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J Occup Health year 2006 volume 48 number 1 page 44 - 48
Classification Original
Title The Effect of Lung Burden on Biopersistence and Pulmonary Effects in Rats Exposed to Potassium Octatitanate Whiskers by Intratracheal Instillation
Author Takako OYABU1, Hiroshi YAMATO1, Akira OGAMI1, Yasuo MORIMOTO1, Izumi AKIYAMA2, Sumiyo ISHIMATSU3, Hajime HORI3 and Isamu TANAKA1
Organization 1Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health, 2Occupational Health Care Office, Mishima plant, Toray Industries, Inc. and 3School of Health Sciences, University of Occupational and Environmental Health, Japan
Keywords Lung burden, Biopersistence, Pulmonary effect, Potassium octatitanate whisker, Intratracheal instillation
Correspondence T. Oyabu, Department of Environmental Health Engineering, Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health, 1-1 Iseigaoka, Yahatanishi, Kitakyushu, Fukuoka 807-8555, Japan
(e-mail: toyabu@med.uoeh-u.ac.jp)
Abstract The Effect of Lung Burden on Biopersistence and Pulmonary Effects in Rats Exposed to Potassium Octatitanate Whiskers by Intratracheal Instillation: Takako OYABU, et al. Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health-In our previous inhalation studies on health effects of the asbestos substitute, potassium octatitanate whiskers (POW), we showed that an excess amount of POW deposition in the rat lung increased biopersistence resulting in fibrotic changes. The critical deposition amount which induced the higher biopersistence was estimated to lie between 1.5 mg and 2.4 mg. In order to find the exact amount, the relationship between the lung POW burden and biopersistence was investigated by the intratracheal instillation method. The chemical formula of POW is K2Ti8O17 and the geometric mean fiber diameter (geometric standard deviation, GSD) and geometric mean fiber length (GSD) are 0.35 microm (1.6) and 4.4 microm (2.7), respectively. Rats were intratracheally instilled with 0.5 mg, 1.0 mg, 2.0 mg or 5.0 mg of POW and sacrificed at 1day and 1, 3, 6 and 12 months after the instillation. The POW amount in each lung was chemically analyzed by ICP-AES after microwave digestion and the biological half time (BHT) of each POW dose was calculated. The BHTs of each group were 10, 15, 20 and 42 months for 0.5, 1.0, 2.0 and 5.0 mg of POW, respectively, and BHT showed a linear dose-dependent increase, but without a threshold within the range of 0.5 mg to 5.0 mg, which was recognized in our earlier inhalation studies. In the histopathological photograph just after the instillation, many macrophages, which had phagocytized many more fibers, existed around the bronchiole compared with the earlier inhalation study at almost the same deposited amount. The relationship between POW amount and biopersistence in this intratracheal instillation study was different from that of our previous inhalation studies, probably due to the unnatural method of the fiber introduction to the lung, which in turn led to a different fiber distribution. It is suggested that an intratracheal instillation study is not an appropriate method for estimating excess deposition amounts of POW and an inhalation study will be needed. However, this intratracheal instillation study clarified that the clearance of POW was delayed as compared with previous inhalation studies at similar deposition amounts and this result has importance for the hazard assessment of dusts in animal experiments.