Women who have been exposed to two now-banned pesticides may have an increased risk of developing endometriosis, a chronic and often debilitating condition that can cause symptoms such as severe pelvic discomfort, painful periods – and even infertility.

Despite the fact that endometriosis affects up to 10 percent of reproductive-aged women, no one has a clear understanding as to why it develops in some women and not others, according to study author Dr. Kristen Upson, a postdoctoral fellow at the epidemiology branch of the National Institute of Environmental Health Sciences.

Based on the knowledge that endometriosis is an estrogen-driven condition, Upson and her fellow researchers decided to examine whether certain chemicals with estrogenic properties might be linked to an increased risk for the disease. They homed in on organochlorine pesticides, which they suspected might interfere with normal hormonal activity.  

In a study published in the journal Environmental Health Perspectives, researchers from the Fred Hutchinson Cancer Research Center studied blood tests of 248 women who had recently been diagnosed with endometriosis, comparing them to blood tests of 538 women without the disease.  

Overall, women who had high levels of exposure to two pesticides – beta-hexachlorocyclohexane and mirex – had a 30 to 70 percent increased risk of having endometriosis.

Beta-hexachlorocyclohexane, was a chemical byproduct of an agricultural insecticide widely used throughout the 1970s. The other chemical, mirex, was used in the 1960s and 1970s as part of an insect control program against fire ants and was aerially applied over millions of acres in the southeastern United States, according to Upson. While both substances were eventually banned or severely restricted over concerns about their effect on the environment and human health, they still linger in the environment.

“If you have chemicals sitting in the sediment of water and you have the little fish (exposed), being eaten by big fish, you’re having this chemical become more and more concentrated,” Upson said.

While these findings may seem concerning, Upson said that these chemicals are gradually disappearing in the environment and will continue to do so as time passes.

“The good news is that these two chemicals are no longer being used or produced in the U.S.,” Upson said. “Generally speaking, in the population, we’re seeing blood concentrations decline over the years and global efforts being made to reduce and eliminate these chemicals as well.”

Overall, Upson hopes this research will highlight the fact that dangerous chemicals can continue to negatively impact the health of the U.S. population for years after being banned.

“I think it’s really important to continue doing endometriosis research just because of the impact on the quality of women’s lives, and it’s important to continue to ask about environmental chemicals and other risk factors,” Upson said. “The key message from our study is that persistent environmental chemicals may affect the current generation of reproductive age women.”