Headspace analysis for screening of volatile organic compound profiles of electronic juice bulk material

Thermal reaction products and formation pathways of two monoterpenes under in situ thermal desorption conditions that mimic vaping coil temperatures

Vaping has become more popular and different brands and types of vaping devices have rapidly emerged. However, little is known about the potential health risks of human inhalation exposures to the volatile chemicals in the vapour, which includes both directly vaporised components of vaping liquid and their reaction products formed during vaping processes. This study investigated reaction products of two monoterpenes (α-pinene and terpinolene) that are used as flavouring agents in vaping liquids with a focus on the identification of reaction products and their formation pathways. The thermal desorption was conducted under an in situ condition that is in the range of heating coil temperature in vaping by thermally desorbing the chemicals at a temperature range of 100-300 °C. Additional clean air was introduced during the thermal desorption. 36 and 29 reaction products were identified from α-pinene and terpinolene, respectively, at a relative concentration of 0.01% and greater in the desorbed mixture. 3-Carene was the dominant reaction product of α-pinene, while reaction products of terpinolene was dominated by p-isopropenyltoluene. Several reaction pathways including ring opening, allylic oxidation, cyclo-etherification, Wagner-Meerwein rearrangement, epoxidation, cleavage and removal of partial structure, and dehydration were involved in the formation of various reaction products. These pathways and resulting relative concentrations of residual parent compound and reaction products were influenced by both temperature and amount of air present during thermal desorption. The study results demonstrate possible existence of reaction products from thermally labile chemicals like monoterpenes in vaping aerosols and can help inform policies regulating vaping devices and products to protect public health.

Recent advances in the analysis of electronic cigarette liquids and aerosols: Sample preparation and chromatographic characterization

Electronic cigarette (e-cigarette) usage has risen dramatically worldwide in recent years. It has been publicized as a safer alternative to the conventional combustible cigarette. This, however, has not yet been supported by robust toxicological research evidence. Analysis of the chemical compositions of e-liquids and generated aerosols is an important step in evaluating the toxicity effects of e-cigarettes. Currently, a broad spectrum of analytical methods have been employed for qualitative and quantitative analysis of chemical compositions of e-cigarette liquids and aerosols. The aim of this article is to review the advances in the chromatographic characterization of chemical composition of the latter in the recent five years. In addition, sample preparation methods for e-liquids and aerosols are surveyed and discussed. A study of the relevant literature indicates that, expectedly, gas chromatography and liquid chromatography with a variety of detection systems, particularly mass spectrometry, have been the main analytical techniques used in this field. Sample preparation procedures primarily include headspace sampling, dilute-and-shoot approach, liquid-liquid extraction and sorbent-based extraction for e-liquids and for aerosols (the latter usually with laboratory-built collection devices). Some challenges of current e-cigarette analytical research, and an overview on prospective work are also presented.

Making Every Single Puff Count-Simple and Sensitive E-Cigarette Aerosol Sampling for GCxIMS and GC-MS Analysis

The analysis of the aerosol from tobaccoless electronic cigarettes (e-cigarettes) is an important part of understanding their impact on human health, yet sampling aerosol from e-cigarettes is still considered a challenge. It lacks a standard method for research and quality control and there are a variety of methods. However, few are simple and inexpensive, and none have been suggested for the use with gas chromatography coupled ion mobility spectrometry (GCxIMS). This work presents and evaluates such a setup made from standard lab equipment to quickly collect a quantitative sample from the aerosol of a single puff (5 s totaling 125 mL). The aerosol condensates directly in the cooled headspace (HS) vial, which is analyzed in the HS-GCxIMS or mass spectrometer (HS-GC-MS). The combined use of GC-MS and GCxIMS allows the simple and sensitive identification of unknown substances in complex mixtures and the identification of degradation products in the aerosols. A calibration of 26 flavor compounds (0.2-20 µg/g) was created using single puffs of a spiked, flavorless commercial refill solution and 2-alkanones as internal standards. This sensitive but easily reproducible setup enables a wide range of further investigations, even for labs that were previously unable to afford it.

Comprehensive characterization of volatile and semi-volatile compounds in e-liquids for electronic cigarette using gas chromatography accurate mass spectrometry

The consumption of electronic cigarettes is a habit with an increasing prevalence, particularly among youths. Knowing the composition of e-liquids used in these devices represents the first step to understand the potential impact of e-smoking in the health of consumers. Herein, a non-target screening methodology was applied to the identification of volatile and semi-volatile compounds in a set of e-liquids from different suppliers, with different flavors, and containing different kinds of additives, such as nicotine or cannabidiol. To this end, samples were characterized by gas chromatography accurate mass spectrometry, using a time-of-flight mass analyzer. Combination of deconvoluted electronic ionization mass spectra with linear retention index values, obtained for two columns with different selectivity, permitted the identification of more than 250 chemicals with different confidence levels. Among them, respiratory pro-inflammatory compounds, acetals of propylene glycol and glycerin with aldehydes, nicotine-related and non-related alkaloids, and psychoactive cannabinoids were confirmed as concerning compounds in e-liquid samples. Concentration ratios between propylene glycol acetals and parent aldehydes varied in the range from 2% (ethyl vanillin) to more than 80% (case of benzaldehyde). The ratios between the concentrations of delta-9-tetrahydrocannabinol and cannabidiol in e-liquids stayed in the range from 0.02% to 0.3%.

