The Impact of Device Settings, Use Patterns, and Flavorings on Carbonyl Emissions from Electronic Cigarettes

Physical and Chemical Characterization of Aerosols Produced from Experimentally Designed Nicotine Salt-Based E-Liquids

Nicotine salt-based e-liquids deliver nicotine more rapidly and efficiently to electronic nicotine delivery system (ENDS) users than freebase nicotine formulations. Nicotine salt-based products represent a substantial majority of the United States ENDS market. Despite the popularity of nicotine salt formulations, the chemical and physical characteristics of aerosols produced by nicotine salt e-liquids are still not well understood. To address this, this study reports the harmful and potentially harmful constituents (HPHCs) and particle sizes of aerosols produced by laboratory-made freebase nicotine and nicotine salt e-liquids. The nicotine salt e-liquids were formulated with benzoic acid, citric acid, lactic acid, malic acid, or oxalic acid. The nicotine salt aerosols had different HPHC profiles than the freebase nicotine aerosols, indicating that the carboxylic acids were not innocent bystanders. The polycarboxylic acid e-liquids containing citric acid, malic acid, or oxalic acid produced higher acrolein yields than the monocarboxylic acid e-liquids containing benzoic acid or lactic acid. Across most PG:VG ratios, nicotine benzoate or nicotine lactate aerosols contained the highest nicotine quantities (in %) and the highest nicotine yields (per milligram of aerosol). Additionally, the nicotine benzoate and nicotine lactate e-liquids produced the highest carboxylic acid yields under all tested conditions. The lower acid yields of the citric, malic, and oxalic acid formulations are potentially due to a combination of factors such as lower transfer efficiencies, lower thermostabilities, and greater susceptibility to side reactions because of their additional carboxyl groups serving as new sites for reactivity. For all nicotine formulations, the particle size characteristics were primarily controlled by the e-liquid solvent ratios, and there were no clear trends between nicotine salt and freebase nicotine aerosols that indicated nicotine protonation affected particle size. The carboxylic acids impacted aerosol output, nicotine delivery, and HPHC yields in distinct ways such that interchanging them in ENDS can potentially cause downstream effects.

Harmful and Potentially Harmful Constituents in E-Liquids and Aerosols from Electronic Nicotine Delivery Systems (ENDS)

In 2012, the U.S. Food & Drug Administration (FDA) published an established list of 93 harmful and potentially harmful constituents (HPHCs) targeting four tobacco product types (cigarettes, cigarette tobacco, roll-your-own tobacco, smokeless tobacco). In 2016, the FDA finalized the deeming rule to regulate electronic nicotine delivery systems (ENDS). However, knowledge gaps exist regarding whether certain HPHCs are present in ENDS e-liquids and aerosols. We identified and addressed these gaps by conducting literature searches and then experimentally quantifying HPHCs in the e-liquid and aerosol of 37 ENDS brands based on gaps in the literature. The literature searches identified 66 e-liquid HPHCs and 68 aerosol HPHCs that have limited to no information regarding the quantifiability of these constituents. A contracted ISO 17025 accredited laboratory performed the HPHC quantifications. The availability of validated analytical methods in the contracted laboratory determined the HPHCs included in the study scope (63/66 for e-liquids, 64/68 for aerosols). Combining the results from the quantifications and literature searches, 36 (39%) and 34 (37%) HPHCs were found quantifiable (≥limit of quantification [LOQ]) in ENDS e-liquids and aerosols, respectively, with 25 HPHCs being quantifiable in both matrices. Quantifiability results imply potential HPHC transfers between matrices, leaching from components, or formations from aerosol generation. The study results can inform the scientific basis for manufacturers and regulators regarding regulatory requirements for HPHC reporting. The HPHC quantities can also inform evaluations of the public health impact of ENDS and public communications regarding ENDS health risks.

