Review of Acute Human-Toxicity Estimates for Selected Chemical-Warfare Agents (1997)
Chapter: CONCLUSIONS AND RECOMMENDATIONS
Conclusions and Recommendations
The subcommittee's conclusions concerning CDEPAT's proposed estimates for GD are summarized in Table 4-1. Of the seven human-toxicity estimates for GD proposed by CDEPAT to protect soldiers from the toxic effects of CW agents, the subcommittee agrees that one estimate is scientifically valid. The subcommittee recommends that two of the estimates be lowered, and three be considered interim estimates. It also concludes that one estimate should be raised.
TABLE 4-1 Evaluation of Human-Toxicity Estimates for GD
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Human-Toxicity Estimates for GB |
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Toxicity Type |
Route and Form of Exposure |
Existing Estimates |
CDEPAT's Proposed Estimates |
Subcommittee's Evaluation of Proposed Estimates for GB |
Rationale for Subcommittee's Evaluation |
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LCt50a |
Percutaneous, vapor |
None |
2,500 mg-min/m3 |
Proposed estimate is scientifically valid |
Proposed estimate based on assumption that GD is 4 times more toxic than GB for percutaneous exposure |
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Inhalation, vapor |
70 mg-min/m3 |
35 mg-min/m3 |
Proposed estimate should be lowered |
Proposed estimate based on the assumption that GD and GB are equipotent via this route; subcommittee recommends that LCt50 estimate for GD be lowered to correspond to lowered estimate for GB; further research recommended |
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ECt50b |
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Threshold effects |
Percutaneous, vapor |
None |
300 mg-min/m3 |
Proposed estimate should serve as an interim value |
In the absence of adequate human or animal data, proposed estimate based on assumption that GD is 4 times more toxic than GB for percutaneous exposure; further research recommended |
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Severe effects |
Inhalation, vapor |
35 mg-min/m3 |
25 mg-min/m3 |
Proposed estimate should be lowered |
In the absence of adequate human or animal data, proposed estimate based on assumption that potenies of GD and GB are comparable; ECt 50 estimate for GD should be lowered to correspond to the lowered estimate for GB; further research recommended |
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Mild effects |
Inhalation, vapor |
None |
0.2 mg-min/m3 |
Proposed estimate should be raised |
In the absence of adequate human or animal data, proposed estimate based on assumption that GD is 2.5 times more potent than GB for miotic effects; subcommittee recommends that the LCt50 estimate for GD be raised to correspond to the recommended raised estimate for GB; further research recommended |
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Human-Toxicity Estimates for GB |
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Toxicity Type |
Route and Form of Exposure |
Existing Estimates |
CDEPAT's Proposed Estimates |
Subcommittee's Evaluation of Proposed Estimates for GB |
Rationale for Subcommittee's Evaluation |
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LD50c |
Percutaneous, liquid |
350 mg for 70-kg man |
350 mg for 70-kg man |
Proposed estimate should serve as an interim value |
Because of wide range of LD50 values in animals, subcommittee's confidence in the proposed estimate is low; CDEPAT's proposed estimate of 350 mg for 70-kg man should serve as an interim value; further research recommended |
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ED50d |
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Severe effects |
Percutaneous, liquid |
None |
200 mg for 70-kg man |
Proposed estimate should serve as an interim value |
In the absence of adequate human or animal data, proposed estimate was derived using the ID50e/LD50 ratio of 0.6; the subcommittee recommends that CDEPAT's proposed estimate serve as an interim value; further research recommended |
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a LCt50: Vapor exposure that produces lethality in 50% of the exposed animals. Ct refers to the product of concentration (c) and exposure time (t). Note that Ct is not necessarily a constant. b ECt50: Percutaneous vapor exposure or inhalation vapor exposure causing a defined effect (e.g., incapacitation, severe effects, mild effects, threshold effects). c LD50: Liquid dose causing lethality in 50% of the exposed animals. d ED50: Liquid dose causing a defined effect in 50% of the exposed animals. e ID50: Liquid dose causing incapacitation in 50% of the exposed population. |
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