Pesticides and Pot: The Environmental Consequences

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By David Schultz

Nov. 5 — As a wildlife ecologist who specializes in studying the effects of toxic chemicals, Mourad Gabriel knows what it looks like when an animal has been poisoned. So when his labrador-retriever mix, Nyxo, suddenly became violently ill and died early last year, Gabriel had a pretty good idea of what killed him.

For several years, Gabriel has been studying the declining population of a type of Northern California weasel called the fisher. He had discovered that many fishers in California were being exposed to rat poison, which was likely being used by clandestine marijuana growers operating deep within remote wilderness areas.

With marijuana legalization measures spreading from state to state, Gabriel's research is one of several signs that increased cultivation of this quasi-legal crop can trigger significant environmental side effects that pose unique challenges to state and federal regulators.

And Gabriel believes his research is what led someone to intentionally poison his dog.

A subsequent necropsy revealed that Nyxo had eaten cubes of red meat that had been stuffed with rat poison—the same poison that Gabriel was finding littered across many of the marijuana fields he was visiting.

Sounding the Alarm

Gabriel was one of the first scientists to sound the alarm about the environmental effects of trespass marijuana farms, especially how the pesticides used on such farms are harming the Pacific Coast fisher. The type of pesticide exposure documented by Gabriel and his colleagues is one of the primary reasons the U.S. Fish and Wildlife Service is now considering whether to place the Pacific fisher on its endangered species list.

Trespass marijuana cultivators use rodenticides and other pesticides not only to protect their highly lucrative crop, but also to prevent small animals from getting into their limited food supplies and to protect themselves from larger carnivores like bears, according to Craig Thompson, a wildlife ecologist at the U.S. Forest Service who has worked extensively with Gabriel.

In a 2012 study published in the journal PLOS ONE, Gabriel, Thompson and their colleagues examined the remains of 58 fishers and found that almost 80 percent had some level of exposure to a type of rat poison called anticoagulant rodenticides, which damage capillaries and prevent blood from clotting, leading to anemia or hemorrhagic shock.

“More than the location of the [marijuana] farms, it's the covert nature,” Thompson told Bloomberg BNA. “There's no regulation. They use chemicals banned in the U.S. and they use them in orders of magnitude greater than what the manufacturer would recommend.”

Gabriel said it wasn't initially obvious that the sources of the rodenticide exposure were marijuana farms. At first, he and his team were baffled by the results they were seeing because the fisher's habitat is nowhere near urban or even rural areas where one would expect they could be exposed to these chemicals.

Some of the fishers they examined “lived their entire lives within a national park or within a wilderness area,” Gabriel told Bloomberg BNA. “This is a roadless area. The only way to enter the area would be to hike.”

Receiving a Tip

Then a law enforcement official approached Gabriel after a presentation he gave on fishers and gave him a tip: The rat poison might be coming from trespass marijuana farms.

The tip seemed credible to Gabriel because part of the fisher's Pacific coast habitat contains California's “Emerald Triangle,” a trio of counties where climactic conditions are ideal for farming cannabis.

When Gabriel visited nearby marijuana plots that growers had recently abandoned—or had been forced to abandon by authorities—what he saw confirmed the tip he had received: Empty packets of rat poison littered indiscriminately across the forest floor.

In 2013, Thompson and Gabriel published another study that made an even stronger scientific link between trespass marijuana cultivation and rodenticide exposure. They found that the likelihood that fishers had been exposed to rodenticides increased with the number of marijuana cultivation sites located within their habitats.

‘Flagship Species.'

Fishers could potentially be the first animal to wind up on the endangered species list as a result of marijuana farming, but Gabriel and Thompson fear they won't be the last.

Sub-lethal exposure to these chemicals can cause changes in fishers' behavior, making them more likely to be preyed upon by other animals higher up the food chain. And, because the rodenticides bioaccumulate within the bodies of creatures that consume them, they “are not just a risk to rodents but to anything that consumes rodents,” Gabriel said.

Gabriel and his colleagues are now starting to conduct post-mortem examinations of bobcats, owls and other animals found in remote areas of California and they are discovering these animals have been exposed to rodenticides as well.

“The fisher was the flagship species that illuminated problem,” Gabriel said.

Legalize It?

That problem could be solved through legalization, say marijuana advocates.

If marijuana were legalized in more states—including in California, which may have a legalization measure on its statewide ballot next year—illegal trespass farmers might be replaced by legal businessmen with incentive to follow environmental regulations, theorized Keith Stroup, legal counsel and co-founder of the National Organization for the Reform of Marijuana Laws, or NORML.

“Even those of us who favor legalization want those illegal growers taken out,” Stroup told Bloomberg BNA. “If they're willing to take the risk of years in prison, they're not willing to take precaution with using … pesticides.”

But in states that have passed marijuana legalization measures, environmental regulators are just beginning to grapple with the new challenges now on their plates.

‘Used to Breaking the Law.'

As of Nov. 5, 23 states have laws legalizing marijuana for medical use. Four states—Alaska, Colorado, Oregon and Washington—and the District of Columbia have passed laws making marijuana fully legal for any purpose.

At a Sept. 21 meeting of pesticide regulators at Environmental Protection Agency headquarters, officials from states that have passed legalization measures said ensuring marijuana growers are using pesticides responsibly is not easy.

