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Suggested Citation:"ED50 for Severe Effects." 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.
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Page 24

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REVIEW OF ACUTE HUMAN-TOXICITY ESTIMATES FOR GA (TABUN) 24 mate could be greater than 0.5 mg-min/m3. At concentrations of 0.7 mg-min/m3 and exposure periods ranging from 2 to 10 min, GA could be detected by smell (Udhe and Moore 1945). However, the number of volunteers detecting the odor was not specified. Tightness of the chest was also observed at exposures of 0.7 mg-min/m3 (Udhe and Moore 1945). In the same study, tightness of the chest and miosis, with impaired vision, occurred at doses ranging from 3.2 to 30 mg-min/m 3 (Udhe and Moore 1945). At higher vapor doses, those effects were accompanied by severe eye pain, headaches, nausea, and vomiting. On the basis of the review of the available data, the subcommittee concludes that CDEPAT's proposed estimate of 0.5 mg-min/m3 can be raised. The subcommittee recommends that further research be conducted to establish the ECt50 estimate with a greater degree of confidence. PERCUTANEOUS LIQUID EXPOSURE Lethal Effects (LD50) CDEPAT's proposed LD50 for percutaneous exposure to GA liquid on bare skin is 1,500 mg for a 70-kg man. The proposed LD50 estimate does not differ from the existing estimate (CDEPAT 1994). LD50 values reported for animals ranged from 1 mg/kg for mice to 30 to 50 mg/kg for dogs. However, it is difficult to use those data for predicting the human LD50 estimate because many of the animal studies involved the use of depilated animals (animals whose hair was removed chemically, thus making them more susceptible to toxic effects of chemicals) and others tested only crude material. The proposed LD50 estimate for men was based on animal data without the use of uncertainty factors to account for inter-species variability. Thus, the subcommittee concludes that the proposed LD50 value for humans is not scientifically defensible because it is based on the use of limited animal data without the use of uncertainty factors. The subcommittee recommends that the proposed estimate be lowered until further research is conducted on GA to establish an LD50 estimate With a greater degree of confidence. ED50 for Severe Effects CDEPAT's proposed estimate for the ED50 for severe effects (that is,

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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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