Environmental agencies such as the EPA regularly monitor water supplies for pharmaceuticals designed to treat human afflictions so as to avoid the contamination of aquatic wildlife. However, illicit drugs can also be a huge concern, especially the highly addictive ones like cocaine or methamphetamines. After a hard weekend of partying or in the aftermath of a festival, the water can be contaminated with trace amounts of illicit drugs after they’re excreted by users.

One study, for instance, found that wastewater in Amsterdam contains 1,028mg of cocaine per one thousand people, the highest recorded in Europe thus far. It’s not clear how exactly aquatic wildlife is affected by drugs flowing through city drains, but a new study raises concerns.

According to recent experiments, brown trout (Salmo trutta) exposed to methamphetamine at concentrations similar to those recorded in the field in certain water treatment areas showed signs of addiction. If wild trout experience the same symptoms, they may experience difficulties reproducing or foraging food.

Meth: dangerously addictive to humans as well as wildlife

Methamphetamine (meth, blue, ice, crystal meth) is a powerful, highly addictive stimulant that affects the central nervous system. The drug produces feelings of euphoria and increased energy but with dangerous side effects such as elevated heart rate and blood pressure, mood swings, insomnia, and even death if overdosed. The major difference between methamphetamine and other amphetamines is that methamphetamine has longer-lasting and more potent effects.

According to a 2021 study published in JAMA Psychiatry, methamphetamine overdose deaths surged in an eight-year period in the United States. Increases in specific-drug mortality are one of the key indicators that public health officials use to identify drug use epidemics. Furthermore, a number of non-mortality metrics also show meth use increasing in the country. According to the 2018 National Survey on Drug Use and Health, 1.1 million people reported meth use, almost twice the number who reported heroin use. Similarly, meth use is skyrocketing in Europe as well.

The brown trout is a European species of salmonid fish that has been widely introduced into suitable environments globally. Although it’s native to Eastern European rivers, it can be found in waters ranging from western Asia to North Africa.

Researchers in the Czech Republic led by Pavel Horký of the Czech University of Life Sciences divided 120 trout into two equal groups, each with its own water tank that was either laced with meth or was clean. The meth concentration was one microgram per liter, an intermediate concentration relative to the values previously recorded in freshwater rivers. After eight weeks, the trout were moved to a different tank for ten days.

Two days after they were transferred to new water tanks, the researchers commenced a battery of behavioral and biological tests to look for any signs of withdrawal.

During one experiment, the trout were exposed to a two-current choice flume whereby one was dosed with the same concentration of meth the fish were previously exposed and the other was clean water. This sort of test is standard among scientists who study how aquatic organisms responded to various pollutants and is considered reliable.

The researchers found that the trout from the methamphetamine-contaminated group preferred to travel down the meth-laced water flume during the first four days they were transferred to their new tank. The control group displayed no particular preference.

Additionally, the trout from the methamphetamine tanks were less physically active than the control group. When the scientists opened up the brains of some of the fish, they found biochemical changes that were associated with withdrawal symptoms.

“Our results suggest that emission of illicit drugs into freshwater ecosystems causes addiction in fish and modifies habitat preferences with unexpected adverse consequences of relevance at the individual and population levels. As such, our study identifies transmission of human societal problems to aquatic ecosystems,” the researchers wrote in the Journal of Experimental Biology.

The study serves as a wake-up call, showing that wastewater is an overlooked route by which drugs can harm wildlife. If fish respond this way to meth, they will likely face behavioral and biological consequences when they interact with the many other drugs that people use such as cocaine, antidepressants, or painkillers. In many instances, these animals may respond in unpredictable ways since it is widely established that drugs can have wildly different effects on humans compared to other species.

As such, this should be enough information for policymakers and responsible organizations to start monitoring waterways and wastewater treatment plants for potentially harmful pharmaceuticals and illicit drugs.