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With No U.S. Standards, Pot Pesticide Use Is Rising Public Health Threat

This undated photo shows workers with harvested marijuana in a legal growing operation.
Food & Environment Reporting Network
This undated photo shows workers with harvested marijuana in a legal growing operation.
With No U.S. Standards, Pot Pesticide Use Is Rising Public Health Threat

Whiteflies and hemp russet mites suck the sap, while the termites drill straight for the roots. The eggs of two-spotted spider mites cling to the bottom of the leaves — if you could see them, they would be round and pearly, a microscopic 1/180th of an inch each. And the bumpy rash on the leaf’s topside? A precursor of powdery mildew, which will, untreated, settle like a thick coat of dust.

Powdery mildew is a major headache for marijuana growers.

“It grows fast,” said Frank Conrad, director of Colorado Green Lab, a private cannabis testing facility in Denver. “It will cover an entire room and destroy the value of that crop.”


In states like Colorado and Washington, there is a tremendous amount of money riding on healthy cannabis crops these days. But unlike, say, a corn farmer, growers in the legal-marijuana industry don’t have a clear understanding yet of which pesticides and fungicides are safe to use – for workers or consumers. Though the Environmental Protection Agency regulates pesticide use on other crops, it has not tested any for use on marijuana because the plant remains illegal at the federal level. And without federal approval, the use of non-registered pesticides is technically a violation of the law.

The result is a regulatory void in which, theoretically, anything goes. And given what is known about the chemicals commonly used on marijuana plants, that means a potential public-health hazard for the hundreds of thousands of people who smoke or consume legal marijuana, as well as those who work at the grow operations.

Pesticides have long been a staple of black-market marijuana growers, but with more than 50 percent of the public favoring legalization, cannabis is out of the closet. Recreational marijuana is now legal for private consumption in four states and the District of Columbia, and on Oct. 1, Oregon became the third state after Washington and Colorado to let dispensaries sell recreational marijuana to the adult public.

Legal or otherwise, pests and mold remain a problem. And the gap in regulation created by pot’s unique place in our culture has left growers confused about how to combat them.

“We are all trying to play catch-up to an actual agricultural industry,” said Pat Currah, a grow facility manager for Green Dream Health Services, a dispensary and grow operation in Boulder. “It’s an ignorance thing, and it’s no surprise — we aren’t trained, we don’t all know what we are doing.”


Cannabis workers on the front lines of the burgeoning industry are at particular risk from exposure, according to Paul Towers, the organizing and media director at Pesticide Action Network, an international coalition that works to eliminate hazardous pesticide use. In Colorado alone, the marijuana industry employs 23,000 people as budtenders, managers or growers.

“If we’re going to create a legitimate market, let’s protect those people who are going to be growing and harvesting and processing, just like we would for people who are growing and harvesting apples,” said Andy Baker-White, chair-elect of the American Public Health Association and author of its report calling for a public health approach to regulating commercial marijuana.

Because of marijuana’s long history as an illegal drug, many growers come to the field with a weak background in pest management.

“This is a culture that’s come from garages,” said Brian Stroh, owner of Washington’s Cannaman Farms. “If it’s the difference between having a couple thousand dollars for the product to survive or fail, it’s going to get sprayed.”

The issue, then, is what – and how – to spray. Without EPA testing, states are scrambling to establish their own piecemeal regulations.

In July, the Colorado Department of Agriculture posted a 21-page list of pesticides on its website of those labels that might be safe to use on cannabis.

“We have spent an exorbitant amount of time finding those products with a low enough toxicity to not pose a public health threat,” said John Scott, the department’s pesticide program manager, adding that more research is needed before anyone can guarantee that these products are safe or effective. “The federal government hasn’t been able to conduct the research and the science; the regulatory system simply hasn’t been able to catch up.”

According to a 2013 study published in the Journal of Toxicology, up to 69.5 percent of the pesticides on a marijuana bud can transfer into the smoker’s lungs.

Jeffrey Raber, who directed the study and owns a cannabis testing lab in California, said the risks to consumers and workers are clear.

“It's easy to understand that these compounds are toxic. We’ve studied that ad nauseum,” he said. “That’s why regulations exist for every other item we consume.”

Slow inspections

State laws require compliance with the Federal Worker Protection Standard to protect employees from acute and chronic pesticide exposure, but the guidelines are complex and enforcement has been slow to materialize.

“Employees are proceeding at their own risk with whatever chemical exposure they’re willing to take on,” said Hilary Bricken, an attorney at Seattle’s Harris Moure, PLCC and chair of the Canna Law Group.