Healthcare costs attributable to e-cigarette use and subsequent uptake of cigarette smoking by Australians who have never smoked

Objective New legislation to curb the rapid increase in e-cigarette use among youth is underway. We estimated the future healthcare costs for chronic diseases from e-cigarette use among never smokers who transition to tobacco smoking. Methods Using population-attributable fractions, we estimated the health expenditure attributable to e-cigarettes based on the prevalence of e-cigarette use, uptake of tobacco smoking, and risk of smoking on developing chronic disease. Data for men and women were derived from published reports on e-cigarette use prevalence, risk of smoking-related disease and addiction, and health expenditure for 25 diseases. Sensitivity analyses were undertaken to address data input variation. Results Future healthcare costs attributed to new e-cigarette-initiated smokers were conservatively estimated to be (in Australian dollars) $179.6 million annually. Collectively, the estimated costs were highest for respiratory diseases ($102.2 million; 57% of total costs), malignant cancers ($49.6 million; 28%), and cardiovascular disease ($27.7 million; 15%). The uptake rate of e-cigarettes was more important in driving healthcare costs than the proportion moving from e-cigarettes to cigarette smoking. Conclusion High avoidable health system costs are predicted for the treatment of chronic conditions created by e-cigarette-initiated smoking. These costs exclude the immediate and direct healthcare harms of e-cigarette-related poisoning, lung injury, and respiratory problems, and costs associated with the unknown health harms of e-cigarette use alone. The proposed regulations to curb recreational e-cigarette use in Australia are set to prevent expensive health care arising sometime in the future from new cigarette smokers.

Nicotine and Cardiovascular Health: When Poison is Addictive - a WHF Policy Brief

Nicotine is universally recognized as the primary addictive substance fuelling the continued use of tobacco products, which are responsible for over 8 million deaths annually. In recent years, the popularity of newer recreational nicotine products has surged drastically in many countries, raising health and safety concerns. For decades, the tobacco industry has promoted the myth that nicotine is as harmless as caffeine. Nonetheless, evidence shows that nicotine is far from innocuous, even on its own. In fact, numerous studies have demonstrated that nicotine can harm multiple organs, including the respiratory and cardiovascular systems. Tobacco and recreational nicotine products are commercialized in various types and forms, delivering varying levels of nicotine along with other toxic compounds. These products deliver nicotine in profiles that can initiate and perpetuate addiction, especially in young populations. Notably, some electronic nicotine delivery systems (ENDS) and heated tobacco products (HTP) can deliver concentrations of nicotine that are comparable to those of traditional cigarettes. Despite being regularly advertised as such, ENDS and HTP have demonstrated limited effectiveness as tobacco cessation aids in real-world settings. Furthermore, ENDS have also been associated with an increased risk of cardiovascular disease. In contrast, nicotine replacement therapies (NRT) are proven to be safe and effective medications for tobacco cessation. NRTs are designed to release nicotine in a slow and controlled manner, thereby minimizing the potential for abuse. Moreover, the long-term safety of NRTs has been extensively studied and documented. The vast majority of tobacco and nicotine products available in the market currently contain nicotine derived from tobacco leaves. However, advancements in the chemical synthesis of nicotine have introduced an economically viable alternative source. The tobacco industry has been exploiting synthetic nicotine to circumvent existing tobacco control laws and regulations. The emergence of newer tobacco and recreational nicotine products, along with synthetic nicotine, pose a tangible threat to established tobacco control policies. Nicotine regulations need to be responsive to address these evolving challenges. As such, governments should regulate all tobacco and non-medical nicotine products through a global, comprehensive, and consistent approach in order to safeguard tobacco control progress in past decades.

