Swimming in Hormones

Does the idea of drinking or swimming in hormones appeal? Probably not. However, a new report finds that hormones excreted by livestock not only end up in their manure, but also run off into the nation's waterways as rains wash through manure-treated fields.

So what? Hormones are terrifically powerful chemicals, agents designed to be biologically active in trace quantities. Their role: to orchestrate the body's every function, telling each tissue when it's time to turn genes on—or off. Let loose a signal at the wrong time and havoc can ensue. Which is why littering waterways can do a number on fish and other aquatic life.

In the new study, Jeanne Kjær of the Geological Survey of Denmark and Greenland and her colleagues measured concentrations of estrogens—female sex hormones—running off of fields that had been fertilized with pig manure. Levels of the hormones were in the low nanograms per liter—that's parts per trillion. Remember, though, these chemicals are designed to work at vanishingly tiny concentrations. Indeed, they often exert a stronger effect at low doses than at higher ones.

Measurable amounts of the sex hormones continued to leach off of fertilized fields for up to 3 months, the scientists will report in an upcoming issue of Environmental Science & Technology. Their article was published early online, last Saturday.

Feminization of male fish has been reported in many waters. I've covered those reports plenty myself in stories for Science News. Most of those reports pointed toward estrogens excreted by humans—and released into waters from sewage-treatment plants—as the likely source of any gender-bending effects witnessed in wildlife.

The new data imply that agriculture could be a substantial additional source of such contamination. Indeed, the authors argue, their findings "indicate an urgent need for further research into the risk of estrogen contamination of the aquatic environment" by manure-fertilized fields.