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Environmental tobacco smoke (ETS), the smoke to which nonsmokers are exposed when they are in a room or house with smokers, is a complex mixture of chemical vapors and particles. Although the exposures of nonsmokers are much lower than those of smokers, there is some evidence that secondhand exposure to tobacco smoke increases the risks of heart disease, lung cancer, asthma and other diseases. The evidence, however, is often conflicting. For example, some studies indicate an increased risk of lung cancer from ETS exposures while other do not. One important reason for the uncertainties in scientific studies is that estimates of the amount of ETS to which nonsmokers are exposed are not quantitative. This makes it more difficult to determine the relationships between ETS exposure and risk of disease.
Many of the vapor-phase chemicals in ETS can be removed from air by sticking or “sorbing” to indoor surfaces (e.g., carpet or furnishings) and then be re-emitted back into the air at a later time. This sorption/desorption behavior is often evident from the odor of cigarette smoke in homes long after smoking has ceased. This means that the chemical composition of ETS changes over time, but we know very little about these dynamic changes or how these changes relate to measurements of single compounds used to trace exposures (e.g., measurements of nicotine in air).
One purpose of this study is to determine how well simple measurements of nicotine and/or a few other chemicals in air contaminated by cigarette smoke provide an estimate of the total exposure (to the entire complex mixture of ETS) for different smoking frequencies (light, medium, heavy) and ventilation rates (low, medium, high). Another purpose is to examine the effectiveness of ventilation in reducing exposures to the entire mixture of ETS, which includes vapors as well as particles. This research should also help improve exposure estimates determined from survey questionnaires by identifying key details to gather (e.g., whether windows are kept open during smoking periods or overnight). |
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Environmental tobacco smoke (ETS) is the complex mixture of ambient chemical vapors and particles that result from tobacco consumption. ETS contains the same toxic compounds inhaled directly by smokers, at lower concentrations and in varying proportions. There is strong evidence linking ETS exposure to a variety of health problems, including lung cancer, heart disease, asthma, and impaired respiratory function. Overall, ETS levels in buildings depend upon smoking periodicity and frequency, mixing volume (room size) and ventilation rate. ETS composition also changes over time as individual gases are selectively removed from air by their tendency to sorb (stick) to indoor surfaces. Sorption reduces exposure to some ETS constituents from recently emitted sidestream smoke, but later desorption can cause indirect exposure long after smoking ends. This project aimed to improve our understanding of the effect of sorption processes on ETS composition and exposure under realistic indoor conditions. Emphasis was placed on gas-phase organics in ETS that are established toxic air contaminants.
The main experimental focus of the project was to measure concentrations of representative ETS organic vapors, including the toxics 1,3-butadiene, acrolein, benzene, naphthalene, cresols, and ETS tracer compounds including nicotine and 3-ethenylpyridine, under varied smoking rate, room ventilation and furnishing levels in a simulated indoor environment. We developed a new concept of “exposure-relevant emission factors” (EREFs) to model exposure that includes the effect of initial sorptive losses and re-emission to and from indoor surfaces. EREFs were quantified for 26 ETS organic vapors in a series of 24 three-day experiments conducted in a living-room sized (50 m3) chamber. The chamber initially contained only painted wallboard and aluminum flooring, with carpet and furniture added in subsequent experiments. Cigarettes were machine smoked over three hours, and concentrations were measured during three daily periods that corresponded to active smoking, post-smoking and background. Smoking rate did not affect EREFs, indicating that sorption was directly related to air concentration. However, higher furnishing levels and lower room ventilation rates each substantially increased the amount of sorption, and thus decreased the effective exposure to less volatile toxics such as naphthalene, phenol, cresols, and to ETS tracers, with the largest effect seen for nicotine. These results highlight the importance of using emission factors that are appropriate to a specific environment to estimate exposures and of selecting tracers that adequately mimic the behavior of toxic ETS vapors. The results also indicated that indirect exposure that occurs outside of the presence of active smoking could be significant for some ETS toxics. A subsequent series of three four-week long experiments was conducted in the same room to investigate the effect of sorption processes on potential exposures when smoking occurs habitually on a daily basis. For sorbing compounds, concentrations during nonsmoking periods rose from day to day over the first one to two weeks. Once a steady cycle was obtained, potential indirect exposures during nonsmoking periods to compounds such as naphthalene and cresols were estimated to be about one-half of the total daily exposures. The experiments also demonstrated that ventilation rate is important with respect to the magnitude of indirect exposures. At two air changes per hour, the compounds are quickly removed from the room. As a result, overall exposures are lower and the majority of exposure to many ETS toxics occurs during active smoking.
This work made significant advancements in ETS exposure analysis methods and provided extensive emission factor and vapor-phase concentration data for a wide range of ETS toxics and tracers under realistic building conditions. These methods and data should enable researchers to more accurately assess risks from exposures to ETS organic vapors. The results also may help to direct public policy with respect to reducing ETS exposures. |
