The U.S. Environmental Protection Agency is asking for public feedback on a petition by a national environmental research and advocacy group to sharply limit use of a weedkiller, trace amounts of which have turned up in popular oat cereals and snacks such as Cheerios and Nature Valley granola bars.

A 30-day public comment period in the Federal Register opens Monday.

It's the latest step in the hot controversy over glyphosate, the active ingredient in Roundup, one of the most widely used herbicides in the world.

General Mills, maker of Cheerios and Nature Valley products, has insisted its foods are safe.

Earlier this week the EPA, which has been reviewing the chemical, concluded that glyphosate is not a carcinogen and poses no threat to the public when it is used according to its current label.

However, a growing body of science has linked glyphosate to cancer in humans, and public sentiment against the chemical has grown.

The Environmental Working Group, which submitted the petition to the EPA after researching glyphosate's presence in oat-based foods, says the chemical's presence in food that children eat presents an unnecessary health risk.

"We believe that parents shouldn't have to worry about whether feeding their kids healthy oat-based cereals for breakfast is giving them a high dose of a chemical linked to cancer," said Colin O'Neil, legislative director for the Environmental Working Group. "Many food companies across the spectrum of the industry agree with us."

O'Neil said that 18 food companies have joined with the group's petition to restrict the amount of glyphosate that can remain on oats. General Mills has not joined the petition.

Glyphosate is a particular issue for oats because farmers spray the oats before harvesting to dry out the crop. And unlike other grains that are heavily processed in making food, oats are very minimally processed after they leave the farm and so more residue remains.

According to the Environmental Working Group, from 1993 to 2008 the EPA increased the amount of glyphosate that oat farmers can spray on their crops. The petition asks the regulator to lower the standard back to the 1993 level, and to prohibit the use of glyphosate as a predrying harvest agent on oats.

Most of the oats consumed in the United States are grown in Canada, O'Neil said. Oats imported for consumption in the U.S. would have to meet the stronger standards for glyphosate residues.

Monsanto, which makes Roundup, and its German owner Bayer, face thousands of lawsuits alleging that Roundup caused non-Hodgkin's lymphoma. In March, in the first federal court trial of the lawsuits, a jury awarded Edwin Hardeman $80 million, including $75 million in punitive damages.

Hardeman, 70, blamed his cancer on Roundup and said he sprayed the chemical for years on his San Francisco Bay Area property to control poison oak and weeds.