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Want Safer Cannabis? Push for Pesticide Testing

by Mike May
Published: Jun 01, 2017   
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In March 2017, the Oregon Liquor Control Commission issued a pesticide warning for cannabis cultivated by one grower, because it contained pyrethrins. These insecticides cause a host of problems, including asthmatic breathing, facial swelling and more—even death from high doses. This insecticide poses a special risk in smokable cannabis products because it can be absorbed quickly through the lungs. This example clearly depicts why cannabis must be tested for pesticides.

Although many U.S. states struggle to institute regulations that limit pesticides in cannabis, Oregon is not one of them. In fact, this state publishes a list of more than 50 pesticides that samples must be tested for, as well as the allowable concentrations, which are all fractions of a part per million.

Likewise, Colorado publishes a list of pesticides that can be used on cannabis. As of March 6, 2017, this list included 307 products. It also notes how they can be used.

This kind of control should be applied to all samples, but that is not the case so far.

Unknown obstacles

It seems simple enough to solve this problem. Just test cannabis for pesticides. Unfortunately, that’s not as easy as it sounds. “Since it’s unregulated,” says Donald Land, Chief Scientific Consultant at Steep Hill Labs, “a large range of pesticides show up, even though most of them are infrequent.”

Again, it sounds easy enough to fix. Test for everything. But, that won’t happen. It costs too much and takes too much expertise. At this point, says Land, “States—one by one—are still trying to figure out how to handle this—deciding which compounds require testing.” It’s a long list to pick from, because the International Organization for Standardization lists names for more than 1,000 pesticides. It does get a little easier however. In 2013, American Herbal Pharmacopeia published a list of the 17 pesticides that are used often in growing cannabis. At the very least, that’s a place to start. It’s worth noting that pyrethrins—mentioned above for the warning—are on that list.

Even if labs know what to test for, the process remains complicated. “One challenge for cannabis is that it has a much richer matrix than most other plants,” Land explains. “It includes several hundred—maybe 500—different compounds, and these can potentially interfere with very tiny amounts of pesticide.”

Modernizing methods

To look for a wide range of pesticides in cannabis samples, scientists typically use a separation method—liquid or gas chromatography—followed by a detection method, usually mass spectrometry. “Pretty much everyone who tests for a long list of pesticides would use that method,” Land says. “You can do spot checks for classes of compounds with an enzyme-linked immunosorbent assay, or ELISA.”

To efficiently process larger amounts of cannabis, labs will need automation. “Instead of hand pipetting, centrifuging, filtering by hand, we can put that on an automated platform,” says Ryan Ravenelle, Scientific Leader for Agriculture, Chemical, Food, Personal and Industrial Care at the Hamilton Company. “We don’t manufacture products specifically geared toward pesticide analysis, but our systems lend the ability to automate that process.”

Ravenelle already reports increasing interest from the cannabis industry. “Lots of the methods and assays they are using are not new,” he says, “and they aren’t aware that lots of the workflows are not unique to their industry.” 

By combining required testing for specific pesticides and adding automation, manufacturers of cannabis-based products will ensure the lowest levels—almost nonexistent—of these contaminants in products. It’s good business and protects consumers from harm.


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