Toxicant Formation from Terpenes Deconstructed
Analysis of the influence of temperature on the formation of toxic compounds while dabbing cannabis extracts
Patients in the medical cannabis community often vaporize their cannabis instead of smoking the plant material (flower) directly. This provides many benefits, as the patient is inhaling less smoke and toxicants produced in combustion, and is inhaling a heated gas containing vaporized terpenes and cannabinoids. Cannabis users who switch from flower to vapor find a significant improvement in lung function and sensitivity of their smell and taste sensations.
Recently, a scientific article published by Portland State University (PSU)1 (here) has created waves of panic in the medical cannabis community, as reports of toxic chemicals being produced during dabbing have been spread around and quickly popularized. Many cannabis patients now feel dabbing to be an unsafe form of medicating and are now unsure of the risks associated with this route of administration.
While dabbing has risks associated with it, such as elevated pesticide levels relative to that found in the source flower, the mechanism of vaporizing cannabinoids produces far fewer breakdown products than combustion of raw plant material. It is for this reason that those in the cannabis and medical communities view less risks associated with vaporizing when compared to smoking. It is relevant to state that not all risks associated with this route of administration have been thoroughly investigated at this time, and risks not deducible with the data presented below may still be present.
Through the evidence presented in this article, we will examine the relative levels of this breakdown products in dabbing when compared to cigarette smoke and exposure to traffic smog. It is fully possible to dab safely and without the generation of toxic chemicals, and the evidence used herein to prove this claim is derived entirely from the data published by the PSU study.1 Before we examine the evidence presented by the research team, let’s do an overview of what exactly is happening from a chemical science perspective.
WHAT ARE THESE TOXICANTS AND WHERE ARE THEY COMING FROM?
Hash oil is an extract of Cannabis that is composed of the cannabinoids and terpenes, the chemicals responsible for cannabis’ therapeutic effects. This means that although flower is about 20% cannabinoids and 1% terpenes, extracts are closer to 50-90% cannabinoids and 1-4% terpenes, and as high as 10% with certain terpene retaining manufacturing procedures such as “live resin” or “cold-trap refortified” techniques occasionally discussed in the cannabis community. This increased purity means that the product can be vaporized and inhaled directly without the need to burn anything.
When carbon compounds like plant material, terpenes and cannabinoids (all of which are mostly carbon) are ignited, they are so hot that all of the atoms react with the oxygen in the air and form carbon dioxide and water (CO2 and H2O, respectively). If the temperature is lowered slightly, these reactions with oxygen begin but do not reach completion, thereby producing oxidation breakdown products of the original carbon compounds. This means oxygen started reacting with the chemicals that are being vaporized, but not enough to turn them into harmless carbon dioxide and water. Instead, these species remain as an intermediate breakdown product, which may be toxic. Scheme 1 from the PSU paper outlines the conversion of terpenes into isoprene, the building block of all terpenes, and its subsequent oxidation to several toxicants, most notably methacrolein and benzene .
Schematic 1: Skeletal diagram showing 3 major terpenes in cannabis, linalool, myrcene, and limonene. The diagram shows the degradation of terpenes into their precursor isoprene, which can be transformed into toxicants. Toxicants displayed are taken from the PSU study. Reaction mechanisms illustrated are hypothetical and provided by the author to illustrate degradation conceptually, and do not reflect empirical or quantitative data.
Although the above reaction scheme is possible under certain conditions, this does not mean that dabbing is unsafe. Below certain temperatures, the rate of this reaction is zero, and that means the patient receives none of the toxicants illustrated here. With proper technique, hazardous substances can be avoided.
EXAMINATION OF DATA
If you’ve read the article from PSU, then you’re probably familiar with these two images, called Table 1 and Figure 1 respectively. Table 1 shows the amount of toxicants found at dabbing experiments done with a variety of terpenes and mixes.
The above table seems to show that all terpenes generate methacrolein and benzene. But all of these experiments, showing 261 parts per million (ppm) toxicants were performed at the maximum temperature: 500-550 °C (932-1022 °F). These temperatures are far too high to be a reasonable approximation for dabbing, as most dabbers keep their temperatures around 376.67 °C (710 °F).
Table 1: The table shows the amount of methacrolein and benzene detected per each mg of terpene dabbed. The temperature for all of these data points is between 500-550 °C (932-1022 °F) which has been highlighted in the above depiction. Data taken from Table 1 from the Portland State University paper.
Figure 1: Bar graph showing amounts of methacrolein detected versus the temperature of the nail during the dab. Data taken from Figure 1 from the Portland State University paper
Figure 1 shows that with temperature increases, the concentration of methacrolein concomitantly increases. This is consistent with the temperature dependent theories of oxidation outlined above. At 322 °C (611.6 °F) no methacrolein was detected by the experiment. Because toxicants were found at temperatures just above the standard dabbing temperature of 376.67 °C (710 °F), examination of the supplementary data tables illustrates how many toxicants were produced at each temperature.
