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

Sample preparation methods for elemental analysis in electronic cigarette aerosols: a critical review

In the last decade, e-cigarettes have been marketed as a less harmful alternative to classical tobacco smoking and are currently being used by millions of people. An e-cigarette consists of an e-liquid and a heating device, generating an aerosol that the user can inhale. Recently, several studies have shown that metals and metalloids, including As, Cd, and Pb, known carcinogens, were present in these aerosols. To ensure the accuracy of dose-toxicity estimations, it is essential to have access to reliable and reproducible methods for estimating the dose in question. Although more standardization methodologies were introduced in the analysis of metal(loid)s from aerosols, a huge divergence in sample preparation can be found in the literature. This work aimed to provide an overview of the sample preparation methods used to quantify these metal(loid)s. Therefore, a literature search was conducted in September 2024, that followed the PRISMA guidelines. Among the 48 articles selected, a wide variability in sample preparation was observed, specifically variations in aerosol generation characteristics and collection techniques. Despite the widespread use of methods as filters and impingers, many studies failed to validate critical steps such as aerosol recovery, blank corrections, and the extent of matrix effects. In addition, poor inorganic methodological practices were often applied, such as excessive use of glass materials for aerosol collection or other sample preparation steps. Therefore, further standardization of methodologies is urgently needed to improve the reliability of metal quantification in e-cigarette aerosols, which could potentially enhance regulatory frameworks and facilitate the routine analysis of e-cigarette emissions.

Multi-Omics Assessment of Puff Volume-Mediated Salivary Biomarkers of Metal Exposure and Oxidative Injury Associated with Electronic Nicotine Delivery Systems

BACKGROUND

Since their inception, electronic nicotine delivery systems (ENDS) have gained increasing popularity, sparking a vaping epidemic among adolescents in the US and globally. Several ENDS safety concerns have emerged as device features and formats that contribute to heavy metal exposure and toxicity continue to evolve and outpace regulatory efforts.

OBJECTIVES

Our objective was to integrate ENDS emission profiles with salivary proteome and metabolome data to characterize exposure factors that may influence adverse vaping-mediated health outcomes.

METHODS

A total of 56 participants (38 exclusive ENDS users and 18 non-ENDS users) were recruited. A subset of 15 exclusive ENDS users completed puffing topography assessments to obtain individual vaping behavior patterns using each participant's ENDS device. Inductively coupled plasma mass spectrometry was used to determine the metal content of emissions (12 ENDS devices) generated using a programmable ENDS aerosol generation system and saliva (15 exclusive ENDS users and 5 non-ENDS users). Saliva samples from 10 exclusive ENDS users and 5 non-ENDS users were analyzed for proteomic, metabolomic, inflammatory, and oxidative stress/damage biomarkers.

RESULTS

A linear puff volume-dependent increase in particle emissions and heavy metals was observed in ENDS aerosols and saliva of exclusive ENDS users. Elevated puff volume-dependent levels of salivary cytokines, including tumor necrosis factor-alpha (TNFα ), interleukin-1 beta (IL-1β ), and IL-6, were observed alongside the oxidative damage indicators malondialdehyde (MDA), superoxide dismutase (SOD), and 8-hydroxy-2'-deoxyguanosine (8-OHdG). Proteome-metabolome network analysis showed a higher risk of potentially developing neurological and respiratory diseases in ENDS users compared with non-ENDS users. Integrated salivary proteome-metabolome-metallome network analysis further demonstrated that heavy metals were associated with proteomic and metabolomic perturbations, with notable alterations in inflammatory response, immune function, and disease-related pathways.

DISCUSSION

A significant correlation between heavy metals, cytokines, and oxidative stress markers reveals a potential role of vaping behavior in exposure to metals and changes in markers associated with DNA damage and inflammation. Our study demonstrates the importance of characterizing vaping behavior and puffing topography when examining the human health implications of ENDS use. https://doi.org/10.1289/EHP14321.

