A rationale for setting the 1,000-d acrolein SMAC and revising existing SMACs is provided.
NASA established the existing SMACs for acrolein in 1996 (Wong 1996). After the toxicologic information in the literature was assessed, one toxicologic end point was identified as being critical (mucosal irritation) and acceptable concentrations (ACs) were developed for this end point. Table 1-1 summarizes the SMACs established for acrolein using mucosal irritation as the toxicologic end point.
Acrolein exposure produces mucosal irritation at concentrations lower than those that produce histopathologic changes in the respiratory tract (Lyon et al. 1970, Weber-Tschopp et al. 1977, Feron et al. 1978, Steinhagen and Barrow 1984). In addition, the eye is more susceptible than the nose to irritation produced by acrolein (Weber-Tschopp et al. 1977). Therefore, both the 1- and 24-h SMACs were established based on minimizing irritation to the eye and nose and to preclude irreversible injury and significant crew performance decrements resulting from exposure.
The 1-h acrolein SMAC was based on the report of Weber-Tschopp et al. (1977) describing moderate eye irritation in humans after 1 h of exposure to acrolein at 0.3 part per million (ppm) (0.68 milligram per cubic meter [mg/m3]). Further evidence from the studies of Weber-Tschopp et al. indicates no effect on the eyes after exposure to acrolein at 0.15 ppm (0.34 mg/m3) for 1.5 min. In addition, Darley et al. (1960) reported decreased eye irritation at progressively lower acrolein exposure concentrations. They observed a reduction in reported eye irritancy (by half a grade, from moderate-to-severe to moderate) when acrolein concentration decreased by 35% to 40%. Weber-Tschopp et al. (1977) observed a reduction in reported eye irritation (from mildly irritating to no effect) when the acrolein exposure concentration declined by a factor of 4 (from 0.6 to 0.15 ppm).
Wong (1996) asserted that the sensitivity of the eyes and nose observed in humans toward irritation caused by acrolein depends on exposure concentration and duration. In longer exposures (1 h), irritation to the eyes prevails over irritation to the nose, whereas short exposures show more irritation to the nose (exposures ≤ 0.3 ppm for 40-60 min) (Weber-Tschopp et al. 1977, Wong 1996). Additionally, 1.5-min exposures to 0.6 ppm of acrolein caused similar irritation in the eyes and nose of human subjects, but 1.5-min exposures to 0.15 ppm of acrolein caused only slight nose irritation and no reported eye irritation (Weber-Tschopp et al. 1977). Wong (1996) proposed that acrolein exposure concentration is more influential than exposure duration in causing acute irritation in humans.