Drinking water across the Midwest is polluted with high levels of the herbicide atrazine and poses a particular risk to infants in the first four months of life, according to a report released yesterday by the Environmental Working Group. The D.C.-based group found that between 1993 and 1998 atrazine contaminated the tap water of some 10.4 million people in seven Corn Belt states, sometimes in concentrations up to 14 times the legal limit. Earlier this week, EWG placed a full-page ad in the New York Times chastising the Environmental Protection Agency for not moving quickly enough on a promise to set tighter limits on atrazine. The agency denied the charge, and the herbicide’s manufacturer, Novartis AG in Switzerland, blasted the study as an attempt to panic parents.