In Europe, the weedkiller atrazine has been banned for nearly two decades because of its suspected links to reproductive problems like reduced sperm quality and birth defects. In the United States, it remains one of the most widely used pesticides, sprayed on corn, sugar cane and other crops, the result of years of industry lobbying. This week, a "Make America Healthy Again" commission led by Health and Human Services Secretary Robert F. Kennedy Jr. is set to issue a report on the causes of chronic illnesses in the United States. And Mr. Kennedy, who worked for years as an environmental lawyer fighting chemical companies, wants the report to highlight the harms of pesticides like atrazine. "We're calling for a ban of 85 pesticides that have already been banned in other countries," said Zen Honeycutt, who leads a coalition of mothers opposed to pesticides and genetically modified organisms, at a national conference of Make America Healthy Again supporters. "Big Ag, Big Food, Big Pharma, the pesticide companies, all of these companies are the delivery mechanisms for toxins," said Tony Lyons, co-president of the newly established MAHA Institute, which hosted the MAHA conference. "Our government agencies shouldn't be protecting a handful of the most powerful companies on earth, protecting their profits over the welfare of its own citizens." The E.P.A. is currently updating its mitigation proposals for atrazine.