Cannabis plants have the ability to absorb heavy metals from the soil, making them useful for remediating contaminated sites. But this ability to soak up toxic metals may also make cannabis dangerous for consumers who ingest it.
A new meta-analysis by researchers at Penn State examines the ability of cannabis plants to absorb heavy metals and discusses the resulting health impacts on consumers. The team proposes a blueprint of strategies for growers to alleviate heavy-metal uptake by their crops.
“Heavy metals, such as lead, mercury, cadmium and chromium, are known to be carcinogenic,” said Louis Bengyella, assistant research professor of plant science, Penn State. “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 cannabis to treat nausea and pain associated with their treatments.”
Compounding the problem, Bengyella said, is the fact that some cannabis strains have been bred specifically for phytoremediation, which is the use of plants to remove pollutants from soil, water, or air.
“The problem is if we use these strains that were developed for phytoremediation without considering why they were developed in the first place, we may unknowingly expose consumers to heavy metals,” he said.
Bengyella and his colleagues conducted a meta-analysis of research studies on heavy-metal contamination in cannabis. Specifically, they investigated available information on the application of cannabis in phytoremediation, the fate of heavy metals in cannabis plants, the medical impact of heavy metals in cannabis and agricultural strategies to mitigate heavy metal uptake.
Their results were published in a recent issue of Toxin Reviews, hosted by Taylor and Francis Ltd.
The team learned that some cannabis strains are commonly used for phytoremediation because of their unique physical characteristics — including long stem length, fast growth, high root, and leaf surface area, high photosynthetic activity, and dependence on relatively few nutrients for survival — which facilitate the absorption of heavy metals. The team also found that lead, cadmium, and chromium, specifically, are capable of being transported and distributed up through the stalk and into the leaves and flowers of the plant. These heavy metals then exit the plant through trichomes, which are hairlike structures located on the flowers.