In the quest for answers about the potential risks of e-cigarettes, a group of scientists thoroughly reviewed 14 studies analyzing the emissions generated by these devices. They focused on carbonyl compounds, chemicals in the aerosol that have always generated concern, misinformation, and controversy.
Critical Review of E-Cigarette Studies:
The study critically reviewed 14 investigations on carbonyl emissions from e-cigarettes.
Essential Criteria for Study Reliability:
Four criteria were established to judge study reliability: detailed experimental information, accurate simulation of e-cigarette use, proper analytical methods, and inclusion of blank samples.
Study Findings:
Of 14 studies, 7 were considered reliable, 5 were partially reliable, and 2 were unreliable.
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“Our review closely examines the chemistry of e-cigarette emissions, highlighting the best analytical methods for measuring specific toxic chemicals called carbonyl compounds. This approach helps establish a new standard for accurately evaluating what’s in e-cigarette vapor.”
Dr. Roberto Sussman, 2024.
In the review article titled “Analytical Methods and Experimental Quality in Studies on Carbonyl Compounds in E-Cigarette Aerosols,” published on August 8, 2024, in Frontiers in Chemistry (Analytical Chemistry Section, Volume 12, 2024), authors Roberto A. Sussman from the Nuclear Sciences Institute of the National Autonomous University of Mexico, Federica Maria Sipala and Simone Ronsisvalle from the Department of Drug and Health Sciences at the University of Catania and the Center of Excellence for the Acceleration of Harm Reduction (CoEHAR) in Italy, along with Sébastien Soulet from Ingesciences in France, delve deeply into the analytical approaches and experimental rigor of studies examining the presence of carbonyl compounds in e-cigarette aerosols.
This analysis is key to understanding and assessing the risks associated with these emerging products and provides a more accurate understanding of their potential hazards.
The new study, published this August, critically reviews the analytical methods and quality of the experimental procedures used in research on carbonyl compounds in e-cigarette aerosols. It highlights the importance of rigorous experimental design and careful selection of methods to ensure reliable results in evaluating the toxicological profiles of these compounds. It paves the way for new and better standards.
Essential Criteria for Reliability in Studies
According to the authors, an e-cigarette study must meet four fundamental criteria for reliability. First, detailed information on the devices and experimental procedures is essential, allowing other researchers to replicate the experiments.
Second, studies should use inhalation protocols that accurately simulate the use of e-cigarettes, ensuring that the results reflect the reality of consumption.
Third, appropriate analytical methods must be applied to ensure the measurement accuracy of compounds present in the aerosol. Finally, it is crucial to include blank samples, i.e., controls that do not contain the compounds of interest, to avoid the detection of false positives due to experimental errors.
The review classified the studies based on their adherence to these quality criteria. Of the 14 studies analyzed, seven were considered reliable, five were classified as partially reliable, and two as unreliable due to failures in quality standards.
Although five studies used blank samples to avoid false positives, six failed to meet the reproducibility criterion, meaning that other researchers could not reliably replicate their experiments.
E-Cigarettes as a Harm Reduction Tool
Despite the limitations found in some studies, all the reproducible ones consistently showed that the amount of carbonyls in e-cigarettes was significantly lower than in tobacco smoke.
“The studies we reviewed were of high quality and consistently found low levels of carbonyls in e-cigarette emissions compared to tobacco smoke. These solid findings support the idea that vaping may be a less harmful alternative to smoking, which contrasts sharply with earlier studies reporting higher toxicity levels due to flawed methods,” adds Federica Maria Sipala.
This finding reinforces the idea that when tested and used correctly, e-cigarettes could serve as harm-reduction products, meaning they are less harmful than conventional cigarettes.
The studies reviewed compared the aerosols generated by e-cigarettes with tobacco smoke, highlighting that these devices avoid much of the physical-chemical complexity inherent in tobacco smoke.
Unlike traditional cigarettes, e-cigarettes do not produce secondary emissions, and their primary emissions lack 97% to 99% of the compounds present in tobacco smoke, including many of those known as toxic compounds (HPHCs).
Among the most common byproducts generated by e-cigarettes are carbonyls, particularly aldehydes such as formaldehyde, acetaldehyde, and acrolein.
These compounds form during the aerosolization process when the ingredients of e-cigarette liquids, such as propylene glycol (PG) and vegetable glycerin (VG), break down due to thermal degradation.
Scientists emphasize a particular concern for these carbonyls due to their association with negative health effects, especially their potential carcinogenicity.
