MESOTHELIOMA IN RATS FOLLOWING INTRAPLEURAL INJECTION OF CHRYSOTILE AND PHOSPHORYLATED CHRYSOTILE (CHRYSOPHOSPHATE)

Pathological effects of asbestos are probably dependent on the size and surface properties of the fibers. Surface-modified chrysotile fibers were injected into the pleural cavity of rats to investigate the potency of the fiber to induce mesothelioma. Chrysotile fibers were modified by a phosphorylation process, resulting in the presence of phosphorus at the fiber surface. Phosphorylated samples were characterized by enhanced durability and reduced affinity for biological macromolecules. Five samples were tested: 1 untreated and 4 phosphorylated. ChrP1, ChrP2 and ChrP3 corresponded to phosphorylated samples obtained by first, second and third passages through an Alpine classifier; Pm was defibrillated ChrP1. The number of fibers per microgram and the size distribution were determined by transmission electron microscopy and classified in 4 size groups. Groups of 35 rats were inoculated with 20 mg of fibers suspended in 0.9% NaCl solution. No mesothelioma was found in the saline controls. All fiber samples were proficient in producing mesothelioma; the percentages were different between groups and untreated chrysotile but not significantly so. The differences may be explained on the basis of the number of fibers injected which were > 8-mu-m in length and < 0.25-mu-m in diameter. The findings of a proficiency of long fibers to produce mesothelioma, previously reported by others for glass fibers, could be applied to chrysotile.