Carbonyls and Aerosol Mass Generation from Vaping Nicotine Salt Solutions Using Fourth- and Third-Generation E-Cigarette Devices: Effects of Coil Resistance, Coil Age, and Coil Metal Material

Aerosol formation and production yields from 11 carbonyls (carbonyl concentration per aerosol mass unit) were investigated (1) from a fourth-generation (4th gen) e-cigarette device at different coil resistances and coil age (0-5000 puffs) using unflavored e-liquid with 2% benzoic acid nicotine salt, (2) between a sub-ohm third-generation (3rd gen) tank mod at 0.12 Ω and a 4th gen pod at 1.2 Ω using e-liquid with nicotine salt, together with nicotine yield, and (3) from 3rd gen coils of different metals (stainless steel, kanthal, nichrome) using e-liquid with freebase nicotine. Coil resistance had an inverse relationship with coil temperature, and coil temperature was directly proportional to aerosol mass formation. Trends in carbonyl yields depended on carbonyl formation mechanisms. Carbonyls produced primarily from thermal degradation chemistry (e.g., formaldehyde, acetaldehyde, acrolein, propionaldehyde) increased per aerosol mass with higher coil resistances, despite lower coil temperature. Carbonyls produced primarily from chemistry initiated by reactive oxygen species (ROS) (e.g., hydroxyacetone, dihydroxyacetone, methylglyoxal, glycolaldehyde, lactaldehyde) showed the opposite trend. Coil age did not alter coil temperature nor aerosol mass formation but had a significant effect on carbonyl formation. Thermal carbonyls were formed optimally at 500 puffs in our study and then declined to a baseline, whereas ROS-derived carbonyls showed a slow rise to a maximum trend with coil aging. The 3rd gen versus 4th gen device comparison mirrored the trends in coil resistance. Nicotine yields per aerosol mass were consistent between 3rd and 4th gen devices. Coil material did not significantly alter aerosol formation nor carbonyl yield when adjusted for wattage. This work shows that sub-ohm coils may not necessarily produce higher carbonyl yields even when they produce more aerosol mass. Furthermore, carbonyl formation is dynamic and not generalizable during the coil's lifetime. Finally, studies that compare data across different e-cigarette devices, coil age, and coil anatomy should account for the aerosol chemistry trends that depend on these parameters.

Carbonyl Emissions and Heating Temperatures across 75 Nominally Identical Electronic Nicotine Delivery System Products: Do Manufacturing Variations Drive Pulmonary Toxicant Exposure?

Studies of factors that impact electronic nicotine delivery systems (ENDSs) carbonyl compound (CC) emissions have been hampered by wide within-condition variability. In this study, we examined whether this variability may be related to heating coil temperature variations stemming from manufacturing differences. We determined the mean peak temperature rise (ΔTmax) and CC emissions from 75 Subox ENDSs powered at 30 W. We found that ΔTmax and CC emissions varied widely, with greater ΔTmax resulting in exponentially higher CC emissions. Also, 12% of atomizers accounted for 85% of total formaldehyde emissions. These findings suggest that major reductions in toxicant exposure might be achieved through regulations focusing on limiting coil temperature.

Menthol flavoring in e-cigarette condensate causes pulmonary dysfunction and cytotoxicity in precision cut lung slices

E-cigarette consumption is under scrutiny by regulatory authorities due to concerns about product toxicity, lack of manufacturing standards, and increasing reports of e-cigarette- or vaping-associated acute lung injury. In vitro studies have demonstrated cytotoxicity, mitochondrial dysfunction, and oxidative stress induced by unflavored e-cigarette aerosols and flavoring additives. However, e-cigarette effects on the complex lung parenchyma remain unclear. Herein, the impact of e-cigarette condensates with or without menthol flavoring on functional, structural, and cellular responses was investigated using mouse precision cut lung slices (PCLS). PCLS were exposed to e-cigarette condensates prepared from aerosolized vehicle, nicotine, nicotine + menthol, and menthol e-fluids at doses from 50 to 500 mM. Doses were normalized to the glycerin content of vehicle. Video-microscopy of PCLS revealed impaired contractile responsiveness of airways to methacholine and dampened ciliary beating following exposure to menthol-containing condensates at concentrations greater than 300 mM. Following 500 mM menthol-containing condensate exposure, epithelial exfoliation in intrabronchial airways was identified in histological sections of PCLS. Measurement of lactate dehydrogenase release, mitochondrial water-soluble-tetrazolium salt-1 conversion, and glutathione content supported earlier findings of nicotine or nicotine + menthol e-cigarette-induced dose-dependent cytotoxicity and oxidative stress responses. Evaluation of PCLS metabolic activity revealed dose-related impairment of mitochondrial oxidative phosphorylation and glycolysis after exposure to menthol-containing condensates. Taken together, these data demonstrate prominent menthol-induced pulmonary toxicity and impairment of essential physiological functions in the lung, which warrants concerns about e-cigarette consumer safety and emphasizes the need for further investigations of molecular mechanisms of toxicity and menthol effects in an experimental model of disease.

