Toxicology of Industrial Compounds

102 CARCINOGENIC POTENTIAL OF MAN-MADE VITREOUS FIBERS
Table 7.4 Summary of lung pathology findings in fibrous glass inhalation study in
rats
a WHO fibers=fibers with length/diameter ≥3, length >5 µm, and diameter 5 µm, and a diameter 10 µm in length in the lung were similar for each of the
different MMVF types (Figures 7.2(a) and 7.2(b)). However, greater
numbers of long fibers (>20 µm. long) were found in the lungs of rats
exposed to RCF 1 and MMVF 21 (rock wool) than for the other fiber
types (Figure 7.2(c)). Even though lung levels of long MMVF 21 fibers
were higher than long RCF 1 fibers, lung fibrosis occurred much later for
MMVF 21 (18 vs 6 months for RCF 1) and no mesotheliomas or significant
increase in lung tumors were observed for MMVF 21. This indicates that
the lung pathogenic potential of a fiber may be determined by more than
dose and dimension.