This study measured the levels of lead, cadmium, arsenic, mercury, and four phthalates (a plastics additive called a plasticizer) in a selection of commercially available CBD products in the US. They also examined CBD labeling for accuracy. It was published in the journal Science of the Total Environment in December 2021.
Cannabis is a well-known bioaccumulator, which means it can absorb toxins from the environment and hold onto them. Hemp is even sometimes used to help remediate toxic soil. Thus, cannabis and hemp growers have to be VERY careful what types of soil, water, and nutrients they use.
The authors' conclusions:
Four edible CBD products exceeded the California Proposition 65 threshold for daily lead consumption of 0.5μg in two servings.
Only 42 % of products fell within ±10 % of the CBD claimed on the manufacturer label.
Low-level heavy metal and phthalate contamination of edible CBD was pervasive.
Tight regulations for CBD product label integrity are needed.
The research paper is behind a paywall, and they say the data is confidential. Nonetheless, MOST of the hemp-derived products available in the US are not tested because there are no requirements to test.
We recommend only purchasing from producers that freely offer copies of the products' Certificate of Analysis (COA).
The abstract and detailed summary is here at ScienceDirect.com.