Jaclyn E. Cañas

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.

Acute effects of Fe2O3, TiO2, ZnO and CuO nanomaterials on Xenopus laevis

Metal oxide nanomaterials have exhibited toxicity to a variety of aquatic organisms, especially microbes and invertebrates. To date, few studies have evaluated the toxicity of metal oxide nanomaterials on aquatic vertebrates. Therefore, this study examined effects of ZnO, TiO(2), Fe(2)O(3), and CuO nanomaterials (20-100 nm) on amphibians utilizing the Frog Embryo Teratogenesis Assay Xenopus (FETAX) protocol, a 96 h exposure with daily solution exchanges. Nanomaterials were dispersed in reconstituted moderately hard test medium. These exposures did not increase mortality in static renewal exposures containing up to 1,000 mg L(-1) for TiO(2), Fe(2)O(3), CuO, and ZnO, but did induce developmental abnormalities. Gastrointestinal, spinal, and other abnormalities were observed in CuO and ZnO nanomaterial exposures at concentrations as low as 3.16 mg L(-1) (ZnO). An EC(50) of 10.3 mg L(-1) ZnO was observed for total malformations. The minimum concentration to inhibit growth of tadpoles exposed to CuO or ZnO nanomaterials was 10 mg L(-1). The results indicate that select nanomaterials can negatively affect amphibians during development. Evaluation of nanomaterial exposure on vertebrate organisms are imperative to responsible production and introduction of nanomaterials in everyday products to ensure human and environmental safety.

Uptake of 17α-ethynylestradiol and triclosan in pinto bean, Phaseolus vulgaris.

Pharmaceuticals and personal care products (PPCPs) have emerged as a group of potential environmental contaminants of concern. PPCPs in soil may enter terrestrial food webs via plant uptake. We evaluated uptake of 17α-ethynylestradiol (EE2) and triclosan in bean plants (Phaseolus vulgaris) grown in sand and soil. The extent of uptake and accumulation of EE2 and triclosan in plants grown in sand was higher than in plants grown in soil. In sand (conditions of maximum contaminant bioavailability), bioconcentration factors (BCFs) of EE2 and triclosan in roots (based on dry weights) were 1424 and 16,364, respectively, whereas BCFs in leaves were 55 for EE2 and 85 for triclosan. In soil, the BCF of EE2 decreased from 154 in the first week to 32 in the fourth week while it fluctuated in leaves from 18 to 20. The BCF for triclosan in plants grown in soil increased over time to 12 in roots and 8 in leaves. These results indicate that the potential for uptake and accumulation of PPCPs in plants exists. This trophic transfer pathway should be considered when assessing exposure to certain PPCPs, particularly with the use of recycled wastewater for irrigation.

Preconcentration/preelution ion chromatography for the determination of perchlorate in complex samples

The determination of perchlorate in complex matrices by ion chromatography (IC) with an online preconcentration and preelution technique is discussed. The method was applied to different sample types containing large concentrations of matrix anions that would otherwise interfere with analysis via conventional IC. The present approach was highly effective in removing most of the matrix anions and was thus resistant to the interferences commonly encountered in a high ionic strength background. Method performance was evaluated by analyzing for low-level perchlorate in synthetic high ionic strength solutions, tissue extracts, and hydroponic nitrate fertilizer samples. Not only is it easier to practice the present method compared to USEPA Method 314.0, but for most of these samples the present approach provided equal to or better recovery of perchlorate than Method 314.0. With a sample of specific conductance 12,650muScm(-1), for example, the present method provided a perchlorate recovery of 101% at the 25mugL(-1) level versus 89% by EPA Method 314.0. Method detection limits of perchlorate in hydroponic fertilizer samples with this method (130-190mugkg(-1)) are the lowest thus far reported.

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.

Patterns of genotoxicity and contaminant exposure: evidence of genomic instability in the marsh frogs (Rana ridibunda) of Sumgayit, Azerbaijan.

