Electronic cigarette aerosol and liquid

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Various bottles of e-liquid.

E-liquid is the mixture used in electronic cigarettes.[1] The main ingredients in the e-liquid usually are propylene glycol, glycerin, nicotine, and flavorings.[2] However, there are e-liquids sold without propylene glycol, nicotine, or flavors.[3][4][5] The liquid typically contains 95% propylene glycol and glycerin.[6] Propylene glycol and glycerine are used to produce the vapor while the flavoring provides the taste and aroma.[7] The flavorings may be natural or artificial.[8] About 8,000 flavors exist as of 2014.[9] There are many e-liquids manufacturers in the USA and worldwide.[10] While there are currently no US Food and Drug Administration (FDA) manufacturing standards for e-liquid, the FDA has proposed regulations that were expected to be finalized in late 2015.[11] Industry standards have been created and published by the American E-liquid Manufacturing Standards Association (AEMSA).[12]

The aerosol of electronic cigarettes is generated when the e-liquid reaches a temperature of roughly 100–250 °C within a chamber.[13] The user inhales the aerosol, commonly called vapor, rather than cigarette smoke.[14] The aerosol provides a flavor and feel similar to tobacco smoking.[15] In physics, a vapor is a substance in the gas phase whereas an aerosol is a suspension of tiny particles of liquid, solid or both within a gas.[14] Vapor from an e-cigarette simulates tobacco smoke, but the process of burning tobacco does not occur.[15] The aerosol is made-up of liquid sub-micron particles of condensed vapor,[16] which mostly consist of propylene glycol, glycerol, water, flavorings, nicotine, and other chemicals.[17] The various chemicals in the aerosol give rise to many issues concerning the safety of electronic cigarettes that have been much discussed.[14][17][18] After a puff, inhalation of the aerosol travels from the device into the mouth and lungs.[14] A 2014 review found that the particles emitted by e-cigarettes are comparable in size and number to particles in cigarette smoke, with the majority of them in the ultrafine range. The particles are of the ultrafine size which can go deep in the lungs and then into the systemic circulation. A 2014 review said local pulmonary toxicity may occur because metal nanoparticles can deposit in the lungs.[18] Others show that the quantities of metals emitted are minimal and permissible by medicinal standards.[17][19][20]

After the aerosol is inhaled, it is exhaled.[14] Emissions from electronic cigarettes are not comparable to environmental pollution or cigarette smoke as their nature and chemical composition are completely different.[17] The particles are larger, with the mean size being 600 nm in inhaled aerosol and 300 nm in exhaled vapor.[8] Bystanders are exposed to these particles from exhaled e-cigarette vapor.[18] There is a concern that some of the mainstream vapor exhaled by e-cigarette users can be inhaled by bystanders, particularly indoors, and have significant adverse effects.[21][22][23] Since e-cigarettes involve an aerosolization process, it is suggested that no meaningful amounts of carbon monoxide are emitted.[24] Thus, cardiocirculatory effects caused by carbon monoxide are not likely.[24] E-cigarette use by an expectant parent might lead to inadvertent health risks to offspring.[25] E-cigarettes pose many safety concerns to children.[25] For example, indoor surfaces can accumulate nicotine where e-cigarettes were used, which may be inhaled by children, particularly youngsters, long after they were used.[25]

Composition[edit]

Aerosol[edit]

The vapor can contain nicotine and usually contains vegetable glycerin, propylene glycol, flavors and aroma transporters.[20] The nicotine levels in the vapor varies either from puff-to-puff or among products of the same company.[14] A 2015 report commissioned by Public Health England concluded that e-cigarettes "release negligible levels of nicotine into ambient air".[26] E-cigarettes without nicotine are also available.[27] The vapor may also contain tiny amounts of toxicants, carcinogens, and heavy metals.[18][20] Contamination with various chemicals has been identified.[8] E-cigarette makers do not fully disclose information on the chemicals that can be released or synthesized during use.[14] The metals have been found in trace amounts in the vapor, some of them at higher amounts than in cigarette smoke.[17] The peak concentration of nicotine delivered by e-cigarette use is comparable to that produced by conventional cigarette smoking.[28]

An example of a commercial e-liquid and an advanced personal vaporizer.

