H. Fissan

The potential risks of nanomaterials: a review carried out for ECETOC

During the last few years, research on toxicologically relevant properties of engineered nanoparticles has increased tremendously. A number of international research projects and additional activities are ongoing in the EU and the US, nourishing the expectation that more relevant technical and toxicological data will be published. Their widespread use allows for potential exposure to engineered nanoparticles during the whole lifecycle of a variety of products. When looking at possible exposure routes for manufactured Nanoparticles, inhalation, dermal and oral exposure are the most obvious, depending on the type of product in which Nanoparticles are used. This review shows that (1) Nanoparticles can deposit in the respiratory tract after inhalation. For a number of nanoparticles, oxidative stress-related inflammatory reactions have been observed. Tumour-related effects have only been observed in rats, and might be related to overload conditions. There are also a few reports that indicate uptake of nanoparticles in the brain via the olfactory epithelium. Nanoparticle translocation into the systemic circulation may occur after inhalation but conflicting evidence is present on the extent of translocation. These findings urge the need for additional studies to further elucidate these findings and to characterize the physiological impact. (2) There is currently little evidence from skin penetration studies that dermal applications of metal oxide nanoparticles used in sunscreens lead to systemic exposure. However, the question has been raised whether the usual testing with healthy, intact skin will be sufficient. (3) Uptake of nanoparticles in the gastrointestinal tract after oral uptake is a known phenomenon, of which use is intentionally made in the design of food and pharmacological components. Finally, this review indicates that only few specific nanoparticles have been investigated in a limited number of test systems and extrapolation of this data to other materials is not possible. Air pollution studies have generated indirect evidence for the role of combustion derived nanoparticles (CDNP) in driving adverse health effects in susceptible groups. Experimental studies with some bulk nanoparticles (carbon black, titanium dioxide, iron oxides) that have been used for decades suggest various adverse effects. However, engineered nanomaterials with new chemical and physical properties are being produced constantly and the toxicity of these is unknown. Therefore, despite the existing database on nanoparticles, no blanket statements about human toxicity can be given at this time. In addition, limited ecotoxicological data for nanomaterials precludes a systematic assessment of the impact of Nanoparticles on ecosystems.

Nanoparticle exposure at nanotechnology workplaces: A review

Risk, associated with nanomaterial use, is determined by exposure and hazard potential of these materials. Both topics cannot be evaluated absolutely independently. Realistic dose concentrations should be tested based on stringent exposure assessments for the corresponding nanomaterial taking into account also the environmental and product matrix. This review focuses on current available information from peer reviewed publications related to airborne nanomaterial exposure. Two approaches to derive realistic exposure values are differentiated and independently presented; those based on workplace measurements and the others based on simulations in laboratories. An assessment of the current available workplace measurement data using a matrix, which is related to nanomaterials and work processes, shows, that data are available on the likelihood of release and possible exposure. Laboratory studies are seen as an important complementary source of information on particle release processes and hence for possible exposure. In both cases, whether workplace measurements or laboratories studies, the issue of background particles is a major problem. From this review, major areas for future activities and focal points are identified.

Number Size Distribution, Mass Concentration, and Particle Composition of PM1, PM2.5, and PM10 in Bag Filling Areas of Carbon Black Production

Number size characteristics and PM10 mass concentrations of particles emitted during the packaging of various kinds of carbon blacks were measured continuously in the bag filling areas of three carbon black plants and concurrently at ambient comparison sites. PM10, PM2.5, and PM1 dust fractions were also determined in the bag filling areas. The filter samples were then analyzed for elemental and organic carbon. Comparisons of the measured number size distributions and mass concentrations during bag filling activities with those measured parallel at the ambient site and with those determined during nonworking periods in the work area enabled the characterization of emitted particles. PM10 mass concentrations were consistently elevated (up to a factor of 20 compared to ambient concentrations) during working periods in the bag filling area. Detailed analysis revealed that the carbon black particles released by bag filling activities had a size distribution starting at ≈ 400 nm aerodynamic diameter (dae) with modes around 1 μm dae and > 8 μm dae. Ultrafine particles (< 100 nm dae), detected in the bag filling areas, were most likely attributed to noncarbon black sources such as forklift and gas heater emissions.

Potential release scenarios for carbon nanotubes used in composites

The expected widespread use of carbon nanotube (CNT)-composites in consumer products calls for an assessment of the possible release and exposure to workers, consumers and the environment. Release of CNTs may occur at all steps in the life cycle of products, but to date only limited information is available about release of CNTs from actual products and articles. As a starting point for exposure assessment, exploring sources and pathways of release helps to identify relevant applications and situations where the environment and especially humans may encounter releases of CNTs. It is the aim of this review to identify various potential release scenarios for CNTs used in polymers and identify the greatest likelihood of release at the various stages throughout the life-cycle of the product. The available information on release of CNTs from products and articles is reviewed in a first part. In a second part nine relevant release scenarios are described in detail: injection molding, manufacturing, sports equipment, electronics, windmill blades, fuel system components, tires, textiles, incineration, and landfills. Release from products can potentially occur by two pathways; (a) where free CNTs are released directly, or more frequently (b) where the initial release is a particle with CNTs embedded in the matrix, potentially followed by the subsequent release of CNTs from the matrix. The potential for release during manufacturing exists for all scenarios, however, this is also the situation when exposure can be best controlled. For most of the other life cycle stages and their corresponding release scenarios, potential release of CNTs can be considered to be low, but it cannot be excluded totally. Direct release to the environment is also considered to be very low for most scenarios except for the use of CNTs in tires where significant abrasion during use and release into the environment would occur. Also the possible future use of CNTs in textiles could result in consumer exposure. A possibility for significant release also exists during recycling operations when the polymers containing CNTs are handled together with other polymers and mainly occupational users would be exposed. It can be concluded that in general, significant release of CNTs from products and articles is unlikely except in manufacturing and subsequent processing, tires, recycling, and potentially in textiles. However except for high energy machining processes, most likely the resulting exposure for these scenarios will be low and to a non-pristine form of CNTs. Actual exposure studies, which quantify the amount of material released should be conducted to provide further evidence for this conclusion.

