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Understanding Aspergillus and Cannabis: Risks, Transmission, and Prevention

UPDATE: Oregon growers came together to challenge the rule that required testing for aspergillus and won the case in the court of appeals, so aspergillus is no longer a required test. With the aspergillus testing, a farmer would fail and be forced to either remediate with irradiation, ozone, or other methods if there was even 1 spore of DNA found. This rule was not based on science and the state of Oregon could not link any cases of harm from smoking cannabis and aspergillus. We are still required to test for mycotoxins, heavy metals, pesticides and other microbials such as salmonella and e-coli.

Recently, new testing requirements have been implemented for cannabis in Oregon, and after speaking with other growers, particularly those focused on organic growing methods, we wanted to create a brief blog post about Aspergillus, a mold that can have an impact on cannabis cultivation and testing.

What is it?

Aspergillus is a genus of mold that is commonly found in the environment, including on plants, soil, and decaying organic matter. While Aspergillus is a natural part of the environment, certain species can cause health problems in humans, particularly if they produce mycotoxins.

We'll explore the risks associated with Aspergillus, how it is transmitted, and what steps you can take to prevent contamination.

Risks Associated with Aspergillus

Exposure to Aspergillus spores and mycotoxins can cause a range of health problems in humans. Mycotoxins produced by Aspergillus species, such as aflatoxins and ochratoxins, are known to be carcinogenic and can cause liver and kidney damage, as well as other health effects, including developmental and immune system issues. According to the CDC "Most people breathe in Aspergillus spores every day without getting sick."

Exposure to Aspergillus spores can also cause respiratory problems, particularly in people with weakened immune systems or respiratory conditions such as asthma or allergies. In some cases, exposure to Aspergillus spores can cause invasive aspergillosis, which is a serious and potentially life-threatening fungal infection that can affect the lungs, sinuses, and other organs.

Why Aspergillus has Cannabis Producers in Oregon concerned

Aspergillus testing has been required in many states but not Oregon until recently. Many farmers are scrambling to figure out if they have a problem and are frustrated as this seems like yet another overly cautious overreach by the government to further regulate cannabis. Even the Oregon Public Health Authority's Toxicologist recommended that this testing not be required due to the nature and commonality of Aspergillus in the environment in their report from 2016. Since mold primarily affects immunocompromised individuals the recommendation by the OHA was to include a warning for people with suppressed immune systems.

Transmission of Aspergillus

Aspergillus spores are commonly found in the environment and can be transmitted to crops in a variety of ways. Some potential sources of Aspergillus contamination include:

  1. Airborne transmission: Aspergillus spores are highly resistant and can survive in the environment for long periods of time. They can be carried by air currents and wind, and can settle on crops, soil, and other surfaces.

  2. Soil contamination: Aspergillus can also be present in soil, and can infect crops through root uptake or through contact with contaminated soil. This is the biggest concern for organic growers as they heavily rely on composts and organic soil amendments which are breeding grounds for Aspergillus.

  3. Waterborne transmission: Aspergillus spores can also be present in water, and can contaminate crops that are irrigated with contaminated water.

  4. Contaminated equipment and surfaces: Aspergillus can also be transmitted through contaminated equipment and surfaces, such as harvesting tools or storage containers. This can occur if the equipment or surfaces are not properly cleaned and sanitized.

  5. Infected plant materials: Aspergillus can also be introduced into crops through infected plant materials, such as seeds or cuttings.

Prevention of Aspergillus Contamination

Aspergillus is ubiquitous to the environment, so there is no way to control for it 100%, but there are strategies to reduce:

  • Control moisture: Aspergillus thrives in moist environments, so it is important to control moisture in environments (which will be difficult to say the least for organic outdoor growers) and to ensure that crops are not exposed to excessive moisture during growth, harvest, or storage.

  • Keep surfaces clean and dry: Regular cleaning of surfaces can help to prevent the buildup of mold spores and other contaminants.

  • Use proper equipment: Equipment used for harvesting or processing crops should be cleaned and disinfected regularly to prevent contamination.

If Aspergillus is suspected or detected, it is important to address the underlying moisture problem and identify any possible sources of contamination to take steps to remediate the mold to prevent further contamination.

Killing Aspergillus

Aspergillus can be killed by a variety of methods:

  1. Heat treatment: Aspergillus can be destroyed by high temperatures, which will ruin your cannabis

  2. UV radiation: Aspergillus spores can be destroyed by exposure to UV radiation, which can damage or remove terpenes making your weed smell like hay or nothing.

  3. Chemical treatment: Certain chemicals, such as hydrogen peroxide and chlorine bleach, can be effective at killing Aspergillus, I don't know about you but this can't be good for your weed.

  4. Antifungal agents: Some antifungal agents, such as those containing azoles or echinocandins, can be effective at killing or inhibiting the growth of Aspergillus. These agents are often used to treat fungal infections in humans, but they can also be used to prevent or treat Aspergillus contamination in food products. The good cannabis producers don't like using pesticides or fungicides and they would probably make your cannabis fail a pesticide test so that won't work.

  5. Physical removal: Aspergillus spores can also be physically removed from surfaces through cleaning and sanitizing methods. This can include using soap and water, steam cleaning, or using specialized cleaning products designed to remove mold. This is not practical for remediating cannabis.

Here lies the big problem. If aspergillus contamination occurs in cannabis there are no great ways to remediate it. The remediation processes that are available essentially ruin the cannabis and are unworthy of being consumed except for perhaps the copious number of discount corporate cannabis shops that are popping up all over the state, where consumers are attracted by big red and white signs advertising $2 grams.


Aspergillus is a common mold that can cause health problems in humans, particularly if it produces mycotoxins. To prevent contamination by Aspergillus and other molds, it is important to control moisture, keep surfaces clean and dry, properly store and handle products, and use proper equipment. If aspergillus contamination is suspected or detected, it is important to address the underlying problem and to take steps to remediate the mold to prevent further contamination.

While killing Aspergillus spores can be done through a variety of methods, it is important to note that eliminating the mold does not necessarily eliminate the risk of health effects from exposure to spores or mycotoxins. It is important to take preventative measures and properly address any contamination to ensure the safety of crops and products, as well as the health of individuals exposed to Aspergillus.

Understanding the risks associated with Aspergillus, how it is transmitted, and how to prevent contamination is crucial for maintaining a safe and healthy environment. By following proper protocols for prevention and remediation, we can ensure that we are minimizing the risk of exposure to Aspergillus and other molds.

While Aspergillus can pose a serious health risk to individuals with weakened immune systems, such as those with HIV/AIDS or undergoing chemotherapy, it is generally not considered harmful to healthy individuals. However, some species of Aspergillus can produce toxic compounds called mycotoxins, which can cause respiratory and other health problems in both healthy and immunocompromised individuals.

In addition to indoor environments, Aspergillus can also be found in various foods, particularly those that are stored in warm, humid conditions, like grains, nuts, and dried fruits. Some species of Aspergillus are used in the production of certain foods, like soy sauce and miso, and in the fermentation of alcoholic beverages like sake and beer.

Overall, while Aspergillus can be found in a variety of environments and foods, it is generally not considered dangerous to healthy individuals.


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