The same synthetic hormone, trenbolone, detected at high levels in the Indiana streams was linked to an all-male population of zebrafish in a 2006 laboratory study by University of Southern Denmark researchers. In addition, a study led by Orlando in 2004 found male minnows in a stream near a confined animal feeding operation had lower than average testosterone and were sexually immature.
Researchers do not know, however, if wild fish populations in agricultural streams have skewed male-female ratios, and whether their fertility has been reduced.
Many animals are implanted with synthetic steroid hormones such as trenbolone, melengestrol and zeranol to make them bigger, improve breeding and increase milk production in cattle. And it works: In 1920, a chicken took about 16 weeks to reach 2.2 lbs., whereas now they can reach five pounds in seven weeks, according to a report from the National Association of Local Boards of Health.
But the practice has spurred controversy as consumer groups have expressed concern over synthetic hormones increasingly getting into food and water supplies.
The manure in the new research came from cattle, dairy, pig and poultry confined animal feeding operations, which are farms with large numbers of animals. In Indiana that means 700 dairy cows, 500 horses, 55,000 turkeys or other combinations.
Indiana has about 625 confined animal feeding operations, which produce 80 percent of the state’s livestock, according to the state’s Department of Environmental Management.
Depending on the type, such farms produce between 2,800 tons and 1.6 million tons of manure a year, according to a report by the U.S. Government Accountability Office.
Some livestock operations sell manure to nearby farmers to fertilize fields – an easy, useful way to get rid of it. Some farmers, including the ones near the streams in the new study, have drains to keep water in the fertilized soil at a desired level. When there’s too much water, it goes down the drain and gets into nearby watersheds.
Each state has its own regulations. Greg Slipher, a livestock specialist with the Indiana Farm Bureau, said that Indiana livestock operations are required to be set back from water – about 100 feet from most water and 500 feet from public water supplies.
Neither Slipher nor representatives from the American Farm Bureau Federation would comment on the new findings.
Iwanowicz, who said he was not speaking for the U.S. Geological Survey, said current regulations aren’t enough.
“We’re increasingly seeing biologically active chemicals getting into our water,” he said. “There is enough data to show that there should be more efforts to minimize that.”
Fish sex determination is complicated and it would be difficult to pin it on one thing, Edwards said. But policymakers should take notice, she said.
“We need to take a careful look at the agricultural practices we have in place, as there’s plenty of evidence that we’re destroying water quality,” Edwards said. “A 3-year-old could say ‘hey, this stream next to the farm does not look good’."
This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.