Herbicide Used on Crops to Kill Weeds 'Probably Carcinogenic to Humans' – Reports W.H.O.

Herbicides, the world's most widely used weed killer, can "probably" cause cancer, the World Health Organization said on Friday.

The International Agency for Research on Cancer, the cancer arm of the W.H.O., said glyphosate, the active ingredient in herbicide, was "classified as probably carcinogenic to humans." It also said there was "limited evidence" that glyphosate was carcinogenic in humans for non-Hodgkin lymphoma.

Concerns about glyphosate on food have been mounting in the United States, leading to the passage in Vermont last year of the country's first mandatory labeling law for foods that are genetically modified. The U.S. government previously said herbicide was considered safe.

Glyphosate is mainly used on crops such as corn and soybeans that are genetically modified to survive the encroachment of weeds. The weed killer has been detected in food, water and in the air after it has been sprayed, according to the W.H.O. agency's report. However, glyphosate use is generally low in and near homes where the public would face the greatest risk of exposure, the report said.

The report said studies of occupational exposure in the United States, Canada and Sweden showed "increased risks for non-Hodgkin lymphoma that persisted after adjustment for other pesticides."

In male mice, "glyphosate induced a positive trend in the incidence of a rare tumor, renal tubule carcinoma" while a second study showed "a positive trend for haemangiosarcoma in male mice," the report said.

"Glyphosate increased pancreatic islet-cell adenoma in male rats in two studies," said the report. "A glyphosate formulation promoted skin tumors in an initiation-promotion study in mice."

The herbicide has been detected in blood and urine of agricultural workers, indicating absorption, the report pointed out.

"Glyphosate and glyphosate formulations induced DNA and chromosomal damage in mammals, and in human and animal cells in vitro," it said.

A study showed increases in blood markers of chromosomal damage (micronuclei) in residents of several communities after spraying of glyphosate formulations, the report noted.

The agency issued the report after 17 experts from 11 countries met in France recently "to assess the carcinogenicity of the organophosphate pesticides tetrachlorvinphos, parathion, malathion, diazinon, and glyphosate."

Glyphosate, the report said, is "currently with the highest production volumes of all herbicides" and used in more than 750 different products for agriculture, forestry, urban, and home applications and development of genetically modified glyphosate-resistant crop varieties.

It is the main ingredient in Monsanto's Roundup herbicide.

The Environment Protection Agency said glyphosate is primarily applied to genetically engineered and glyphosate-resistant soybeans, corn, canola and cotton.

Monsanto, the world's largest seed company, contested the report, saying in a statement that scientific data do not support the agency's conclusions and called on W.H.O. to hold an urgent meeting to explain the findings.

"As recently as January, the German government completed a rigorous, four-year evaluation of glyphosate for the European Union. They reviewed all the data the I.A.R.C. considered, plus significantly more, and concluded 'glyphosate was unlikely to pose a carcinogenic risk in humans,'" said Dr. Philip Miller, Monsanto's vice president global regulatory affairs.

He said there is no new research or data that was used in the I.A.R.C. report and relevant scientific data were excluded from the review. He added that the conclusion is not supported by scientific data.

"There is no link between glyphosate and an increase in cancer when the full data set is included in a rigorous review," he said.

He added, "We don't know how I.A.R.C. could reach a conclusion that is such a dramatic departure from the conclusion reached by all regulatory agencies around the globe."