Metal concentrations in electronic cigarette aerosol: Effect of open-system and closed-system devices and power settings

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.

Composition of e-cigarette aerosols: A review and risk assessment of selected compounds

The potential harms and benefits of e-cigarettes, or electronic nicotine delivery systems (ENDS), have received significant attention from public health and regulatory communities. Such products may provide a reduced risk means of nicotine delivery for combustible cigarette smokers while being inappropriately appealing to nicotine naive youth. Numerous authors have examined the chemical complexity of aerosols from various open- and closed-system ENDS. This body of literature is reviewed here, with the risks of ENDS aerosol exposure among users evaluated with a margin of exposure (MoE) approach for two non-carcinogens (methylglyoxal, butyraldehyde) and a cancer risk analysis for the carcinogen N-nitrosonornicotine (NNN). We identified 96 relevant papers, including 17, 13, and 5 reporting data for methylglyoxal, butyraldehyde, and NNN, respectively. Using low-end (minimum aerosol concentration, low ENDS use) and high-end (maximum aerosol concentration, high ENDS use) assumptions, estimated doses for methylglyoxal (1.78 × 10-3-135 μg/kg-bw/day) and butyraldehyde (1.9 × 10-4-66.54 μg/kg-bw/day) corresponded to MoEs of 227-17,200,000 and 271-280,000,000, respectively, using identified points of departure (PoDs). Doses of 9.90 × 10-6-1.99 × 10-4 μg/kg-bw/day NNN corresponded to 1.4-28 surplus cancers per 100,000 ENDS users, relative to a NNN-attributable surplus of 7440 per 100,000 cigarette smokers. It was concluded that methylglyoxal and butyraldehyde in ENDS aerosols, while not innocuous, did not present a significant risk of irritant effects among ENDS users. The carcinogenic risks of NNN in ENDS aerosols were reduced, but not eliminated, relative to concentrations reported in combustible cigarette smoke.

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.

Examining the Oxidation States of Metals in Aerosols Emitted by Electronic Cigarettes

Electronic cigarettes (ECs) emit many toxic substances, including metals, that can pose a threat to users and the environment. The toxicity of the emitted metals depends on their oxidation states. Hence, this study examines the oxidation states of metals observed in EC aerosols. X-ray photoelectron spectroscopy analysis of the filters that collected EC aerosols identified the oxidation states of five primary metals (based on surface sample analysis), including chromium(III) (close to 100%) under low power setting while a noticeable amount of chromium(VI) (15%) at higher power settings of the EC, and copper(II) (100%), zinc(II) (100%), nickel(II) (100%), lead(II) (65%), and lead(IV) (35%) regardless of power settings. This observation indicates that the increased temperature due to higher power settings could alter the oxidation states of certain metals. We noted that many metals were in their lesser toxic states; however, inhaling these metals may still pose health risks.

Quantification of Free Radicals from Vaping Electronic Cigarettes Containing Nicotine Salt Solutions with Different Organic Acid Types and Concentrations

Electronic (e-) cigarette formulations containing nicotine salts from a range of organic acid conjugates and pH values have dominated the commercial market. The acids in the nicotine salt formulations may alter the redox environment in e-cigarettes, impacting free radical formation in e-cigarette aerosol. Here, the generation of aerosol mass and free radicals from a fourth-generation e-cigarette device was evaluated at 2 wt % nicotine salts (pH 7, 30:70 mixture propylene glycol to vegetable glycerin) across eight organic acids used in e-liquids: benzoic acid (BA), salicylic acid (SLA), lactic acid (LA), levulinic acid (LVA), succinic acid (SA), malic acid (MA), tartaric acid (TA), and citric acid (CA). Furthermore, 2 wt % BA nicotine salts were studied at the following nicotine to acid ratios: 1:2 (pH 4), 1:1 (pH 7), and 2:1 (pH 8), in comparison with freebase nicotine (pH 10). Radical yields were quantified by spin-trapping and electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra of free radicals in the nicotine salt aerosol matched those generated from the Fenton reaction, which are primarily hydroxyl (OH) radicals and other reactive oxygen species (ROS). Although the aerosol mass formation was not significantly different for most of the tested nicotine salts and acid concentrations, notable ROS yields were observed only from BA, CA, and TA under the study conditions. The e-liquids with SLA, LA, LVA, SA, and MA produced less ROS than the 2 wt % freebase nicotine e-liquid, suggesting that organic acids may play dual roles in the production and scavenging of ROS. For BA nicotine salts, it was found that the ROS yield increased with a higher acid concentration (or a lower nicotine to acid ratio). The observation that BA nicotine salts produce the highest ROS yield in aerosol generated from a fourth-generation vape device, which increases with acid concentration, has important implications for ROS-mediated health outcomes that may be relevant to consumers, manufacturers, and regulatory agencies.

Challenges in current inhalable tobacco toxicity assessment models: A narrative review

Emerging tobacco products such as electronic nicotine delivery systems (ENDS) and heated tobacco products (HTPs) have a dynamic landscape and are becoming widely popular as they claim to offer a low-risk alternative to conventional smoking. Most pre-clinical laboratories currently exploit in vitro, ex vivo, and in vivo experimental models to assess toxicological outcomes as well as to develop risk-estimation models. While most laboratories have produced a wide range of cell culture and mouse model data utilizing current smoke/aerosol generators and standardized puffing profiles, much variation still exists between research studies, hindering the generation of usable data appropriate for the standardization of these tobacco products. In this review, we discuss current state-of-the-art in vitro and in vivo models and their challenges, as well as insights into risk estimation of novel products and recommendations for toxicological parameters for reporting, allowing comparability of the research studies between laboratories, resulting in usable data for regulation of these products before approval by regulatory authorities.

Prosopis africana exerts neuroprotective activity against quaternary metal mixture-induced memory impairment mediated by oxido-inflammatory response via Nrf2 pathway

The beneficial effects of Prosopis africana (PA) on human health have been demonstrated; however, its protective effects against heavy metals (HM) are not yet understood. This study evaluated the potential neuroprotective effects of PA in the cerebral cortex and cerebellum. To accomplish this, we divided 35 albino Sprague Dawley rats into five groups. Group I did not receive either heavy metal mixture (HMM) or PA. Group II received a HMM of PbCl2 (20 mg/kg), CdCl2 (1.61 mg/kg), HgCl2 (0.40 mg/kg), and NaAsO3 (10 mg/kg) orally for a period of two months. Groups III, IV, and V received HMM along with PA at doses of 500, 1000, and 1500 mg/kg, respectively. PA caused decreased levels of HM accumulation in the cerebral cortex and cerebellum and improved performance in the Barnes maze and rotarod tests. PA significantly reduced levels of IL-6 and TNF-α. PA increased concentrations of SOD, CAT, GSH, and Hmox-1 and decreased the activities of AChE and Nrf2. In addition, levels of MDA and NO decreased in groups III, IV, and V, along with an increase in the number of live neurons. In conclusion, PA demonstrates a complex neuroprotective effect with the potential to alleviate various aspects of HM-induced neurotoxicity.

Does vaping increase the likelihood of SARS-CoV-2 infection? Paradoxically yes and no

Data on the relationship between electronic cigarettes (ECs) and SARS-CoV-2 infection are limited and contradictory. Our objectives were to investigate the impact of EC aerosols on SARS-CoV-2 infection of human bronchial epithelial cells and identify the causative chemical(s). Fully differentiated human bronchial epithelial tissues (hBETs) were exposed at the air-liquid interface (ALI) to aerosols produced from JUUL "Virginia Tobacco" and BLU ECs, as well as nicotine, propylene glycol (PG), vegetable glycerin (VG), and benzoic acid, and infection was then evaluated with SARS-CoV-2 pseudoparticles. Pseudoparticle infection of hBETs increased with aerosols produced from PG/VG, PG/VG plus nicotine, or BLU ECs; however, JUUL EC aerosols did not increase infection compared with controls. Increased infection in PG/VG alone was due to enhanced endocytosis, whereas increased infection in PG/VG plus nicotine or in BLU ECs was caused by nicotine-induced elevation of the aerosol's pH, which correlated with increased transmembrane protease, serine 2 (TMPRSS2) activity. Notably, benzoic acid in JUUL aerosols mitigated the enhanced infection caused by PG/VG or nicotine, offering protection that lasted for at least 48 h after exposure. In conclusion, the study demonstrates that EC aerosols can impact susceptibility to SARS-CoV-2 infection depending on their specific ingredients. PG/VG alone or PG/VG plus nicotine enhanced infection through different mechanisms, whereas benzoic acid in JUUL aerosols mitigated the increased infection caused by certain ingredients. These findings highlight the complex relationship between ECs and SARS-CoV-2 susceptibility, emphasizing the importance of considering the specific aerosol ingredients when evaluating the potential effects of ECs on infection risk.NEW & NOTEWORTHY Data on the relationship between electronic cigarettes (ECs) and SARS-CoV-2 infection are limited and contradictory. We investigated the impact of EC aerosols and their ingredients on SARS-CoV-2 infection of human bronchial epithelial cells. Our data show that specific ingredients in EC aerosols impact the susceptibility to SARS-CoV-2 infection. Propylene glycol (PG)/vegetable glycerin (VG) alone or PG/VG plus nicotine enhanced infection through different mechanisms, whereas benzoic acid in JUUL aerosols mitigated the increased infection caused by these ingredients.

