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Hamster response to chronic test toner inhalation
Hamsters (SG) were exposed 6 hours/day, 5 days/week for up to 18 months, to a special test toner at 0,4,16 or 64 mg/m³, TiO2 at 30 mg/m³ or SiO2 at 3 mg/m³ by the inhalation route, followed by a 5 months observation. The mean retained mass of toner, TiO2 and SiO2 at the termination of exposure were 0, 0.15, 0.87, 9.32 and 19.6 and 1.66 mg/ lung respectively. Mortality was lower than published values and causes of death were independent of treatment. There were no primary tumors of the usual epithelial types found in the lungs, nasal cavities and laryngo-pharynx of the control and toner exposed groups. Neuroendocrine cell hyperplasia and tumors were observed in the larynx and trachea which were independent of exposure. Interstitial fibrosis of a slight-very slight degree was observed in 49 per cent of toner medium, 83 per cent of toner high, 82 per cent of TiO2 and 91 per cent of SiO2 exposed groups. These responses, accompanied by the previously reported lung changes areascribed to LU NG OVERLOAD. An increased frequ ency of squamous cell proliferative lesions of the forestomach was detected in all particulate exposed groups. Since all treatment groups were affected, and there was no dose response relationship among of the toner groups, the effect is non-specific and is of no predictive value for assessing human carcinogenicity.