A study led by researchers from Penn State has outlined a range of strategies that cannabis growers should employ to minimize the plant’s uptake of heavy metals from the soil. The study suggests that consuming cannabis contaminated with heavy metals could potentially lead to chronic diseases, including neurological disorders such as Alzheimer’s.
Phytoremediation, a process that utilizes plants to remove environmental contaminants from soil, often involves the use of cannabis due to its fast growth, minimal nutrient requirements, and ability to absorb significant amounts of heavy metals such as lead, cadmium, and chromium.
Specifically, cannabis plants transport these heavy metals to their leaves and flowers, where they tend to concentrate in the trichomes—hairlike structures that also store cannabinoids like THC and CBD.
Industrial hemp plants have previously been employed to decontaminate the soil near the Chernobyl nuclear power plant, and certain cannabis strains have been bred specifically for phytoremediation purposes.
This new meta-analysis examines 25 previously published studies that investigate heavy metal contamination in cannabis. The potential health implications of consuming cannabis contaminated with heavy metals are discussed, and agronomic strategies are suggested to mitigate these potential issues.
“Cannabis consumed through combustion poses the greatest risk to human health, as analysis of cannabis smoke has revealed the presence of selenium, mercury, cadmium, lead, chromium, nickel, and arsenic,” explains Louis Bengyella, an author of the study. “It is concerning to realize that cannabis products being used by consumers, particularly cancer patients, may be causing unnecessary harm to their bodies.”
The researchers highlight that these heavy metals are often not metabolized by the human body. Instead, they gradually accumulate in various parts of the body, leading to potential health problems.
The study offers several recommendations to establish best practices for future cannabis cultivation. These include conducting comprehensive air and soil testing when establishing new cannabis farms, avoiding land previously used for industrial purposes, and implementing formalized “heavy metal free” certifications for cannabis products intended for commercial sale.
While these suggestions may seem burdensome, the issue raised by this research is far from hypothetical. Current regulations for recreational cannabis cultivation in the United States vary by state, but most regions have some level of contamination testing protocols in place.
However, these regulations are not always stringent. For example, earlier this year, a significant recall of cannabis occurred in Colorado after soil samples from one farm revealed high levels of cadmium. Similarly, in 2020, there was a recall of cannabis-infused edibles in Ohio due to cadmium-related concerns.
Bengyella argues that addressing the problem requires implementing regulations to control agricultural practices. With the recreational cannabis market expected to grow substantially in the coming years, it is crucial to resolve this issue.
“The problem lies with the consumer who uses cannabis products, but the solution must come from the agricultural level,” says Bengyella. “We believe that is where we should focus our efforts to solve the problem.”
The study was published in the journal Toxin Reviews.