The charge to the committee is to review the proposed AEGLs for scientific validity, completeness, internal consistency, and conformance to the 1993 National Research Council guidelines report; review the NAC’s research recommendations and—when appropriate—identify additional priorities for research to fill data gaps; and periodically review the recommended standard procedures for developing AEGLs.
This interim report presents the committee’s conclusions and recommendations for improving the NAC’s AEGL documents for 17 chemicals: acetaldehyde, arsenic trioxide, benzene, 1,3-butadiene, butane, chloroacetaldehyde, chlorobenzene, hexane, jet propellant fuels 5 and 8, ketene, methylene chloride, oleum, propane, propionaldehyde, sulfuric acid, sulfur trioxide, and trichloroethylene. It also summarizes the committee’s conclusions and recommendations for improving the SOP).
At its meeting held on October 27-29, 2009, the committee reviewed the AEGL technical support document (TSD) on acetaldehyde. A presentation on the TSD was made by Joanne Nijhof, of the Netherlands National Institute for Public Health and the Environment (RIVM). The following is excerpted from the executive summary of the TSD:
Acetaldehyde is a colorless, highly volatile liquid at ambient temperature and pressure…. Available data for acetaldehyde included several recent human volunteer studies with very short exposure times, and two older volunteer studies with longer and more relevant exposure periods. Animal data were available for lethal and non-lethal endpoints in various species, and included also genotoxicity and carcinogenicity data. The AEGL-1 values are based on [a] human volunteer study … where workers experienced only mild respiratory irritation and no eye irritation following chamber exposure to acetaldehyde at a measured concentration of 134 ppm for 30 minutes…. The AEGL-2 values are based on histopathological changes observed in a study in rats…. The AEGL-3 values are based on 4-hour lethality data in rats.
A revised document should be returned to the committee for review.
The committee recommends that the acetaldehyde and propionaldehyde TSDs be combined into one document because the observed effects are generally similar at comparable concentrations. The acetaldehyde TSD should provide more information on the metabolism of acetaldehyde in humans and its polymorphism. The AEGL-3 values for acetaldehyde were adopted for propionaldehyde.
The authors of the TSD state that the human exposure studies using aerosol exposures for durations of 2-4 min were not useful for AEGL derivations. Although the exposure durations of the studies were too short for this purpose, their results—bronchoconstriction and other respiratory airway effects—are certainly relevant to the uncertainty factor for intraspecies variability. That the experiments were done via mouth breathing does not invalidate their findings and relevance: a sizable fraction of people are primarily mouth breathers, and some may have nasal obstructions (such as colds) that result in mouth breathing. In addition, under substantial stress or exercise, as may occur during an emergency alert and evacuation order, breathing shifts to a mixture of nose and mouth breathing. Finally, even regular nose breathers will inhale some fraction of their respirations via the mouth. In an emergency situation, exposures may occur via the nose, the mouth, or both. Those exposure routes therefore are relevant for assessing the uncertainty factor (UF) or intraspecies variability.
A table should be developed to present the data from the human exposure experiments to facilitate review of exposure concentration and durations and the resulting health effects. It should be