Adequate Uncertainty Factor for Exposure Limit
am879 at FreeNet.Carleton.CA
Thu Oct 19 16:41:29 EST 1995
Brian C. Lee (bclee at access2.digex.net) writes:
> A liver carcinoma is considered benign? What kind of cell type was it?
> 25-fold sounds pretty low. Was there any human exposure data to show
> a non-carcinogenic exposure level?
Sorry, I was mistaken in my initial post. The 75 ppm LOEL in males rats
was for adenomas; carcinomas and adenomas were elevated at 375 ppm. The
current occupational exposure level is 10 ppm. The proposal was to reduce
that to 3 ppm in light of the new data, but that seems inadequate given the
LOEL for liver adenoma in male rats.
> : 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.
Ottawa, Ontario, CANADA
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