Dioxin linked to reproductive disorder.
In a study of rhesus monkeys exposed to TCDD, Sherry E. Rier of the University of South Florida College of Medicine in Tampa and her colleagues found that TCDD's effects on the body's hormonal and immune systems (SN: 1/11/92, p.24) may underlie the endometriosis-dioxin link, she says. "Chronic immunosuppression in combination with hormonal dysregulation may have facilitated the aberrant growth of endometrial tissue" in the monkeys, the team writes in the November FUNDAMENTAL AND APPLIED TOXICOLOGY.
In endometriosis, endometrial cells grow outside their usual home in the uterus, form nodules in such places as the fallopian tubes or ovaries.
The study is "strongly supportive" of a link between TCDD exposure and the disease, says Linda S. Birnbaum, director of environmental Protection Agency in Research Triangle Park, N.C.
Endometriosis had been found in rhesus monkeys exposed to polychlorinated biphenyls (PCBs) and to radiation. TCCD, however, had not been implicated.
For four years beginning in 1978, Rier's group fed 14 monkets a TCDD-laced diet as part of a study on the health effects of that chemical. Autopsies on three monkeys that died between 1990 and 1992 uncovered endometriosis and prompted the researchers to examine the other animals.
The team found that five of the seven animals that had received a large dose of the chemical -- 25 parts of TCCDD per trillion parts of flood (ppt) -- developed moderate to severe endometriosis. There of the seven given 5 ppt of TCDD had moderate to severe disease. Other monkeys, including two of six fed a normal diet, developed a very mild form of the disease.
Stores of TCDD peaked at 100 to 800 parts per trillion in the body fat of the monkets, says Robert E. Bowman, a retired behavioral toxicologist and member of the study team. However, people and animals vary considerably in how much dioxin they store, he warns. At about 100 ppt of TCDD, monkeys "are getting into dangerous territory" regarding the risk of endometriosis, he says. The body fat of most humans contains about 7 ppt of TCDD, says Bowman.