LC01 in female SD rats (the susceptible gender) are the points of departure for agent VX AEGL-3 estimations, which are thus protective. The AEGL values are estimates for VX vapor exposures only.

Uncertainty factors/rationale: Based on assumption previously stated from Grob and Harvey (1958) and Sidell and Groff (1974) studies showing that potency of agent VX is approximately 4 times that of agent GB (please see derivation for GB AEGL-3).

Total uncertainty factor: 100

Interspecies: 3—female rat data. The full default value of 10 is not considered appropriate because the mechanism of toxicity in lab rodents and humans is ChE inhibition.

Intraspecies: 10—for possible susceptible human individuals. Some individuals possess abnormally low levels of blood cholinesterase and carboxylesterase activity that may make them especially susceptible to the effects of cholinesterase inhibitors such as nerve agents (Morgan 1989; Wills 1972; Opresko et al. 1998). Therefore, a factor of 10 was retained.

Modifying factor: 3 (for sparse VX database).

Animal to human dosimetric adjustment: None applied (insufficient data)

Time scaling: Cn×t=k where n=2 and k=1.16×10−4 mg/m3×h, based on the assumption that the scaling function for agent VX is similar to that derived for agent GB from the experimental rat data of Mioduszewski et al. (2000, 2001, 2002a,b). Extrapolation from 6-h experimental value to 8-h AEGL-3.

Data adequacy: The scarcity of dose-response data for agent VX forces the AEGL analysis to rely on assumptions of relative potency. Thus, AEGL values for agent VX are derivative. The relative potency assumptions for estimating AEGL-3 values for agent VX from the available database for agent GB need experimental confirmation.

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