Users of marijuana had higher levels of toxic heavy metals lead and cadmium in their blood and urine than people who do not use weed, a recently published scientific study found, but the amount of the toxins does depend on the composition of the soil in which the marijuana is grown, so not all marijuana is equal.
“Compared to non-users, marijuana users had 27% higher levels of iron in their blood, and 21% higher levels in their urine,” said lead author Tiffany Sanchez, an assistant professor of environmental health sciences at Columbia University Mailman School of Public Health in New York City.
There is no safe level of lead in the body, according to the US Environmental Protection Agency.
Marijuana users also had 22% higher cadmium levels in their blood than non-users, and 18% higher levels in their urine, Sanchez said.
“Both cadmium and lead stay in your body for quite a long time,” she said. “Cadmium is absorbed in the renal system and is filtered out to through the kidney. So, when you’re looking at urinary cadmium, that’s a reflection of total body burden, how much you have taken in over a long period of chronic exposure.”
The study, published Wednesday in the journal Environmental Health Perspectives, used data between 2005 and 2018 collected by the annual National Health and Nutrition Examination Survey, or NHANES, which tracks the health of Americans.
Blood and urine tests of 7,254 people who said they had used marijuana in the last 30 days were examined for levels of heavy metals, which makes the new study “unique” — most studies have simply measured metal levels in the cannabis plants, and not the people using marijuana, Sanchez said.
Heavy metals bind to cells in the body, limiting their function, according to the Cleveland Clinic, and have been linked to cancer, chronic disease and neurotoxic effects.
Heavy metals aren’t just in marijuana — tobacco smokers are exposed to even more types of toxins. E-cigarettes, for example, contain high aerosol levels of nickel, chromium, lead and zinc, while researchers have found e-liquids and the tanks of e-cigarettes contain arsenic, lead, nickel, tin, manganese, copper and chromium, according to studies.
As natural elements, heavy metals are in the soil in which crops are grown and can’t be avoided, a key reason they exist in the air, water and food supply. Some crop fields and regions, however, contain more toxic levels than others, partly due to the overuse of metal-containing pesticides and ongoing industrial pollution.
Not all plants can absorb high levels of containments without harm. But cannabis has a special property – it is a “known hyperaccumulator,” which means it’s extremely good at absorbing heavy metals, pesticides, petroleum solvents, crude oil and other potentially harmful chemicals without harm to itself.
Due to its deep, wide roots and ability to grow in poor soil, the plant can be grown in many environments. In fact, hemp been successfully used to naturally leach toxic heavy metals from the soil around the Chernobyl nuclear power plant disaster and pesticides such as dioxin from heavily contaminated farms in Italy, according to a 2022 review.
Use of the plant is so promising, according to the review, that the US Department of Agriculture is sponsoring research on how to bioengineer the plant to absorb even greater levels of toxins.
While that’s good news for the environment, it’s worrisome for marijuana users. A 2021 study found the lead, cadmium and chromium absorbed by the plant was transported and distributed up through the stalk and into the leaves and flowers of the plant–the parts most likely to be smoked.
