Meth Pollution in Waterways Turns Trout Into Addicts

Like humans, fish can get addicted to methamphetamines and go through withdrawal

Brown trout
A brown trout caught in Seedskadee National Wildlife Refuge USFWS Mountain-Prairie via Flickr [CC BY 2.0]

When humans dispose of trash or chemicals in waterways, our aquatic neighbors might regard that waste as food. In a new study published in the Journal of Experimental Biology, researchers tested the effect of methamphetamine, a common drug found in wastewater, on brown trout (Salmo trutta) by placing them in a water tank spiked with the drug. The outcome isn’t exactly surprising: Brown trout can get hooked on meth, too.

Meth use has skyrocketed in the United States and Europe in recent years, especially during the pandemic, reports Carrie Arnold for National Geographic. But meth isn’t completely absorbed when consumed, eventually exiting the body in excrement. In their current state, wastewater treatment plants aren’t equipped to remove this kind of contaminant. As a result, meth-laced sewage water released back into the environment still contains high levels of the substance.

"Where methamphetamine users are, there is also methamphetamine pollution of freshwaters," writes study author Pavel Horký, a behavioral ecologist at the Czech University of Life Sciences Prague, to Nicoletta Lanese of Live Science in an email.

The team of researchers studied the effects of the drug on brown trout by replicating meth-polluted wastewater conditions in the lab. The researchers placed 60 trout in a water tank spiked with methamphetamine that matched the levels of discharge from wastewater treatment plants in Czechia and Slovakia. The trout were forced to quit cold turkey after two months of swimming in meth-y waters. These trout moved around less than the clean trout—a sign of withdrawal, according to the researchers. Horký’s team also found traces of meth in the trout’s brains up to ten days after the exposure.

The researchers also gave meth-doped trout and clean trout the option of entering either a stream contaminated with meth or another without. Compared to the clean trout, meth-exposed trout preferred to return to the stream with the drug, which the researchers inferred as a sign of addiction.

The observed change in trout behavior due to meth consumption could be detrimental for trout in the wild, Live Science reports. Torpid trout could have difficulties finding food, adhering to their usual migration patterns and finding mates. They may even be sitting ducks for predators. Trout addicts could also deliberately seek out sources of the drug, which may encourage them to congregate around wastewater treatment areas. The shift in trout distribution in their natural habitats will ripple across the food web and affect the broad range of predators that feed on them, per National Geographic. Trout are important food sources to birds, other fish and even humans.

The story of drug waste wreaking havoc in aquatic environments isn’t unique. Per National Geographic, a 2018 study found that cocaine pollutants could disrupt the migratory behavior of critically endangered European eels. The same year, a drug test administered by scientists on mussels in Puget Sound found positive traces of opioids in these shellfish, reports Susan Scutti for CNN. Another study showed that contraceptive pills were feminizing male fathead minnows in Ontario: High estrogen doses caused the male fishes to develop eggs in their testes.

"There are a lot of contaminants of emerging concern—not only illicit drugs, but also standard prescription medicines, like antidepressants," Horký tells Live Science.

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