Levels and Distribution of Health-Relevant Heavy Metals in Commercially Grown Cannabis in Colorado

ABSTRACT As more US states legalize recreational and medicinal cannabis use, legal market cannabis products present a new and growing potential source of heavy metal exposure. Currently, most states with legal markets only require testing for the “big four” heavy metals: arsenic, lead, cadmium, and mercury. However, cannabis and hemp plants are known hyperaccumulators of heavy metals from soil and water and may be subject to a much broader array of contaminants. Heavy metal exposure is associated with a wide array of negative health impacts, including cardiovascular and respiratory system damage, making appropriate regulatory limits in consumer products a public health priority. The goal of this study was to characterize levels of 20 heavy metals in Colorado market cannabis flower using newly validated laboratory methods. Flower samples were anonymized and randomly selected from within the inventory of a laboratory that conducts state regulatory testing of cannabis and hemp in Colorado. Flower samples were analyzed using inductively coupled plasma-mass spectrometry. Heavy metal concentrations were generally within previously established ranges for tobacco and cannabis products, with some heavy metals at markedly lower levels than what has been observed in tobacco products. Flower samples that failed state regulatory testing for one of the “big four” heavy metals had higher levels of chromium and lower levels of beryllium than samples that did not fail for any of the “big four” heavy metals. Flower samples from indoor grow operations had lower levels of barium, lithium, and selenium than samples from outdoor grow operations. These findings highlight the need for more research into the levels of heavy metal contaminants in consumer cannabis products in Colorado and other US legal markets.