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Public Radio's Environmental News Magazine (follow us on Google News)

Gender-Bending Fish

Air Date: Week of

There’s something fishy about Colorado’s South Platte River. Researchers there have found increasing numbers of mutant fish – male fish with female attributes. And they suspect wastewater carrying estrogenic compounds like birth control pills might be the source of the mutations. Host Steve Curwood talks with head researcher David Norris, of the University of Colorado, about the downstream implications of these mutant fish.


CURWOOD: Millions of gallons of municipal wastewater are released into the nation’s rivers every day. Although most of it is filtered and treated to remove impurities, some pollutants still float into waterways downstream.

Researchers in Colorado have been looking at fish populations downstream of Denver and Boulder. In two waterways, the South Platte River and Boulder Creek, the scientists have made some surprising discoveries which they attribute to estrogenic compounds contained in the wastewater.

David Norris is the head of the research team. He teaches at the University of Colorado and joins us now from Boulder.

CURWOOD: So Professor Norris, tell me what exactly have you find in the fish populations of the South Platte and Boulder Creek?

NORRIS: Well, upstream from the sewage treatment plants, what we’ve noticed is a relatively normal sex ratio of roughly 1:1, males to females, and a mixture of adult and juvenile fishes and we don’t find any inter-sex fish. Downstream, we find many more females than males, roughly ten to one, and among the juveniles we find a number of inter-sex fish.

CURWOOD: Now, inter-sex—what do you mean by that?

NORRIS: Inter-sex is a situation where you find both the egg-forming tissue, and you find sperm-forming tissue in the same organ.

CURWOOD: That sounds like a mess downstream.

NORRIS: We were quite alarmed to see the amount of disruption in the downstream fish. When we first saw the inter-sex fish, we were sort of excited because we had hypothesized that they would be there, based on what we knew was in the water and what we knew from laboratory studies and the studies elsewhere. And we were just surprised at how much disruption there was.

CURWOOD: How long have you been looking at Boulder Creek and South Platte River?

NORRIS: We started about three years ago, looking at the fish because of the reports of estrogens in the water, both in the South Platte and in Boulder Creek, and in reference to studies that have been reported in England where below sewage effluence – usually mixtures of industrial and domestic sewage – they have found inter-sex fishes.

CURWOOD: What exactly are the sources of these compounds that lead to these inter-sex fish?

NORRIS: Many of these come from plastics. Nonaphenol is one of the most estrogenic ones, and it’s used in the softer plastics to make them more flexible.

CURWOOD: Mm-hmm.

NORRIS: And we know that these compounds can leach out of the plastic containers. For example, culture dishes used to culture breast cancer cells, were discovered to actually activate those breast cancer cells. Compounds like bisphenol A come from your polycarbonate plastics. And this particular compound is also found in dental sealants which are used quite a bit with children, and they’re used to line metal cans that we put food in. And we know from a number of studies that these compounds leak out of these plastics and can produce estrogenic effects on organisms.

CURWOOD: Now, if these estrogenic compounds are in the water and there’s an effect on people, what’s going on for the folks who are downstream from these sewage treatment plants that you’ve looked at in Boulder Creek and the Platte River there? There must be some cities and towns that take their water from that river.

NORRIS: There are quite a number of them, I would guess, and I imagine that as you go further downstream you’re having more and more people dumping in as well as taking out. And I think that we should be concerned about more downstream. The fact that we’re seeing inter-sex fishes in Boulder Creek, for example, we’re pretty far upstream. People come to Colorado in the mountains because they expect really clean water, and it’s already fairly well-contaminated.

And this is a domestic source. We’re not looking at industrial sources here. It’s primarily what I and other residents of Boulder are choosing to do every day—what detergents we’re using, personal care products, things of this sort—and then we’re dumping them down the drain.

CURWOOD: Now, with these estrogenic compounds that wind up in the water, what can be done about this? How easy is it to remove this stuff from the water?

NORRIS: Well, apparently the technology exists, through filtration and reverse osmosis, that we could remove these materials. But to retrofit every sewage treatment plant would be an expensive proposition, at least to begin with, as well as it will take time. But we have the technology that we could be returning perfectly clear water back into the river.

CURWOOD: So what would you say are really the most significant aspects of the data that you’re coming up with in the fish populations there?

NORRIS: Well, I think there are certainly important questions related to the fish themselves and the ecosystem. But I think a more important question is the fact that this is not an isolated phenomenon; it’s probably occurring all over the country. And because of the additive nature of these chemicals and the many multiple sources, especially the populations that are downstream that are recycling this water and this material are at risk.

CURWOOD: David Norris teaches at the Department of Integrative Physiology at the University of Colorado in Boulder. Thanks for taking this time with me today.

NORRIS: You’re welcome.

[MUSIC: Gus Gus "Anthem" p MUSIC FOR THE MOTION PICTURE (Thrive – 1998)]



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