Characterization of e-cigarette users according to device type, use behaviors, and self-reported health outcomes: Findings from the EMIT study

INTRODUCTION

Electronic cigarettes (e-cigarettes) rapidly evolved from large modifiable (MOD) devices, to small and affordable 'POD' devices. Detailed information on user demographics and preferences according to device type, which can inform potential chemical exposure and policy recommendations, is currently limited. The goal of this study is to describe user demographics, use behaviors and preferences, as well as self-reported health outcomes according to the e-cigarette device type used.

METHODS

From April 2019 to March 2020, 91 participants from Maryland (18 MOD users, 26 POD users, 16 dual users (use of both combustible and e-cigarettes), and 31 non-users (never e-cigarette users and never smokers or >6 months former use) were recruited. A comprehensive questionnaire collected sociodemographic characteristics, e-cigarette/tobacco use behaviors, self-reported health outcomes, device characteristics and preferences. Chi-squared tests for categorical variables, ANOVA for continuous variables, qualitative thematic analysis, linear and logistic regressions were used to assess relationships between variables and groups.

RESULTS

POD users were younger (average 22.5 years) than MOD users (30.8 years) or dual users (34.3 years) (p<0.001). MOD users reported more puffs per day (mean ± SD: 373 ± 125 puffs) compared to POD users (123.0 ± 172.5). E-cigarette users who were former smokers used 1.16 mg/mL lower nicotine concentrations compared to lifetime exclusive e-cigarette users (p=0.03) in linear models. Exclusive POD users self-reported more coughing than exclusive MOD or dual users (p=0.02). E-cigarette users reported more shortness of breath, headaches, and fatigue from their e-cigarette use compared to non-users.

CONCLUSIONS

We found significant differences between user demographics, e-cigarette preferences, device characteristics, and use behaviors by user group. This information can help explain exposure to chemicals from e-cigarettes, including compounds with known toxic effects (e.g. metals, formaldehyde), and help inform the design of prevention and intervention strategies and policy decisions.

Metal Concentrations in E-Cigarette Aerosol Samples: A Comparison by Device Type and Flavor

BACKGROUND

The rapid evolution of electronic cigarette (e-cigarette) products warrants surveillance of the differences in exposure across device types-modifiable devices (MODs), cartridge ("pod")-containing devices (PODs), disposable PODs (d-PODs)-and flavors of the products available on the market.

OBJECTIVE

This study aimed to measure and compare metal aerosol concentrations by device type and common flavors.

METHODS

We collected aerosol from 104 MODs, 67 PODs (four brands: JUUL, Bo, Suorin, PHIX), and 23 d-PODs (three brands: ZPOD, Bidi, Stig) via droplet deposition in a series of conical pipette tips. Metals and metalloids [aluminum (Al), arsenic (As), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), antimony (Sb), tin (Sn), and zinc (Zn)] were measured using inductively coupled plasma mass spectrometry (ICP-MS), results were log-transformed for statistical analysis, and concentrations are reported in aerosol units (mg / m 3 ).

RESULTS

Of the 12 elements analyzed, concentrations were statistically significantly higher in MOD devices, except for Co and Ni, which were higher in PODs and d-PODs. Of the POD brands analyzed, PHIX had the highest median concentrations among four metals (Al, Ni, Pb, and Sn) compared to the rest of the POD brands. According to POD flavor, seven metals were three to seven orders of magnitude higher in tobacco-flavored aerosol compared to those in mint and mango flavors. Among the d-POD brands, concentrations of four metals (Al, Cu, Ni, and Pb) were higher in the ZPOD brand than in Bidi Stick and Stig devices. According to d-POD flavor, only Cr concentrations were found to be statistically significantly higher in mint than tobacco-flavored d-PODs.

DISCUSSION

We observed wide variability in aerosol metal concentrations within and between the different e-cigarette device types, brands, and flavors. Overall, MOD devices generated aerosols with higher metal concentrations than PODs and d-PODs, and tobacco-flavored aerosols contained the highest metal concentrations. Continued research is needed to evaluate additional factors (i.e., nicotine type) that contribute to metal exposure from new and emerging e-cigarette devices in order to inform policy. https://doi.org/10.1289/EHP11921.

Association between metal exposure from e-cigarette components and toxicity endpoints: A literature review

Electronic cigarette is often promoted and perceived as an 'healthy' alternative compared to conventional cigarettes. However, growing body of evidence indicate the possible adverse health effect associated with e-cigarette. Here we reviewed the literature with a focus on metal exposure in relation to e-cigarette use and related toxicity endpoints. Twenty-nine studies were identified for full text screening after applying the screening criteria of which 5 in vitro studies and 11 epidemiological studies were included for data extraction. Cr, Cu, Ni, Sn are the most found metal in all studies. In vitro, metal from e-cigarette (liquid or aerosols) induced cytotoxicity, oxidative stress, genotoxicity and pro-inflammatory responses. It was observed that the presence of nicotine can influence metal-induced in vitro toxicity. Based on epidemiological studies, the metal burden in e-cigarette users showed to be elevated in different populations (including e.g. NHANES). However, most often such studies were limited by the missing user characteristics, and information of other potential sources of metal exposure. In general, metals from e-cigarette use can be associated with toxicity endpoints but to uncover the metal related hazard of e-cigarette in users, more detailed data on metals in vapors and e-liquids; user habits and user demographics are needed.

Determination of chemical constituent yields in e-cigarette aerosol using partial and whole pod collections, a comparative analysis

Literature reports the chemical constituent yields of electronic nicotine delivery systems (ENDS) aerosol collected using a range of aerosol collection strategies. The number of puffs to deplete an ENDS product varies widely, but collections often consist of data from the first 50-100 puffs. However, it is not clear whether these discrete puff blocks are representative of constituent yields over the life of a pod. We aimed to assess the effect of differing aerosol collection strategies on reported yields for select chemical constituents in the aerosol of closed pod-based ENDS products. Constituents analyzed were chosen to reflect important classes of compounds from the Final Premarket Tobacco Product Application Guidance. Yields were normalized to total device mass loss (DML). Collection strategies that consisted of partial pod collection were valid for determining yields of constituents whose DML normalized yields were consistent for the duration of pod life. These included primary aerosol constituents, such as propylene glycol, glycerol, and nicotine, and whole pod yields could be determined from initial puff blocks. However, changes were observed in the yields of some metals, some carbonyl compounds, and glycidol over pod life in a chemical constituent and product dependent manner. These results suggest that collection strategies consisting of initial puff block collections require validation per chemical constituent/product and are not appropriate for chemical constituents with variable yields over pod life. Whole pod collection increased sensitivity and accuracy in determining metal, carbonyl, and glycidol yields compared to puff block-based collection methodologies for all products tested.

A State-of-the-Science Review on Metal Biomarkers

PURPOSE OF REVIEW

Biomarkers are commonly used in epidemiological studies to assess metals and metalloid exposure and estimate internal dose, as they integrate multiple sources and routes of exposure. Researchers are increasingly using multi-metal panels and innovative statistical methods to understand how exposure to real-world metal mixtures affects human health. Metals have both common and unique sources and routes of exposure, as well as biotransformation and elimination pathways. The development of multi-element analytical technology allows researchers to examine a broad spectrum of metals in their studies; however, their interpretation is complex as they can reflect different windows of exposure and several biomarkers have critical limitations. This review elaborates on more than 500 scientific publications to discuss major sources of exposure, biotransformation and elimination, and biomarkers of exposure and internal dose for 12 metals/metalloids, including 8 non-essential elements (arsenic, barium, cadmium, lead, mercury, nickel, tin, uranium) and 4 essential elements (manganese, molybdenum, selenium, and zinc) commonly used in multi-element analyses.

