by Environmental Working Group

About the author: The Environmental Working Group is a Washington, D.C., environmental organization that studies concerns such as agriculture, pesticides, drinking water, and toxic waste.

Beginning on May 15, 1995, a network of environmental organizations began testing tap water for weed killers in cities across the U.S. Corn Belt, in Louisiana, and in Maryland.

Samples were collected every three days from people’s homes or offices. Samples collected were sent to the Iowa State Hygienic Lab and analyzed for the presence of atrazine and cyanazine, two of the most heavily used pesticides in all of the United States.

On or about the first day of June and July, larger samples were taken from the same locations and more extensively tested for 11 weed killers and their by- products.

The purpose...