Is Pollution Wrecking Your Fertility?

What they discovered astonished them. Seventy-nine percent of the monkeys had the condition; the more dioxin in their diets, the worse the disease. "The results were so striking we almost fainted," says Ballweg.

Rier's finding galvanized endometriosis research and, more generally, persuaded scientists to study how chemicals in the environment may affect women's health by disrupting their hormonal and immune systems. In the disease, which affects about five million American women, the abnormally located tissue is not a benign phenomenon. It often develops into lesions or cysts that can cause scarring and infertility. Endometrial growths may bleed once a month, but while blood sloughed from the uterus can rain from the body, blood from endometriosis is trapped, causing inflammation and terrible cramping. (In one poll of 4,000 patients, 79 percent said they had experienced pain so severe that they had been incapacitated from one to six days at a stretch.)

The usual treatments—painkillers, hormones, or surgical removal of lesions, cysts, and scar tissue—work spottily at best, perhaps because scientists don't understand endometriosis. The lack of good treatment doesn't merely frustrate women, consigning them to cyclic pain; it may lead to problems.

Researchers have linked endometriosis to a higher incidence of breast and ovarian cancers and malignant melanoma, as well as to autoimmune disorders such as fibromyalgia and lupus. "We'd been looking at many causes for endometriosis"—like a malfunctioning immune system and menstrual blood flowing in the wrong direction—"but not dioxin," Ballweg says. "Who'd think that dioxin would have anything to do with it?"

Dioxin, or TCDD, is considered the most poisonous man-made, organic chemical, second in toxicity only to radioactive waste. It belongs to a class of substances known as endocrine disruptors, which have a discombobulating effect on human hormones—mimicking or blocking hormone function and disrupting everything from the thyroid and adrenal systems to the reproductive system.

An unwanted byproduct of the manufacture, molding, and burning of plastics and organic chemicals that contain chlorine, dioxin is a contaminant in certain herbicides (most notoriously, the Vietnam-era defoliant Agent Orange), and the byproducts. Today the biggest sources are uncontrolled burning of waste, certain metal processes, and dioxin-contaminated sediment in reservoirs and rivers that gets stirred up to the surface.

Exposure can cause cancer, heart disease, diabetes, reproductive abnormalities, and developmental problems in children—everything from low IQ to fragile teeth, according to the Environmental Protection Agency (EPA). Just a tiny amount may be too much. Some of the rhesus monkeys were fed only five parts per trillion of dioxin per day—an amount roughly equal to spitting into an Olympic-size swimming pool.