RECENT FINDINGS

We conclude that not all metal biomarkers are adequate measures of exposure and that understanding the metabolic biotransformation and elimination of metals is key to metal biomarker interpretation. For example, whole blood is a good biomarker of exposure to arsenic, cadmium, lead, mercury, and tin, but it is not a good indicator for barium, nickel, and uranium. For some essential metals, the interpretation of whole blood biomarkers is unclear. Urine is the most commonly used biomarker of exposure across metals but it should not be used to assess lead exposure. Essential metals such as zinc and manganese are tightly regulated by homeostatic processes; thus, elevated levels in urine may reflect body loss and metabolic processes rather than excess exposure. Total urinary arsenic may reflect exposure to both organic and inorganic arsenic, thus, arsenic speciation and adjustment for arsebonetaine are needed in populations with dietary seafood consumption. Hair and nails primarily reflect exposure to organic mercury, except in populations exposed to high levels of inorganic mercury such as in occupational and environmental settings. When selecting biomarkers, it is also critical to consider the exposure window of interest. Most populations are chronically exposed to metals in the low-to-moderate range, yet many biomarkers reflect recent exposures. Toenails are emerging biomarkers in this regard. They are reliable biomarkers of long-term exposure for arsenic, mercury, manganese, and selenium. However, more research is needed to understand the role of nails as a biomarker of exposure to other metals. Similarly, teeth are increasingly used to assess lifelong exposures to several essential and non-essential metals such as lead, including during the prenatal window. As metals epidemiology moves towards embracing a multi-metal/mixtures approach and expanding metal panels to include less commonly studied metals, it is important for researchers to have a strong knowledge base about the metal biomarkers included in their research. This review aims to aid metals researchers in their analysis planning, facilitate sound analytical decision-making, as well as appropriate understanding and interpretation of results.

Exposure to metals among Electronic Nicotine Delivery System (ENDS) users in the PATH study: A longitudinal analysis

BACKGROUND

Few studies have evaluated Electronic Nicotine Delivery Systems (ENDS) in longitudinal studies, as a potential source of metals which may have carcinogenic, neurotoxic, and cardiotoxic effects. We evaluated metal body burden by ENDS use status in a longitudinal population-based national survey.

METHODS

We used the Population Assessment of Tobacco and Health (PATH) Study wave 1 (2013-2014), wave 2 (2014-2015), and wave 3 (2015-2016) adult data to assess urinary concentrations of seven metals among (1) ENDS only users who never used any nonelectronic tobacco products (n = 50), (2) ENDS only users who were former users of any nonelectronic tobacco products (n = 123) and (3) Never users (n = 1501) of any tobacco product.

RESULTS

Among ENDS only users who never used any nonelectronic tobacco products (n = 50), the geometric mean ratios (GMRs) of Cd and Pb were 1.25 (95%CI: 1.09-1.42) and 1.19 (95%CI: 1.05-1.34), respectively, compared to never users after adjustment for PATH Study wave, age, sex, race/ethnicity, education, region, secondhand smoke at home and work, and cannabis and other substance use. After the same adjustment, the corresponding GMRs were 1.48 (95%CI: 1.32-1.67) and 1.43 (95%CI: 1.28-1.60) for ENDS only users who were former users of any nonelectronic tobacco products (n = 123). No difference was observed in urinary concentrations of other metals comparing ENDS users to never users of any tobacco product.

DISCUSSION

ENDS users show higher urinary levels of Cd and Pb, including lifetime exclusive ENDS users compared to never users of any tobacco product. These findings are limited by the small sample size and could be related to underreporting of past combustible tobacco use or other factors. Metals typical of ENDS such as nickel and chromium unfortunately are not available in PATH. Studies assessing metal exposure associated with long term lifetime exclusive ENDS use (≥5 years) with larger sample size are needed.

Electronic Nicotine Delivery System: End to Smoking or Just a New Fancy Cigarette

Smoking and tobacco chewing are the predominant causes of oral cancer. Tobacco is the second-most widely consumed psychoactive substance. There are numerous ways to quit smoking, of which one is electronic cigarettes (e-cigarettes). E-cigarette use is a brand-new, global trend. E-cigarette is a battery-operated device that heats a liquid to create a vapor that the consumer inhales. Several countries have acknowledged that the first step toward electronic nicotine delivery system (ENDS) management is a precise classification of ENDS within the limits of current legislation. Countries have currently categorized ENDS into four generations. People's perceptions about tobacco products have altered recently as a consequence of the advertising of ENDS. The likelihood of starting to smoke cigarettes was four times higher in adolescents who used ENDS, and the probability of quitting was reduced and often prolonged in those who used ENDS. In addition, ENDS normalizes smoking-like actions including inhaling in and exhaling smoke. Adverse marketing via geographic locations and social media platforms, as well as nicotine's irreversible effects on growing adolescent and young adult brains that predispose individuals to addicted behaviors, may be responsible for their rising appeal among teenagers. Despite this, ENDS use has risen among young individuals who have never smoked and undoubtedly face more health risks than those who do not use ENDS. The oral cavity is the first to encounter ENDS in individuals and where it initially affects the human system. As a known contributor to cardiovascular diseases, neurological conditions, and cancers, nicotine seems to be a serious cause for concern. This review provides a concise summary of the research on the components, mode of action, applications, and effects of e-cigarettes on oral as well as systemic systems.

Heavy metals in ENDS: a comparison of open versus closed systems purchased from the USA, England, Canada and Australia

INTRODUCTION

Electronic nicotine delivery systems (ENDS) are known to contain heavy metals such as lead (Pb), nickel (Ni) and chromium (Cr). The presence of heavy metals in ENDS may be due to contamination of e-liquids or leaching from elements of the ENDS device. This study investigates differences in ENDS metal concentrations between product type, year of purchase, country of purchase and e-liquid flavour.

METHODS

Various open-system (refill e-liquids; n=116) and closed-system (prefilled with e-liquid; n=120) products were purchased in 2017 and 2018 from the USA, England, Canada and Australia. Electrothermal atomic absorption spectroscopy was used to analyse each product for Pb, Ni and Cr. Multiple linear regression and Kruskal-Wallis non-parametric statistical tests were conducted using GraphPad.

RESULTS

Linear regression showed system type, year of purchase (not supported by Kruskal-Wallis), country of purchase and flavour type each had significant impacts on heavy metal concentrations. Open-system e-liquid samples showed no quantifiable levels of heavy metals. Closed-system samples contained concerningly high concentrations of Pb, Ni and Cr. Closed-system samples from the USA commonly displayed higher average heavy metal concentrations than those from England. Some fruit and mint-flavoured closed-system products showed higher heavy metal concentrations than tobacco-flavoured products.

CONCLUSION

The presence of heavy metals only in closed-system products suggests that metals may be leaching from ENDS device parts. Highly variable heavy metal concentrations between ENDS products demonstrate that various product characteristics may affect the degree of leaching and that there is a need for further regulation of these products.

Arsenic and arsenic species in MOD, POD, and disposable POD electronic cigarette aerosols: a pilot study

The growing popularity of electronic cigarettes (e-cig) has raised questions about the health effects of e-cig use, or vaping. Previous studies have reported on the potential of exposure to arsenic (As) and other metal(loid)s from vaping, but little is known about the speciation of As in the inhaled aerosols, an important determinant of toxicity. Inorganic As (iAs) species AsIII and AsV are generally more hazardous than organic As species. This study aimed to investigate total and speciated As in condensed aerosols of popular commercial e-cig products and to compare them with regulatory exposure limits. High-performance liquid chromatography and inductively-coupled plasma mass spectrometry were used for As measurements of e-cig aerosol condensates. The analysis included samples from three types of e-cig devices: MODs, PODs, and disposable pod (d-POD) devices. iAs species were identified in all 23 analyzed e-cig aerosol condensate samples, with the highest aerosol concentrations measured in MODs. The geometric mean (range) iAs concentration of 2.3 (1.2-5.1) μg/m3 observed in MOD devices in this study exceeded the recommended exposure limit of 2 μg/m3 for 15-min or shorter inhalation exposures set by the United States National Institute for Occupational Safety and Health. These preliminary results suggest that iAs species are present in inhalable aerosols of some MOD products at levels above regulatory limits for iAs inhalation.

Occurrence of metals in e-cigarette liquids: Influence of coils on metal leaching and exposure assessment

Electronic cigarettes are generally recognized as a safer alternative than conventional cigarettes. Nevertheless, previous research suggests metal (loid) leaching due to coil contact, potentially transferring to the e-liquid and its aerosolized form. In this study, Cr, Cd, Ni, and Pb levels were measured by inductively coupled plasma mass spectrometry (ICP-MS) on 17 samples of e-liquids with different chemical properties (e.g., pH, nicotine content, flavoring, free-base, and nicotine salts). Twelve e-liquids were then put in contact with 36-gauge Kanthal A-1, Nichrome 80, Stainless steel 317 L and disposable coils such as Juul, and Aspire BVC for three days at 200-250 °C for 1 h each day. Metal levels expressed as mean (standard deviation) metal concentration, were below detection (Cd) to very low in bottle samples (Ni ≤ 76 (18); Pb ≤ 16 (1.5); and Cr ≤ 386 (15.6) μg/kg). In the coil extracts, varying concentrations of the same metal (loid) were found, indicating that metal leaching capacity may differ per sample. All samples contained Ni and Cr, followed by Pb to a much lesser extent. Cd levels were mostly below detection limits. Coil + e-liquid combinations with the highest Ni, Cr, and Pb concentrations were: Aspire BVC + Melon 0 mg/mL: Ni = 1.22 E+04 (281); Aspire BVC + Hit Nicotine 40 mg/mL: Cr = 864 (116); and Nichrome 80 + Melon 0 mg/mL: Pb = 56 (5) μg/kg. Overall, results suggest that nicotine salts at 40 mg/mL enhance Cr and Ni transfer. Stainless steel 317 L released very low metal concentrations. A conservative screening level risk characterization showed that 10.5% and 3.5% of the coil extracts may exceed Ni and Cr (III) safe concentrations, respectively. In the aerosol phase, 8.8% of samples might be above Ni equivalent daily dose for chronic exposure and 1.8% for intermediate exposure. Further studies on coil metal leaching could aid in establishing coil manufacturing regulations.

