Canada’s medical marijuana growers will have to start testing all their products for unauthorized pesticides, says Health Canada, stepping up the government’s response to concerns about tainted marijuana.

The policy was announced Friday night as the department released test results that showed another marijuana producer, Ontario-based Peace Naturals Project Inc., had a plant test positive for a pesticide ingredient not approved for use on cannabis. Peace Naturals identified the source of the problem as cross-contamination from a product used to sanitize a plant harvest room.

On Tuesday, Gatineau’s The Hydropothecary Corporation voluntarily suspended sales after Health Canada informed the company that myclobutanil, an unapproved pesticide, had been found on plant leaves.

The 43 producers licensed by Health Canada provide medical marijuana for more than 130,000 patients across Canada. Health Canada requires the companies to test for mould, heavy metals, and harmful bacteria, but has relied on them to police themselves when it comes to pesticide use.

That changed Friday, when Health Canada said mandatory pesticide testing was necessary to “ensure that Canadians can continue to have confidence in obtaining safe, quality-controlled medical cannabis.”

Only 17 pesticides are approved for use on cannabis, the department warned in a statement. “There are no exceptions to these requirements, and no situations in which using a pesticide that is not authorized … for cannabis cultivation would be acceptable.”

Concern has been growing in the last several  months, after three marijuana producers recalled products found to contain unapproved pesticides, including myclobutanil. Some patients who say tainted marijuana made them sick have joined three class-action lawsuits now seeking certification in the courts.

Myclobutanil has been used by illegal pot growers to control mould. The pesticide is approved for use on some fruits and vegetables, but not for plants that are dried and smoked.

Health Canada maintained that the levels of myclobutanil found in the recalled products from legal producers would not cause serious health problems. But officials also stepped up enforcement. In March they began a series of random, unannounced inspections to test plants, dried weed, cannabis oils and pest-control products for unapproved pesticides.

Test results from plant samples taken at seven sites came in this week, which revealed the problems at Hydropothecary and Peace Naturals. Plants at the five other companies showed no signs of pesticide contamination, said Health Canada. They are Tweed in Smiths Falls; RedeCan and 7 Acres in Ontario; and Tilray and Broken Coast in B.C. Results of tests on dried weed and oils at the seven sites aren’t available yet.

The substance found on a leaf from Peace Naturals, piperonyl butoxide, was at a low level of 0.78 parts per million, said Health Canada. Piperonyl butoxide is combined with pesticides to increase their effectiveness, and is considered an “active ingredient” in pesticides, said Health Canada. It is not contained in any of the pesticides approved for use on cannabis.

A statement from Cronos Group Inc., the parent company of Peace Naturals, identified the source as “cross contamination from a sanitation protocol” the company no longer uses. 

The piperonyl butoxide was in an approved product used to sanitize empty rooms between harvests, said the statement released on Twitter.

That sanitation method has “not been practiced since new management implemented an improved production methodology after taking control of Peace,” said the statement. Cronos Group took over the company in September 2016.

“There is no evidence to suggest that (piperonyl butoxide) at these levels is likely to cause any adverse health effects when inhaled or ingested,” said the statement.

“However, out of an abundance of caution, Peace is in the process of assessing which lots have been impacted, notifying patients, and will voluntarily recall any products that have even potentially been implicated.”

“We take safety testing seriously and are working closely with Health Canada to determine next steps,” said  Mike Gorenstein, the Cronos Group CEO, in the statement.

At Hydropothecary, the co-founder said the company voluntarily stopped sales as a “precautionary measure” while it searches for the source of the pesticide.

“We want to be clear that we have no confirmed evidence that unapproved pesticides or foliar sprays were intentionally applied to any of our plants or plant materials by our staff,” the company said in an update posted on its website.