Suitable methods for assessing the potential for adverse health effects resulting from exposure to environmental tobacco smoke (ETS) are limited by the complexity of the composition of the mixture. In vivo and in vitro assays are commonly used to establish carcinogenicity and in some cases to extrapolate risks to humans. For complex mixtures such as ETS, these assays may be done on the mixture itself or on individual chemical constituents. Many properties of ETS change as the smoke “ages” after its initial generation. Aging probably affects the bioavailability, as well as physicochemical characteristics, of the smoke.
As inhalation is the primary route by which humans are exposed to tobacco smoke, it is obviously the preferred method of administration in animal models for evaluating the toxicological properties of both cigarette smoke and ETS. While extensive inhalation studies have been performed on the toxicological properties of mainstream cigarette smoke (MS), far fewer studies have been performed on sidestream smoke (SS) and ETS. The selection of appropriate animal models requires familiarity with exposure systems, as well as with basic anatomical differences between the model and human respiratory tracts.
Methods other than inhalation, such as in vitro assays, have been developed for the evaluation of MS. A few of these methods have been applied to the assessment of the relative toxicological properties of SS versus MS. These methods are frequently criticized because of differences in the way the smoke constituents