Babies born to mothers with high levels of perchlorate during their first trimester are more likely to have lower IQs later in life, according to a new study.

The research is the first to link pregnant women's perchlorate levels to their babies’ brain development. It adds to evidence that the drinking water contaminant may disrupt thyroid hormones that are crucial for proper brain development.

Perchlorate, 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.

“We would not recommend action on perchlorate levels from this study alone, although our report highlights a pressing need for larger studies of perchlorate levels from the general pregnant population and those with undetected hypothyroidism,” the authors from the United Kingdom, Italy and Boston wrote in the study published in The Journal of Clinical Endocrinology & Metabolism.

The Environmental Protection Agency for decades has debated setting a national drinking water standard for perchlorate. The agency in 2011 announced it would start developing a standard, reversing an earlier decision. In the meantime, two states, California and Massachusetts, have set their own standards.

EPA officials said they expect to unveil their proposed standard in the summer of 2015, missing their deadline by two years. They would not comment on the new findings.

The researchers analyzed perchlorate levels in the first trimester of 487 pregnant women in Cardiff, Wales, and Turin, Italy, who had iodine deficiency and thyroid dysfunction during pregnancy and examined their children’s IQ scores at 3 years old. Children born to mothers’ with perchlorate levels in the highest 10 percent were more than three times as likely to have an IQ score in the lowest 10 percent.

Dr. Craig Steinmaus, an associate adjunct professor of epidemiology at the University of California, Berkeley School of Public Health, said it was a strong, first-of-its-kind study. “It’s not definitive, but it is certainly intriguing,” said Steinmaus, who was not involved in the research.

The study, however, did not factor in information about the home environment and the mothers’ IQs, which can affect children’s IQs.

Thomas Zoeller, a biology professor who specializes in thyroid hormones at University of Massachusetts-Amherst, said it is “very well established” that perchlorate can inhibit transport of iodine to the thyroid. Iodine is an essential component of thyroid hormones, and “severe iodine deficiency is the leading preventable cause of mental deficiency in childhood,” the authors wrote.

“Even mild hypothyroidism and/or hypothyroidism for a short period of time may have adverse neurocognitive effects in later childhood,” said Dr. Angela Leung, a clinical assistant professor of medicine at the University of California, Los Angeles, who was not involved in the study.

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.

The new results were “somewhat surprising,” said Dr. Elizabeth Pearce, the study’s senior author and associate professor at the Boston University School of Medicine, because an earlier study of the same women found that perchlorate levels were not associated with the women’s thyroid function. It’s possible, however, that the perchlorate acted directly on fetal hormones since it is transmitted across the placenta.

The study is limited in that perchlorate has a short half-life so a one-time urine test is not a good measure of long-term exposure, Zoeller said. If perchlorate did reduce the babies’ cognitive function, it would be a time-sensitive event, he said.

“We can’t say the fetus in the first trimester is impervious to maternal thyroid disruption from perchlorate exposure. But we don’t have evidence that it is a sensitive time either,” Zoeller said.

The researchers didn’t measure the newborns’ hormone levels, so they couldn’t confirm that perchlorate exposure altered them. Previous research shows it’s possible: A 2010 study of a half million California babies linked estimated perchlorate exposure to an increase in thyroid stimulating hormones, which indicates a drop in thyroid hormones. 

All of the women in the new study had perchlorate in their urine. The median in the highest 10 percent was more than 5 times higher than the median levels of women in a past study of U.S. women and 10 times higher than a study of Thai women. While this study took place in Europe, perchlorate exposure is “pretty much ubiquitous,” Pearce said. “We’re all exposed to low levels.” It isn’t clear how the women in the study were exposed.

Aerospace industry groups and water suppliers have long maintained that the levels of perchlorate found in some food and drinking water do not pose risk to human health and do not warrant federal regulation.

The American Water Works Association, which would not comment on the new study, advocated for more information on iodine intake instead of perchlorate regulation in a 2012 letter to the EPA. 

Cleaning up perchlorate in groundwater and water supplies could cost billions of dollars.

In April, the EPA announced a $1.1 billion perchlorate settlement at a former Kerr-McGee Chemical manufacturing site in Henderson, Nev., which has the nation’s largest perchlorate groundwater plume. The plume contaminated Lake Mead, which feeds into the Colorado River. The river provides much of the drinking water in the Southwest.

Also, in 2012, multiple companies and the Department of Defense paid a settlement of almost $50 million to clean up perchlorate-contaminated groundwater in Rialto, Calif. 

“Clearly [perchlorate] is ubiquitous, and various studies keep showing that it could harm health, especially for sensitive populations like pregnant women, fetuses and infants,” said Andria Ventura, a program associate with Clean Water Action based in Oakland, California. “We need to regulate it nationally.”

This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.