Wednesday, May 11, 2005

Asbestos Effect Levels in Lab Studies

German colleagues provide a revealing review connecting laboratory studies of carcinogenicity of inhaled asbestos to those in people. The Houdini risk assessment community argues rats are too sensitive to particulate inhalation, since tumors [from particulates including asbestos] appear in rats, but not in mice or hamsters.

[Notably, solvent vapors cause lung tumors in mice but not rats under bioassay conditions. Therefore, the Houdinist community argues that people are like rats when it comes to vapors, and mice when it comes to particles.]

Rarely mentioned is the effect level in those studies, which is in the range of 1000 fibers/cc. BrooklynDodger opines that relative toxicity of alternative materials can be ballparked by comparing effect levels in laboratory studies, but that relative toxicity should be applied to effect levels of asbestos in people, not quantitated back from the lab tests in rats.

The investigators reviewed published data on the carcinogenicity of asbestos fibres in laboratory studies to compare effect levels to studies of exposure to man-made vitreous fibres (MMVF). [Now called synthetic mineral fibers, since some are likely made by women.]Various dust samples of chrysotile, crocidolite, and amosite were used as reference materials in studies with experimental animals. Data from biopersistence studies show that focusing only on fibres longer than 20 microm and using weighted half-time for a characterization of risk may be misleading. Inhalation experiments with rats need fibre exposure concentrations over 100 times higher to match the lung cancer risk of asbestos workers, and about 1,000 times higher to reach the same mesothelioma risk. Also, the striking difference between the low lung burden of amphibole fibres of asbestos workers with mesothelioma and the more than 1,000 times higher lung burden of rats with a low mesothelioma risk demonstrates the low sensitivity of the inhalation test model for the carcinogenic potency even of crocidolite fibres. The rat inhalation model is also not sensitive enough to predict the cancer risk of other fibre types for humans.

Int Arch Occup Environ Health. 2000 Jun;73 Suppl:S53-9.

Asbestos as reference material for fibre-induced cancer.

Muhle H, Pott F.Fraunhofer Institute of Toxicology and Aerosol Research, Hannover, Germany.

No comments: