#02 Is Cannabis Safe? – Part Two: Contaminants in Cannabis

Episode Description: Continuing from our previous episode, we continue exploring the basic question, “Is Cannabis Safe?”, this time focusing on contaminants that could be found in Cannabis or Cannabis products. We speak with biochemist Dr. Anthony Smith about what contaminants labs are commonly finding in Cannabis. We also speak with herbal scientist, Travis Simpson, about his concerns regarding Cannabis processing operations and the potential contaminants that may be introduced to products through bad manufacturing practices. Finally we talk again with neurologist and cannabinoid researcher, Dr. Ethan Russo, to discuss the “vaping crisis” that has claimed the lives of as many as 37 people in the United States and affected nearly 2000 users. This is part two of a three part series exploring the question, “Is Cannabis Safe?”



You’re listening to the Curious About Cannabis Podcast.

[Intro Preview]


Hey everybody, this is Jason Wilson with the Curious About Cannabis podcast. Thanks so much for tuning in once again. This episode is part two of a three-part series exploring Cannabis safety and harm reduction. If you haven’t listened to the first part of this series, I really recommend stopping this episode and going back to listen to this series from the beginning.

Previously we explored some of the main chemicals in Cannabis, the adverse health risks associated with Cannabis, and how Cannabis can interact with medications.[1] Today we will be focusing on a critical topic that has a huge impact on the safety of Cannabis products – Cannabis contaminants.


What contaminants might be found in Cannabis products?

Anthony Smith is a biochemist that has spent that last five years analyzing Cannabis products for potency and purity in labs all across the United States and Canada.


Before we continue, let’s talk a little more about pesticides. Many pesticides are designed to disrupt the nervous systems or hormone signaling in insects.[2] The problem is that this same effect can happen in humans, if someone is exposed to enough of a certain pesticide for long enough periods of time.[3] Additionally, some pesticides, like myclobutanil, a common fungicide[4], can degrade into toxic compounds like hydrogen cyanide when heated.[5]

You might be thinking, what’s the big deal about pesticides in Cannabis? Aren’t we already exposed to pesticides through our food? Well, that’s true, but the problem relates to the way in which Cannabis is consumed. When you eat something, your body works hard to ensure that any toxins are captured, broken down, and excreted from the body before they have a chance to reach your blood stream.[6] But when you smoke something, you are bypassing those metabolic processes, and the compounds that enter the lung will pass directly into the blood stream.[7] So essentially when you smoke you are bypassing your body’s natural defense systems that might otherwise keep you safer.

It’s also really important to point out that many pesticides, as well as mycotoxins, can become concentrated in Cannabis extracts. The process of making a Cannabis concentrate can elevate contaminants like pesticides as much as 5 to 10 times the concentration found in the Cannabis flower[8], meaning that if you are consuming a Cannabis concentrate, you are potentially being exposed to much greater doses of contaminants than if you were consuming the Cannabis flower used to produce that concentrate. I also want to point out that it’s not enough to simply test Cannabis flower for contaminants prior to making a concentrate. It is possible for there to be very trace amounts of pesticides or other contaminants present in the flower that won’t show up on a standard contaminant screening – but when concentrated they suddenly become present in dangerous levels.


The leaching of contaminants[9] [10] from cultivation, processing or packaging equipment is an issue that people working in the natural products industry have had to think about for quite some time. However some Cannabis companies are still learning about typical herbal processing and manufacturing best practices – putting consumers at risk. I spoke with Travis Simpson, an herbal scientist that has spent the past several years working with hemp in the Cannabis industry. He shared some of his concerns regarding contaminants from manufacturing and packaging equipment.


One of the important things to note regarding most of these contaminants, including pesticides, metals, and mycotoxins, is that you won’t necessarily have an immediate reaction when you are exposed to these toxins. They can build up in the body over time, and you may not exhibit any symptoms for a long time before the body finally reaches a tipping point.[11] So just because you may have consumed a Cannabis product and didn’t notice any adverse effects, that does not mean that you are not being exposed to harmful contaminants.

The takeaway from my discussions was clear – know the purity of your Cannabis before consuming. But this is easier said than done. There are still many places in the US and abroad that have not legalized Cannabis or established strict testing requirements for Cannabis.[12] For users getting their Cannabis from the black market, they are left at the mercy of their supplier’s quality.

Unfortunately, this can sometimes lead to tragic consequences.


Dr. Russo is referring to a recent string of fatalities linked to lung infections or lung damage associated with vape pens.[13]


At the time of this recording, there have been 29 recorded deaths, and over 1300 reported cases of lung infections or damage linked to vape pens[14]. And these reports are growing at a rapid rate. While the exact culprit responsible for these illnesses and deaths has not yet been identified, investigators suspect it has to do with additives or contaminants.