The log-normal size distribution theory of brownian aerosol coagulation for the entire particle size range : part I analytical solution using the harmonic mean coagulation kernel

Abstract Brownian aerosol coagulation was studied theoretically using the moment method of log-normal size distribution functions. An analytic solution to the size distribution of a coagulating aerosol was derived. In order to cover the entire size range the harmonic mean of the near-continuum and the free-molecule coagulation coefficient were applied. Therefore, the analytic solution is valid for the entire particle size range, i.e. covering from the free-molecule regime, via both the transition and the near-continuum regimes, to the continuum regime. The present work represents the first analytical solution to the Brownian aerosol coagulation problem that addresses the entire particle size range.

Tailored nanoparticle films from monosized tin oxide nanocrystals: Particle synthesis, film formation, and size-dependent gas-sensing properties

In order to investigate the change of gas-sensitive properties of undoped tin oxide nanoparticle films depending on particle size, a thin film synthesis technique has been developed. Well-defined tin oxide nanoparticles have been prepared using a gas-phase condensation method. Pure SnO was used as starting material and was evaporated at T=820 °C. The resulting particles were sintered and crystallized in-flight at T=650 °C. Size-selected nanoparticles ranging from 10 to 35 nm were produced to form a nanoparticle film by means of electrostatic precipitation or low pressure impaction. The effect of in-flight oxidation, sintering, and crystallization on the structure, size, and size distribution of nanoparticles have been studied in detail. The samples show n-type semiconductors’ behavior like bulk SnO2. The influence of particle size on gas sensitivity and response behavior is investigated for C2H5OH at operating temperatures 200–300 °C using silicon substrates having an interdigitated contact pattern and an...

Thermophoretic effect of particle deposition on a free standing semiconductor wafer in a clean room

Abstract The thermophoretic effect of particle deposition on a free standing wafer was studied experimentally and numerically. The experimental study consisted of generating a monodisperse polystyrene latex (PSL) aerosol, transporting the aerosol to a vertical test chamber, depositing the monodisperse aerosol on a wafer surface heated to a desired temperature, and analysing the deposited particles with a wafer inspection system. Experimental data of particle deposition velocity to a free standing wafer at 30 cm s−1 of free stream velocity were obtained for a temperature difference between the wafer surface and the airflow of 10–40°C, and a particle diameter range of 0.6–5 μm. The data were then compared with a numerical model which took into account deposition mechanisms due to convection, diffusion, sedimentation and thermophoresis. The comparison shows good agreement between the measured particle deposition velocity and the numerical results.

Experimental Comparison of Four Differential Mobility Analyzers for Nanometer Aerosol Measurements

ABSTRACT The performance of four differential mobility analyzers (DMAs), namely the TSI-long, the TSI-short, the Hauke 3/150, and the Spectrometre de Mobillte Electrique Circulaire (SMEC) were evaluated under the same conditions of flow rates, flow ratio, input monodisperse aerosols, and transport-line lengths. The evaluations were performed under the conditions of 10 1/min sheath air and 1 1/min aerosol flow rates, and at a flow ratio of 10:1. Monodisperse aerosols in the size range of 6 nm to 50 nm were obtained by classifying condensation aerosols using a Hauke DMA operated at 20:1 flow ratio. The transfer functions of all four DMAs have been obtained by deconvoluting the scan results of the evaluated DMA (DMA2), and by using the empirical transfer function of the first DMA (DMA1, the Hauke DMA at 20:1 flow ratio). The half-width, height, and area of the transfer functions have been compared for the four DMAs tested. These results provide a quantitative comparison of the mobility resolution and diffusi...

Positioning of nanometer-sized particles on flat surfaces by direct deposition from the gas phase

Arrangements of nanometer-sized particles were obtained on plane oxidized silicon substrates by direct deposition from the gas phase. The particles were attracted onto charge patterns created by contact charging. Monodisperse, singly charged indium aerosol particles with a diameter of 30 nm were used as a test case to illustrate this process. Due to the surface treatment, the deposition is highly selective. We were able to create lines of particles with widths as narrow as 100 nm and several millimeters in length. The resolution of the pattern depends mainly on the surface treatment and the tool geometry. Our approach opens the possibility of creating patterns composed of nanometer-sized particles on a flat substrate surface by the simple transfer of charge patterns, without a lithographical process.

Bipolar charge distributions of aerosol particles in high-purity argon and nitrogen

The bipolar diffusion charging has been studied for monodisperse sodium chloride and silver particles of 5–100 nm in atmospheric air, argon and nitrogen. The particles were bipolarly charged in a neutralizer by ions, produced by beta-rays from a Kr 85 source. The differently charged particle fractions were separated in a differential mobility analyzer and measured with an aerosol electrometer. The experimentally determined results in atmospheeric air are comparable with earlier measured asymmetric bipolar charge distributions. They show good agreement with the theoretically determined results based on the extended Fuchs model with four-input ion parameters: mobilities and masses of positive and negative ions. The experimentally determined bipolar charge distributions in argon and nitrogen are more asymmetric than in atmospheric air. The theoretically determined distributions, based on the extended Fuchs model, can be fitted to the experimental data. Furthermore, the extended Fuchs model is strongly depend...