This has been demonstrated for three different chrysotile samples from Canada, the United States, and Brazil. The initial results of the inhalation biopersistence study on the Canadian chrysotile were reported earlier.
This article presents the full results through 365 days after cessation of exposure. In order to fully understand the dynamics of the clearence of chrysotile from the lung, the study included a standardised inhalation biopersistence study following the recommendation of the European Commission (EC) Interim Protocol for the Inhalation Biopersistence of synthetic mineral fibers in which the lungs were digested to evaluate fiber content remaining. In addition, confocal microscopy was used to examine lungs in three dimensions to determine where and what size the remaining fibers were in the lung tissue.
The results showed that Canadian chrysotile is cleared from the lung with a clearance half-time of 11.4 days for the fibers longer than 20 pm. Canadian chrysotile clears in a range similar to that of glass and stone wools. It remains less biopersistent than ceramic and special purpose glasses and considerably less biopersistent than amphibole asbestos. At 1 yr after cessation of exposure, no long (L > 20 pm) chrysotile fibers remained in the lung. In contrast, with amosite asbestos there were 4 x 105 tong fibers (Z ) 20 p,m) remaining in the lungs at one year after cessation of exposure.