Male starlings were less attracted—and more aggressive—to females given antidepressants. Study is the latest to suggest drug-tainted wastewater is messing with wildlife.
Female birds on antidepressants don't excite potential mates the way their drug-free counterparts do, raising concerns that environmental exposure to the drugs could impact populations, according to new research.
In a study led by scientists at the University of York in the U.K. and published in the journal Chemosphere, male European starlings sang less to females that had been fed a diet of worms spiked with fluoxetine—known by the trade name Prozac—at concentrations found at wastewater treatment facilities, where the birds often forage.
The findings add a new dimension to mounting worries that water bodies polluted with pharmaceuticals could become dangerous for the animals that live and eat there.
"Here is the first evidence that low concentrations of an antidepressant can disrupt the courtship of songbirds," said University of York behavioral ecologist and study co-author Kathryn Arnold in a statement. "This is important because animals that are slow to find a mate often won't get to breed. With many wildlife populations in decline, we have to ask whether more could be done to remove chemical contaminants like pharmaceuticals from our sewage."
The researchers captured 24 wild starlings for the study. Over the course of 28 weeks—a period meant to simulate the birds' winter and spring feeding at wastewater plants—they fed half the birds regular waxworms and the other half waxworms dosed with fluoxetine at the high end of concentrations found at treatment facilities. They then put one male and one female together in a small courtship area. Each male performed the experiment once with an untreated female and once with a fluoxetine-fed female.
There were clear differences in behavior based on whether or not the female birds had ingested the drug. Males sang more than twice as often and as long to females from the control group than to those that had been fed fluoxetine. Males also were more aggressive toward the females on Prozac, clawing or pulling their feathers instead of wooing them.
"Singing is a key part of courtship for birds, used by males to court favored females and used by females to choose the highest quality male to father their chicks," said lead author and University of York Ph.D. student Sophia Whitlock in a statement.
Doctors in the U.K. issued nearly 65 million prescriptions for antidepressants in 2016, the researchers note. The drugs are also widely used in the United States, where government data show that more than 12 percent of people older than 12 years old took antidepressants between 2011 and 2014.
Like other pharmaceuticals, those drugs make their way into sewer systems through patients' waste or when they're flushed directly down the toilet. Wastewater treatment plants are designed primarily to remove bacteria and solids; one study found that about half of prescription drugs and other "chemicals of emerging concern" made it past treatment.
A U.S. Environmental Protection Agency study of 50 large wastewater plants found several drugs in more than 90 percent of the treated discharge sampled, and fluoxetine in nearly 40 percent of them. Researchers are developing new treatment technologies to capture drugs, but they haven't been widely adopted.
“If we put something into the environment, we need to understand what happens to it”
The new study's implications for human health are unclear—the Prozac concentrations used were far lower than the medical dosage—but the findings add to growing evidence that even minor levels of pharmaceuticals in the environment may affect wildlife, experts say.
In a 2014 paper, Arnold and colleagues reported that a low dose of fluoxetine changed feeding behavior in starlings, potentially affecting their survival. Other research teams have found that fluoxetine and other antidepressants accumulate in fish downstream from wastewater treatment plants, and can alter reproductive behavior in fish and make shrimp more vulnerable to predators.
Researchers also warn that antidepressants aren't isolated in the environment, but mix with other drugs and compounds, forming a chemical cocktail with unknown combined effects.
One particular concern about the new study's findings was the absence of any outward physiological change in the drugged birds, Kate Buchanan, an ecologist at Deakin University in Australia, told EHN via email.
"This means that at a population level the impact of such chemicals may be difficult to determine until after populations have crashed, because bird banding studies would not detect changes in condition," said Buchanan, who was not involved in the research but has studied how endocrine-disrupting chemicals alter starling song.
With the world's human population increasingly concentrated in cities and towns, it's important for scientists to learn more about the prevalence of pharmaceuticals in urban watersheds and their effects on ecosystems and animal behavior, Bryan Brooks, director of the Environmental Health Science Program at Baylor University, told EHN. Brooks has researched fluoxetine in wastewater but wasn't part of the new study.
"This study is touching on an ecologically important and timely topic, given the increased urbanization we're seeing around the world," Brooks said. "If we put something into the environment, we need to understand what happens to it, we need to understand how long it sticks around, and we need to understand what kinds of wildlife come into contact with it."