Humans' meth use is getting fish addicted - study

People are smoking so much methamphetamine they might be getting fish addicted, a new study has found. 

When people use drugs, traces of it end up in the water supply - this is how researchers around the world, including here in New Zealand, have been able to track trends in the use of illicit substances like MDMA and meth, as well as legal drugs like alcohol.

Pavel Horký from the Czech University of Life Sciences Prague wondered if enough of it was ending up in freshwater rivers to affect wildlife.

"Whether illicit drugs alter fish behaviour at levels increasingly observed in surface water bodies was unclear," he said.

To find out, Dr Horký and his team put brown trout - also found in New Zealand - into a tank of water laced with methamphetamine at a level commonly found in Europe - about one microgram (one-millionth of a gram) per litre.

After eight weeks they were offered the choice of staying in the meth-tainted water or switching to fresh.

"If the fish had become addicted to the low levels of methamphetamine in their water, they would be feeling the effects of withdrawal and would seek the drug when it was available."

And they did, choosing the meth water for days afterwards - while fish kept in clean water showed no such preference. The fish that had been swimming in meth also moved more slowly while experiencing withdrawal, if they happened to choose the clean water one day. 

"In addition, the addicted fish were less active than trout that had never experienced the drug, and the researchers found evidence of the drug in the fish's brains up to 10 days after the methamphetamine was withdrawn," the study, published in the Journal of Experimental Biology, said. "It seems that even low levels of illicit drugs in our waterways can affect the animals that reside there."

Brown trout.
Brown trout. Photo credit: Getty

Testing of New Zealand wastewater has found levels of methamphetamine "high compared to that reported for Western nations", research published in June found, though it's not clear whether this extends to freshwater sources. 

Writing for The Conversation, scientists Matt Parker and Alex Ford of the University of Portsmouth said sewage treatment plants aren't designed to filter out byproducts of people's illicit drug use, and if fish can get addicted to our meth leftovers, the effects could be devastating. 

"If the trout are 'enjoying' the drugs, as they appear to be in the recent study, they may be inclined to hang around pipes where effluent is discharged," the pair wrote. 

"One of the hallmarks of drug addiction is a loss of interest in other activities – even those that are usually highly motivated, such as eating or reproducing. It’s possible that the fish might start to change their natural behaviour, causing problems with their feeding, breeding and, ultimately, their survival. They may, for instance, be less likely to evade predators.

"Exposure to drugs not only affects the fish themselves, but their offspring. In fish, addiction can be inherited over several generations. This could have long-lasting implications for ecosystems, even if the problem was fixed now."

It's not just meth though, they note - pharmaceutical drugs like antidepressants and contraceptive pills can also be detected in waterways, and appear to be having detrimental effects on wildlife behaviour. 

"We must get to grips with the amount of pharmaceuticals in our waterways. The world is some way from fixing the problems of addiction and illicit drug use. But, at the very least, more should be done to improve filtration in sewage treatment plants, and to force water companies to take more responsibility for ensuring effluent doesn't affect wildlife."