- Friday, 05 April 2013 20:32
Metals and nanoparticles in e-cigarettes-Commentary
An interesting study was just published at PloS One by researchers from the University of California. The study evaluated the presence of heavy metals and silicate particles present in electronic cigarette cartomizer fluid and aerosol.
The researchers at first dissected some cartomizers and performed centrifugation to detect which metals could be present in the various components of the particular cartomizer. Although useful, this information has no clinical significance. Even the process of “dissecting” the cartomizer could lead to production of small particles that otherwise would not be present in vapor. So, I will not focus on the results of these procedures. A surprising finding was that most of the cartomizers were previously used (although acquired as “brand new”), probably for testing purposes. However, in some cases they were overused, with characteristic burning spots in the Poly-fil fibers.
The cytotoxic study, evaluating the effects on human pulmonary fibroblasts, is also of minimal clinical significance. First of all they tested the liquid in liquid form, while we know that in reality the user is exposed to vapor. Moreover, they produced an artificial mixture of liquid plus particles obtained by centrifugation that was tested on fibroblasts, reproducing settings that are not applicable to the real user.
The most interesting part of the article was the examination of vapor for the detection of heavy metals. The findings are somewhat expected. The question of particles coming from the wick and from the metal parts and soldering has been raised since a long time in e-cigarette forums. It was unknown territory until now. It should be emphasized that only small particles are able to penetrate deep into the respiratory system, so the “dust” that many users have seen from using the e-cigarette has no clinical significance. Indeed, researchers found several particles in nanometer size, that are able to penetrate deep into the lungs. The numbers they report show that e-cigarette produces 880 times less particles compared to conventional cigarettes (they say that 100 puffs-similar to approximately 10 cigarettes- will expose the user to 100 million nanoparticles, while one cigarette delivers 8800 million particles.
Significant part of the article was dedicated to discussion about the presence of tin, coming from the soldering. First of all, it should be emphasized that they did not find lead in the soldering, in line with the worldwide ban on its use. Concerning tin toxicity, stannosis (the disease caused by inhalation of tin particles) is a benign form of pneumoconiosis. It has been observed in workers processing tin from scrap, and according to ATSDR (also referenced in the article) “In all cases, chest x-rays of the workers showed discrete opaque shadows throughout the lungs, attributed to stannic oxide deposits. However, there was “no impairment of pulmonary function or systemic disease”
The Permissible Exposure Limits of tin (as defined by OSHA-Occupational Safety and Health Organization and other public health organizations) in air is set at levels of 2mg/m3
What does this mean in relation to the study findings? Table 1 of the study indicates that they found 0.037micrograms of tin per 10 puffs of e-cigarette. Assuming that 10 puffs are equal to 500ml of vapor and air inhaled (50ml/puff-a very modest estimation), we can conclude that the concentration of th metal per 1m3 (1000 liters) will have 0.037 x 2000 = 74micrograms per m3. This is 27 times less than the upper limit of normal for occupational exposure (8 hours continuous exposure at those limits). It should be mentioned that tin is much more dangerous in organic form, unlike the inorganic form found in this study.
Lead is an important and highly toxic metal. Using similar methodology with tin, we can calculate an exposure level of 34micrograms per m3, while the safety limits are 50microg/m3
Similarly for aluminum, the exposure level is measured at 788micrograms per m3 (0.788mg/m3) compared to the currently-defined safety levels of 5mg/m3
Another method of measuring exposure to these metals is by taking into account the maximum permissible daily exposure, as defined by US Pharmacopeia Convention
According to the 2013 revision (concerning inhalation exposure), the levels were 5 micrograms/day for lead, 1.5 micrograms/day for nickel, 100 micrograms/day for cooper and 25 micrograms/day for chromium. According to our calculations (measurements in experienced vapers), 13 puffs in 5 minutes lead to consumption of 60mg of e-liquid, thus 1gram (approximately 1ml) is consumed by 216 puffs. Taking into account a mean consumption of 4ml e-liquid/d, vapers take approximately 880 puffs per day. According to the study measurements, they would get 1.5 micrograms/day lead (5 is the safety limit), 0.44 micrograms/day nickel (1.5 is the safety limit), 17 micrograms/day copper (100 is the safe limit) and 0.6 micrograms/day chromium (25 is the limit). All levels are significantly lower compared to safety limits, even for a daily consumption of more than 10ml of e-liquid.
Finally, it should be mentioned that in another study which evaluated cadmium, nickel and lead presence in e-cigarettes, they found levels similar to what is present in pharmaceutical nicotine inhaler.
As a conclusion, this study is important because it reminds us that electronic cigarettes are not an absolutely healthy habit. It also shows that in chemical studies the results depend solely on what you search for. Meaning that in several other studies no heavy metals were detected because they did not search for them. Therefore, we cannot trust chemical studies, because they do not provide the whole picture and they do not measure the effect of use. However, once again, it seems that the amount of exposure to harmful substances is far less compared to tobacco cigarettes. Let us not forget that several other toxic chemicals (nitrosamines, polycyclic aromatic hydrocarbons, free-radicals) are present in tobacco cigarettes and are blamed for promoting disease, and these were not addressed in this study. I have always maintained the opinion that we should search for the safest possible product, even though we expect every e-cigarette to be safer than tobacco. Thus, based on this study, it is important to examine other types of atomizers that may be safer compared to the cartomizers tested. Quality of manufacturing should (and can) definitely be improved.
Dr Konstantinos Farsalinos