A new report from the World Health Organization has found possible cancer links to popular weed killers commonly used by Canadian farmers and across the world.

The report also found that an insecticide used by the city of Winnipeg to ward off mosquitos could contribute to the development of non-Hodgkin's lymphoma and prostate cancer.

In the study published on Friday, Malathion, glyphosate -- more commonly known as Roundup – as well as diazinon were classified as "probably carcinogenic to humans."

In March, 17 experts from 11 countries met in Lyon, France at the International Agency for Research on Cancer to discuss the relationship between five different insecticides and herbicides – glyphosate, malathion, diazinon, tetrachlorvinphos and parathion -- and cancer in humans.

Malathion is used regularly in Winnipeg to fend off pesky mosquitos. Chemical fogging was adopted by the city in 2005 to combat the spread of the West Nile virus. Even though the practice was established in many other places, Winnipeg is the last Canadian city that continues to use the insecticide as part of an ongoing program.

Glyphosate is one of the most common agricultural herbicides in the world, and is used by the farmers across Canada. The popular weed killer is sold over the counter under the name Roundup.

In the report, the researchers state that there is "limited evidence" that malathion could contribute to development of non-Hodgkin's lymphoma and prostate cancer. They cite studies from the U.S., Canada and Sweden on human exposure.

The research also points to past studies conducted on rodents, which connected malathion to the growth of tumours. It goes on to specify that the insecticide causes "chromosomal damage" and disrupts "hormone pathways."

Debate about its use has raged in the city for more than a decade. Critics have long argued that the chemical sprayed into the air to kill adult mosquitos was instead hurting humans.

Dave Nickarz, who spearheaded protests against the insecticide's use in the early 2000s, told CTV Winnipeg that the WHO study is an important step forward.

"It's really something that needed to stop 10 years ago," Nickarz said.

"I don’t think the momentum is on our side, but the evidence is," he added.

In light of the new classification by WHO, the City of Winnipeg says it will review the report and consult with Health Canada.

One of the other chemicals mentioned in the report, glyphosate, was also categorized as "probably carcinogenic to humans."

"There was limited evidence for carcinogenetic in human," said Kathryn Guyton, a WHO scientist.

"In addition to that there's convincing evidence that glyphosate also can cause cancer in laboratory animals," she added.

WHO's report also linked the chemical to cases of non-Hodgkin's lymphoma. It citied agricultural studies done in the U.S., Canada, and Sweden since, as well as tests that showed the development of tumours in mice.

The chemical has seen several back-and-forth changes to its classification in the past 30 years, but the WHO report said that an U.S. study done by the Environmental Protection Agency, and several other recent positive results, were enough to conclude that there is "sufficient evidence" of carcinogenicity in tests performed on animals.

The report goes on to say that glyphosate caused "DNA and chromosomal damage" in humans.

In response to WHO's findings, the multinational agrochemical and biotechnology company Monsanto said that researchers "disregarded dozens of scientific studies that support the conclusion that glyphosate is not a human health risk."

In an email to CTV News, Health Canada says it will review its stance on the chemicals "once the full report is available" from the WHO. A spokesperson from Health Canada said the WHO's release contained "only the bottom line classification" and lacked a risk assessment for the chemicals.

The department's policy is to re-evaluate pesticides on a 15-year-basis to ensure products meet current scientific standards

Diazinon is currently being phased-out because of safety concerns. However, glyphosate and malathion remain classified as safe.

With a report from CTV Winnipeg’s Jill Macyshon