Caroline Peyrot

Aggregation of titanium dioxide nanoparticles: role of calcium and phosphate

FCS Technique A laser light is focussed into a sample of interest using confocal optics. In this manner, an open, illuminated volume element with dimensions of ~0.5–1.0 μm 3 (confocal volume) is created. At any point in time, the confocal volume is occupied by one or only a few fluorescent molecules. In the absence of chemical reactions or other dynamic processes, temporal fluctuations in the measured fluorescence intensity in the confocal volume can be attributed solely to the translational diffusion of the fluorescent particle. Variations in the fluorescence intensity are analysed using an autocorrelation function that assumes a three-dimensional Gaussian

Effects of cadmium telluride quantum dots on cadmium bioaccumulation and metallothionein production to the freshwater mussel, Elliptio complanata.

Nanotechnology has gained increasing commercial attention over recent years and its use has raised concerns about its potential release in the environment. The purpose of this study was to determine the size distribution of CdTe in freshwater, bioavailability and potential toxic effects of cadmium telluride quantum dots (CdTe QD) to the freshwater mussel Elliptio complanata. Mussels were exposed to increasing concentrations (0 to 8 mg Cd L(-1)) of CdTe and 0.5 mg/L CdSO4 for 24 h at 15 degrees C to examine the initial uptake and toxic effects of Cd from CdTe QDs and dissolved CdSO4. After the exposure period, Cd bioaccumulation in the gills, digestive gland and gonad tissues and metallothionein (MT) levels were determined. The results revealed that about 80% of Cd was retained by a 450 nm pore filter (aggregates) and that 14% of the Cd was in the dissolved phase (i.e., eluted through a 1 kDa ultrafiltration membrane) which suggested that uncoated CdTe QDs were not stable in freshwater. In mussels, Cd was accumulated principally by the gills and digestive gland and the bioaccumulation factors of Cd from CdTe were similar to that of dissolved Cd. Indeed, tissue-levels of Cd were below the proportion of dissolved Cd from CdTe which suggests that Cd rather comes from the dissociation of Cd from the ingested QDs than from the internalization of the QDs in mussel tissues. The levels of MT were induced in both the digestive gland and gonad but were readily decreased in the gills by both CdTe and CdSO4. The observed decrease in the metallic form of MT might result from the oxidative stress by CdTe and dissolved Cd. In conclusion, uncoated CdTe QD in freshwater leads to aggregates and a dissolved component of Cd where the latter explained the contribution of the observed accumulation pattern in mussel tissues and effects on MT levels in mussels.

Improvements to Single Particle ICPMS by the Online Coupling of Ion Exchange Resins

Single particle ICPMS (SP-ICPMS) is becoming a very promising technique for nanoparticle detection and characterization, especially at very low concentrations (~10(-12)-10(-10) M). Nonetheless, the ability of the technique to detect smaller nanoparticles is presently limited by the setting of threshold values for the discrimination of nanoparticles from the dissolved metal background. In this study, a new approach to attaining lower particle size detection limits has been developed by the online coupling of an ion exchange column (IEC) with SP-ICPMS (IEC-SP-ICPMS). The IEC effectively removes the continuous signal of dissolved metal, allowing for both lower detection limits and an improved resolution of solutions containing multiple particles. The feasibility and the efficiency of this coupling were investigated using silver nanoparticles in the presence of various concentrations of Ag(+) and other major ions (Mg(2+), Ca(2+), Na(+), K(+), and Cl(-)). The online elimination of the dissolved metal made data processing simpler and more accurate. Following the addition of 1 to 4 μg L(-1) of Ag(+) spikes, symmetric particle size distributions were obtained using IEC-SP-ICPMS, whereas the use of SP-ICPMS alone led to asymmetric distributions, especially for nanoparticle sizes below 60 nm. Although this proof of principle study focused on nanosilver, the technique should be particularly useful for any of the metal based nanoparticles with high solubilities.

