Document 4yr6xO4kD0ydJxd66kGZdgnV

AUTHOR/SCIENTIST KING (1946) VORWALD (1951) KLOSTERKOTTER (1968) TIMBRELL and SKIDMORE (1968) WEBSTER (1970) DAVIS (1972) GROSS (1974) SHORT vs. LONG ASBESTOS FIBERS METHOD OF STUDY Administered chrysotile fibers to rabbits by way of intratracheal injection. Same as above. Intratracheal or intra abdominal injection. Studies with rats and guinea pigs exposed to short-fibered amosite and long-fibered as bestos. Monkeys treated with a finely ground crocidolite dust. Injected long and short chrysotile fiber samples into the pleural cavities of mice. Injected chrysotile dust intratracheally into rats. FINDINGS/CONCLUSIONS A greater tissue reaction was reported in the animals that received the long fibers. "This appears to be due to the fact that the process of phagocytosis is easier with the shorter than with the longer fiber." "... the minimum length of fiber possessing the capacity to produce the typical peribronchiolar fibrosis in animals is somewhere between 20 and 50 microns." Both chrysotile and crocidolite ground to an average fiber length of less than 5 microns produced no fibrosis when injected intratra cheally or intra-abdominally. "A minimal reaction has been observed to short fibers but a marked reaction has been observed to the longer fibers." Obtained only a macrophage reaction in the lungs. "... The greatest point of difference is that long fiber dusts are the only ones to produce adhesions." Fibers less than 5 microns in length "could induce no more than a macrophage reaction." HWBUI0005910 AOTHOR/SCIENTIST HOLT (1965) STANTON and WRENCH (1972) STANTON (1972) SMITH (1972) MAROUDAS (1972) POTTS and FRIEPRfCfi (1972 ) SHORT vs. LONG ASBESTOS FIBERS METHOD OF STUDY Applied asbestos to the pleura of rats. Pleural response of rats in relation to fiber di mensions of glass. Injected hamsters intrapleurally with chrysotile. Studied incidence of meso thelioma in rats after vivo exposure to asbestos fibers Attempted to grow cultured fibroblasts in the pre sence of asbestos fibers. Same >s"above. S' 2- - FINDINGS/CONCLUSIONS Short fibers ("too small to be seen under the light microscope") do produce asbestosis in the guinea pig. Smaller fiber size was responsible for the de creased carcinogenicity. "Presumably, the 20-32 % tumor incidences resulting from this sample were related to those particles that re tained their fibrous structure in the optical range." "Morphologic observations indicated that fibers less than or equal to 8 microns in length were inactivated by phagocytosis. The negligible carcinogenicity of short fibers is perhaps re lated to the historical observation that vir tually all coarse and fine diameter fibers with lengths of 8 microns or less are efficiently trapped by phagocytes." Animals injected with less than 1 micron did not develop mesothelioma while those injected with fiber lengths of 5.3 to 6.9 microns did develop the tumor. Fibers less than 20 microns in length were not able to provide the necessary substrate for tumor growth, i.e., there were no mesotheliomas ob served in vivo or in vitro. Did repopte-'peritoneal mesothelioma with samples made^jip of fibers shorter than 2 microns. HWBUI0005911