Drugs in Waterways
are Harming Aquatic Life
August 7, 2002 (ENS) - The overuse of antibiotics and other
drugs may be harming zooplankton, tiny organisms that support
the health of all freshwater ecosystems.
"Pharmaceuticals can be detected in many surface water
streams and lakes, yet we know little about how these
strongly biologically active chemicals affect the ecology
of aquatic organisms," said Stanley Dodson, a zoologist
specializing in freshwater ecology at the University of
This pollution, argues Colleen Flaherty, a UW-Madison
zoologist, has direct ties to humans, either through the
improper disposal of unwanted pharmaceuticals or through
the ingestion of the drugs.
"Up to 80 percent of drugs taken by humans and domesticated
animals can be excreted in their biologically active form,"
Flaherty explained. This means that the antibiotics, antidepressants
and anti-inflammatory pills that humans take or throw
out can end up polluting the environment and harming the
organisms that live in it.
Flaherty's research is the first to look at the effects
of common prescription drugs on Daphnia, a zooplankton
that is integral to freshwater ecosystems. She will present
findings from her study on Thursday at the annual meeting
of the Ecological Society of America in Tucson.
"Daphnia play a key ecological role in freshwater sources,"
Flaherty said. "They are an intermediate organism in these
ecosystems - they eat the algae and are eaten by the fish.
If something happens to Daphnia, it could affect both
the algae and the fish populations."
To determine the influence of pharmaceuticals on this
key freshwater species, Flaherty tested Daphnia's biological
response to drugs that have been found in European and
U.S. waters, including cholesterol lowering clofibric
acid, an antidepressant called fluoxetine, and five antibiotics.
Flaherty performed short and long term studies to find
out what happens to a female Daphnia and her offspring
when exposed to a particular drug. The effects she found
In the short term studies, the antibiotics and cholesterol
drug at concentrations of just 10 parts per billion appear
to stunt growth and result in more male offspring.
In the long term studies, these differences were diminished:
offspring exposed to the antibiotics tended to have longer
lifespans, while those exposed to the cholesterol lowering
drug showed no apparent effects.
Exposure to the antidepressant produced no differences
in the shorter trials, but did result in a greater number
of offspring in the longer studies.
"When Daphnia were exposed to a single pharmaceutical
throughout their entire [30 day] life span, as in the
long term studies, they seemed to become acclimated to
the polluted environment," Flaherty said.
But, Flaherty pointed out, Daphnia swim in waters tainted
with not just one drug, but many.
"Some of these drugs may not have significant effects
by themselves," she said, "but, when you combine them
in a 'pharmaceutical cocktail,' the effects can be lethal."
When Flaherty exposed the organisms to a combination
of the cholesterol drug and the antidepressant during
the short term studies, up to 90 percent of them died.
Their offspring were more likely to be female, and to
have deformities that hinder swimming.
"I never expected that two drugs that had virtually
no individual effects could be so lethal when combined,"
Because of these findings, Flaherty argues that scientists
must look at not just one chemical, but combinations of
them, to understand the ecological effects of pharmaceuticals
or other manmade chemicals on freshwater ecosystems.