Health Canada says a popular weed-killer used by farmers around the world does not pose a threat to human health, and says it’s standing behind a review it conducted of glyphosate in 2017.

Glyphosate is the active ingredient in Roundup, a popular weed treatment made by U.S. agrochemical giant Monsanto, now owned by German chemical company Bayer. Bayer and Monsanto merged in June 2018.

In a statement released Friday, the federal health department said it had taken a second look at its April 2017 decision that re-approved glyphosate for use in Canada after it received eight notices of objection. The department said there had “also been concerns raised publicly about the validity of some of the science” used in its review.

“Our scientists left no stone unturned in conducting this review,” Health Canada said, noting it was conducted by 20 department scientists who were not part of the 2017 evaluation.

“After a thorough scientific review, we have concluded that the concerns raised by the objectors could not be scientifically supported, when considering the entire body of relevant data,” the department wrote.

“The objections did not create doubt or concern regarding the scientific basis for the 2017 re-evaluation decision for glyphosate. Therefore, the department’s final decision will stand.”

Health Canada re-approved glyphosate for use in April 2017, including an updated label, and said glyphosate is unlikely to increase the risk of cancer in humans. The department also said food and water exposed to the chemical were unlikely to threaten human health.

The 2017 report was challenged by environmental groups, including Équiterre, Ecojustice, and the David Suzuki Foundation, which said the federal department “dismissed credible evidence” in its re-evaluation. The environmentalists claimed Health Canada relied on scientific reports that were secretly influenced by Monsanto, known as the Monsanto Papers.

The groups want Health Canada to restrict the use of glyphosate in Canada.

“The Monsanto Papers are actually review papers; they’re not new studies,” Dr. Connie Moase, a director with Health Canada’s Pest Management Regulatory Agency, told reporters during a technical briefing.

“We had looked at the individual studies, the raw data, and looked at (them) independently of the Monsanto papers, and had come to our own conclusions.”

The department said it will meet with the groups that filed the objections on Friday. Each objector will also receive a letter from the department that addresses their specific concerns.

Glyphosate is used by farmers around the world, who insist the product does not pose a threat to human health and is essential to protect crops from disease.

But many consumers and environmentalists believe it’s toxic to human and environmental health.

Glyphosate does not pose a risk to human health if the residues are within regulated Maximum Residue Limits (MRLs). A recent study by the Canadian Food Inspection Agency found more than 98 per cent of foods that tested positive for glyphosate were within the acceptable limit. Health Canada’s current MRL limit for glyphosate residues in wheat is five parts per million.

The herbicide ingredient was at the centre of a high-profile court case in California last August. As Reuters reported, a jury ordered Monsanto to pay school groundskeeper Dewayne Johnson $383 million in damages. Johnson alleged the chemical caused his cancer.

Monsanto has said it will appeal the verdict, arguing that decades of scientific study have proven the chemical is safe.

The World Health Organization’s International Agency for the Research on Cancer (IARC) classified glyphosate as a probable carcinogen for humans in 2015 — a determination disputed by scientists and regulators around the world, including Canada.

A Reuters investigation later found that the IARC’s report had been heavily edited from its draft form, with any findings or evidence at odds with its final conclusion deleted and/or heavily edited. The IARC disputed the Reuters article in a January 2018 statement and defended its finding.

On Friday, Health Canada told reporters the IARC review in 2015 did not take into account existing MRLs for glyphosate.

“It is important to note that the level of exposure to the pesticide is not factored into the approach used by the (IARC),” Moase said. “Health Canada took this hazard classification into consideration, but found that the levels to which Canadians are exposed do not cause any harmful effects, including cancer.”

Health Canada, Moase said, has not filed “a formal report or action regarding the IARC report,” noting IARC and Health Canada have different responsibilities. “Their role is completely different from our role as a regulatory body,” she said.

The department said its review findings are in line with those of other regulators.

“No pesticide regulatory authority in the world currently considers glyphosate to be a risk to human health, including cancer … at the levels at which humans are currently exposed,” Moase said Friday, adding Health Canada will continue to “monitor for new information related to glyphosate.”