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Microorganisms such as fungi and mycotoxins, which commonly appear as mold, that can occur in cannabis. Microbial contamination of cannabis can be common, and there are health risks in absorbing these into the body when consuming cannabis products, primarily for immunocompromised patients. To protect public health, microbial testing is required of all cannabis products sold in regulated markets, though testing practices can be very different from state to state. Several methods of remediation exist to rid cannabis products of contaminates.

“Microbials are one of the many types of contaminants that cannabis labs test for.”

What are microbials?

Like any plant, cannabis can be susceptible to microbes, such as fungi, mycotoxins, and bacteria—the most common of these is mold. 

Microbial testing on cannabis is usually divided into:

  • Mycotoxin testing, to find toxins produced by certain molds
  • Bacteria testing, to look for specific species of bacteria
  • Foreign materials, including mold, as well as other contaminants such as ash, hair, etc. 

Many states require testing for fungi species Aspergillus fumigatus, A. flavus, A. niger, and A. terreus, but methods of testing can be radically different. Common mycotoxins tested for include: Aflatoxin G1, Aflatoxin G2, Aflatoxin B1, Aflatoxin B2, and Ochratoxin A, which are not actually molds but byproducts of certain species of mold. 

Generally, the most common bacteria tested for are Salmonella and varieties of Enterobacteria (E.coli). While microbial contamination is common with cannabis, it appears that fungal infections and mycotoxins are the biggest health threats posed by microbes in cannabis. 

Health risks of microbials

The biggest risk of contamination with microbes is during cultivation and harvesting—microbes can be brought in on clothing or shoes from outside a growing or harvesting space. California’s Steep Hill Labs did a study in 2018 looking at 20 random cannabis products and found that “All had detectable levels of microbial contamination, and many had significant pathogenic microorganism contamination.” In total, Steep Hill found over a dozen different microbes. 

The best way to mitigate risk of microbial contamination is to treat your grow space like a clean room and change into sanitary clothing when entering the space, rather than walking in with street clothes. It is important to note that even after harvesting, when drying and curing, cannabis can still become contaminated with microbials if not stored properly, i.e., if it’s too wet or humid.

Microbial remediation

Some hope exists for cannabis that has been contaminated by microbes during the cultivation and harvesting processes: post-harvest remediation. X-rays, such as UV light, can destroy microbes, decontaminating cannabis products. But while X-rays can be used to kill microbes, they will not remove all traces of microbes, such as enzymes, proteins, DNA, and RNA. 

For some cannabis patients who are immunocompromised, even dead microbes can possibly trigger allergies or asthma. In order to remove these traces of microbes, remediators would also need to use an ozone chamber, which will destroy the cell walls of microbes, fully eliminating them. But even an ozone chamber has its limits, and it may not fully eliminate mycotoxins produced by some mold microbes.