Fish on Drugs–Part 2

Perch on low levels of an anti-anxiety drug might live longer—at least in a laboratory setting.

The new study from Swedish scientists revisits the issue of pharmaceutical pollution in wastewater. The team also raises questions about whether risk assessment tests should consider broader issues. The study appears in this month’s issue of Environmental Research Letters.

In the study, the researchers dosed Eurasian perch with Oxazepam. That common anti-anxiety drug belongs to the general class of drugs known as benzodiazepines.

The Eurasian perch, Perca fluviatilis. 1879 image by Alexander Francis Lydon through Wikimedia Commons (public domain in the U.S., U.K., and various other countries).

The Eurasian perch, Perca fluviatilis. 1879 image by Alexander Francis Lydon through Wikimedia Commons (public domain in the U.S., U.K., and various other countries).

As with many medications, some of what goes into people typically comes out in one form or another through urine. Most wastewater treatment plants are not capable of removing pharmaceuticals, however. Thus, they flow out into lakes and rivers with the rest of the plants’ discharge.

The concentrations found in the environment are very dilute, so the research team kept the levels used in their study far below the lethal dosage as well. At different points during embryonic development, groups of perch were exposed to different levels of the anti-anxiety drug. A control group of roe had no exposure.

After the roe hatched, the team monitored the behavior and survival rates. The concentration of the drug and the days when the roe were exposed made a difference on how long the fry survived. The bottom line: Perch in the higher-dose group lived longer than those in the lower-dose group and the control.

Does this mean having fish on drugs is a good thing? Not really.

Just last year, four of the five co-authors for the new study reported in Science that exposure to Oxazepam significantly increased perch boldness and feeding behavior. I reported on that study for Great Lakes Echo last year.

On the one hand, it makes sense that getting more food could help the fish live longer, especially in a safe lab setting. Out in the environment, though, bolder fish foraging for food could expose themselves to more predators. The fishes’ increased feeding could also potentially upset aquatic food webs. And other organisms that are key to the aquatic food web could suffer from hormone disruption or other ill effects. And, of course, there’s not one drug, but a whole brew in low concentrations in wastewater plant effluent.

Yet the new study raises an important question about the nature of risk assessments. Almost by definition, most studies focus on risks of harmful effects.

“A new, conceptual view of ecotoxicological testing should include the possibility that a substance can improve the health of an organism and make individuals affected by contamination more competitive than non-affected individuals,” co-author Tomas Brodin says in a press release from the Institute of Physics, which publishes Environmental Research Letters.

In theory, “standard” studies should already reflect some potential therapeutic effects. If something is helpful, there will be fewer ill effects as compared to a control. And in practice, considering all the pros and cons for every species in an aquatic food web is difficult.

I expect the new study by Brodin and his team will draw lots of comments among the scientific community. Meanwhile, low levels of drugs keep flowing out with wastewater discharge.


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