Assessment of worker chemical exposures in California vape shops

E-cigarettes are battery-operated devices that heat a liquid mixture to make an aerosol that is inhaled, or vaped, by the user. Vape shops are retail environments designed to fulfill customer demand for diverse e-liquid flavors and hardware options, which create unique worker exposure concerns. To characterize exposures to vape shop workers, especially to flavoring chemicals associated with known respiratory toxicity, this study recruited vape shops from the San Francisco Bay Area. In six shops, we measured air concentrations for volatile organic compounds, formaldehyde, flavoring chemicals, and nicotine in personal and/or area samples; analyzed components of e-liquids vaped during field visits; and assessed metals on surface wipe samples. Interviews and observations were conducted over the course of a workday in the same six shops and interviews were performed in an additional six where sampling was not conducted. Detections of the alpha-diketone butter flavoring chemicals diacetyl and/or 2,3-pentanedione were common: in the headspace of purchased e-liquids (18 of 26 samples), in personal air samples (5 of 16), and in area air samples (2 of 6 shops). Two exceedances of recommended exposure limits for 2,3-pentanedione (a short-term exposure limit and an 8-hr time-weighted average) were measured in personal air samples. Other compounds detected in the area and personal air samples included substitutes for diacetyl and 2,3-pentanedione (acetoin and 2,3-hexanedione) and compounds that may be contaminants or impurities. Furthermore, a large variety (82) of other flavoring chemicals were detected in area air samples. None of the 12 shops interviewed had a health and safety program. Six shops reported no use of any personal protective equipment (PPE) (e.g., gloves, chemical resistant aprons, eye protection) and the others stated occasional use; however, no PPE use was observed during any field investigation day. Recommendations were provided to shops that included making improvements to ventilation, hygiene, use of personal protective equipment, and, if possible, avoidance of products containing the alpha-diketone flavoring chemicals. Future research is needed to evaluate the long-term health risks among workers in the vape shop retail industry and for e-cigarette use generally. Specific areas include further characterizing e-liquid constituents and emissions, evaluating ingredient health risks, evaluating the contributions of different routes of exposure (dermal, inhalation, and ingestion), and determining effective exposure mitigation measures.

In utero exposure to electronic-cigarette aerosols decreases lung fibrillar collagen content, increases Newtonian resistance and induces sex-specific molecular signatures in neonatal mice

Approximately 7% of pregnant women in the United States use electronic-cigarette (e-cig) devices during pregnancy. There is, however, no scientific evidence to support e-cig use as being 'safe' during pregnancy. Little is known about the effects of fetal exposures to e-cig aerosols on lung alveologenesis. In the present study, we tested the hypothesis that in utero exposure to e-cig aerosol impairs lung alveologenesis and pulmonary function in neonates. Pregnant BALB/c mice were exposed 2 h a day for 20 consecutive days during gestation to either filtered air or cinnamon-flavored e-cig aerosol (36 mg/mL of nicotine). Lung tissue was collected in offspring during lung alveologenesis on postnatal day (PND) 5 and PND11. Lung function was measured at PND11. Exposure to e-cig aerosol in utero led to a significant decrease in body weights at birth which was sustained through PND5. At PND5, in utero e-cig exposures dysregulated genes related to Wnt signaling and epigenetic modifications in both females (~ 120 genes) and males (40 genes). These alterations were accompanied by reduced lung fibrillar collagen content at PND5-a time point when collagen content is close to its peak to support alveoli formation. In utero exposure to e-cig aerosol also increased the Newtonian resistance of offspring at PND11, suggesting a narrowing of the conducting airways. At PND11, in females, transcriptomic dysregulation associated with epigenetic alterations was sustained (17 genes), while WNT signaling dysregulation was largely resolved (10 genes). In males, at PND11, the expression of only 4 genes associated with epigenetics was dysregulated, while 16 Wnt related-genes were altered. These data demonstrate that in utero exposures to cinnamon-flavored e-cig aerosols alter lung structure and function and induce sex-specific molecular signatures during lung alveologenesis in neonatal mice. This may reflect epigenetic programming affecting lung disease development later in life.

Model Predictions of Occupational Exposures to Diacetyl and 2,3-Pentanedione Emitted From Roasted Whole Bean and Ground Coffee: Influence of Roast Level and Physical Form on Specific Emission Rates

Roasted coffee emits hazardous volatile organic compounds including diacetyl and 2,3-pentanedione. Workers in non-flavored coffee roasting and packaging facilities might inhale diacetyl and 2,3-pentanedione from roasted coffee above occupational exposure limits depending on their work activities and proximity to the source of emissions. Objectives of this laboratory study were to: (1) investigate factors affecting specific emission rates (SERs) of diacetyl and 2,3-pentanedione from freshly roasted coffee, (2) explore the effect of time on SERs of coffee stored in sealed bags for 10-days, and (3) predict exposures to workers in hypothetical workplace scenarios. Two roast levels (light and dark) and three physical forms (whole bean, coarse ground, and fine ground) were investigated. Particle size for whole bean and ground coffee were analyzed using geometric mean of Feret diameter. Emitted chemicals were collected on thermal desorption tubes and quantified using mass spectrometry analysis. SERs developed here coupled with information from previous field surveys provided model input to estimate worker exposures during various activities using a probabilistic, near-field/far-field model. For freshly roasted coffee, mean SER of diacetyl and 2,3-pentantedione increased with decreasing particle size of the physical form (whole bean < coarse ground < fine ground) but was not consistent with roast levels. SERs from freshly roasted coffee increased with roast level for diacetyl but did not change for 2,3-pentanedione. Mean SERs were greatest for diacetyl at 3.60 mg kg−1 h−1 for dark, fine ground and for 2,3-pentanedione at 3.88 mg kg−1 h−1 for light, fine ground. For storage, SERs of whole bean remained constant while SERs of dark roast ground coffee decreased and light roast ground coffee increased. Modeling demonstrated that near-field exposures depend on proximity to the source, duration of exposure, and air velocities in the near-field further supporting previously reported chemical air measurements in coffee roasting and packaging facilities. Control of source emissions using local exhaust ventilation especially around grinding activities as well as modification of work practices could be used to reduce exposures in this workforce.

