Cannabis cultivators and processors must be aware of these potentially life-threatening chemicals

While pests like hemp russet mites and spider mites pose an immediate threat to a cultivator’s crops, one of the most prominent dangers to consumers can come in the form of mycotoxins found on or in the plant and its extracts.

Mycotoxins are a secondary metabolite produced by fungi and some molds that readily colonize crops and can cause disease and death in animals, including humans. There are regulations by the U.S. Food and Drug Administration (FDA) concerning allowable amounts of mycotoxins in human feed and animal feed, the highest of which is 20 parts per billion for direct human exposure. To put this into perspective, for one kilogram of product, no more than 0.02 milligrams can be attributed from mycotoxins.

Fungi Aspergillus, black mold which produce aflatoxins and cause pulmonary infection aspergillosis, 3D illustration


Two of the primary types of mycotoxins that are associated with cannabis are aflatoxins and ochratoxins. Aflatoxins are chemical mycotoxins produced by the Aspergillus parasiticus and Aspergillus flavus fungal species that suppress the immune system, mutate DNA, cause liver cancer (hepatocarcinoma) and can cross the placenta to exert harmful effects into the fetus.

Ochratoxins also have a similar carcinogenic and mutagenic profile as aflatoxins. Ochratoxin A is produced by Penicillum verucosum as well as Aspergillus ochraceus. These fungal products are deemed mutagenic and carcinogenic due to their ability to break DNA strands and inhibit their repair mechanisms. There is also significant data linking exposure to Ochratoxin A to a serious and fatal kidney disease called Balkan Endemic Nephropathy.

After years of research, aflatoxins have been shown to have a malignant profile. The liver naturally metabolizes foreign substances such as pharmaceutical drugs and other environmental toxins so that they can be more easily excreted from the body, including mycotoxins. Research shows that after significant aflatoxin exposure, there is a specific mutation in the p53 human tumor-suppressor gene.  This mutation inhibits the liver’s ability to prevent harmful substances from damaging DNA or other cellular division processes, which can lead to excessive cell replication, over-growth and life-threatening tumors. Therefore, it is logical that the harmful carcinogenic effect of aflatoxins resides in the organ that seeks to modify and detoxify their chemical characteristics.

Laboratory experiment with healthy and moldy kernels of corn with aflatoxin in Petry dish.


There are five types of aflatoxins to be aware of: aflatoxin B1, B2, G1, G2 and M1. In general, aflatoxins are classified as Level 1 carcinogens, or compounds that are known to be carcinogenic in humans. It is the most toxic classification a molecule can have. Aflatoxin M1 is not a direct product of Aspergillus, but is an animal metabolite coming from animals that have consumed aflatoxin-contaminated feed. This is especially concerning to the dairy industry, given that aflatoxin M1 from cow milk has the strictest regulatory limit of 0.5 parts per billion by the FDA.

When there is profound aflatoxin contamination in a crop, there is little, if anything, that can be done about it. Diluting a batch of contaminated material by mixing it with a non-contaminated batch of the same material is generally not allowed for consumable crops under the FDA regulations, although there have been extenuating circumstances in the past where exceptions have been made.

Other methods, such as chemical remediation with ammonia, are strictly prohibited for aflatoxin-contaminated crops.

Another property of aflatoxins that makes them so threatening is their molecular stability. These molecules maintain their molecular integrity in temperatures higher than 160 degrees Celsius, well above the melting point of known cannabinoids. If mycotoxins are present in cannabis during harvest, they have the potential to become concentrated above the FDA limits during processing into oils and extracts.

Belathur, India – October 28, 2013: Closeup of heap of damaged and rotten, brown-white-yellow corn cobs dumped on dark brown farm dirt.

Staying Safe

The threat of aflatoxin and ochratoxin production is seemingly unavoidable when these species are present; but these biological processes can be minimized. Aspergillus is a fungus that grows in soil and numerous other places, under the right conditions. Aflatoxin contamination can occur anywhere from seed to harvest, as well as production and storage.

Like many microorganisms, Aspergillus favors environments with ample oxygen and moisture. Most pre-harvest strategies to prevent these mycotoxins involve chemical treatment, and are therefore not ideal for the cannabis industry. Rather, preventing aflatoxin production during harvest and storage are the most practical stages for mitigation. Studies have confirmed a positive correlation between aflatoxin production with increased water activity, or moisture percentage. Water activity is becoming a more common laboratory test; it can and should be used to determine how likely microbes may grow on a given crop.
Despite the lack of cannabis protocols and guidelines for reducing mycotoxin contamination, there are some basic practices that can be utilized from other agricultural facets that will help avoid the production of aflatoxins and ochratoxins.

Methods to protect your crop during harvest:

– Avoid late harvesting (fresh, dense plant material contains significant amounts of water, which promotes fungal growth); and

– Have effective pest control (according to relevant state guidelines).
Methods to protect cannabis during storage:

– Minimize lag time between harvesting and drying plant material for storage;
– Maintain hygiene of storage facility and storage containers;
– Dry the product to below 14% moisture content (less than 0.7 water activity, or aw);
– Maintain pest control post-harvest (the presence of other insects can introduce extra water and heat into the environment, providing fungi and bacteria the opportunity to grow); and
– Control the gaseous environment by reducing oxygen content and replacing it with nitrogen or carbon dioxide to reduce the production of aflatoxin and ochratoxin.
It is crucial to understand the threats of aflatoxins and ochratoxins so that proper steps can be made to avoid their production. When guidelines for other crops are applied correctly to cannabis, the threat of aflatoxin and ochratoxin contamination can be significantly impeded. A good place to start is a clean environment for the drying and storing processes by reducing humidity, oxygen and pest insects.


Stephen Goldman is the lab director of PhytaTech in Colorado. He is an analytical chemist with extensive industrial and academic laboratory experience. Prior to joining PhytaTech, he served as an analytical chemist at Forensic Laboratories, overseeing toxicology testing.

Andrea Nolte is an analytical chemist for PhytaTech with experience in quality control and laboratory maintenance. She has a bachelor’s degree in biochemistry and a minor in chemistry from the University of Colorado.


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