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Synthetic female hormones in sewage are toxic to male fish over generations

2014 June 23

By Kristen Keteles

I’m a toxicologist at EPA in Denver, Colorado, and I study how pollutants can affect ecological and human health. I work with a team of scientists from academia (Colorado State University, University of Colorado Denver) and U.S. Geological Society to understand the potential effects of hormones and medications that are discharged into the environment. Did you know a very potent synthetic female hormone used in prescription drugs can be found in water and could be harming fish? We’re finding in our study that it can wipe out fish populations over several generations, and it’s the male fish that are most affected. Some studies have found that male fish below waste water treatment plants, and exposed to female hormones, can lose their masculine characteristics and become indistinguishable from females. Our new study found that a potent form of the female hormone estrogen used in prescription drugs not only causes the males to look female, it also appears to be toxic to male fish and these effects may impact future generations of fish.

Where do these hormones and medications come from? All of us. Humans excrete hormones and medications, which often end up in our rivers and streams from sewage. Disposing of medications by flushing can also contribute to pharmaceuticals in the environment. A growing human population, combined with effects of climate change like decreasing precipitation, has resulted in many streams containing higher concentrations of waste water. In fact, some streams in the west are 90% waste water. Not a nice thought if you like to kayak and fish, like I do. The water IS treated, but many hormones and pharmaceuticals are not completely removed by the waste water treatment plants. So, more people and less water equals more hormones and drugs in the water. My team is trying to determine what this means for fish, and ultimately for people, too. Although, currently, EPA does not have water quality standards for these types of chemicals, our study may help determine if such water quality standards are needed.

We looked at effects of exposure to a synthetic estrogen used in prescription drugs to fathead minnows over multiple generations by conducting experiments, both in the laboratory and in outdoor water tanks that mimic natural conditions.

Chemical exposure to female hormones in prescription drugs was found to increase the chances of death in male fish, but not females. And, fish exposed when they were young, but not as adults, were not able to reproduce later on in life. In addition, fish that weren’t even exposed to the prescription drugs, but were born to parents who were exposed, were less likely to reproduce. It could be that synthetic estrogen in prescription drugs, combined with other natural and synthetic hormones in the water, are reducing male fish fertility and could affect fish populations.

This is why it’s important to do what we can to protect fish breeding habitats in unpolluted areas. What are some things that your community can do to protect fish habitat? Read our information on how to dispose of unused medications to reduce the amount of pharmaceuticals that end up in water.

About the author: Kristen Keteles is a toxicologist in the Support Program of the Office of Ecosystems Protection and Remediation in EPA Region 8 in Denver. She has been with EPA for six years.

Fish A is a normal male fathead minnow. Fish C is a normal female fathead minnow. Fish B is a male that was exposed to female hormones in prescription drugs and looks more like a female than a male.

Fish A is a normal male fathead minnow. Fish C is a normal female fathead minnow. Fish B is a male that was exposed to female hormones in prescription drugs and looks more like a female than a male.


EPA Fish Team scientists: Al Garcia, Kristen Keteles, Elaine Lai, and Adrian Krawczeniuk.

EPA Fish Team scientists: Al Garcia, Kristen Keteles, Elaine Lai, and Adrian Krawczeniuk.

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action, and EPA does not verify the accuracy or science of the contents of the blog.

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6 Responses leave one →
  1. Elizabeth M.T. O'Nan permalink
    June 23, 2014

    I am also concerned about the continual amounts of fluoride dumped into our streams from our sewage treatment plants. Has anyone ever studied the effects of fluoride on downstream fish or wildlife? I sounds as if we need far more effective sewage treatments before allowing water back in our streams.

  2. D.Thomas permalink
    June 23, 2014

    Great work, great article. This is a serious problem that soon needs to be addressed. For years we have been ruining the majority of ecosystems in this nations nations waters, and The practices that cause that cannot continue. I know that the wastewater treatment system is extremely complex and faces a lot of challenges seeing as it is one of advanced societies newer technologies, but even so the system here has, for the most part been able to maintain a pretty good reputation, but I believe it has the potential to be better. Just because the US is a currently a world leader in these technologies, does not mean that the knowledge cannot be expanded upon, and a new standard cannot be set. More specifically on you and your teams work, I think it is great, the evidence there is undeniable, but the thing I would like to know is what are the implications on human populations? Are people who swim, fish, and possibly even drink this treated, but not pure water susceptible to the same types of changes as the fish? That is something I would love to see further research on. Also do you believe that waster water treatment will get to the point where all pollutants can fully be removed from the water supply placed in the streams, or do you believe that contaminated waters should be prohibited to man made isolated streams, where there is no wildlife or recreational activities?

  3. Christina Scheltema permalink
    June 24, 2014

    Great blog! Love the photos showing those poor fish and your team in action.

  4. Kristen Keteles permalink
    June 27, 2014

    Thanks, everyone for the comments!

    You makes some good points and raise some intersting questions, @D.Thomas. At this point any potential impacts to humans are unknown, but EPA is partnering with the Agency for Toxic Substances and Disease Registry (ATSDR) through the Urban Waters Initiative to look into that issue. There is evidence that some of the advanced treatment technlogies that remove nutrients also remove estrogens from waste water. In fact, since the Boulder Colorado Waste Water Treatment Plant was upgraded to remove nutrients, we’ve seen evidence that the impacts from the enviromenmental estrogens were also mitigated. For example, before the upgrade there were “intersex” fish (male fish that had female egg cells) and significantly more female fish than males. After the upgrade, the male:female ratio returned to normal and also no “intersex” fish were found. So that’s good news and an added benefit to nutrient removal! If you want more info on that study which was partially funded by EPA check out

    @Elizabeth M.T. O’Nan, fluoride at high levels can be toxic to fish and wildlife. It also occurs naturally in groundwater and surface water. Some streams have naturally high levels of fluoride in the water, and the toxicty also depends on the species of the fish, temperature, and the water chemistry. EPA does include fluoride levels in discharge permits when appropriate and has standards for fluoride to protect human health and the environment.

  5. Kathleen Foley permalink
    June 30, 2014

    There was a vagueness as to which pharmaceuticals (estrogen-producing) were of most concern. If it is birth control, then could the upset be more balanced if there also was discharge of corresponding male hormones?

  6. Kristen Keteles permalink
    July 2, 2014

    Very good question, @Kathleen Foley! Unfortunately, we don’t have a good handle on the effects of complex mixutures. In many discharges, some chemicals can be estrogenic and androgenic (male hormones), but also there may be anti-estrogenic (blocks estrogens) and anti-androgens (blocks androgens). The bottom line is that we need more research to look at mixtures of these classes of chemicals to see what the effects are given there could be interactions. Depending on chemicals are present, the effects could increase or decrease. It’s really hard to study because every mixture is different, but EPA Office of Research and Development is currently developing methods to study these chemical interactions.

    The pharmaceutical that we used in this study is 17α-ethinylestradiol, an active ingredient in human birth control and a VERY potent estrogen.

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