Elevated toxicant yields with narghile waterpipes smoked using a plastic hose
Introduction
With the ongoing global resurgence of the narghile waterpipe as a tobacco smoking device (American Lung Association, 2007, Smith-Simone et al., 2007, Chaaya et al., 2004, Maziak et al., 2004, Shediac-Rizkallah et al., 2002), entrepreneurs have brought a number of modern innovations to market which may have unforeseen consequences for toxicant intake. One such innovation is the use of plastic instead of leather to construct the hose through which the user draws smoke (Fig. 1). In recent visits to waterpipe cafés and supply shops in Beirut, Lebanon, we have noted several cafés that served waterpipes exclusively with plastic hoses, and several tobacco supply outlets, including a major supermarket chain, which only sold plastic hoses, though most sold both. While the plastic hose is promoted as a more durable and easy-to-clean alternative, the air-tight character of plastic, as opposed to the conventional porous leather, gives rise to the concern that the smoke reaching the mouthpiece will be less dilute, potentially resulting in greater toxicant exposure. Cigarette paper permeability has for some time been understood as a key determinant of toxicant uptake by smokers (e.g. Owen and Reynolds, 1967). During a puff, the negative pressure in the cigarette rod gives rise to the infiltration of fresh air which can dilute the smoke. In addition, the permeable flow boundary can allow mobile gas molecules such as CO and CO2 to escape by diffusion to the ambient surroundings. For example, measurements by Durocher et al. (1978) showed that 26–32% of the CO generated in the cigarette during a puff escapes by diffusion through the paper before reaching the smoker.
In addition, the greater the flow rate of infiltrating air the lower the flow rate through the burning tobacco of the waterpipe head or cigarette tip for a given draw velocity at the mouthpiece . Replacing a porous waterpipe hose with a sealed one will result in a net increase in air volume drawn through the tobacco in the head that could affect the smoke aerosol production temperatures and chemistry. In summary, at least three phenomena are affected which can alter toxicant yields when a porous leather hose is replaced by a non-porous plastic one: (1) escape of mobile species through the hose walls, (2) simple dilution, and (3) varying combustion/pyrolysis/distillation chemistry.
Despite its long history and recent global resurgence few studies (Shihadeh and Saleh, 2005, Shihadeh, 2003, Sajid et al., 1993, Hoffmann et al., 1963, Rakower and Fatal, 1962) have been conducted to measure the toxicant content of the narghile waterpipe (see Table 1 for previously measured toxicant yields), and no consideration has been made for the potential role of hose permeability as a determinant of toxicant delivery. This study was conducted to examine whether the conventional leather hose used with the waterpipe exhibits significant permeability under typical use conditions, and to compare TPM, nicotine, and CO yields measured with a leather hose to those measured with a non-porous “washable” plastic hose. Apart from their importance as key toxicants, CO and nicotine were selected for study because they, respectively, represent a highly diffusive gas phase component, and a low vapor pressure particle phase smoke component and thereby span the range of behaviors expected of various smoke components in a flow bounded by permeable walls.
Section snippets
Smoke generation and sampling
The smoke generation and sampling procedures were identical to those presented in Shihadeh and Saleh (2005). In brief, a digital waterpipe smoking machine (described in Shihadeh and Azar, 2006) was programmed to produce a smoking regimen consisting of 171 puffs of 530 ml and 2.6 s duration, spaced 17 s apart. These puffing parameters were derived from a field study in which topographies of 52 smokers in a café in Beirut were recorded, and represent an “average” waterpipe smoking session (Shihadeh
Infiltration rate
Infiltration rates for the 23 hoses are given in Table 2. Difference in infiltration rate by hose construction material was highly significant (p < 0.001). For the leather hoses, infiltration was found to be large (up to ∼25% of the mouthpiece flow) and varied both within and across type. In contrast, except for type “I”, plastic hoses did not exhibit any measurable infiltration. Hoses A2 (leather) and F (plastic) were chosen for the subsequent toxicant analyses with a lighted waterpipe since
Discussion
This study was undertaken to address the dearth of information regarding the importance of hose type on toxicant delivery to narghile users. Measurements of air infiltration rates in leather and plastic hoses under typical use conditions showed that the leather hoses are highly permeable, allowing up to 31% of the volume of gases reaching the mouthpiece during a puff to be made up of fresh air infiltrating through the hose. In contrast, the plastic hoses were air-tight. The importance of
Conclusions
Taken together, the data reveal a complex role of hose permeability on waterpipe toxicant generation and transport by overlapping the effects of dilution, diffusion, and mass transfer, and point to at least two important practical implications. First, for a fixed smoking behavior, non-permeable plastic waterpipe hoses lead to greater absolute and nicotine-normalized yields of CO and TPM than leather hoses. Second, because leather hoses exhibited widely varying permeability within and across
Conflict of Interest statement
We have no conflict of interest in connection with the research reported in this manuscript.
Acknowledgements
The authors thank Elizabeth Sepetdjian for carrying out the nicotine analyses, and the Environment Core Laboratory in the AUB Faculty of Medicine for providing access to and support using the GC-MS. They also thank Nancy Daher and Hiba Sheheitli for their assistance in executing the experiments. Professor O.A. Ezekoye of the Department of Mechanical Engineering at the University of Texas at Austin is gratefully acknowledged for hosting the corresponding author as a visiting scholar during the
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