Two more licensed medical marijuana producers have voluntarily recalled hundreds of grams of the drug after traces of a controversial pesticide banned in Canada were detected in their supply, raising questions about Ottawa's oversight of an industry expected to explode with the upcoming legalization of cannabis.

Last week, Organigram, a publicly traded grower based in Moncton, expanded a Dec. 28 recall of a small amount of product to include almost all of its cannabis buds and oils produced in 2016.

On Monday, Aurora Cannabis Enterprises Inc., a publicly traded firm based in Alberta, announced it had recalled seven lots of cannabis it had bought from Organigram and sold to its clients – through the mail-order system overseen by Health Canada – from August to October of last year.

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Health Canada listed both recalls on its online database and confirmed that both cases involved traces of chemicals bifenazate and myclobutanil, which are prohibited for use on legal cannabis in Canada.

Myclobutanil is permitted in small doses on certain crops that are eaten, since the chemical compounds are metabolized by the digestive system and rendered non-toxic. It is also approved for crops that don't retain high levels of pesticide residue as they grow.

The pesticide is not approved for use on plants that are combusted, such as tobacco or cannabis, and is known to emit hydrogen cyanide when heated. Lawmakers in Colorado, Washington and Oregon moved quickly to ban myclobutanil, in some cases enacting emergency legislation when they discovered growers using it.

Myclobutanil was also found in product recalled in November by Mettrum Ltd., a Toronto-based medical marijuana company.

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Organigram has said it does not know how the substance entered its crops but is working with Health Canada to find out more, noting it is a certified organic grower and does not use pesticides in its production processes. Organigram's CEO, Denis Arsenault, was unreachable for comment on his cellphone Monday.

However, Colette Rivet, executive director of Cannabis Canada, a trade association representing half of the country's 30 licensed producers, said Health Canada should require growers to test for more substances – such as myclobutanil – than just the 13 pesticides currently approved for use on medical marijuana.

"The list of pesticides hasn't been really focused on in the past, this should be another matter Health Canada should be looking at," she said Monday. "If the system identifies a gap for us, then we really should be doing something about that and make sure the gap gets filled."

When Health Canada was asked by The Globe in September what the government would do if a banned pesticide such as myclobutanil was found in product grown by one of the country's 30 licensed medical marijuana producers, the department said it had a zero-tolerance policy.

"If the Department had reason to believe that a licensed producer was using unauthorized pesticides or other chemicals, it would take immediate enforcement action," Health Canada said at the time. Such steps "could include detention of product, recalls or potentially revoking the producer's licence," Health Canada said, referencing two banned pesticides: myclobutanil and dodemorph.

On Monday, Health Canada spokesman Andre Gagnon said that both Organigram and Aurora have undertaken a series of corrective actions, "including strengthening monitoring, enhancing internal operating procedures, and expanding their product testing regimes."

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He added that Health Canada's own testing determined that the products affected by the recalls represent a low health risk and that it has not had any patients complain about adverse reactions after these product recalls. Aurora was counselling affected patients to destroy any remaining product hit by the recall and, along with Organigram, was offering patients refunds.

Last month, The Globe and Mail reported that neither licensed producer Mettrum nor Health Canada informed the wider public of a continuing recall involved myclobutanil. Health Canada has now begun listing cannabis recalls, regardless of the level of risk, online.

Kirk Tousaw, a Nanaimo-based lawyer who helped win a constitutional challenge that led to the overhaul of the medical-marijuana system this summer, said many in the cannabis world are frustrated that there is no regulatory regime that allows the hundreds of illegal dispensaries to test their cannabis products.

"People are frustrated by the hypocrisy, by the demonization of dispensaries by [licensed producers], when they are clearly cutting corners and not following the rules," he said. "And by the failure of government to really regulate the dispensary industry in an honest and above-board manner so that all consumers can benefit from whatever standards are out there."

Ms. Rivet said these recalls show the system works, but needs to be tweaked.

"It's good that we did have this check on what's been happening here and we can actually recall every product that we sell. So this is a good thing for the future as well."

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With a report from Grant Robertson