Background
The demand and availability of commercially available cannabidiol (CBD) products has grown substantially, which is of particular interest among medically vulnerable people. Because the cannabis plant is recognized as a bioaccumulator, which is highly effective at absorbing and retaining contaminants (e.g., heavy metals) in soil, it is important to characterize the degree of contamination in CBD products and their label accuracy to better estimate potential health benefits and risks associated with consumption.

Methods
Levels of lead, cadmium, arsenic, mercury, four phthalates, and CBD labeling accuracy were quantified in a selection of commercially available CBD products in the US. Heavy metal concentrations were quantified by inductively coupled plasma-mass spectrometry. Phthalates were quantified by liquid chromatography-tandem mass spectrometry. CBD labeling accuracy was determined by extracting samples into a suitable organic solvent and analyzing using liquid chromatography with diode array detection.

Results
Lead was detected in 42 %, cadmium in 8 %, arsenic in 28 %, and mercury in 37 % of 121 edible CBD products. Four edible CBD products exceeded the California Proposition 65 threshold for daily lead consumption of 0.5μg in two servings. The percentage of edible products with detectable phthalate concentrations varied between 13 % and 80 % across the four phthalates, with DEHP being most prevalent. Among all products tested for CBD labeling accuracy (topicals, edibles, N = 516), 40 % contained <90 % of the CBD indicated on the product label, 18 % contained >110 %, and only 42 % of products fell within ±10 % of the CBD claimed on the manufacturer label. Concentrations of heavy metals and phthalates were not associated with CBD potency.

Conclusions
Low-level contamination of edible CBD products with heavy metals and phthalates is pervasive. There is substantial discrepancy between the product label claims for CBD potency and the amount measured in both edible and topical products, underscoring the need for tight regulations for CBD product label integrity to protect consumers.