Chronic sublethal exposure to silver nanoparticles disrupts thyroid hormone signaling during Xenopus laevis metamorphosis

Nanoparticles (NPs) are engineered in the nanoscale (<100 nm) to have unique physico-chemical properties from their bulk counterparts. Nanosilver particles (AgNPs) are the most prevalent NPs in consumer products due to their strong antimicrobial action. While AgNP toxicity at high concentrations has been thoroughly investigated, the sublethal effects at or below regulatory guidelines are relatively unknown. Amphibian metamorphosis is mediated by thyroid hormone (TH), and initial studies with bullfrogs (Rana catesbeiana) indicate that low concentrations of AgNPs disrupt TH-dependent responses in premetamorphic tadpole tailfin tissue. The present study examined the effects of low, non-lethal, environmentally-relevant AgNP concentrations (0.018, 0.18 or 1.8 μg/L Ag; ∼10 nm particle size) on naturally metamorphosing Xenopus laevis tadpoles in two-28 day chronic exposures beginning with either pre- or prometamorphic developmental stages. Asymmetric flow field flow fractionation with online inductively coupled plasma mass spectrometry and nanoparticle tracking analysis indicated a mixture of single AgNPs with homo-agglomerates in the exposure water with a significant portion (∼30-40%) found as dissolved Ag. Tadpoles bioaccumulated AgNPs and displayed transient alterations in snout/vent and hindlimb length with AgNP exposure. Using MAGEX microarray and quantitative real time polymerase chain reaction transcript analyses, AgNP-induced disruption of five TH-responsive targets was observed. The increased mRNA abundance of two peroxidase genes by AgNP exposure suggests the presence of reactive oxygen species even at low, environmentally-relevant concentrations. Furthermore, differential responsiveness to AgNPs was observed at each developmental stage. Therefore, low concentrations of AgNPs had developmental stage-specific endocrine disrupting effects during TH-dependent metamorphosis.

Characterization of polymeric nanomaterials using analytical ultracentrifugation.

The characterization of nanomaterials represents a complex analytical challenge due to their dynamic nature (small size, high reactivity, and instability) and the low concentrations in the environment, often below typical analytical detection limits. Analytical ultracentrifugation (AUC) is especially useful for the characterization of small nanoparticles (1-10 nm), which are often the most problematic for the commonly used techniques such as electron microscopy or dynamic light scattering. In this study, small polymeric nanomaterials (allospheres) that are used commercially to facilitate the distribution of pesticides in agricultural fields were characterized under a number of environmentally relevant conditions. Under most of the studied conditions, the allospheres were shown to have a constant hydrodynamic diameter (dH) of about 7.0 nm. Only small increases in diameter were observed, either at low pH or very high ionic strength or hardness, demonstrating their high physicochemical stability (and thus high mobility in soils). Furthermore, natural organic matter had little effect on the hydrodynamic diameters of the allospheres. The concentration of the nanoparticles was an important parameter influencing their agglomeration-results obtained using dynamic light scattering at high particle concentrations showed large agglomerate sizes and significant particle losses through sedimentation, clearly indicating the importance of characterizing the nanomaterials under environmentally relevant conditions.

The influence of zinc chloride and zinc oxide nanoparticles on air-time survival in freshwater mussels.

The purpose of this study was to determine the cumulative effects of exposure to either dissolved zinc or nanozinc oxide (nanoZnO) and air-time survival in freshwater mussels. Mussels were exposed to each forms of zinc for 96h then placed in air to determine survival time. A sub-group of mussels before and after 7days of exposure to air were kept aside for the determination of the following biomarkers: arachidonate-dependent cyclooxygenase (COX) and peroxidase (inflammation and oxidative stress), lipid metabolism (total lipids, esterases activity, HO-glycerol, acetyl CoA and phospholipase A2) and lipid damage (lipid peroxidation [LPO]). The results showed that air-time survival was decreased from a mean value of 18.5days to a mean value of 12days in mussels exposed to 2.5mg/L of nanoZnO although it was not lethal based on shell opening at concentrations below 50mg/L after 96h. In mussels exposed to zinc only, the median lethal concentration was estimated at 16mg/L (10-25 95% CI). The air-time survival did not significantly change in mussels exposed to the same concentration of dissolved Zn. Significant weight losses were observed at 0.5mg/L of nanoZnO and at 2.5mg/L for dissolved zinc chloride, and were also significantly correlated with air-time survival (r=0.53; p<0.01). Air exposure significantly increased COX activity in control mussels and in mussels exposed to 0.5mg/L of nanoZnO and zinc chloride. The data also suggested fatty acid breakdown and β-oxidation. Mussels exposed to contaminants are more susceptible to prolonged exposure to air during low water levels.

