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Suggested Citation:"ECt50 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 37

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REVIEW OF ACUTE HUMAN-TOXICITY ESTIMATES FOR GD (SOMAN) 37 until further research is conducted to establish the ECt50 estimate for thresh-old effects with a greater degree of confidence. INHALATION VAPOR EXPOSURE Lethal Effects (LCt50) CDEPAT's proposed estimate for the LCt50 following inhalation exposure to GD vapor is 35 mg-min/m3, assuming exposure durations of 2 to 10 min, minute volumes of 15 liters, and moderate temperatures. The existing toxicity estimate is 70 mg-min/m3. CDEPAT's proposed estimate for the LCt50 is based on the assumption that GD and GB are equipotent. The equipotency of GD and GB via inhalation is supported by recent data reported by Schoene et al. (1985). The subcommittee agrees with CDEPAT's approach of basing the LCt50 estimate for GD on toxicity data from GB for reasons previously stated. The subcommittee also agrees with CDEPAT's conclusion that the confidence in the LCt50 estimate is low because the data on both compounds are sparse. Because the subcommittee recommends lowering the LCt50 estimate for GB, it also recommends that the estimate for GD be lowered correspondingly. The subcommittee recommends that further research be conducted to establish the LCt50 estimate with a greater degree of confidence. ECt50 for Severe Effects CDEPAT's proposed estimate for ECt50 for severe effects following inhalation exposure to GD vapor is 25 mg-min/m3, assuming exposure durations of 2 to 10 min, minute volumes of 15 liters, and moderate temperatures. The existing toxicity estimate is 35 mg-min/m3, (CDEPAT 1994). The inhalation data needed to develop an estimate for the severe effects of GD are insufficient. CDEPAT assumed that the potencies of GD and GB via the inhalation route are comparable and proposed identical toxicity estimates. The subcommittee agrees with CDEPAT's approach of basing the ECt50 estimate for GD on toxicity data from GB, because (1) GD and GB belong to the same class of chemicals (organophosphates) and are structurally similar, and (2) animal data support the assumption that GD is equipo

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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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