Oh D. Determination of Methanol in Commercialized Alcohol-based Hand Sanitizing and Other Similar Products using Headspace GC-MS

Background:

Demand for alcohol-based products, including gel- and aqueous-type hand sanitizers, room sprays, and mouthwashes, has sharply increased during the ongoing COVID-19 pandemic because of their microbicidal properties. However, toxic methanol can be found from intentional addition of methanol by manufacturers and invariable production during the manufacture alcohol (ethanol). Although the FDA has recommended that such products should contain less than 630 ppm of methanol, it is only a temporary measure established specifically to regulate such products during the current COVID-19 pandemic and hence is not strictly regulated.

Objective:

This study aims to detect and quantify the level of methanol in alcohol-based products. However, some manufacturers unethically add methanol in their products and promote them as methanol-free. Besides, they do not provide proficiency and toxicity test results. Therefore, these kinds of products need to be analyzed to determine if they are acceptable to use.

Method:

This study qualitatively and quantitatively investigates the amount of methanol in commercial alcohol-based products using a newly developed headspace gas chromatography/mass spectrometry method. Moreover, alcohol beverages which contain methanol were analyzed to be compared with the levels of methanol in alcohol-based products and determine if their methanol levels are acceptable.

Results:

Methanol concentrations in gel-type hand sanitizers (517 ppm) and mouthwashes (202 ppm) were similar to those in white wine (429 ppm) and beer (256 ppm), respectively, while that of aqueous-type hand sanitizers (1139 ppm) is 1.5 times more than that of red wine (751 ppm).

Conclusion:

Methanol levels in most of the alcohol-based products did not exceed the FDA-recommended limit.

Effect of Puffing Behavior on Particle Size Distributions and Respiratory Depositions From Pod-Style Electronic Cigarette, or Vaping, Products

The current fourth generation ("pod-style") electronic cigarette, or vaping, products (EVPs) heat a liquid ("e-liquid") contained in a reservoir ("pod") using a battery-powered coil to deliver aerosol into the lungs. A portion of inhaled EVP aerosol is estimated as exhaled, which can present a potential secondhand exposure risk to bystanders. The effects of modifiable factors using either a prefilled disposable or refillable pod-style EVPs on aerosol particle size distribution (PSD) and its respiratory deposition are poorly understood. In this study, the influence of up to six puff profiles (55-, 65-, and 75-ml puff volumes per 6.5 and 7.5 W EVP power settings) on PSD was evaluated using a popular pod-style EVP (JUUL® brand) and a cascade impactor. JUUL® brand EVPs were used to aerosolize the manufacturers' e-liquids in their disposable pods and laboratory prepared "reference e-liquid" (without flavorings or nicotine) in refillable pods. The modeled dosimetry and calculated aerosol mass median aerodynamic diameters (MMADs) were used to estimate regional respiratory deposition. From these results, exhaled fraction of EVP aerosols was calculated as a surrogate of the secondhand exposure potential. Overall, MMADs did not differ among puff profiles, except for 55- and 75-ml volumes at 7.5 W (p < 0.05). For the reference e-liquid, MMADs ranged from 1.02 to 1.23 μm and dosimetry calculations predicted that particles would deposit in the head region (36-41%), in the trachea-bronchial (TB) region (19-21%), and in the pulmonary region (40-43%). For commercial JUUL® e-liquids, MMADs ranged from 0.92 to 1.67 μm and modeling predicted that more particles would deposit in the head region (35-52%) and in the pulmonary region (30-42%). Overall, 30-40% of the particles aerosolized by a pod-style EVP were estimated to deposit in the pulmonary region and 50-70% of the inhaled EVP aerosols could be exhaled; the latter could present an inhalational hazard to bystanders in indoor occupational settings. More research is needed to understand the influence of other modifiable factors on PSD and exposure potential.

Modeled Respiratory Tract Deposition of Aerosolized Oil Diluents Used in Δ9-THC-Based Electronic Cigarette Liquid Products

Electronic cigarette, or vaping, products (EVP) heat liquids ("e-liquids") that contain substances (licit or illicit) and deliver aerosolized particles into the lungs. Commercially available oils such as Vitamin-E-acetate (VEA), Vitamin E oil, coconut, and medium chain triglycerides (MCT) were often the constituents of e-liquids associated with an e-cigarette, or vaping, product use-associated lung injury (EVALI). The objective of this study was to evaluate the mass-based physical characteristics of the aerosolized e-liquids prepared using these oil diluents. These characteristics were particle size distributions for modeling regional respiratory deposition and puff-based total aerosol mass for estimating the number of particles delivered to the respiratory tract. Four types of e-liquids were prepared by adding terpenes to oil diluents individually: VEA, Vitamin E oil, coconut oil, and MCT. A smoking machine was used to aerosolize each e-liquid at a predetermined puff topography (volume of 55 ml for 3 s with 30-s intervals between puffs). A cascade impactor was used to collect the size-segregated aerosol for calculating the mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD). The respiratory deposition of EVP aerosols on inhalation was estimated using the Multiple-Path Particle Dosimetry model. From these results, the exhaled fraction of EVP aerosols was calculated as a surrogate of secondhand exposure potential. The MMAD of VEA (0.61 μm) was statistically different compared to MCT (0.38 μm) and coconut oil (0.47 μm) but not to Vitamin E oil (0.58 μm); p < 0.05. Wider aerosol size distribution was observed for VEA (GSD 2.35) and MCT (GSD 2.08) compared with coconut oil (GSD 1.53) and Vitamin E oil (GSD 1.55). Irrespective of the statistical differences between MMADs, dosimetry modeling resulted in the similar regional and lobular deposition of particles for all e-liquids in the respiratory tract. The highest (~0.08 or more) fractional deposition was predicted in the pulmonary region, which is consistent as the site of injury among EVALI cases. Secondhand exposure calculations indicated that a substantial amount of EVP aerosols could be exhaled, which has potential implications for bystanders. The number of EVALI cases has declined with the removal of VEA; however, further research is required to investigate the commonly available commercial ingredients used in e-liquid preparations.

