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X-Rays Can Decontaminate Cannabis While Retaining Terpenes, Study Finds

By Leo Bear-McGuinness

Published: Nov 30, 2022   
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Cannabis flower can be safely sterilized with low levels of X-ray radiation, according to a new study.

This level of radiation can successfully impair four types of Aspergillus fungi without damaging the cannabinoid and terpene chemicals prized by many cannabis consumers, say the researchers, who were from California’s Department of Cannabis Control (DCC).

Irradiated cannabis

Aspergillus fungi produce a type of carcinogenic mycotoxin that can cause liver failure in large doses, particularly among those with weakened immune systems.

The mold can grow on cannabis plants, so most US state cannabis regulators require products to be tested for Aspergillus before they can be sold.

To avoid failing such tests, many cannabis producers sterilize their flower beforehand, in an attempt to kill as many unwelcome microbes as possible. But some of these sterilization techniques, such as heating and the use of chemical reagents, can damage the flower’s cannabinoids and terpenes, thereby reducing the appeal of the products.

Published in PLOS One, the new study from the DCC researchers investigated whether X-rays could decontaminate cannabis samples without compromising their prized chemicals.

To get their findings, the researchers first cultured four different species of Aspergillus. The team then spiked different cannabis flower samples with each of the species of mold. The contaminated flower samples (and some uncontaminated samples to act as a control group) were then exposed to 2, 2.5, or 5 kilograys (kGy) of X-rays.

After 2.0 kGy of X-ray irradiation, some growth was detected in samples spiked with Aspergillus. fumigatus and A. flavus. No Aspergillus growth, however, was observed after 2.5 and 5.0 kGy of X-ray irradiation.

Indeed, after 2.5 kGY of X-rays, none of the cannabis flower contaminated with any of the four pathogenic Aspergillus species hosted significant mold, at least a spiking level of 104 colony-forming units per gram.

At this level of radiation and higher (5 kGy), most terpenes and cannabinoids remained intact, according to mass spectrometry analysis, although there was a slight dip in the levels of caryophyllene, beta-panasinsene, and eudesma-3,7(11)-diene – all terpenes. Levels of alpha-humulene, another terpene, also dipped at the highest treatment level (5.0 kGy).

Levels of CBN, a cannabinoid, increased in line with radiation, though.

“CBN is an oxidation and degradation byproduct of the Delta9-THC and the slight increase may be due to slight increase in temperatures at higher levels of the X-ray treatment,” the researchers wrote in their paper.

The researchers also found that the genetic material of killed Aspergillus fungi remained in the irradiated flower and was detectable via polymerase chain reaction techniques.

“This is a very important finding and should be taken into consideration when deciding what detection method to use to assess the success of the decontamination process,” the researchers wrote in their paper.

“We recommend using a culture-based method in addition to molecular-based methods to test the decontaminated product and thus determine the true clearance of the live organism.”

With this precaution in mind, the research team conclude that X-ray technology may be a useful method to inactivate Aspergillus in contaminated cannabis flower. But further research would be beneficial, to clarify whether such radiation in any way impairs the cannabis flower’s genetic or chemical profile.


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