New Study Finds Metal Particles in Unused Cannabis Vape Liquids
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Even unused cannabis vape pens may contain metal particles, according to a new study led by researchers at the National Research Council of Canada (NRC).
Published in ACS Omega, the study originally set out to analyze the metal content of a range of legal and illegal market cannabis vape liquids. The researchers found high levels of lead, nickel, and other heavy metals in the vape liquids, well above the currently established tolerance limits referenced by Canada’s Cannabis Regulations.
The researchers also noticed an unusually large relative standard deviation in metal content between samples taken from identical devices. Upon further testing, they found evidence confirming the presence of metal particles in the vape liquids.
These metal particles dispersed through the vape liquids would explain the poor measurement reproducibility observed, the researchers say. However, additional research is still sorely needed if these particles, their origins, and their compositions are to be fully understood.
High levels of lead and nickel found in unused vape liquids
In this study, inductively coupled plasma mass spectrometry (ICP-MS) was used to study the metal content of 20 legally purchased cannabis vapes. A further 21 illegal cannabis vape pens, provided by the Ontario Provincial Police, were also assessed.
The researchers found that the concentrations of arsenic, mercury, and cadmium in both the legal and illegal vapes all fell well within the generally accepted tolerance limits used for cannabis products. But one legal vape pen and six illegal products were found to contain lead concentrations higher than this limit. While only a handful of the vapes exceeded limits for cobalt and vanadium, significantly more samples were above the generally accepted limits for chromium, copper, and nickel.
The researchers also found that it was very common for samples to exceed tolerance limits for more than one metal. For example, several of the legal vape liquids that contained high amounts of nickel also contained chromium and/or copper in excess of their respective tolerance limits. Among the illegal products, samples that were high in lead also tended to exceed limits for copper, nickel, and zinc.
The extent to which these products violated generally accepted tolerance limits is also a concern. In one illegal vape, the lead levels measured were approximately 100 times the lead tolerance limit. Another four illegal vapes were found to contain nickel levels up to 900 times above their established limit.
Metal particles in the liquids are limiting measurement reproducibility
The presence of metals in vape liquids is a safety risk; studies on tobacco vapes have already concluded that metals from vape aerosol can accumulate in the lungs and cause a variety of respiratory injuries. But the presence of metals in the vape liquid itself can also pose problems for analytical testing.
In this study, the researchers began to notice significant differences in the metal fractions observed even when testing vape liquids from the same batch were taken from two identical devices.
“When we do this kind of analysis of samples, we always do replicate measurements,” lead author and NRC researcher Dr. Zuzana Gajdosechova told Analytical Cannabis.
“And as I made these repeated measurements, I could see that the values which I was getting for individual sub-samples were very different from each other. Then when you calculate an average value and add to it standard deviations, those were really high – extremely high – compared to what we normally see in samples.”
Poor homogeneity can be one explanation for a high relative standard deviation (RSD), Gajdosechova explained, but each vape liquid was specially prepared to be as homogenous as possible before testing. An alternative explanation might be the presence of metal particulates.
“Because of the sort of concentrations that I saw in the samples, it looked like there could be some dense materials of metals, which would be coming from metal particles,” Gajdosechova said.
To test this hypothesis, the researchers examined droplets of selected replicate vape liquids using electron scanning microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS) and laser ablation ICP-MS (LA-ICP-MS).
“Although very viscous, these vape liquids are still liquid. So for the few rounds of analysis, we couldn't see any particles and we thought it was most probably because of the sedimentation,” Gajdosechova recalled.
“The capsules in which you do the analysis, they contain few microliters of liquid. So when you put the liquid in there and leave it in a vacuum chamber for a while, the particles naturally sediment. And the nature of SEM is that it scans the surface.”
Despite these limitations, the researchers were able to clearly detect copper-, zinc-, lead-, and manganese-containing particles in the vape liquid sample. Each of these metals is commonly found in the metal alloys used to make vape device hardware, but the researchers say it is too early to draw any conclusions about the exact origin of the particles.
“There is going to be a follow-up research project, which will be looking more into the particles within the liquids,” Gajdosechova said. “So, using different techniques and trying to provide more information about the size and composition of the particles.”
Heavy metals and vaping
Across North America, legal cannabis products are routinely subject to heavy metals analysis to detect the “big four” metals: lead, arsenic, cadmium, and mercury. But as demonstrated in this study, and in others, other metals including chromium, copper, nickel, and manganese may also be of concern.
In recent years, there has been a distinct push for the use of vape aerosol testing methods, with the view that these methods can evaluate the levels of contaminants that consumers are actually exposed to. Using this approach, metal nanoparticles have been detected in cannabis vape aerosol in numerous studies. And now, this new study would suggest that similar metal nanoparticles are already present in vape liquids before the vaporization process begins.
“There is very limited data so far on these devices, and generally on cannabis. Probably just because there's not that many countries which have legalized cannabis,” Gadjosechova said. “But it would be very helpful if there would be more research going on and we could compare data between individual research groups or different publications, because right now, there is very little available.”