U.S. Water News Online
RICHLAND, Wash. -- While several studies have focused on
how estrogen from contraceptives may alter sex organs of juvenile
fish, few studies have analyzed how exposure to estrogen affects
adult fish as they make their way through rivers, lakes and streams
Now, a study by scientists at the Department of Energy's Pacific
Northwest National Laboratory suggests that when adult male fish are
exposed to short-term and low concentrations of a synthetic estrogen,
their fertility can drop by as much as 50 percent.
The study, conducted with the University of Idaho, appeared in the
June issue of Environmental Toxicology and Chemistry.
Previous research reported that high concentrations of estrogen
could change sex organs, causing juvenile male fish to develop female
organs. Estrogen is an active ingredient in most oral contraceptives
and often finds it way into surface waters through sewer systems. The
PNNL study looked at the impact of a synthetic estrogen called
ethynylestradiol, which is the chemical in oral contraceptives.
Irvin Schultz, PNNL toxicologist who led the study, said the
research reinforces that impacts aren't limited to juvenile fish.
"We can see that adult fish aren't immune to the effects of
estrogen in waterways. Even short-term exposure to low levels of
synthetic estrogen can impact their fertility," Schultz noted. "Our
results indicate that the fertility of a healthy male trout that has
developed normally still can be affected, if that exposure takes
place during a critical sexual maturation stage before spawning."
In a controlled laboratory experiment, PNNL scientists from the
lab's Marine Sciences Laboratory in Sequim, Wash., exposed adult male
rainbow trout for 62 days to three different concentrations of
ethynylestradiol -- 10, 100 and 1,000 nanograms per liter of water.
The sperm of exposed fish were harvested then used in a controlled
in-vitro fertilization process with eggs from a healthy female
rainbow trout. After 28 days, a measurable decrease in fertilization
was observed in the treated trout compared with a control group.
In some experiments, a 50 percent decrease in sperm fertilization
capacity was noted in semen collected from the trout exposed to 10
nanograms of ethynylestradiol per liter. For example, in an
experiment using 50,000 sperm for one egg, the exposed fish had 22
percent fertilization compared with 45 percent fertilization for
That impact is important, say researchers, because 10 nanograms
per liter is a level found in some surface water samples.
Schultz and his colleagues, including co-author Jim Nagler of the
University of Idaho, studied the possible mechanisms for reduced
fertility, specifically sperm motility and decreased hormone levels.
While they were able to rule out sperm motility as the mechanism,
their research revealed increased -- not decreased -- hormone levels
in the blood plasma of fish exposed to 10 nanograms per liter of
ethynylestradiol. But hormone levels did decrease in fish exposed to
the larger concentration of 100 nanograms of ethynylestradiol.
"While other research has shown the visible change that can take
place when young male fish are exposed to high levels of estrogen,
we're suggesting that low and short-term exposure can have just as
significant -- but not physically observable -- effects," Schultz
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