From a study conducted in Munich, Scherer et al. reported mean concentrations of nicotine in the living room at about 4 µg/m3 in 20 smokers’ homes, about 200´ as large as the mean for ten nonsmoking homes. Matt et al. used passive samplers to measure gas-phase nicotine concentrations in San Diego County homes with infants of mothers who did or didn’t smoke. The study sites included three groups: “no exposure” with non-smoking mothers and no indoor smoking; “indirect exposure” with maternal smokers but no indoor smoking; and “direct exposure” , with maternal smokers and unrestricted indoor smoking. The indoor air nicotine levels varied systematically across the three groups households, with geometric means reported for both living rooms and the infant’s bedroom. For the no exposure group, levels were 0.10 µg/m3 in the living room and 0.09 µg/m3 in the infant’s bedroom. For the indirect exposure group, geometric mean concentrations were 0.32 µg/m3 in the living room and 0.23 µg/m3 in the infant’s bedroom. The direct exposure group had geometric mean concentrations of 2.6 µg/m3 in the living room and 1.5 µg/m3 in the infant’s bedroom. Gehring et al. measured nicotine concentrations in the homes of 347 German and 335 Dutch children using passive samplers. In homes with a light to moderate smoker , the median nicotine concentrations were 0.59 µg/m3 in Germany and 0.25 µg/m3 in the Netherlands. In homes with a heavier smoker the median nicotine concentrations were 1.4 µg/m3 in Germany and 0.65 µg/m3 in the Netherlands. A Korean study reported a median concentration of 3.2 µg/m3 in ten homes with smokers consuming ≥ 6 cigarettes/day. In summary, in homes where no smoking occurs and no smokers live, gas-phase nicotine levels tend to be less than about 0.1 µg/m3 ; in homes with moderate smoking, nicotine levels are commonly between 0.3 and 1 µg/m3 ; and in homes with heavy smoking,flood table levels are between 1 and 5 µg/m3. At 25 °C, nicotine’s vapor pressure is reported to be 0.11 mm Hg and 6 Pa. Its log value has been calculated to be 8.1.
Nicotine’s partitioning to airborne particles and settled dust, if water contents are low, is expected to be dominated by sorption to weakly polar organic matter in the particles or dust, and can be estimated using the octanol-air partition coefficient . When this condition holds, a semivolatile compound’s dust/gas partition coefficient is expected to be lower than the particle/gas partition coefficient , with reported central tendencies of Kd/Kp being 0.12 and 0.25.Based on several studies, in environmental tobacco smoke , ~ 95% of indoor airborne nicotine is gaseous . Typical indoor particle concentrations are lower than particle levels in smoking environments, which would further favor nicotine’s presence in the gas phase. However, indoor particles may have a larger water content and lower pH than the particle phase of ETS. Hence, it is difficult to estimate the fraction of airborne nicotine that is gaseous in indoor environments without active smoking. Regardless, nicotine is often detected in samples of household dust. The total amount of nicotine in dust or particles is expected to be enhanced if the dust is acidic and if there is sufficient associated water for ionization to occur. Matt et al. collected vacuumed floor dust samples from the same San Diego homes where they measured gas-phase nicotine with passive samplers. In the 13 homes with indirect exposure, the geometric mean nicotine levels in dust were 1.8 µg/m2 in the living room and 0.7 µg/m2 in the infant’s bedroom. Corresponding results in the 15 homes with direct exposure were 6.9 µg/m2 in the living room and 5.4 µg/m2 in the infant’s bedrooms. Willers et al. collected dust samples from the homes of 23 children with asthma using two different methods. Among these households, n = 8 had no current household ETS exposure, based on self-report, whereas n = 15 were classified as having current ETS exposure. Samples from vacuum cleaner bags had a median nicotine mass fraction of 31 µg/g for the no-current-exposure group as compared to 121 µg/g for the exposure group.
For dust samples collected from household surfaces, the median nicotine level was 20 µg/g for the unexposed and 212 µg/g for the exposed groups. They found that urinary concentrations of cotinine, a nicotine metabolite, were strongly associated with the mass fraction in dust. Kim et al.463 collected dust samples from 37 Baltimore homes. Among the 7 homes that were self-reported as nonsmoking, the median mass fraction in dust was 12 µg/g. Among the 30 homes self-reported as smoking, the median was 43 µg/g. They found a significant association between the mass fraction of nicotine in dust and the self-reported number of cigarettes smoked per day per home. In contrast, they did not find such an association for gas-phase nicotine, nor did they find an association between gas-phase nicotine and mass fraction in dust. Whitehead et al. measured total nicotine in dust samples collected from homes in Northern California during the period 1999-2007. In homes where no one had smoked in the month prior to dust collection , the median mass fraction of nicotine in dust was 0.26 µg/g. In homes where smoking had occurred , the median mass fraction was 1.26 µg/g. Based on concurrently self-reported household cigarette smoking, the authors concluded that the mass fraction of nicotine in indoor dust was a reasonable surrogate for indoor smoking. In dust samples collected in 2008 from bedrooms of Danish children, the median mass fraction of nicotine was 1.1 µg/g. In the homes of smokers , the median level was 6.6 µg/g, while in the home of nonsmokers the median level was 0.53 µg/g. It is instructive to compare these values to an earlier study of dust samples collected in 72 Danish homes in 1989. In that study, the median level in all homes was 50 µg/g; it was 242 µg/g in the homes of smokers and 18 µg/g in the homes of nonsmokers .