E-liquid[edit]

E-liquid,[29] e-fluid, or e-juice[30] is the mixture used in vapor products including e-cigarettes.[3] E-Liquids come in many variations, including different nicotine strengths and many different flavors.[31] The main ingredients are propylene glycol, glycerine, and flavorings; and most often, nicotine in liquid form.[2] The liquid typically contains 95% propylene glycol and glycerin, and the remaining 5% being flavorings and nicotine.[6] E-liquid can be made with or without nicotine, with >90% of e-liquids containing some level of nicotine.[32] The most regularly used base carrier chemical is propylene glycol with or without glycerin.[18] E-liquid containing glycerin and water made without propylene glycol are also sold.[3] Unless clearly stated, it is uncertain whether the nicotine used in e-liquid is manufactured using a United States Pharmacopeia (USP) grade nicotine, a tobacco plant extract, tobacco dust or a synthetic nicotine.[33] Most e-cigarette liquids contain nicotine, but the level of nicotine varies depending on user-preference and manufacturers.[27] Although some e-juice is nicotine-free, surveys demonstrate that 97% of responders use products that contain nicotine.[4] A 2015 review suggests that 1% of users use liquid without nicotine.[34]

Aerosol[edit]

The primary parts that make up an e-cigarette are a mouthpiece, a cartridge (tank), a heating element/atomizer, a microprocessor, a lithium based battery,[35][unreliable source?] and possibly a LED light on the end.[36] An atomizer comprises a small heating element that vaporizes e-liquid and wicking material that draws liquid onto the coil.[37] When the user pushes a button.[38] or inhales a pressure sensor activates the heating element that atomizes the liquid solution;[39] The e-liquid reaches a temperature of roughly 100–250 °C within a chamber to create an aerosolized vapor.[13] The user inhales the aerosol, commonly called vapor, rather than cigarette smoke.[14] The aerosol provides a flavor and feel similar to tobacco smoking.[15] However, variable voltage devices can raise the temperature where the user adjusts the vapor.[8] The vapor contains similar chemicals to the e-liquid which vary in composition and concentration across and within manufacturers.[14]

First-hand[edit]

E-cigarettes produce particles, in the form of an aerosol.[14][40] In physics, a vapor is a substance in the gas phase whereas an aerosol is a suspension of tiny particles of liquid, solid or both within a gas.[14] The aerosol is made-up of liquid sub-micron particles of condensed vapor,[40] which mostly consist of propylene glycol, glycerol, water, flavorings, nicotine, and other chemicals.[17] This aerosol that is produces resembles cigarette smoke.[14] After a puff, inhalation of the aerosol travels from the device into the mouth and lungs.[14]

A 2014 review found that the particles emitted by e-cigarettes are comparable in size and number to particles in cigarette smoke, with the majority of them in the ultrafine range. The ultrafine particles can go deep in the lungs and then into the systemic circulation. Pulmonary toxicity may occur because metal nanoparticles can deposit in the lungs.[18] The review also found that fine particles can be chemically intricate and not uniform, and what a particle is made of, the exact harmful elements, and the importance of the size of the particle is mostly unknown.[18] They found that because these things are uncertain, it is not clear whether the ultrafine particles in e-cigarette vapor have health effects similar to those produced by traditional cigarettes.[18]

A 2014 WHO report found e-cigarettes release a lower level of particles than traditional cigarettes.[41] Comparable to a traditional cigarette, e-cigarette particles are tiny enough to enter the alveoli, enabling nicotine absorption.[30] E-cigarettes companies assert that the particulates produced by an e-cigarette are too tiny to be deposited in the alveoli.[42] Exactly what comprises the vapor varies in composition and concentration across and within manufacturers.[14] Different devices generate different particle sizes and cause different depositions in the respiratory tract, even from the same nicotine liquid.[43] Reports in the literature have shown respiratory and cardiovascular effects by these smaller size particles, suggesting a possible health concern.[44]

Second-hand[edit]

After the aerosol is inhaled, it is exhaled.[14] Emissions from electronic cigarettes are not comparable to environmental pollution or cigarette smoke as their nature and chemical composition are completely different.[17] The particles are larger, with the mean size being 600 nm in inhaled aerosol and 300 nm in exhaled vapor.[8] The exhaled aerosol particle concentration is 5 times lower from an e-cigarette than from a combustible tobacco cigarette.[45] The density of particles in the vapor is lower than in cigarette smoke by a factor of between 6 and 880 times lower.[17]

