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Irradiatedcannabismight still harbour toxic fungi and residues, 91˿Ƶ study finds

Researchersraise concerns aboutpossible healthrisks for vulnerable users, point to a need forbetter methods and safeguards
Published: 15 January 2026

Gamma irradiation,an industry-standard sterilization method for medicinal and recreational cannabis,does not fullyeliminatetoxic fungi or their chemical residues, a 91˿Ƶ study has found.Current testing practices may also miss contamination, raising concerns about health risks for vulnerable users, particularly those with weakened immune systems.

The researchers said this isespeciallysignificantgiven that70per cent of cannabis is consumed by smoking or vaping, whichmaydeliver toxins directly intothelungsandexacerbatesmoking-relatedinjury to lung tissues.

Thesefindingspoint to aneedforstricter testing and better safeguards, they said.

Major health hazards

Gamma irradiationworks bydamagingthe DNA and RNA ofmicrobes anddegradingmycotoxins–harmful compounds produced by certain fungi.While this process significantly reduces microbial loads, researchers foundviablespores ofmycotoxigenic fungi, DNA fragmentsand traces of toxins remained after irradiation.

Theseremnantsposemajor health hazards, with heightened risk forsuchpopulations as cancer patients, transplantrecipientsand individuals with HIV/AIDS.However, thestudyalsocites multiple case reports of fungal lung infections and other opportunistic infectionsinhealthypeople exposedto contaminatedcannabisproducts.

Combined methodscanimprove testing

Researchersanalyzeddriedcannabis buds from a licensed producerandready-to-use productsfroma licensed producerthat werelegallyon the market.Theyusedthreecomplementary approaches:

  • Culture-based methods to grow andidentifyliving fungi and bacteria.

  • Molecular tests (PCR and qPCR) to detect fungal DNA and toxin-producing genes.

  • Antibody-based ELISA assaystomeasure mycotoxins such as aflatoxins and ochratoxins.

The team found that ELISA,the current industry standard,is not sensitive enough on its own to detect trace amounts of mycotoxins left after irradiation, nor is mass spectrometry when used in isolation.Addingmolecular and culture-based methodsallows testerstotracksmaller fragments that ELISAor mass spectrometryalone might miss.

“Asingle spore can cause disease, so we had to go beyondtheELISA limit to see.To the generalpopulation, thismay not have much significance,butimmunocompromised peoplewill be at much higher risk,”said Saji George, study co-author and Professorat the Department of Food Science andAgriculturalChemistry.

Industry collaboration and next steps

The researchersstressedthatoncecontamination occurs, it is extremely difficult to remove, so prevention is key. They are working with industry partnersonsuchsolutionsas beneficial bacteria thatpreventharmful fungifromestablishingonthe crop.

“Cannabisbudshavesticky resins, sothey arereally susceptibleto contamination. These fungi are everywhere, so we need to be more careful at every stage, from growingandharvesting toprocessingandstorage,” said Mamta Rani, study co-author and Research Associate atthe(SAFE-Nano lab)at 91˿Ƶ.

“It is possible to produce clean cannabis. Some companies we work with have achieved this through strict hygiene practices and controlled environments,”she said.

Added George:“We are not trying to tarnish the industry, but to help make it more sustainable and provide guidelines for safer products.We needstricter safety standards,especially for medicinal cannabis.”

About this study

“,” byMamta Rani,Mohammad Jamil Kaddoura,JamilSamsatly,Guy Chamberland,Suha Jabaj andSaji George, was published inToxins.

Theresearch was funded by Tetra Biopharma Inc. (G253375).

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