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An Exposure System for Combined Administration of an Organic Solvent to Rodents by Inhalation and Water‐Drinking and its Operational Performance

An Exposure System for Combined Administration of an Organic Solvent to Rodents by Inhalation and Water‐Drinking and its Operational Performance: Hirokazu Kano, et al. Japan Bioassay Research Center, Japan Industrial Safety and Health Association—In order to obtain bioassay data for carcinogenicity and chronic toxicity of an organic solvent being absorbed into the body through multiple media by inhalation and ingestion, an exposure system for combined inhalation and oral exposures of rats to the organic solvent was constructed. Operational performance of the system was examined by monitoring air and water concentrations of chloroform or 1,4‐dioxane in both an inhalation exposure chamber and an automatic watering system, while groups of 50 male rats each were exposed to chloroform or 1,4‐dioxane by inhalation for 6 h/d, 5 d/wk and 104 wk and by water drinking for 24 h/d and 7 d/wk throughout the 104 wk. Day‐to‐day and time‐to‐time variations in concentrations in the exposure chamber were maintained at less than 0.8% C.V. and 4.8% C.V., respectively, in the case of chloroform, and less than 1.2% and 8.1 %, respectively, in the case of 1,4‐dioxane. The mean 6‐h averaged concentrations deviated by less than 0.4% from the respective target concentrations for all sets of the combined exposures. The watering system which was composed of a drinking valve, in‐between piping, a container and a solenoid drainage valve was used for giving ad libitum drinking water containing 1000 ppm chloroform or 1,4‐dioxane to rats. Mean water concentrations of chloroform and 1,4‐dioxane were attenuated by 3‐8% and by 1% in the container after 1 ‐week's supply, respectively. It was concluded that this exposure system can give accurate and reproducible air and water concentrations of chloroform and 1,4‐dioxane for long‐term combined inhalation and oral exposure.