Enhanced study design for acute inhalation studies with hydrophobic surface-treated particles to determine toxicological effects including suffocation.

High concentrations of low-density particles may cause effects in acute inhalation toxicity studies which can be easily underestimated or misinterpreted following strictly the OECD TG 436, i.e., limited parameters as mortality and gross lesions will be evaluated only.

Particle aerosol generation and potential altering in airflow used for acute/repeated inhalation toxicity testing.

Reproducible aerosol generation in combination with stable aerosol properties are essential prerequisites for compliant performance of acute or repeated inhalation toxicity tests of particulate materials according to OECD TG 403, 436, 412, or 413. A frequent problem of powder aerosol generation is the formation of coarse agglomerates with low shear resistance, which are beyond the tolerable size range but not detected by the prescribed aerodynamic measurement techniques by cascade impactor as the measurement conditions cause a disintegration into smaller fragments. But such agglomerates are observed during the transport to the inhalation chambers.

Issues in the inhalation toxicity testing and hazard assessment for low density particulate materials such as synthetic amorphous silica (SAS).

Inhalation toxicity testing of particulate materials is mandated for classification. According to CLP, particulate materials should be tested as marketed and many particulate materials are marketed as non-respirable particles. However, OECD TG 413 requires exposure to particle sizes that are respirable and reach the alveoli.

Experimental Study on the Transport and Alteration Behavior of Aerosols From Low Density Powders for Acute Inhalation Toxicology Studies.

Low density powders have a bulk density of less than 100 kg/m3 and are produced technically by flame pyrolysis of silicon tetrachloride (pyrogenic powders such as pyrogenic silica) or wet-chemically by sol-gel processes (e.g. silica-gel) or precipitation reactions using sodium silicate solution and a mineral acid.

Physical Obstruction of Nasal Cavities With Subsequent Asphyxia, Causes Lethality of Rats in an Acute Inhalation Study With Hydrophobic HMDZ Surface-Treated Synthetic Amorphous Silica (SAS).

The aim of the present study was to understand the mechanism of lethality associated with high dose inhalation of a low-density hydrophobic surface-treated SAS observed in some acute inhalation studies. It was demonstrated that physical obstruction of the upper respiratory tract (nasal cavities) caused the effects observed. Hydrophobic surface-treated SAS was inhaled (flow-past, nose-only) by six Wistar rats (three males and three females) in an acute toxicity study at a concentration of ~500 mg/m for an intended 4-hr exposure.

Evaluation of preparation methods for suspended nano-objects on substrates for dimensional measurements by atomic force microscopy.

Dimensional measurements on nano-objects by atomic force microscopy (AFM) require samples of safely fixed and well individualized particles with a suitable surface-specific particle number on flat and clean substrates. Several known and proven particle preparation methods, i.e.

Particle characterisation in highly concentrated dispersions using ultrasonic backscattering method.

Determining particle size and concentration in highly concentrated suspensions and emulsions is challenging, especially under process conditions. In general, ultrasound therefore can be used for particle characterisation due to the ability of sound waves to pass opaque dispersions, whereas optical detection principles mostly are limited to low particulate contents. An established acoustic method, the ultrasonic attenuation spectroscopy, uses a transmission setup for measuring the attenuation of a dispersion.