Electrical features, liquid composition and toxicant emissions from ‘pod-mod’-like disposable electronic cigarettes

INTRODUCTION

Electronic cigarettes (e-cigarettes) are devices that use an electrical heater to heat and aerosolize a liquid for user inhalation.[1] E-cigarette use has increased in popularity in recent years among adults,[2–6] and youth.[7–11] In 2017, there was a large jump in the use of “pod-mod” devices, with one product, JUUL, capturing the greatest market share in this product class.[12] Some authorities have considered or implemented policies to prevent youth uptake and use of these products. For example, in February 2020, the United States Food and Drug Administration (FDA) issued a ban on flavored “cartridge-based” e-cigarettes other than tobacco or menthol flavored products.[13] However, flavored disposable e-cigarettes that resemble pod-mod e-cigarettes have been recently introduced to the market (e.g., Puff Bars). While these products resemble in appearance pod-based systems like the JUUL, these disposable e-cigarettes are not refillable; they are also cheaper, are sometimes labeled as containing high concentrations of salt-based nicotine (up to 7% nicotine content), and often feature vibrant colors and youth-appealing flavors.[14]

While some disposable e-cigarettes recently were ordered off the market by the FDA, including the popular Puff Bar,[15] many pod-mod-like disposable e-cigarettes are still available for purchase from brick and mortar and online retailers. For example, while the Puff Bar manufacturers no longer sell devices on their website, Puff Bar products can still be found on other online vape shops.[16–18] Importantly, despite the popularity of pod-mod-like disposable e-cigarettes, little is known about the design, toxicant emissions profiles, or how disposable pod-mod-like e-cigarettes may impact health or cause and maintain dependence. The purpose of this study was to examine device characteristics, liquid composition, and toxicant emissions from pod-mod-like disposable e-cigarettes. The toxicant emissions examined included nicotine, carbonyl species, and heavy metals.

Carbonyl species are a product of the thermal decomposition of glycerol and propylene glycol, the primary constituents of e-cigarette liquids, and are a class of chemicals thought to be responsible for the preponderance of non-cancer pulmonary disease in smokers.[19] Heavy metals in e-cigarette aerosols are thought to be leached from the e-cigarette core assembly or other sources of contamination, and can include species that are associated with cancer and other adverse health effects.[20]

METHODS

We analyzed and compared the construction, electrical characteristics, liquid composition, and aerosol emissions of five disposable e-cigarettes and one JUUL (Classic Tobacco, 5% nicotine) product procured from the USA in 2020: Ezzy Oval (Berry Cool and Mango Lychee flavors), Hyde (Cherry Lemonade), SEA (Mint), and Puff Bar (Banana Ice). These devices were identified as popular disposable e-cigarette devices by participants in an ongoing study.

For the disposable e-cigarettes, power (W) was calculated from battery voltage (V) and electrical resistance (Ω) measured using a standard laboratory multimeter. Because the JUUL device incorporates a variable voltage temperature control system that continuously adjusts voltage during each puff, we computed average power for JUUL by sampling the voltage continuously using a data acquisition system, as described in Talih et al., 2020 [21].

Propylene glycol and vegetable glycerin in the liquid were measured by gas chromatography–flame ionization detector (GC-FID) as in El-Hellani, Salman [22]. Liquid nicotine concentration and form were measured using a liquid-liquid extraction method and gas chromatography-mass spectrometry (GC-MS), as in El-Hellani, El-Hage [23]. Liquid pH was measured using a Starter 3100 OHAUS pH-meter.

Nicotine, carbonyl compounds, and metals in the aerosol were measured by drawing 15 4-sec puffs at 1 L/min flow rate (similar to that of an experienced ECIG user)[24] using the AUB Aerosol Lab Vaping Instrument,[22] for all devices except the Ezzy Oval which required a minimum flow rate of 1.2L/min to trigger activation. The aerosol exiting the e-cigarette was split into two parallel flow streams, with each stream drawn through a 47 mm quartz filter (Pall Type A/E) for nicotine and metal analysis, respectively. One filter was followed by a 2,4-Dinitrophenylhydrazine (DNPH) cartridge (Sigma-Aldrich/LpDNPH H30) to trap gas-phase carbonyl species. The filter dedicated for metals determinations was pre-washed in a 1% nitric oxide solution and air-dried prior to sampling.

Total particulate matter (TPM) was determined gravimetrically by weighing the filter pads pre- and post-sampling. Nicotine was determined by soaking the filters in an ethyl-acetate solvent and analyzing the solution by GC-MS, as in El-Hellani, Salman [22].

Carbonyl compounds trapped and derivatized on the DNPH cartridges were eluted with 90/10 (vol/vol) ethanol/acetonitrile and quantified by high-performance liquid chromatography ultraviolet (HPLC-UV), as in El-Hellani, Salman [22]. The species analyzed, and the limit of detection and limit of quantitation were respectively as follows (µg): formaldehyde, 0.002 and 0.007; acetaldehyde, 0.004 and 0.012; acetone, 0.001 and 0.004; acrolein, 0.003 and 0.012; propionaldehyde, 0.008 and 0.028; benzaldehyde 0.009 and 0.029; valeraldehyde, 0.002 and 0.007; glyoxal, 0.014 and 0.047; and methylglyoxal, 0.027 and 0.091.

