SITNFlash

Greetings SITN members!

The SITN seminar series is well under-way, and we thank all of you who have made the time to attend and to invigorate the lectures with your questions. We are about halfway through the series now, but there's still time to join us! Please see below for the full schedule. If you can't make it to our seminars, and especially if you don't live in the metropolitan Boston area, you can listen to all of our seminars online through our new podcast service! It's completely free, and you can catch up on the science behind the news anytime you wish. For more information, visit our website at http://sitn.hms.harvard.edu/podcasting/. We hope you'll enjoy it!

--The SITN Staff

Last month, a story worthy of the “X-files” made newspaper headlines. While investigating a sharp increase in fish deaths in the Potomac River, scientists with the National Fish Health Laboratory discovered that virtually all of the male small mouth bass they examined had characteristics normally only encountered in female fish. Some of the male fish carried immature eggs in their testes, while others tested positive for a female-specific yolk protein. Scientists are not sure what is causing the “intersex” condition, but they suspect the involvement of endocrine disrupting chemicals (EDCs) in the river water. These chemicals are considered safe in small doses, but their dramatic effect on fish are causing some to wonder about the scope of EDCs effects on the environment --and on human health.

Strange but True: Gender-changing Fish

How do male small mouth bass develop eggs and effectively become “intersex”? In mammals and birds, after the reproductive organs (known as the gonads) form during embryogenesis, they do not change. However, in fish, sex determination is more flexible. In many fish species, males can change into females, exchanging their testes for ovaries, and vice versa, one or more times within their lifetimes. Usually these sex changes are in response to environmental cues and/or changing social conditions. EDCs, are thought to trigger fish to become intersex by tapping into this plasticity.

What are EDCs and where do they come from?

Some EDCs are man-made chemicals, but natural compounds produced by plants and animals can also be EDCs. Only a small proportion of man-made chemicals have been identified as EDCs, but these are commonly used in coating plastics, as well as in pesticides, fertilizers, detergents and pharmaceuticals.

How do EDCs fool the body into gender bending? As the name implies, they interact with an organism’s endocrine system (the collection of glands and the hormones that regulate mood, growth, metabolism, and development and function of the reproductive organs). EDCs can interfere with the endocrine system either as antagonists (suppressing hormone production) or agonists (activating hormone production inappropriately). The latter is the case for the male small mouth bass whose bodies interpret the EDCs as estrogen (the primary female sex hormone), and thus start to produce eggs.

It is unknown whether the intersex condition is affecting the bass population in the Potomac. There have been several bad spawning years there in the past decade as well as several large die-offs, but neither has been conclusively linked to the intersex problem. This most recent report wasn’t the first case of intersex bass in the Potomac. Samples of male bass in 2003 and 2004 also turned up intersex fish: 42% and 72%, respectively. Although this year’s finding, that nearly 100% of male small mouth bass are intersex is disturbing, the researchers stressed that only a small number of fish were examined (thirteen, out of conservation concerns), not enough to make any statistically significant conclusions, only to describe a general trend.

Over the past few decades evidence has been accumulating that EDC pollution can adversely affect a variety of species. For example, the waste from paper mills masculinizes female mosquitofish. And several studies have shown that fish living downstream of sewage treatment plants suffer the same fate as the male bass in the Potomac. Cattle feedlot runoff also affects the morphology of both sexes of fathead minnows. While these reports are becoming more frequent, many questions remain unanswered. What are the particular EDCs responsible? Are these fish populations declining in EDC-polluted areas? And of course, the most pressing question to those who drink tap water originating in the Potomac: can EDCs in the water affect human health?

EDCs and human health

At this point, there is no strong and direct evidence that EDC pollution poses a health threat to humans. High levels of EDCs have not been detected in the Potomac, and therefore authorities maintain that the water is safe to drink. However, it is worth noting that although EDCs in small quantities may be harmless, it is thought that combinations of EDCs (as are often found in wastewater and sewage) can have synergistic effects. Because liquid waste often ends up in waterways, aquatic organisms are often the earliest indicators of something amiss.

What is being done about EDC pollution?

While some scientists are assessing what threat (if any) EDCs pose to humans and wildlife populations, others are asking “What can we do to eliminate EDCs from our waste and our water?” One solution that is being implemented at several wastewater treatment plants across the country is the use of “activated sludge”. This refers to a mixture of bacteria, fungi, and one-celled microorganisms that are mixed with waste-water to eliminate various substances by allowing the microorganisms to break them down into smaller inactive bits. Research so far has shown that this process can eliminate several of the common EDCs found in waste-water.
Increasing awareness of EDC pollution will hopefully lead to more research on understanding its effects on the environment and wildlife as well as on methods for eliminating these pollutants from the waste-water.

-- Alexandra Petrova, Harvard Medical School

For More Information:

Male Bass Across Region Found to Be Bearing Eggs, Washington Post 09.06.06: <http://www.washingtonpost.com/wp-dyn/content/article/2006/09/05/AR2006090501384.html>
Third of male fish in rivers are changing sex, Daily Mail (UK), 07.19.06: <http://www.dailymail.co.uk/pages/live/articles/news/news.html?in_article_id=396612&in_page_id=1770>
Phthalates harm male reproductive development, BBC 05.27.05: <http://news.bbc.co.uk/1/hi/health/4585603.stm>
Activated Sludge: <http://www.college.ucla.edu/webproject/micro7/studentprojects7/Rader/asludge2.htm>
Activated Sludge (Wiki article): <http://en.wikipedia.org/wiki/Activated_sludge>

Here's the schedule for the 2006 lecture series! This year we will be continuing to offer or lectures on two night at two locations, so feel free to attend the seminar that is more convenient for you! Here is the full schedule:

Of course, for the latest updates, check http://sitn.hms.harvard.edu/!