Effects of E-Cigarette Flavoring Chemicals on Human Macrophages and Bronchial Epithelial Cells

E-cigarettes utilize a wide range of flavoring chemicals with respiratory health effects that are not well understood. In this study, we used pulmonary-associated cell lines to assess the in vitro cytotoxic effects of 30 flavoring chemicals. Human bronchial epithelial cells (BEAS-2B) and both naïve and activated macrophages (THP-1) were treated with 10, 100, and 1000 µM of flavoring chemicals and analyzed for changes in viability, cell membrane damage, reactive oxygen species (ROS) production, and inflammatory cytokine release. Viability was unaffected for all chemicals at the 10 and 100 µM concentrations. At 1000 µM, the greatest reductions in viability were seen with decanal, hexanal, nonanal, cinnamaldehyde, eugenol, vanillin, alpha-pinene, and limonene. High amounts of ROS were elicited by vanillin, ethyl maltol, and the diketones (2,3-pentanedione, 2,3-heptanedione, and 2,3-hexanedione) from both cell lines. Naïve THP-1 cells produced significantly elevated levels of IL-1β, IL-8, and TNF-α when exposed to ethyl maltol and hexanal. Activated THP-1 cells released increased IL-1β and TNF-α when exposed to ethyl maltol, but many flavoring chemicals had an apparent suppressive effect on inflammatory cytokines released by activated macrophages, some with varying degrees of accompanying cytotoxicity. The diketones, L-carvone, and linalool suppressed cytokine release in the absence of cytotoxicity. These findings provide insight into lung cell cytotoxicity and inflammatory cytokine release in response to flavorings commonly used in e-cigarettes.

Diacetyl and Other Ketones in e-Cigarette Aerosols: Some Important Sources and Contributing Factors

Background: Concerns over the presence of the diketones 2,4 butanedione (DA) and 2,3 pentanedione (AP) in e-cigarettes arise from their potential to cause respiratory diseases. Their presence in e-liquids is a primary source, but they may potentially be generated by glycerol (VG) and propylene glycol (PG) when heated to produce aerosols. Factors leading to the presence of AP, DA and acetoin (AC) in e-cigarette aerosols were investigated. We quantified direct transfer from e-liquids, examined thermal degradation of major e-liquid constituents VG, PG and 1,3 propanediol (1,3 PD) and the potential for AC, AP and DA production from sugars and flavor additives when heated in e-cigarettes.

Method: Transfers of AC, AP and DA from e-liquids to e-cigarette aerosols were quantified by comparing aerosol concentrations to e-liquid concentrations. Thermal generation from VG, PG or 1,3 PD e-liquids was investigated by measuring AC, AP and DA emissions as a function of temperature in an e-cigarette. Thermal generation of AC, AP and DA from sugars was examined by aerosolising e-liquids containing sucrose, fructose or glucose in an e-cigarette. Pyrolytic formation of AP and DA from a range of common flavors was assessed using flash pyrolysis techniques.

Results: AC transfer efficiency was >90%, while AP and DA were transferred less efficiently (65%) indicating losses during aerosolisation. Quantifiable levels of DA were generated from VG and PG, and to a lesser extent 1,3 PD at coil temperatures >300°C. Above 350°C AP was generated from VG and 1,3 PD but not PG. AC was not generated from major constituents, although low levels were generated by thermal reduction of DA. Aerosols from e-liquids containing sucrose contained quantifiable (>6 ng/puff) levels of DA at all sucrose concentrations tested, with DA emissions increasing with increasing device power and concentration. 1% glucose, fructose or sucrose e-liquids gave comparable DA emissions. Furanose ring compounds also generate DA and AP when heated to 250°C.

Conclusions: In addition to less than quantitative direct transfer from the e-liquid, DA and AP can be present in the e-cigarette aerosol due to thermal decomposition reactions of glycols, sugars and furanonse ring flavors under e-cigarette operating conditions.

Strategy for the identification of flavor compounds in e-liquids by correlating the analysis of GCxIMS and GC-MS

This work presents a strategy to correlate the results from gas chromatography coupled ion mobility spectrometry (GCxIMS) and mass spectrometry (GC-MS) to enable a simpler and cheaper analysis of flavor compounds in e-liquids. The use of the retention index for GCxIMS measurements was validated for its application to correlate results with GC-MS data. The easy detection of the GCxIMS for substances at concentrations as low as 1 μg/L can therefore be combined with the identification power of the MS. The use of the MS' mass signals and wide-spread availability of mass spectra libraries reduces the effort necessary to choose the correct reference standards for the identification of unknown substances. Between both detectors, correlating of the retention time indices was achieved for ± 1%. 2-Alkanones were used as an alternative reference point for the IMS and the well-established alkanes for the MS. The application on flavor compounds in e-liquids shows equal or better results than those presented for more complex, hardware-based correlations like line splitting. Additionally, the inverted reduced mobility combined with the retention index of a non-polar column enables simple extrapolation for the confirmation of expected substances as well as the use in a transferable database. For the first time, this comprehensive application allows an extensive, simplified, and cheap identification of flavor compounds in e-liquids by GCxIMS and GC-MS.

