Horticulture Techniques

Blast Off You Dirty Creatures

An assessment of gamma irradiation for inducing microbial sterility

Before we begin, let me add a few words to assuage you. This article reports on using radiation to kill microorganisms. Radiation, I know, is a controversial topic. The writing of this article doesn’t endorse the practice. It merely reports on a relevant topic in cannabis science. And that, after all, my friends, is our job. So, R-E-L-A-X…

A 2016 investigation by Arno Hazekamp, Ph.D., evaluated the use of gamma irradiation on cannabis in an attempt to rid the plant from microbial contamination. [1] Hazekamp listed the common methods for sterilizing cannabis to be free of microbes as heat, chemical, high pressure, filtration, or radiation treatments. Of these, he stated: “For herbal materials such as cannabis, the only currently viable option for treatment is the use of ionizing radiation.” The other decontamination treatments “either affect chemical content or texture (i.e., heat, chemicals, pressure, steam) or would not penetrate beyond the surface of the dense cannabis flowers (i.e., ultraviolet light).”

If you’ve seen the electromagnetic spectrum, gamma rays are the most intense, above x-rays. Thus, it should be obvious that there are safety considerations when using high-powered radiation. Gamma rays work at eradicating microbial infestation because they strike the invaders at their core, damaging microbial deoxyribonucleic acid (DNA), effectively making them sterile.

This type of decontamination protocol is used in decontaminating food, and those irradiated foods have been published as being safe. “Go ahead and eat them, then,” you might retort. And that’s fair. But the rebuke falls flat since you’re likely eating them already. The US Food and Drug Administration (FDA) has approved blasting everything from shellfish to crustaceans, sprouts to spices.

Hazekamp says that “Irradiation-induced changes in food components are generally small and not significantly different from those reported in other conventional preservation processes…”. Despite this assurance, and the fact that the World Health Organization, FDA, Health Canada, and the European Union deem irradiated foods as okay, Hazekamp also recognized that there is a stigma in the public’s perception, which is why his paper sought to explore the topic. [1]

A natural question to ask is ‘Does the radiation affect chemistry’? Hazekamp points to a study [2] on cilantro that showed diminished terpenes like myrcene and linalool. [1] Would this happen in cannabis?

The cannabis was visually inspected before and after radiation treatment. No visual differences were detected in a macroscopic analysis of the trichomes. You can perhaps scope it out for yourself here.

The cannabinoid and terpene profiles were quantified. No effects were measured on total THC or total CBD weight percentages. Several terpenes, however, were affected by gamma irradiation, predominantly the monoterpenes, such as myrcene, cis-ocimene, and terpinolene, and the sesquiterpenes gamma-selinene and the melodiously named eudesma-3,7(11)-diene. A 10-20% loss in these terpenes was typical, but in one case, terpinolene content was reduced by 38%. While this may seem egregious, Hazekamp points to the aforementioned cilantro study. Those researchers determined that their observed terpene loss was insignificant compared to normal, everyday evaporation of the terpenes from being stored in the fridge. Ah, the counterpoint.

Remember the dab toxicant article, and the alarms raised from the benzene and methacrolein reported from heating terpenes to extremely high temps? [3] If you heated limonene to 550°C (1022°F), you could form 63 nanograms of benzene per milligram of terpene, the article reported. The Agency for Toxic Substances and Disease Registry reports that the average cigarette smoker (32 squares per day) inhales 1.8 milligrams of benzene, while the average non-smoker inhales 10 times less, or 180 micrograms/day, or 180,000 nanograms/day. A little perspective in a drama-fueled world isn’t so bad, is it?

The terpene loss in Hazekamp’s study mirrored that reported from storing cannabis in a paper bag, as evaluated at Ole Miss. [4] The hypothesis is that gamma irradiation may accelerate evaporation of some terpenes. Interestingly, and well worth future investigation, the terpenes weren’t affected the same across the different cultivars evaluated. Hazekamp postulates that a “protective effect” might be possible when phytochemicals are present in specific quantities.

Opinions that the irradiation of cannabis changes the organoleptic properties often can’t be authenticated since, as Hazekamp points out, the consumer typically doesn’t have access to irradiated and non-irradiated products, or may not know how or if the product was decontaminated. Yet he poignantly demonstrates that, if the terpene profile is altered, a change in smell or taste may be possible. [1]

So, it’s literally a matter of taste (amongst other things). An immunocompromised might not fret over losing some terpenes while ensuring the eradication of the creatures infesting their medicine. Yet, those terpenes might resonate with your specific sensory and physiological needs and wants to the point where nixing them isn’t viable, and another decontamination method might be warranted.

See, just the facts, man, just the facts.


[1] Hazekamp, A. “Evaluating the Effects of Gamma-Irradiation for Decontamination of Medicinal Cannabis.” Frontiers in Pharmacology, 2016, volume 7, article 108. [journal impact factor = 3.845; cited by 13 (ResearchGate)] [2] Fan, X. and Sokorai, K. “Changes in Volatile Compounds of γ-Irradiated Fresh Cilantro Leaves during Cold Storage,” J. Agric. Food Chem., 2002, volume 50, issue 26, pp. 7622-7626. [journal impact factor = 3.571; cited by 46 (ResearchGate)] [3] Meehan-Atrash, J. et al. “Toxicant Formation in Dabbing: The Terpene Story,” ACS Omega, 2017, volume 29, pp. 6112-6117. [journal impact factor = 2.584; cited by 9 (ResearchGate)] [4] Ross, S. and ElSohly, M. “The Volatile Oil Composition of Fresh and Air-dried Buds of Cannabis sativa,J.Nat.Prod., 1996, volume 59, pp. 49–51. doi:10.1021/np960004a. [journal impact factor = 4.257; cited by 89 (ResearchGate)]

Image Credit: Wallpaper Cave

About the author

Jason S. Lupoi, Ph.D.

Jason S. Lupoi, Ph.D.

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