Relationship between domestic smoking and metals and rare earth elements concentration in indoor PM2.5
Graphical abstract
Introduction
Cigarette smoking is the most important risk factor for preventable diseases affecting the lungs, the heart, and the human health in general. Cigarette smoking causes approximately 80,000 deaths per year in Italy (Ministry of Health of Italy, 2009), 6,000,000 worldwide (WHO, 2017). The health effects of smoking originate from the interaction between human body and numerous toxic constituents in cigarette smoke through repeated inhalations. Active smokers mostly inhale mainstream cigarette smoke: smoke is drawn through the burning tobacco column and filter tip and exits through the cigarette mouthpiece. Nonsmokers, instead, are exposed to the so-called “second-hand” and “third-hand” smoke. Second-hand smoke includes both mainstream smoke exhaled by the smoker and sidestream smoke, emitted between puffs into the surrounding air from the end of the smoldering cigarette. This type of smoke is the major source of environmental tobacco smoke (ETS) and is characterized by smaller particles and higher toxicity than mainstream smoke (Rodgman and Perfetti, 2009). Moreover, residual smoke can remain in the air after the burning end has been extinguished and/or can be absorbed on surfaces (indoor furnishing materials, clothing, skin, hair, etc.), where it can be subsequently released from. These chemical species, known as third-hand smoke, are not eliminated even ensuring ventilation while or after a cigarette is smoked. Third-hand smoke may cause the greatest harm to infants and young children, who crawl on the floor, eat from their hands or may be cuddled up to a smoker with toxins on his skin and clothes (Ferrante et al., 2013, Matt et al., 2011). Moreover, it has been shown that third-hand smoke may react with environmental pollutants, producing new, even more toxic species. This is the case, for example, of the reaction with nitrous acid, which leads to the formation of tobacco-specific nitrosamines (Sleiman et al., 2010).
ETS is considered as the main source of gaseous and particulate toxic chemical species in indoor environments (Sleiman et al., 2014). As urban population typically spends most time indoors (Meng et al., 2009, Simoni et al., 1998), it is important to understand how exposure to particles generated by indoor sources affects human health and to identify and to apportion smoking among the many other sources of particulate matter (PM). Indoor exposure to ETS is harmful and hazardous to general population (Simoni et al., 2002, Simoni et al., 2004) and particularly dangerous to children (Hofhuis et al., 2003). In this age group, it increases the risk of serious respiratory problems, such as a larger number and severity of asthma attacks and lower respiratory tract infections (Hofhuis et al., 2003, Constant et al., 2011). Moreover, ETS is also a well-known human carcinogen (cancer-causing agent) (IARC, 2004): inhaling second-hand and third-hand smoke causes increased risk for lung cancer and coronary heart disease in nonsmoking adults (Department of Health and Human Services, 2006). It is important, therefore, to evaluate the indoor exposure of both children and adults to second- and third-hand smoke and thus to identify the contribution of smoke to indoor pollution.
Over 7000 chemical compounds, from many different classes, are produced by pyro-synthesis or liberated during cigarette combustion, organics and inorganics, in the gaseous and in the particulate phase (Rodgman and Perfetti, 2009). Among the species in the particulate phase, many scientific studies have been focused on elements. Most elements found in cigarette smoke originate from the burning of tobacco leaves. Tobacco plants absorb elements from the soil (Pappas et al., 2007, Verma et al., 2010, Lugon-Moulin et al., 2004) or from deposited atmospheric dust (Geiss and Kotzias, 2007) and accumulate them in their leaves. Consequently, heavy metals and other elements in tobacco are higher when plants grow in environments characterized by high heavy metal concentrations (Sebiawu et al., 2014, Xiao et al., 2004a, Xiao et al., 2004b). Many elements, including As, Cd, Mn, Pb, Sb, Sr, Tl, and Zn, have been identified in tobacco smoke (Bernhard et al., 2005, Swami et al., 2009); a few studies also include rare earth elements (REE), such as Ce and La (Slezakova et al., 2009). Most of the above elements are toxic. Some of them, such as cadmium, are significant contributors to toxicological non-cancer indices of health risks for respiratory and cardiovascular diseases such as peripheral artery disease (Fowles and Dybing, 2003). Thallium is highly toxic, it is comparable to, and certain cases more toxic than, elements such as arsenic, cadmium, nickel, mercury or lead (Xiao et al., 2012). Data about the toxicity of REE are scanty and little attention has been paid to them. Several reports show that REE such as Ce and La may cause lung parenchymal inflammation and fibrosis (Haley, 1991). However, cases of dendriform pulmonary ossification (a rare form of diffuse pulmonary ossification) were associated with the inhalation of industrial rare earth metals (Hedrick, 2004). At present, Ce and La are not mentioned in the comprehensive reviews of the International Agency for Research on Cancer (IARC, 2004).
