By Cat Holmes
University of Georgia
Researchers at the University of Georgia have found that low-
level exposure to a common class of antidepressants found in
streams and ponds delays both development in fish and
metamorphosis in frogs.
The scientists are studying toxicity of a widely used group of
antidepressants called selective serotonin reuptake inhibitors
(SSRIs).
The study has important environmental implications because some
of these widely-prescribed drugs, which include Prozac, Zoloft,
Paxil and Celexa, have been found in low concentrations in
surface water, particularly wastewater.
“While these compounds are not acutely toxic at concentrations
detected in the environment, our longer term studies indicate
delayed development (in fish) and delayed metamorphosis (in
frogs),” said UGA aquatic toxicologist Marsha Black who led the
study.
Fish
The researchers found that low concentrations of fluoxetine
(Prozac), the most commonly prescribed SSRI, significantly
slowed development in Gambusia, or mosquitofish, which are
often used to study toxicity on aquatic organisms.
“We found that male sexual development slowed by two to four
weeks,” said Ted Henry, a UGA researcher who also worked on the
project.
When the fish were around 80-85 days old, he said, the sexual
maturity of those exposed to low levels of fluoxetine was
significantly delayed. However, by the end of the study, when
the fish were 145 days old, the same fish had caught up
developmentally with the unexposed fish.
“We’re scratching our heads right now as to exactly what this
means,” Black said. “But we know that in water, timing is
everything. Reproduction for some species is timed to coincide
with algae blooms for example. And possibly if sexual
development is delayed, timing of reproduction could be
affected and you could see some population impact.”
For the next phase of the study, the researchers will more
closely examine the reproductive tissue of the fish affected by
fluoxetine.
Are they able to reproduce? Is there a reduction in the number
of embryos? Or is there no ultimate effect? “These are some of
the questions we’d like to answer,” Black said. “There are
still a lot of unanswered questions.”
Frogs
The researchers also found that metamorphosis in frogs exposed
to low levels of fluoxetine took longer than usual. For
frogs, particularly the land-based frogs of North America, such
a delay could be a matter of life and death, Black said,
because frog eggs are often laid in temporary water beds –
ephemeral ponds and wetlands that dry up.
“If the tadpoles have not developed and undergone metamorphosis
by the time the water has evaporated, they’ll dessicate with
the ponds,” Black said.
The researchers strongly suspect that results implicate a
disruption of thyroid function and will carry out further
research this spring to confirm or deny their suspicions.
“We know that the thyroid levels peak with metamorphic climax,
when the legs and arms form and the tail resorbs” Black
said. “We believe that fluoxetine inhibits the thyroid so
we’re measuring the thyroid hormone levels next.”
SSRIs in the environment
The number of prescriptions for SSRIs has exploded since Prozac
first came on the market 15 years ago. SSRIs are most often
prescribed for depression, but are also used to treat anxiety,
panic disorder, obsessive compulsive disorder, eating
disorders, and social phobia.
Because they are prescribed for chronic conditions, people take
them for months or years, increasing the likelihood of build-up
in surface water, Black said.
A recent study by Baylor toxicologist Bryan Brooks found traces
of fluoxetine in the tissue of bluegills in a Texas creek fed
by discharges from a wastewater treatment plant.
“Treated municipal drinking water should be fine, but
[pharmaceuticals like SSRIs] may not be filtered out of
wastewater,” Black said. “We should be putting a high priority
on implementing technologies that remove them and other
pharmaceuticals from municipal wastewater discharges.”
The findings of the UGA study will be presented at the 24th
Annual Meeting of the Society of Environmental Toxicity and
Chemistry next month.
(Cat Holmes is a news editor for the University of Georgia
College of Agricultural and Environmental Sciences.)
