Endocrine Disruptors — The Dirt on Pollution

Circa 2010

With its unique composition and multitude of resources, the planet Earth allows us to manufacture virtually anything we need and innumerable things we don’t. And how do we dispose of such resources when we’re finished with them? We “trash” them in the only place that we can: our planet.

Herein lies the problem. Most of the things that we create and use have been so significantly modified during the process of their production, that they cannot simply “go back” into the natural state of the Earth. Instead, they stick around and cause trouble. We know this as pollution.

In 2010, the effects of pollution influence the air we breathe and taint the very water we drink. Much has been said and written about greenhouse gases, pesticides, heavy metals and other pollutants. But let’s address another cadre of pollutants on the list: endocrine disruptors.

Endocrine disruptors (EDs) are a cumbersome list of chemicals and compounds that are imbibed or absorbed by animals via the water supply. They not only come from industrial processes, but also from our medicines, beauty products, and herbicides. EDs can affect animals’ lives in a variety of ways, and at a variety of developmental stages.

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An important element of human and animal life, the endocrine system secretes hormones in the blood stream that influence organs throughout the body. Pollutants that mimic these hormones, as EDs do, may in fact be causing mutations in several animal species. At the beginning of the new millennium, scientists discovered frogs with extra limbs and even male animals possessing ovaries. These types of mutations are curious and troubling, particularly in respect to reproductive organs, which are the most critical parts of the endocrine system.

The discovery of “intersex” fish (males with immature female eggs in their testicles) has opened yet another Pandora’s Box of pollution. The Potomac River and its tributary, the Shenandoah River in Washington, DC and northern Virginia are most noted for such discoveries. Understanding how and why these mutations occur requires some basic sex education—yes, much like we got from our high school gym teachers.

An embryo is a recently fertilized egg, early in its quest to be born and grow into adulthood. As the embryo develops, genes influence the formation of its sex organs. Males grow testicles that produce and store sperm, while females develop ovaries that produce and store eggs. In the case of “intersex” fish, however, we can presume that the fish embryos are being mutated or warped as a result of exposure to chemicals which have been determined safe for human consumption or use (such as pharmaceuticals or some pesticides). It is believed that these chemicals may accumulate in the sediment at the bottom of the rivers where fish lay their eggs.

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Exposure of fish eggs to such chemicals in sediment can disrupt normal sexual development, causing males to develop “oocytes” (immature eggs) in their testes. It is not likely, however, that any one contaminant acts alone as the culprit. Amazingly, despite having immature eggs in their testes, intersex males are still able to produce sperm and reproduce.

As of yet, there do not seem to be cases of these male eggs combining with their own sperm to result in the formation of an embryo, though there are organisms in which this is the normal means of reproduction. These organisms, known as hermaphrodites, are comprised of both male and female sexual organs. Auto-fertilization of female eggs in the male testes would not work in fish or mammals, however, since the males in these groups don’t have the organs required to sustain an embryo.

Fortunately, there is no solid evidence to suggest effects of endocrine disruptors on humans. Moreover, a relative few species are known to experience effects of EDs, and there is no reason to believe similar effects would occur in exposed humans. On the other hand, efforts to establish a link between human reproductive dysfunction and endocrine disruptors are hampered by technical difficulties—so effects on humans cannot be entirely excluded, either.

by E. Thomas Chappell, MD

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