Major Constituents of Cannabis Vape Oil Liquid, Vapor and Aerosol in California Vape Oil Cartridge Samples

During the E-cigarette or Vaping product use Associated Lung Injury (EVALI) outbreak of August 2019 to February 2020, the California Department of Public Health, Food and Drug Laboratory Branch received numerous cannabis vape oil cartridge investigation samples from throughout the state. Many of these products were directly linked to patients; others were collected as part of investigations. We determined the major ingredients and additives in twelve unused cannabis vape oil cartridge samples obtained before (n = 2) and during the EVALI outbreak (n = 10) in California from September 2018 to December 2019. We tested for major constituents in vape oil liquid, vape oil vapor, and vape oil aerosol phases. A nontargeted Gas Chromatography Mass Spectrometry direct injection screening method was developed for vape oils, a headspace heating module used for vape oil vapors and a solid-phase microextraction (SPME) vaping rig for aerosols generated by vaping. We have identified more than 100 terpenes and natural extracts, 19 cannabinoids, and other potential toxic additives such as Vitamin E Acetate, Polyethylene Glycols, and Medium Chain Triglycerides. We determined more terpenes and minor cannabinoids can be produced via vaporizing and aerosolizing the vape oil. Delta9-THC and potential toxic additives were found at lower levels in the vapor and aerosol than in the vape liquid.

Review of data on chemical content in an aerosol resulting from heating a tobacco or a solution used in e-cigarettes and in the smoke generated from the reference cigarettes

BACKGROUND

The article presents a review of the literature on the chemical composition of smoke generated from a standard cigarette and the aerosol generated after heating tobacco and chemical compounds formed in the aerosol of electronic cigarettes.

METHODS

The literature review was carried out on the PubMed online bibliographic database, Google search engine, Google Scholar based on science articles published in recent 20 years.

RESULTS

The bibliographic analysis shows that: replacing smoking in the traditional way by heating tobacco modifies significantly the content of chemical substances found in aerosol, the substances found in aerosols generated by e-cigarettes have proven toxic effects, e.g. pro-inflammatory effect on lung epithelial cells (e.g. crotonaldehyde) or a mutagenic effect (e.g. NNK), using e-cigarette aerosol does not rule out a health risk for people, which is not fully recognized at present.

CONCLUSIONS

Replacing smoking in the traditional way by heating tobacco modifies significantly the content of chemical substances found in aerosol. Using e-cigarette aerosol does not rule out a health risk for people, because the substances found in aerosols generated by e-cigarettes have proven toxic effects.

Impact of the Revised European Tobacco Product Directive on the Quality of E-cigarette Refill Liquids in Belgium

INTRODUCTION

Since its introduction, the e-cigarette has become a commonly used consumer product. In this study, we investigate whether regulatory changes had an impact on the quality of refill liquids (e-liquids) available on the Belgian market through analysis of their chemical composition. Hence, the nicotine concentration accuracy was investigated in samples before, during and after the implementation of the revised Tobacco Product Directive (TPD) as an indicator of good manufacturing practices. This is, however, not enough to assure the quality. Therefore, extra criteria were also assessed based on TPD requirements.

METHODS

By using in-house validated methods, a total of 246 e-liquids purchased prior (2013-2015), during (2016) and after (2017-2018) the implementation of the TPD revisions, were analyzed for the presence of nicotine, nicotine-related impurities, volatile organic compounds (VOCs), caffeine and taurine, and the flavors diacetyl and acetylpropionyl.

RESULTS

Although not all manufacturers managed to produce and label their products accurately, nicotine labeling discrepancies have decreased over time. Moreover, also the number of e-liquids, containing high-risk VOCs (10% in 2016 vs. none of the samples in 2017-2018), caffeine (16% in 2017 vs. 5% in 2018), and diacetyl and acetylpropionyl (50% in 2017 vs. 27% in 2018 of sweet-flavored samples) diminished over time.

CONCLUSION

Our results demonstrate that the overall quality of the e-liquids has improved after the implementation of the revised TPD. However, the results also show that periodic quality control might be required to ensure further compliance to the TPD.

IMPLICATIONS

This study clearly demonstrates that the implementation of the revised TPD has improved the quality of the e-liquids on the Belgian market. However, there are still e-liquids that are not in agreement with the TPD due to nicotine concentration label discrepancies, presence of e-liquid impurities and controversial flavors diacetyl and acetylpropionyl or the additive caffeine.

A review of constituents identified in e-cigarette liquids and aerosols

INTRODUCTION

Identification of chemicals present in e-liquids and aerosols is a vital first step in assessing the human health effects of e-cigarettes. We aim to identify the qualitative and quantitative constituents present in e-cigarette liquids and aerosols.

METHODS

A comprehensive search of scientific databases included literature up to July 2020. A total of 28 articles met inclusion criteria; 18 articles assessed e-liquid constituents and 15 articles assessed aerosol constituents. Of these, 5 assessed constituents present in both mediums. We included English-language publications that examine qualitative and/or quantitative constituents in e-cigarette liquids and aerosols.

