A Chemical Whirlwind on the Horizon : Health: Environmental toxics cause hormonal aberrations such as low sperm counts. Watch for industry’s denial.

Over the past two generations, human sperm counts in many parts of the world have fallen by half and a rising percent of sperm are deformed and nonfunctional. Testicular cancer is on the rise, as are birth defects such as undescended testicles. Many kinds of animals are suffering from hormone derangements that produce masculinized females and feminized males.

These unsettling phenomena are caused by chemicals we throw into the environment-- chemicals that behave like hormones.

Hormones are specific, subtle, fleet, ephemeral message-carriers in the body. They are made in the endocrine glands--the pituitary, for example, or the adrenals sitting atop the kidneys, or the ovaries or testes. They spread through the body, turning on and off different chemical processes in different cells.

Particularly important are the hormones that control reproduction--estrogen, testosterone, progesterone. Most of us know from our experience of adolescence, pregnancy, menstruation or menopause that these hormones affect not only our skin, body temperature and sexuality, but our moods and personalities as well. They also affect, in ways we are only beginning to understand, the growth and division of cells, which means both our ability to have children and our propensity to get cancer.

Hormones work by fitting into special cellular receptors designed to receive them as a lock is designed to receive a particular key. This is where endocrine disrupters come in. They are foreign chemicals--PCBs, dioxins, many pesticides, some common ingredients in plastics, detergents and cleaning agents--that happen, by chemical accident, to fit into hormone receptors. There they may mimic hormones, turning on cellular processes that shouldn’t be turned on. Or they may block the receptors, preventing real hormones from getting through.

Bollixing up one of the main information systems of the body can be problematic enough in an adult. In a developing fetus it can be disastrous. Infinitesimal concentrations of an endocrine disrupter hitting a fetus at the wrong moment of unfolding can derail development, change the sex or sexuality of the unborn child, or, most insidiously, affect its future ability to generate sperm or egg cells. The resulting defects may appear only in the next generation, if there is a next generation.

Endocrine disrupters will probably hit a publicity climax in March, when a readable book called “Our Stolen Future,” by biologists Theo Colborn and J.P. Myers and journalist Dianne Dumanoski, will be released by Dutton. The book is meticulous in describing the years of research that have led to current understanding of endocrine disruption. But most of us who have followed the story are apprehensive that we are about to see another typical media cycle of overdramatized reports followed by denial.

The chemical industry is set to produce the denial. Watch for the standard responses, perfected by the tobacco industry: “Those extremists always raise false alarms . . . Chemicals like these already exist in nature . . . You can’t prove what caused that effect . . . People want those products . . . Regulation would cost money and jobs.”

As the action and reaction rage, it would help to keep three facts in mind:

* This story is not just about sperm. Endocrine disrupters affect the fertility of females as well as males. They disturb other processes in addition to reproduction. The sperm count is what makes the headlines, but the story is much bigger than that.

* It is not just about humans. The picture was pieced together primarily by Theo Colborn, a wildlife biologist, who saw common problems in Great Lakes fish and Arctic bears, seabirds and alligators, seals and otters. Endocrine chemistry is common to most higher forms of life, and so is endocrine disruption.

* It is not just about chlorine. Many potent endocrine disrupters, such as dioxins, DDT and PCBs, are organic molecules with chlorine atoms attached. They are especially noxious because they are stable for a long time in the environment and they are fat-soluble, so they accumulate in living tissue. But beware of a clarion call to “ban chlorine.” All endocrine disrupters are not chlorinated and all organochlorines are not endocrine disrupters.

After the hype is over, I hope we’ll see the enduring lessons in these new biological discoveries. Chemicals, unlike people, should be assumed guilty until proved innocent. When we throw them out into the environment in million-ton quantities, they have ways of getting back into us, or into our children. As long as we are able to have children, anyway.