The wetlands of Sumgayit in the Azerbaijan Republic contain complex mixtures of contaminants, including polycyclic aromatic hydrocarbons (PAHs), mercury, organochlorine pesticides, and polychlorinated biphenyls. Marsh frogs (Rana ridibunda) were collected from several contaminated wetlands within the city as well as from two reference sites outside the city. Sediment samples revealed heterogeneous patterns of PAH and mercury concentrations throughout Sumgayit, with the highest levels occurring east of the Sumgayit River, within the industrial zone. Flow cytometry and micronucleus assay revealed elevated estimates of genetic damage in frogs from the wetlands east of the Sumgayit River compared to frogs from the reference sites. Flow cytometric data showed a significant correlation with sediment mercury concentrations, whereas population micronucleus frequencies were significantly correlated with high-molecular-weight PAHs.

Organochlorine contaminants in eggs: the influence of contaminated nest material

Snake eggs were placed in a synthetic nest contaminated with known concentrations of six organochlorines (OCs) to evaluate whether OCs from contaminated nest material accumulate in eggs. It was hypothesized that contaminated nest material may have contributed to OC burdens in eggs observed previously. The six OCs tested included lindane, heptachlor, aldrin, dieldrin, endrin, and DDT. Eggs were removed at 0, 4, and 6 weeks and analyzed using gas chromatography with electron capture detection. Lindane was found at the highest concentration (153 ng/g at 4 weeks and 162 ng/g at 6 weeks). The next highest uptake was for endrin (25 ng/g at 4 weeks and 106 ng/g at 6 weeks). Heptachlor, aldrin, and dieldrin were also taken up into the eggs, but DDT was not detected in any of the eggs at any sampling period. The concentration of OCs increased from week 4 to week 6 for all the OCs except DDT. Structure-activity relationships were examined to determine which physicochemical properties of the OCs tested could be used as predictors of uptake into the eggs. A variety of physicochemical properties were evaluated including vapor pressure and molecular connectivity (a numerical description of topology). Octanol-water partition coefficient (Kow) was a good predictor (r2 = 0.63, p = 0.06) of OC uptake into the eggs using this limited data set.

A cleanup method for perchlorate determination in urine

There is increasing concern about perchlorate exposure because of perchlorates potential effects on organisms as a thyroid hormone disruptor, as well as its contamination of the environment being much more widespread than previously thought. Perchlorate is excreted primarily into urine, therefore, evaluating perchlorate residues in urine should be a reasonable approach for determining exposure and if successful could be used as an effective biomarker of perchlorate exposure. Since the presence of ions and other biomolecules in matrices like urine usually confounds accurate determination of perchlorate by ion chromatography, it is necessary to develop efficient methods for perchlorate determination in these matrices. We developed a method that reduces the background signal of urine, which is typically the problem with the analysis of biological fluids and tissues by ion chromatography. Relatively high recovery of perchlorate was shown. In cow urine samples spiked with perchlorate at 2.5, 10, and 100mug/L, perchlorate recoveries were 67%+/-2.5, 77%+/-3.6, and 81%+/-1.7 (mean+/-S.D.), respectively. In addition, the detection limit was as low as 12.6, 12.3, and 18.7mug/L in cow, vole, and human urine samples, respectively.

Development of an extraction method for perchlorate in soils

Perchlorate originates as a contaminant in the environment from its use in solid rocket fuels and munitions. The current US EPA methods for perchlorate determination via ion chromatography using conductivity detection do not include recommendations for the extraction of perchlorate from soil. This study evaluated and identified appropriate conditions for the extraction of perchlorate from clay loam, loamy sand, and sandy soils. Based on the results of this evaluation, soils should be extracted in a dry, ground (mortar and pestle) state with Milli-Q water in a 1 ratio 1 soil ratio water ratio and diluted no more than 5-fold before analysis. When sandy soils were extracted in this manner, the calculated method detection limit was 3.5 microg kg(-1). The findings of this study have aided in the establishment of a standardized extraction method for perchlorate in soil.

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.