When the synthetic estrogen that is an active ingredient in birth control pills — 17α-ethynyloestradiol (EE2) — makes its way from toilets to municipal wastewater streams to a freshwater environment, it can decimate the intricate network of food sources that sustain aquatic species. This agent is a notorious endocrine disrupting chemical (EDC), which does not affect simple organisms such as algae or zooplankton but can play havoc with key reproductive processes in fish. The effects can quickly drive these fish populations to the brink of extinction, but new research has demonstrated that these same damaged populations can also recover quickly once the EDC is removed.

Karen Kidd, a biology professor at the University of New Brunswick in Saint John, was part of a group that recently published this finding in the Philosophical Transactions of the Royal Society B. Their work goes back to 2001, when small amounts of this EDC were introduced into an isolated lake that is part of the scientifically reserved and internationally renowned Experimental Lakes Area of northwestern Ontario.  

The researchers focused on the fathead minnow, a smaller fish that serves as important prey for larger fish species. At concentrations of several nanograms of EE2 per litre of lake water (parts per trillion), within two years this EDC had produced the notorious “gender-bending” changes in the male fish, causing them to produce egg yolk protein and eggs and delaying the development of their sperm cells. The same effect has been found in a number of Canadian waterways that receive municipal wastewater: Wascana Creek in Saskatchewan, the South Saskatchewan River in Alberta and the Grand River in southwestern Ontario. 

With their reproductive capacity effectively crippled, the population monitored by Kidd and her colleagues crashed to one percent of its original level. Other species that consume the minnows, such as trout, subsequently showed significant decreases in their population. After the addition of the EDC to the lake was halted, the researchers began studying whether the minnows recovered. Kidd notes that the changes to the reproductive systems of the male fish were as dramatic as before. “The same thing happened in the recovery, only in reverse of what we saw during the EDC additions,” she says. “As soon as they had the ability to reproduce successfully, their population came back. It was essentially a reproductive boom.”

Within three years, the number of minnows in the lake rebounded to what it was before the study started. Kidd regards this as very good news, since it means that eliminating these EDCs from wastewater streams could completely undo the environmental damage. “We were all surprised and pleased to see such a dramatic and complete recovery of the fish population,” she says. “It is great to share a good news story this time.”