Heteroagglomeration of nanosilver with colloidal SiO2 and clay

Environmental context The fate of nanomaterials in the environment is related to their colloidal stability. Although numerous studies have examined their homoagglomeration, their low concentration and the presence of high concentrations of natural particles implies that heteroagglomeration rather than homoagglomeration is likely to occur under natural conditions. In this paper, two state-of-the art analytical techniques were used to identify the conditions under which nanosilver was most likely to form heteroagglomerates in natural waters. Abstract The environmental risk of nanomaterials will depend on their persistence, mobility, toxicity and bioaccumulation. Each of these parameters is related to their fate (especially dissolution, agglomeration). The goal of this paper was to understand the heteroagglomeration of silver nanoparticles in natural waters. Two small silver nanoparticles (nAg, ~3nm; polyacrylic acid- and citrate-stabilised) were covalently labelled with a fluorescent dye and then mixed with colloidal silicon oxides (SiO2, ~18.5nm) or clays (~550nm SWy-2 montmorillonite). Homo- and heteroagglomeration of the nAg were first studied in controlled synthetic waters that were representative of natural fresh waters (50μg Ag L–1; pH 7.0; ionic strength 10–7 to 10–1 M Ca) by following the sizes of the nAg by fluorescence correlation spectroscopy. The polyacrylic acid-coated nanosilver was extremely stable under all conditions, including in the presence of other colloids and at high ionic strengths. However, the citrate-coated nanosilver formed heteroaggregates in presence of both colloidal SiO2 and clay particles. Nanoparticle surface properties appeared to play a key role in controlling the physicochemical stability of the nAg. For example, the polyacrylic acid stabilized nAg-remained extremely stable in the water column, even under conditions for which surrounding colloidal particles were agglomerating. Finally, enhanced dark-field microscopy was then used to further characterise the heteroagglomeration of a citrate-coated nAg with suspensions of colloidal clay, colloidal SiO2 or natural (river) water.

An improved experimental methodology to evaluate the effectiveness of protective gloves against nanoparticles in suspension

ABSTRACT Recent studies underline the potential health risks associated to the “nano” revolution, particularly for the workers who handle engineered nanoparticles (ENPs) that can be found in the formulation of several commercial products. Although many Health & Safety agencies recommend the use of protective gloves against chemicals, few studies have investigated the effectiveness of these gloves towards nanoparticle suspensions. Moreover, the data that are available are often contradictory. This study was designed to evaluate the effectiveness of protective gloves against nanoparticles in suspension. For this purpose, a new methodology was developed in order to take into account parameters encountered in the workplace such as mechanical deformations (MD) that simulate hand flexion and sweat. The effects of the precise experimental protocol on the concentrations of nanoparticles that were detected in the sampling suspension were assessed. Several samples of nitrile rubber gloves (73 µm thick), taken from different boxes, were brought into contact with gold nanoparticles (5 nm) in water. During their exposure to ENPs, the glove samples submitted systematic mechanical deformations and were placed in contact with a physiological solution simulating human sweat. Under these conditions, results obtained by inductively coupled plasma mass spectrometry (ICPMS) showed that the 5 nm gold nanoparticles passed through the protective gloves. This result was acquired, in spite of the observation of significant losses during the sampling phase that will be important for future experiments evaluating the effectiveness of these materials.

Towards understanding the mechanisms and the kinetics of nanoparticle penetration through protective gloves

Parallel to the increased use of engineered nanoparticles (ENP) in the formulation of commercial products or in medicine, numerous health & safety agencies have recommended the application of the precautionary principle to handle ENP; namely, the recommendation to use protective gloves against chemicals. However, recent studies reveal the penetration of titanium dioxide nanoparticles through nitrile rubber protective gloves in conditions simulating occupational use. This project is designed to understand the links between the penetration of gold nanoparticles (nAu) through nitrile rubber protective gloves and the mechanical and physical behaviour of the elastomer material subjected to conditions simulating occupational use (i.e., mechanical deformations (MD) and sweat). Preliminary analyses show that nAu suspensions penetrate selected glove materials after exposure to prolonged (3 hours) dynamic deformations. Significant morphological changes are observed on the outer surface of the glove sample; namely, the number and the surface of the micropores on the surface increase. Moreover, nitrile rubber protective gloves are also shown to be sensitive to the action of nAu suspension and to the action of the saline solution used to simulate sweat (swelling).