Antidepressants in waterways make crayfish braver and more prone to getting eaten

BREVARD COUNTY, Fla. – Crayfish on antidepressants act a bit bizarre, leaving their hiding places and boldly going where crayfish don't normally go, scientists have found. 

A new study led by the University of Florida suggests that antidepressants that get into waterways are making crayfish too daring at times, putting the freshwater crustaceans at increased risk from predators, with uncertain long-term ecological consequences. 

“Crayfish exposed to the antidepressant came out into the open, emerging from their shelter, more quickly than crayfish not exposed to the antidepressant," said Lindsey Reisinger, a co-author of the study and an assistant professor at UF. 

Crayfish play a key ecological role by scavenging algae, rotting plants and anything else along the bottom of streams and ponds. "If they are getting eaten more often, that can have a ripple effect in those ecosystems,” Reisinger added. 

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Prescription for eco-imbalance? 

So with more than 1 in 10 Americans on antidepressants and 50 species of crayfish in Florida, such a heavily dosed, aging populace might be a prescription for long-term ecological imbalance, the researchers say. 

"Our study is the first to look at how crayfish respond when exposed to antidepressants at levels typically found in the streams and ponds where they live," A.J. Reisinger, lead author of the study and an assistant professor at UF, said in a release. “Low levels of antidepressants are found in many water bodies. Because they live in the water, animals like crayfish are regularly exposed to trace amounts of these drugs. We wanted to know how that might be affecting them.”

The researchers found crayfish exposed to low levels of antidepressants behaved more “boldly.” They emerged more quickly from hiding and spent much more time searching for food. In the wild, that can put them in the crosshairs of predators.

They're typically nowhere to be found, Lindsey Reisinger said but go out at night with a flashlight and it's crayfish galore.

"There's crayfish everywhere, and I think a lot of reason why people don't know that is that they're always hiding," Lindsey Reisinger said.

The findings raise concerns about what might be getting into largemouth bass and other crayfish predators, as well as for humans who eat those fish, the researchers say, given that some antidepressants accumulate at higher levels as they move up the food chain.

The scientists placed crayfish in artificial streams that simulated the crustaceans' natural environment in the lab, where the researchers could control the levels of antidepressants in the water and easily observe crayfish reactions. 

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They exposed some crayfish to "environmentally realistic" levels of antidepressant in the water for a few weeks. A separate control group of crayfish was not exposed. The researchers used a common type of antidepressant called a selective serotonin reuptake inhibitor, or SSRI.

They set up what's called a "Y-maze" to test how antidepressant exposures changed crayfish behavior. The maze's short entrance branched into two lanes, like the letter "Y." They put each crayfish in a container or "shelter," and placed the container at the maze's entrance. When researchers opened the "shelter," they timed how long it took the crayfish to emerge and which lane it chose in the Y-maze. One lane emitted chemical cues for food, the other emitted cues signaling the presence of another crayfish.

Compared to the control group, crayfish exposed to antidepressants emerged earlier from their shelters and spent more time pursuing food. They tended to avoid the crayfish side of the maze, which the researchers suspect is a sign that the antidepressant levels used in the study didn’t increase crayfish aggression. 

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“The study also found that crayfish altered levels of algae and organic matter within the artificial streams, with potential effects on energy and nutrient cycling in those ecosystems,” A.J. Reisinger said. “It is likely that the altered crayfish behavior would lead to further impacts on stream ecosystem functions over a longer time period as crayfish continue to behave differently due to the SSRIs. This is something we’d like to explore in future studies.”

The study was conducted while A.J. Reisinger was a post-doctoral researcher at the Cary Institute of Ecosystem Studies, a nonprofit research group based in New York. The study, co-authored with Erinn Richmond of Monash University and Emma Rosi of the Cary Institute of Ecosystem Studies, is published in the journal “Ecosphere.” 

A landmark study by the U.S. Geological Survey in 2002 found pharmaceuticals, hormones and other organic wastewater contaminants in 80% of streams tested nationwide. They found 82 of the 95 chemicals they tested for at least once.

What researchers found

The three most commonly detected were steroids, nonprescription drugs and an insect repellent (DEET). Detergent byproducts, steroids and plasticizers were found at the highest concentrations.

In another USGS study from 2004 to 2009, scientists found that pharmaceutical manufacturing facilities can be a significant source of pharmaceuticals to the environment. Wastewater from two sewer plants that receive a discharge from pharmaceutical manufacturing facilities had 10 to 1,000 times higher levels of pharmaceuticals than effluents from 24 sewer plants across the country that didn't receive discharge from pharmaceutical manufacturing facilities. 

Doctors who overprescribe contribute to the problem, as do patients who fail to take their full course of prescribed antibiotics, breeding a stronger next generation of bacteria. The human toll is drugs that eventually won’t work.

Antidepressants and other drugs flushed down the toilet can be difficult to remove at sewer and drinking water treatment plants.

The amount of antidepressants taken by Americans increases with age, according to the Centers for Disease Control and Prevention which found that 7.9% among adults ages 18-39 use them compared to 14.4% for those ages 40-59, and 19% for those ages 60 and over. Use is higher among women (17.7%) than men (8.4%). 

People on antidepressants excrete and flush trace amounts of the drugs, and those traces wind up in waters via reclaimed water or leaky septic systems and sewage spills.

There are ways to temper the flow of antidepressants and other pharmaceuticals into water bodies, A.J. Reisinger said.

"The answer is not for people to stop using medications prescribed by their doctor. One big way consumers can prevent pharmaceuticals from entering our water bodies is to dispose of medications properly," he said.

Pharmacies hold drug-take-back days. The Drug Enforcement Agency's 2021 National Drug Takeback Day in April collected 420 tons of drugs, according to DEA.

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Follow Jim Waymer on Twitter: @JWayEnviro.