Adequate Uncertainty Factor for Exposure Limit

Brian C. Lee bclee at
Thu Oct 19 00:58:41 EST 1995

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?

Lawrence Segal (am879 at FreeNet.Carleton.CA) wrote:
: 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.  

bclee at     brian.lee at
Miscellaneous Et Cetera    Potomac, MD  USA

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