A newly discovered biological property of DDT may be a key factor in the worldwide rise of male reproductive abnormalities in animals and humans, including malformed sexual organs, testicular cancer and related problems.
Scientists have reported such conditions with growing frequency over the past 50 years, a period coinciding with the introduction and widespread use of DDT. Many researchers believe the insecticide is responsible for many male reproductive problems because it chemically mimicks natural estrogens, a family of female sex hormones, and thus would have a “feminizing” effect on male fetal development.
This “estrogenicity” of DDT has been implicated in events as diverse as the fact that insecticide-exposed alligators in Florida’s Lake Apopka have abnormally small penises, the controversial reports that sperm counts in some European populations are dropping by as much as 2 percent per year, and the recent dramatic increase in testicle cancer rates in Denmark.
Now researchers from the Environmental Protection Agency and the University of North Carolina have found yet another sex-linked function of the compound. They report in Thursday’s issue of the journal Nature that a substance called DDE which is DDT’s principal breakdown product in the body - is a very powerful inhibitor of male sex hormones called androgens.
That property, they suggest, may help cause “the reported increased incidence of developmental male reproductive system abnormalities in wildlife and humans.”
The scientists determined that, in lab rats, DDE prevents androgens from binding to their specialized receptors in the body, and thus keeps them from doing their jobs, one of which is making male fetuses masculine in structure.
After confirming the compound’s “hormone-blockade” effects in test-tube studies, the team fed large amounts of the substance to pregnant rats. Their male pups were born with numerous female characteristics, including nipples on the chest. When normal young rats were fed the compound, their puberty was delayed. When normal adult male rats got DDE, their seminal vesicles and prostates became smaller than those of the untreated control group.
Could the same thing happen in people? “We are fairly certain that if concentrations of these chemicals reach high enough levels in humans, you would be seeing similar effects,” said research biologist William R. Kelce of EPA’s National Health and Environmental Effects Research Laboratory in Research Triangle Park, N.C.
Although DDT has been banned in the United States and most Western countries since 1972, it persists for decades in the environment and accumulates in the food chain. As a result, tens of millions of Americans still have substantial amounts of DDT or more likely DDE stored in body fat. (A few may also be exposed to vinclozolin, a fungicide currently used on some grape crops and also a potent androgen-receptor blocker. Kelce found that pregnant rats given that compound gave birth to male pups with deformed penises - a condition some say is increasing in humans.)
The average person would not have anywhere near the DDE levels present in the force-fed lab rats. But Kelce and colleagues found that the compound’s anti-androgen effect began at concentrations of about 64 parts per billion (ppb).