Cannabis vape cartridges (“carts”) are a popular delivery method. Many vapers perceive them as less harmful since they have the option to heat the oil only to the point of vaporization, which is lower than that of combustion (smoking). Still, there are safety concerns beyond the obvious that need to be considered. You may have read our previous article on the safety of cannabis vape cartridge materials; this article will focus on the safety of the material being vaporized.
A study published in ACS Omega addresses the need to create a test method for evaluating heavy metal content in the vapor you get from heating a cannabis vape cartridge.  Due to the nonpolar chemical nature of cannabis aerosols, traditional aqueous testing methods used for testing e-cigarettes or tobacco are not accurate. The research team created a new method and evaluated the heavy metal content of cannabis vape carts. Vape carts were tested for the presence and amount of ten heavy metals with the new method: arsenic, cadmium, cobalt, chromium, copper, mercury, manganese, nickel, lead, and tin.
What is in a Cannabis Vape Cartridge?
Cannabis vape carts are usually sold as pre-filled cartridges that either attach to a battery or are a disposable unit with the battery included. The cartridges themselves can be made of a variety of metals. They generally heat to 135°C to 334°C, but dry coil heat can reach 1000°C (which is much higher than is needed).
The researchers define cannabis concentrates in vaporizer cartridges as “highly viscous mixtures that contain 40–90% by weight cannabinoid molecules with the remainder of the solution containing a combination of other plant-derived hydrocarbons such as terpenoids and phospholipids.” They add that the concentrates “are often mixed with diluents to adjust viscosity or cannabis-derived or other botanically derived terpene mixtures for flavoring.” The diluents used are much more heavily scrutinized now than several years ago due to e-cigarette or vaping use-associated lung injury (EVALI) and other concerns over diluents like propylene glycol. Terpenes are a common additive to reduce viscosity. 
The Future of Cannabis Vape Cartridge Testing
Testing cannabis for heavy metals is important because it is a plant that readily takes up and stores metals from the soil. Those metals can become concentrated in the plant and have carcinogenic effects when inhaled by humans. The results of the study showed that this test method could be key to compliance with new mandates like Colorado Marijuana Enforcement Division’s proposed rules for cannabis vape cartridge emission testing.
The researchers spiked vaporizer cartridges and observed that heavy metal content became more concentrated in the cartridge after it had been vaped down (with a puff machine). They also noted that vape cartridge construction could contribute to heavy metal content, especially nickel and copper which were very prevalent in the results. Heavy metals were vaporized/aerosolized at low levels.
Cannabis Emissions Testing Method
To spike the concentrates, the researchers added 10 g cannabis concentrate to 15 mL of 2-propanol, warmed it to 45 ºC, then added 10 μL of 1000 μg/mL standards of each metal. They experimented with different impingers and solvents for the aerosol collection phase; aqueous (e.g.,10% hydrogen peroxide) and organic (e.g., hexane) impingers were implemented. The organic solvents were needed to dissolve the droplets, boosting collection of some metals, but the aqueous impinger was required to capture mercury. Microwave digestion with nitric acid, hydrochloric acid, and water (based on EPA method 3052) followed by dilution prepared the samples for analysis. For this last step, the researchers employed a Shimadzu inductively coupled plasma (ICP) mass spectrometer (MS) 2030.
They validated the digestion and ICP-MS steps for quantifying metals. That said, “not all metals…can be fully recovered in the aerosol capture processes at standard voltage settings or combustion temperatures.” Although the method makes significant progress toward quantifying heavy metals in vape aerosol, the research team has launched additional research on the quest for a “robust method for testing aerosol mixtures from cannabis products.” 
1- Coffin M. Viscosity reduction of high potency cannabis oils: The case for 100% cannabis-derived formulations. Extraction Magazine. Nov-Dec 2019.
2- Mallampati SR, et al. Strategies for nonpolar aerosol collection and heavy metals analysis of inhaled cannabis products. ACS Omega. 2021;6(26):17126-17135. https://pubs.acs.org/doi/full/10.1021/acsomega.1c02740. [Impact Factor: 3.512; Times Cited: n/a]