Comment regarding categorization of Third-hand smoke exposure in 'Third-hand Exposure at Homes: Assessment Using Salivary Cotinine'

摘要

We read with interest "Third-hand Exposure at Homes: Assessment Using Salivary Cotinine" by Lidon-Monayo et al. (Lidon-Moyano et al., 2020), which highlights the importance of recognizing thirdhand smoke (THS) as a ubiquitous but largely unrecognized source of indoor environmental pollution and a grave public health hazard (Jacob et al., 2017). In this study, the authors categorized 736 nonsmoking adults into one of three tobacco smoke exposure (TSE) groups (1) Not Exposed to SHS or THS (i.e., Unexposed group): live with nonsmokers and have no home SHS: (2) Only THS Exposed (i.e., THSe-only group);- live with smokers but have no home SHS; and (3) SHS and THS Exposed (i.e., SHSe/THSe group): live with smokers and have home SHS and THS. We find the categorizations of participants in the unexposed group and the THSe-only group problematic. With respect to the unexposed group, given decades of high smoking prevalence and unrestricted indoor smoking in Spain and other industrialized countries, there are good reasons to expect significant remaining reservoirs of THS pollutants in private homes and work environments that are now homes and workplaces of nonsmokers, respectively. Data reported in Figure 2 (Lidon-Moyano et al., 2020) suggest that 50% of participants in the unexposed group may unknowingly be exposed to SHS or THS. With respect to the THSe-only group, it is important to remember that nonsmokers who live with smokers can still be exposed to SHS if they are occasionally exposed to active smoking, if there are inconsistent smoking bans, if they live in multiunit housing (MUH) where other residents smoke, or if smoking occurs in close proximity to their homes (Gatzke-Kopp et al., 2019; Matt et al., 2020a). For example, if participants in the THSe-only group lived with smokers who immediately came inside their home after smoking or lived in homes where smoking occurred on a balcony or at a window, then these participants could have been exposed to SHS through off-gassing or seepage of SHS (Jacob et al., 2017; Sheu et al., 2020). Further, 54.2% of THSe-only participants were exposed to SHS in other locations, and these participants may have been better placed in the SHSe/THSe group. Additionally, 51.5% of participants in the unexposed group were exposed to SHS in other settings; thus, this group was also exposed to SHS and THS. Nonsmokers in both of these two groups could subsequently be exposed to THS pollutants via inhalation, ingestion, and dermal absorption from pollutants present in smokers' homes (Jacob et al., 2017). The presence of THS pollution is evident in research conducted in nonsmoking environments where smoking has previously occurred, such as in homes of former smokers (Matt et al., 2016), in casinos and hotels that are now smoke-free (Matt et al., 2014, 2018), and in homes where thorough cleaning methods have unsuccessfully eliminated THS (Matt et al., 2020b). In these and other studies, nicotine on surfaces, in dust, and in the air serves as an environmental marker of THS pollution, and nicotine present on nonsmokers' hands may serve as a biomarker of THSe (Mahabee-Gittens et al., 2018, 2019; Matt et al., 2014, 2016, 2018, 2020b).