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To pass state-mandated pesticide testing and ensure that their products are safe for sale and consumption, it is advantageous for cultivators to understand the common regulations and science behind pesticide use and testing.

With states like California and Colorado recently rolling out new testing regulations, growers must understand pesticide testing not only in instances where they may use pesticides on their own crops, but also in cases where a facility’s previous owner has sprayed pesticides that left traces behind.

Charlotte Peyton, vice president of business development for Stratos, a line of pharmaceutical-grade cannabis products based in Pueblo, Colo., has 30 years of experience in analytical chemistry and has worked at Zinca Ag, an agricultural chemical company, where she conducted research and development and generated data for EPA registration of the company’s products. Here, she shares insights to help cultivators better understand pesticide testing in cannabis.

1. There is no ‘zero’ in analytical chemistry.

Labs can get three different types of results when testing for pesticide molecules, Peyton says: a measured answer in parts per million (ppm); an amount that is detected, but that is lower than what the lab can measure, called the limit of quantitation (LOQ); or an undetectable amount, called the limit of detection (LOD), which cannot be identified by the lab’s equipment.

“So, the limit of detection—in between the LOD and LOQ, you can say, ‘Yes, this is the molecule I am looking for, but I cannot assign a number to it,’” Peyton says. “So, anything below an LOD, you can’t even say for sure what it is—it could be what we call baseline noise. That’s the one thing to understand: There is no ‘zero’ in analytical chemistry. It all depends on the ability of the instrument that you use and the type of method that you use.”

Each lab’s testing methods and instruments are evaluated for the LOQ, among other criteria, Peyton says. State regulations then specify the pesticides the labs need to test for, outlining which ones are allowed and which ones are prohibited, as well as the tolerances for each. The lab’s instruments produce a peak on a chromatogram, and the data contained within the peak offers information about the result, which falls under a measured amount of a pesticide or into the LOQ or LOD ranges, Peyton says.

2. State regulations are based on regulators’ best logical decisions.

Pesticide use in the U.S. is typically regulated by the Environmental Protection Agency (EPA); however, since cannabis remains federally illegal, the EPA has been hesitant to get involved in the industry, Peyton says.

“Also, the framework with the EPA is that the pesticide manufacturing company would be the source of crop trials that would generate the data around the pesticide use,” she adds. “It’s like a clinical trial for the FDA. With no data from the manufacturers and a reluctance from the EPA, the states are just doing the best that they can to make logical decisions with the information that they have.”

Synthetic pesticides are generally not banned in state-legal cannabis cultivation programs, Peyton says, although the fungicide myclobutanil has a zero tolerance in most states because it can be converted to the poisonous hydrogen cyanide gas when heated, as through smoking or vaping.

“It’s different if you ingest it—if you heat it, it could turn into hydrogen cyanide,” Peyton says. “So, the testing result needs to be ‘non-detect’ for that instead of a ppm number.”

For a list of EPA pesticide residue tolerances, click here.  

Pesticide use is often a balancing act between what is more harmful: the pest or the pesticide, Peyton adds. “Will the fungus that’s on the cannabis make people sick, or will the fungicide that is sprayed on the crop make them sick?”

3. Biological controls may cause testing failures.

To help avoid using pesticides on a crop, cultivators should keep their growing environment as clean and sterile as possible, Peyton says.

“Pests, insects, fungus and microorganisms can be transferred from grow to grow, even greenhouse to greenhouse, on the grower’s clothes, their shoes. [They] could be transferred by clones,” she says. “Once an area or a strain is infected, it becomes very difficult to return to the uninfected state in the beginning. So, cleanliness, paying attention to what you bring into your area, is really important.”

Should pests and diseases ultimately reach your crop, integrated pest management strategies—such as using biological controls like bacteria and microorganisms—are an alternative to pesticides, although these can also cause testing failures in some cases, Peyton says.

“For instance, Colorado requires a standard yeast and mold test for microorganisms,” she says. “So, the problem lies in the fact that not everything that fails the yeast and mold test is harmful to humans. It’s a very general test.”

For example, Peyton says, the yeast in beer would cause a nonspecific yeast and mold test to fail but the yeast is not inherently harmful to humans.   

Other states have very specific microorganism testing for different species, she added, which eliminates testing failures for nonharmful microorganisms.

4. Testing methods and processes are improving.

In the past, pesticide testing consisted of single molecule analytical methods developed by chemical companies that were registering molecules with the EPA, Peyton said. This method took a day or two to process the sample into a concentrate that could be tested. Then, in the mid-1990s, the QuEChERS multi-residue method surfaced for pesticide detection on agricultural products. This allowed testing labs to implement a screening method that can quickly detect up to 600 pesticides, she said.   

“Mass spectrometry allows us to see a very small concentration of chemicals, and it’s very, very specific to certain molecules, so there’s less chance of a false positive for the results,” she added.

5. Know the answer before you ask the question.

Understanding how different chemicals impact your environment and performing in-house testing to ensure the product is clean before it is tested by a third party can help growers anticipate their lab results, Peyton says. In-house testing also alerts growers to pesticide residue that might be lingering in their facility, she adds.

“The scariest component that I can think of is not what you are doing, but what have other people that were growing in the same space before you done?” Peyton says. “Myclobutanil can persist for three to six generations of clones that you’re taking, and it can linger in air ducts on dust and in grows where there was previous use.”

Cultivators should have documented protocols that help eliminate the possibility of cross contamination, she adds. Employees often wear suits that can be worn only in certain rooms and washed regularly to ensure that if there is a problem in one area of the facility, it does not get transmitted to another, Peyton says. “Recording pesticide use and the timing and comparing [that data ] to the pesticide residue results that you get will also help. So, if I know I sprayed x amount at this point in time, and then later on I got a residue of x, then I can start correlating what I do to what I get and be more scientific about how you handle it.”

Overall, cultivators should have a deep understanding of their facilities and business practices so test results never come as a surprise, Peyton adds.

“My best advice to them is know the answer before you ask the question—that’s what I prefer to do when it comes to testing,” she says. “So, if you can, get in-house testing on something and screen [to] make sure that you don’t have a problem before you submit your

. Understand the history of your space because a lot of the indoor spaces have been bought and sold over the years, and what’s allowed for sprays has changed a lot, so it would be a shame to get in trouble for something that somebody else has done.”

See also: 5 Things Cultivators Should Know About Cannabis Potency Testing

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