Cannabis Safety Testing: Heavy Metals

Author: Shauna Kelley | Posted: 06.14.2023

What Are Heavy Metals?

Heavy metals are a group of metallic chemical elements that cannot be degraded or destroyed by any physical or biological process. They are natural components of Earth’s crust with relatively high densities and atomic weights. Heavy metals arise from natural and man-made sources. Natural sources include volcanic eruptions, soil formation, and rock weathering. Heavy metals are mainly introduced to ground water by man-made sources. These sources include mining, land filling, industry, and agriculture. In agriculture, factors such as fertilizers, pesticides, wastewater, and livestock manure contribute to heavy metals entering the groundwater and soil. Essential heavy metals are required for biochemical and physiological processes but are toxic in high concentrations. Non-essential heavy metals such as lead, mercury, arsenic, and cadmium are very toxic and have no function in plants or animals. Cannabis sativa is a hyperaccumulator, capable of absorbing and accumulating metals into its tissues. A hyperaccumulator is a plant that can grow in contaminated water or soil with a high concentration of heavy metals and store concentrated levels of contaminants in its tissues. Cannabis can be contaminated with heavy metals, so it must be screened by a cannabis testing laboratory to ensure the
product is clean.


Where Can Contamination Originate From?

Cultivators should check their fertilizer, water, and soil for heavy metals prior to growing cannabis. The overuse of fertilizers puts a greater concentration of heavy metals into the soil. Cadmium occurs naturally as an impurity in phosphate rock, contributing to its concentration in phosphate fertilizers. Trace element (micronutrient) fertilizers may contain lead and cadmium and should be checked before use. Growers should also regularly check their water because lead, arsenic, chromium, and copper can be found in water. Reverse osmosis (RO) water will remove common chemical contaminants such as lead, chromium, arsenic, and copper. Flushing plants at the end of the grow period will not get rid of heavy metals; cultivators should ensure they have clean water, fertilizer, and soil before growing crops. The heavy metals will already be accumulated in the plant’s tissues by the end of the grow period, and flushing the soil will not help. It is important to test the grow matrix and nutrients before growing cannabis to ensure the product is free of heavy metals.


Physiological Effects of Heavy Metals

Cannabis is a hyperaccumulator, capable of absorbing high concentrations of metals from the soil and storing the contaminants in its tissues. Using cannabis products that are contaminated with heavy metals can cause a variety of possible negative effects, depending on the concentration. Within the body, heavy metals mimic natural essential elements and replace them, preventing bodily functions from working properly. This can cause side effects varying from headaches to organ problems.


  • Lead poisoning can lead to high blood pressure, memory loss,
    aggressive behavior, and damage to reproductive organs.
  • Mercury poisoning can cause lung damage, brain damage, vision
    problems, and gastrointestinal problems.
  • Arsenic poisoning may lead to low blood pressure, neurological
    problems, and gastrointestinal problems.
  • Cadmium poisoning can cause breathing problems, muscle pain, and
    decreased lung and kidney function.


This is a small list of possible issues with heavy metal poisoning; you should consult a healthcare professional with any questions on side effects. In 2008, there was a case in Germany where 29 patients from four different hospitals had the same symptoms of lead poisoning. The link between the patients was later discovered to be contaminated black market cannabis. Serious health problems that arise from heavy metal consumption make it a necessity to test these cannabis products.


Electronic Cannabis Device Contamination

Even with clean cannabis products, heavy metal contamination is still possible. The components of electronic cannabis devices used for vaping can leach heavy metals from the coil and core into clean cannabis oil. When heated to an aerosol, the metals are carried by oil droplets or directly vaporized to be inhaled by the consumer. Massachusetts only requires four heavy metals to be tested in vape cartridges, but a study from 2021 has found that copper, nickel, manganese, and tin can leach from the core or heating device into vape oil. It is important to test the product in the electronic cannabis device before it is sold.


Importance of Testing for Heavy Metals

Testing for heavy metals such as arsenic, mercury, cadmium, and lead in cannabis products is a critical analysis to ensure safe cannabis consumption. Cannabis can absorb and accumulate heavy metal contaminants from the soil into its tissues. Cultivators should be knowledgeable about their fertilizer, soil, and water sources prior to growing cannabis. If any of the growing factors are contaminated, the plants and products down the line can be affected. A variety of health problems can arise from heavy metal poisoning, which is why heavy metal safety testing is required to sell cannabis flower and concentrates. Manufacturers need to guarantee the components of electronic cannabis devices are not going to leach heavy metals into the cannabis oil. Heavy metals can be introduced from the starting point of cultivation all the way to manufacturing products at the end, and employees should be educated on the sources of contamination throughout the process. Testing cannabis for heavy metals is necessary to ensure consumer safety.