|Budget Amount *help
¥2,600,000 (Direct Cost : ¥2,600,000)
Fiscal Year 1999 : ¥1,000,000 (Direct Cost : ¥1,000,000)
Fiscal Year 1998 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1997 : ¥1,000,000 (Direct Cost : ¥1,000,000)
Carcinogencity of 12 types of fibrous samples (JFM standard) was evaluated by the incidence of peritoneal mesothelioma in female F344 rats two years after the intraperitoneal administration. Peritoneal mesothelioma were induced in the rats administered silicon carbide whisker (SC), UICC chrysotile B (UC), potassium titanate whisker(PT), ceramic fiber 1(RF 1), ceramic fiber 2(RF2) or aramid fiber(AR). No significant lethal effect and tumor induction was observed in rats exposed to mullite fiber (RF3), wollastonite (WO), rockwool (RW), glasswool (GW), TiO2 whisker (TO) or micro glass fiber (MG). The rat having peritoneal mesothelioma was found easily by the accumulation of bloody ascites. Tumor cells diffused on abdominal wall forming small nodules (1 to 3 mmφ). Adhesive proliferations between diaphragm and liver were observed in most mesothelioma case. There was no metastasis of tumor to remote organ or tissue in any rats. Histopathiogically, sarcomatous type and mixed type were more th
an the epithelial type. Among these mesotheliomas, 6% showed the osseous differentiation of tumor.
Based on these results, we tried to evaluate the carcinogenic potency of man-made fibers in comparison with UC. Because the dose of UC was logarithmically in inverse proportion with 50% survival period (due to mesothelioma), equivalent dose to UC could be calculated by the 50% survival period of SC and PT. When the number and weight ratios of UC, Sc and PT fibers are same, it is estimated that breathing air containing 1.3 X 10ィイD1-6ィエD1 fiber/ml (WHO) or 4×10ィイD1-6ィエD1 fiber/ml (EPA) of asbestos for entire life will result one life time risk for cancer in 1,000,000, identically, 0.5 X 10ィイD1-6ィエD1 fiber/ml (WHO) or 1.7 X 10ィイD1-6ィエD1 fiber/ml (EPA) of SC and 5.7x 10ィイD1-6ィエD1 fiber/ml (WHO) or 1.7x 10ィイD1-6ィエD1 fiber/ml (EPA) of PT have equal risk. On the regulation of working environment, 0.2 fiber/ml of asbestos is the permissible exposure limit (PEL-OSHA) and is equal to 0.09 fiber/ml for SC and 0.90 fiber/ml for PT. Threshold limit value (TLV-ACGIH) is 0.5 fiber/ml for asbestos and the level is equivalent to 0.21 fiber/ml for SC or 2.2 fiber/ml for PT. Less