21 oat-based cereal and snack products such as Cheerios tested positive for traces of glyphosate.

The chemical is the active ingredient in Roundup, which has been at the center of several trials alleging the weedkiller causes cancer.

All but four of the products tested had glyphosate levels higher than what an environmental group considers safe for children.

Twenty-one oat-based cereal and snack products popular with children contain traces of glyphosate, the active ingredient in the weed killer Roundup, according to tests from the Environmental Working Group. EWG said the tests found glyphosate levels above what it considers safe for children in all but four of the products.

The 21 products that were tested are made by General Mills, including six varieties of Cheerios and 14 of General Mills' Nature Valley products, such as Nature Valley granola bars.

General Mills said food safety is a "top priority" for the company, which said it's working to minimize the use of pesticides on the ingredients it uses. "Most crops grown in fields use some form of pesticides and trace amounts are found in the majority of food we all eat," the company said in an emailed statement. "Experts at the FDA and EPA determine the safe levels for food products," which it adheres to, as well as farmers that grow the crops, it added.

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The report is the latest from the EWG to detect traces of glyphosate in cereals. The environmental advocacy group found traces of the chemical in dozens of Cheerios and Quaker brand products in October. Glyphosate has been at the center of several high-profile lawsuits alleging the chemical causes cancer. A California jury awarded a couple $2 billion in punitive damages after concluding that sustained exposure to Monsanto's popular Roundup weed killer led to their cancer diagnoses. Monsanto is now owned by Bayer.

Bayer issued a statement to CBS News saying, "The glyphosate levels in this report are far below the strict limits established by the EPA to protect human health."

"An adult would have to eat 158 pounds of the oat-based food every day for the rest of their life to reach the strict limits set by the EPA," the company said in a statement. "The group behind the new report has a long history of spreading misinformation about pesticide residues. The reality is that regulatory authorities have strict rules when it comes to pesticide residues and the levels in this report are far below the established safety standards."

Highest glyphosate levels

The two highest levels of glyphosate were detected in Honey Nut Cheerios Medley Crunch and Cheerios, at 833 parts per billion and 729 parts per billion, respectively, the group said. It considers anything over 160 parts per billion to be unsafe for children.

However, the U.S. Environmental Protection Agency has a far higher threshold for glyphosate content, ranging from 0.1 to 310 parts per million, rather than per billion.

Even though several juries have found in favor of cancer patients who claim their illness is linked to glyphosate exposure, there are conflicting scientific studies. The World Health Organization's cancer agency has said the weedkiller is "possibly carcinogenic to humans," but other organizations have said they believe the link is unlikely.

Glyphosate and oats

Glyphosate is sprayed on oats to dry out the crop, making it easier to harvest, the EWG said. The group said the practice increases the chances the chemical will end up in children's cereal.

"The only way to quickly remove this cancer-causing weedkiller from foods marketed to children is for companies like General Mills and Quaker to use oats from farmers who do not use glyphosate as a desiccant," it said in the report.

The four products that tested below the EWG's threshold of 160 parts per billion are:

Honey Nut Cheerios

Nature Valley Fruit & Nut Chewy Trail Mix Granola Bars, Dark Chocolate & Nut



Nature Valley Sweet & Salty Nut granola bars, Cashew



Nature Valley Soft-Baked Oatmeal Squares, Cinnamon Brown Sugar



For details on Bayer's position on glyphosate, visit here.