I am currently reviewing information concerning a proposed occupational
exposure limit for an industrial chemical. The substance is a
non-genotoxic carcinogen, which has been tested in both mouse and rat
chronic/onco studies. In males of both species, statistically significant
increases in liver adenomas/carcinomas were observed at exposure levels of
75 ppm. The company that manufactures the substance is proposing a TWA
occupational exposure limit of 3 ppm. This provides a 25-fold
uncertainty factor applied to the LOEL in the rodent studies. The company
considers this to be an adequate safety factor, because the liver tumours
were benign, there was no significant increase in mortality at 75 ppm
relative to control, and the latency period was long.
I find the 25-fold safety factor being proposed for this substance too
small. I would have thought a safety factor of *at least* 100 fold would
be more appropriate for a non-genotoxic carcinogen such as this.
Do any of the readers of the newsgroup, especially those in regulatory
agencies, have comments regarding the adequacy of the proposed 25-fold
safety factor?
--
Lawrence Segal
Ottawa, Ontario, CANADA
