September 4, 2023: Users of marijuana, the third most commonly used drug in the world, have high levels of lead and cadmium metals in their blood and urine, according to a study.
In one of the first and largest studies on biomarker metal levels, researchers at the Columbia University Mailman School of Public Health found that marijuana may be an important and “under-recognised” source of lead and cadmium exposure.
The researchers looked beyond metal levels in the cannabis plant and linked it to self-report use of the drug to metal exposure within the body.
“Because the cannabis plant is a known scavenger of metals, we had hypothesized that individuals who use marijuana will have higher metal biomarker levels compared to those who do not use,” said Katelyn McGraw, postdoctoral researcher in Columbia Public Health.
“Our results therefore indicate marijuana is a source of cadmium and lead exposure,” first author, Ms McGraw said.
The researchers combined data from the National Health and Nutrition Examination Survey (NHANES) for the years between 2005 and 2018. The survey is a biannual program of studies designed to assess the health and nutritional status of adults and children in the US.
Measurements reported by participants for exclusive marijuana use compared to nonmarijuana-tobacco had significantly higher lead levels in blood (1.27 ug/dL) and urine (1.21 ug/g creatinine).
McGraw and colleagues classified the 7,254 survey participants by use — non-marijuana/non-tobacco, exclusive marijuana, exclusive tobacco, and dual marijuana and tobacco use.
The researchers used four NHANES variables to define exclusive marijuana and tobacco use.
Public health concern
It listed current cigarette smoking, serum cotinine levels, self-reported marijuana use, and recent marijuana use.
Five metals were measured in the blood and 16 in urine.
“Going forward, research on cannabis use and cannabis contaminants, particularly metals, should be conducted to address public health concerns related to the growing number of cannabis users,” said Tiffany R. Sanchez, assistant professor of environmental health sciences at Columbia Public Health, and senior author.
Marijuana is the third most commonly used drug in the world behind tobacco and alcohol.
As of last year, 21 states and Washington DC, covering more than 50% of the US population, have legalized recreational use of marijuana.
48.2 million users in US
Medical marijuana is legal in 38 states and Washington DC. In 2019, 48.2 million people, or 18% of Americans, reported using marijuana at least once within the last year.
Despite the robust literature on metal biomarker levels among cigarette smokers and growing evidence of metal contents in marijuana products, few studies have reported biomarker metal levels among marijuana users.
Metal and metalloid contamination of marijuana products occurs during growth, production, and consumption, posing potential harmful effects to end users.
The cannabis plant, from which marijuana is derived, is a known hyperaccumulator of metals present in water, soil, fertilizers, and pesticides. Unfiltered marijuana smoke contains high concentrations of metals and vape delivery devices have shown metal leaching in cannabis aerosols.
Though marijuana is illegal at the federal level, regulation of contaminants in all cannabis-containing products remains piecemeal and there has been no guidance from federal regulatory agencies like the FDA or EPA.
While 28 states regulate inorganic arsenic, cadmium, lead, and total mercury concentrations in marijuana products, regulation limits vary by metal and by state.
The results of the study were published in the journal Environmental Health Perspectives.