Nursing mothers could inadvertently be feeding their newborns nearly twice the recommended safe amount of perchlorate, a key ingredient of rocket fuel, according to a new study from Texas Tech University.
Iodine deficiency has been linked to thyroid disorders in developing children, which can slow brain development and lead to mental retardation.
If the findings can be verified in a wider study, they could become the most powerful weapon yet in a fight led by environmental groups to clean up perchlorate-contaminated sites around the United States.
The contamination is mostly caused by leaks and dumps at factories owned by the aerospace and defense industry, according to the National Academy of Sciences.
The perchlorate is then thought to seep into sources of public drinking water and irrigation channels.
"A national drinking water standard must be set promptly and all known sources of contamination cleaned up," said the Washington, D.C.-based Environmental Working Group in a statement issued Tuesday.
"After years of delay in setting of safety standards and cleaning up contaminated sites, the high levels of perchlorate found in breast milk should be a wake-up call to state regulators, U.S. EPA, the Department of Defense and the Bush administration that no more delays can be tolerated."
In an analysis of breast milk samples from 36 women in 18 states, researchers at Texas Tech found that all the samples had some level of perchlorate contamination, with an average of 10.5 parts per billion.
Under new guidelines from the Environmental Protection Agency, newborn infants should ingest no more than half that amount.
The researchers found that higher levels of perchlorate in the breast milk were linked to lower levels of iodide, the form of iodine found in the human body.
For its part, the EPA is being careful not to set a water quality standard that is too low or high.