropogenic sources. The contaminants impact eco-system and human health via food chain. Animals, including humans, are likely to accumulate contaminants in their bodies from direct exposure or feeding behavior, resulting in toxicity. Therefore, evaluation of the toxicity of contaminants is an important issue. Metals are highly toxic but the toxicity depends on many factors, including the valance and the complex form of metals, the organic matter level in the environment, the reducing/oxidizing condition of the environment, and etc. Since the level of metal amount does not directly correlate to bioavailability, cell culture is usually used for toxicity evaluation. In this study, a microfluidic chip was developed to evaluate the cell toxicity from exposure to metals, copper and thallium. Compared to traditional cytotoxicity assay using static state culture with tetrazolium reagent, this microfluidic chip can generate various shear stresses by changing geometry of culture areas or flow rate. Enhancement of shear stresses could increase cell sensitivity toward metal exposure. Therefore, this platform provides a more sensitive platform for quantitative analysis of cell toxicity and could be applied to evaluate toxicity from environmental samples.

Characterization and modeling analysis for metal-semiconductor-metal GaAs diodes with Pd/SiO2 mixture electrode.

Characterization and modeling of metal-semiconductor-metal (MSM) GaAs diodes using to evaporate SiO2 and Pd simultaneously as a mixture electrode (called M-MSM diodes) compared with similar to evaporate Pd as the electrode (called Pd-MSM diodes) were reported. The barrier height (φ(b)) and the Richardson constant (A*) were carried out for the thermionic-emission process to describe well the current transport for Pd-MSM diodes in the consideration of the carrier over the metal-semiconductor barrier. In addition, in the consideration of the carrier over both the metal-semiconductor barrier and the insulator-semiconductor barrier simultaneously, thus the thermionic-emission process can be used to describe well the current transport for M-MSM diodes. Furthermore, in the higher applied voltage, the carrier recombination will be taken into discussion. Besides, a composite-current (CC) model is developed to evidence the concepts. Our calculated results are in good agreement with the experimental ones.

Stabilization or oxidation of nanoscale zerovalent iron at environmentally relevant exposure changes bioavailability and toxicity in medaka fish.

Nanoscale zerovalent iron (nZVI)-based nanotechnologies are increasingly being used for environmental remediation; however, the fate and ecotoxicologic effects of nZVI remain unclear. Larvae of medaka fish (Oryzias latipes) underwent 3-14 days' aqueous exposure to thoroughly characterized solutions containing carboxymethyl cellulose (CMC)-stabilized nZVI, bare nZVI, nanoscale iron oxide (nFe(3)O(4)) or ferrous ion [Fe(II)(aq)] at µg/L-mg/L levels to assess the causal toxic effect(s) of iron nanoparticles (NPs). Acute larval mortality was decreased in the order of Fe(II)(aq) > CMC-nZVI > nZVI > nFe(3)O(4). CMC-nZVI (100 mg/L) increased hypoxia and reactive oxygen species (ROS) and Fe(II)(aq) production, thus increasing mortality and oxidative stress response as compared with unstabilized nZVI. Additionally, nFe(3)O(4) and nZVI were more bioavailable than suspended CMC-nZVI or Fe(II)(aq). Antioxidant activities were significantly altered by induced intracellular ROS levels in larvae with subchronic exposure to nFe(3)O(4) or Fe(II)(aq) at environmentally relevant concentrations (0.5-5 mg/L). We report on different organizational biomarkers used for rapidly assessing the lethal and sublethal toxicity of nZVI and its stabilized or oxidized products. The toxicity results implicate a potential ecotoxicological fate and impact of nZVI on the aquatic environment.

Toxicity assessments of nanoscale zerovalent iron and its oxidation products in medaka (Oryzias latipes) fish.

Iron-based nanotechnologies are increasingly used for environmental remediation; however, toxicologic impacts of iron nanoparticles on the aquatic ecosystem remain poorly understood. We treated larvae of medaka fish (Oryzias latipes) with thoroughly characterized solutions containing carboxymethyl cellulose (CMC)-stabilized nanoscale zerovalent iron (nZVI), aged nanoscale iron oxides (nFe-oxides) or ferrous ion (Fe[II]) for 12-14 days' aqueous exposure to assess the causal toxic effect(s) of iron NPs on the fish. With the CMC-nZVI solution, the dissolved oxygen level decreased, and a burst of reactive oxygen species (ROS) was generated as Fe(II) oxidized to ferric ion (Fe[III]); with the other two iron solutions, these parameters did not significantly change. CMC-nZVI and Fe(II) solutions caused acute lethally and sublethally toxic effects in medaka larvae, with nFe-oxide-containing solutions causing the least toxic effects. We discuss modes of toxic action of iron NPs and chronic toxic effects in terms of hypoxia, Fe(II) toxicity and ROS-mediated oxidative damage.