Growers Network Staff

November 12, 2018 5 min read
November 12, 2018
5 min read

Aflatoxins: What are they and where do they come from?

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Andrea Nolte and Stephen Goldman of Evio Labs explain one of the dangers associated with Aspergillus species: Aflatoxins.

Andrea Nolte | Stephen Goldman

The following is an article produced by a contributing author. Growers Network does not endorse nor evaluate the claims of our contributors, nor do they influence our editorial process. We thank our contributors for their time and effort so we can continue our exclusive Growers Spotlight service.

Aflatoxins are a variety of mycotoxins produced by Aspergillus parasiticus and Aspergillus flavus that suppress the immune system, mutate DNA, cause liver cancer (technical name: hepatocarcinoma), and can cross the placenta to exert harmful effects upon a fetus.

After years of research, researchers have elucidated a malignant profile for aflatoxins:

  1. Normally the liver metabolizes a variety foreign substances, including pharmaceutical drugs, mycotoxins, and environmental toxins. This metabolism prepares these foreign substances for excretion.
  2. After significant exposure to aflatoxin, the liver experiences a specific mutation in the p53 human tumor-suppressor gene.
    1. This mutation inhibits the liver from its normal metabolic processes. This means that harmful substances can damage DNA or other cellular processes, which can lead to cancerous growth and life-threatening tumors.

Due to this fact, aflatoxins are classified as level 1 carcinogens. Level 1 carcinogens are compounds which are known to be carcinogenic in humans, and it is the most toxic classification a molecule can have. There are five types of aflatoxins that the public should be aware of:

  1. Aflatoxin B1
  2. Aflatoxin B2
  3. Aflatoxin G1
  4. Aflatoxin G2
  5. Aflatoxin M1
    1. Aflatoxin M1 is not a direct product of Aspergillus species, but instead is an metabolite produced by animals that have consumed aflatoxin-contaminated feed.

Another class of mycotoxins found in Cannabis, called ochratoxins, have similar carcinogenic and mutagenic profiles to aflatoxins. Ochratoxin A is produced by Penicillum verucosum and Aspergillus ochraceus. These fungal products are deemed mutagenic (and therefore carcinogenic) due to their ability to break DNA strands and inhibit DNA repair mechanisms.

What can be done if you detect aflatoxins?

When there is a profound aflatoxin contamination in a crop, there is little, if anything, that can be done to remediate it. Some individuals may try “mixing” or “cutting” a contaminated batch with a non-contaminated batch in order to dilute the problem. This is generally not allowed for consumable crops by FDA regulation, although there have been extenuating circumstances in the past where exceptions have made.

Some methods of remediation, such as treatment with ammonia, are strictly prohibited, while other methods, such as heat treatment, are ineffective. Aflatoxins are chemically stable, allowing them to withstand temperatures higher than 160⁰ Celsius, well above the melting point of cannabinoids. If these mycotoxins are present in cannabis during harvest, then they cannot be removed simply. They also have the potential to become concentrated during cannabis extraction processes that yield cannabis oils, making them potentially even more potent.

The threat of aflatoxins and ochratoxins is seemingly unavoidable when Aspergillus species are present; but you can take steps to minimize their risk. Preventing aflatoxin production during harvest and storage is the most practical solution for mitigation. Aspergillus species are fungi that prefer to grow in oxygenated, moist environments.

Despite the lack of cannabis protocols from the FDA, there are some basic techniques that can be utilized to reduce or avoid the production of aflatoxins and ochratoxins. These suggestions pertain to growing, harvesting, and storage:


  1. Keep your RH well under the dewpoint to prevent fungal growth
  2. Prevent wild temperature fluctuations in your growing space.
  3. Do not leave standing water.


  1. Avoid late harvesting (dense buds contain significant amounts of water and air, which promote fungal growth)
  2. Maintain effective pest control strategies (according to relevant state-guidelines)


  1. Minimize lag time between harvesting and drying
  2. Maintain strict hygiene of storage facilities and containers
  3. Dry the product to below 14% moisture content (less than 0.7 water activity, aw)
  4. Maintain pest control post-harvest (insects can introduce extra water and heat into the environment, giving fungi and bacteria the opportunity to grow)
  5. Control the gaseous environment by reducing oxygen content and replacing with nitrogen or carbon dioxide. This may also be applicable for pre-packaging processes prior to dispensary distribution.

It is crucial to understand the threats of aflatoxins and ochratoxins so that proper steps can be made to avoid their production. The most fundamental aspects are starting with a clean environment for the drying and storing processes by reducing humidity, oxygen and pest insects. When guidelines published in relation to other crops are applied correctly to cannabis, it is likely that the threat of aflatoxin and ochratoxin contamination can be significantly impeded.

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  1. Want to read some of the sources for this article? Check these out:
    1. Aflatoxins. International Agency for Research on Cancer (IARC) 100F. Available at . Accessed 12 Oct. 2017.
    2. Federal Drug and Food Administration (1994). FDA Mycotoxin Regulatory Guidance: A Guide for Grain Elevators, Feed Manufacturers, Grain Processors and Exporters. Washington D.C.: National Grain and Feed Association, pp.1-15.
    3. Naresh Magan, David Aldred, Post-harvest control strategies: Minimizing mycotoxins in the food chain, In International Journal of Food Microbiology, Volume 119, Issues 1–2, 2007, Pages 131-139, ISSN 0168-1605,
  2. Want to learn more about subjects similar to those touched upon in this article? Check out our articles on subjects such as:
    1. Growers Network's Pest Profile: Caterpillars
    2. Growers Network’s Pest Profile: Fungus Gnats
    3. Aspergillus: The Most Dangerous Cannabis Pathogen
    4. Vapor Pressure Deficit
    5. A Short History of Cannabis Consumption
  3. Want to get in touch with EVIO Labs? They can be reached via the following methods:
    1. Website:
    2. Email: [email protected]

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About the Author

EVIO Labs is the leading national provider of accredited cannabis testing, providing high quality analytical and consulting services for agricultural and biomedical industries in North America. EVIO Labs is dedicated to providing clients with superior customer service, reliable results, and world class expertise. No matter which lab in the EVIO Labs network you choose, you will receive the same high level of accuracy, customer service, and professionalism.