Deconstructing contemporary disposable vapes: A material and elemental analysis

Disposable e-cigarettes (vapes) are becoming increasingly popular but there are concerns about their impacts on human health, the environment and resource sustainability. A better understanding of these impacts and potential solutions requires characterisation and quantification of the materials and chemicals used in their construction. In the present study we dismantle nine types of popular, single-use vapes and analyse the components by X-ray fluorescence spectrometry and pyrolysis-gas chromatography mass spectrometry. The median dry mass of vapes was about 50 g, and the main material contribution was either plastic (up to about 80 %) or metal (up to about 85 %, and including the battery). Polycarbonate was the principal plastic used in the casing and nylon was always employed in the wick, but a range of other polymers were identified in other components used in wire insulation, sleeving, packaging, bundling and sealing. Various elements, as additives, residues or contaminants, were encountered in these parts that included As, Ba, Bi, Cr, Hg, Pb and Sb. Metal components were constructed of Al (often with Ti), stainless steel or Ni-based alloys (mainly in the coils), but other metals were often incorporated in alloys (e.g., Bi, Pb, W) or were present in trace quantities (including Co and Nb). Common metals in the Al-plastic-laminated Li-ion batteries were Cu, Co, Fe and Ni, but Au, Ba, Hg and Pb were also detected, while additional metals in the Cu-based printed circuit boards included Ag, Al, Ni, Sn, Ti and V, with traces of Ag, Bi, Mn, Nb and Pb present. The presence of toxic or potentially toxic metals in the vapes poses an environmental hazard through leaching after littering or landfilling, while metals within or in contact with the wick raise concerns about transfer to the e-liquid and exposure to the user. The overall material and chemical complexity of vapes presents challenges for safe disposal and component recycling, but the presence of critical elements, like Bi, Co, Nb, Sb, Sn, V and W, has additional implications for resource management.

Metal in biological samples from electronic cigarette users and those exposed to their second-hand aerosol: a narrative review

Introduction

Electronic nicotine delivery systems (ENDS) are gradually becoming more popular, particularly, among today's youth. Despite being marketed as safe by the tobacco industry, the notable absence of regulation in their composition is evident. Both the generated fluids and aerosol exhibit a wide variety of substances that are not yet fully identified. In addition to additives, the aerosol contains metals, the presence of which can be attributed to the excessive heating of metallic filaments used in vaporizing the liquid.

Objective

This review aimed to identify and describe studies that have assessed metal levels in biological samples obtained from electronic cigarette users and those exposed to their second-hand aerosol. This involved detailing the types and concentrations of metals identified and the biological samples in which the metals were detected.

Methods

Two independent researchers conducted searches in the MEDLINE and EMBASE databases to identify studies that measured the metal levels in human non-invasive biological samples from electronic cigarette users and second-hand exposure. Data were presented as a narrative review.

Results

In total, 18 articles were included in this review. Overall active and passive exposure to ENDS was related to higher levels of many metals, including lead and cadmium, in biological samples. ENDS users, in general, have lower metal concentrations in biological samples compared to the users of combustible cigarettes.

Conclusion

The exposure to primary and second-hand e-cigarette aerosol is related to higher metal concentrations in the biological samples. The adverse effects of this exposure on long-term users are yet to be determined.

Consideration of vaping products as an alternative to adult smoking: a narrative review

Tobacco harm reduction is a public health approach to reduce the impact of cigarette smoking on individuals. Non-combustible alternatives to cigarettes, such as electronic cigarettes (e-cigarettes), deliver nicotine to the user in the absence of combustion. The absence of combustion in e-cigarettes reduces the level of harmful or potentially harmful chemicals in the aerosol generated. This narrative review examines the published literature that studied the chemistry of e-cigarette aerosols, the related toxicology in cell culture and animal models, as well as clinical studies that investigated short- and long-term changes in biomarkers of smoke exposure after switching to e-cigarettes. In the context of the literature reviewed, the evidence supports the harm reduction potential for adult smokers who switch to e-cigarettes.

Carcinogenic and non-carcinogenic health risk assessment of organic compounds and heavy metals in electronic cigarettes

E-cigarettes are now very popular in the world. Compared to traditional cigarettes, e-cigarettes are often considered safer and healthier. However, their safety remains controversial and requires further research and regulation. In this study, we aimed to understand the possible hazards to humans of four compounds (formaldehyde, acetaldehyde, acrolein, and acetone) and seven heavy metals (arsenic, cadmium, manganese, lead, copper, nickel, and chromium) contained in e-cigarette liquids and aerosols and perform a health risk assessment. We searched PubMed, CNKI, and other databases for relevant literature to obtain data on organic compounds and heavy metals in e-cigarette liquids and aerosols, and conducted acute, chronic, and carcinogenic risk assessments of various chemicals by different exposure routes. This study showed that exposure to four organic compounds and seven heavy metals in e-cigarette aerosols and e-liquids can cause varying levels of health risks in humans through different routes, with the inhalation route posing a higher overall risk than dermal exposure and oral intake. Various chemicals at high exposure doses can produce health risks beyond the acceptable range. E-cigarette designers must improve their products by changing the composition of the e-liquid and controlling the power of the device to reduce the health effects on humans.

