When considering the risks of exposure to environmental tobacco smoke (ETS) by nonsmokers, it is not enough to evaluate exposure and response. The actual dose received should be considered. Typically, for smokers, the exposure is given in terms of number of cigarettes smoked per day or cumulative pack-years. For nonsmokers, the exposure is usually characterized in terms of particle or gas concentration in micrograms per cubic meter. But what is known about the total integrated dose to the respiratory tract resulting from exposure to ETS by nonsmokers? What fraction of inspired particles and gases is deposited and fails to exit with the expired air? Moreover, what is the fate of the deposited smoke?
Although highly variable in concentration, ETS includes many of the same constituents as the smoke entering the active smoker’s lungs. Both particulate and gaseous phases are present, as described in Chapter 2. In principle, the retained dose for either inhaled particles or gases can be approximated in a straightforward manner:
The deposited dose, in micrograms per hour, equals the ventilation rate in cubic meters per hour times the concentration of particle or gas in the inspired air in milligrams per cubic meter ([C]), times the collection efficiency (CE). CE has no dimensions; it is the fraction of the inhaled particle or gas that deposits and thus