Human hormones mess with male fish | Science Matters | David Suzuki Foundation

By David Suzuki with Faisal Moola

Most people alive today were born after 1950. To these people, our modern world is just the way things have always been. Imagining life without TV, radio, telephones and the Internet is next to impossible. Teenagers probably have a hard time imagining life without text messaging!

And it's true, human reach is now profound. We are the most integrated, interconnected and mobile species that has ever existed on this planet. Some of these interconnections produce marvelous results. We get to know other cultures. We understand more about history and each other. We can easily chat with friends and family on the other side of the world.

But we have to remember that, although we are connected with each other more than ever, we are also intimately connected to the rest of the natural world. These connections can manifest themselves physically, such as through global warming. But they can also manifest themselves biologically — and in some surprising ways.

Recently, researchers writing in the U.S. journal Proceedings of the National Academy of Scientists reported that male fish became "feminized" when exposed to human hormones. Some of the fish, a type of fathead minnow, produced early-stage eggs in their testes while others actually developed tissues for both reproductive organs.

How would fish be exposed to female human hormones? Through treated or untreated municipal wastewater, of course. It seems that widespread use of birth control pills has elevated the amount of estrogenic substances going into our waste stream. Remember, things that go down our toilets don't just disappear. They can actually survive simple sewage treatment processes and end up in our rivers, lakes and oceans.

Reports of fish feminization due to human female hormones are today fairly well documented — but long-term studies of what impact this can have on fish populations have not been done. For this latest study, researchers actually added the synthetic estrogen found in contraceptive pills to a remote lake in northern Ontario in amounts that are normally found in human wastewater. They did this for three years, and monitored the results over a period of seven years.

The results were startling. As expected, the male fish developed some feminized characteristics, such as producing proteins normally synthesized in females. But what really disturbed the scientists was how populations of the fish crashed to near extinction levels by the end of the experiment. Feminization of the males combined with hormonal changes to the females apparently damaged their overall reproductive capacity to the point that the fish were unable to maintain their population.

Conclude the researchers: "The results from this whole-lake experiment demonstrate that continued inputs of natural and synthetic estrogens and estrogen mimics to the aquatic environment in municipal wastewaters could decrease the reproductive success and sustainability of fish populations."

This spells trouble. Most Canadians have probably never heard of the fathead minnow, but these fish are a vital food source for well-known and popular sport fish that people have heard of — such as walleye, lake trout and northern pike. They are also well-studied and often used in toxicology testing because they have short life cycles, adapt well to lab conditions and are representative of a large family of fish.

The report authors describe the fathead minnow as "a freshwater equivalent of the miner's canary." In other words, what happens to the fish, as with the bird, could happen to humans in short order unless we are very careful. Cell phones and the Internet aren't our only connections with each other and with the world. We are biological creatures too and we have to remember that these are the connections that ultimately matter the most.

October 19, 2007
http://www.davidsuzuki.org/blogs/science-matters/2007/10/human-hormones-mess-with-male-fish/