Several constituents of SHS can be measured in air including nicotine, particulates, carbon monoxide, and other chemicals. The levels of these pollutants in the air of specific venues, when combined with information on frequency and duration of visits to those venues, allows estimation of an individual’s overall exposure to SHS. Concentrations of tobacco-derived pollutants in indoor workplaces where smoking is allowed can equal or exceed the levels in homes of smokers, and the highest workplace levels have been found in bars and smoking sections of aeroplanes. The California Environmental Protection Agency (EPA) has estimated that indoor levels of particulates in entertainment venues such as casinos can range from less than 15 mg/m3 in venues where smoking is prohibited to 350 mg/m3 in those in which smoking is allowed. Inside a closed vehicle, levels of over 1000 mg/m3 have been recorded.
Self-Reported Exposure To SHS
Because of the limitations of biomarkers as indicators of longer-term exposure, self-reports of exposure are used in many studies on health impacts of SHS, sometimes supplemented by measurement of biomarkers. The principal difficulty in self-reporting is in estimating the dose of SHS that an individual is exposed to. This has usually been estimated for indoor exposure by asking about the number of smokers nearby, the number of cigarettes consumed, and the number of hours of exposure. However, this neglects issues such as the size of the room and does not cover outdoor exposure such as at a bus stop. Many of the studies on health impact are based on reports of having a smoking spouse or, for children, whether the parents smoke or used to smoke. This imprecision hinders quantification of impacts and reduces the statistical power of epidemiological studies. Another source of error that may lead to underestimates of health impacts is that even those who consider themselves not exposed to SHS are often found to have measurable levels of biomarkers, which demonstrates how difficult it can be to avoid exposure to SHS.
Epidemiology
Prevalence Of Exposure
Although the magnitude of the risks for many of the chronic and fatal diseases associated with passive smoking are relatively small compared with those for active smoking, the potential exposure of nonsmokers is large. Such exposure can take place in the home, workplaces, leisure venues such as restaurants, bars, and bowling alleys, and public places such as shopping malls, streets, and bus stops, or anywhere that smoking is allowed. Even smokers are exposed to the SHS from other smokers and some recent studies have indicated an impact of SHS over and above that from active smoking.
The third National Health and Nutrition Examination Survey (NHANES) in the United States found that 88% of nonsmokers in 1988 had detectable serum cotinine levels indicating exposure to SHS. Among nonsmoking workers, the highest mean levels of cotinine were found in waiters (0.47 ng/mL) and the lowest in farmers and nursery workers (0.06 ng/mL) (Wortley et al., 2002). Since then, many states have made vast improvements in reducing exposure of nonsmokers. California, for example, is one of the leaders in smoke-free legislation and the proportion of workers there reporting smoke-free workplaces increased from 35% in 1990 to 93% in 1999 (Gilpin et al., 2002). Over the same period, the proportion of nonsmoking indoor workers in the state who were exposed to SHS decreased from 29% to 16% and the proportions of adults and those under 18 years with smoke-free homes rose from 38% to 74% and 82%, respectively. In Europe, exposure of nonsmokers to SHS at home or work declined from 41% to 24% over about 9 years from the early 1990s ( Janson et al., 2006). However, in other countries, smoke-free legislation has been slower and exposure of nonsmokers continues. For example, in Latin America in 2000 to 2002, airborne nicotine was discovered in over 90% of the public places surveyed (Navas-Acien et al., 2004). In many countries around 50% of children are exposed to SHS in their homes.