RESULTS

In total, articles identified 60 compounds in e-liquids and 47 compounds in aerosols. A total of 22 compounds were identified in both e-liquids and aerosols. These are: acenaphthylene, acetaldehyde, acetol, antimony, benzaldehyde, benzene, chromium, copper, diacetyl, formaldehyde, glycerol, lead, limonene, naphthalene, nickel, nicotine, nicotine-N'-oxides, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), N-Nitrosonornicotine (NNN), propylene glycol, toluene, and vegetable glycerin. Some of the identified chemicals have been labeled as harmful, toxic, or cancerous through human, animal, and cell line studies. A variety of laboratory methods were used for analyses, which made reported levels less consistent.

CONCLUSIONS

E-liquids and aerosols contain a variety of chemicals with potential health effects from inhaling them. Further, secondhand health effects are unknown because of limited understanding of the dose of exposure by non-users. Identification of constituents in e-cigarettes is the first step to determine their risks to humans and support evidence-based regulations and health policies.

The Evolving E-cigarette: Comparative Chemical Analyses of E-cigarette Vapor and Cigarette Smoke

Background: E-cigarette designs, materials, and ingredients are continually evolving, with cotton wicks and diverse coil materials emerging as the popular components of atomisers. Another recent development is the use of nicotine salts in e-liquids to replicate the form of nicotine found in cigarette smoke, which may help cigarette smokers to transition to e-cigarettes. However, scientific understanding of the impact of such innovations on e-cigarette aerosol chemistry is limited.

Methods: To address these knowledge gaps, we have conducted a comparative study analyzing relevant toxicant emissions from five e-cigarettes varying in wick, atomiser coil, and benzoic acid content and two tobacco cigarettes, quantifying 97 aerosol constituents and 84 smoke compounds, respectively. Our focus was the potential for benzoic acid in e-liquids and cotton wicks to form aerosol toxicants through thermal degradation reactions, and the potential for nickel–iron alloy coils to catalyze degradation of aerosol formers. In addition, we analyzed e-cigarette emissions for 19 flavor compounds, thermal decomposition products, and e-liquid contaminants that the FDA has recently proposed adding to the established list of Harmful and Potentially Harmful Constituents (HPHCs) in tobacco products.

Results: Analyses for benzene and phenol showed no evidence of the thermal decomposition of benzoic acid in the e-cigarettes tested. Measurements of cotton decomposition products, such as carbonyls, hydrocarbons, aromatics, and PAHs, further indicated that cotton wicks can be used without thermal degradation in suitable e-cigarette designs. No evidence was found for enhanced thermal decomposition of propylene glycol or glycerol by the nickel–iron coil. Sixteen of the 19 FDA-proposed compounds were not detected in the e-cigarettes. Comparing toxicant emissions from e-cigarettes and tobacco cigarettes showed that levels of the nine WHO TobReg priority cigarette smoke toxicants were more than 99% lower in the aerosols from each of five e-cigarettes as compared with the commercial and reference cigarettes.

Conclusions: Despite continuing evolution in design, components and ingredients, e-cigarettes continue to offer significantly lower toxicant exposure alternatives to cigarette smoking.

Identification of flavouring substances of genotoxic concern present in e-cigarette refills

E-cigarettes have become very popular, a trend that has been stimulated by the wide variety of available e-liquid flavours. Considering the large number of e-liquid flavours (>7000), there is an urgent need to establish a screening strategy to prioritize the flavouring substances of highest concern for human health. In the present study, a prioritization strategy combining analytical screening, in silico tools and literature data was developed to identify potentially genotoxic e-liquid flavourings. Based on the analysis of 129 e-liquids collected on the Belgian market, 60 flavourings with positive in silico predictions for genotoxicity were identified. By using literature data, genotoxicity was excluded for 33 of them whereas for 5, i.e. estragole, safrole, 2-furylmethylketon, 2,5-dimethyl-4-hydroxyl-3(2H)-furanone and transhexanal, there was a clear concern for in vivo genotoxicity. A selection of 4 out of the remaining 22 flavourings was tested in two in vitro genotoxicity assays. Three out of the four tested flavourings induced gene mutations and chromosome damage in vitro, whereas equivocal results were obtained for the fourth compound. Thus, although there is a legislative framework which excludes the use of CMR compounds in e-liquids, flavourings of genotoxic concern are present and might pose a health risk for e-cigarette users.

Breath analysis of smokers, non-smokers, and e-cigarette users

Solid phase micro extraction-Gas Chromatography/Mass Spectrometry (SPME-GC/MS) analysis was performed in exhaled breath samples of 48 healthy volunteers: 20 non-smokers, 10 smokers and 18 e-cigarette (EC, vape) users. Each volunteer provided 1 L of exhaled breath in a pre-cleaned Tedlar bag, in which an SPME fiber was exposed to absorb the emitted breath volatile organic compounds (VOCs). The acquired data were processed using multivariate data analysis (MDA) methods in order to identify the characteristic chemicals of the three groups. The results revealed that the breath of non-smokers demonstrated inverse correlation with a variety of molecules related to the breath from smokers including furan, toluene, 2-butanone and other organic substances. Vapers were distinguished from smokers by the chemical speciation of the e-liquids, such as that of esters (e.g. ethyl acetate), terpenes (e.g. α-pinene, β-pinene, d-limonene, p-cymene, etc.) and oxygenated compounds (e.g. 3-hexen-1-ol, benzaldehyde, hexanal, decanal, etc). Two classification models were developed (a) using principal component analysis (PCA) with hierarchical cluster analysis (HCA) and (b) using partial least squares-discriminant analysis (PLS-DA). Both models were validated using 8 new samples (4 vapers and 4 smokers), collected in addition to the 48 samples of the calibration set. The combination of GC/MS breath analysis and MDA contributed successfully in classifying the volunteers into their respective groups and highlighted the relevant characteristic VOCs. The respective dynamic combination (SPME-GC/MS and MDA) provides a means for long term non-invasive monitoring of the population's health status for early detection purposes.

