Dose concepts for inhaled vapors and gases.

"Dose" for any toxicant is a shifting concept; thus, there is a frequent need for modifiers such as "administered" or "effective," when referring to dose. When applied to inhaled gases and vapors, "dose" is even more vague. The wide range of physicochemical properties associated with gases and vapors, the different target tissues that may be affected, and the variety of mechanisms involved in producing toxic effects combine to make a useful dose descriptor for one gas inadequate for another. Although models have been developed to describe dose for inhaled gases and vapors having a broad range of properties, it is often not clear which models are appropriate for which inhalant. In an attempt to resolve this dilemma, a classification scheme for inhaled gases and vapors, based on physicochemical properties, is offered in this report. In addition, various concepts of dose for inhaled gases and vapors are discussed with reference to the classification scheme. Finally, avenues for further research in the area of gas and vapor dosimetry are suggested.