The dog had been housebroken. Then Joseph von Mering and Oskar Minkowski decided to operate. They took out its pancreas–a tricky business in 1889 in the then-German city of Strassburg–so that they could better study how the body reabsorbs fats. The operation succeeded; the dog recovered. Then it started peeing on the floor.
Take polychlorinated biphenyls, PCBs, until recently used to insulate and fireproof electrical equipment. They can interfere with thyroid hormones, which stimulate brain development in the growing fetus. “Only thyroxine (T4), bound to transthyretin, is capable of entering the fetal brain,” Dr. Ted Schettler of Physicians for Social Responsibility told a July 14 symposium in Chicago on endocrine disrupters. “Some PCBs lower T4 levels and displace T4 from transthyretin” so it can’t get in, a problem that might lead to hypothyroidism. PCBs are stored in body fat and are shared across the placenta between mother and child. “Longitudinal studies of humans over time show that even transient hypothyroidism at birth is associated with IQ deficits later in life.”
Endocrine disrupters are usually accused of deforming or sickening people or animals, not killing them outright. But Rabb and some other herpetologists speculate that they might have something to do with the disappearance of frog species around the world. Rabb mentioned the work of field biologist Karen Lips, who earlier this year found just 24 amphibian species in a protected Panamanian mountain forest that had sheltered more than 55 in 1995. “I found 54 dead or dying frogs belonging to 10 species,” she wrote in “Froglog” (June), the newsletter of the Declining Amphibian Populations Task Force. “Many of the casualties still had a very life-like appearance; most were found during morning surveys, still sitting in a perched position.” (Lips didn’t mention endocrine disrupters in her report. She suspected a virus or other disease.)
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“We’re not just affecting humans–we’re affecting all life,” Rabb said, then paused. “And we’d better know what we’re doing.” He walked away from the microphone and out of the room.
Along with synthetic chemicals, the body’s endocrine system itself is a 20th-century discovery. “Before 1920 endocrinologists basically dealt with the unusual,” Henry Anderson, chief medical officer of Wisconsin’s Bureau of Public Health, told the July 14 endocrine-disrupter symposium. “They dealt empirically with patients who were too fat, too thin, too short, too tall, too tired, too hairy or not hairy enough, and those with all sorts of sexual problems.” Experiments, as we have seen, were crude.
Trial and error showed the way again in 1975 when a Hopewell, Virginia, spill exposed workers to the now-banned pesticide kepone. Researchers found that kepone was a weak estrogen and that male workers exposed to the stuff had very low sperm counts. This effect became the subject of national scientific conferences in 1979 and 1985. A chemical designed for another purpose altogether, with a molecular structure quite unlike natural estrogens, had disrupted normal hormone-message transmission in the body. How many others could do that? With what results? Clearly the great human endocrine-disrupting experiment was already in high gear–an unintended experiment with no controls, on subjects who neither knew about nor consented to it.
A recent study of mice and DES by the University of Missouri’s Frederick vom Saal and his colleagues also shows that less can be more. When male mouse fetuses were given DES in parts per trillion they grew up to have significantly and permanently enlarged prostate glands. But when they got a thousand times more DES (parts per billion), their prostates were reduced in size. In normal toxicology the dose makes the poison, and more is worse. In endocrine-disrupter land, high and low doses may have opposite effects.
