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Endocrine Disruption: Sex-Changing Fish and More

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Detailed Description

We talk with Carl Schreck, USGS biologist, on the effects humans are having on aquatic life by introducing chemicals and waste products into lakes and streams. How do these contaminants affect aquatic species' reproductive systems, metabolism, mood, growth development, and more? Listen to find out.




Public Domain.


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Dave Hebert, Scott Horvath, Jenn LaVista, Jessica Robertson [voices]

In a world full of natural hazards . . .

Earthquakes, hurricanes, wildfires—and it doesn't stop there! [earthquake, wind, and fire sound effects under]

They thought they had nowhere to turn . . . nowhere to run . . .

Just what are we supposed to do? Where can we learn more . . .?


But then one Web site came to help . . .

Hey, look at this!

It gave them valuable, compelling info about natural hazards . . .

Wow, this is interesting!

It gave them clear explanations of scientific concepts . . .

Huh—this actually makes sense.

It gave them hope . . .

I think we're gonna make it!

The USGS Natural Hazards Gateway . . .

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Come to the Web site if you want to live . . . safely

The USGS Hazards Gateway: Now showing everywhere on the Web at

Music credit

"Throu" by Calpomatt; "Barbarossa III—A Call to Arms (verse)" by Lee I. Garnett

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Hello and welcome back. This is the USGS CoreCast, Episode 3. I'm Steve Sobieszczyk.

First off, we'd like to thank all our new listeners out there. We sort of sneaked out our podcast launch a few weeks ago. We didn't put much promotion behind it; yet, we've still managed to reach listeners from around the world. And we think that's pretty sweet. We really appreciate all the emails you've sent, as well; and keep it up, we look forward to hearing more from you as we continue with each new episode. We do welcome your input about future episodes. So if there is something you'd like use to look into, or if you have a scientific question you'd like answered, or if you'd just want to drop us a line and say hi, you can send us an email at's show is a good one. In a minute I'll be joined on the phone by Carl Schreck. Carl's a biologist with the USGS out here on the left coast of the U.S.; he's stationed down in Corvallis, Oregon, at the Oregon State University campus. Go Beavs!

I'm going to be asking Carl questions about what kind of impact we as humans have on aquatic life. In particular, what affect does the introduction of certain chemicals and waste products into lakes and streams have on the endocrine system of aquatic species? For example, do these chemicals interfere in the endocrine system, and what type of chemicals may act as endocrine disruptors?

For those unfamiliar with the endocrine system, it is essentially a group of organs and glands that work together to regulate, amongst other things, a body's metabolism, growth and development, reproduction, and even mood. These functions are controlled by the release of hormones through the bloodstream. Examples of organs from the endocrine system include the thyroid gland, the pancreas, sex organs-male and female, the pituitary gland and so forth. With that little primer out of the way...Carl, welcome to the show.


Hi Steve, it's my pleasure.


First off, what are endocrine disruptors? And what effect do they actually have on the endocrine system?


Endocrine disrupters basically are compounds that in someway either emulate the endocrine system or interfere with it. They're compounds that can act just like hormones, those that are actually designed to function like hormones, but there are many substances like the DDT metabolites that are still very widespread in our environment. DDT can act like estrogen. So it can act like a hormone, it's also possible that these substances can interfere with the actual action of hormones in the body. Basically prevent the body from responding to its own hormonal systems. And then in addition, it's possible that it can interfere with the production and synthesis of hormones or the clearance of natural hormones from the body. So it's a whole wide array of ways these can work. But usually endocrine disruptors are thought of as either mimicking hormones or interfering with the action of hormones.


During my research for this episode, I've noticed that everything from pharmaceuticals to agricultural pesticides seemed to be linked to endocrine disruption. Can you discuss a little bit about what types of chemicals act as endocrine disruptors and why they work the way they do?


Yeah, as you mentioned there are a number of different products that can do this. You can think about them in two different categories. One would be products like drugs that have specific targeted reactions in people. And because they are targeted that would mean that they might have similar sort of effect in other vertebrate biota. Now fishes respond with their endocrine system just like people do, they have the exact same types of hormones that people have.

So there drugs, for example, birth control pills that would have an action in a person, those same products would very likely have a very similar effect in other vertebrates, such as fish. These sort of compounds pass fairly freely through sewage treatment plants and therefore wind up in waters. Of course, then there are other types of compounds, for example the pesticides that are targeting a very different set of actions and while these were not specifically designed to have endocrine effects, some of the side effects are that they can interfere with the hormonal actions in vertebrate species, such as fish. And then in addition, there are other compounds, for example, breakdown products of detergents that can also act like hormones or interfere with the endocrine system.


