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Suggested Citation:"Lethal Effects (LCt50)." National Research Council. 1997. Review of Acute Human-Toxicity Estimates for Selected Chemical-Warfare Agents. Washington, DC: The National Academies Press. doi: 10.17226/5825.
Page 61

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REVIEW OF ACUTE HUMAN-TOXICITY ESTIMATES FOR HD 61 of eight men (clothed, wearing protective gas masks, and not exercising) in which exposures of 500 mg-min/m3 for over 1 hr produced severe scrotal effects in four of the eight men (Heinen et al. 1945). The estimate is supported by the results of exposure to lower concentrations of HD in the same study. The subcommittee concludes that the proposed estimates for hot and moderate temperatures are scientifically valid. ECt50 for Threshold Effects CDEPAT's proposed ECt50 estimates for threshold (minimal) effects from percutaneous exposure to HD vapor are 50 mg-min/m3 for moderate temperatures and 25 mg-min/m3 for hot temperatures, assuming exposure durations of 30 to 50 min. There are no existing estimates for the threshold effects of HD (CDEPAT 1994). Human data used to support the proposed estimate, which apparently came from the Project Coordination Staff (PCS) report of 1946, were not given in sufficient detail in the CDEPAT report to allow for full evaluation. The PCS report concluded that the maximum safe exposure to HD for percutaneous exposure is 50 mg-min/m3. At that exposure, HD was associated with no important injury. More data on the effects of low vapor doses would have to be available to evaluate these estimates fully. The subcommittee recommends that these ECt50 estimates (for hot and moderate temperatures) serve as interim values until further research is conducted to establish the estimates with a greater degree of confidence. INHALATION VAPOR EXPOSURE Lethal Effects (LCt50) CDEPAT's proposed estimate for the LCt50 effects from inhalation exposures to HD vapor, assuming exposure durations of 2 to 10 min and minute volumes of 15 liters, was reduced from the existing value of 1,500 mg-min/m3 to the value of 900 mg-min/m3 (CDEPAT 1994). Because of the nature of the end point (lethality), the LCt50 estimates were based on animal data. CDEPAT averaged the LCt50 from all the 10-min LCt50 data in different animal species to arrive at its estimate. No animal LCt50 studies on HD are adequate for use in estimating the human

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No reliable acute-exposure1 standards have been established for the particular purpose of protecting soldiers from toxic exposures to chemical warfare (CW) agents. Some human-toxicity estimates are available for the most common CW agents—organophosphorus nerve agents and vesicants; however, most of those estimates were developed for offensive purposes (that is, to kill or incapacitate the enemy) and were intended to be interim values only. Because of the possibility of a chemical attack by a foreign power, the Army's Office of the Surgeon General asked the Army's Chemical Defense Equipment Process Action Team (CDEPAT) to review the toxicity data for the nerve agents GA (tabun), GB(sarin), GD (soman), GF, and VX, and the vesicant agent sulfur mustard (HD) and to establish a set of exposure limits that would be useful in protecting soldiers from toxic exposures to those agents. This report is an independent review of the CDEPAT report to determine the scientific validity of the proposed estimates.


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