Little is known about the sources or magnitudes of exposure to 243 compounds designated by California legislation as "toxic air contaminants" (TACs). This study estimates the contribution of environmental tobacco smoke (ETS) to the exposure of nonsmoking Californians for 17 of these compounds known to be emitted from burning tobacco. Two distinct approaches were used in the assessment: (a) measured 24-h personal exposures to selected compounds, such as benzene, were compared for individuals who reported ETS exposure against those who reported no exposure; and (b) information on activity patterns of Californians was combined with estimates of ETS concentrations in indoor environments. The first method was applied for nonsmokers (age Ò 7 y) for the mid-to-late 1980’s. The second method was separately applied for adults, adolescents, and children for both the mid-to-late 1980’s and for the late 1990’s. Averaged over all nonsmoking Californians in the late 1980’s, ETS is estimated to have contributed 5-15 µg h m-3 to daily benzene exposure, corresponding to 2-5% of the total inhalation exposure of nonsmokers. Among those nonsmokers exposed to ETS, average exposure for adolescents was in the range 65-95% of the average for adults; the corresponding range for children was 80-130%. In the late 1990’s, as a result of reduced smoking prevalence among adults and legislation that severely restricts smoking in public buildings, ETS exposures are estimated to be reduced. The fraction of adult nonsmokers exposed to ETS indoors on a given day is predicted to have declined from 52% to 16-19% during the last decade. For adolescents, the corresponding change is from 63% to 33-35%, whereas for children the reduction is from 33% to 21-23% exposed. Among individuals still exposed, the average level of exposure is not predicted to have changed markedly. Using emission factor data, ETS contributions to exposure are estimated for these compounds: acetaldehyde, acetonitrile, acrylonitrile, benzene, 1,3-butadiene, 2-butanone, o-cresol, m,p-cresol, ethyl acrylate (upper bound, only), ethylbenzene, formaldehyde, n-nitrosodimethylamine, phenol, styrene, toluene, o-xylene, and m,p-xylene.

Environmental tobacco smoke contributes significantly to the exposure of nonsmokers to toxic air contaminants. Among nonsmoking Californians exposed to ETS, the estimated average contribution of ETS was 3-10% of total benzene exposure in the mid to late 1980s (see Table 5.10). For styrene and xylenes, ETS is also a significant contributor to nonsmokers’ exposure, responsible for 6-18% of average styrene exposure, 1-8% of average o-xylene exposure, and 1-5% of average m,p-xylene exposure (again, among nonsmokers exposed to ETS; see Table 5.10). Averaged over all nonsmoking Californians, the corresponding contributions of ETS to total inhalation exposures were 2-5% for benzene, 3-10% for styrene, 0.4-5% for o-xylene, and 1-3% for m,p-xylene (see Table 5.11). For other toxic air contaminants considered in this study – acetaldehyde, acetonitrile, acrylonitrile, 1,3-butadiene, 2-butanone, o-cresol, m,p-cresol, ethyl acrylate, ethylbenzene, formaldehyde, n-nitrosodimethylamine, phenol, and toluene – the extent of exposure from ETS was quantified (see Tables 5.3-5.5), but total human exposures are unknown. As of the late 1980’s, the most important exposure sites for adults were in one’s own home and in occupational settings, together contributing about 60% to the total ETS exposure (see Figure 5.3). For adolescents and children, residential exposures dominated, contributing roughly half of the total for adolescents and 70-75% of the total for children (see Figures 5.4 and 5.5). Among those nonsmokers exposed to ETS, average exposure for adolescents was in the range 65-95% of the average for adults; the corresponding range for children was 80-130% (see data in Table 5.10). Again, among those exposed, mean daily exposure to benzene from ETS is estimated to have been in the range 9-31 µg h m-3 for adults, 9-20 µg h m-3 for adolescents, and 12-24 µg h m-3 for children, with the ranges being indicative of the uncertainty in the estimates (see Tables 5.3-5.5).

As of the late 1990’s, following implementation of AB13, smoking is no longer permitted in most workplaces in California. Assuming the law is observed, the only significant remaining indoor sites of ETS exposure are in private residences and in vehicles. The prevalence of smoking among adult Californians has also declined during the 1990’s (see Figure 6.1), reducing the frequency and intensity of ETS exposure. These factors are estimated to have substantially reduced the exposure to toxic air contaminants from ETS, primarily by reducing the number of people exposed on a given day. For nonsmoking adults in California, the percentage exposed to ETS on a given day (in microenvironments modeled in this study) is estimated to have declined from 52% in the late 1980’s to 16-19% in the late 1990’s. Corresponding changes for adolescents are from 63% to 33-35% and for children from 33% to 21-23% (see Figure 3.4). The reduction in the mean exposure for all nonsmokers is predicted to be in the range 60-75% for adults, 40-50% for adolescents, and 20-40% for children (see Table 6.8 and Figure 6.10). The proportionally smaller reduction for adolescents and children is predicted because, relative to adults, a larger portion of their exposure occurs in unregulated indoor environments such as private residences. Although the number exposed has declined, average exposure levels for those who remain exposed have not changed markedly, especially for adolescents and children (compare Tables 5.3-5.5 to Tables 6.2-6.4). Among those exposed, mean daily exposure to benzene from ETS in the late 1990s is estimated to be in the range 12-21 µg h m-3 for adults, 9-22 µg h m-3 for adolescents, and 12-28 µg h m-3 for children (see Tables 6.2-6.4). A large portion of the late 1990s exposure is predicted to occur in personal residences, contributing 58-69% of the total exposure for adults, 58-66% for adolescents, and 72-83% for children (see Figures 6.6-6.8). The average daily exposures to 17 toxic air contaminants were estimated for the Californian nonsmoking population, separately for adults, adolescents, and children, for late 1990’s, both for those exposed to ETS on a given day (Tables 6.2-6.4) and for all nonsmokers (Table 6.8). Information on the variability of exposures among individuals is also provided (Figures 6.4 and 6.5).