US EPA's acute reference exposure methodology for acute inhalation exposures.

The US Environmental Protection Agency (EPA) National Center for Environmental Assessment is engaged in the development of a methodology for Agency use to perform risk assessments for non-cancer effects due to acute inhalation exposures. The methodology will provide general guidance for deriving chemical-specific acute exposure benchmarks called acute reference exposures (AREs). Chemical-specific AREs are analogous to reference concentra tions (RfCs) for chronic non-cancer effects and will be incorporated in chemical-specific files in the US EPA's Integrated Risk Information System (IRIS) as they are developed and reviewed. AREs will have wide applicability in assessing the potential health risks of accidental and routine acute releases of chemicals to the environment. The proposed methodology for ARE development provides a framework for choosing an optimal derivation approach, depending on the type of data available, from the no-observed-adverse-effect level (NOAEL), benchmark concentration (BMC), or categorical regression approaches. Uncertainty factors are applied to the point of departure, determined by one of the recommended approaches, to derive the ARE. Due to the capability to use more exposure-response information than the NOAEL approach allows, exposure-response analyses such as BMC and categorical regression are favored as methods to develop the point of departure when the available database will support such analyses. The NOAEL approach is suitable when the data are insufficient to support exposure-response modeling. Applications of the proposed ARE methodology are illustrated by the derivation of example AREs for hydrogen sulfide and hexachlorocyclopentadiene, which showcase the categorical regression and NOAEL approaches, respectively. In addition, a recent review of the proposed ARE methodology by the US EPA Risk Assessment Forum is discussed.