The Case for Taking Precautions
Rier's account of the sick monkeys, first published in 1993, jolted researchers around the world. In the next 10 years, the researchers pieced together evidence of a "strong association" between dioxin and endometriosis, says Dr. Linda Birnbaum, PhD, one of the EPA's leading dioxin experts and director of experimental toxicology at the agency's National Health and Environmental Effects Research Laboratory in Research Triangle Park, North Carolina. Dr. Birnbaum, EPA colleague Audrey Cummings, and their coworkers discovered that surgically implanted endometrial growths in rats and mice increased in size as doses of dioxin increased. Several smaller studies have suggested elevated blood levels of dioxin in women with the disorder. Also, Rier and other researchers have found similar abnormalities in the monkeys' immune systems and in those of women with the disease.
What scientists haven't yet found is definitive proof that dioxin causes endometriosis in humans—or, if it does, exactly how the chemical wreaks its havoc. This doesn't bother patient-activists such as Lynn Castrodale, the Endometriosis Association's former environmental coordinator. "Human studies are hard to do with all the toxins we're exposed to over a lifetime," she says. "What we subscribe to is the precautionary principle. We know dioxin causes cancer and endometriosis in animals. We feel industry, government, and human beings in general should be more careful about how this chemical is dispersed."
Despite stiff environmental laws and improved industrial processes, dioxin remains among the most ubiquitous poisons on the planet. What's more, says Dr. Birnbaum, "It doesn't go away." The contaminant has a half-life of 10 years, giving it plenty of time to accumulate in soil, water, and, especially, in fatty tissues in animals and humans.
The earlier the exposure, the more damage the chemical seems to cause. In studies of the residents of Seveso, Italy, who survived an industrial accident in 1976 that spewed huge amounts of dioxin into the air, researchers found that girls younger than age 10 who were exposed had higher levels of the chemical in their blood later in life than did the adults. "This suggests that girls exposed before puberty may have more difficulty getting rid of compounds than adults," says Rier.
Other research indicates that prenatal exposure may be especially problematic. In a recent EPA study, fetal mice exposed to dioxin were significantly more vulnerable to a second dose later in life, developing larger lesions than mice that hadn't been exposed in the womb.
Ballweg and others believe such "hardwiring" may explain why the incidence of endometriosis seems to be rising in industrial countries. "Japan has 10,000 times the level of dioxin that we do, because they burn all their waste," she says. "They have a huge endometriosis problem." In the United States, "the disease is starting younger, and we know it's more severe and disabling than it used to be," she adds. Her theory: "These kids were exposed to dioxin prenatally."