One problem for states is that, because marijuana is still illegal at the federal level, the EPA cannot play its traditional role in pesticide regulation: evaluating the science and approving chemicals for use on specific crops. Therefore legal marijuana growers cannot legally use most of the chemicals other farmers take for granted in the fight against insects, weeds, fungi and other pests.

Jack Housenger, the EPA's top pesticide regulator, sent a May 19 letter to the Colorado Department of Agriculture stating that the agency might be willing to allow states themselves to approve some pesticides for use on marijuana under the EPA's Special Local Need provision (40 C.F.R. 162). But the states would need to submit significant amounts of data showing that these pesticides can be safely used on crops that are grown, processed and consumed in a similar manner to marijuana—tobacco, for example, or hops.

Another challenge for states, according to John Scott, head of the Colorado Department of Agriculture pesticides division, is that some growers would rather pay a fine for pesticide misuse than not use a pesticide and risk damage to a crop that can yield them between $1,000 and $4,000 per plant.

“This is a unique industry in that this particular industry is used to breaking the law and flying under the radar,” Scott said. “The cost of doing business to meet any type of civil penalties is miniscule compared to the amount of money they can make from their crop.”

Indoor v. Outdoor

Kirk Cook, an ecologist with the Washington State Department of Agriculture, said the vast majority of marijuana cultivation in states that have legalized it takes place indoors or in greenhouses. In such settings, pesticide misuse can have serious consequences for workers as well as for the consumers purchasing a product with excessive levels of pesticide residue .

However, Cook said his state also allows marijuana to be grown outdoors. In outdoor grows, he said, the ramifications of pesticide misuse are multiplied; in addition to worker and consumer harm, wildlife can be affected and nearby water sources can be impaired.

Cook said his department has not yet begun conducting environmental monitoring near outdoor marijuana cultivation sites and is not particularly eager to do so. Any positive test results would instantly become a political cudgel in the heated local debate over marijuana, he said, and they would undoubtedly trigger calls for the Washington State Department of Agriculture to spend more of its scarce resources overseeing the marijuana industry.

“If we look for something, we'll likely find it. If we find it, then what? People at our department are reluctant to get involved in this,” Cook said.

Growing Pains?

These regulatory challenges represent what Keith Stroup of NORML calls a marijuana “learning curve.”

The nascent legal marijuana industry is going through some growing pains, along with the government officials who are trying to figure out how to oversee it. Within a few years, or even months, Stroup said, states and the EPA may be able to work through these issues and allow legal marijuana growers to protect their crops from pests without violating the law or damaging the environment.

And the state regulators at the Sep. 21 meeting acknowledged that many if not most of the post-legalization growers who misuse pesticides are doing so not out of malice or bad faith.

“There are a lot of folks in this industry that would like to do this right, but they need help with what doing it right means,” Erik Johansen, a Washington State Department of Agriculture policy assistant, said. “This is an agricultural commodity. We need to start treating it as such.”

Legal vs. Illegal?

However, sorting out regulatory growing pains still wouldn't address the issue of the illegal growers like those Mourad Gabriel and Craig Thompson are studying. Those growers probably aren't reading the safety warnings on pesticide labels and probably don't care whether the chemicals they are using have been approved by the EPA, state regulators said.

Gabriel says he is worried that, as cultural attitudes toward marijuana change and usage grows more widely accepted, demand for marijuana will continue to rise, creating a stronger financial incentive for drug trafficking organizations to set up grow operations in remote areas.

But Stroup believes that, if and when more states pass legalization measures and it becomes easier to grow and sell marijuana legally, consumers will flock to above-board marijuana retailers, extinguishing the economic motivations of the illegal growers.

“Even if we have to pay a little premium over black market prices, most consumers are willing to have it handled in a professional manner and not take the personal risks,” Stroup said.

Future of the Fisher

Until then, there are signs that things will continue to get worse before they get better for the fisher and other wildlife that happen to make their homes in prime marijuana cultivation territory.

The number of marijuana plants seized by the Drug Enforcement Agency may be trending upward after years of decline. In 2013, the agency seized 4,033,513 plants from outdoor grow operations, an 11 percent increase from the prior year, according to a DEA report.

And in a new study published Nov. 4 in PLOS ONE that involved post-mortem examinations of 167 fishers, Gabriel, Thompson and their colleagues found a rodenticide exposure rate of 85 percent, slightly higher than in his 2012 study.

The Fish and Wildlife Service expects to make a final determination on the listing status of the Pacific Coast fisher in April, a Service spokesman told Bloomberg BNA.

‘Tight-Lipped Community.'

In addition to producing more research, Gabriel and his allies also have offered a $20,000 reward for information that can help find out who poisoned his dog.

Despite the reward, the sheriff's office in Humboldt County—one of the three counties that comprise the Emerald Triangle—said it has identified no suspects or persons of interest almost two years after the incident.

“We live in a very tight-lipped community,” Gabriel said.

To contact the reporter on this story: David Schultz in Washington at

To contact the editor responsible for this story: Larry Pearl at

For More Information

Gabriel and Thompson's scientific research is available at:

Jack Housenger's letter to the Colorado Department of Agriculture is available at

A summary of the DEA's 2014 National Drug Threat Assessment is available at

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