High-CBD Cannabis Vapor Attenuates Opioid Reward and Partially Modulates Nociception in Female Rats

Chronic pain patients report analgesic effects when using cannabidiol (CBD), a phytocannabinoid found in whole-plant cannabis extract (WPE). Several studies suggest that cannabis-derived products may serve as an analgesic adjunct or alternative to opioids, and importantly, CBD may also attenuate the abuse potential of opioids. Vaping is a popular route of administration among people who use cannabis, however both the therapeutic and hazardous effects of vaping are poorly characterized. Despite the fact that chronic pain is more prevalent in women, the ability of inhaled high-CBD WPE to relieve pain and reduce opioid reward has not been studied in females. Here, we present a comprehensive analysis of high-CBD WPE vapor inhalation in female rats. We found that WPE was modestly efficacious in reversing neuropathy-induced cold allodynia in rats with spared nerve injury (SNI). Chronic exposure to WPE did not affect lung cytoarchitecture or estrous cycle, and it did not induce cognitive impairment, social withdrawal or anxiolytic effects. WPE inhalation prevented morphine-induced conditioned place preference and reinstatement. Similarly, WPE exposure reduced fentanyl self-administration in rats with and without neuropathic pain. We also found that WPE vapor lacks of reinforcing effects compared to the standard excipient used in most vapor administration research. Combined, these results suggest that although high-CBD vapor has modest analgesic effects, it has a robust safety profile, no abuse potential, and it significantly reduces opioid reward in females. Clinical studies examining high-CBD WPE as an adjunct treatment during opioid use disorder are highly warranted.

Toxicological Assessment of Particulate and Metal Hazards Associated with Vaping Frequency and Device Age

Electronic nicotine delivery systems (ENDS) aerosols are complex mixtures of chemicals, metals, and particles that may present inhalation hazards and adverse respiratory health risks. Despite being considered a safer alternative to tobacco cigarettes, metal exposure levels and respiratory effects associated with device aging and vaping frequency have not been fully characterized. In this study, we utilize an automated multi-channel ENDS aerosol generation system (EAGS) to generate aerosols from JUUL pod-type ENDS using tobacco-flavored e-liquid. Aerosol puff fractions (1-50) and (101-150) are monitored and sampled using various collection media. Extracted aerosols are prepared for metal and toxicological analysis using human primary small airway epithelial cells (SAEC). ENDS aerosol-mediated cellular responses, including reactive oxygen species (ROS), oxidative stress, cell viability, and DNA damage, are evaluated after 24 h and 7-day exposures. Our results show higher particle concentrations in later puff fractions (0.135 mg/m3) than in initial puff fractions (0.00212 mg/m3). Later puff fraction aerosols contain higher toxic metal concentrations, including chromium, copper, and lead, which elicit increased levels of ROS followed by significant declines in total glutathione and cell viability. Notably, a 30% increase in DNA damage was observed after 7 days because of later puff fraction exposures. This work is consistent with ENDS aerosols becoming more hazardous across the use of pre-filled pod devices, which may threaten respiratory health.

