in the trenches/endocrine disrupters

 

1. In Twelve Hundred Words or Less...

Deformed frogs and gender-bent birds and fish. Falling human sperm counts, precocious puberty in girls, and rising hormone-related cancers of the testicles, prostate, and breast. Polluted water, contaminated fish, pesticides in breast milk. Is there a connection? What's going on in the environment? In our bodies?

Scientists have studied environmental pollutants for 30 years, generally focusing on potential DNA damage and cancer. Now it seems these are not the only dangers of chemical exposure. Accumulating evidence suggests that something else is going on in wildlife, and perhaps humans too. Certain chemicals can scramble critical messages within the body, the hormone messages of the endocrine system. Such chemicals are usually called endocrine disrupters or modulators, environmental estrogens, or hormone mimics.

The endocrine system is a sophisticated communications network made up of glands (including the thyroid, pituitary, pancreas, ovaries and testes), the hormones they secrete and the target tissues that respond. The endocrine system is exquisitely sensitive to tiny amounts of hormones, and also interacts with the immune and nervous systems. All animals with backbones (fish, amphibians, reptiles, birds and mammals) have similar endocrine glands and hormones. Hormone interactions are both subtle and complex and play crucial roles in growth, development and reproduction. Timing of exposure is at least as important as the dose.

Central in the endocrine disrupter fracas is the receptor for the female hormone estrogen. When estrogen encounters its receptor, the combined molecules may prompt or halt various cellular events. Problems arise because the estrogen receptor can't distinguish between estrogen and certain chemicals, so messages get derailed. Blockers prevent the real hormone from delivering its message. Mimics trigger events in the cell that shouldn't happen, at least not right then. Estrogen effects have gotten the most attention but chemicals are also suspected of meddling with communications systems of the male hormone androgen and also thyroid.

What are the alleged chemical culprits and where? Many go by the general name of organochlorines-organic compounds with chlorine attached. Though often present in small amounts, suspect chemicals are widespread, appearing in pesticides (fungicides, herbicides, insecticides), various plastics, solvents, detergents, food packaging, paper products and more. They include Bisphenol-A, nonylphenol, polyvinyl chloride (PVC), dioxin, polychlorinated biphenyls (PCBs) and DDT.

While it's true that DDT and PCBs were banned in the United States years ago, it's also true that these types of chemicals can persist in the environment for decades, perhaps centuries, depending on circumstances. Another characteristic is that these chemicals cling to fat and tend to bioaccumulate, becoming progressively concentrated in animals higher up the food web--like humans. They leave their flabby abode when the body draws upon fat stores during dieting and lactation. Thus they're found in breast milk.

DDT is an infamous example. When DDT bioaccumulated in birds, their egg shells broke, and populations declined. But broken eggs weren't the only reason for reproductive failures. When seagull eggs were exposed to DDT, the embryos developed as females even if genetically male. Gender bender chemicals have resulted in feminized or even intersex (both male and female organs) fish and birds. From alligators in Florida to otters in Oregon, research has documented that higher concentrations of suspect chemicals in the tissues correspond with greater abnormalities. Aberrations have been found among 16 major species exposed to estrogenic chemicals in the Great Lakes. Accidental human chemical exposures have shown we're not immune to similar effects.

Unsettled issues, complexities and controversies abound. Few dispute the evidence from wildlife, but no one knows how widespread the problem is, and what levels of exposure produce abnormalities. As for humans, no undisputed links between environmental chemicals and abnormalities have been proven yet. Reports of falling sperm counts and increased cancers must be considered along with conflicting reports and alternative explanations. Recent re-analysis of existing studies indicates that sperm counts apparently have fallen in the U.S. and Western Europe, but no one knows yet why or what it means. Conducting epidemiological studies on human populations is notoriously difficult and expensive. Another problem is that this is an embryonic field and there's no agreed upon method for screening and identifying possible endocrine disrupters.

Complex biological issues take time to sort out. Potency of estrogenic compounds varies greatly, and some people say that we get more "estrogen equivalents" from naturally occurring chemicals in our food than from chemicals on our food. This is not a simple either-or-debate between environmentalists and the chemical industry. Academic scientists fall in across the full spectrum of opinion. Everyone agrees more research is necessary, and these efforts are underway.

Carried by wind and water, environmental chemicals respect no borders. Seabirds from mid-ocean environments thought to be pristine have DDT, PCBs and other synthetic chemicals in their tissues. So do Eskimos. In all likelihood, so do you. Once released into the environment, chemicals can't be recalled. Nor can damage to wildlife, and possibly humans, be repaired. Ultimately, preventing exposure to dangerous chemicals is the only strategy, which means preventing their release into the environment in the first place.

Some advocates say we need stricter chemical regulations that shift the burden of proof to chemical manufacturers, requiring them to demonstrate product safety. The current system presumes chemicals innocent, some say, and to the extent that they're tested, acute toxicity and carcinogenesis are emphasized, not cumulative or subtle effects such as endocrine disruption. Possible interactions of chemical mixtures have been ignored until recently, as have the disproportionate effects on the most vulnerable, children.

The reasons for what many consider inadequate testing are not as simple as denial, ignorance, greed or meanness. Screening tens of thousand of chemicals, in various combinations, for all possible effects is simply impossible. Decisions often boil down to estimates balancing risk and benefit. Like it or not, society is chemically dependent, and nothing is risk free. Still, essentially everyone involved, including the chemical industry, agrees that serious questions have been raised. Congress has ordered EPA to examine the issue and report back by August 1998. (see Hotspots) Scientists, environmental organizations, industry and policy makers are discussing what we know, what more we need to know, and what we should do. It's going to be an interesting year. We'll help keep you up-to-date.

What can you do while waiting for answers? Our Stolen Future and some Websites listed here outline steps you can take to lower your exposure, which include choosing food wisely, reducing or eliminating use of products likely to contain potential endocrine disrupters (i.e., buy organic, avoid fat and plastics, etc.), and learning about the drinking water and chemical use in your community. As always, you can educate yourself, starting with the links that follow. And you can speak up.

 

More on Endocrines:
Table of Contents | Twelve Hundred Words or Less... | Web Resources
Activist Groups | Voices | New in the Literature | Hotspots
On the Other Hand... | Funders | What You Can Do