Marijuana users have elevated levels of cadmium and lead in their blood and urine

By Dr. Priyom Bose, Ph.D.Sep 3 2023Reviewed by Benedette Cuffari, M.Sc.

A recent Environmental Health Perspectives study compares the levels of metal biomarkers in the blood and urine of marijuana users with non-users.

Study: Blood and Urinary Metal Levels among Exclusive Marijuana Users in NHANES (2005–2018). Image Credit: Inside Creative House / Shutterstock.com

Background

Marijuana is one of the most commonly used drugs throughout the world. Although many states have legalized marijuana use for recreation and medical purposes, this drug remains illegal at the federal level in the United States.

According to 2019 estimates, about 48 million people in the U.S. used marijuana at least once within the last year. This reflects the popularity of the product and its widespread use.

The cannabis plant is a metal scavenger or hyperaccumulator of metals present in soil, fertilizers, water, and pesticides. High concentrations of metals have been detected in unfiltered marijuana smoke and vaping devices. The contamination of metals and metalloids, which are collectively referred to as metals, in marijuana could manifest during the production of cannabis plants, which could significantly harm consumers.

The levels of metallic contaminants such as cadmium (Cd), arsenic (As), lead (Pb), and total mercury (Hg) in marijuana products are legally regulated; however, regulation limits vary between U.S. states. Exposure to these metals is associated with an increased risk of cancer and cardiopulmonary diseases; therefore, it is important to evaluate metal contaminants in marijuana.

The National Health and Nutrition Examination Survey (NHANES) between 2009 and 2016 reported the presence of Cd in urine and blood samples of prolonged marijuana users. Thus, there remains an urgent need to assess the presence of other metals in addition to Cd from recently collected biospecimens.

About the study

The current NHANES is led by the National Center for Health Statistics (NCHS) at the U.S. Centers for Disease Control and Prevention (CDC). The primary goal of NHANES is to evaluate the health and nutritional levels of people residing in the U.S.

The current study acquired NHANES data between 2005 and 2018 to analyze more geographically diverse samples. Out of 70,190 NHANES participants identified in the study period, 10,921 participants provided data on metals present in their blood and urine samples.

Individuals 18 years and older were included in this study. A total of 7,254 participants were considered in this study, as they fulfilled all eligibility criteria.

Inductively coupled plasma dynamic reaction cell mass spectrometry (ICP-DRC-MS) and high-performance liquid chromatography (HPLC) were used to assess the concentrations of several metals from blood and urine samples.

Four NHANES variables were used to define marijuana and tobacco use by participants. These included serum cotinine levels, current cigarette smoking, self-reported marijuana use, and recent marijuana use.

Study findings

Compared to non-users, average exclusive marijuana users were likelier to be younger, educated, have a higher income, be non-Hispanic White males, and have a lower body mass index (BMI). Among the participants who were not currently using marijuana or tobacco, 47% reported the use of marijuana in their lifetime.

In comparison to non-marijuana or non-tobacco users, this nationally represented cohort exhibited higher concentrations of Cd and Pb in blood and urine among exclusive marijuana users. More specifically, higher Cd and Pb levels were observed in exclusive marijuana users who used marijuana within the last seven days of biospecimens collection.

As compared to exclusive marijuana users, Cd levels were significantly higher in exclusive tobacco users. This difference in Cd levels could be due to differences in frequency of use or differential Cd accumulation in tobacco and cannabis plants.

Similar Pb concentrations were measured in both biospecimens collected from exclusive tobacco and marijuana users. Individuals who used both marijuana and tobacco also exhibited higher levels of Pb and Cd as compared to non-users. 

These findings are consistent with previous studies reporting a higher concentration of Cd in marijuana users. Importantly, Cd levels are positively correlated with increased frequency and duration of marijuana use. The current study highlights that blood Cd is a robust but short-term biomarker of Cd exposure, whereas urinary Cd is a long-term indicator of past cigarette smoking.

Female marijuana users exhibited higher urinary Cd levels than males. The extent of metal accumulation did not vary concerning race and ethnicity; however, a marginally strong association between marijuana use and blood Cd levels was observed in non-Hispanic White participants.

A higher level of Hg was observed in exclusive marijuana users; however, Hg levels decreased with increasing time since the last use. Comparatively, exclusive tobacco use was associated with higher concentrations of antimony, barium, Cd, Pb, tungsten, and uranium.

In the future, the long-term exposure of these metals to human health must be evaluated. Likewise, the presence of other cannabis contaminants should also be investigated to understand their effect on the health of cannabis users.