Heavy metals in cannabis

In 1986, following the tragedy at Chernobyl nuclear power plant, industrial hemp was planted in order to help clean heavy metals and radioactive elements that had seeped into the ground. The cannabis plant, known for being a hyper-accumulator of heavy metals as well as pesticides, can seep up contaminants where other methods fail.1 While this is a boon to contaminated environmental sites, it poses a risk to both recreational and medical cannabis users, as contaminants can be extremely toxic to humans.2 These contaminants include such heavy metal as lead, arsenic, cadmium, and mercury, and pesticides such as bifenthrin, and diaxinon.4 As well, due to lack of federal regulation of the burgeoning cannabis market, these contaminants can occur at many points along the growth and processing cycles. Therefore, it is important to the know the contaminants and heavy metal content of cannabis products, as unlike pharmaceuticals, there is rarely a maximum daily dose set.

              The amalgamation of pesticides and heavy metals occurs in cannabis because of its phytoremediation properties.  Industrial hemp is often used for cleaning environmental sites. Cannabis moves water and nutrients through its roots and plant through a process called transpiration.3 As the stomata open to release water to evaporate, negative pressure creates a vacuum that pulls more water and nutrients in the plant. This is what also causes the cannabis plant to soak up many heavy metals.3 Unfortunately, there are many ways that cannabis can leech contamination during processing and growing. First, as mentioned above, is the natural environment in which the cannabis is planted. Soil can contain contaminants from years before that only cannabis can draw out of the ground.  It is extremely important to have a soil analysis done prior to picking a growing site. Prior agricultural sites may often have the presence of fertilizers and pesticides that may not have affected past crops but can greatly affect cannabis. Unfortunately, because of illegal status of cannabis federally, there are not standard pesticides recommended for growing cannabis.

Other contamination can occur also during testing and processing. Some organic solvents that are used in laboratories may pose health hazards to the medical cannabis community. Solvents like butane, ethanol, and benzene are used to test and process cannabis, but they do pose neurotoxic and carcinogenic risks as well.4 Labs, however, also test for contaminants. For heavy metals, scientists use inductively coupled plasma mass spectrometry (ICP-MS) to detect, at the very least, cadmium, arsenic, lead, and mercury.5 Again, due to the status of cannabis as a Schedule I drug, there is no federal standardization among testing requirements.  States must decide what exactly what requirements should be in place for testing. Unfortunately, this leads to many states doing less testing than what may be needed to keep patients safe.

The main reason for the necessity of testing is to keep toxic levels of contaminants to a minimum to protect the health of the cannabis patient.  While it is important to eliminate the use of pesticides such as chlorpyrifos and methamidophos in cannabis agricultural, it as important, if not more, to minimize heavy metal consumption. Lead poisoning can cause dizziness, muscle pain, and gastrointestinal issues. Cadmium poisoning can lead to cancerous tumors. Mercury poisoning can cause extensive neurological damage. Arsenic is also extremely toxic as well as carcinogenic.5 Different states have different regulations on the levels of numerous contaminants that can exist in cannabis.  Unfortunately, some of those states do not consider some sources of contamination and may miss when toxic levels are present in products.  As well, unlike regular pharmaceuticals, cannabis users tend not to check levels of contaminants in the number of products they use.  With regular heavy use of cannabis, whether smoking, vaping, applying topical products, or using oral products, it easier to exceed toxic levels of contaminants as cannabis doses tend to be more in a range, rather than a maximum dose.  It is up to the federal government, when cannabis is legalized, to set standards for pesticides and all heavy metals that could pose any risk to the cannabis community.  Although states where medical cannabis is legal do testing for contaminants, the collective knowledge of all states can help further develop better standards, processes, and testing for the cannabis industry.


  1. Thomas R. Regulating heavy metals in cannabis: what can be learned from the pharmaceutical industry? Part 1. Analytical Cannabis website. https://www.analyticalcannabis.com/articles/regulating-heavy-metals-in-cannabis-part-i-what-can-be-learned-from-the-pharmaceutical-industry-312336. Accessed on November 29, 2020.
  2. Jaishankar M, Tseten T, Anbalagan N, Mathew BB, Beeregowda KN. Toxicity, mechanism and health effects of some heavy metals. Interdiscip Toxicol. 2014;7(2):60-72.
  3. Thomas R. Regulating heavy metals in cannabis: what can be learned from the pharmaceutical industry? Part 2. Accessed on November 29, 2020.
  4. Pizzorno J. What Should We Tell Our Patients About Marijuana (Cannabis indica and Cannabis sativa)?. Integr Med (Encinitas). 2016;15(6):8-12.
  5. Kariuki L. Heavy metals in cannabis: important things to know. Extraction Magazine website. https://extractionmagazine.com/2020/04/04/heavy-metals-in-cannabis-important-things-to-know. Accessed December 1, 2020.

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