ABSTRACT
The available literature addressing the toxicity of VX vapor includes two studies that dealt with the toxic effects of chemically neutralized VX in rats (Manthei et al., 1990; Muse et al . , 2002). Several studies have dealt with either aerosolized VX (Bide and Risk, 2000) or VX mixed with other compounds (Weimer and Ballard, 1960; Dimmick et al., 1979). One recent study examined the toxicity of VX vapor inhalation in rats using a “ nose-only ” exposure design (Bide et al., 1996), but did not address the issue of fi rst noticeable effect (FNE) associated with very low concentrations of VX vapor. The concept of FNE is used to defi ne the threshold concentrations of nerve agents below which there are no observable effects and above which more severe measurable effects are produced. Defi ning the FNE for a whole-body inhalation exposure to VX vapor is necessary for any comprehensive risk assessment dealing with exposure to VX vapor. Previous studies in our laboratory using GB (Mioduszewski et al., 2002) and GF (Whalley et al., 2004) vapor have shown miosis to be the FNE resulting from a whole-body inhalation exposure. In those two studies and the present study, miosis was used as the experimental end point. Miosis was defi ned as a 50% reduction in pupil diameter relative to preexposure baseline measurements.