From a forensic toxicology perspective, the health effects of pesticides can be difficult to isolate in workers because they are chronic, not acute. It could take years for symptoms to show.

"I know these businesses are very happy to forgo employee safety because, frankly, it's a cost, and most of them are startups,” said Bricken.

“Unless they're required to do it, they are very unlikely to engage in best practices unless, for example, their lawyer points out to them that you could have liability down the road.”

The Colorado Marijuana Enforcement Division (MED) has said for more than a year that it plans to roll out a mandated pesticide testing program. Yet the agency does not have a set timeline for testing.

“The MED, along with the Department of Agriculture and other state departments, are working very hard on this issue to come up with a process that our licensees can be compliant with,” said Thomas Moore, a spokesman for the agency.

Conrad, of Denver’s Colorado Green Lab, said the costs and labor needed to purchase testing equipment and organize random spot-checks is still prohibitive for the state.

For now, the primary way Colorado regulators learn of pesticide misuse is through regular building-code inspections by the Denver Fire Department, and sporadic workplace inspections, which are slow to materialize in the rapidly expanding industry.

According to the Department of Agriculture’s John Scott, his agency has inspected about 100 of the 1,000-plus licensed grow facilities in operation. The Washington Liquor and Cannabis Board, meanwhile, has inspected 381 of the state’s 709 producers and processors, issuing six violations for pesticide misuse.

Last spring, citing safety concerns about improper pesticide use, the City of Denver quarantined tens of thousands of cannabis plants at 11 of the city’s grow facilities, many after inspections by the fire department.

“I think that through this process, there has been a lot of education for the state and the city and the industry, and everyone is on a better level than we were six months ago,” said Dan Rowland, a spokesman for the City and County of Denver. “The industry has a better understanding of what they can and can’t do – and that’s only a benefit to them and their consumers.”

But in early September, a spot-check investigation and private testing by the Denver Post found illegal levels of pesticide residue were still present on products being sold to consumers, prompting a recall by state and city inspectors.

“We initiated an investigation the very next day after that article came out,” Scott said, explaining how seriously the CDA takes allegations of pesticide misuse.

Employee safety remains a primary concern. Worker complaints about misuse are directed to the department, and it is currently looking into several cases, though Scott said they cannot discuss them in detail until the cases are resolved.

“That’s one of the conversations that came up when all of this started: What is going on in these facilities? Are the people that are working there being put in harm’s way without even knowing what’s going on?” Rowland said. “We have a lot of city employees who are going in there and we have to make sure that our employees, the city inspectors, are safe when they are going in there.”

And while local authorities in Denver have received other complaints from employees, Rowland says the real effort to enforce workplace safety has to come from the state.

A national issue

Regulation is an ever-evolving patchwork of state and local laws, but signs of normalcy in the cannabis industry have begun to appear. According to a “state of the industry” report released in September by Convergex, a global brokerage company, prices for recreational marijuana are finally stabilizing in Colorado’s highly competitive market.

Another sign of the industry’s maturity is the nascent effort to organize workers.

Since November 2013, the United Food and Commercial Workers’ (UFCW) Cannabis Workers Rising chapter has signed up some 3,000 employees in states where marijuana is legal, and it is working to integrate cannabis employees into existing UFCW health and safety curriculums across the country.

A worker is shown tending plants in a legal marijuana growing operation in this undated photo.
Food & Environment Reporting Network
A worker is shown tending plants in a legal marijuana growing operation in this undated photo.

One of the first victories for organizers came in the spring of 2013, when an employee from the Wellness Connection of Maine, a group of medical marijuana dispensaries, called a state hotline about the use of a pyrethrin-based insecticide in a grow facility. Throughout its investigation, the Maine Department of Health and Human Services received 22 more tips from employees, according to the Portland Press Herald.

At the time, the state had set a zero-pesticide tolerance for cannabis. At one of multiple worker protests in the wake of the complaints, production assistant Barbara Heap told the Press Herald, “Too many workers are out sick.”

After an unannounced inspection at the grow sites, the department cited the dispensary group for 20 violations of state policy and fined it $18,000.

“Because of Wellness Connection in Maine it has become very clear federally that this is an industry where workers can come together and they can organize,” said Evan Yeats, a spokesman for UFCW.

But without federal testing on cannabis use, there is no consensus about when it is time to raise the red flag. Pyrethrin, the chemical cited in the Maine case, is listed on both Washington and Colorado’s “approved” pesticide lists, even though the EPA cites it as a likely carcinogen and the Pesticide Action Network has it on its “Bad Actors” list of toxic chemicals.