Critical Review of the Recent Literature on Organic Byproducts in E-Cigarette Aerosol Emissions

We review the literature on laboratory studies quantifying the production of potentially toxic organic byproducts (carbonyls, carbon monoxide, free radicals and some nontargeted compounds) in e-cigarette (EC) aerosol emissions, focusing on the consistency between their experimental design and a realistic usage of the devices, as determined by the power ranges of an optimal regime fulfilling a thermodynamically efficient process of aerosol generation that avoids overheating and "dry puffs". The majority of the reviewed studies failed in various degrees to comply with this consistency criterion or supplied insufficient information to verify it. Consequently, most of the experimental outcomes and risk assessments are either partially or totally unreliable and/or of various degrees of questionable relevance to end users. Studies testing the devices under reasonable approximation to realistic conditions detected levels of all organic byproducts that are either negligible or orders of magnitude lower than in tobacco smoke. Our review reinforces the pressing need to update and improve current laboratory standards by an appropriate selection of testing parameters and the logistical incorporation of end users in the experimental design.

Kinetics of Aldehyde Flavorant-Acetal Formation in E-Liquids with Different E-Cigarette Solvents and Common Additives Studied by 1H NMR Spectroscopy

Flavorants, nicotine, and organic acids are common additives found in the e-liquid carrier solvent, propylene glycol (PG) and/or glycerol (GL), at various concentrations. Some of the most concentrated and prevalent flavorants in e-liquids include trans-cinnamaldehyde, vanillin, and benzaldehyde. Aldehyde flavorants have been shown to react with PG and GL to form flavorant-PG and -GL acetals that have unique toxicity properties in e-liquids before aerosolization. However, there is still much that remains unknown about the effects of different e-cigarette solvents, water, nicotine, and organic acids on the rate of acetalization in e-liquids. We used 1H NMR spectroscopy to determine the first-order initial rate constant, half-life, and % acetal formed at equilibrium for flavorant-acetal formation in simulated e-liquids. Herein, we report that acetalization generally occurs at a faster rate and produces greater yields in e-liquids with higher ratios of GL (relative to PG). trans-Cinnamaldehyde acetals formed the fastest in 100% PG-simulated e-liquids, followed by benzaldehyde and vanillin based on their half-lives and rate constants. The acetal yield was greatest for benzaldehyde in PG e-liquids, followed by trans-cinnamaldehyde and vanillin. Acetalization in PG e-liquids containing aldehyde flavorants was inhibited by water and nicotine but catalyzed by benzoic acid. Flavorant-PG acetal formation was generally delayed in the presence of nicotine, even if benzoic acid was present at 2-, 4-, or 10-fold the nicotine concentration, as compared to the PG e-liquids with 2.5 mg/mL flavorant. Thus, commercial e-liquids with aldehyde flavorants containing a higher GL ratio (relative to PG), little water, no nicotine, nicotine with excess organic acids, or organic acids without nicotine would undergo acetalization the fastest and with the highest yield. Many commercial e-liquids must therefore contain significant amounts of flavorant acetals.

Effects of Common e-Liquid Flavorants and Added Nicotine on Toxicant Formation during Vaping Analyzed by 1H NMR Spectroscopy

