A group of mothers, scientists and environmentalists met with U.S. Environmental Protection Agency regulators on Tuesday over concerns that residues of Roundup, the world's most popular herbicide, had been found in breast milk.

The meeting near Washington D.C., followed a five-day phone call blitz of EPA offices by a group called "Moms Across America" demanding that the EPA pay attention to their demands for a recall of Roundup.

"This is a poison and it's in our food. And now they've found it in breast milk," said Zen Honeycutt, founder of Moms Across America. "Numerous studies show serious harm to mammals. We want this toxic treadmill of chemical cocktails in our food to stop."

Roundup is an herbicide developed and sold by Monsanto Co. since the 1970s, and used in agriculture and home lawns and gardens. The chief ingredient, glyphosate, is under a standard registration review by the EPA. The agency has set a deadline of 2015 for determining if glyphosate use should continue as is, be limited or halted.

The agency expects to have a preliminary risk assessment completed late this year, Neil Anderson, chief of the risk management and implementation branch at the EPA's pesticide re-evaluation division, told the group. He said more than 100 studies have been reviewed, many of which were provided by chemical makers, that so far have shown no reason for new restrictions on the pesticide.

Some studies that did show potential risks were not seen as valid, Anderson said. All of the information will be available for public review and comment later this year, he said.

Monsanto and other chemical makers say glyphosate has been extensively studied and has a long track record of safe and effective use.

But environmentalists, consumer groups and plant scientists from several countries have said in recent years that heavy use of glyphosate is causing problems for plants, people and animals. They say some tests have raised alarms about glyphosate levels found in urine samples and breast milk. In 2011, U.S. government scientists said they detected significant levels of glyphosate in air and water samples.

The group told the EPA Tuesday that a new U.S. study of glyphosate levels in breast milk is planned this year.

The use of glyphosate in agriculture has jumped dramatically since the mid-1990s after Monsanto started introducing crops genetically engineered to withstand direct sprays of Roundup, so farmers could more easily kill weeds without harming their crops. Glyphosate is sprayed on most of the corn and soybean crops in the United States, as well as over sugar beets, canola and other crops.

Last year, the EPA agreed to raise the permitted tolerance levels for glyphosate residue in food. The agency said at that time that toxicity data and studies it reviewed shows glyphosate is not a cancer risk and is generally safe at the approved levels.