While there are likely multiple factors responsible for the lower levels in 2008 compared to 1989, these results are consistent with a decrease, among smokers with children, of smoking inside their homes. When comparing the homes of nonsmokers, the lower levels in 2008 may partially reflect less nicotine exposure outside the home and subsequently less nicotine brought into the home sorbed to clothing. As the abundance of water on or in a surface increases and as a surface becomes more acidic, its capacity for total nicotine increases .Several studies have examined the sorption of nicotine to indoor surfaces. Van Loy et al. reported the sorption of nicotine to the surfaces of a 20-m3 stainless-steel chamber with 45.2 m2 of nominal surface area. They found that the amount of nicotine in the gas phase was small compared to that sorbed on chamber walls. For example, at a gas-phase concentration of 33 µg/m3, the surface level was 660 µg/m2 indicating that 98% of the nicotine was sorbed to chamber surfaces. In a follow-up study, Van Loy et al. measured the dynamics of nicotine and phenanthrene sorbing to and desorbing from three different surface materials: stainless steel, a deep pile nylon carpet and gypsum wallboard covered on one side with latex paint. The results were reported, in part, in terms of a partitioning coefficient,hydroponic flood table representing the sorbed surface density normalized by the gas-phase concentration. The partitioning coefficient of stainless steel for sorbed phenanthrene was about 3.6 times as large as for sorbed nicotine. Remarkably, however, for nylon carpet and painted gypsum board, partitioning coefficients for nicotine were 2-3 orders of magnitude greater than for phenanthrene. Van Loy et al. did not address the underlying reason for these differences. At the relative humidities of these experiments, the amount of water on the stainless-steel surface is anticipated to be small while that on and within the deep pile nylon carpet and gypsum wallboard is likely large, since both of these materials are hygroscopic, and gypsum wallboard is porous. Hence, the larger capacity of nylon carpet and gypsum board for nicotine compared to phenanthrene may be partially due to the higher water solubility of nicotine.
The pH of sorbed water may also play a role if the pH of water in the carpet and gypsum board is lower than about 7 . However, as already noted, if the water content of the carpet or gypsum board is large enough, the fraction of nicotine in the material will be much larger than nicotine’s gaseous abundance, independent of pH. It may also be that relatively polar nylon carpet and gypsum board more strongly sorb polar nicotine compared to nonpolar phenanthrene, regardless of the sorbed water content. In studies conducted in a 50-m3 room that was variably furnished, Singer and colleagues examined the influence on airborne concentrations of sorptive partitioning of nicotine and other gas-phase organics associated with tobacco smoke.Unsurprisingly, they found that for otherwise identical conditions, the sorptive loss of nicotine was largest in a fully furnished room, less in a room with just wallboard and carpet, and even less is in a room with only wallboard. Most of the nicotine emitted from cigarettes remained sorbed to room surfaces three days after smoking. Singer et al. introduced the metric exposure relevant emission factor that implicitly accounts for sorptive uptake and reemission to give the net mass of individual ETS constituents available for inhalation exposure over a day in which smoking occurs according to a representative indoor pattern. For nicotine, the EREF decreased with decreasing ventilation rate, suggesting continued sorptive uptake by the indoor surfaces over the duration of the experiments. Sorption reduced nicotine concentration during the smoking period and increased its concentration during nonsmoking periods, “resulting in fractionally higher indirect exposures.” When evaluating exposure to gas-phase constituents of ETS, nicotine, as a strongly sorbing constituent, is a poor surrogate for weakly sorbing constituents. Furthermore, given that the sorptive capacity of a surface for nicotine can be influenced by pH, it is a poor surrogate for other gas-phase constituents of ETS that do not ionize and are not affected by pH. In a related experiment, twenty volatile organics were rapidly vaporized into the fully furnished 50-m3 room and their gas-phase concentrations were measured during a sorption period, a flush period, and a desorption period.Nicotine sorbed quickly, with 99% sorbed to room surfaces within two hours of initial introduction. During the flush period, nicotine’s gas-phase concentration declined, but only a small fraction of nicotine’s total mass in the room was removed during flushing. Nicotine returned to a gas-phase concentration that was close to its pre-flush level when the room was resealed. Matt et al. measured nicotine levels on surfaces in the San Diego homes where they also measured gas-phase and dust-associated nicotine. For the no-exposure group, nicotine was below the detection limit on all sampled surfaces. For the indirect exposure group, the 40-50% of samples were quantifiable. Considering only quantifiable samples, geometric means for surface-associated nicotine levels were 10 µg/m2 in the living room and 8 µg/m2 in the infant’s bedroom. In the direct exposure group, 90% of the samples were quantifiable and the geometric mean nicotine surface levels for those samples were 51 µg/m2 in the living room and 42 µg/m2 in the infant’s bedroom. The paper does not discuss whether these surface levels include the contribution from dust on the sampled surfaces. In simulating a typical residence, using sorption parameters obtained from previous chamber experiments, Klepeis and Nazar off estimated that in a room with chronic smoking it would take more than five years for surface nicotine levels to plateau.The extensive sorption of nicotine to typical indoor surfaces indicates that in rooms where smoking regularly occurs, the surfaces remain a strong source of nicotine for extended periods after smoking has ceased. Given that the capacity of a material for nicotine increases as the pH of water in the material decreases, acidic sorptive materials are anticipated to require more time to equilibrate with ETS nicotine and to remain strong sources of nicotine for longer periods than sorptive materials that are chemically basic. Secondhand smoke is a mixture of side stream smoke from tobacco combustion and mainstream smoke exhaled by a smoker. Residual constituents of secondhand smoke that sorb to exposed indoor surfaces, including settled dust, are often referred to as thirdhand smoke .