Method Validation Approaches for Analysis of Constituents in ENDS

OBJECTIVE

We assessed how many peer-reviewed publications reporting chemical quantities and/or yields from electronic nicotine delivery systems (ENDS) have included adequate method validation characteristics in the publication for appropriate interpretation of data quality for informing tobacco regulatory science.

METHODS

We searched 5 databases (Web of Knowledge, PubMed, SciFinder, Embase, EBSCOhost) for ENDS publications between January 2007 and September 2018. Of the 283 publications screened, 173 publications were relevant for analysis. We identified the publications that report a certain degree of control in data quality, ie, the publications that report marginally validated methods (MVMs). MVMs refer to the methods that: (1) report 3 or more International Conference on Harmonisation (ICH) method validation characteristics, (2) state the method was validated, (3) cite their own previous publication(s) that report MVMs, or (4) use a method within the accreditation scope of an accredited laboratory.

RESULTS

Overall, 97 publications (56%) report MVMs in their studies. This percentage also reflects the publication distribution for the majority of the 28 chemicals measured by MVMs.

CONCLUSIONS

This study highlights the need for reporting sufficient validation characteristics following appropriate guidance to ensure the accuracy and reliability of the published analytical data for proper data interpretations that may support policy.

Passive exposure of non-smokers to E-Cigarette aerosols: Sensory irritation, timing and association with volatile organic compounds

AIM

The current study examined symptoms of irritation reported by non-smokers passively exposed to e-cigarette aerosols and their timing and association with the concentrations of volatile organic compounds (VOCs) produced.

METHODS

40 healthy non-smoking adults were exposed to e-cigarette aerosols for 30 min in a 35 m³ room. Second-hand e-cigarette aerosol (SHA) was produced by an experienced e-cigarette user using a standardized topography and two resistance settings (exposure 0.5 Ohm and 1.5 Ohm), in addition to a control session (no emissions). PM_2.5 and PM_1.0 were continuously measured over the duration of exposure, while Volatile Organic Compounds (VOCs) were recorded at 0, 15 and 30 min (t₀, t₁₅ and t₃₀) of exposure. Each participant completed an irritation questionnaire at t₀, t_15, t₃₀ of exposure and t₆₀ (30 min post-exposure) on ocular, nasal, throat-respiratory symptoms of irritation and general complaints. Kruskal-Wallis H test for PM comparisons, repeated measures ANOVA for VOCs and Generalized Estimating Equations for symptoms of irritation and association with VOCs were used for statistical analysis.

RESULTS

20 males and 20 females, with a mean age of 24.6 years (SD = 4.3) and exhaled CO < 7 ppm participated. PM concentrations in both experimental sessions were higher than the Control (p < 0.001). The most commonly reported symptoms were burning, dryness, sore throat, cough, breathlessness and headache. During both experimental sessions, ocular, nasal, throat-respiratory symptoms and general complaints increased significantly (p < 0.05). Ocular and nasal symptoms returned to baseline by t₆₀ (p > 0.05) while throat-respiratory symptoms were still significantly higher at t₆₀ (p = 0.044). VOCs were significantly associated with reported nasal and throat-respiratory symptoms in both experimental sessions (p < 0.05).

CONCLUSION

A 30-min exposure to SHA provoked symptoms of sensory irritation and general complaints that lasted up to 30 min after the exposure and were positively associated with the concentrations of the VOC mixture emitted.

Potential Hazards Not Communicated in Safety Data Sheets of Flavoring Formulations, Including Diacetyl and 2,3-Pentanedione

Objectives

Workers using flavoring formulations containing diacetyl and 2,3-pentanedione may be at risk of inhalational exposure, as these volatile hazardous chemicals are emitted from the bulk material, especially at elevated temperatures. However, flavoring formulations that contain diacetyl and 2,3-pentanedione might not list these ingredients because they are generally recognized as safe to ingest, may be part of a proprietary mixture deemed a trade secret, or may not be required to be listed if they are present at <1% composition. The objective of this study was to investigate whether potential inhalational hazards present in flavoring samples were reported as chemical ingredients on their corresponding safety data sheets (SDSs).

Methods

A convenience sample of 26 bulk liquid flavorings obtained from two coffee roasting and packaging facilities in the USA was analyzed for 20 volatile organic chemicals present in the headspaces of vials containing flavoring liquids using gas chromatography-mass spectrometry. Flavoring samples were included in the study if headspace analysis results and SDSs were available. Flavoring samples included hazelnut, French vanilla, amaretto, chocolate, and caramel as well as some flavoring mixtures containing added fruit flavors such as cherry and raspberry. The presence of a chemical in the flavoring formulation was then compared to the ingredient list on the SDSs.

Results

All the flavoring SDSs contained trade secret designations. None of the SDSs listed diacetyl or 2,3-pentanedione. Headspace analyte concentrations revealed that diacetyl was present in 21 of 26 samples (81%) with a maximum concentration of 5.84 × 10(4) µg m-3 in flavor 18 (caramel). 2,3-Pentanedione was present in 15 flavors (58%) with a maximum concentration of 3.79 × 10(5) µg m-3 in flavor 24 (oatmeal cookies).

Conclusions

A majority of the flavorings tested had diacetyl, 2,3-pentanedione, or both as volatile constituents in the headspace. These chemicals were not listed on the SDSs, but inclusion of diacetyl and 2,3-pentanedione on SDSs would serve to protect downstream users from unrecognized exposure and potential respiratory disease. The headspace technique presented here is a viable tool to rapidly screen for volatile hazardous chemicals that may be present in flavoring formulations. Facilities that use flavorings should be aware that constituents in flavorings may present a potential inhalational hazard even if not identified as such by the SDS. A precautionary approach is warranted when working with flavorings, including exposure monitoring and effective exposure control strategies such as containment and local exhaust ventilation.