External Factors Modulating Vaping-Induced Thermal Degradation of Vitamin E Acetate

Despite previous studies indicating the thermal stability of vitamin E acetate (VEA) at low temperatures, VEA has been shown to readily decompose into various degradation products such as alkenes, long-chain alcohols, and carbonyls such as duroquinone (DQ) at vaping temperatures of <200 °C. While most models simulate the thermal decomposition of e-liquids under pyrolysis conditions, numerous factors, including vaping behavior, device construction, and the surrounding environment, may impact the thermal degradation process. In this study, we investigated the role of the presence of molecular oxygen (O2) and transition metals in promoting thermal oxidation of e-liquids, resulting in greater degradation than predicted by pure pyrolysis. Thermal degradation of VEA was performed in inert (N2) and oxidizing atmospheres (clean air) in the absence and presence of Ni-Cr and Cu-Ni alloy nanopowders, metals commonly found in the heating coil and body of e-cigarettes. VEA degradation was analyzed using thermogravimetric analysis (TGA) and gas chromatography/mass spectrometry (GC/MS). While the presence of O2 was found to significantly enhance the degradation of VEA at both high (356 °C) and low (176 °C) temperatures, the addition of Cu-Ni to oxidizing atmospheres was found to greatly enhance VEA degradation, resulting in the formation of numerous degradation products previously identified in VEA vaping emissions. O2 and Cu-Ni nanopowder together were also found to significantly increase the production of OH radicals, which has implications for e-liquid degradation pathways as well as the potential risk of oxidative damage to biological systems in real-world vaping scenarios. Ultimately, the results presented in this study highlight the importance of oxidation pathways in VEA thermal degradation and may aid in the prediction of thermal degradation products from e-liquids.

Electronic Nicotine Delivery Systems: An Updated Policy Statement From the American Association for Cancer Research and the American Society of Clinical Oncology

Combustible tobacco use has reached historic lows, demonstrating the importance of proven strategies to reduce smoking since publication of the 1964 Surgeon General's report. In contrast, the use of electronic nicotine delivery systems (ENDS), specifically e-cigarettes, has grown to alarming rates and threatens to hinder progress against tobacco use. A major concern is ENDS use by youth and adults who never previously used tobacco. While ENDS emit fewer carcinogens than combustible tobacco, preliminary evidence links ENDS use to DNA damage and inflammation, key steps in cancer development. Furthermore, high levels of nicotine can also increase addiction, raise blood pressure, interfere with brain development, and suppress the immune system. The magnitude of long-term health risks will remain unknown until longitudinal studies are completed. ENDS have been billed as a promising tool for combustible tobacco cessation, but further evidence is needed to assess their potential efficacy for adults who smoke. Of concern, epidemiological studies estimate that approximately 15%-42% of adults who use ENDS have never used another tobacco product, and another 36%-54% dual use both ENDS and combustible tobacco. This policy statement details advances in science related to ENDS and calls for urgent action to end predatory practices of the tobacco industry and protect public health. Importantly, we call for an immediate ban on all non-tobacco-flavored ENDS products that contain natural or synthetic nicotine to reduce ENDS use by youth and adults who never previously used tobacco. Concurrently, evidence-based treatments to promote smoking cessation and prevent smoking relapse to reduce cancer incidence and improve public health remain top priorities for our organizations. We also recognize there is an urgent need for research to understand the relationship between ENDS and tobacco-related disparities.

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.

Electronic Nicotine Delivery Systems: An Updated Policy Statement from the American Association for Cancer Research and the American Society of Clinical Oncology

Combustible tobacco use has reached historic lows, demonstrating the importance of proven strategies to reduce smoking since publication of the 1964 Surgeon General's report. In contrast, the use of electronic nicotine delivery systems (ENDS), specifically e-cigarettes, has grown to alarming rates and threatens to hinder progress against tobacco use. A major concern is ENDS use by youth and adults who never previously used tobacco. While ENDS emit fewer carcinogens than combustible tobacco, preliminary evidence links ENDS use to DNA damage and inflammation, key steps in cancer development. Furthermore, high levels of nicotine can also increase addiction, raise blood pressure, interfere with brain development, and suppress the immune system. The magnitude of long-term health risks will remain unknown until longitudinal studies are completed. ENDS have been billed as a promising tool for combustible tobacco cessation, but further evidence is needed to assess their potential efficacy for adults who smoke. Of concern, epidemiological studies estimate that approximately 15% to 42% of adults who use ENDS have never used another tobacco product, and another 36% to 54% "dual use" both ENDS and combustible tobacco. This policy statement details advances in science related to ENDS and calls for urgent action to end predatory practices of the tobacco industry and protect public health. Importantly, we call for an immediate ban on all non-tobacco-flavored ENDS products that contain natural or synthetic nicotine to reduce ENDS use by youth and adults who never previously used tobacco. Concurrently, evidence-based treatments to promote smoking cessation and prevent smoking relapse to reduce cancer incidence and improve public health remain top priorities for our organizations. We also recognize there is an urgent need for research to understand the relationship between ENDS and tobacco-related disparities.

A Critical Review of Recent Literature on Metal Contents in E-Cigarette Aerosol

The inhalation of metallic compounds in e-cigarette (EC) aerosol emissions presents legitimate concerns of potential harms for users. We provide a critical review of laboratory studies published after 2017 on metal contents in EC aerosol, focusing on the consistency between their experimental design, real life device usage and appropriate evaluation of exposure risks. All experiments reporting levels above toxicological markers for some metals (e.g., nickel, lead, copper, manganese) exhibited the following experimental flaws: (i) high powered sub-ohm tank devices tested by means of puffing protocols whose airflows and puff volumes are conceived and appropriate for low powered devices; this testing necessarily involves overheating conditions that favor the production of toxicants and generate aerosols that are likely repellent to human users; (ii) miscalculation of exposure levels from experimental outcomes; (iii) pods and tank devices acquired months and years before the experiments, so that corrosion effects cannot be ruled out; (iv) failure to disclose important information on the characteristics of pods and tank devices, on the experimental methodology and on the resulting outcomes, thus hindering the interpretation of results and the possibility of replication. In general, low powered devices tested without these shortcomings produced metal exposure levels well below strict reference toxicological markers. We believe this review provides useful guidelines for a more objective risk assessment of EC aerosol emissions and signals the necessity to upgrade current laboratory testing standards.

On the toxicity of e-cigarettes consumption: Focus on pathological cellular mechanisms

Tobacco smoking remains without a doubt one of the leading causes of premature death worldwide. In combination with conventional protocols for smoking cessation, e-cigarettes have been proposed as a useful tool to quit smoking. Advertised as almost free of toxic effects, e-cigarettes have rapidly increased their popularity, becoming a sought-after device, especially among young people. Recently some health concerns about e-cigarette consumption are being raised. It is well known that they can release several toxic compounds, some of which are carcinogenic to humans, and emerging results are now outlining the risks related to the onset of respiratory and cardiovascular diseases and even cancer. The present review shows the emerging evidence about the role of technical components of the devices, the e-liquid composition as well as customization by consumers. The primary topics we discuss are the main toxicological aspects associated with e-cigarette consumption, focusing on the molecular pathways involved. Here it will be shown how exposure to e-cigarette aerosol induces stress/mitochondrial toxicity, DNA breaks/fragmentation following the same pathological pathways triggered by tobacco smoke, including the deregulation of molecular signalling axis associated with cancer progression and cell migration. Risk to fertility and pregnancy, as well as cardiovascular risk associated with e-cigarette use, have also been reported.

