Stéphane Hallé

Effects of inhaled nano-TiO2 aerosols showing two distinct agglomeration states on rat lungs

Nano-aerosols composed of large agglomerates (LA) (>100nm) are more likely to promote pulmonary clearance via macrophages phagocytosis. Small agglomerates (SA) (<100nm) seem to escape this first defense mechanism and are more likely to interact directly with biological material. These different mechanisms can influence pulmonary toxicity. This hypothesis was evaluated by comparing the relative pulmonary toxicity induced by aerosolized nano-TiO(2) showing two different agglomeration states: SA (<100nm) and LA (>100nm) at mass concentrations of 2 or 7mg/m(3). Groups of Fisher 344 male rats were nose-only exposed for 6h. The median number aerodynamic diameters were 30 and 185nm at 2mg/m(3), and 31 and 194nm at 7mg/m(3). We found in rats bronchoalveolar lavage fluids (BALF) a significant 2.1-fold increase in the number of neutrophils (p<0.05) in the group exposed to the 7mg/m(3) LA nano-aerosol suggesting a mild inflammatory response. Rats exposed to the 7mg/m(3) SA nano-aerosol showed a 1.8-fold increase in LDH activity and 8-isoprostane concentration in BALF, providing evidence for cytotoxic and oxidative stress effects. Our results indicate that biological responses to nanoparticles (NP) might depend on the dimension and concentration of NP agglomerates.

Numerical Simulation of Dynamic Stall Around an Airfoil in Darrieus Motion

The objective of this study is to investigate the two-dimensional unsteady flow around an airfoil undergoing a Darrieus motion in dynamic stall conditions. For this purpose, a numerical solver based on the solution of the Reynolds-averaged Navier-Stokes equations expressed in a streamfunction-vorticity formulation in a non-inertial frame of reference was developed. The governing equations are solved by the streamline upwind Petrov-Galerkin finite element method (FEM). Temporal discretization is achieved by second-order-accurate finite differences. The resulting global matrix system is linearized by the Newton method and solved by the generalized minimum residual method (GMRES) with an incomplete triangular factorization preconditioning (ILU). Turbulence effects are introduced in the solver by an eddy viscosity model. The investigation centers on an evaluation of the algebraic Cebeci-Smith model (CSM) and the nonequilibrium Johnson-King model (JKM). In an effort to predict dynamic stall features on rotating airfoils, first the authors present some testing results concerning the performance of both turbulence models for the flat plate case. Then, computed flow structure together with aerodynamic coefficients for a NACA 0015 airfoil in Darrieus motion under dynamic stall conditions are presented.

Experimental evaluation of the penetration of TiO2 nanoparticles through protective clothing and gloves under conditions simulating occupational use

Titanium dioxide nanoparticles (nTiO2) are found in numerous manufactured products. While a few studies have been carried out to measure the efficiency of chemical protective clothing and gloves against nanoparticles (NPs), they have generally not considered the conditions prevailing in occupational settings. This study was designed to evaluate the resistance of protective clothing against NPs under conditions simulating occupational use. Nitrile and butyl rubber gloves, as well as cotton/polyester woven and polyolefin non-woven clothing samples were placed into contact with nTiO2 in the form of powders or colloidal solutions. Simultaneously, mechanical deformations were applied to the samples. Preliminary results showed that nTiO2 may penetrate some of the materials after prolonged dynamic deformations and/or when the NPs are in colloidal solutions. The effect was partly attributed to modifications in the physical and mechanical properties of protective materials that were induced by repetitive mechanica...

