Furthermore, the chemical composition of SAS does not

indicate a sensitising potential. The inhalation of respirable particles of SAS produces a time- and dose-related inflammation response of the lung tissue in animal studies. Exposure of rats for 13 weeks to an average concentration of Raf inhibitor 1.3 mg/m3 of pyrogenic SAS resulted in mild reversible pro-inflammatory cell proliferation rather than a pathologically relevant tissue change. Given the low-grade severity of this common lung-tissue response, 1 mg/m3 can be established as NOAEL and LOEL (sub-chronic, 13 weeks). At the LOAEL (5.9 mg/m3) signs of adverse effects were found by the microscopic evaluation of tissues (stimulation of collagen production, increase in lung weight, incipient interstitial fibrosis, and slight focal buy Venetoclax atrophy in the olfactory epithelium). All these effects were reversible following discontinuation of exposure. In the same study also precipitated and surface-treated hydrophobic SAS forms were investigated. All tested forms showed qualitatively

the same effects, however, the pyrogenic form induced somewhat more severe inflammatory effects (for details see Reuzel et al., 1991 and ECETOC, 2006 and OECD, 2004). A dose-dependent inflammatory response after exposure to colloidal silica was found by Lee and Kelly (1992) and Warheit et al., 1991 and Warheit et al., 1995 at concentrations ≥50 mg/m3 (6 h/day, 5 days/week for 2 or 4 weeks). The test material was “Ludox grade CL-X”, obtained from Du Pont Chemicals and consisting of approximately 46% silica in water along with about 0.2% sodium oxide and 5% ethylene glycol. About 200 ppm of formaldehyde was present as a biocide. The pH of the liquid was 9 and the average primary particle size was about 22 nm. MMADs of the particles in

the test atmosphere were reported as 2.9, 3.3 and 3.7 μm for the 10, 50 or 150 mg/m3 groups, respectively. Three months after exposure, all biochemical parameters returned to control values. Lung-deposited silica particles were cleared rapidly from the lungs, with half-times of approximately 40 and 50 days for the 50 and 150 mg/m3 treatment groups, respectively. The lungs did not show formation of fibrotic scar Fenbendazole tissue or alveolar bronchiolarisation. The NOEL for Ludox in this study was at 10 mg/m3. Chen et al. (2008) found that pulmonary inflammation was more severe in old (20 months) rats than in young or adult rats after exposure to amorphous silica particles (purity >99.9%, particle size 37.9 ± 3.3 nm; specific surface area 6.83 × 105 cm2/g, particle number 1.52 × 1010 per μg; purchased from Jiangsu Haitai Nano Material Company Limited, Jiangsu/China). The rats were exposed for a period of 4 weeks at a concentration of 24.1 mg/m3 for 40 min/day. Cardiovascular function changes were observed only in old animals. Takizawa et al. (1988) tested food-grade micronised SAS by oral administration at dose levels of 0, 1.25, 2.5, and 5% for ca.