The Acute Exposure Guideline Level (AEGL) program: applications of physiologically based pharmacokinetic modeling

The primary aim of the Acute Exposure Guideline Level (AEGL) program is to develop scientifically credible limits for once-in-a-lifetime or rare acute inhalation exposures to high-priority, hazardous chemicals. The program was developed because of the need of communities for information on hazardous chemicals to assist in emergency planning, notification, and response, as well as the training of emergency response personnel. AEGLs are applicable to the general population, including children, the elderly, and other potentially susceptible subpopulations. AEGLs are the airborne concentrations of chemicals above which a person could experience notable discomfort or irritation (AEGL-1); serious, long-lasting health effects (AEGL-2); and life-threatening effects or death (AEGL-3). AEGLs are determined for five exposure periods (10 and 30 min and 1, 4, and 8 h). Physiologically based pharmacokinetic (PBPK) models can be very useful in the interspecies and time scaling often required here. PBPK models are used for the current article to predict AEGLs for trichlorethylene (TCE), based on the time course of TCE in the blood and/or brain of rats and humans. These AEGLs are compared to values obtained by standard time-scaling methods. Comprehensive toxicity assessment documents for each chemical under consideration are prepared by the National Advisory Committee for AEGLs, a panel comprised of representatives of federal, state, and local governmental agencies, as well as industry and private-sector organizations. The documents are developed according to National Research Council (NRC) guidelines and must be reviewed by the NRC Subcommittee on Acute Exposure Guideline Levels before becoming final. AEGLs for 18 chemicals have been published, and it is anticipated that 40 to 50 chemicals will be evaluated annually.