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UNIVERSITY PARK, Pa. — Cannabis, regardless of what product it’s in, may be harmful to use — depending on where it’s coming from. Researchers at Penn State say cannabis’ ability to absorb metals from soil make it possible for these relatively safe products to expose users to toxic chemicals.

Study authors note that the ability to absorb heavy metals from soil make cannabis plants a useful crop in areas with contaminated grounds. However, these toxins may still be present when cannabis farmers turn the plants into products for consumption.

“Heavy metals, such as lead, mercury, cadmium and chromium, are known to be carcinogenic,” says Louis Bengyella, assistant research professor of plant science from Penn State, in a university release. “The heavy-metal content of cannabis is not regulated; therefore, consumers could unknowingly be exposed to these toxic metals. This is bad news for anyone who uses cannabis but is particularly problematic for cancer patients who use medical marijuana to treat the nausea and pain associated with their treatments.”

The research team wrote a new meta-analysis on past studies looking into heavy-metal contamination in cannabis.

Their results show some marijuana strains are more effective in absorbing metals and other pollutants from soil, water, or air. The downside of this is cannabis farmers breeding these strains are unknowingly putting their customers at high risk for poisoning.

Unique characteristics seen in these marijuana strains include long stem length, fast growth, high root and leaf surface area, high photosynthetic activity, and little dependence on nutrients for survival. Heavy metals such as lead, cadmium, and chromium are able to move from the soil through the stalk and spread into the leaves and flowers of the plant. The heavy metals can then leave the plant through hairlike structures on flowers called trichomes.

Trichromes are important for storing CBD oil and have the tetrahydrocannabinol (THC) needed for marijuana products.

cannabis metals
(CREDIT: Penn State)

Researchers explain that heavy metals within cannabis have a link to multiple health problems because they rarely metabolize and can build up in specific areas of the human body. The reactive oxygen species and free radicals produced by heavy metals can damage your enzymes, proteins, lipid, and nucleic acids. They can also increase the risk of cancer and neurological problems.

Cannabis consumed in combustive form represents the greatest danger to human health, as analysis of heavy metals in the smoke of cannabis revealed the presence of selenium, mercury, cadmium, lead, chromium, nickel and arsenic,” Dr. Bengyella adds. “It is disturbing to realize that the cannabis products being used by consumers, especially cancer patients, may be causing unnecessary harm to their bodies.”

To reduce the risk of heavy metals in cannabis plants, the researchers suggest avoiding the cultivation of cannabis plants near industrial areas. Farmers should also conduct air quality tests on the site before production and use a soil pH test to check for contaminated soil.

The study is published in the journal Toxin Reviews.

About Jocelyn Solis-Moreira

Jocelyn is a New York-based science journalist whose work has appeared in Discover Magazine, Health, and Live Science, among other publications. She holds a Master's of Science in Psychology with a concentration in behavioral neuroscience and a Bachelor's of Science in integrative neuroscience from Binghamton University. Jocelyn has reported on several medical and science topics ranging from coronavirus news to the latest findings in women's health.

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