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Contaminants to Look Out for in Cannabis

While cannabis consumption has been legal in much of the U.S. for a while now, it’s not entirely safe to assume that all commercially-sold cannabis products have been tested properly for all contaminants in a reputable lab. Contaminants can easily find their way into cannabis at any point of the process, from cultivation to the point of purchase, cannabis is susceptible to various forms of contamination. Therefore, it's important to understand what the different cannabis contaminants are so you can safely navigate cannabis consumption.

cannabis being sent to a lab for testing
Photo by Jess Loiterton

What are cannabis contaminants?

Cannabis is an organic matter which makes it subject to contamination. Cannabis is also a bioremediator, which means it draws in other elements at a high rate such as water and soil. This leads cannabis to easily absorb other elements, such as heavy metal substances, microbes, and chemical toxins from pesticides, which are categorized as common contaminants that may be found in cannabis (Gomes, 2022). The safety level of contaminants found in cannabis can be difficult to quantify, but they can cause anywhere from minor, temporary health effects to severe and possibly permanent health effects. This includes carcinogenicity, developmental impacts, infection, reproductive issues, or even death (Dryburgh, et al., 2018).

Types of cannabis contaminants

Contaminants in cannabis are largely categorized into three different categories which include heavy metal substances, microbes, and pesticides.

Heavy metals in cannabis

Cannabis can retain elements like heavy metals so well, that the plant is used as a source of remediation for contamination sites. Although this exact benefit is concerning about cannabis plants, as they can be too good at absorbing heavy metal substances in the stems and leaves, and eventually exiting through its trichomes. The most common heavy metals found in cannabis are lead, cadmium, and chromium, but heavy metals such as arsenic, mercury, nickel, and selenium can also be found in cannabis (LaJeunesse, 2021).

Cannabis can be contaminated by heavy metal substances through three different routes, which include soil and water absorption, cross-contamination, and post-processing adulteration. If a cannabis plant is planted or exposed to soil and water that is contaminated with heavy metal substances, the plant will act like a sponge and absorb these elements. During the cultivation process, cross-contamination may also occur, such as during the drying and curing process. Lastly, cannabis can become contaminated with heavy metal substances through post-processing adulteration, which is the deliberate addition of these metals to increase weight so that the product can be marketed for a higher value (Dryburgh, et al., 2018).

While most of these heavy metals aren’t typically harmful in small doses, being exposed to or consuming these metals daily through cannabis in high concentrations can be extremely harmful to your health (Gomes, 2022). Additionally, since heavy metals are rarely metabolized by the human body, they can accumulate in different places inside the body, causing various health problems. When the human body begins experiencing the effects of heavy metal toxicity, a common occurrence is “the production of reactive oxygen species and free radicals, which can damage enzymes, proteins, lipids, and nucleic acids, and cause cancer and neurological issues,” (LaJeunesse, 2021).

Microbes in cannabis

One of the most common reasons a cannabis product fails a lab test is due to microbial contamination since the plant is highly susceptible to bacteria and mold spores (Steadfast Labs, 2022). Mold can form at any point during the cultivation process, from improper preparation and processing to storing cannabis products. Though, wet and humid conditions are often the culprit behind microbial contamination.

With humid environmental conditions, fungal infections such as budworm, botrytis, mildew, or mite infestations may occur. Another fungal spore commonly reported in cannabis is Aspergillus, a species of mold that produces mycotoxins, which are a known human toxin and carcinogen (Dryburgh, et al., 2018; Steadfast Labs, 2022). There have also been reports throughout history of bacterial contamination of cannabis including Enterobacter, Klebsiella, Salmonella, and Streptococcus (Dryburgh et al., 2018).

When consuming cannabis with microbial contamination, some immediate reactions may include allergic reactions, coughing, dizziness, fatigue, headaches, nausea, sinus issues, and vomiting (Makowski, 2022; Santos-Longhurst, 2020). An allergic reaction to consuming cannabis with mold contamination may cause effects such as congestion, drainage, sinus pain, and wheezing (Santos-Longhurst, 2020).

Exposure to vaporized fungal spores can also cause fungal pneumonia, even in very low concentrations (Dryburgh, et al., 2018). Microbial contamination with mold species such as Aspergillus, Cryptococcus, and Mucor can affect the brain, central nervous system, and lungs, causing some serious health complications when exposed to these microbes (Santos-Longhurst, 2020). This means its integral for each step of the cultivation to operate without mistake, otherwise an entire product may become spoiled and contaminate nearby cannabis plants or products, making it unsafe for human consumption.

Luckily, cannabis contaminated by mold can be easier to identify than heavy metal and pesticide contamination. Cannabis plants with mold will appear unhealthy, with a powdery or fuzzy substance on the stems or leaves (Makowski, 2022). Mold on cannabis plants may also cause discoloration and cast a white-gray appearance on the plant. Mold also has a distinct scent, and is often described as a musty or mildewy smell, or sometimes like the smell of hay (Santos-Longhurst, 2020).

Pesticides in cannabis

The use of pesticides during cannabis cultivation has been well established, yet there is still cause for concern with pesticide consumption via cannabis. While administering pesticides to cannabis during the growth phase can be beneficial for preventing pests from damaging crops, these same pesticides can also be harmful for human consumption and exposure. Consumption of a high concentration of pesticides daily can result in serious, negative health effects, including developmental issues, endocrine disorders, malignancy, neurological disorders, and reproductive issues (Dryburgh, et al., 2018).

Cannabis lab testing facilities will administer heavy metal, microbial, and pesticide analysis, alongside other chemical toxin tests to ensure products are safe for human consumption. Therefore, it’s important to verify your product has been tested and approved before purchasing and consuming a cannabis product. When considering cannabis products, you can request a Certificate of Analysis to ensure the product has been tested and is safe for consumption.

Trust in Steep Hill Illinois

Whether interested in laboratory testing, data analysis, or consulting services, you can always rely on Steep Hill Illinois to provide accurate, reliable results on the latest cannabis production practices. Email us today at to get started!


Dryburgh, L. M., Bolan, N. S., Grof, C. P. L., Galettis, P., Schneider, J., Lucas, C. J., & Martin, J. H. (2018, August 1). Cannabis contaminants: sources, distribution, human toxicity and pharmacologic effects. British Journal of Clinical Pharmacology.

Gomes, A. (2022, April 4). What’s in your weed? MCR Labs.

LaJeunesse, S. (2021, December 14). Cannabis may contain heavy metals and affect consumer health, study finds. Penn State University.

Makowski, A. (2022, June 2). The risks of consuming mold-infested cannabis. Medical Alternatives Clinics. Retrieved April 28, 2023, from,you%20smoke%20moldy%20weed%20regularly.

Santos-Longhurst, A. (2020, March 31). Moldy weed: What to look for and how to handle it. Healthline. Retrieved April 28, 2023, from

What consumers need to know about moldy weed testing. Steadfast Labs. (2022, September 9). Retrieved April 21, 2023, from

Photo by Jess Loiterton:

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