Table 2: Table showing the amount of benzene and methacrolein detected in simulated dabs at various temperatures. Data taken from Supplemental Data Table 7 from the PSU paper
Table 2 shows that for benzene and methacrolein, temperature increases led to higher amounts of detected toxicants. This table also shows that benzene appears at lower levels than methacrolein at the same temperature, and that benzene requires a higher temperature to be formed. Lets take this table of data and represent it in a way that is more graphical and intuitive to understand:
Figure 2: Data from Table 2 represented as a bar graph. The X axis shows increasing temperature. For reference, 376.67 °C (710 °F), the ideal dabbing temperature is illustrated.
The relationship between temperature and toxicants produced is obvious. At the highest temperature several ng of benzene, and over 150 ng of methacrolein are formed. At the next lowest temperature benzene is no longer detectable and at 322 °C (611.6 °F) neither benzene nor methacrolein can be detected. The ideal dabbing temperature, 376.67 °C (710 °F), is between the lowest temperature in the study for which methacrolein was detected and the temperature at which no toxicants were detected. This means that 376.67 °C (710 °F) may or may not contain methacrolein, but if it does it will be below the concentration seen at 403 °C (757.4 °F). This data indicates that although terpenes can be converted into benzene and methacrolein at very high temperatures, they are detected at around 50 ng per 40 mg dab at 403 °C (757.4 ºF) and have not been detected at 322 °C (611.6 °F). Using this reasoning, it is likely that at the ideal dabbing temperature, 376.67 °C (710 °F), less than 50 ng of methacrolein and no detectable benzene would be present per dab.
INTERPRETATION OF DATA
Judging from the data examined above, dabbing at or below the ideal dabbing temperature of 376.67 °C (710 °F) has a low probability of methacrolein exposure and very low probability for benzene exposure. The paper does refer to the use of e-nails and their convenience and safety in keeping dabbing nails in a safe temperature range. A patient using a traditional nail with a butane torch as a heat source, can inexpensively purchase an infrared (IR) thermometer, which is a gun with an IR laser that will read the temperature of whatever you point it at. Different guns are calibrated for different temperature ranges, it’s important to find one that serves the temperature ranges desired. With this technology, consumers can make informed choices about how long to let the dabbing nail cool before administering a dose, such that toxicants can be safely avoided. Given the current data outlined here, the best way to minimize exposure to methacrolein and benzene is to dab at or below 322 °C (611.6 °F).
Although more data is needed to indicate if 322 °C (611.6 °F) is sufficiently hot to completely vaporize all cannabinoids present in the dab, from the author’s personal experience as a cannabis patient, temperatures below 300°C (572 °F) do not create a noticeable decrease in THC bioavailability. More data will also need be collected on the ideal dabbing temperature, to truly pinpoint what the lowest possible temperature is that will consistently vaporize all cannabinoids from the nail. The origins of the current ideal dabbing temperature are shrouded in mystery, but are believed to have come from a mixture of patient experimentation with qualitative measurements such as taste and pharmacological “feel” (feeling high), and the arbitrary decision to use the hash oil community’s symbolic number “710”, which is known for mimicking the word “OIL” when viewed upside-down. This indicates the possibility that the current ideal dabbing temperature recognized in the hash oil community may be higher than is necessary.
This study detected toxicants in the range of 0-190 ng per 40 mg dab. To give a context for this, consider the relative amounts of these compounds found elsewhere. Cigarette smoke has been shown to have a greater amount of methacrolein compared to cannabis products. A study found that a single cigarette contained 104 μg (104,000 ng) of methacrolein.2 Another study found that the methacrolein content of a smoked cigarette to be 8 μg (8,000 ng).3 Compare these numbers with the highest methacrolein value found in the PSU, approximately 190 ng of methacrolein per 40 mg dab at 526 °C (978.8 °F).
Benzene concentrations in cigarette smoke are found to be much larger than anything found in dabbing experiments. One study found that a commercial cigarette’s worth of smoke contained 57 μg (57,000 ng) benzene.4 Another study found similar values, with 50 μg benzene (50,000 ng) per commercial cigarette.5 An air quality study done in Asia showed that urban residential environments had 15,110 ng of benzene per cubic meter of air, and that industrial areas had 15,070 ng of benzene per cubic meter of air.6 Compare these number with the highest amount of benzene found in the PSU study, about 18 ng per dab at 526 °C (978.8 °F).
