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. Aging probably affects the bioavailability, as well as physicochemical characteristics, of the smoke. 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. These methods are frequently criticized because of differences in the way the smoke constituents are presented to the test system as compared with that which occurs in the human situation.
Several methods are available to evaluate the potential health effects of inhaled pollutants.
Direct measurement requires analysis of major components and their metabolites in tissues as well as in urine and feces or measurement of the amounts of material in the inspired and expired air. Aside from calculating dose based upon particle aerodynamic size and physiological data on lung function of experimental animals, tracers can provide reasonable estimates of exposure. Inhalation exposure chambers are used for those studies in which whole-body exposure is desired. The ability to expose a large number of animals at one time and the absence of a need to restrain or anesthetize the animals are among the advantages in using this approach. There are, however, several major disadvantages.