Inhalation Toxicity of Sarin (Gb) Vapor in Rats as a Function of Equilibration Time for Ten Minute Exposures

摘要

Characterizing the toxicity of airborne exposures to chemical warfare agents requires sensitive, accurate and reliable analytical chemistry methods as well as adequate methods for generating and controlling the test atmosphere. In addition to concentration and exposure time, it is necessary to examine what effect the chamber equilibration time (t99) has on measured biological endpoints for shorter duration inhalation exposures (i.e. less than or equal 10 minutes). The t99 is defined as the time necessary for an exposure chamber to reach 99% of its experimental concentration. Once this value is reached, the chamber concentration will not rise more than an additional 1%, regardless of exposure time. MacFarland (1975) has suggested that for short- term dynamic exposures, exposure time (t) should be greater than (or equal to) 13(t99) (MacFarland's Rule). Although there is no problem in adhering to this guideline for longer exposures (e.g. 60 or 240 min), adherence is not practical for exposures of 10 min or less where chamber dynamics will only allow the t99 value be kept to a minimum. The present study examined dose- response (lethality) relationships for GB vapor in rats derived from 10-minute exposures with t99 values that do not adhere to MacFarland's Rule, i.e., 2.1, 5.2, or 8 minutes. It was generally concluded that differences in LCt50 values collected under the above t99 conditions were minimal and would not be considered statistically significant.