The most widely used herbicide in the world, glyphosate, the active ingredient in the Monsanto product Roundup, was classified as "probably carcinogenic to humans,” in a report released Friday by cancer researchers affiliated with the World Health Organization.

The International Agency for Research on Cancer (IARC) announced its assessment of glyphosate after convening a meeting this month of 17 cancer experts from 11 countries. They looked at the available scientific evidence on five different pesticides, including glyphosate, to determine whether to classify them as carcinogens. Carcinogens are substances that can lead to cancer under certain levels of exposure.

Glyphosate caused DNA and chromosomal damage in mammals, and in human and animal cells studied in laboratories, the report said. Studies of workers who had been exposed to the chemical in the U.S. Canada, and Sweden found “increased risks for non-Hodgkin lymphoma that persisted after adjustment for other pesticides,” the report said.

Glyphosate is usually used on crops, including corn and soybeans, that are genetically modified to survive it. The herbicide has been detected in food water, and in the air after it has been sprayed, according to the IARC report. “Its use has increased sharply with the development of genetically modified glyphosate-resistant crop varieties,” the report said.

Monsanto, the agrochemical giant, objected to the findings.

"We don't know how IARC could reach a conclusion that is such a dramatic departure from the conclusion reached by all regulatory agencies around the globe," Philip Miller, Monsanto's vice-president of global regulatory affairs, said in a statement.

WHO's based its classification of glyphosate on evidence from studies of exposure, mostly agricultural, in the United States, Canada, and Sweden that were published since 2001.

The U.S. government has said the herbicide is considered safe, and the Environmental Protection Agency approved a Monsanto request to increase legal tolerance levels for glyphosate in 2013.

Glyphosate was originally used as a descaling agent to clean out mineral deposits from pipes because of its ability to avidly bind to heavy metals. The chemical bonds to arsenic, cadmium and other heavy metals found in groundwater.

Scientists and farmers elsewhere have raised other concerns over glyphosate and tried to ban its use.

Channa Jayasumana, with Rajarata University of Sri Lanka, published a study in the International Journal of Environmental Research and Public Health in 2014 on a possible link between glyphosate and chronic kidney disease in farmworkers. His research found that excessive heat and dehydration may weaken the workers' bodies, making them more susceptible to pesticides and heavy metals, which can lead to kidney disease.

Based on that research, the Sri Lankan government moved to ban glyphosate in spring of 2014. But Monsanto raised objections to the report's findings, and the ban was lifted. The chemical was, and continues to be, widely used on farms in the country.

The research also suggested a link between glyphosate and a mysterious kidney disease that has killed thousands of farmworkers in Central America. At least 20,000 farm workers have died of chronic kidney disease in Nicaragua in the last two decades, The Guardian reported in February. Researchers who have studied the disease in Central America say that it mainly affects agricultural laborers working under conditions of excessive heat and dehydration, but other factors, including pesticides, may play a role.

With wire services