Although adverse health effects of vaping THC cartridges have been found to include abdominal pain, nausea, chest pain, shortness of breath, and acute respiratory distress,they have not to date been fatal. In contrast, sudden deaths and hospitalizations from EVALI were linked to a compound called vitamin E acetate , the chemically stable esterified form of vitamin E .VEA is thought to have been used as a cutting or diluting agent in THC cartridges because it has a similar viscosity to THC oil, therefore allowing the dilution or adulteration of the THC oil as a means to increase profit margins while not being visually evident.FDA laboratories confirmed that VEA was present in 81% of THC-containing vaping cartridges confiscated from 93 EVALI patients.VEA was also found in the bronchoalveolar fluid samples from 48 of 51 patients but not in samples from the healthy comparison control group. The VEA fraction in vaping cartridges confiscated from EVALI patients ranged from 23 to 88%.Duffy et al.analyzed 38 samples of 10 EVALI cases in New York and found a VEA content of up to ∼58% and a Δ9 -THC content of up to ∼66% in the confiscated cartridges. This work aims to study vaping aerosols from e-liquids relevant to the content of these cartridges in a controlled laboratory setting. Both aerosolized VEA itself and its thermal degradation products were shown to be toxic or potentially toxic in vivo. However, currently,cannabis grow setup there is not sufficient evidence to rule out the contribution of other ingredients in the confiscated cannabis vaping e-liquids or their synergistic effects with VEA.
Terpenes in cannabis vapes,for example, can also degrade into toxic products such as benzene and methacrolein.Radiological and histological analyses of some EVALI patients did not find exclusive evidence of lipoid pneumonia that would beexpected from the lipid-like VEA in some cases of lung injury.Instead, ground glass opacities and other observations have been made that could implicate smaller toxic compounds, instead of inhaled VEA. In vitro and animal studies also suggest that pure VEA is not entirely equivalent to confiscated vape cartridges in its biological effects.Thus, it is important to study the mixture of VEA with cannabis-based extracts to understand whether VEA has unique, additive, or synergistic effects modifying the chemical characteristics or biological effects of the aerosol that is vaped. It is also not clear if extreme temperatures and/or use conditions are required for toxicant formation that contribute to EVALI. Temperatures that are sufficiently high to initiate combustion and pyrolysis may produce, for example, toxic ketene gas from VEA.Although high temperatures may occur under certain conditions of use, including those potentially associated with EVALI,users may also choose to avoid such scenarios due to unpleasant sensations and taste.This study focuses on a detailed characterization of the composition and degradation chemistry of vaping aerosols from VEA, purified THC oil, and a mixture of the two, in a temperature programmable third-generation “mod” device and using puffing regimen that is consistent with CORESTA recommendations.A temperature range of 100−300 °C was chosen to represent wet- or partially wet wick conditions for mods and clearomizers,which is sufficient to degrade VEA.Gravimetric analysis is used to evaluate aerosolization efficiency. High-performance liquid chromatography coupled with highresolution mass spectrometry is used to characterize thermal degradation carbonyls and acids, as well as cannabinoids and oxidized cannabinoids. Gas chromatography−mass spectrometry was used to quantify particle-phase terpenoids.
Thermal degradation and mechanisms for the oxidation of THC and VEA are proposed, which may prove useful for policy guidance and future research.A temperature-controlled third-generation Evolv DNA 75 modular e-cigarette device with a refillable e-liquid tank and single-mesh stainless steel coils was used for aerosol generation . The mod enabled variable output voltages with a coil resistance of ∼0.12 Ω. This device allows for temperature control and facile coil temperature measurements. Coil temperature was measured by a flexible Kapton-insulated K-type thermocouple in contact with the center of the coil surface and output to a digital readout. The temperature set by the device is not truly representative of the measured coil temperature.Discrepancies between set and measured coil temperature arise from variations in the air flow rate, e-liquid viscosity, and coil resistance , which alter the relationship between applied power and output temperature that drive aerosol chemistry. The puff duration is 3 s with a flow rate of 1.1−1.2 L/min, quantified by a primary flow calibrator , corresponding to a puff volume of 55−60 mL.The e-liquids used for vaping in this work are: pure VEA , purified THC oil extracted from cannabis ; and a mixture of VEA and THC oil . The THC oil was commercially obtained from Biopharmaceutical Research Company , and all work was performed in the BRC facility under their DEA licensure. Composition analysis of the cannabinoid content of the THC oil demonstrated the most abundant cannabinoids to be: Δ9 -tetrahydrocannabinol , Δ9 -tetrahydrocannabinol acid , and cannabigerolic acid .