Beyond the label: current evidence and future directions for the interrelationship between electronic cigarettes and mental health

Electronic cigarette use has dramatically increased over the last decade. With this recent technological development and wide range of constituents in various products, putative adverse effects on the brain and body have been largely unexplored. Here, we review current evidence linking electronic nicotine cigarette use with potential health consequences and provide evidence supporting an association between drug use and depression in humans. We also examine the biological effects of individual constituents in electronic cigarette aerosols, which include labeled ingredients, such as propylene glycol, vegetable glycerin, nicotine, and flavorants, as well as unlabeled ingredients found in the aerosols, such as carbonyls and heavy metals. Lastly, we examine the effects of electronic cigarette use on endogenous metabolism via changes in cytochrome P450 enzymes, which can thereby impact therapeutic outcomes. While the current evidence offers insight into the potential effects of electronic cigarette use on biological processes, further studies are necessary to determine the long-term clinical relevance of aerosol inhalation.

Passive exposure to electronic cigarette aerosol in pregnancy: A case study of a family

BACKGROUND

Passive exposure to the aerosols of electronic cigarettes (e-cigarettes) has been little studied. We assessed this exposure in late pregnancy in a woman and her 3-year-old child, exposed through e-cigarette use by another household member.

METHODS

This prospective longitudinal case study involved a family unit consisting of an e-cigarette user, a pregnant woman who delivered an infant during the study, and the couple's older 3-year-old son. At 31, 36, and 40 weeks of the pregnancy, we measured biomarkers (nicotine metabolites, tobacco-specific nitrosamines, propanediols, glycerol, and metals) in the urine and hair of all three participants and in the saliva of the adults, in cord blood at delivery, and in the breast milk at the postpartum period.

RESULTS

Samples from the e-cigarette user showed quantifiable concentrations of all analytes assessed (maximum urinary cotinine concentration, 4.9 ng/mL). Among samples taken from the mother, nicotine and its metabolites were found mainly in urine and also in saliva and hair, but not in cord blood. During the postpartum period, we found cotinine concentrations of 2.2 ng/mL in the mother's urine and 0.22 ng/mL in breast milk; 1,2-propanediol was generally detected in urine and saliva, but not in cord blood or breast milk. The maximum urinary cotinine concentration in the 3-year-old child was 2.6 ng/mL and propanediols also were detected in his urine. Nitrosamines were not detected in samples taken from the mother or the 3-year-old. Metals found in the refill liquid were detected at low levels in both the mother and the 3-year-old.

CONCLUSIONS

We detected low but not negligible concentrations of e-cigarette-related analytes (including cord blood and breast milk) in an exposed pregnant non-user and in a 3-year-old child also living in the home. Passive exposure to e-cigarette aerosols cannot be disregarded and should be assessed in larger observational studies.

Chemical Elements, Flavor Chemicals, and Nicotine in Unused and Used Electronic Cigarettes Aged 5-10 Years and Effects of pH

The concentrations of elements/metals, nicotine, flavor chemicals and acids were compared in the e-liquids of unused and used first-generation electronic cigarettes (ECs) that were stored for 5-10 years. Metal analysis was performed using inductively coupled plasma optical emission spectroscopy; nicotine and flavor chemical analyses were performed using gas chromatography/mass spectroscopy. Of the 22 elements analyzed, 10 (aluminum, chromium, copper, iron, lead, nickel, selenium, silicon, tin, zinc) were often found in the e-liquids. Five elements had the highest average concentrations: copper (1161.6 mg/L), zinc (295.8 mg/L), tin (287.6 mg/L), nickel (71.1 mg/L), and lead (50.3 mg/L). Nicotine concentrations were always lower than label concentrations indicated. Of the 181 flavor chemicals analyzed, 11 were detected in at least one sample, with hydroxyacetone being present in all samples. In used products, some flavor chemicals appeared to be by-products of heating. E-liquids with the highest concentrations of acids and the lowest pH levels also had the highest concentrations of elements/metals. Metal concentrations in e-liquids increased after use in some products, and some metal concentrations, such as nickel, were high enough to be a health concern. Leachates from discarded ECs could contribute toxic metals/chemicals to the environment, supporting the need for better regulation of atomizer design, composition, and disposal.

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.

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.

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.