Effects of flavoring compounds used in electronic cigarette refill liquids on endothelial and vascular function

Electronic cigarette refill liquids are commercially provided with a wide variety of flavoring agents. A recent study suggested that several common flavors may scavenge nitric oxide (NO) and cause endothelial dysfunction. It was the aim of the present study to investigate the effects of these flavors on NO/cyclic GMP-mediated signaling and vascular relaxation. We tested the flavoring agents for effects on Ca²⁺-induced cGMP accumulation and NO synthase activation in cultured endothelial cells. NO scavenging was studied with NO-activated soluble guanylate cyclase and as NO release from a NO donor, measured with a NO electrode. Blood vessel function was studied with precontracted rat aortic rings in the absence and presence of acetylcholine or a NO donor. Cinnamaldehyde inhibited Ca²⁺-stimulated endothelial cGMP accumulation and NO synthase activation at ≥0.3 mM. Cinnamaldehyde and diacetyl inhibited NO-activated soluble guanylate cyclase with IC₅₀ values of 0.56 (0.54–0.58) and 0.29 (0.24–0.36) mM, respectively, and caused moderate NO scavenging at 1 mM that was not mediated by superoxide anions. The other compounds did not scavenge NO at 1 mM. None of the flavorings interfered with acetylcholine-induced vascular relaxation, but they caused relaxation of pre-contracted aortas. The most potent compounds were eugenol and cinnamaldehyde with EC₅₀ values of ~0.5 mM. Since the flavors did not affect endothelium-dependent vascular relaxation, NO scavenging by cinnamaldehyde and diacetyl does not result in impaired blood vessel function. Although not studied in vivo, the low potency of the compounds renders it unlikely that the observed effects are relevant to humans inhaling flavored vapor from electronic cigarettes.

Adolescents' E-Cigarette Use: Increases in Frequency, Dependence, and Nicotine Exposure Over 12 Months

PURPOSE

This study examined changes in e-cigarette and dual-use frequency, levels of nicotine exposure and e-cigarette dependence, and device and e-liquid preferences over 12 months.

METHODS

Adolescents (N = 173, aged 13-18 years) who reported past-month e-cigarette use and at least 10 lifetime uses were recruited from the San Francisco Bay Area. The sample was 75.1% male, 54.9% non-Hispanic White, mean age 16.6 years (standard deviation = 1.2); 26.6% reported past-month cigarette smoking at baseline (i.e., dual use). At baseline, 6-month, and 12-month follow-up, participants provided saliva samples for cotinine testing and self-reported e-cigarette use frequency, dependence, past-month smoking, product preference, and flavor preference.

RESULTS

Most (80.3%) were still using e-cigarettes at 12 months, and daily use increased from 14.5% to 29.8%. Model testing indicated an overall increase from baseline to 12 months in frequency of e-cigarette use (F(2, 166) = 5.69, p = .004), dependence (F(2, 164) = 5.49, p = .005), and cotinine levels (F(2, 103) = 4.40, p = .038). Among those reporting only e-cigarette use at baseline, 28.8% reported combustible cigarette use during follow-up. Among those reporting dual use at baseline, 57.1% were still dual using at 12 months, 31.4% reported e-cigarette use only, and none abstained from both products. Higher nicotine delivering e-cigarette devices (i.e., Juul, mods) became more popular over time, whereas flavor preferences (i.e., fruit, mint/menthol, and candy) remained stable.

CONCLUSIONS

Adolescents' e-cigarette use persisted over a 12-month period with significant increases in frequency of use, nicotine exposure, and e-cigarette dependence. Transitions from single to dual and dual to single nicotine product use were observed in approximately one in three users over the study period.

Measuring e-cigarette addiction among adolescents

BACKGROUND AND OBJECTIVES

With high rates of use and uncertain consequences, valid electronic cigarette (e-cigarette) use frequency and addiction measures for adolescents are needed. This cross-sectional study examined correlations for multiple measures of adolescent e-cigarette use with nicotine exposure quantified with salivary cotinine levels.

METHODS

Adolescents (N=173, age 13-18) who reported past-month e-cigarette use were recruited from the San Francisco Bay Area. Participants self-reported: (1) days of e-cigarette use in a typical month, (2) number of e-cigarette sessions in a typical day (sessions per day; SPD) and the (3) E-Cigarette Addiction Severity Index (EASI). Participants also completed the 10-item Penn State Electronic Cigarette Dependence Index (ECDI), which we examined in full and as a 2-item Heaviness of Vaping Index (HVI; the sum of the ECDI items on use frequency and time to first vaping on wakening). Sessions per month (SPM) were calculated using days per month and SPD. Cotinine levels, SPD and SPM were log-transformed.

RESULTS

Among frequency measures, SPM correlated most strongly with cotinine (r=0.59), followed closely by days per month (r=0.58) and SPD (r=0.57), p<0.001. Among dependence measures, the EASI correlated most strongly with cotinine (r=0.51), closely followed by the ECDI and HVI (r's=0.50), all p's<0.001.

CONCLUSIONS

Adolescents' reports of frequency of e-cigarette use and degree of addiction correlated significantly with cotinine as a biomarker of nicotine exposure. We recommend the EASI and days per month as brief general measures. SPM and the ECDI are more extensive measures that may yield a more nuanced understanding of use.