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May 21, 2007
Feminized to Extinction
All across the world, people are
polluting waterways with estrogen. Excreted in urine, the hormone
passes through most wastewater plants and ends up in
streams and lakes, where some studies suggest it is
feminizing male fish. Now a large experiment has shown
that even a very low level of estrogen in
a lake can cause enough reproductive harm to wipe
out an entire population of minnows in 2 years.
Extra
estrogen isn't good for male fish. Laboratory studies have
shown that chronic exposure to low doses causes males
to produce eggs in their testes and takes away
their secondary sex characteristics, such as darker coloration and
tubercules on their noses. The big question was what
those levels mean for populations in the wild. To
find out, researchers led by Karen Kidd of the
University of New Brunswick, Canada, performed an experiment in
a lake in western Ontario. Each summer for 3
years, they spiked the lake with a few parts
per trillion of 17?-ethynylestradiol--the active ingredient in birth-control pills--in
concentrations like those found in streams and lakes elsewhere.
The experiment took place in a remote area set
aside for research.
Within weeks of the first doses, male
minnows started making vitellogenin, a protein that helps eggs
mature in females. They wound up with levels 8000
to 10,000 times normal. (Females increased production to 8
to 80 times their usual levels, and the estrogen
somehow slowed egg development.) Sexual development was delayed in
the males, and fewer and fewer fish were found;
apparently, the fish had stopped reproducing. After the second
year, the researchers couldn't find any fathead minnow nests.
"We didn't expect to see such a dramatic and
quick response," Kidd says. It took more than 2
years after researchers stopped adding estrogen for the population
to begin to recover.
Other male fish in the lake,
such as suckers and trout, also produced vitellogenin, but
their populations were not as hard hit, presumably because
these larger species have longer natural life spans. However,
chronic exposure might cause similar effects, the researchers speculate.
"These
are dire consequences," says Dave Epel of Stanford University
in Palo Alto, California. "This is a red flag."
But it is difficult to gauge the impact of
estrogen on populations of fathead minnows across North America,
Kidd notes. The fish are still found in rivers
receiving treated sewage, so apparently some populations survive the
hormonal onslaught. And without baseline data, it's impossible to
know whether populations have fallen. Still, given the wide
range of fish affected by estrogen, Kidd says it
would be prudent for cities to adopt modern treatment
systems that remove up to 95% of the estrogen.
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