Opposition critics in Newfoundland and Labrador are asking why the provincial government continues to aerial spray an herbicide flagged as a potential health risk to humans.

Health Canada is considering new risk reduction measures for glyphosate, a product the World Health Organization described earlier this year as “probably carcinogenic to humans.”

Provincial officials confirmed the herbicide was sprayed this week over about 350 hectares of forest in northern Newfoundland near the town of Springdale and Plum Point.

They said Forza, containing glyphosate, was mixed with water and sprayed to kill weeds in areas planted with conifer or evergreen seedlings. The goal is to reforest sites harvested for pulpwood and sawlogs to support the lumber industry in future.

Provincial spokesman Roger Scaplen said in an email that the herbicide is registered by Health Canada, and that the federal department has not indicated any public risk if it’s used as directed.

“Health Canada’s advice regarding any products whose active ingredients are undergoing re-evaluation is to continue to use them as per existing label directions unless otherwise advised by Health Canada — this applies to products using glyphosate.”

Scaplen also stressed that the provincial Environment and Conservation Department issues licenses for herbicide programs. It’s an extra effort “to further mitigate against any potential non-target effects on both human health and the environment,” he said.

But Liberal environment critic Christopher Mitchelmore and his NDP counterpart, George Murphy, said the government should stop using glyphosate while Health Canada completes a re-evaluation expected next year.

“There are very obvious concerns being raised publicly, by the World Health Organization and others, about the possible cancer-causing side effects of glyphosate,” Mitchelmore said in a statement. “When the health of our residents is a concern it is always better to make sure the benefits outweigh the risks.”

Murphy noted that several countries, including Sri Lanka and France, have already moved to restrict use of glyphosate-based products such as Roundup, one of the world’s most popular lawn and garden weed killers.

“Even though Health Canada has got it under review, the (province) has chosen to go ahead anyway,” he said in an interview.

“If it’s a possible carcinogenic and they have all these organizations asking questions on it, why aren’t we asking questions as a government?”

Health Canada said in an emailed response that its re-evaluation includes more than 450 peer-reviewed studies.

Monsanto and other manufacturers of glyphosate-based products strongly rejected the WHO’s position released in March. They cited a 2012 ruling by the U.S. Environmental Protection Agency that the herbicide was safe.

Monsanto has also demanded a retraction from the International Agency for Research on Cancer, a French research arm of the WHO.

The agency has referred to “limited evidence” indicating the herbicide can cause non-Hodgkin’s lymphoma in humans. It also referred to “convincing evidence” that it can cause other forms of cancer in both rats and mice, and noted that glyphosate has been found in the blood and urine of agricultural workers who work most with it.

Toxicologists critical of the agency’s conclusions say the actual hazard posed by glyphosate or any other potentially harmful substance depends on exposure levels.

Health Canada has said its re-evaluation of glyphosate as a condition of continued registration includes whether the product should be re-labelled. New proposals include advising a restricted-entry interval of 12 hours after agricultural use, and that it only be sprayed when potential drift to populated regions is minimal.

Glyphosate is the most widely used herbicide in the country for major crops such as soybean and wheat.