In addition to their possible health effects, the determination of elements in atmospheric PM can be a useful tool for the identification of pollution sources and for the evaluation of their strength. Elements are robust and reliable tracers of several sources of atmospheric PM as they are chemically stable (chemically conserved from the emission source to the receptor site), of primary origin (not formed in the atmosphere) and easy to be determined by using multi-parametric analytical techniques (Qi et al., 2016a, Qi et al., 2016b, Canepari et al., 2014, Saraga et al., 2017). In addition to these features, a good tracer must be emitted preferentially by some sources and not by others. In the case of smoking, it is thus important to single out elements that are released by smoking and that are present at very low concentration in outdoor air and in other indoor sources. In indoor environments, in facts, many pollution sources in addition to smoking contribute to the build-up of PM concentration. Among these, infiltration from outside, combustion processes (biomass burning for domestic heating or cooking), re-suspension, use of cleaning materials, release of bioaerosol from humans and pets. To evaluate the exposure to second- and third-hand smoking it is thus necessary to identify reliable tracers of smoking and to determine their atmospheric concentration in indoor PM samples.
The present work was aimed at determining the elemental composition of PM samples collected in smokers’ and non-smokers’ dwellings, indoors and outdoors, identifying selective tracers of smoking and evaluating the link with some specific effects on the respiratory health of adolescents. We choose to collect PM samples in occupied apartments during the regular like of their occupants, also thanks to the use of very quiet PM samplers (<35 dB). To ensure the representativeness of the samples we carried out continuous 48-h samplings in each environment during weekdays only. Moreover, to differentiate among the possible indoor and outdoor PM sources, we carried out simultaneous indoor and outdoor samplings in each dwelling.
Being smoke emission almost exclusively in the fine fraction of PM, the study was focused on PM2.5 (particles having aerodynamic diameter below 2.5 µm). Moreover, the choice of this size fraction allows a reduction of the contribution of re-suspension. This source, which is almost completely confined in the coarse fraction, has been demonstrated to be one of the main contributors to indoor PM (Perrino et al., 2016). In order to improve the traceability of PM sources (Canepari et al., 2006a, Canepari et al., 2006b, Canepari et al., 2009a, Canepari et al., 2009b) and to evaluate the bio-accessibility of the measured species, the total elemental content was fractionated into two chemical fractions (extracted and mineralized) prior to the analysis by inductively-coupled plasma mass spectroscopy (ICP-MS).
Section snippets
Study design
Between March and December 2012 in the context of RESPIRA project, within the Cross-Border Cooperation Program Italy-Malta 2007–2013, an epidemiological survey was performed in Sicily, a Mediterranean region of Southern Italy, on 1325 schoolchildren, aged 10–15 yrs, selected from all the secondary schools, first degree, of the town of Gela (GE, 77,000 inhabitants/660 evaluated subjects), close to a petrochemical complex, and of the villages of Niscemi (NI, 26,400/355), Mazzarino (MZ,
Identification of smoke tracers
The results of PM2.5 and element concentrations in all the studied environments (27 smokers and 46 non-smokers) are summarized in Fig. 1; element concentrations were calculated as the sum of the extracted and residual fractions. A statistically significant difference (p < 0.01) was found between indoor and outdoor concentrations of PM2.5 (Fig. 1, panel A): indoor values were significantly higher than outdoor ones. Similarly, concentrations of As, Cd, Ce, La and Sr indoors (Fig. 1, panels B-G)
Discussion
In order to identify which elements are significantly released by indoor sources, we compared indoor and outdoor concentrations in all the considered dwellings. It is worth recalling that in indoor environments particulate matter is the sum of two contributes, one infiltrated from outdoor and one due to indoor sources. In general, fine dust can easily infiltrate from outdoor into indoor environments. The effect is a high penetration coefficient, usually in the range 0.7–1.0, which depends on
Conclusions
European Commission recommendation on smoke-free environments (2009) called on Member States to adopt and implement laws to protect citizens from exposure to tobacco smoke in enclosed public places, workplaces, and public transport. It also called for the enhancement of smoke-free laws with supporting measures to protect children, encouraged efforts to quit smoking and displayed pictorial warnings on cigarette packages. A statewide law banning smoking in enclosed work places and public places
Acknowledgements
The authors thank the study participants and their parents for their active participation in the study. This research was supported by the Operational Programme Italy-Malta 2007–2013, Project code A1.2.3-72.
Competing financial interests declaration
The authors have no conflicts of interest to disclose
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