To assess the health risks for e-cigarette users, scientists argue that it is essential to quantify the toxic compounds present in the aerosols these devices generate.
However, the wide variety of e-cigarettes, with variations in devices, resistances, liquids, nicotine levels, and flavors, can cause the results of these studies to vary significantly, complicating the task of drawing definitive conclusions.
The Importance of Control in Laboratory Tests
However, the authors point out a significant deficiency in almost all the studies reviewed: few reported how the samples, e-cigarette liquids, and devices were stored before analysis.
They explain that improper storage could lead to deterioration or the occurrence of secondary reactions in the liquids, affecting the accuracy of the results.
According to guidelines, devices and aerosols should be stored at room temperature, while liquids should be kept in airtight containers to avoid contamination with water. If immediate analysis is impossible, they should be stored at at least −10°C.
Recent studies have shown that storage temperature, storage period, and the type of cartomizer can influence the concentration of metals in the liquids.
Additionally, it is essential to control atmospheric conditions during analysis to avoid interference and ensure that collected aerosol samples are stored appropriately if not analyzed immediately.
This meticulous approach to sample preparation and handling is vital for obtaining reliable and accurate results in e-cigarette research.
The inhalation regime during laboratory tests has a crucial impact on the amount of carbonyls emitted by e-cigarettes. This regime is defined by four essential parameters: inhalation duration and volume, intervals between inhalations, and airflow speed. Even small variations in these factors can significantly alter the results.
Laboratory tests must follow a standardized inhalation protocol to ensure quality control and device comparison accuracy. Most of the studies reviewed use the ISO 20768:2018 CORESTA standard, designed for low-power devices, which are common in the tobacco industry. Of the 30 studies analyzed, 24 employed this standard or minor variations of it, which is suitable for these devices.
Previous reviews have noted that this protocol can cause overheating and problems such as “dry puff” inhalation when applied to high-power devices. However, this issue was irrelevant to the studies reviewed in this research.
Critical Evaluation and Future Direction in E-Cigarette Research
Since the emergence of e-cigarettes as potentially safer alternatives to tobacco cigarettes, numerous studies have been conducted to analyze the chemical content of their emissions.
These studies are essential for understanding the toxicity and risk profile of vaping, and they guide consumers, health professionals, public agents, regulators, and the industry.
Emission studies represent the first step in assessing the risks associated with e-cigarettes, followed by preclinical and clinical research.
However, for these reviews to be truly useful, they must go beyond merely listing results and studies and offer critical evaluations of the methodology employed and the consistency of the results.
This particular review focused on 14 recent studies on carbonyl emissions, especially aldehydes, the most common toxic byproducts in e-cigarettes.
A “traffic light” rating system was used to assess the reliability of these studies based on four essential criteria: the ability to reproduce the experiments, appropriate inhalation parameters, the application of precise analytical methods, and the use of blank samples.
The results showed that seven studies were rated as Reliable, five as Partially Reliable, and two as Unreliable. Although most applied appropriate analytical methods and reported low levels of aldehydes compared to tobacco smoke, significant methodological flaws were detected, such as the lack of blank samples in nine studies and replicability issues in six.
These deficiencies are common in many emission studies and must be corrected to improve test quality.
This review suggests updating laboratory standards, requiring blank samples, and providing detailed information for reproducing experiments. Additionally, the rigidity of current standards is criticized, as they do not always adapt to the variety of devices available.
Finally, the authors emphasize the importance of involving users in experimental logistics, given that e-cigarettes are intended for them.
Improving testing standards is a fundamental step toward obtaining a more accurate assessment of e-cigarettes’ risk profile, which would provide valuable information for all stakeholders.
The review concludes with the commitment to continue evaluating emission studies and conducting future research under the highest quality standards.
“Our review,” explains Dr. Roberto Sussman, “closely examines the chemistry of e-cigarette emissions, highlighting the best analytical methods for measuring specific toxic chemicals called carbonyl compounds. This approach helps establish a new standard for accurately evaluating what’s in e-cigarette vapor.”
“We also found broad consensus between industry and independent studies, which strengthens the reliability of the data suggesting that vaping may be a much safer option than smoking. It is important to incorporate consumer experience into the studies. Unfortunately, many studies do not take into account the peculiarities of e-cig users’ patterns, so they do not provide tailored information to apply the results in effective health policies to combat the scourge of smoking,” concluded Simone Ronsisvalle.