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9 In 10 Illicit Marijuana Samples Contained Pesticides In ‘Striking Contrast’ To Regulated Products, Study Finds



A new study reveals the “striking contrast” in safety between marijuana grown for the legal versus illegal markets in Canada, with 92 percent of unregulated cannabis testing positive for numerous pesticides compared to just six percent of regulated products.

The study, published in the Journal of Cannabis Research last week, involved testing 36 marijuana samples from licensed retailers and 24 illicit samples that were seized by law enforcement. The analysis allowed researchers to see if the products were grown with or contaminated by any of 327 different pesticides.

For the legal cannabis, the contamination rate was just six percent, with trace amounts of “only two pesticide residues detected, myclobutanil and dichlobenil.” The latter pesticide is not among the 96 that are subject to mandatory testing under Canadian statute.

Pesticides in the illicit market samples, however, were ubiquitous. Ninety-two percent of the samples contained potentially dangerous chemicals, the study found, identifying “23 unique pesticide active ingredients with 3.7 different pesticides identified on average per sample.”

“Chlorpyrifos, imidacloprid, and myclobutanil were measured in illicit samples at concentrations up to three orders of magnitude above” the method’s lowest calibrated level of 0.01 μg/g, the study’s authors said. “One illicit sample alone contained nine different pesticide active ingredients.”

Notwithstanding the six percent of legal samples that contained low amounts of pesticides, researchers said “the licensed Canadian cannabis sector has greatly improved.” Prior to mandatory testing requirements in 2019, the contamination rate stood at around 30 percent.

“To the authors’ knowledge, this study is the only extensive pesticide multiresidue analysis that compares pesticides in the licenced and illicit cannabis markets in a nation-wide jurisdiction where cannabis has been legalised,” authors said. “Albeit being a small study, our results do support the Government of Canada messaging where ‘Consuming illegal products could lead to adverse effects and other serious harms. Testing of illegal cannabis has found contaminants like pesticides and unacceptable levels of bacteria, lead and arsenic.’”

In other words, the findings affirm what cannabis reform advocates have long been saying: Regulating marijuana sales gives consumers access to safer products.

A separate study published last year examined marijuana testing rules in U.S. state markets and found that the patchwork of laws has caused public confusion and underscores the “urgent” need for “unified regulatory approach” and “national-level guideline on the contaminant regulations of cannabis.”

Developing such a national framework is challenging under federal prohibition, however. The Environmental Protection Agency (EPA) has approved the use of certain pesticides for hemp after the crop was federally legalized under the 2018 Farm Bill, but it’s declined to do the same for marijuana while it remains illegal.

Meanwhile, a pair of Republican congressional lawmakers has reintroduced legislation this session aimed at combatting the use of banned pesticides at illegal marijuana grows. The bill’s co-sponsor said in March that one effect of the bill would be to protect the health of consumers—especially medical cannabis patients.

In 2019, the nonprofit organization Beyond Pesticides urged supporters to contact their congressional representatives with a letter calling for federal regulations on pesticides used in marijuana in order to promote public health and safety.

That year, a rash of vaping-related lung injuries and deaths erupted following the addition of hazardous additives in vape cartridges. A study later found that injuries were lower in states with legal marijuana sales and homegrow.

Also in 2019, the federal National Science Foundation awarded a $250,000 grant to a biotech startup that was developing technology to remove dangerous pesticides from a variety of crops, including marijuana.

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Photo courtesy of Brian Shamblen.

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