So there's this weed killer used just about everywhere in the U.S. For some details:

Atrazine is the second-most widely used herbicide in the United States. Manufactured by the chemical giant Syngenta, farmers have sprayed, on average, 70 million pounds of the weed killer on cropland across the country for the last twenty years. Half of the corn grown in the United States — some tens of millions of acres — is treated with atrazine.