Transfer of Metals to the Aerosol Generated by an Electronic Cigarette: Influence of Number of Puffs and Power

Electronic cigarettes (e-cigarettes) are increasing in popularity despite uncertainties about their health hazards. Literature studies have shown that e-cigarettes may be a source of toxic heavy metal exposure to the user, but the mechanism by which metals are transferred from the e-cigarette parts into the aerosol plume that is inhaled by the user is poorly understood. The goal of this study was to quantify the potentially harmful heavy metals chromium, nickel, copper, and lead systematically during the simulated use of a mod-type e-cigarette in order to better understand the mechanism of metal transfer from the e-cigarette parts into the aerosol plume and into the liquid in the storage tank. Aerosol was collected and aliquots of the remaining liquid in the storage tank were collected from 0 to 40 puffs in 10 puff increments and analyzed with atomic absorption spectroscopy. It was found that the concentration of metals increased in both the aerosol and tank liquid the more times the e-cigarette was puffed, but at varying rates for each element and depending on the power applied to the heating coil. For copper, lead, and nickel, the concentrations of metals in the aerosol and tank increased with increasing power but for chromium, the concentration varied with power. Additionally, it was observed that chromium and nickel concentrations were greater in the aerosol than in tank liquid, consistent with the direct transfer of those metals to the aerosol from heating of the nichrome coil element used in this study. For copper and lead, the concentrations were similar or greater in the tank compared to the aerosol, consistent with transfer first into the storage tank liquid, followed by vaporization into the aerosol.

Acrylamide levels in smoke from conventional cigarettes and heated tobacco products and exposure assessment in habitual smokers

Acrylamide (AA) is a neurotoxic, genotoxic, and carcinogenic compound developed during heating at high temperatures. Foods such as potatoes, biscuits, bread and coffee are the main foodstuffs containing AA. Cigarette smoke may be a significant additional source of exposure. However, AA content may vary among different types of cigarettes. The study aimed to evaluate the AA content in conventional cigarettes (CC) and heated tobacco products (HTP) and its resulting exposure through their use. AA levels from the two types of cigarettes were determined by GC-MS and the daily exposure to AA was also ascertained. The margin of exposure (MOE) was calculated for neurotoxic and carcinogenic risk based on benchmark dose lower confidence limit for a 10% response (BMDL10) of 0.43 and 0.17, 0.30, and 1.13 mg/kgbw/day. AA level in CC ranged from 235 to 897 ng/cigarette, whereas HTP reported AA levels in the range of 99-187 ng/cigarette. The data showed a low neurotoxic risk for either CC or HTP, whereas a carcinogenic risk emerged through the smoking of CC based on different Benchmark doses. The carcinogenic risk for CC based on the highest Benchmark dose that was considered showed unsafe levels, as little as 10 CC cigarettes/day, whereas it was almost always of low concern for HTP. Another approach based upon the incremental lifetime cancer risk (ILCR) analysis led to similar results, exceeding, in some cases, the safety value of 10-4, as far as CC are concerned. Overall, the results confirmed that CC are a significant source of AA, and its levels were five times higher than in HTP.

Examining Metal Contents in Primary and Secondhand Aerosols Released by Electronic Cigarettes

The usage of electronic cigarettes (ECs) has surged since their invention two decades ago. However, to date, the health effects of EC aerosol exposure are still not well understood because of insufficient data on the chemical composition of EC aerosols and the corresponding evidence of health risks upon exposure. Herein, we quantified the metals in primary and secondhand aerosols generated by three brands of ECs. By combining aerosol filter sampling and inductively coupled plasma mass spectrometry (ICP-MS), we assessed the mass of metals as a function of EC flavoring, nicotine concentration, device power, puff duration, and aging of the devices. The masses of Cr, Cu, Mn, Ni, Cu, and Zn were consistently high across all brands in the primary and secondhand aerosols, some of which were above the regulated maximum daily intake amount, especially for Cr and Ni with mass (nanograms per 10 puffs) emitted at 117 ± 54 and 50 ± 24 (JUUL), 125 ± 77 and 219 ± 203 (VOOPOO), and 33 ± 10 and 27 ± 2 (Vapor4Life). Our analysis indicates that the metals are predominantly released from the EC liquid, potentially through mechanisms such as bubble bursting or the vaporization of metal-organic compounds. High metal contents were also observed in simulated secondhand aerosols, generally 80-90% of those in primary aerosols. Our findings provide a more detailed understanding of the metal emission characteristics of EC for assessing its health effects and policymaking.

Assessing variability of aerosols generated from e-Cigarettes

While some in vitro and in vivo experiments have studied the toxic effects of e-cigarette (e-cig) components, the typical aerosol properties released from e-cigarettes have not been well characterized. In the present study, we characterized the variability in mass concentration and particle size distribution associated with the aerosol generation of different devices and e-liquid compositions in an experimental setup. The findings of this study indicate a large inter-day variability in the experiments, likely due to poor quality control in some e-cig devices, pointing to the need for a better understanding of all the factors affecting exposures in in vitro and in vivo experiments, and the development of standardized protocols for generation and measurement of e-cig aerosols.

The Impact of the Storage Conditions and Type of Clearomizers on the Increase of Heavy Metal Levels in Electronic Cigarette Liquids Retailed in Romania

The growing popularity of electronic cigarettes has raised several public health concerns, including the risks associated with heavy metals exposure via e-liquids and vapors. The purpose of this study was to determine, using atomic absorption spectrometry, the concentrations of Pb, Ni, Zn, and Co in some commercially available e-liquid samples from Romania immediately after purchase and after storage in clearomizers. Lead and zinc were found in all investigated samples before storage. The initial concentrations of Pb ranged from 0.13 to 0.26 mg L⁻¹, while Zn concentrations were between 0.04 and 0.07 mg L⁻¹. Traces of nickel appeared in all investigated e-liquids before storage but in very small amounts (0.01–0.02 mg L⁻¹). Co was below the detection limits. We investigated the influence of the storage period (1, 3, and 5 days), storage temperature (22 °C and 40 °C), and type of clearomizer. In most cases, the temperature rise and storage period increase were associated with higher concentrations of heavy metals. This confirms that storage conditions can affect metal transfer and suggests that the temperature of storage is another parameter that can influence this phenomenon.

Effects of e-liquid flavor, nicotine content, and puff duration on metal emissions from electronic cigarettes

Vaping is the action of inhaling and exhaling aerosols from electronic cigarettes. The aerosols contain various amounts of toxic chemicals, including metals. The purpose of this study was to evaluate factors that can influence metal levels, including flavor and nicotine content in the e-liquid, and puff duration. Aerosols were collected from both closed-system (cartridge-based) and open-system e-cigarettes using e-liquids with different flavors (fruit, tobacco, and menthol), nicotine content (0, 6, 24, and 59 mg/mL), and different puff durations (1, 2, and 4 s). The concentrations of 14 metals in the collected aerosols were measured using inductively coupled plasma mass spectroscopy. Aerosol concentrations of As, Fe, and Mn varied significantly among fruit, tobacco, and menthol flavors in both closed-system and open-system devices. Concentrations of Al, Fe, Sn, and U were significantly higher in tobacco or menthol flavored aerosols compared to fruit flavors in closed-system devices. Aerosol W levels were significantly higher in tobacco flavored aerosols compared to fruit flavors in open-system devices. Concentrations of As, Fe, and Mn were higher in tobacco flavored aerosols compared to menthol flavors in both types of devices. The median Pb concentration decreased significantly from 15.8 to 0.88 μg/kg when nicotine content increased from 0 to 59 mg/mL, and median Ni concentration was 9.60 times higher in aerosols with nicotine of 59 mg/mL compared to 24 mg/mL (11.9 vs. 1.24 μg/kg) for closed-system devices. No significant differences were observed in aerosol metal concentrations for different puff durations. Aerosol metal concentrations varied widely between different flavors and nicotine content but not by puff duration. Flavor and nicotine content of the e-liquid could be potential factors in metal emissions. Some elements showed higher concentrations under certain conditions, highlighting the urgent need of developing strict product regulations, especially on e-liquid composition and nicotine content to inform e-cigarette users about metal exposure through vaping.

Toxic Metals in Liquid and Aerosol from Pod-Type Electronic Cigarettes

High-quality, accurate data on liquid contents and aerosol emissions from electronic nicotine delivery systems (ENDS, e.g., e-cigarettes) are crucial to address potential health concerns as these devices evolve and mature. Metals are an important class of ENDS constituents that merit attention as they have various health implications. Proper sampling, handling and aerosol trapping materials are essential to generate accurate quantitative metal data and to reduce the likelihood of inaccurate results originating from inappropriate collection vessels and materials that contribute to high background levels. Published methods that meet these criteria were applied to the analyses of chromium, nickel, copper, zinc, cadmium, tin and lead in liquid and aerosol from mint/menthol and tobacco flavors of currently popular pod-based devices from three manufacturers. Metal concentrations from pods that had not been used for generating aerosol ranged from below our lowest reportable level to 0.164 µg/g for Cr, 61.3 µg/g for Ni, 927 µg/g for Cu, 14.9 µg/g for Zn, 58.2 µg/g for Sn and 2.56 µg/g for Pb. Cadmium was included in our analyte panel and was not present above detection limits in liquid or aerosol. Aerosol metal concentrations (using a 55-mL puff) ranged from below our lowest reportable level to 29.9 ng/10 puffs for Cr, 373 ng/10 puffs for Ni, 209 ng/10 puffs for Cu, 4,580 ng/10 puffs for Zn, 127 ng/10 puffs for Sn and 463 ng/10 puffs for Pb. Our results showed some metal delivery from all the products examined and highly variable metal levels between manufacturer, brand and package.