Metals were analyzed by digesting the filter in 4mL of nitric acid and 2mL of hydrogen peroxide at 200°C for 20 min. The obtained solution was diluted in 10mL of deionized water prior to analysis by inductively coupled plasma mass spectrometry (ICP-MS). Blank filters were digested in the same manner as the sampled filters for background subtraction. Spiked Blank filters of 5ppb and 50ppb standard solutions were used to estimate the accuracy, precision, and ruggedness of the method. The species analyzed and the limits of detection were as follows (ng): antimony 5, chromium 5, iron 500, nickel 5, copper 5, arsenic 5, cadmium 5, tin 50, manganese 5, molybdenum 5, selenium 5, strontium 5, thallium 5, and tungsten 5.

Liquid composition and toxicant emissions were determined in triplicate for each device. Outcome variables, including device characteristics and toxicant yields, were summarized as mean (standard deviation). Outcome variables were compared between each of the disposable e-cigarettes and the JUUL device using independent sample t-tests with an alpha level of 0.05 to determine significance.

RESULTS

All pod-mod-like disposables had a single heating coil that was wrapped around a silica (SEA and Hyde) or cotton (Ezzy Oval and Puff Bar) wick. The coil and wick were enclosed in a textile sheath that was covered by a liquid-soaked polyfill material (Figure S1, S2). This basic architecture is the same as that of first-generation “cigalike” e-cigarettes and cartomizers.[25] Unlike JUUL, none of the disposable devices contained a microcontroller circuit, and all showed discoloration of the wick where it contacts the heating coil, indicating corrosion.

Electrical characteristics, liquid composition, and toxicant emission results are shown in Table 1. Mean battery voltage ranged narrowly from 3.74–3.92 V. With the exception of the SEA, all devices had similar coil resistances (1.64–1.91 Ohms vs. SEA 2.78 Ohms).

The measured liquid nicotine concentration for three disposable products (Ezzy Oval Mango Lychee, Hyde, and Puff Bar) was significantly greater than the labeled concentration (57–61 mg/mL vs. 75–86 mg/mL). One product, the Hyde e-cigarette, exhibited much greater nicotine concentration than the others. Based on measured pH, all products had nicotine predominantly in the protonated form (94% or greater using the Henderson–Hasselbalch equation). Propylene glycol to vegetable glycerin ratio varied widely across products and ranged between 20/80–50/50.

Except for the SEA device, disposable products generated significantly greater TPM (65–125mg), nicotine (3.1–6.7mg), and total carbonyls (36–138µg) than JUUL (37mg of TPM, 1.7mg of nicotine, and 17.7 µg of carbonyls). Metal emissions were similar across devices, except for the Puff Bar, which generated significantly greater levels of antimony (410 ng) and nickel (310 ng) than JUUL (BDL and 90 ng, respectively). Total metal emissions varied widely and ranged between 1084 and 5804 ng in 15 puffs (Table S1).

DISCUSSION

This study found that disposable pod-mod-like e-cigarettes use liquids that contain high nicotine concentrations – often greater than indicated on the product labels – and can emit several-fold the nicotine of a JUUL. For example, Puff Bar, the most popular disposable product among young people in the USA,[26] emits four times the nicotine of a JUUL, predominantly in the palatable protonated (salt) form [27]. Disposable e-cigarettes also emitted greater levels of carbonyls, a class of powerful pulmonary toxicants. This finding is consistent with the finding that the disposable devices were not temperature controlled, unlike the JUUL. However, we note that previously reported values for JUUL carbonyl species emissions [21, 28–30] vary considerably, and that some of the reported values are within the ranges of some of the disposable devices reported here. For example, formaldehyde emissions in 15 puffs, were reported to be equal to 1.7 µg by Mallock, Trieu [28], 2 µg by Son, Bhattarai [29] , and 4 µg by Talih, Salman [21], for roughly similar conditions. The reason for the differences in reported JUUL carbonyl emissions across studies is not known. Metals emissions varied widely across and within device. In general, we found no significant differences in metal emissions between pod-mod-disposables and JUUL.

We found that the internal construction of the disposable devices indicated poor quality control in manufacturing, a feature also reflected in the fact that the measured nicotine concentration was different than the advertised value by up to 1.5 times. Previous comparisons between measured and labeled nicotine concentrations have shown similar discrepancies.[31]

A limitation of this study is that differences in flavors may contribute to differences in toxicant emissions across the examined devices.[32] The degree to which the varying flavors may confound the varying carbonyl emissions is unknown. In addition, we tested a small number of pod-mod-like disposable devices; other devices and brands are available in the market and may exhibit different emission profiles. Nonetheless, the data of this study indicate that there is reason for concern that this product class, whose use is prevalent with some groups [32], may be more toxic and more addictive than similar form factor devices such as the JUUL, a product whose manufacturer is being investigated by public health authorities for its widespread uptake by youth.[33, 34]

In conclusion, our results suggest that pod-mod-like disposable e-cigarettes can have low quality construction and unreliable labeling, contain high liquid nicotine concentrations, and, relative to e-cigarette devices that are similar in appearance, exhibit elevated emissions of nicotine and non-nicotine toxicants that cause dependence and pulmonary disease in smokers. Given their high nicotine dose, appealing flavors, and popularity among youth and young adults, disposable e-cigarettes warrant scrutiny by public health authorities.

Supplementary Material