IF YOU KNEW WHAT YOU WERE SEEING, the signs were already appearing at the dawn of the chemical age. In 1947, ornithologists noticed that eagles in Florida had lost their drive to mate and nest. In the 1960s, ranch minks that were fed fish from Lake Michigan failed to reproduce. In 1977, female gulls in California were nesting with females. In the 1980s, alligators in Florida's Lake Apopka were turning up with shrunken penises. In 1992, Danish researchers announced that human sperm counts worldwide had plunged by 50 percent between 1938 and 1990. If there was a pattern here, linking lesbian gulls to men shooting blanks, it wasn't obvious. But Theo Colburn of the World Wildlife Fund thought she discerned one: exposure to man-made chemicals that have an uncanny ability to mimic powerful natural hormones. Now 51 such impostors have been identified, each able to unleash a torrent of effects such as regulating sperm production and cell division and sculpting the developing brain.
Small wonder these "endocrine impostors" have become the toxic scare du jour. Colburn's book, "Our Stolen Future" (306 pages. Dutton. $24.95), written with Dianne Dumanoski of The Boston Globe and zoologist John Peterson Myers, hits stores this week on a wave of media hype. The chemical industry and its boosters are matching them fax for fax, trotting out scientists who dispute the idea that synthetic chemicals wreak havoc on the endocrine system. Vice President Al Gore wrote an impassioned foreword to "Stolen Future," laying out a tomorrow plagued by "infertility; genital deformities . . . breast and prostate [cancer] and neurological disorders," and this week he makes a major speech warning of the dangers the hormone mimics pose. The National Academy of Sciences has launched a study of the chemicals, and the Environmental Protection Agency is poised to make them a top research priority. And even while denying that the chemicals are dangerous, industry is scrambling to find substitutes that do not act like hormones.
As usual with suspect chemicals, the most damning evidence comes from animal studies. Vinclozolin, a fungicide whose residues are often found on fruit, slips into the receptor meant for testosterone, causing male rats to become hermaphrodites. Dioxin, produced when chlorine-containing compounds burn, can mimic estrogen: it halves sperm production in rats. PCBs, used in electrical transformers, ape thyroid hormones, which sculpt the developing brain; rats exposed to PCBs in the womb and infancy tend to be hyperactive. A plastic called p-nonylphenol masquerades as estrogen; in lab animals, finds John Sumpter of Britain's Brunel University, it can inhibit the growth of testicles. Another estrogen mimic, bisphenol-A, can leach from the five-gallon polycarbonate jugs of bottled water, reports Stanford University's David Feldman, as well as from the plastic lining of food cans.
"Stolen Future" concedes that "no one yet knows how much it takes of these . . . chemicals to pose a hazard to humans." But early signs are not reassuring. Rates of testicular cancer, which is linked to estrogen, are up -- in Denmark, by 300 percent over the last 50 years. Prostate cancer, also estrogen-sensitive, has risen 126 percent in the United States since 1973, even after taking into account the aging of the population, finds the National Cancer Institute. And studies of children whose mothers ate PCB-laced fish during pregnancy find IQ deficits of about four points and abnormalities such as attention-deficit disorder. "PCBs, which mimic thyroid hormones, have a profound effect on the developing brain," says neuroendocrinologist Peter Hauser of the University of Maryland. And unlike chemicals whose ability to cause cancer shows up only in megadoses, endocrine disrupters exert effects at tiny, real-world doses.
Even critics don't dismiss these findings entirely. The Chemical Manufacturers Association says the "theory deserves a full and complete scientific investigation." One issue is whether the effects of the hormone impostors on gators are relevant to people. Toxicologist Stephen Safe of Texas A&M, for one, contends that "you can't extrapolate from wildlife to humans." While it's a cliche to call for more research, CMA is right to. Which plastics leach the most potent hormone mimics? Who is more vulnerable to hormone disruptions, a fetus or a newborn? If it's the infant, should women breast-feed, since human milk is laced with PCBs? Is the rise in prostate and breast cancers real, or an artifact of more screening? Are sperm counts falling? A paper by Columbia University's Harold Fisch will report no decline in counts among men in three U.S. cities in the last 25 years. Still, as industry and government scramble for answers, it may be prudent to try the bottled waters that come in glass. ..MR.-
51 synthetic chemicals have been found to act like hormones, triggering biological reactions that affect the brain and the immune and reproductive systems. Among them:
leaches from polycarbonate water jugs
a near-ubiquitous byproduct of combustion
added to PVC plastic; also a byproduct of the breakdown of industial detergents and pesticides
in electrical transformers
a common fungicide