Rapid short-term clearance of chrysotile compared with amosite asbestos in the guinea pig

Compared with amphibole forms of asbestos, chrysotile asbestos fails to accumulate in lung tissue; the mechanism of this effect is disputed. To investigate this problem, we administered a mixture of the amphibole, amosite, and chrysotile to guinea pigs by intratracheal instillation. At 1 day, 1 week, and 1 month after instillation, animals were killed, and the numbers, types, sizes, and compositions of fibers in the lungs were determined by analytical electron microscopy. Both chrysotile and amosite fiber concentrations decreased with time, but relative chrysotile clearance was significantly greater than amosite clearance. There was no evidence of magnesium leaching from chrysotile fibers of any size at any time. Analysis of fiber lengths and widths showed a time trend toward shorter and narrower fibers (particularly toward fibers of less than 2 microns long and less than 0.025 microns wide) for chrysotile. This effect was not seen for amosite. We conclude that (1) failure of chrysotile accumulation in lung results from preferential chrysotile clearance during the first few days to weeks after exposure; (2) there is no evidence that fiber dissolution plays a role in chrysotile clearance; (3) preferential clearance may be a result of fragmentation and rapid removal of chrysotile fibers.