Subchronic and chronic developmental effects of copper oxide (CuO) nanoparticles on Xenopus laevis.

Metal oxide nanoparticles, such as copper oxide (CuO), are mass produced for use in a variety of products like coatings and ceramics. Acute exposure to CuO nanoparticles has caused toxicity to many aquatic organisms, yet there is no information on the effect of prolonged CuO nanomaterial exposures. This study examined effects of chronic exposure to CuO nanoparticles on Xenopus laevis growth and development. Experiments included a 14 d subchronic exposure and a 47 d chronic exposure throughout metamorphosis. The subchronic exposure caused mortality in all tested CuO concentrations, and significant growth effects occurred after exposure to 2.5 mg L(-1) CuO. Chronic exposure to 0.3 mg L(-1) CuO elicited significant mortality and affected the rate of metamorphosis. Exposure to lower concentrations of CuO stimulated metamorphosis and growth, indicating that low dose exposure can have hormetic effects.

Effects of ZnO nanomaterials on Xenopus laevis growth and development.

The objectives of this study were to quantify uptake and developmental effects of zinc oxide nanomaterials (nano-ZnO) on Xenopus laevis throughout the metomormosis process. To accomplish this, X. laevis were exposed to aqueous suspensions of 40-100 nm nano-ZnO beginning in-ovo and proceeding through metamorphosis. Nanomaterials were dispersed via sonication methods into reconstituted moderately hard water test solutions. A flow-through system was utilized to decrease the likelihood of depletion in ZnO concentration. Exposure to 2 mg/L nano-ZnO significantly increased mortality incidence to 40% and negatively affected metamorphosis of X. laevis. Tadpoles exposed to 2 mg/L nano-ZnO developed slower as indicated by tadpoles with an average stage of 56 at the conclusion of the study which was significantly lower than the control tadpole stages. No tadpoles exposed to 2 mg/L of nano-ZnO completed metamorphosis by the conclusion of the study. Tadpoles exposed to 0.125 mg/L nano-ZnO experienced faster development along with larger body measurements indicating that low dose exposure to nano-ZnO can stimulate growth and metamorphosis of X. laevis.

Bacterial community dynamics in high and low bioavailability soils following laboratory exposure to a range of hexahydro-1,3,5-trinitro-1,3,5-triazine concentrations.

Few studies have examined the potential long-term effects of high concentrations of hexahydro-1,3,5-trinitro-1,3,5-triaxine (RDX) on bacterial communities in soil. In the present study, a sandy loam soil and a silt loam soil (high and low bioavailability, respectively) were artificially contaminated with RDX (0, 50, 500, 1,500, 5,000, 10,000, and 15,000 mg/kg soil). Bacterial communities from each treatment were monitored over 63 d to characterize the effects of RDX exposure on bacterial activity, biomass, functional diversity (Biolog microtiter plates), and structural diversity (denaturing gradient gel electrophoresis of 16S rDNA). Bacterial communities native to the high bioavailability soil were inherently different than bacterial communities native to the silt loam soil, not only in terms of bacterial activity and biomass, but also in terms of bacterial community functional and structural diversity. Soil RDX contamination was correlated with decreased bacterial biomass in the silt loam soil treatments and with decreased bacterial activity in the sandy loam soil treatments on day 7. Soil RDX contamination did not cause a significant shift in the functional diversity of the bacterial communities native to the silt loam soil, but was correlated with a shift in identities of substrates used by bacterial communities native to the sandy loam soil on day 7. Bacterial community structure was insensitive to the gradient of RDX concentrations at the beginning of the incubation. However, the identities of carbon substrates used by bacterial communities in both soil types were affected by long-term incubation with RDX.

Effects of functionalized and nonfunctionalized single-walled carbon nanotubes on root elongation of select crop species.

Single-walled carbon nanotubes have many potential beneficial uses, with additional applications constantly being investigated. Their unique properties, however, create a potential concern regarding toxicity, not only in humans and animals but also in plants. To help develop protocols to determine the effects of nanotubes on plants, we conducted a pilot study on the effects of functionalized and nonfunctionalized single-walled carbon nanotubes on root elongation of six crop species (cabbage, carrot, cucumber, lettuce, onion, and tomato) routinely used in phytotoxicity testing. Nanotubes were functionalized with poly-3-aminobenzenesulfonic acid. Root growth was measured at 0, 24, and 48 h following exposure. Scanning-electron microscopy was used to evaluate potential uptake of carbon nanotubes and to observe the interaction of nanotubes with the root surface. In general, nonfunctionalized carbon nanotubes affected root length more than functionalized nanotubes. Nonfunctionalized nanotubes inhibited root elongation in tomato and enhanced root elongation in onion and cucumber. Functionalized nanotubes inhibited root elongation in lettuce. Cabbage and carrots were not affected by either form of nanotubes. Effects observed following exposure to carbon nanotubes tended to be more pronounced at 24 h than at 48 h. Microscopy images showed the presence of nanotube sheets on the root surfaces, but no visible uptake of nanotubes was observed.