Generating Nano-Aerosols from TiO2 (5 nm) Nanoparticles Showing Different Agglomeration States. Application to Toxicological Studies

Agglomeration of nanoparticles (NP) is a key factor in the generation of aerosols from nano-powders and may represent an important parameter to consider in toxicological studies. For this reason, the characterization of NP aerosols (e.g., concentration, size, and structure of agglomerates) is a critical step in the determination of the relationship between exposure and effects. The aim of this study was to generate and characterize aerosols composed of TiO2 (5 nm) NP showing different agglomeration states. Two concentrations were tested: 2 and 7 mg/m3. Stable mass concentrations over 6 hr were successfully generated by a wet method using Collison and Delavan nebulizers that resulted in aerosols composed of smaller agglomerates (<100 nm), while aerosols composed of larger agglomerates (>100 nm) were obtained by dry generation techniques using either a Palas dust feeder or a Fluidized Bed. Particle size distributions in the aerosols were determined by an electrical low pressure impactor. Median number aerodynamic diameters corresponding to the aerosol with smaller and larger agglomerates were 30 and 185 nm, respectively, for the 2 mg/m3 concentration, and 31 and 194 nm for the 7 mg/m3 experiment. Image analysis by transmission electron microscopy showed the presence of compact or agglomerates with void spaces in the different nano-aerosols. These characterized nano-aerosols will be used in further experiments to study the influence of agglomerate size on NP toxicity.

Modelling nanoparticle transport in an animal exposure chamber: a comparison between numerical and experimental measurements

Nanoparticles transport in an exposure chamber is investigated using computational fluid dynamics (CFD). This exposure chamber is used to assess the lung toxicity in rats resulting from the inhalation of airborne NPs. The mathematical model for airflow is based on the three-dimensional Reynoldsaveraged Navier-Stokes equations with turbulence modelling. Simulations of airborne NPs are based on assumptions such that their motions are similar to the ones of a single sized diameter distribution of a passive contaminant.

Experimental evaluation of the resistance of nitrile rubber protective gloves against TiO2 nanoparticles in water under conditions simulating occupational use

Manufactured nanoparticles (NPs), including titanium dioxide nanoparticles (nTiO2), now enter in the formulation of several commercial products. Some studies have been carried out to assess the resistance of protective gloves against NPs, they have generally not considered the conditions prevailing in occupational settings. This study was designed to evaluate the behavior of protective gloves materials against NPs in solution under conditions simulating occupational use. Mechanical deformations, simulating those produced by flexing the hand, were applied to nitrile rubber glove samples in contact with nTiO2 in water. The first analysis showed that nTiO2 solution penetrates some of the materials after prolonged dynamic deformations. These results were partly attributed to modifications in the physical and mechanical properties of protective gloves materials that were induced by repetitive mechanical deformations and/or the presence of the colloidal solution.

Swelling of elastomers in solutions of TiO2 nanoparticles

Elastomers used in protective gloves can be sensitive to the action of solvents used to disperse commercial solutions of nanoparticles. These effects may include the swelling of the polymer, leading to a modification of its mechanical and chemical properties. Modifications to the properties of the polymer will impact the protection provided by the protective gloves. The goal of this work was therefore to study the swelling of several elastomers when exposed to commercial solutions of nanoparticles. The study involved four elastomers and three commercial solutions of colloidal titanium dioxide (). Swelling was assessed by measurements of mass gain and length change. Tests were also performed with technical and ultrapure solvents corresponding to the liquid carriers. The solutions had a significant effect on the swelling of nitrile rubber, latex, and neoprene. A large mass gain was recorded for short immersion times, indicating a possible penetration of the nanoparticle liquid carrier into these elastomers. Length change measurements revealed a swelling anisotropy effect with nitrile rubber and latex in the solutions of colloidal . No effect was measured with butyl rubber. The results show that great care must be taken when selecting protective gloves for the handling of nanoparticle dispersions.