Effect of Heating on Physicochemical Property of Aerosols during Vaping

Many electronic cigarette manufacturers have offered different types of “high-end mods” that allow for controlled heating of the e-liquid. However, the controlled heating condition can drastically alter the inhaled aerosols’ physical properties and chemical substances, causing potential health risks. To investigate the contribution of heating on aerosol properties, we used four common power settings in the mods to conduct a physicochemical analysis. Our data showed that the aerosol mass and nicotine content in the aerosols increased at high power. Additionally, high power led to aerosolization of a viscous component in the e-liquid, increasing the viscosity of aerosol. However, the pH of the aerosol was constant regardless of the applied power. In addition, high-power operation made nicotine prone to oxidation, resulting in the color of the aerosol turning yellow. Lastly, we demonstrated that e-cigarette aerosol could contain various metals, including aluminum, arsenic, cadmium, chromium, copper, iron, magnesium, nickel, lead, and zinc. Even though these metal contents proportionally increased with the power setting, they remained far below the recommended exposure limits. Our finding demonstrates that the heating conditions of the e-cigarette change the physicochemical properties of the aerosols and their metal contents, thereby possibly affecting users’ oral and respiratory systems.

An Automated Aerosol Collection and Extraction System to Characterize Electronic Cigarette Aerosols

Electronic cigarette (e-cigarette) market increased by 122% during 2014–2020 and is expected to continue growing rapidly. Despite their popularity, e-cigarettes are known to emit dangerous levels of toxic compounds (e.g., carbonyls), but a lack of accurate and efficient testing methods is hindering the characterization of e-cigarette aerosols emitted by a wide variety of e-cigarette devices, e-liquids, and use patterns. The aim of this study is to fill this gap by developing an automated E-cigarette Aerosol Collection and Extraction System (E-ACES) consisting of a vaping machine and a collection/extraction system. The puffing system was designed to mimic e-cigarette use patterns (i.e., power output and puff topography) by means of a variable power-supply and a flow control system. The sampling system collects e-cigarette aerosols using a combination of glass wool and a continuously wetted denuder. After the collection stage, the system is automatically washed with absorbing and extracting liquids (e.g., methanol, an acetaldehyde-DNPH solution). The entire system is controlled by a computer. E-ACES performance was evaluated against conventional methods during measurements of nicotine and carbonyl emissions from a tank type e-cigarette. Nicotine levels measured using glass fiber filters and E-ACES were not significantly different: 201.2 ± 6.2 and 212.5 ± 17 μg/puff (p = 0.377), respectively. Differences in formaldehyde and acetaldehyde levels between filter-DNPH cartridges and the E-ACES were 14% (p = 0.057) and 13% (p = 0.380), respectively. The E-ACES showed reproducible nicotine and carbonyl testing results for the selected e-cigarette vaping conditions.

Metals in Cannabis Vaporizer Aerosols: Sources, Possible Mechanisms, and Exposure Profiles

In recent years, cannabis vaporizer cartridges have increased in popularity and availability, and there are concerns regarding exposure to heavy-metal compounds from their use. The physical components of the cartridge devices themselves have been implicated as a potential source of metal exposure, but it is not known if these metals migrate into the inhalable vapor. This study analyzes the components of vaporizer cartridges for 10 different metals and also collects aerosol mixtures from 13 randomly purchased commercially available cannabis cartridges from Washington State to compare their elemental profiles. Results indicate that chromium, copper, nickel, as well as smaller amounts of lead, manganese, and tin migrate into the cannabis oil and inhaled vapor phase, resulting in a possible acute intake of an amount of inhaled metals above the regulatory standard of multiple governmental bodies. Noncartridge heating methods of cannabis flower and concentrate were compared, and results indicate that the heating device itself is a source of metal contamination. As safety and compliance testing regulations evolve, it will be important to include more than the standard As, Cd, Hg, and Pb to the list of regulated metals.

ICP-MS Determination of 23 Elements of Potential Health Concern in Liquids of e-Cigarettes. Method Development, Validation, and Application to 37 Real Samples

The lack of interest in the determination of toxic elements in liquids for electronic cigarettes (e-liquids) has so far been reflected in the scarce number of accurate and validated analytical methods devoted to this aim. Since the strong matrix effects observed for e-liquids constitute an exciting analytical challenge, the main goal of this study was to develop and validate an ICP-MS method aimed to quantify 23 elements in 37 e-liquids of different flavors. Great attention has been paid to the critical phases of sample pre-treatment, as well as to the optimization of the ICP-MS conditions for each element and of the quantification. All samples exhibited a very low amount of the elements under investigation. Indeed, the sum of their average concentration was of ca. 0.6 mg kg-1. Toxic elements were always below a few tens of a μg per kg-1 and, very often, their amount was below the relevant quantification limits. Tobacco and tonic flavors showed the highest and the lowest concentration of elements, respectively. The most abundant elements came frequently from propylene glycol and vegetal glycerin, as confirmed by PCA. A proper choice of these substances could further decrease the elemental concentration in e-liquids, which are probably barely involved as potential sources of toxic elements inhaled by vapers.

Metal exposure and biomarker levels among e-cigarette users in Spain

The use of electronic cigarettes (e-cigarettes) has increased due to the belief that they are healthier than tobacco cigarettes. E-cigarettes contain a metallic heating coil (composed of Ni, Cr, Al and other metals) to heat a solution (commonly called e-liquid) and convert it into an aerosol. This aerosol is inhaled (vaped) by the users who can be potentially exposed to a wide variety of metals. We investigated the possible transfer of metals from the coil to the e-liquid and the generated aerosol, and how the exposure to this aerosol can increase metal body burden in e-cigarette users. We recruited 75 e-cigarette users (50 who only vaped and 25 dual users who vaped and smoked) and 25 controls who neither vaped nor smoked. E-liquid samples before (dispenser e-liquid) and after (tank e-liquid) being added to their devices were collected. Aerosol samples were collected using a condensation method. All participants provided urine and hair samples. All samples were analyzed for metals by ICP-MS. We observed higher metal concentrations in the aerosol and tank e-liquid (in contact with the coil) compared to the dispenser e-liquid (before contact with the coil). The median concentrations for some of the metals with the most remarkable increases in aerosol and tank e-liquid vs. dispenser e-liquid were 36.90 and 62.73 vs. 18.29 μg/kg for Al; 6.71 and 28.97 vs. 0.98 μg/kg for Cr; 91.39 and 414.47 vs. 1.64 μg/kg for Ni; 738.99 and 744.24 vs. 16.56 μg/kg for Zn; and 10.17 and 22.31 vs. 0.88 μg/kg for Pb. We also found detectable and potentially high concentrations of other metals such as Mn, Cu, Sb and Sn. In urine, increases in the median levels (μg/g creatinine) in vapers/duals vs. controls were observed for some metals, including Cr (0.34/0.28 vs. 0.20), Cu (1.72/2.36 vs. 1.46), Sn (0.26/0.31 vs. 0.18) and Pb (0.39/0.44 vs. 0.22). In hair, there were no differences in metal concentrations among the three groups. In conclusion, e-cigarettes are likely a source of metals such as Cr, Cu, Ni, Pb or Sn. These metals come from the device, likely the heating resistance, as their concentrations were low in the dispenser e-liquid and higher in the aerosol and the e-liquid left in the tank. Although the exposure to e-cigarette aerosol can have an influence in the body burden of metals, aerosol metal levels were not clearly associated with metal levels in biological samples such as urine or hair in e-cigarette users in this study.

Exposure to e-cigarette aerosol over two months induces accumulation of neurotoxic metals and alteration of essential metals in mouse brain

Despite a recent increase in e-cigarette use, the adverse human health effects of exposure to e-cigarette aerosol, especially on the central nervous system (CNS), remain unclear. Multiple neurotoxic metals have been identified in e-cigarette aerosol. However, it is unknown whether those metals accumulate in the CNS at biologically meaningful levels. To answer this question, two groups of mice were whole-body exposed twice a day, 5 days a week, for two months, to either a dose of e-cigarette aerosol equivalent to human secondhand exposure, or a 5-fold higher dose. After the last exposure, the olfactory bulb, anterior and posterior frontal cortex, striatum, ventral midbrain, cerebellum, brainstem, remaining brain tissue and spinal cord were collected for metal quantification by inductively coupled plasma mass spectrometry and compared to tissues from unexposed control mice. The two-month exposure caused significant accumulation of several neurotoxic metals in various brain areas - for some metals even at the low exposure dose. The most striking increases were measured in the striatum. For several metals, including Cr, Cu, Fe, Mn, and Pb, similar accumulations are known to be neurotoxic in mice. Decreases in some essential metals were observed across the CNS. Our findings suggest that chronic exposure to e-cigarette aerosol could lead to CNS neurotoxic metal deposition and endogenous metal dyshomeostasis, including potential neurotoxicity. We conclude that e-cigarette-mediated metal neurotoxicity may pose long-term neurotoxic and neurodegenerative risks for e-cigarette users and bystanders.

