While most people understand the dangers of flushing toxic chemicals into the ecosystem through municipal sewer systems, one potentially devastating threat to wild fish populations comes from an unlikely source: oestrogen.
After an exhaustive seven-year research effort, Canadian biologists found that miniscule amounts of estrogen present in municipal wastewater discharges can decimate wild fish populations living downstream.
The research, led by Dr. Karen Kidd, an NSERC-funded biology professor at the University of New Brunswick (Saint John) and the Canadian Rivers Institute, confirms that synthetic oestrogen used in birth control pills can wreak havoc on the sex lives of fish. Small amounts of oestrogen are excreted naturally by women whether or not they are taking birth control pills.
Male fish exposed to oestrogen become feminized, producing egg protein normally synthesized by females. In female fish, oestrogen often retards normal sexual maturation, including egg production.
“We’ve known for some time that oestrogen can adversely affect the reproductive health of fish, but ours was the first study to show the long-term impact on the sustainability of wild fish populations,” explains Kidd. “What we demonstrated is that oestrogen can wipe out entire populations of small fish — a key food source for larger fish whose survival could in turn be threatened over the longer term.”
Kidd and her colleagues reported the findings last year in the Proceedings of the National Academy of Sciences of the United States of America. She is also presenting the research at the prestigious 2008 American Association for the Advancement of Science (AAAS) Conference during a session entitled, From Kitchen Sinks to Ocean Basins: Emerging Chemical Contaminants and Human Health.
Estrogen is part of a broader class of sex-changing chemical compounds known as endocrine disrupting substances. These contaminants, also present in pulp mill effluents, can seriously interfere with normal hormonal processes, notes Kidd, the Canada Research Chair in Chemical Contamination of Food Webs.
To better understand the impacts of estrogen on fish, the researchers conducted a seven-year, whole-lake study at the Experimental Lakes Area in northwestern Ontario. Over three summers, they added tiny amounts — low parts per trillion — of the synthetic oestrogen used in birth control pills to the lake to recreate concentrations measured in municipal wastewater.
During that period, they observed that chronic exposure to oestrogen led to the near extinction of the lake’s fathead minnow population as well significant declines in larger fish, such as pearl dace and lake trout.
“Generally, the smaller the fish, the more vulnerable they are to oestrogen,” remarks Kidd.
Part of the reason, she adds, is that smaller fish have a shorter lifespan and will often die after reproducing only once.
The researchers used synthetic oestrogen because it tends to persist longer in the environment than natural oestrogens. Yet the problem with oestrogen is not its environmental persistence but rather its persistent discharge in municipal wastewater into surface waters.
Kidd says the risk is greatest for aquatic ecosystems downstream from municipalities that either discharge untreated wastewater or maintain only primary treatment facilitisses.
It is now understood, she says, that removing oestrogen through wastewater treatment can reverse the adverse impact of this substance/hormone on wild fish. In fact, three years after halting additions of synthetic estrogen to the experimental lake, the researchers discovered that the fathead minnow population was on the rebound.
“To me, that’s the good news. Once you take the stressor out the system, we now have ample evidence that suggests affected fish populations will recover.”
(Source: Proceedings of the National Academy of Sciences: Doré Dunne: University of New Brunswick: February 2008)