With the initial understanding of the relationship of asbestos to disease, little information was available on whether the two different groups of minerals which are called asbestos were of similar or different potency in causing disease. Asbestos was often described as a durable fiber which if inhaled would remain in the lung and cause disease. It has been only morerecently with the development of a standardised protocol for evaluating the biopersistence of mineral fibers in the lung that the clearance kinetics of the serpentine chrysotile have been shown to be dramatically different from those of amphibole asbestos with chrysotile clearing rapidly from the lung. In addition, recent epidemiology studies also differentiate chrysotile form amphibole asbestos.
The above mentioned biopersistence studies have indicated that chrysotile from Canada and California clear rapidly from the lung once inhaled. However, variations in chrysotile mineralogy have been reported depending upon the region. This is most likely associated with variations in the forces which created the chrysotile fibers centuries ago. In the present study, the dynamics and rate of clearance of chrysotile from the Cana Brava mine in central Brazil was evaluated in a comparable inhalation biopersistence study in the rat.
For synthetic vitreous fibers, the biopersistence of the fibers longer than 20 µm has been found to be directly related to their potential to cause disease. This study was designed to determine lung clearance (biopersistence) and translocation and distribution within the lung. As the long fibers have been shown to have the greatest potential for pathogenicity, the chrysotile samples were specifically chosen to have more than 450 fibers/cm3 longer than 20 µm in length present in the exposure aerosol.