Toxicology of Industrial Compounds

124 PULMONARY TOXICITY STUDIES WITH MAN-MADE ORGANIC FIBRES
Table 8.1 Pulmonary inflammation and fibre biodurability in the lungs of
chrysotile asbestos and p-aramid-exposed rats
0 h=immediately after exposure; 5 D=5 days; 1 M=1 month; 3 M=3 months; 6
M=6 months;
ND=not determined.
Lung digestion/biodurability studies
Preliminary dimensional analysis studies demonstrated that median lengths
of fibres recovered from digested asbestos-exposed lung tissue were
increased over time suggesting that short asbestos fibres were selectively
cleared from the lungs, with apparent insignificant or pulmonary clearance
and greater durability/retention of long fibres (Table 8.1).
Preliminary studies with p-aramid fibrils recovered from the lungs of
exposed rats are consistent with earlier data suggesting biodegradability of
inhaled p-aramid fibrils (Warheit et al., 1992; Kelly et al., 1993)
(Table 8.1). These data also are in agreement with the results of a current
interim report authored by the Institute of Occupational Medicine in
Edinburgh, Scotland. In addition, as previously reported (Warheit et al.,
1992), a transient increase in fibre numbers at early postexposure time
periods was measured following cessation of exposure. These results
indicate that the increase in p-aramid fibres is due to fibre shortening and as
a consequence, increased numbers of shorter fibres. This is accounted for
by a substantial reduction in the median lengths of recovered fibres
concomitant with only a slight decrease in fibre diameter.