Are industrial pollutants blurring the genetic boundaries between male and female?
Forget about doomsday asteroids and the Ebola virus. The real threat to life on earth may be the Florida alligator’s vanishing penis. That’s only one example of a curious blurring of the sexes that researchers have been finding among wild animals around the world. In terms of reproductive health, the males of certain species aren’t measuring up. Though a definite cause has yet to be found, several studies point to “gender-bender” pollutants that may be disrupting animal hormones—including ours.
Hormones are the chemical messengers of the body’s endocrine system. As Catherine Dold writes in Discover (Sept. 1996), hormones travel from the various endocrine glands to “tell cells what to do and when to do it.” Their role in fetal development is profound. Hormones “tell the fetal cell what it will be when it grows up,” a process that determines, among many other things, an individual’s sex.
The problem, writes Dold, is that “chemical impostors” may be upsetting fetal growth at the crucial moment of sexual differentiation. “Many researchers now believe that a small army of common chemicals can somehow imitate natural hormones,” she adds, and “derail an animal’s development, permanently distorting its reproductive, immune, and neurological systems.” The theory would explain why male alligators in Florida’s Lake Apopka, the site of a pesticide spill in 1980, developed stunted reproductive organs. And why male fish near sewage plants emptying into Britain’s rivers produce a protein normally found in females’ eggs. Similar cases have appeared among eagles, whales, otters, and other animals.
The list of possible “endocrine disrupters” now tops 50, including the usual suspects: pesticides like DDT, atrazine, and chlordane as well as dioxin, PCBs, and heavy metals. Even more disturbing, several seemingly less odious chemicals—such as certain substances in plastics, paints, cosmetics, adhesives, and inks—may have a similar effect.
In the case of male sexual development, there are at least two possible causes of “demasculinization.” Chemicals may be blocking the androgens, or male hormones like testosterone, by binding to fetal cells in their rightful place. They can also mimic estrogen, the female hormone, thus triggering estrogenic effects. The amounts needed are small; in fact, in terms of damage, less is often more. Odder yet, these substances don’t resemble estrogen in a molecular sense, which only complicates the puzzle.
As Diana Lutz reports in The Sciences (Jan.-Feb. 1996), some scientists link endocrine disrupters with declining reproductive health among human males. The rates of testicular cancer and genital deformities have risen, while male fertility has fallen, according to some studies. One in six couples now has trouble conceiving. Researchers once assumed these problems originated with women, but now suspect that men may be the cause as often as half the time. Though there’s no ironclad proof that gender-bending chemicals are to blame, “the general feeling is that the evidence gained so far is too plausible to ignore.”
No one doubts that endocrine disruption can be chemically induced in humans. Between 1945 and 1971, 5 million women took diethylstilbestrol, or DES, a synthetic estrogen thought to prevent miscarriages. Its role as an agent of abnormal fetal development—in males as well as females—is now well documented.
Even so, some think the danger posed by synthetic endocrine disrupters may be overstated. They note, for instance, that many fruits contain natural substances that mimic estrogen. But proponents of the theory argue that animals exposed to such substances for millions of years have developed ways to neutralize them. That can’t be said of a molecule whipped up in a lab only a few decades ago. Synthetic chemicals may also biodegrade more slowly and thus accumulate in the body.
If the risk of endocrine disrupters proves to be real, more than sexual development may be affected. Theo Colborn, a senior scientist with the World Wildlife Fund and co-author of Our Stolen Future (Dutton, 1996), thinks such chemicals may be causing other impairments, including subtle forms of nerve and brain damage in children.
Colborn’s theory bucks the current tendency to seek the cause of many disorders in the genes. Profound changes in an organism can occur without genetic involvement, she notes, which in a way is good news: A “cure” lies simply in changing the beliefs and habits that lead to the overuse of industrial chemicals, beginning with the models now used to determine “safe” levels of chemical exposure. The real issue may not be how much of a toxic substance causes cancer or knocks you dead, but how little can alter a being’s destiny at the very earliest stages of life.