The certificate of analysis of the THC oil advertises 40−60% dry weight of Δ9 -THC, with <5% of CBD and CBN; thus, the THCA and CBDA contents may not have been included in the original analysis or may have been converted from their neutral counterparts prior to receipt of the materials. Duffy et al.also found THCA in confiscated cannabis vapes associated with EVALI. All other cannabinoids were found to be below 3% of the total peak area . Δ8 -THC, with a retention time of 0.3 min after the Δ9 isomer, was not detected in the mixture. THC oil presumably also contains terpenoids, alkanes, and alkenes, although these were not able to be characterized in the unvaped e-liquid. Three temperatures were chosen for the particle generation within the range of the vaping device, with a temperature variance of 10−20 °F. Carbonyls, acids, and cannabinoids in the vaping aerosol , which represent the majority of expected products,were collected onto 2,4-dinitrophenylhydrazine cartridges for HPLCHRMS analysis. A total of 10 puffs of aerosol with a frequency of 2 puffs/min was loaded onto the cartridge. Consecutive sampling with three DNPH cartridges demonstrated a collection efficiency >98.4% for carbonyl-DNPH adducts in the first cartridge.DNPH was conserved in the cartridge after the collection to maximize derivatization efficiency . DNPH cartridges were extracted with 2 mL of acetonitrile into autosampler vials and analyzed by HPLC-HRMS. Consecutive extractions of DNPH cartridges for samples confirmed that >97% of both DNPH and its hydrazones were extracted after the first 2 mL volume of acetonitrile. Cannabinoids were trapped in the silica without modification. The collection efficiency for cannabinoids is unknown, as only a limited amount of THC oil was available for experimentation, thus quality control tests were not performed. Glass fiber filters were used to collect the aerosolized particulates as in other ecigarette studies.Glass fiber filter and DNPH cartridge collection of aerosols occurred separately. The particulate mass collected on filters was determined gravimetrically on a microbalance by weighing the filter mass immediately before and after puffing under the specified experimental conditions. Particles on polytetrafluoroethylene filters were also collected for select chemical analyses. Due to potential losses of particles through the collection apparatus,rolling flood tables particle measurements are used in this work to indicate relative changes due to e-liquid composition or coil temperature instead of absolute quantities. The standard deviation of triplicate gravimetric analysis was determined to be ∼20%, primarily due to variations in puffing idiosyncrasies of the mod. Chemical analyses were also performed in triplicate, and standard deviation of the data are reported in relation to the specific analysis performed.Table 1 shows the aerosol particulate mass collected on filters at three temperatures and various e-liquid compositions. Due to the high molecular weight of the e-liquid ingredients, we expect particle mass to be the major fraction of total aerosolized mass. Increasing temperature increased the particle mass collected on the filter, which was consistent with expectations.The particle mass production at any particular temperature was suppressed after adding VEA, with pure VEA having the lowest aerosolization efficiency.
