The World Health Organization's cancer arm said Friday that an ingredient in the world's most widely used weed killer "probably" causes cancer.
Glyphosate is the main ingredient in Roundup weed killer, manufactured by the U.S. chemical giant Monsanto. Many homeowners use it to kill weeds. But Roundup is generally used in fields of genetically modified crops that can withstand the chemical.
The International Agency on Cancer Research said Friday that glyphosate is "probably carcinogenic to humans." It based its findings on studies carried out in the United States, Canada and Europe.
The U.S. Environmental Protection Agency classified glyphosate as a possible carcinogen in 1985, but reversed its conclusion six years later.
Monsanto disputed the WHO report, saying it did not understand how the agency could make such a "dramatic departure" from the conclusions of a number of regulatory agencies.