An in vitro estimation of pH of mainstream smoke from smoked tobacco products using a custom fabricated smoking device – A pilot study

INTRODUCTION

The oral cavity is exposed to various external factors, including dietary habits, microorganisms, temperature fluctuations, and tobacco among individuals with the habit. Saliva’s buffering capacity maintains a neutral pH, counteracting these effects and balances acidity and alkalinity, keeping the pH within a range of 6.2–7.6, with an average of 6.7.^[1] Tobacco consumption is increasing and available in diverse forms, determined by stimulating constituents’ delivery.^[2] Preferences for specific forms are based on their delivery mode and stimulation rate. These harmful habits, stemming from long-term tobacco use, alter oral cavity pH, rendering the oral mucosa susceptible to various oral and dental diseases.^[3]

The study utilized a custom-fabricated device to determine the pH of mainstream smoke from three heated tobacco products (HTPs); filtered and unfiltered cigarettes and beedi.

MATERIAL AND METHODS

The study was approved by the Institutional Ethics Committee, April 27, 2023, Ethical approval number 296 (IEC/Approval No.296). All procedures performed in the study were conducted in accordance with the ethical standards given in the 1964 Declaration of Helsinki, as revised in 2013.

Study size

The study comprised three groups of 25 samples each: unfiltered and filtered cigarettes, and beedis. For all groups, only one brand of the commercially available filtered cigarette and beedi was utilized. For unfiltered cigarettes, the filter was sliced and the cigarette rod carrying the tobacco was utilized. A custom-fabricated apparatus was developed for estimating the pH of mainstream smoke. The design was a modified version of the device used by Gellner et al.^[3,4] The device comprised a disposable plastic container with a lid filled with 20 mL of distilled water (immediately after distillation). Two holes were cut on the lid to insert two flexible plastic tubings (one long and one short) that were used to carry the smoke from and away the HTP. One end of the long tubing was placed into the distilled water (below the surface), while the other short tubing was above the surface of the distilled water. The tobacco product was carefully attached to the other end of the long tubing that carried the mainstream smoke into the distilled water. A 5 mL disposable syringe was attached to the free end of the short tubing to simulate an individual’s inhaled breath by creating a negative pressure in the distilled water and forcing the mainstream smoke through the water. After collecting mainstream smoke from the cigarette or beedi, the pH was measured with a digital pH meter. The schematic design and the actual apparatus are shown in Figure 1. For standardization of mainstream smoke, the international organization for standardization (ISO) and federal trade commission cigarette filter test (FTC CFT) method smoking regimens recommendation of one puff per minute with a 35 mL volume over 2 s to a defined butt length was followed.^[4]

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Figure 1:

(a) The schematic design and (b) the custom fabricated device.

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RESULTS

The mean pH of mainstream smoke in the three study groups was 6.532, with a standard deviation of 0.621. The pH of unfiltered and filtered cigarette mainstream smoke was 6.286 and 6.057, respectively, while the pH of beedi mainstream smoke was 7.253. Using one-way ANOVA, a statistical difference with P = 0.001 was observed between the pH of the mainstream smoke of three study groups, as shown in Table 1 and Figure 2.

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Figure 2:

Graphical representation of pH of the mainstream smoke of study groups: Unfiltered and filtered cigarette and beedi.

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The mean weights of the unfiltered and filtered cigarette and beedi were 0.507, 0.665, and 0.321, respectively. The mean weights of the remaining unfiltered and filtered cigarette and beedi were 0.309, 0.272, and 0.069. The mean weights of the ash from the filtered, unfiltered cigarette and beedi after collecting the mainstream were 0.073, 0.048 and 0.037, respectively. A high statistical difference with P < 0.001 was observed between the weights of tobacco products before and after being lit. A statistical difference was also observed between the ash of tobacco products with P = 0.031, as shown in Table 2.

DISCUSSION

Tobacco products are detrimental recreational consumables that have gained appeal despite their adverse impact on the human body. These products are commercially available in a variety of forms and designs, each evolved to individual preferences. Notably, a recent modification to this form is the HTP, a derivative of the smoked format that is assumed to have a lower negative impact on the lungs and related organs. Regardless of design, the composition of these tobacco products remains generally same, differing primarily in the method of delivery that allows customers to get maximal stimulation. One of these factors by which the delivery and absorption of the toxic ingredients is facilitated is by altering the pH of the tobacco products.^[4-6]

Saliva is the first biological fluid to be exposed to mainstream smoke from HTPs, and it is the fluid that not only maintains the oral cavity’s neutral pH but also buffers the acidic and alkaline substances to which the oral cavity is exposed. Any significant changes in the pH of the oral cavity can result in a variety of diseases affecting the hard and soft tissues of the oral cavity. Therefore, the present study considers distilled water with a neutral pH of 7 to accurately estimate the tobacco product’s pH.