A broad variety of e-liquids are used by e-cigarette consumers. Additives to the e-liquid carrier solvents, propylene glycol and glycerol, often include flavorants and nicotine at various concentrations. Flavorants in general have been reported to increase toxicant formation in e-cigarette aerosols, yet there is still much that remains unknown about the effects of flavorants, nicotine, and flavorants + nicotine on harmful and potentially harmful constituents (HPHCs) when aerosolizing e-liquids. Common flavorants benzaldehyde, vanillin, benzyl alcohol, and trans-cinnamaldehyde have been identified as some of the most concentrated flavorants in some commercial e-liquids, yet there is limited information on their effects on HPHC formation. E-liquids containing flavorants + nicotine are also common, but the specific effects of flavorants + nicotine on toxicant formation remain understudied. We used 1H NMR spectroscopy to evaluate HPHCs and herein report that benzaldehyde, vanillin, benzyl alcohol, trans-cinnamaldehyde, and mixtures of these flavorants significantly increased toxicant formation produced during e-liquid aerosolization compared to unflavored e-liquids. However, e-liquids aerosolized with flavorants + nicotine decreased the HPHCs for benzaldehyde, vanillin, benzyl alcohol, and a "flavorant mixture" but increased the HPHCs for e-liquids containing trans-cinnamaldehyde compared to e-liquids with flavorants and no nicotine. We determined how nicotine affects the production of HPHCs from e-liquids with flavorant + nicotine versus flavorant, herein referred to as the "nicotine degradation factor". Benzaldehyde, vanillin, benzyl alcohol, and a "flavorant mixture" with nicotine showed lower HPHC levels, having nicotine degradation factors <1 for acetaldehyde, acrolein, and total formaldehyde. HPHC formation was most inhibited in e-liquids containing vanillin + nicotine, with a degradation factor of ∼0.5, while trans-cinnamaldehyde gave more HPHC formation when nicotine was present, with a degradation factor of ∼2.5 under the conditions studied. Thus, the effects of flavorant molecules and nicotine are complex and warrant further studies on their impacts in other e-liquid formulations as well as with more devices and heating element types.

Thirdhand smoke from tobacco, e-cigarettes, cannabis, methamphetamine and cocaine: Partitioning, reactive fate, and human exposure in indoor environments

A source of chemical exposure to humans, thirdhand smoke (THS) refers to the contamination that persists indoors following the cessation of a smoking event. The composition of thirdhand smoke depends on the type of substance from which it originates. Although past studies have investigated the effects of tobacco THS on indoor air quality and human health, few have focused on the chemical composition and health impacts of other sources and components of THS. Here we review the state of knowledge of the composition and partitioning behavior of various types of indoor THS, with a focus on THS from tobacco, e-cigarettes, cannabis, and illicit substances (methamphetamine and cocaine). The discussion is supplemented by estimates of human exposure to THS components made with a chemical fate and exposure model. The modeling results show that while very volatile THS compounds (i.e., aromatics) are likely to be taken up by inhalation, highly water-soluble compounds tended to be dermally absorbed. Conversely, minimally volatile THS compounds with low solubility are predicted to be ingested through hand-to-mouth and object-to-mouth contact.

Carbonyl Composition and Electrophilicity in Vaping Emissions of Flavored and Unflavored E-Liquids

It has been demonstrated that propylene glycol (PG), vegetable glycerin (VG), and flavoring chemicals can thermally degrade to form carbonyls during vaping, but less is known about carbonyl emissions produced by transformation of flavoring chemicals and the interactive effects among e-liquid constituents. This study characterized carbonyl composition and levels in vaping emissions of PG-VG (e-liquid base solvents) and four e-liquid formulations flavored with trans-2-hexenol, benzyl alcohol, l-(-)-menthol, or linalool. Utilizing gas chromatography (GC)- and liquid chromatography (LC)-mass spectrometry (MS) methods, 14 carbonyls were identified and quantified. PG-VG emitted highest levels of formaldehyde, acetaldehyde, and acrolein. However, flavored e-liquids contributed to the production of a wider variety of carbonyls, with some carbonyls directly corresponding to the oxidation of alcohol moieties in flavoring compounds (e.g., trans-2-hexenol and benzyl alcohol transformed into trans-2-hexenal and benzaldehyde, respectively). Detections of formaldehyde-GSH and trans-2-hexenal-GSH adducts signify interactions of carbonyls with biological nucleophiles. The global reactivity descriptors (I, A, μ, η, and ω) and condensed Fukui parameters (fk0, fk-, fk+, and dual-descriptor) were computed to elucidate site reactivities of selected simple and α,β-unsaturated carbonyls found in vaping emissions. Overall, this study highlights carbonyl emissions and reactivities and their potential health risk effects associated with vaping.