Carcinogenicity studies on natural and man-made fibres with the intraperitoneal test in rats.

Female Wistar rats were injected intraperitoneally (i.p.) with a suspension of 11 fibrous and 3 granular dusts. A dose of 0.25 mg actinolite or UICC chrysotile induced tumours of the peritoneum in more than 50% of the animals. Even 0.05 and 0.01 mg proved to be carcinogenic, although no adhesions of the abdominal organs could be observed. The findings are in conflict with the hypothesis that a scar is always the morphological precondition for the development of an asbestos-induced tumour. Actinolite injected i.p. in a solution of polyvinylpyridine-N-oxide gave a lower tumour incidence than when suspended only in saline, possibly due to inactivation of the fibre surface. Persistent glass fibres were less effective than actinolite having a similar fibre size distribution. On the other hand, relatively thick basalt fibres and ceramic fibres gave higher tumour incidences than expected. Wollastonite fibres were not carcinogenic, probably because of their low durability. Large amounts of polyvinylchloride, alpha-ferric oxide hydrate and wood dust also led only to adhesions of the abdominal organs and fibrosis; a definite carcinogenic effect was not detected.