Testing for residues of an herbicide developed by Monsanto Co. that has been linked to cancer has turned up high levels in honey from the key farm state of Iowa, adding to concerns about contamination. The Food and Drug Administration began glyphosate residue testing in a small number of foods earlier this year after the International Agency for Research on Cancer classified glyphosate as a probable human carcinogen. Research by FDA chemist Narong Chamkasem and John Vargo, a chemist at the University of Iowa, shows that residues of glyphosate - the chief ingredient in Monsanto's branded Roundup herbicide - have been detected [in honey] at ... more than 10 times the limit of 50 ppb allowed in the European Union. "According to recent reports, there has been a dramatic increase in the usage of these herbicides, which are of risk to both human health and the environment," Chamkasem and Vargo stated in their laboratory bulletin. Because there is no legal tolerance level for glyphosate in honey in the United States, any amount could technically be considered a violation, according to statements made in FDA internal emails, obtained through Freedom of Information Act (FOIA) requests. The Environmental Protection Agency may soon move to set a tolerance, however. The agency has set tolerance levels for glyphosate residues in many foods the EPA expects might contain residues of the weed killer.