These days, parents can choose from a wide variety of baby formulas, including versions enriched with vitamins, iron and even brain-boosting fatty acids. A new study from scientists at the Centers for Disease Control and Prevention, however, found a chemical not mentioned on the label: perchlorate, a component of rocket fuel that's linked to thyroid disease. In a small study of 15 powdered formulas, scientists found that all were contaminated with perchlorate. Cow's milk formula with lactose had the highest perchlorate levels, compared to formulas that were soy-based, lactose-free or "elemental," which are made with synthetic amino acids for babies who can't digest standard formulas. Scientists did not name the brands tested. Perchlorate has been found to contaminate the drinking water in 28 states and territories, according to the Environmental Working Group, which supports stronger regulation of the chemical. In this study, scientists mixed the baby formula using only perchlorate-free water, according to the study, published online March 18 in the Journal of Exposure Science and Environmental Epidemiology. Authors said that perchlorate harms the thyroid -- which acts as the body's thermostat, regulating a variety of essential functions -- by preventing the body from properly taking in iodine. Concerned parents should make sure that their infants have a diet with sufficient iodine, which can counteract perchlorate's harmful effects, authors say. Authors added that their study didn't actually measure perchlorate in infants. That sort of study is essential, they say, because it will tell scientists if infants are absorbing the perchlorate to which they may be exposed. Lisa Jackson, the new administrator of the Environmental Protection Agency, has pledged to act quickly to reduce perchlorate contamination in drinking water. --By Liz Szabo, USA TODAY