The aerosolization of e-liquids in response to a heated coil is some combination of thermally induced phase change and chemistry. The thermal stability of THC is lower compared to VEA ; this is similar to the trend of the vacuum boiling points vs VEA .The normal boiling point of VEA cannot be measured as it degrades before it boils at atmospheric pressure.These thermodynamic properties indicate that it takes more energy to induce a change in VEA compared to THC, whether that change is a change in phase or chemical bonding, consistent with their aerosolization trends and the observation of degradation products during vaping. It is noteworthy that the suppression in aerosol formation did not scale with VEA volume content in the e-liquid at the same temperature, e.g., the 1:1 THC/VEA sample produced only a tenth of the particle mass of the THC sample. It is likely the addition of VEA produces a non-ideal solution with the THC oil by introducing significant intermolecular interactions between VEA and cannabinoids. This is consistent with the observation of Lanzarotta et al.that hydrogen bonding occurs between VEA and THC. The number of hydrogen-bond interactions in a mixture is shown to be directly proportional to its viscosity.While the viscosities of the e-liquid solutions tested are notknown, it is likely that extensive hydrogen bonding can change the physical characteristics of the e-liquid that could lead to aerosolization differences. Thermal degradation or oxidation products of VEA and THC were observed at the measured coil temperature of 450 ± 20 °F , similar to the temperature that VEA began to degrade in the work of Riordan-Short et al.Single-ion chromatograms of aerosolized components from VEA, THC oil, and the 1:1 mixture show that the aerosol composition is quite complex but that aerosols from the vaped 1:1 mixture of THC oil and VEA more closely resembles that from the vaped THC oil. Carbonyls and acids that can be generated from the thermal degradation of both VEA and THC oil are the small compounds such as formaldehyde,acetaldehyde, acetone, diacetyl, glyoxal, etc., and their associated carboxylic acids . The blue line in Figure 2 represents the carbonyls and acids only from the thermal degradation of VEA, and the magenta line represents both carbonyls and cannabinoids from the vaping aerosol of THC oil. Some isomers have ambiguous identification, e.g., C6H12O can be assignable to either hexanal or 4-methylpentanal. While hexanal can be formed from terpenes,4-methylpentanal is uniquely formed from the thermal degradation VEA according to the proposed thermal degradation pathway in Scheme 1. Since C6H12O is highly enhanced in the VEA aerosol , we assign the majority of this emission to 4-methylpentanal. Approximately 10 carbonyls and acids identified in Table 2 have also been reported by Riordan-Short et al.However, carbonyls with VEA-specific structures are newly identified here . Riordan-Short et al.also identified several esters and alkanes with GC-MS. The lack of standard spectra for VEA-derived compounds in GC-MS libraries may have prevented the identification of these peaks previously. Moreover, some carbonyls identified by RiordanShort et al. were not found in this work . The cause of discrepancy is unknown; however, it could be hypothesized that it may be partially due to the difference in vaporization method . To determine the influence of VEA on the formation of carbonyls, it is informative to normalize the mass of carbonyls produced by the particle mass collected at the same temperature . Figure 3 shows the normalized mass of nine selected thermal degradation carbonyls from vaping VEA, THC oil, and their mixture at 450 °F . Some carbonyls such as formaldehyde, hexanal/4-methylpentanal, glyoxal, and C4H6O2 were produced in higher abundance from VEA compared to THC oil. While e-cigarette users who use nicotine products will self-titrate nicotine intake, there is also evidence that people who use higher potency cannabis for recreational purpose can also titrate their THC dose.For high-VEA-mixture fractions, users who selftitrate may be exposed to high levels of VEA-related products. Within the C4−C6 carbonyls shown in Figure 3, butyraldehyde, valeraldehyde, and hexanal appear to originate from the thermal degradation of cannabinoids and terpenes, which is consistent with Tang et al.,while isobutyraldehyde, isovaleraldehyde, and 4-methylpentanal are from the thermal degradation of VEA . Although some products like formaldehyde can be produced from both VEA and THC oil, the production of formaldehyde from VEA appears more favorable since it involves a bond cleavage at a more substituted carbon , which forms a more stable alkyl radical intermediates than those from the unbranched aliphatic side chain of THC.