Everyone is familiar with the offensive smell that emanates from smokers after they have taken a “cigarette break.” This gaseous and particulate residue adsorbed onto smokers' clothing and/or skin, as well as any other surfaces such as walls, carpets, and furniture of indoors environments, has been coined “third-hand smoke” (Winickoff et al. 2009). It has been demonized in the popular press, which describe it as a “toxic stew” of chemicals capable of eliciting a host of potential health problems, particularly for infants and children. However, scientific studies supporting this position are sparse, and even fewer studies evaluate exposure risks and potential deleterious health implications of third-hand tobacco smoke residues on surfaces such as walls, carpets, and furniture of indoor environments.

Studies over the past 2 decades have concluded that polycyclic aromatic hydrocarbons (PAHs), a suite of chemicals produced from the incomplete combustion of carbon-containing materials, are present in mainstream and sidestream smoke at concentrations as high as 0.1 to 0.25 ng/cigarette (Menzie et al. 1992). Toughening indoor smoking laws has undoubtedly led to reductions in exposure of these and other chemicals to nonsmokers. However, Matt et al. (2004) concluded that limiting smoking to the outdoors contaminated indoor settings 5 to 7 times more than not smoking at all. Third-hand smoke may represent a significant vector for carcinogen exposure, especially to high-risk individuals such as infants who ingest 0.05 to 0.25 g of dust per day, including any PAHs that have adsorbed onto carpet or clothing material (Matt et al. 2004), or may come into contact with a smoker's skin.

To date, most of the limited research regarding third-hand smoke has focused on either using nicotine as an indicator for third-hand residue, or it has investigated nicotine's hypothesized role as a precursor in the formation of carcinogenic compounds within indoor environments (Sleiman et al. 2010). The myriad of other potential health hazardous compounds within third-hand smoke, including PAHs, have largely been ignored, and it was our intention to go beyond the studies that focused on nicotine contamination and evaluate PAH residues in third-hand smoke.

Because there are few published values for PAH concentrations in third-hand tobacco residues, we conducted a preliminary study quantifying PAH concentrations in third-hand smoke residues remaining on smokers' hands. We used “swipes” of hands, an increasingly popular and simple method for collecting adsorbed compounds from surfaces. Alcohol-soaked cotton ball swipes from the hands of 170 smokers (after smoking 1 cigarette) and 160 nonsmokers were analyzed. Individual swipes of treatment and control groups were composited to 8 to 10 swipes (to constitute a “sample”) to increase instrumental detection limits.

Composited swipe samples were extracted with hexane using a Soxhlet extractor for 18 h and “cleaned-up” using bench-top solid-liquid chromatography with alumina as the stationary phase and hexane as the mobile phase. Samples were subsequently concentrated under N gas and a perdeuterated PAH (fluoranthene-d10) was added as the internal standard. Twenty individual PAHs were quantified by gas chromatography mass spectrometry using a 5-point calibration curve. Mean recoveries of a perdeuterated PAH (perylene-d12) surrogate were 67%.

Given the ubiquitous nature of PAHs in the environment, it was not surprising that all PAH compounds were detected above blank-based detection limits from swipes collected from both the smokers' and nonsmokers' hands. However, concentrations (expressed as the sum of all PAH compounds per swiped hand) were significantly higher (confidence interval at 90% for 17 of 20 PAHs) for hands directly exposed to tobacco smoke versus nonsmokers' hands (34 ng/hand vs 13 ng/hand, respectively). From this preliminary study, we conclude smoking cigarettes significantly increases PAH residue on smokers' hands by approximately 3 times that of nonsmokers.

This study attempted to be as realistic as possible when evaluating third-hand PAH residues resulting from 1 cigarette. Smokers were not asked to change their smoking habits, except to continuously hold the cigarette in 1 hand during the entire duration of the cigarette's burning. Hand size (that is, the adsorptive surface area), duration of smoking, and environmental conditions such as wind, temperature, and humidity, in addition to other factors, may potentially influence PAH concentration. We conducted our third-hand smoke studies outdoors under environmental conditions, and therefore hypothesize that a similar study conducted in the more stable conditions of an indoor environment may reveal higher levels of contaminant residues on surfaces and smokers' bodies.

Moir et al. (2008) quantified PAH concentrations in second-hand tobacco smoke, defined as environmental tobacco smoke that is inhaled involuntarily or passively by someone who is not smoking. Using their study and our data set, we carried out a “back of the envelope” calculation to estimate the percentage of sidestream smoke (i.e., second-hand smoke) that becomes third-hand smoke. We conclude that the PAH inventory on 1 hand of a smoker represents 0.1% to 6% of that emitted from sidestream smoke.

Third-hand PAH residues on a smoker's hand represent only a fraction of the total PAH reservoir for a smoker (compared to residues on all exposed skin and clothing). We have begun to quantify this load of chemicals as the first step in assessing the potential for smokers to act as vectors for impairment of indoor air quality. To completely capture the health risk posed by third-hand smoke, further studies from our research group and others need to address the off-gassing or desorption potential of these compounds and more fully evaluate the significance of third-hand smoke residues in impairing indoor air quality and/or increasing PAH exposure to subpopulations such as children. A thorough ranking of the importance of this exposure route compared to other exposures modes (e.g., release of PAHs from cooking methods such as open fires, incense burning, indoor tobacco smoking, etc.) also remain to be quantified.


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