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A new study has found that the introduction of small amounts of estrogen from birth control pills into a Canada lake ecosystem nearly wiped out its entire population of fathead minnows. Researchers discovered that exposure to estrogen—which currently ends up in municipal sewage and, eventually, several Canadian waterways—interferes with the fish’s ability to reproduce as males become feminized and start to produce eggs.
“It was really unexpected that they would react so quickly and so dramatically,” said Karen Kidd, the lead researcher of the University of New Brunswick study, which was published Monday. “The crash in the population was very evident, very dramatic, very rapid, and related directly to the estrogen addition.” Researchers began adding small amounts of estrogen to the freshwater facility in 2001. Shortly after, the number of fathead minnows plummeted to just one percent of the original population. Fortunately, after removing the estrogen from its habitat, the fathead minnow population rebounded fully, and just as quickly.
According to Kidd and her team, the dramatic depopulation of minnows set off a chain reaction within the lake ecosystem. Lake trout, the fathead minnow’s main predator, also began to decline. Meanwhile, the number of insects, the minnow’s main food source, began to increase.
According to CBC News, the study was designed to determine both the direct and indirect effects of endocrine-disrupting chemicals (EDCs), specifically the synthetic estrogen used in the birth control pill, on an ecosystem. Based on results from the test, which was conducted at the Experimental Lakes Area in northwestern Ontario and has been in the works since the late 1990s, Kidd is calling for improvements in wastewater treatment in order to remedy a problem of feminized male fish that currently affects several Canadian waterways.