For particulate matter emissions, e-cigarettes slightly exceeded the WHO guidelines, but emissions were 15 times less than traditional cigarette use.[46] In January 2014, the International Union Against Tuberculosis and Lung Disease stated "Adverse health effects for exposed third parties (second-hand exposure) cannot be excluded because the use of electronic cigarettes leads to emission of fine and ultrafine inhalable liquid particles, nicotine and cancer-causing substances into indoor air."[47] The dense vapor consists of liquid sub-micron droplets.[40][dead link]

Exposure[edit]

Since e-cigarettes have not been widely used long enough for evaluation, the long-term health effects from the second-hand vapor are not known.[18] There is insufficient data to determine the impact on public health from e-cigarettes.[48] The potential harm to bystanders from e-cigarettes is unknown.[49] This is because no long-term data is available.[20]

Since e-cigarettes do not burn (or contain) tobacco, no side-stream smoke or any cigarette smoke is produced.[18] Only what is exhaled by e-cigarettes users enters the surrounding air.[20] Exhaled vapor consists of nicotine and some other particles, primarily consisting of flavors, aroma transporters, glycerin and propylene glycol.[20] Bystanders are exposed to these particles from exhaled e-cigarette vapor.[18] A mixture of harmful substances, particularly nicotine, ultrafine particles, and volatile organic compounds can be exhaled into the air.[50] The liquid particles condenses into a viewable fog.[8] The vapor is in the air for a short time, with a half-life of about 10 seconds; traditional cigarette smoke is in the air 100 times longer.[8] This is because of fast revaporization at room temperature.[8]

There is a concern that some of the mainstream vapor exhaled by e-cigarette users can be inhaled by bystanders, particularly indoors, and have significant adverse effects.[21][23] Since e-cigarettes involve an aerosolization process, it is suggested that no meaningful amounts of carbon monoxide are emitted.[24] Thus, cardiocirculatory effects caused by carbon monoxide are not likely.[24] However, in an experimental study, e-cigarettes increased levels of carcinogenic polycyclic aromatic hydrocarbons in the surrounding air.[24]

E-cigarettes used in indoor environments can put at risk nonsmokers to elevated levels of nicotine and aerosol emissions.[45] Nonsmokers exposed to e-cigarette aerosol produced by a machine and pumped into a room were found to have detectable levels of the nicotine metabolite cotinine in their blood. The same study stated that 80% of nicotine is normally absorbed by the user, so these results may be higher than in actual second hand exposure.[18] In 2015 a report commissioned by Public Health England concluded that e-cigarettes "release negligible levels of nicotine into ambient air with no identified health risks to bystanders".[26]

A 2014 review of limited data concluded this vapor can cause indoor air pollution and is not just water vapor as is frequently stated in the advertising of e-cigarettes.[18] A 2014 practice guideline by NPS MedicineWise states, "Although data on health effects of passive vapour are currently lacking, the risks are argued to be small, but claims that e-cigarettes emit only water vapour are nevertheless incorrect. Serum cotinine levels (a metabolite of nicotine) have been found to be similar in bystanders exposed to either e-cigarette vapour or cigarette smoke."[51][52] The 2015 California Department of Public Health has reported that "Mainstream and second hand e-cigarette aerosol has been found to contain at least ten chemicals that are on California's Proposition 65 list of chemicals known to cause cancer, birth defects, or other reproductive harm."[53] However, it has been demonstrated that e-cigarettes causes nonusers to be exposed to nicotine but not to tobacco-related combustion toxicants.[21]

A no smoking or vaping sign from the US.

A white paper published in 2014 by the American Industrial Hygiene Association concluded e-cigarettes emit airborne contaminants that may be inhaled by the user and those nearby.[44] They urged indoors restrictions similar to smoking bans, until research has shown the aerosol has no risk of harm.[44] A 2014 review indicated that the levels of inhaled contaminants from the e-cigarette vapor are not of significant health concern for human exposures by the standards used in workplaces to ensure safety.[27] The use of e-cigarettes in a smoke-free area could expose non-users to toxins.[54] The effect on bystanders would likely be much less harmful than traditional cigarettes.[20]

2014 WHO report stated passive exposure was as a concern, indicating that current evidence is insufficient to determine whether the levels of exhaled vapor are safe to involuntarily exposed bystanders.[41] The report stated that "it is unknown if the increased exposure to toxicants and particles in exhaled aerosol will lead to an increased risk of disease and death among bystanders."[41] The British Medical Association (BMA) reported in 2013 that there are "concerns that the use of e-cigarettes could threaten the norm of not smoking in public places and workplaces."[55]

