Investigation of mainstream smoke aerosol of the argileh water pipe

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Abstract

A first-generation smoking machine and protocol have been developed in order to study the mainstream smoke aerosol and elucidate thermal-fluid processes of the argileh water pipe. Results using a common mo'assel tobacco mixture show that, contrary to popular perceptions, the mainstream smoke contains significant amounts of nicotine, “tar” and heavy metals. With a standard smoking protocol of 100 puffs of 3 s duration spaced at 30-s intervals, the following results were obtained in a single smoking session: 2.25 mg nicotine, 242 mg nicotine-free dry particulate matter (NFDPM), and relative to the smoke of a single cigarette, high levels of arsenic, chromium and lead. It was found that increasing puff frequency increased the NFDPM but had little effect on nicotine delivery, while removing the water from the bowl increased by several-fold the nicotine, but had little effect on NFDPM. It was also found that the charcoal disk heat source contributed less than 2% of total particulate matter (TPM), and that characteristic temperatures of the tobacco varied from 450 °C nearest the heat source to 50 °C furthest away, indicating that the NFDPM is likely a result of devolatilization rather than chemical reaction, and will thus differ significantly in composition from that of cigarette smoke.

Introduction

A sharp increase in the use of the argileh water pipe has been noted in recent years in south-west Asia and north Africa, particularly among young people (Attah, 1997, Shediac-Rizkallah et al., 2002). The rise in popularity appears to be correlated with the advent on store shelves of an array of fruit-flavored tobacco mixtures, which list “molasses” as a primary ingredient. As the tobacco mixture is smoked, it releases an aroma of caramelizing sugar, similar to that from a cotton candy machine. In this form, the flavored tobacco mixture is popularly known as mo'assel, and is contrasted to the more traditional ‘unflavored’ tobacco, known as ‘ajami which is favored by older generations, especially men.

A widespread perception among smokers, and even physicians (Kandela, 1997), is that the water through which the smoke bubbles acts as a filter, rendering it considerably less harmful than that of cigarettes; this perception may be aided by the fact that the smoke is significantly cooled as it passes through the water bowl and long delivery pipe, adding to its ‘smoother’ quality. There have been few studies of the health effects on argileh smokers (Macaron et al., 1997, Zahran et al., 1982, Al-Fayez et al., 1988, Zahran et al., 1985, Nuwayhid et al., 1998, El-Hakim and Uthman, 1999), and none to determine the chemical profile of the smoke they inhale, or the importance of the physico-chemical processes unique to the argileh. This has left researchers, public health officials and the general public with little information to rank the potential hazards of argileh smoking.

The research described here is a ‘first-cut’ at developing the methods to characterize the mainstream smoke and important thermal-fluid phenomena of the argileh. Preliminary results using these methods are reported.

Plate 1 illustrates the main features of the argileh water pipe. The head, body, bowl and hose are the primary ‘elements’ from which an argileh is assembled, and each can be purchased separately in standard sizes. The smoker typically presses the fired-clay head onto the metal body, using tissue paper or a rubber fitting at the joint to make a seal. The interface between the body and the glass water bowl, which is typically rinsed and re-filled each smoking session, is similarly sealed, as is the interface between the body side-arm and hose. The flexible hose is typically made of leather or other fibrous material, with each end terminating in a hollow wood fitting.

When a smoker inhales through the hose, a vacuum is created in the headspace of the water bowl sufficient to overcome the small (typically 3 cm H2O) static head of the water above the inlet pipe, causing the tobacco smoke to bubble into the bowl. Depending on the flow rate, the static head of the water is generally the primary flow resistance in the system felt by the smoker. During each puff, air is drawn over and heated by the coals, some of it participating in the coal combustion, as evinced by the visible red glow that appears during each puff. It then passes through the tobacco, where, due to hot air convection and thermal conduction from the coal, the mainstream smoke aerosol is produced. Unlike the cigarette, there is practically no visible sidestream smoke rising from the head either during or between puffs.

While the argileh body and bowl are manufactured in a variety of sizes, there are two common configurations for the clay head in which the tobacco is placed, depending on whether the smoker is using mo'assel or ‘ajami tobacco. When mo'assel is used, smokers fill a relatively deep (approximately 3 cm) head with the tobacco mixture (10–20 g), and cover it with an aluminium foil sheet that they perforate (approx. 1 mm diameter holes) for air passage. The already burning coal is placed on top of the aluminium foil, and may be changed a number of times during a particular smoking session. In the second case, that of the traditional ‘ajami tobacco, smokers mix a small amount of water with the pre-shredded and dried tobacco to make a moldable matrix which they then shape into a small mound atop a shallow head. The burning coal is placed directly on the moisturized tobacco, and both are directly exposed to the surrounding air.

In both cases flow passages are located at the base of the clay head to allow the smoke to pass into the central conduit of the body that leads to the water bowl. Owing to its high moisture content, the limited availability of air (particularly with mo'assel smoking), and the large heat-conducting surface of the head with which it is in intimate contact, the tobacco does not burn in a self-sustaining manner; it requires the continuous external heat source provided by the wood-derived charcoal. Products of the charcoal combustion are therefore also present in the smoke.

Because of the long path traversed by the smoke as it passes from the head, through the body, to the water bowl, and through the hose to the smoker, there are ample opportunities for gas and particulate phase deposition, diffusion, and evaporation/condensation processes to occur.

Section snippets

Smoking machine development

The argileh ‘puff’ can be characterized as a low-resistance inhalation in which a large fraction of the smoker's chest cavity is filled with smoke, corresponding to a volume of the order of 1 l (average tidal air during quiet respiration is about 500 ml for an adult male; maximum air displaced is 3700 ml). This is an order of magnitude greater than the 35-ml puff volume specified by the FTC test method for cigarettes.

Assuming that the flow can be characterized as quasi-steady during the puff, a

Temperature

Fig. 3 shows typical temperature profiles during a 100-puff 3/30 standard smoking session, where temperatures ranging from 450 °C closest to the coal to 50 °C at the head outlet were recorded. Each temperature spike corresponds to a puff as air is drawn over the burning coal and into tobacco mixture. Owing to this convective heating, as well as the continuous heat conduction between puffs from the coal to the tobacco (as evidenced by steady-state tobacco temperature of 75 °C in a quiescent

Discussion

This study was undertaken to address the dearth of information regarding the composition of argileh smoke and to highlight methods and directions for further investigation. A smoking machine was designed and smoke from an argileh fueled with charcoal and loaded with 10 g of mo'assel tobacco mixture was generated using puffing parameters selected to approximate those of argileh smokers. The importance of the argileh water was tested by including a condition where no water was present in the

Acknowledgements

The author acknowledges Carol Sukhn, Ekatherina Touma, Rima Bazzi, Osan Nashalian, and Dr. Mohammad Zuheir Habbal of the Environment Care Laboratory of the Faculty of Medicine at the American University of Beirut for carrying out the GC and ICP work. The author also acknowledges Antoine Derjani who assisted in carrying out the experiments, and Adham Zakout and Mohamad Darbi for their contributions to the field study. This work was funded by the University Research Board at the American

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