Evaluation of diffusion models for airborne nanoparticles transport and dispersion

The diffusion coefficient is a property that plays a significant role in the transport of airborne nanoparticles. However, there seems to be no general agreement in the literature on the most appropriate model to use for nanoparticle numerical simulations to be used in risk exposure assessments. This paper begins by presenting a brief review of some of the main models for small particles diffusion. A general dynamic equation for aerosol transport is briefly discussed next. Since the particle diffusion coefficient can be expressed in terms of a friction coefficient, three relationships are then presented and their influences on the friction and diffusion coefficients are considered for the particular case of TiO2 nanoparticles. Although, all the models studied here predict a decrease in the value of the diffusion coefficient with increasing particle diameter, some significant variations can be observed between the models. A specific diffusion model, chosen between those studied, is finally applied to estimate the purge time of airborne TiO2 nanoparticles in a simple closed space the size of a glovebox. It is shown that the sedimentation and the diffusion processes do not play a major role in the evaluation of the purge time.

A SIMPLIFIED APPROACH FOR MODELLING AIRBORNE NANOPARTICULES TRANSPORT AND DIFFUSION

A simplifi ed approach is proposed and used to study the TiO 2 nanoparticle transport and diffusion in an exposure chamber. This exposure chamber is used to assess lung toxicity in rats resulting from the inhalation of airborne nanoparticles. The simplifi ed approach uses computational fl uid dynamics (CFD) commercial software. The mathematical model for airfl ow is based on the three-dimensional Reynoldsaveraged Navier–Stokes equations with turbulence modeling. The mathematical model for airborne nanoparticles transport is based on assumptions such that their motions are similar to those of a singlesized diameter distribution of a passive contaminant. This model is valid as long as the nanoparticle concentration is low and the particle diameter is small enough that settling is negligible, which is the case for the exposure chamber studied. With this model, the diffusion coeffi cient is a property that plays a signifi cant role in the transport of airborne nanoparticles. The particle diffusion coeffi cient can be expressed in terms of a friction coeffi cient, and three possible relationships to model particle diffusion are presented. Their infl uences on the friction and diffusion coeffi cients are considered for the particular case of TiO 2 nanoparticles. Although all the models studied here predict a decrease in the value of the diffusion coeffi cient with increasing particle diameter, some signifi cant variations can be observed between the models. A specifi c diffusion model is selected and then used with the simplifi ed approach. The simplifi ed approach is fivalidated against available correlations for particle deposition on walls. Correlation for deposition loss rate in the case of a room agrees with numerical prediction for particle diameter between 10 and 200 nm. Particle mass concentration distribution inside the exposure chamber is also studied. The computed concentration distribution is quite uniform inside the exposure chamber and corresponds to single point measurements.

CALL FOR THE DEVELOPMENT OF AN ADAPTATIVE TOOL FOR ASSESSING HUMAN HEALTH POSED BY ENGINEERED NANOPARTICLE RISK

Assessing the risks associated with engineered nanoparticles (particles having at least one dimension in the 1–100 nm range) faces three major challenges: (1) lack of standard methodological approaches; (2) uncertainty surrounding the risk factors and their relative signifi cance; and (3) lack of control strategies. Among the approaches that have been proposed are (1) adapting risk evaluation tools used in industrial hygiene; (2) use of evaluation concepts borrowed from the insurance industry; (3) determining the consensus among experts; (4) rating risk control measures; (5) construction of infl uence diagrams; and (6) use of techniques drawn from multi-criteria decision-making. Knowledge has advanced rapidly in the fi eld of engineered nanoparticles, but comparison of studies is diffi cult and major gaps remain in the characterization of these materials and the risks they represent. Since they are already being introduced into commercial products and processes, the need is urgent for a fl exible and dynamic tool for compiling and sharing detailed knowledge of the associated risks. Uncertainties need to be expressed and reduced. This tool must aid the decision-making of business managers, scientists, and other stakeholders. To the best of our knowledge, no approach suggested in the literature meets these criteria. Thus, the authors call to develop an adaptive, multidimensional decision support tool that indicates infl uence relationships among risk factors and fosters the gathering and sharing of knowledge, including uncertainties.