Several research studies have assessed smokers’ saliva pH. When a cigarette is lit, it releases two primary types of smoke: “Side stream smoke” from the combustion end and “mainstream smoke” from the end of an individual’s inhale. Some studies have estimated the pH of smoked tobacco products using “smoking machines” that replicate smoking behavior. The advantage of such studies is that they eliminate the need for contaminated saliva or other habits that can alter pH, allowing for standardized assessments.^[3,5]

The present study adopted a custom-fabricated apparatus to determine the pH of mainstream smoke from three commercially utilized tobacco products; unfiltered and filtered tobacco products and beedi. The design of the device was a modified version of the device used by Gellner et al. with a basic principle of a smoking machine.^[3,4] Among the various standardizations available to collect mainstream smoke, the ISO and FTC CFT method smoking regimens recommendation was used.^[7,8]

The pH levels of mainstream smoke from unfiltered and filtered cigarettes exhibited acidity, while the smoke from beedis had an alkaline pH. In comparison to unfiltered cigarettes, the mainstream smoke of filtered cigarettes demonstrated a higher level of acidity. These findings suggest that the inclusion of a filter led to elevated acidity levels. As a result, filtered cigarettes displayed an acidic nature, while both unfiltered cigarettes and beedis retained their alkaline pH. These results imply that by utilizing of filter limits the passage of specific tobacco constituents yet concurrently contributing to the heightened acidity in the inhaled mainstream smoke.^[9-11] The higher acidity in the mainstream smoke of filtered cigarettes, compared to unfiltered cigarettes, can be attributed to the filter’s ability to trap basic compounds, leaving acidic substances in greater concentration. This was due to its presence in the mainstream smoke inhaled by the consumer. This change in smoke composition lowers the pH of saliva, creating an acidic oral environment conducive to the activation of tobacco-specific carcinogens, such as nitrosamines, which are more harmful in acidic conditions. The acidic environment also impairs the protective function of salivary enzymes, which would otherwise neutralize harmful substances. Consequently, the use of filters, while reducing certain harmful constituents, contributes to conditions that promote carcinogenesis by enhancing the activation of carcinogens and weakening natural defenses.^[12,13]

Another notable aspect involved the measurement of tobacco product weights both before and after ignition, as well as the weight of the resulting ash post-ignition. Research on dimensions of smoked tobacco products has shown no statistical significance in the exposure of constituents. Interestingly, the presence of filters led to an increase in the cigarette’s weight, simultaneously causing a reduction in the length of the tobacco portion after ignition. This suggests that the act of inhaling the smoke would likely lead to a more substantial consumption of the tobacco product. In contrast, an unobstructed inflow of inhaled air allowed for relatively lower consumption per breath when compared to filtered cigarettes.^[14,15] Similar trends were evident in the case of beedis. The absence of a filtering mechanism allows more air to flow through the beedi while smoking, causing it to burn more quickly and resulting in a shorter beedi length. This unrestricted airflow can increase the rate at which the beedi is consumed, comparable to the manner by which filters in cigarettes influence smoking dynamics by affecting burn rate and consumption patterns. The same findings can be applied to the weights of the ash collected before and after being lit. The findings of the present study indicate that the filter of cigarette had not only reduced the pH of the mainstream smoke but also causes increased consumption of the cigarette, thus annulling the purpose of the filter mechanism. Research findings suggest that the presence of filters in smoking products can lead to a deceptive sense of reduced health risk among smokers. These studies indicate that smokers might perceive filtered cigarettes as being safer or less harmful due to the perception that the filter is effectively removing or reducing the harmful components of the smoke. However, this perception can be misleading, as filters may not significantly alter the overall health risks associated with smoking. As a result, individuals who use filtered cigarettes could potentially underestimate the potential health consequences of their smoking habit. In addition, another observation is that employing filters could lead to an escalation in the number of cigarettes consumed by each individual, which serves as a method utilized by manufacturers to drive sales growth.^[16,17]

CONCLUSION

The pH values of HTP mainstream smoke deviate from the normal pH range of the oral cavity, according to the research findings. Extended exposure with this smoke not only associates with the carcinogens in these products but it is also a strategy utilized by manufacturers to enhance bloodstream absorption. Another significant finding is that leveraging filters may contribute to an increase in the number of cigarettes smoked per person, which manufacturers employ in favor of sales growth.