Many Breakfast Cereals Still Contaminated With Weed Killer

(CNN) -- Several popular breakfast foods, including Cheerios and Nature Valley products, continue to test positive for trace amounts of a controversial herbicide that may increase the risk of cancer, according to a report released Wednesday by an environmental advocacy group.

The Environmental Working Group, which has links to the organics industry, found that all 21 of the products it tested had levels of glyphosate that were "higher than what EWG scientists consider protective for children's health."

Manufacturers maintain that their foods are safe, and the findings aren't unprecedented: The group also found in October that most of the breakfast cereals it tested contained glyphosate, the main ingredient in the weed killer Roundup.