Characterizing the Chemical Landscape in Commercial E-Cigarette Liquids and Aerosols by Liquid Chromatography-High-Resolution Mass Spectrometry

The surge in electronic cigarette (e-cig) use in recent years has raised questions on chemical exposures that may result from vaping. Previous studies have focused on measuring known toxicants, particularly those present in traditional cigarettes, while fewer have investigated unknown compounds and transformation products formed during the vaping process in these diverse and constantly evolving products. The primary aim of this work was to apply liquid chromatography-high-resolution mass spectrometry (LC-HRMS) and chemical fingerprinting techniques for the characterization of e-liquids and aerosols from a selection of popular e-cig products. We conducted nontarget and quantitative analyses of tobacco-flavored e-liquids and aerosols generated using four popular e-cig products: one disposable, two pod, and one tank/mod. Aerosols were collected using a condensation device and analyzed in solution alongside e-liquids by LC-HRMS. The number of compounds detected increased from e-liquids to aerosols in three of four commercial products, as did the proportion of condensed-hydrocarbon-like compounds, associated with combustion. Kendrick mass defect analysis suggested that some of the additional compounds detected in aerosols belonged to homologous series resulting from decomposition of high-molecular-weight compounds during vaping. Lipids in inhalable aerosols have been associated with severe respiratory effects, and lipid-like compounds were observed in aerosols as well as e-liquids analyzed. Six potentially hazardous additives and contaminants, including the industrial chemical tributylphosphine oxide and the stimulant caffeine, were identified and quantified in the e-cig liquids and aerosols analyzed. The obtained findings demonstrate the potential of nontarget LC-HRMS to identify previously unknown compounds and compound classes in e-cig liquids and aerosols, which is critical for the assessment of chemical exposures resulting from vaping.

Sex-specific neurotoxic effects of heavy metal pollutants: Epidemiological, experimental evidence and candidate mechanisms

The heavy metals lead (Pb), mercury (Hg), and cadmium (Cd) are ubiquitous environmental pollutants and are known to exert severe adverse impacts on the nervous system even at low concentrations. In contrast, the heavy metal manganese (Mn) is first and foremost an essential nutrient, but it becomes neurotoxic at high levels. Neurotoxic metals also include the less prevalent metalloid arsenic (As) which is found in excessive concentrations in drinking water and food sources in many regions of the world. Males and females often differ in how they respond to environmental exposures and adverse effects on their nervous systems are no exception. Here, we review the different types of sex-specific neurotoxic effects, such as cognitive and motor impairments, that have been attributed to Pb, Hg, Mn, Cd, and As exposure throughout the life course in epidemiological as well as in experimental toxicological studies. We also discuss differential vulnerability to these metals such as distinctions in behaviors and occupations across the sexes. Finally, we explore the different mechanisms hypothesized to account for sex-based differential susceptibility including hormonal, genetic, metabolic, anatomical, neurochemical, and epigenetic perturbations. An understanding of the sex-specific effects of environmental heavy metal neurotoxicity can aid in the development of more efficient systematic approaches in risk assessment and better exposure mitigation strategies with regard to sex-linked susceptibilities and vulnerabilities.

The chemistry and toxicology of vaping

Vaping is the process of inhaling and exhaling an aerosol produced by an e-cigarette, vape pen, or personal aerosolizer. When the device contains nicotine, the Food and Drug Administration (FDA) lists the product as an electronic nicotine delivery system or ENDS device. Similar electronic devices can be used to vape cannabis extracts. Over the past decade, the vaping market has increased exponentially, raising health concerns over the number of people exposed and a nationwide outbreak of cases of severe, sometimes fatal, lung dysfunction that arose suddenly in otherwise healthy individuals. In this review, we discuss the various vaping technologies, which are remarkably diverse, and summarize the use prevalence in the U.S. over time by youths and adults. We examine the complex chemistry of vape carrier solvents, flavoring chemicals, and transformation products. We review the health effects from epidemiological and laboratory studies and, finally, discuss the proposed mechanisms underlying some of these health effects. We conclude that since much of the research in this area is recent and vaping technologies are dynamic, our understanding of the health effects is insufficient. With the rapid growth of ENDS use, consumers and regulatory bodies need a better understanding of constituent-dependent toxicity to guide product use and regulatory decisions.

The effect of electronic cigarettes exposure on learning and memory functions: behavioral and molecular analysis

Objective: Electronic cigarettes (ECIGs) are battery-powered devices that emit vaporized solutions for the user to inhale. ECIGs are marketed as a less harmful alternative to combustible cigarettes. The current study examined the effects of ECIG aerosol exposure on learning and memory, expression of brain derived neurotrophic factor (BDNF), and the activity of antioxidant enzymes in the hippocampus.Methods: Male Wistar rats were exposed to ECIG aerosol, by a whole-body exposure system, 1 h/day for 1 week, 4 weeks, and 12 weeks. Spatial learning and memory were tested using the Radial Arm Water Maze (RAWM). Hippocampal BDNF protein level, and oxidative stress biomarkers (GPx, SOD, GSH, GSSG, GSH/GSSG ratio) were also assessed.Results: ECIG aerosol exposure for 4 and 12 weeks impaired both short- and long- term memory and induced reductions in the hippocampus BDNF, SOD and GPx activities, and GSH/GSSG ratio (p < 0.05). No changes in any examined biomarkers were observed after 1-week exposure to ECIG aerosol (p > 0.05).Conclusions: ECIG aerosol exposure impaired functional memory and elicited changes in brain chemistry that are consistent with reduced function and oxidative stress.

Impact of e-Liquid Composition, Coil Temperature, and Puff Topography on the Aerosol Chemistry of Electronic Cigarettes

E-cigarette aerosol is a complex mixture of gases and particles with a composition that is dependent on the e-liquid formulation, puffing regimen, and device operational parameters. This work investigated mainstream aerosols from a third generation device, as a function of coil temperature (315-510 °F, or 157-266 °C), puff duration (2-4 s), and the ratio of propylene glycol (PG) to vegetable glycerin (VG) in e-liquid (100:0-0:100). Targeted and untargeted analyses using liquid chromatography high-resolution mass spectrometry, gas chromatography, in situ chemical ionization mass spectrometry, and gravimetry were used for chemical characterizations. PG and VG were found to be the major constituents (>99%) in both phases of the aerosol. Most e-cigarette components were observed to be volatile or semivolatile under the conditions tested. PG was found almost entirely in the gas phase, while VG had a sizable particle component. Nicotine was only observed in the particle phase. The production of aerosol mass and carbonyl degradation products dramatically increased with higher coil temperature and puff duration, but decreased with increasing VG fraction in the e-liquid. An exception is acrolein, which increased with increasing VG. The formation of carbonyls was dominated by the heat-induced dehydration mechanism in the temperature range studied, yet radical reactions also played an important role. The findings from this study identified open questions regarding both pathways. The vaping process consumed PG significantly faster than VG under all tested conditions, suggesting that e-liquids become more enriched in VG and the exposure to acrolein significantly increases as vaping continues. It can be estimated that a 30:70 initial ratio of PG:VG in the e-liquid becomes almost entirely VG when 60-70% of e-liquid remains during the vaping process at 375 °F (191 °C). This work underscores the need for further research on the puffing lifecycle of e-cigarettes.

Effects of Manufacturing Variation in Electronic Cigarette Coil Resistance and Initial Pod Mass on Coil Lifetime and Aerosol Generation

This work investigated the effects of manufacturing variations, including coil resistance and initial pod mass, on coil lifetime and aerosol generation of Vuse ALTO pods. Random samples of pods were used until failure (where e-liquid was consumed, and coil resistance increased to high value indicating a coil break). Initial coil resistance, initial pod mass, and e-liquid net mass ranged between 0.89 to 1.14 [Ω], 6.48 to 6.61 [g], and 1.88 to 2.00 [g] respectively. Coil lifetime was µ (mean) = 158, σ (standard deviation) = 21.5 puffs. Total mass of e-liquid consumed until coil failure was µ = 1.93, σ = 0.035 [g]. TPM yield per puff of all test pods for the first session (brand new pods) was µ = 0.0123, σ = 0.0003 [g]. Coil lifetime and TPM yield per puff were not correlated with either variation in initial coil resistance or variation in initial pod mass. The absence of e-liquid in the pod is an important factor in causing coil failure. Small bits of the degraded coil could be potentially introduced to the aerosol. This work suggests that further work is required to investigate the effect of e-liquid composition on coil lifetime and TPM yield per puff.

