Cannabis users at risk from traces of toxic metals

Toxic metals such as lead have been linked to several health problems, including high blood pressure, kidney disease, and cancer. Toxic metals are thought to find their way into cannabis via the soil. Lead and other toxic metals, such as cadmium, enter cannabis plants through soil. Metals are naturally present in the ground, but higher levels are often the result of overuse of pesticides or nutrient feed, the process of construction and other industrialization. Cannabis is also a hyperaccumulator, meaning it is particularly good at absorbing heavy metals through the roots of its growing environment.

The study authors have warned that the problem has never been more critical as marijuana use in the US continues to increase, with an estimated 42 million regular users in the US.

The study, published in the journal Environmental Health Perspectives this month, used data from the annual National Health and Nutrition Examination Survey (NHANES) collected between 2005 and 2018. They examined blood and urine tests from 7,254 participants who had used cannabis within the last 30 days.

Cannabis users were found to have 1.27 micrograms per deciliter of lead in their blood compared to 0.93 ug/dl in non-users—a 27 per cent increase. Those studied also found 1.21 micrograms of lead in their urine, 21 per cent more than the control group, which came in at just 0.96. 

The Environmental Protection Agency (EPA) has been quoted as saying that there is no safe level of lead in the body. Exposure to lead poisoning in adulthood has been linked to issues, including high blood pressure, kidney damage, and infertility. 

Levels of the metal cadmium were also examined in the study. In cannabis users, cadmium levels were 22 and 18 per cent higher in blood and urine than in non-cannabis users. 

The International Agency for Research on Cancer (IARC) has classified cadmium as a known human carcinogen, meaning it can cause cancer. According to the CDC, high levels of cadmium can be linked to lung issues, gastrointestinal problems, abdominal pain, kidney disease, and fragile bones. 

The study comes as cannabis use enjoys a rise across the US. A 2019 study by the Substance Abuse and Mental Health Services Administration (SAMHSA) found that almost 18% of Americans, more than 42 million, used cannabis in the past 12 months. This is up from 45% in 2019 before the COVID-19 pandemic hit.

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