Dr. Paul Winchester’s passion is delivering healthy babies.

In 2001, he moved to Indiana to work at a hospital based in Indianapolis. But he soon grew alarmed at the high number of premature babies and birth defects he was seeing among newborns. “(From 1999 to 2002) Indiana had more birth defects than the rest of the country,” says Winchester, who is now director of his hospital’s neonatal intensive care unit and a professor of pediatrics at Indiana University’s school of medicine.

Winchester began looking for the cause of the birth defects, convinced they were being triggered by an environmental contaminant. “It needed to be a contaminant that can be seen in just about everyone,” he explains, “something that would have affected the whole state. And atrazine fits that bill.”

Indiana is smack in the heart of America’s corn belt. And corn farmers spray their crops with the herbicide atrazine to kill weeds. Manufactured primarily by the Swiss agribusiness conglomerate Syngenta AG, atrazine is one of the world’s most popular herbicides – and the one most commonly found in drinking water in the US, and probably worldwide. “We find that drinking water in Indiana is almost never free from atrazine,” says Winchester.

Winchester felt atrazine might be causing birth defects because the number of cases increased during the period when atrazine was sprayed most heavily on crops – from April to July. During those critical months, surface-water concentrations of pesticides and other agricultural chemicals rose. “We, in a sense, discovered the tip of an iceberg of correlations between pesticides and adverse outcomes,” notes Winchester.

He began writing papers for medical journals linking atrazine to birth defects. Winchester’s research was also used in a lawsuit launched by Stephen Tillery, a St. Louis, MO-based lawyer, who sued Syngenta in 2004 on behalf of Illinois towns and Midwest water districts, claiming atrazine had contaminated their water supplies. This lawsuit was settled in 2012 for (US) $105-million without going to trial – and after Tillery got access to Syngenta’s internal files. “It’s unbelievable,” remarks Tillery. “I mean, imagine why somebody would pay you one hundred per cent of your damages plus your fees? Why would they do that? I mean, they didn’t want me to have a trial.”

But it’s not only birth defects atrazine is linked to: it’s been fingered for wiping out frog, fish and other aquatic wildlife populations, causing sexual abnormalities in amphibians (and possibly people), and of triggering various forms of cancer. In fact, the EU banned atrazine in 2003 due to its contamination of groundwater.