One of the more amazing, yet troubling aspects of endocrine disruptors are their ability to change the sex, the gender of a fish. How does this happen?


These compounds are acting either as surrogates for sex hormones or interfering with the action of normal sex hormones that the fishes have. Just like sex hormones can have an effect in people, in other words, males can respond to female sex hormones and visa versa, the same thing could happen in fishes. So it's possible that estrogenic substances can actually feminize male fish into tricking the physiological systems into producing products that a normal female would produce. In fact, it's even possible to sex reverse fish.


You had mentioned the "feminization" of fish because of these estrogenic compounds. What about other products or pharmaceuticals? Do they have different impacts on development? For example, would medications for male enhancement "masculinize" a fish? Or would appetite suppression medication reduce the amount a fish will eat?


You know that's a really good question. We know much more about reproductive effects of these things in fish just because they've been more studied. Yes, any substance that would act as a hormone in people would have somewhat similar effect in the fish. It's known, for example, that in waters receiving runoff from places where anabolic steroids have been fed to animals, that there is actually masculinization in those fishes.

We really don't know to my knowledge effects about appetite depressing drugs and so forth. There's no reason to suspect that these thing shouldn't have an effect. And if you think of the whole milieu of substances that are found in our waters from the drugs related to appetite, as well as drugs involved in the immune system and all those sort of things, fish being vertebrates have a capacity to respond very similar to people. So, it's likely that endocrine disruptors would effect feeding, growth, immune system and all the physiological other systems that are regulated by hormones.


I've been focusing, sort of, on the obvious disruptive compounds, the pharmaceuticals and the chemicals, and the waste products, are there any examples of endocrine disruptors that may be surprising to people?


There are a lot of compounds we haven't talked about, you know, for example, flame retardant. Flame retardants can be endocrine disruptive, some of these are actually banned in Europe already. Twenty-five percent of the furniture we sit on are flame retardants. And it's the manufacture of these; the manufacturer puts this stuff in the air and then it fractionates out and winds up in the environment. The other biggy are plastics. Plastizers are endocrine disruptive if there's prolonged exposure. The single largest man-made item floating in the oceans nowadays is plastic.


The obvious follow-up question to all this discussion of endocrine disruption in aquatic species, primarily fish, is as humans, are we in danger of consuming "disruptive" fish? I guess would be the term to use. How does this endocrine disruption in the food we consume impact us?


There have been some studies that have tried to determine tolerance levels of these substances in people, safety thresholds, you know, like we've all read about the levels of mercury that have accumulated in fishes and certain amount of fish that can be consumed weekly and those sort of things. So some of these safety criteria do exist for some of these other substances but we really, I don't think, have enough background information, in terms of the concentrations of various contaminants in fishes in the wild to be able to generalize very well.

I do think that its something we do need to worry about however, I'm not saying fishes in the wild aren't safe to eat, what I'm saying is that there needs to be more study on the actual concentrations of these substances in fishes to be able to clearly document if tolerance levels have been exceeded in certain places.


How serious of a risk is it for just consuming water that has traces of these type of disruptive chemicals in there?


I would actually think that drinking the water should not have that much of an effect because the concentrations are so low and the real impact is through bioaccumulation through the food chain. A lot of these things are fat soluble, so they accumulate in fatty tissue, and they just hang around for long periods of time until that fat is metabolized away. So I don't think that drinking water should be that much of an issue.


I'm looking over my notes and it looks like that's all I have for you today, Carl. Thanks for joining me.


Oh, it was a pleasure.


This has been another episode of the USGS CoreCast. The CoreCast is a product of the Department of the Interior. Check back in a few weeks for our next episode as we'll take a closer look at the USGS seismic network. With all the recent seismic activity in the news, from mine collapses to earthquakes, we thought it would be interesting to examine what type of events are actually captured by the seismic network. You'll be pretty surprised at some of the things that actually leave a seismic signature. So be sure to come back for that.

Once again, thanks for putting aside some time to give us a listen, we know there are lots of options out there for scientific podcast, and we're going to do our best to keep the USGS CoreCast something worth listening to. So, until next time, I'm Steve Sobieszczyk, rock on!

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Music credit:

Opening: "Love in Vain" by Robert Johnson, 

Closing: "Walk Right In" by Cannon's Jug Stompers

Mentioned in this segment:

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