Screening of different metal oxide nanoparticles reveals selective toxicity and inflammatory potential of silica nanoparticles in lung epithelial cells and macrophages.

In cell culture studies, foetal calf serum (FCS) comprising numerous different proteins is added, which might coat the surface of engineered nanomaterials (ENMs) and thus could profoundly alter their biological activities. In this study, a panel of industrially most relevant metal oxide nanoparticles (NPs) was screened for toxic effects in A549 lung epithelial cells and RAW264.7 macrophages in the presence and absence of FCS. In medium without FCS amorphous SiO2-NPs were the most cytotoxic NPs and induced a significant pro-inflammatory response in both cell types. An increased anti-oxidative response after exposure to SiO2-NPs was, however, only observed in RAW264.7 macrophages. Furthermore, pre-coating of SiO2-NPs with FCS proteins or simply bovine serum albumin abrogated responses in A549 lung epithelial cells. Thus, the protein corona bound to the surface of SiO2-NPs suppresses their biological effects, an issue which needs to be more carefully considered for in vitro-in vivo extrapolations.

Formation of nanoparticles in flames; measurement by particle mass spectrometry and numerical simulation.

The size distributions of nanoparticles in flames are measured using a novel particle mass spectrometer (PMS), which is developed for the size range between 0.3 and 50 nm and for number concentrations between 10(9) and 10(13). Using this instrument the particles are sampled without prior dilution from the flame into a molecular beam. The charged nanoparticles are then deflected by an electric field, to determine the mass according to the time-of-flight principle. The PMS is installed in a low pressure combustion chamber operated at 30 mbar. Measurements are made on primary soot particles and iron oxide particles in a laminar, premixed acetylene/oxygen flame. The soot particles increase in size as a function of the height above the burner and the C/O ratio from 2 up to 10 nm. Iron oxide particles of 3-5 nm are detected as a function of burner height. The soot particles form more rapidly than the iron oxide particles. A model calculation for the formation of silica and iron oxide in hydrogen/oxygen flames is developed, based on previously published reaction mechanisms. On adding a mono-disperse particle coagulation scheme, the time history of the particle number concentration and the particle size is calculated. In agreement with experimental data, the calculations show that iron oxide particles are formed more slowly than silica particles.

Adsorption of PCDD/F on MWI fly ash.

The removal of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) from waste incinerator off-gas is a costly task, because a considerable part of the PCDD/F may exist in the gas phase (often 50-100% around 200 degrees C). The volatile fraction passes the particle filter and the subsequent gas cleaning equipment, so that an additional unit is needed to remove the gaseous PCDD/F from the flue gas. Moreover, dioxins and furans can accumulate in some parts of the equipment in a way that they can act as a latent source. In this work, we investigate the possibility to adsorb the PCDD/F at the fly ash particles and to remove them during the filtration. The gas/particle partitioning of the PCDD/F depends on the temperature, the vapor pressure, the particle size, the particle number density and on the physical and chemical properties of the particle surface. These relationships are investigated by model calculations and by pilot scale experiments (500 Nm3/h) which employ one selected hexachlorinated dioxin congener. At room temperature, approx. 90% of the HxCDD are found in the particulate phase, while at 135 degrees C that portion is only 10%. This means that at ambient temperatures, the gas/particle partitioning of the dioxin corresponds well to the sublimation equilibrium. At higher temperatures, it is much different from the sublimation equilibrium and the apparent adsorption enthalpy is smaller than the enthalpy of sublimation. This observation is in agreement with literature data. From the above experiments and from similar literature data, the efficiency of fly ash particles as a sink for PCDD/F can be evaluated. The data suggest that the adsorption rate is not the limiting factor for the transfer into the particulate phase. The important factors appear to be the chemical composition of the fly ash and the temperature.