Fish on Drugs

The Mellowing of Minnows and Other Consequences of Antidepressants in the Water

By Melissa Knopper

Minnows don't swim away from predators after they're exposed to antidepressants

Minnows don’t swim away from predators after they’re exposed to antidepressants.
© Photos: U.S. Fish & Wildlife Service

Back in the 1990s, Theo Colborn, then-senior scientist with the World Wildlife Fund, sounded the first alarms about endocrine disrupters. In the book Our Stolen Future (Plume) Colborn describes her early findings that connected these endocrine disruptors—via chemicals in plastics, pesticides and pharmaceuticals—with male fish laying eggs and bald eagle eggs crumbling into tiny pieces. Soon, scientists developed new research techniques to study these estrogen-like compounds, which are highly active at trace levels. Now, those new research tools are putting the spotlight on an extremely persistent, and perhaps equally disruptive, group of contaminants: antidepressants. A new body of evidence is building. Study after study shows widely prescribed drugs such as Prozac, Effexor and Celexa disrupt the natural order when they are excreted into the water. Scientists in Mississippi discovered antidepressants are interfering with the way tadpoles develop into frogs. They also interfere with the ability of tiny minnows to escape predators. Experts say these early signs could point to long-term problems for the aquatic food chain as a whole.

Edward T. Furlong, Ph.D., a research chemist for the United States Geological Survey’s (USGS) National Water Quality laboratory in Denver, Colorado, says the reasons antidepressants wreak havoc on fish is because they work on the body’s serotonin system. Most organisms on Earth have this important neurotransmitter in their bodies, from the tiniest nematode (microorganisms in soil) to the largest mammals and humans. Once antidepressants disperse in the environment (in this case by traveling down streams in wastewater effluent), they can affect a wide range of living creatures.

Comic: Take one three times a day, or you can just drink the local water.

In fish, Furlong explains, serotonin is associated with aggression, predation and escape instincts. “The fish is in water continuously,” he says, “so dissolved antidepressants can cross the gills 24/7.”

USGS scientists wanted to learn more about how these compounds—found in both water and sediment—might affect fish behavior. One 2010 study produced a surprising discovery: The antidepressants most common in stream water were not the ones that showed up in fish brains. “There are many reasons why this selective uptake may occur—including differences in fat versus water solubilities of the antidepressants,” Furlong says.

So what happens when fish have antidepressants in their brains? Just like people, they mellow out. Some studies showed striped bass that uncharacteristically didn’t pursue smaller fish. Another important finding showed tiny fathead minnows who neglected to swim away when threatened by a simulated predator.

Dana Kolpin, a researcher with the USGS Toxic Substances Hydrology Program, says that minnows usually react to predators with what is a called a C-start mechanism. These fish didn’t. “It’s an innate behavior for fish. It’s how they escape predators,” he says. “They bend into a ‘C’ and escape with higher velocity.”

The researchers are still trying to discover why this affected only the minnows in the larval stage—a very vulnerable part of their lifecycle. What’s clear is that this is not a good sign for the fish. “A slower response to predators is not helpful when you are on the lower end of the food chain,” Furlong says.

And what about the long-term impact on the environment? It’s still early to say, scientists say. But fathead minnows are a key food source for other fish species, such as trout and bass. Also, USGS research shows antidepressants persist in the water and travel as far as five miles downstream from wastewater treatment plants. “As with many contaminants, there is the potential for them to move up the food chain,” Kolpin says.

Officials from the U.S. Environmental Protection Agency (EPA) say they are aware of the new research on antidepressants and fish. “We value the data collected by other agencies and organizations as it will contribute to EPA’s ongoing work to better understand the occurrence, risk and treatment of pharmaceuticals in water, as well as methods for preventing pharmaceuticals from entering water,” the agency said in a statement. U.S. Food and Drug Administration officials said they are also keeping track of the latest USGS fish research. However, FDA officials add, “We don’t believe these low levels of pharmaceuticals in the waterway pose any risk to human health.”

Environmentalists like Renee Sharp, senior scientist with the Environmental Working Group (EWG), say this new research on fish and antidepressants points to the need for better testing. “It speaks to the need for more testing to look for ecological impacts,” Sharp says. “There are gaping holes in many aspects of our regulatory system.”

Sharp points to one promising solution: the green pharmaceutical movement. “We need to think about redesigning drugs so they’re effective, but they don’t cause problems,” she says.

Comic: Drug Portal to the WorldMeanwhile, EWG urges consumers who have leftover antidepressants or prescription drugs to dispose of them responsibly, instead of flushing them. Prescription drug take-back programs are available in many communities. “Antidepressants are definitely helping to heal a lot of suffering,” Sharp says. “But we have a lot of chemicals at very low levels that are all interacting with one another. It’s a real concern.”

MELISSA KNOPPER is an environmental journalist living in Denver, Colorado, who has written two books on medicine and the environment.