Marijuana sold in Colorado dispensaries is often polluted with pesticides, heavy metals and fungi, according to Charas Scientific, one of eight Colorado labs certified to test cannabis. Andy LaFrate, founder of the lab, told the Smithsonian Magazine that edibles, though marketed as a healthier alternative, often use harmful compounds to prepare their products.
On the other hand, some of those contaminants might be essential to the plant, LaFrate told the magazine:
But for now it's unclear just how much marijuana growers need to clean up their product. "Like ourselves, this plant is living with bacteria that are essential to its survival. In terms of microbial contamination, it's kind of hard to say what's harmful and what's not," he adds. "So the questions become: What's a safe threshold, and which contaminants do we need to be concerned about?"