Interview Conducted by Jason S. Lupoi, Ph.D.
(Note: this is not a doom and gloom, fear-mongering story but one geared towards empowering cannabis consumers with information about what may occur inside a vape cartridge.)
With each passing year, our societal concept of modern medicine metamorphosizes a little further to include cannabis. Once pervasive images of stoners and the stereotype of what that actually means have waned, and the idea that one can ingest cannabis for myriad therapeutic benefits holds much more weight now that valuable anecdotal testimonials are being bolstered with science.
Whether one ingests cannabis for medicinal purposes or for so-called “recreational” purposes is irrelevant, however, when it comes to understanding potential hazards associated with the consumption of cannabis-derived products. In a previous interview, we spoke with Robert Strongin, Ph.D., about the potential for toxicants to form as terpenes degrade at elevated dabbing temperatures. Although these molecules may be in much lower concentrations than what’s found in cigarette or joint smoke, it’s still worth knowing what you may be ingesting that’s potentially harmful.
When we consider the safety of utilizing vape pens, our minds may be transported back to 2019, EVALI (e-cigarette or vaping use-associated lung injury), and the discovery of ingredients in vape carts that never should have been there in the first place.
Amber Wise, Ph.D., and her colleagues at Medicine Creek Analytics, a cannabis testing laboratory located in Fife, Washington, have evaluated vape carts in a different regard, demonstrating that heavy metals can leach into oils inside of the cartridges and into the vapor, highlighting the need for testing the oils after they are put into the cartridges and heated as done by consumers. [1,2] I spoke with Dr. Wise to learn more about this pivotal research into possible contaminants introduced by vape hardware.
Jason S. Lupoi, Ph.D.: How did you capture the aerosol generated from a vape cart for subsequent analysis?
Amber Wise, Ph.D.: We actually demonstrated two different methods that are equivalent for capturing cannabis aerosols; one was condensing it on the inside of a long tube and then rinsing out the residue for analysis. The second was bubbling the aerosol through some liquids and then processing and analyzing the liquids. The important difference we showed from nicotine aerosol collection is that you need to use an organic solvent such as acetone in the collection because the cannabis aerosol contains oily droplets that are not captured fully with traditional water-only methods. We also were not able to capture everything with only a filter paper.
JSL: What metals did you detect in the oils prior to heating, and how did that compare to post-heating? What levels did you detect?
AW: There are two different post-heating analyses you can look at; the oil left over in the cartridge after heating for some number of cycles, or the oil after the cartridge just sits around for a while (like it would between when it’s filled and when you buy it). To start, there was essentially no metals present in the oil prior to putting in the cartridges. After the cartridges sat around at room temperature and in a slightly warm environment (42oC, just above body temperature, i.e., a hot car) and then were removed from the cartridge and tested, there were elevated levels of metals in the oil (but not the aerosol). The metals we detected in the aerosol originated from the hardware, not the oil.
JSL: When you get vape cart samples to test, I’m assuming you get the oil that’s going to be put into the cartridge, and not the oil already in the cartridge. Is that right?
AW: Yes. In Washington, there is actually no requirement to test oil for metals, so we only screen a smaller number of samples for metals compared to other labs in other states. Most other states do require a heavy metals screen and the labs generally receive the oil sample in a small container that’s not the final cartridge. In California however, the final/packaged product must be submitted, so they fill the cartridges, then send them to the lab. So, the labs do have to open up the cartridges and remove the oil in California.
JSL: It’s interesting that a product could pass a heavy metals profile initially, but once it’s put into a cartridge, a retest of that extract may fail, especially if one measures the aerosol generated by the device. Or, worse, metals leached from the hardware may go undetected since some regulations do not require that final form product to be tested. Do you see laboratory testing changing to require tests of the product after it’s put into a cartridge, and aerosolized?
AW: Colorado will be requiring testing of aerosols in inhalable cannabis products for metals very soon. I assume other states will enact similar requirements but it’s still unclear what the testing standards and accreditation process will be.
JSL: What components of a vape cartridge and battery may contribute to this heavy metal leaching? When you did your testing, did you consider different manufacturers of the hardware, and if yes, what did the spread in that data look like? Was it pretty universal, or did some hardware perform much better by not causing leaching under the same experimental conditions?
AW: We did not compare specific brands in our study, but averaged a number of commercially-available cartridges. There were different brands represented. We were able to correlate some parts of the hardware with the metals profile we were seeing – mostly the heating coil components were found in the aerosols and the internal metal parts (central core) was found in the leaching studies.
There was definitely a large range of metals measured – a few had very high values while some had essentially none, even within the same brand. This tells us that the manufacturing or the heating profiles are very inconsistent and there are probably other variables that affect the metals’ ability to vaporize such as the type of battery/voltage/temperature, the formulation of the oil in the cartridge, the length and depth of puff an individual draws, how quickly you re-heat the battery (many puffs quickly or a few puffs over a long period of time). There is still a lot we don’t understand about the mechanisms of transfer.
JSL: What advice can you offer regarding practices consumers should avoid?
AW: Cartridges should be stored in a cool location and lots of repeated puffs avoided to allow cooling between puffs. We did not investigate the effect of temperature or voltage setting in our studies, but other studies show that lower temperatures result in fewer organic biproducts from being formed and would make it more difficult for metals to aerosolize. So, anytime you have the choice for a temperature or voltage setting, I’d turn it down. Not necessarily related to metals exposure, but I always recommend if people choose concentrates in cartridges to look for a full spectrum oil that is not distillate—made from supercritical carbon dioxide or butane extraction. Ideally it has cultivar-specific, cannabis-derived terpenes at less than 10% concentration and nothing else! I do not believe that flavorings, added terpenes, and thickening or thinning agents can be trusted as inhalables without further research.
JSL: You measured products with and without terpenes. What differences did you find?
AW: We found formulations with some terpenes had lower metals in the aerosol than formulations that were very thick with no terpenes. It was a limited study, but the two theories we hypothesize that contribute to this phenomenon are 1) the terpenes are more volatile and the evaporative heat that is dissipated as they vaporize creates a locally cooler area (less likely metals will aerosolize) or 2) the thinner/less viscous solution coats the heating coil more easily while the thicker oil creates air pockets where the heating coil can super-heat or oxidize and give off metal particles or gas.
JSL: How did your results compare to your evaluations of non-cartridge heating methods?
AW: We only did a small comparison between flower combustion (smoking) in a glass pipe and a concentrate in an electronically-heated quartz dab surface. The cartridges showed higher levels of a couple of metals, but the flower showed higher levels of manganese (which is naturally occurring in plants).
I think a couple take-home messages I’d like to emphasize are that the amounts of metals are very small and if the cartridges were used as medical devices under the Food & Drug Administration, they would pass the metal contaminant guidelines at 50 puffs per day. Another important thing to keep in mind is that inhaling anything that isn’t pure, clean air is not “good” for us, but if the medical benefits of a small amount of inhaled cannabis outweigh some of the risks, smoked or vaporized cannabis products can be used safely in moderation.
References
[1] McDaniel C, Mallampati SR, Wise A. Metals in cannabis vaporizer aerosols: Sources, possible mechanisms, and exposure profiles. Chem Res Toxicol. 2021;34(11):2331-2342. [journal impact factor = 3.739][2] Mallampati SR, McDaniel C, Wise AR. Strategies for nonpolar aerosol collection and heavy metals analysis of inhaled cannabis products. ACS Omega. 2021;6(26):17126-17135. [journal impact factor = 3.512; times cited = 3]
