Heavy Metals Part 3: Mercury

In this third of 5-part heavy metals series, we discuss the common sources of mercury. Learn about the origins of mercury heavy metal in cannabis flower and cannabis products, its health effects, and how you can minimize contamination


As the cannabis industry continues to grow, ensuring the safety and quality of cannabis products has become a top priority. One significant concern for growers and processors is the presence of heavy metals, particularly mercury, in cannabis flower and cannabis products. In this post, we will delve into the origins of mercury contamination in cannabis, the potential health effects, and provide suggestions for minimizing mercury contamination. By understanding these issues, growers and processors can provide a safer and healthier product for consumers.

Origins of Mercury in Cannabis

Mercury, a toxic heavy metal, can find its way into cannabis plants through several pathways. Mercury vapor that is released into the air from artisanal gold mining, other industrial processes, or even from natural sources, such as volcanic eruptions, is eventually deposited back on Earth through precipitation. Many artisanal gold miners still use mercury today to create a mercury gold amalgam to extract gold form ore. The amalgam is typically collected by hand and then heated in open air, causing the release of the mercury as vapor. It is then introduced back into the food chain as it is taken up by plants through soil.

The three primary sources of mercury contamination are [2]:

  1. Soil: Mercury can accumulate in soil from natural processes, such as volcanic activity and weathering of rocks, or human activities, including industrial pollution and waste disposal. Cannabis plants absorb nutrients from the soil and can inadvertently take up mercury as well.

  2. Water: Mercury can contaminate water sources from industrial pollution, waste, or natural processes. Cannabis plants require water to grow, and contaminated water can introduce mercury to the plant.

  3. Air: Atmospheric mercury pollution, originating from sources such as coal-fired power plants, can deposit onto plant surfaces or be absorbed directly by the plant through stomata, the microscopic openings in plant leaves.

Detrimental Health Effects of Mercury in Cannabis

Common sources of mercury exposure in humans can include primarily ingestion of food containing mercury, mercury vapor from dental amalgam restorations, and various sources of industrial pollution. The severity of exposure for most people is determined by the amount of fish one consumes, presence of dental amalgams, and one’s occupation [1,3-4].

Exposure to mercury, even in small amounts, can have serious health consequences. When ingested through cannabis consumption, mercury can affect the nervous, digestive, and immune systems, as well as the lungs, kidneys, and eyes. Long-term exposure to mercury can lead to:

  1. Neurological issues: Cognitive and motor impairments, memory loss, and mood disorders.
  2. Cardiovascular problems: High blood pressure, heart disease, and increased risk of heart attack.
  3. Reproductive complications: Reduced fertility and birth defects.

Minimizing Mercury Contamination in Cannabis Products

Growers and processors can take several steps to minimize mercury contamination in cannabis products:

  1. Soil testing: Regularly test the soil in which cannabis plants are grown to detect the presence of mercury and other heavy metals. If contamination is found, remediate the soil or choose a different growing site.

  2. Water testing: Ensure that water sources used for irrigation are free of mercury and other contaminants. If necessary, use water filtration systems to remove pollutants.

  3. Air purification: Implement air purification systems, such as activated carbon filters or HEPA filters, to reduce the presence of airborne contaminants, including mercury, in indoor growing environments.

  4. Analytical testing: Partner with a reputable analytical cannabis testing laboratory to test cannabis flower and products for mercury and other contaminants. Regular testing ensures that cannabis products meet safety standards and helps identify any contamination issues early.

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  1. U.S. Geological Survey. (2018). Mercury in the environment. Retrieved from https://www.usgs.gov/centers/forest-and-rangeland-ecosystem-science-center/news/identifying-sources-mercury-water
  2. McPartland, J.M., McKernan, K.J. (2017). Contaminants of Concern in Cannabis: Microbes, Heavy Metals and Pesticides. In: Chandra, S., Lata, H., ElSohly, M. (eds) Cannabis sativa L. - Botany and Biotechnology. Springer, Cham. https://doi.org/10.1007/978-3-319-54564-6_22
  3. United States Environmental Protection Agency. (2021). Basic Information about Mercury from https://www.epa.gov/mercury/basic-information-about-mercury
  4. U.S. Geological Survey. (2018). Mercury in the environment. Retrieved from https://www.usgs.gov/centers/forest-and-rangeland-ecosystem-science-center/news/identifying-sources-mercury-water
  5. Grimalt, J. O., & Ferrer, M. (2018). Review on environmental alterations and effective population size reductions in fish populations in the NW Mediterranean Sea. Science of The Total Environment, 612, 845-854. https://doi.org/10.1016/j.scitotenv.2017.08.285
  6. Mahaffey KR. Mercury exposure: medical and public health issues. Trans. Am. Clin. Climatol. Assoc. 2005;116:127–154
  7. Esdaile, LJ, Chalker, JM. The mercury problem in Artisanal and small-scale gold mining. Chemistry 2018; 24(27): 6905–6916.