E-cigarette aerosol collection using converging and straight tubing Sections: Physical mechanisms

HYPOTHESIS

Identification and quantification of harmful chemicals in e-cigarette aerosol requires collecting the aerosolized e-liquid for chemical analysis. In 2016, Olmedo at al. empirically developed a simple method for aerosol collection by directing the aerosol through a sequence of alternating straight and converging tubing sections, which drain the recovered e-liquid into a collection vial. The tubing system geometry and flow conditions promote inertial impaction of aerosolized e-liquid on tube walls, where it deposits and flows into the collection vial.

EXPERIMENTS

We use high-speed optical imaging to visualize aerosol transport in proxies of the collection system. We also determined collection efficiencies of various configurations of the collection system.

FINDINGS

A turbulent jet emerges from converging conical sections and impinges onto the wall of downstream tubing sections, resulting in inertial impaction and deposition of the aerosol. For inertial impaction to occur the tip radius of the converging section must be small enough for a jet to be formed and the sequence of tubing sections must be curved in a polygon-like manner such that the jet emerging from a converging section impinges on the downstream tube wall. The collection efficiency is significantly smaller without such curvature.

Comparison of the chemical composition of aerosols from heated tobacco products, electronic cigarettes and tobacco cigarettes and their toxic impacts on the human bronchial epithelial BEAS-2B cells

The electronic cigarettes (e-cigs) and more recently the heated tobacco products (HTP) provide alternatives for smokers as they are generally perceived to be less harmful than conventional cigarettes. However, it is crucial to compare the health risks of these different emergent devices, in order to determine which product should be preferred to substitute cigarette. The present study aimed to compare the composition of emissions from HTP, e-cigs and conventional cigarettes, regarding selected harmful or potentially harmful compounds, and their toxic impacts on the human bronchial epithelial BEAS-2B cells. The HTP emitted less polycyclic aromatic hydrocarbons and carbonyls than the conventional cigarette. However, amounts of these compounds in HTP aerosols were still higher than in e-cig vapours. Concordantly, HTP aerosol showed reduced cytotoxicity compared to cigarette smoke but higher than e-cig vapours. HTP and e-cig had the potential to increase oxidative stress and inflammatory response, in a manner similar to that of cigarette smoke, but after more intensive exposures. In addition, increasing e-cig power impacted levels of certain toxic compounds and related oxidative stress. This study provides important data necessary for risk assessment by demonstrating that HTP might be less harmful than tobacco cigarette but considerably more harmful than e-cig.

It's Not All Smoke and Mirrors: The Role of Social Norms, Alcohol Use, and Pandemic Partying in e-Cigarette Use During COVID-19

E-cigarette use among college students is increasing. In the era of COVID-19, such usage is especially dangerous given that the virus can be deadly for those with impaired respiratory systems. A small but growing body of research suggests that social norms may predict e-cigarette use. However, one's perception of e-cigarette use behaviors (descriptive norms) and approval by peers (injunctive norms) have yet to be studied in college students. The overarching purpose of this study is to determine whether descriptive and injunctive norms for e-cigarette use contribute unique variance to past 30-day e-cigarette use. Methods: Using a sample of 191 students (138 women) surveyed from introductory-level courses at a university in the northeastern United States, we explored the relationships between student demographic characteristics, alcohol use, binge drinking, COVID-19 non-compliant party attendance on and off campus, and social norms with past 30-day e-cigarette use using sequential regression. Two models were utilized to determine if descriptive and injunctive e-cigarette use norms predicted e-cigarette use after controlling for demographic characteristics in the social norms model, and above and beyond demographics and COVID-19 noncompliant party attendance, alcohol use, and binge drinking in the party behaviors model. Results: The results demonstrated that descriptive and injunctive norms for e-cigarette use significantly predicted e-cigarette use in both models, controlling for all covariates. Conclusions/Importance: Findings highlight the importance of social norms in predicting e-cigarette use during the COVID-19 pandemic, identifying areas for prevention and intervention for public health officials and higher education administrators.

Effects of Electronic Nicotine Delivery Systems and Cigarettes on Systemic Circulation and Blood-Brain Barrier: Implications for Cognitive Decline

Electronic nicotine delivery systems (often known as e-cigarettes) are a novel tobacco product with growing popularity, particularly among younger demographics. The implications for public health are twofold, as these products may represent a novel source of tobacco-associated disease but may also provide a harm reduction strategy for current tobacco users. There is increasing recognition that e-cigarettes impact vascular function across multiple organ systems. Herein, we provide a comparison of evidence regarding the role of e-cigarettes versus combustible tobacco in vascular disease and implications for blood-brain barrier dysfunction and cognitive decline. Multiple non-nicotinic components of tobacco smoke have been identified in e-cigarette aerosol, and their involvement in vascular disease is discussed. In addition, nicotine and nicotinic signaling may modulate peripheral immune and endothelial cell populations in a highly context-dependent manner. Direct preclinical evidence for electronic nicotine delivery system-associated neurovascular impairment is provided, and a model is proposed in which non-nicotinic elements exert a proinflammatory effect that is functionally antagonized by the presence of nicotine.

Ethyl maltol enhances copper mediated cytotoxicity in lung epithelial cells

Ethyl maltol (EM) is a flavoring agent commonly used in foods that falls under the generally recognized as safe category. It is added to many commercial e-cigarette vaping fluids and has been detected in the aerosols. Considering that EM facilitates heavy metal transport across plasma membranes, and that heavy metals have been detected in aerosols generated from e-cigarettes, this study examines whether EM enhances heavy metal mediated toxicity. A decrease in viability was observed in the Calu-6 and A549 lung epithelial cell lines co-exposed to EM and copper (Cu) but no decrease was observed after co-exposure to EM with iron (Fe). Interestingly, co-exposure to EM and Fe decreased viability of the HEK293 and IMR-90 fibroblast cell lines but co-exposure to EM and Cu did not. Increases in the apoptotic markers Annexin V staining and fragmented nuclei were observed in Calu-6 cells co-exposed to EM and Cu. Co-exposure to EM and Cu in Calu-6 cells resulted in DNA damage as indicated by activation of ATM and expression of γH2A.x foci. Finally, co-exposure to EM and Cu caused oxidative stress as indicated by increases in the generation of reactive oxygen species and the expression of ferritin light chain mRNA and hemeoxygenase-1 mRNA and protein. These data show that co-exposure to EM and Cu, at concentrations that are not toxic for either chemical individually, induce apoptosis and evoke oxidative stress and DNA damage in lung epithelial cells. We suggest that there is a greater risk of lung damage in users of c-cigarette who vape with vaping fluid containing EM.

Early Cardiovascular Risk in E-cigarette Users: the Potential Role of Metals

PURPOSE OF REVIEW

Electronic cigarettes (e-cigs) are a source of metals. Epidemiologic and experimental evidence support that metals are toxic to the cardiovascular system. Little is known, however, about the role that e-cig metals may play as toxicants for the possible cardiovascular effects of e-cig use. The goal of this narrative review is to summarize the evidence on e-cig use and metal exposure and on e-cig use and cardiovascular toxicity and discuss the research needs.

RECENT FINDINGS

In vitro studies show cytotoxicity and increased oxidative stress in myocardial cells and vascular endothelial cells exposed to e-liquids and e-cig aerosols, with effects partially reversed with antioxidant treatment. There is some evidence that the heating coil plays a role in cell toxicity. Mice exposed to e-cigs for several weeks showed higher levels of oxidative stress, inflammation, platelet activation, and thrombogenesis. Cross-over clinical experiments show e-cig use alters nitric oxide-mediated flow-mediated dilation, endothelial progenitor cells, and arterial stiffness. Cross-sectional evidence from large nationally representative samples in the USA support that e-cig use is associated with self-reported myocardial infarction. Smaller studies found associations of e-cig use with higher oxidized low-density protein and heart variability compared to healthy controls. Numerous studies have measured elevated levels of toxic metals in e-cig aerosols including lead, nickel, chromium, and manganese. Arsenic has been measured in some e-liquids. Several of these metals are well known to be cardiotoxic. Numerous studies show that e-cigs are a source of cardiotoxic metals. Experimental studies (in vitro, in vivo, and clinical studies) show acute toxicity of e-cigs to the vascular system. Studies of long-term toxicity in animals and humans are missing. Longitudinal studies with repeated measures of metal exposure and subclinical cardiovascular outcomes (e.g., coronary artery calcification) could contribute to determine the long-term cardiovascular effects of e-cigs and the potential role of metals in those effects.