The PSU study makes reference to the “purported” health benefits of terpenes, perhaps because these claims are often associated strictly with the cannabis industry and community. It is important, however, to show the cannabis patient community that the health benefits of terpenes have been studied and are well understood by scientists. There are many sources showing the health benefits of terpenes7, 8, 9, 10, 11, 12, and many sources studying the health benefits of terpenes specifically in cannabis13, 14, 15, 16, 17, 18. In conclusion, the argument that terpenes have benefits for human health is strong in the scientific literature.
Although the PSU study did much to contribute to our knowledge on the dangers associated with dabbing, more data could be collected in further experiments to help answer some unanswered questions. The data from the PSU paper gave us a good idea of how and when different toxicants form at high dabbing temperatures. Now we are left with the question: what the ideal dabbing temperature truly is? The cannabis community currently uses the value of 376.67 °C (710 °F), and the data from the PSU study indicates that while it’s possible this may produce no toxicants, it more likely to have somewhere between 1-50 ng of methacrolein. Only the lower temperature 322 °C (611.6 °F) was found to have no detectable toxicants. Repeating the experiment with more temperature graduations would allow us to examine 376.67 °C (710 °F) more closely, but also permit a better understanding the precise temperature at which toxicants begin to form. In addition to this data, a study that is also collecting data on the amount of cannabinoid vaporized in the sample could bring additional insight. By comparing the formation of toxicants, presumably at the higher end of the temperature scale, with the loss of cannabinoid vaporization on the lower end, a tableau of dabbing dynamics can be constructed and a truly ideal dabbing temperature can be discovered and proven analytically.
Meehan-Atrash, Jiries, Wentai Luo, and Robert M. Strongin. "Toxicant Formation in Dabbing: The Terpene Story." ACS omega 2.9 (2017): 6112-6117.
Stedman, Russell L. "Chemical composition of tobacco and tobacco smoke." Chemical Reviews 68.2 (1968): 153-207.
Falk, Hans L. "Chemical agents in cigarette smoke." Comprehensive Physiology (1977).
Wallace, Lance A. "Major sources of benzene exposure." Environmental health perspectives 82 (1989): 165.
Darrall, KeitháG, JohnáA Figgins, and RichardáD Brown. "Determination of benzene and associated volatile compounds in mainstream cigarette smoke." Analyst 123.5 (1998): 1095-1101.
Lee, S. C., et al. "Volatile organic compounds (VOCs) in urban atmosphere of Hong Kong." Chemosphere 48.3 (2002): 375-382.
Dillard, Cora J., and J. Bruce German. "Phytochemicals: nutraceuticals and human health." Journal of the Science of Food and Agriculture 80.12 (2000): 1744-1756.
Craig, Winston J. "Health-promoting properties of common herbs." The American journal of clinical nutrition 70.3 (1999): 491s-499s.
Steflitsch, Wolfgang, and Michaela Steflitsch. "Clinical aromatherapy." Journal of Men's Health 5.1 (2008): 74-85.
Patocka, Jiri. "The chemistry, pharmacology, and toxicology of the biologically active constituents of the herb Hypericum perforatum L." Journal of Applied Biomedicine 1.2 (2003): 61-70.
Hao, Cherng-Wei, et al. "Antidepressant-like effect of lemon essential oil is through a modulation in the levels of norepinephrine, dopamine, and serotonin in mice: Use of the tail suspension test." Journal of Functional Foods 5.1 (2013): 370-379.
Crowell, Pamela L., et al. "Chemoprevention of mammary carcinogenesis by hydroxylated derivatives of d-limonene." Carcinogenesis 13.7 (1992): 1261-1264.
Russo, Ethan B. "Taming THC: potential cannabis synergy and phytocannabinoid‐terpenoid entourage effects." British journal of pharmacology 163.7 (2011): 1344-1364.
Fine, Perry G., and Mark J. Rosenfeld. "The endocannabinoid system, cannabinoids, and pain." Rambam Maimonides medical journal 4.4 (2013).
McPartland, John M., and Ethan B. Russo. "Cannabis and cannabis extracts: greater than the sum of their parts?." Journal of Cannabis Therapeutics 1.3-4 (2001): 103-132.
Burstein, Sumner H., and Robert B. Zurier. "Cannabinoids, endocannabinoids, and related analogs in inflammation." The AAPS journal 11.1 (2009): 109.
Sarris, Jerome, Erica McIntyre, and David A. Camfield. "Plant-based medicines for anxiety disorders, part 1." CNS drugs 27.3 (2013): 207-219.
Sarris, Jerome, Erica McIntyre, and David A. Camfield. "Plant-based medicines for anxiety disorders, part 2: a review of clinical studies with supporting preclinical evidence." CNS drugs 27.4 (2013): 301-319.