An anti-anxiety medication that has found its way from water
treatment plants into ponds and streams of Europe may alter the behavior
of perch even at low concentrations, according to a study published
today (February 14) in Science.
Fish exposed to the drug, called oxazepam, tended to eat more quickly
and were more active and less social than they had been prior to drug
exposure and compared with their unexposed peers.
“It’s definitely an interesting study,” said David Skelly,
an ecologist at Yale University who was not involved in the research.
“It’s joining a group of exposure studies that are showing very clearly
that the individual chemicals that are showing up as environmental
contaminants are ecologically relevant.”
Previously researchers have raised concerns about all manner of pharmaceuticals in the water, from estrogens suggested to cause reproductive abnormalities in frogs to psychoactive drugs linked
to autism in fish. Oxazepam is a type of benzodiazepine, drugs that
work by binding to GABA receptors and are used to treat anxiety. Since
many animals have these receptors, it stands to reason that
benzodiazepines might influence animal behavior, Brodin said, but they
“weren’t being studied [in animals] in environmentally relevant
quantities.”
Testing effluent from a sewage treatment plant in Sweden and downstream water from the River Fyris, environmental scientist Tomas Brodin
of Umeå University and colleagues found 0.58 micrograms of oxazepam per
liter in the river and 0.73 micrograms per liter in the treated
wastewater—concentrations consistent with previously reported levels of
benzodiazepine drugs in other parts of the world.
The researchers then took European perch raised in clean water and put
them in water with either a low dose of 1.8 micrograms of oxazepam per
liter, or a high dose of 910 micrograms per liter. By the end of the
7-day treatment, the fish on the lower drug dose had accumulated levels
of oxazepam in their tissues similar to those found in wild perch in the
River Fyris.
Following exposure to the medicated water at either the high or low
dose, fish spent more time swimming around their tanks. When the
scientists put zooplankton in water, the exposed fish found and ate them
more rapidly than the control fish, but showed low interest in other
fish. The researchers also found that fish treated with the high dose of
the drug scored higher on tests of boldness, or their willingness to
explore novel situations.
Bodin suggested that the behavioral changes could have ecological
consequences. For instance, hungry, drug-dosed fish might deplete
algae-eating plankton, which could in turn cause algal blooms. On the
other hand, an asocial, highly active fish might be at increased risk of
being eaten.
But Skelly cautioned against going too far predicting ecological
effects. “Just because you saw these changes, you can’t say very much
about how it’s going to pan out in the field,” he says. In the wild, the
very presence of predators might change the fish’s behavior, he noted.
Oxazepam might also interact with a cocktail of other drugs that had
made it into the water.
Still, Brodin said, the results are an indication of the effects
benzodiazepines and many other psychoactive drugs could be having on a
whole range of animals. “It’s very probable that these behavioral
changes are going on in aquatic species around the world as we speak,”
he said.