As of 2013, the only clinical study currently published evaluating the respiratory effects of passive vaping found no adverse effects were detected.[17] A 2014 review found it is safe to infer that their effects on bystanders are minimal in comparison to traditional cigarettes.[17] A E-cigarette vapor has notably fewer toxicants than cigarette smoke and is likely to pose less harm to users or bystanders.[18]

Third hand[edit]

E-cigarette use by a parent might lead to inadvertent health risks to offspring.[25] E-cigarettes pose many safety concerns to children.[25] For example, indoor surfaces can accumulate nicotine where e-cigarettes were used, which may be inhaled by children, particularly youngsters, long after they were used.[25] A policy statement by the American Association for Cancer Research and the American Society of Clinical Oncology has reported that "Third-hand exposure occurs when nicotine and other chemicals from second-hand aerosol deposit on surfaces, exposing people through touch, ingestion, and inhalation".[4] Public health England, looking at the available research said the amount of nicotine deposited was low and that an infant would have to lick 30 square meters to be exposed to 1 mg of nicotine.[26] The statement noted there are no published studies of third hand exposure from e-cigarettes, however initial data suggests that nicotine from e-cigarettes may stick to surfaces and would be hard to remove.[4]

E-liquid[edit]

Contents[edit]

The e-liquid is sold in bottles or pre-filled disposable cartridges, or as a kit for consumers to make their own e-juices.[56] Some vendors of e-liquids, offer options to change the amounts of flavorings or nicotine strengths, and build each bottle customized for the purchaser.[56] E-liquids are made with various tobacco, fruit, and other flavors,[18] as well as variable nicotine concentrations (including nicotine-free versions).[2] The standard notation "mg/mL" is often used on labels to denote nicotine concentration, and is sometimes shortened to "mg".[57] In surveys of regular e-cigarette users, the most popular e-liquids had a nicotine content of 18 mg/mL, and the preferred flavors were largely tobacco, mint and fruit.[20] A cartridge may contain 0 to 20 mg of nicotine.[50] EU regulations cap the concentration of nicotine in e-liquid at a maximum of 20 mg/mL.[30] A refill bottle can contain up to 1 g of nicotine.[50] Refill liquids are often sold in the size range from 15 to 30 mL.[58] One cartridge may typically last as long as one pack of cigarettes.[59] Some liquids without flavoring is also sold.[5] The flavorings may be natural or artificial.[8] There is even certified organic liquid.[60] About 8,000 flavors exist as of 2014.[9] A user does not normally consume a whole cartridge in a single session.[61] Most e-liquids are produced by a few manufacturers in China, the US and Europe.[20] An e-cigarette user will usually obtain 300 to 500 puffs per mL of liquid.[58]

The two most common e-liquid bases are propylene glycol (PG) and vegetable glycerin (VG).[62] Propylene glycol is tasteless and odorless, and therefore it doesn't affect the flavor of the e-liquid. It is known, however, to cause allergic reactions in some users, and in such case it is advised to stop the use immediately. Vegetable glycerin, on the other hand, is a lot thicker in consistency, and it doesn't cause allergic reactions. It also produces significantly more vapor, which has a slight sweet taste.[63][unreliable source?]

Manufacturing[edit]

E-liquids are manufactured by many producers, both in the US and across the world.[10] First tier manufacturers use lab suits, gloves, hair covers, inside of certified clean rooms with air filtration similar to pharmaceutical-grade production areas.[10]

Standards[edit]

Standards for e-liquid manufacturing have been created by American E-liquid Manufacturing Standards Association (AEMSA), which is trade association dedicated to creating responsible and sustainable standards for the safe manufacturing of e-liquids used in vapor products.[64] AEMSA has published a comprehensive list standards and best known methods, which are openly available for use by any manufacturer of e-Liquids. The AEMSA standards cover nicotine, ingredients, sanitary manufacturing rooms, safety packaging, age restrictions, and labeling.[12]

Regulation[edit]

There are no current governmental or US Food and Drug Administration (FDA) manufacturing standards for e-liquid. The FDA has sought to regulate e-liquid through use of the Tobacco Control Act, passed into law in 2009. In April 2014, the FDA issued its "Deeming" proposals for public comment, which would cover e-liquids manufacturing. The Final Rule, (in final form) giving the FDA authority to regulate e-liquids was released on May 5, 2016.[65]

There is a limit in the UK on the nicotine content, meaning the nicotine strength of any e-liquid cannot exceed 20 mg/mL (2.0%).[66]

References[edit]

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