“When I saw a hundred-plus parts per million, I definitely thought it was problematic,” says Rodger Voelker, an analytical chemist, the lab director at OG Analytical (a private company that does cannabis-pesticide testing), and a co-author of the white paper. “Even if there are no direct obvious health consequences, which we don’t know, the bottom line is that levels like that are considered unacceptable for normal agriculture simply because when you see levels like that, that’s an indication of misuse.”
Whether there are direct health consequences to growers and consumers is unknown because there is virtually no research on how pesticides may affect people working with or consuming marijuana. Usually, companies that make pesticides will contract with third-party labs to test their pesticides’ toxicity, and then hand the labs’ data to the EPA to get their labels approved. Because of cannabis’ federal drug scheduling, going through that process with marijuana-specific pesticides would be a non-starter.
But so far, many universities have been hesitant to get involved in research surrounding marijuana cultivation, including pesticide research. For example, Washington State University’s extension program, which provides scientific education in farming communities throughout the state, has forbidden its employees to work with cannabis growers “until there is reconciliation of both state and federal law on the legality of this crop.”
“The university has given us instructions that we cannot work with a grower or an association in terms for giving them pest management advice or cultivation advice, or anything to do with crop production,” says Catherine Daniels, the pesticide coordinator and director at of Washington State’s Pest-Management Resource Service. “We can’t help them.”
According to Dave Stone, a pesticide toxicologist at Oregon State University and director of the National Pesticide Information Center, the toxicity of a pesticide depends both on its residue levels and how it is ingested. With pot, the high levels of pesticides in edible products could pose health problems, he says, but at least with ingested materials, the liver provides some protection.
Inhalation is another story, and the scant research on pesticide residues on similar crops, like tobacco, provides few clues as to how inhaled pesticides may affect the body. “Toxicologically, inhalation can pose some risks that are definitely different [than oral consumption] and we frankly have not done our homework to get at what those risks are,” Stone says. “We punted with tobacco as far as I can tell.”
“I’m used to dealing with uncertainty as a toxicologist,” he adds. “But this is a level of uncertainty that is making me quite uncomfortable.”
But forgoing pesticides completely could pose other health problems. While pests like spider mites are mostly a threat for economic reasons, molds and bacteria can contaminate cannabis plants, too, and those microbes can be harmful to consumers. This is especially the case for medical-marijuana patients with compromised immune systems, who could get secondary infections by inhaling pathogens. “If we’re going to have medical-marijuana programs, mold and mildew and microbes need to be part of that discussion,” Stone says.