There is other evidence that contaminants in Cannabis have caused very serious problems for some people, which in rare cases has led to death. There are several case studies available of patients that contracted fatal lung infections, such as a condition called aspergillosis.[15] [16] Aspergillosis is a condition where the spores of certain species of Aspergillus fungi get nestled in small scrapes and crevices in the lungs where they begin to grow, forming a fungal mass called an aspergilloma[17]. This ultimately starts to break down lung function and can be fatal. In some fatal aspergillosis cases reported, contaminated Cannabis was deemed to be a contributing factor, and possibly the sole cause.[18]

This is more common in immunocompromised users than regular healthy users, but that just highlights the tragedy here. Many people with serious health conditions are turning to Cannabis as a medicine – and those patients are the ones most vulnerable to the adverse health effects of consuming contaminated Cannabis.

So let’s review what we’ve learned so far:

  • There are a lot of different contaminants that can appear in Cannabis and Cannabis products such as pesticides, residual solvents, metals, mycotoxins, molds, and bacteria.
  • Metals and molds tend to appear most frequently in Cannabis flower, however metals do sometimes show up in extracts due to leaching from incompatible packaging
  • Bacteria tend to appear most frequently in Cannabis infused products.
  • Pesticides, solvents, and mycotoxins are more common in Cannabis extracts, because the process of making a concentrate actually concentrates these contaminants.
  • Contamination is not always direct. Contamination can come from contaminated soil, water, drift from nearby farms, leaching from manufacturing equipment or packaging equipment.
  • Contaminants or toxic additives have been responsible for fatalities associated with Cannabis consumption. Users with compromised immune systems are the most at risk.

By now we seem to be getting a pretty good picture about the safety profile of Cannabis. But we’re not done yet. There is one more issue that we haven’t discussed yet – and that’s adolescent Cannabis use. What unique risks might young Cannabis users face?

Find out in the third and final part of this series where we finish our curious quest to discover, “Is Cannabis Safe?”



Citations and Resources

[1] “#01 Is Cannabis Safe? Part One”. The Curious About Cannabis Podcast. Natural Learning Enterprises. 2019. https://cacpodcast.weebly.com/episodes/01-is-cannabis-safe-part-one

[2] How Pesticides Work. Kentucky Pesticide Safety Education Program. http://www.uky.edu/Ag/Entomology/PSEP/12pesticides.html

[3] Kim et al. Exposure to pesticides and the associated human health effects. Science of the Total Environment. 2017. 575(1): 525-535.

[4] https://www.nbcnews.com/health/vaping/tests-show-bootleg-marijuana-vapes-tainted-hydrogen-cyanide-n1059356

[5] Product Safety Assessment: Myclobutanil. Dow Chemical. http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_08d6/0901b803808d60fd.pdf?filepath=productsafety/pdfs/noreg/233-01023.pdf&fromPage=GetDoc

[6] Pond SM, Tozer TN. First-pass elimination. Basic concepts and clinical consequences. Clin Pharmacokinet. 1984. 9(1): 1-25.

[7] Huestis MA. Human Cannabinoid Pharmcokinetics. Chem Biodivers. 2009. 4(8): 1770-1804.

[8] Voelker R, Holmes M. Pesticide Use on Cannabis. Cannabis Safety Institute. 2015. https://cannabissafetyinstitute.org/wp-content/uploads/2015/06/CSI-Pesticides-White-Paper.pdf

[9] https://www.coleparmer.com/chemical-resistance

[10] https://www.scilabware.com/en/chemicalcompatibility/

[11] Williams et al. Human aflatoxicosis in developing countries: a review of toxicology, exposure, potential health consequences, and interventions. The American Journal of Clinical Nutrition. 2004. 80(5):1106-1122.

[12] https://norml.org/laws

[13] https://www.cdc.gov/tobacco/basic_information/e-cigarettes/severe-lung-disease.html

[14] https://www.sciencenews.org/article/vaping-tied-nearly-1300-lung-injuries-29-deaths-united-states

[15] Gargani et al. Too Many Mouldy Joints – Marijuana and Chronic Pulmonary Aspergillosis. Mediterr J Hematol Infect Dis. 2011. 3(1): e2011005.

[16] Ruchlemer et al. Inhaled medicinal cannabis and the immunocompromised patient. Support Care Cancer. 2015. 23(3):819-822.

[17] https://www.mayoclinic.org/diseases-conditions/aspergillosis/symptoms-causes/syc-20369619

[18] Gargani et al. Too Many Mouldy Joints – Marijuana and Chronic Pulmonary Aspergillosis. Mediterr J Hematol Infect Dis. 2011. 3(1): e2011005.

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