Women exposed to high levels of flame retardants take substantially longer to get pregnant, indicating for the first time that the widespread chemicals may affect human fertility, according to a study published Tuesday.

Furniture cushions, carpet padding and other household items contain hormone-disrupting flame retardants called polybrominated diphenyl ethers, or PBDEs. Two of the most widely used compounds have been banned in the United States since 2004, but they remain ubiquitous in the environment, inside homes and in the food supply.

Epidemiologists from the University of California at Berkeley studied 223 pregnant women in California’s Salinas Valley, an agricultural community with predominantly low-income, Mexican immigrants.

More than 97% of the women had PBDEs in their blood, and those with high levels were half as likely to conceive in any given month as the women with low levels.

“This study provides the first evidence that PBDEs may impact human fertility,” wrote the authors, led by epidemiologist Kim Harley, in the study published online in Environmental Health Perspectives. "If confirmed, this finding would have strong implications to women trying to conceive given that exposure to PBDEs is nearly universal in the United States and many other countries."

Harley said “the results are surprisingly strong.”

“These findings need to be replicated, but they have important implications for researchers,” she said.

Each ten-fold increase in a woman’s blood was linked to a 30 percent decrease in her odds of getting pregnant.

Previously, laboratory tests have found altered male hormones and reduced sperm counts in animals exposed to PBDEs. But this study is the first to find reduced human fertility.

“Very little research” related to the flame retardants has been conducted in humans, Harley said.

The researchers do not know how the chemicals may be reducing fertility. They did not study the fathers, who probably also were highly exposed, so it is possible that the men’s fertility was reduced, not the women’s, particularly since it is males who are harmed in the animal tests. Some PBDEs mimic estrogen, while others can block testosterone.

Dr. Arnold Schecter, a University of Texas School of Public Health environmental scientist who was not involved in the study, said even though nearly all the women in the study were Hispanic, "the results might be generalizable to many American women."

"Elevated levels of PBDEs might be a risk factor for reduced fertility," said Schecter, who studies how people are exposed to the flame retardants.

None of the women - chosen for the research because they were pregnant - were infertile, and they conceived, on average, after three months.

But the chemicals may be pushing some women into the ranks of the sub-fertile, which means it is difficult to conceive. About 15 percent of the women in the study took longer than 12 months to conceive.

More than 2.1 million couples in the United States are infertile, according to the Centers for Disease Control and Prevention.

“Because exposure to PBDEs is ubiquitous in industrialized nations, even small decreases in fecundability may have wide-reaching public health impacts,” the scientists said in their study.

The tests measured the chemicals in the women's blood while they were pregnant,  so their levels when they were trying to conceive could have been higher or lower. A similar study should be done in women before pregnancy, Schecter said.

The PBDE study was part of a decade-long project by the UC Berkeley scientists to examine whether environmental factors are harming the health of Salinas Valley mothers and children. The women are highly exposed to pesticides, which also have been shown to reduce fertility, but the researchers controlled for pesticide exposure in their study, as well as length of time in the United States, smoking and other potential factors.

In addition to reproductive effects, animal tests have found that PBDEs can alter brain development and thyroid hormones, which regulate growth and development of cells and many key bodily functions.

Scientists say the brominated flame retardants are among the most worrisome contaminants because they accumulate in animal and human tissues – including breast milk - and they persist in the environment.

Because of their widespread use in the United States, Americans are the most highly contaminated with PBDEs, carrying 20 times higher levels in their bodies than Europeans. Californians are the highest exposed, probably because manufacturers added PBDEs to polyurethane furniture cushions to meet the state’s stringent flammability rules.

Brenda Eskenazi, a UC Berkeley epidemiologist who was the study’s principal author, said exposure to the chemicals “is likely to continue for many years.”

“In our research, we have found that low-income children in California are exposed to very high levels of PBDEs, and this has us concerned about the next generation of Californians,” Eskenazi said.

Nearly every American tested contains traces of penta and octa BDE, the two formulations most widely used in furniture. California banned penta and octa in 2004, then the U.S. Environmental Protection Agency followed.

Couches, carpet pads and other products manufactured before 2005 still contain the compounds, and they leach out, contaminating dust and getting into the environment, including the food supply.

Linda Birnbaum, director of the National Institute of Environmental Health Sciences, said in a recent interview with Environmental Health News that she is concerned about the levels of PBDEs that remain in households and in the environment.

“There is no convincing evidence that PBDEs are declining in people or wildlife in the United States. It’s too soon...The chemicals are still getting into the environment from existing products,” she said.

Concentrations in Europeans have been decreasing. But Schecter found that they are increasing in the United States, despite the bans. "There is no reason to believe a POP [persistent organic pollutant] will quickly decrease in the environment or in people," he said.

In addition, new brominated and chlorinated flame retardants are replacing the old ones, and their potential human effects are unknown.

Some scientists wonder if the new flame retardants are just as bad as the banned ones.

"In this country, we kind of jump from the proverbial fry pan into the fire without thinking about the alternative,” Birnbaum said.

Last month, the EPA listed PBDEs as “chemicals of concern,” which means they “may present an unreasonable risk of injury to health and the environment.” That triggers a review by the EPA that may lead to regulation.

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