Washington has established slightly more stringent pesticide guidelines than Colorado, and only allows those pesticides that are exempt from the EPA’s tolerance-level requirements – the thresholds at which residues become harmful.

A few of the Colorado pesticides that do have EPA tolerances – such as the insecticide Fenoxycarb and the fungicide Thiophanate-Methyl – also are on the PAN “Bad Actors” list, and are noted as carcinogens and developmental and reproductive toxins. Though Colorado registration for Fenoxycarb has expired, growers are allowed to use up their existing stocks.

Unfortunately, identifying the health risks of pesticide use in the industry is far more complex than just isolating a specific chemical, said Conrad, of Colorado Green Labs.

“There are so many aspects to consider. You have to look at its use; you have to look at the environmental impact,” he said. “You have to see what is going to happen to it and at what levels for the end user. It’s unprecedented to have these kinds of chemicals without federal testing or parameters.”

Many of these pesticides arrive as unwieldy solids or powders, so it is standard procedure for farmers to dissolve the pesticides to make spray application easier, according to Conrad. One of the most popular solvents, naphtha, is a known neurotoxin that is absorbed through the lungs and skin and has a chronic risk of neural defects. For example, exposure to the pesticide imidacloprid — found frequently on marijuana — can cause thyroid problems, but when combined with naphtha, it is potentially carcinogenic, said Conrad.

With proper protective equipment and training, most workers are fine using naphtha. But in the Wild West landscape of the legal marijuana industry, workers often operate without much if any training on pesticide application or protective equipment — which is not uniformly available — and without regular workplace safety inspections. Furthermore, many grows are indoor, in industrial warehouses that may lack proper ventilation.

“If you have been exposed to (naphtha) consistently even over a year or six-month period, you can start developing damage to your central nervous system,” Conrad said. “That is one of the clearest risks to workers if they are not wearing protective equipment when applying pesticides to marijuana.”

Beyond the combination effects of pesticides, toxicity differs greatly based on the type of exposure. The extraction and concentration process used to produce edibles and topical products can cause pesticide residue to accumulate at levels 10 times higher than on dried plants, according to a June 2015 study released by the Oregon-based Cannabis Safety Institute.

And though the EPA has not tested specific pesticides for inhalation with cannabis, many of the chemicals used in grow operations are known to cause noxious fumes at high temperatures.

For instance, when heated to decomposition, Thiophanate-Methyl emits “very toxic fumes” of nitrogen oxides and sulfur oxides, according to the National Center for Biomedicine Information. Myclobutanil, the active ingredient in Eagle-20 – which has repeatedly been found in grows around the country – will form hydrogen cyanide when heated, which can be fatal if inhaled.

Raber, the scientist behind the Journal of Toxicology study, said consumers need to understand that the risks of smoking contaminated marijuana are different than consuming a non-organic vegetable. Unlike produce, consumers are not rinsing their marijuana buds, so even if some of the pesticides are water-soluble, they likely aren’t breaking down for a long time. And inhaling is similar to injecting, in that it bypasses filtration in the liver and instead flows straight into the bloodstream.

“It’s a really, really difficult problem and when testing isn’t mandatory it’s worse because nobody wants to pay for it,” said Raber. Tests for pesticide residue at third-party labs typically costs more than $300 per sample, according to the Cannabis Safety Institute.

In mid-May, the embattled industry learned of a bureaucratic loophole that would allow the EPA to selectively test and legalize pesticides for cannabis use on a state-by-state basis. In a letter to the Colorado agriculture department, the EPA confirmed that states could apply to have certain chemicals registered under the “Special Local Needs” (SLN) section of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA).

Jim Jones, the EPA’s assistant administrator for the Office of Chemical Safety and Pollution Prevention, said that though the crop remains an illegal Schedule 1 drug, his office is willing to conduct the necessary toxicology tests to determine safety and residue levels for certain pesticides on cannabis.

“The evaluation would be somewhat complicated because you would need to look at multiple pathways of exposure,” Jones said. If states submit applications for pesticides already regulated for both food and tobacco use, “then we would be in a reasonable position to work with them to do the analysis that would be necessary to make the appropriate safety findings.”

Once the EPA signs off on a specific state’s SLN application, the state can amend the label on a given chemical to allow for its use on cannabis. But more than four months after the agency sent its letter, it has yet to receive an application from any state.

Without proper testing and regulation from both state and federal agencies, thousands of workers in Colorado, and across the country could face severe health risks in this new agricultural frontier.

Corrected: April 19, 2024 at 2:22 AM PDT
This article was produced in collaboration with the Food & Environment Reporting Network, an independent, nonprofit news organization producing investigative reporting on food, agriculture, and environmental health.