Perchlorate (environmentalhealthnews.org), which is both naturally occurring and manmade, is used in rocket fuel, fireworks and fertilizers. It has been found in 4 percent of U.S. public water systems serving an estimated 5 to 17 million people, largely near military bases and defense contractors in the U.S. West, particularly around Las Vegas and in Southern California.
Previous studies have linked perchlorate exposure to altered thyroid function in mothers and women. However, Zoeller said what scientists don't know is how and to what extent perchlorate in a pregnant woman might impair the mental abilities of her children. He said it is "very difficult" to pin chemical exposure during pregnancy to impacts on the fetus or child.