ALREADY FEELING DEPRESSED? NOW CONSIDER HOW DRUGS CAN HARM FISH

Water pollution can take many forms.

When we think about it, we probably first imagine things like oil and chemical spills, industrial outfalls, sewage discharges, and agricultural runoff.  Yes, such things are bad, and have the potential to do real harm to both marine and inland fisheries.

But there are also subtle pollutants out there, things that we rarely think of, and haven’t yet made a meaningful effort to control.  They can also be doing real harm.

Pharmaceutical pollution is one of those.

People take a lot of drugs, and a significant portion of what they take ends up in aquatic ecosystems.  Some of that happens in the obvious ways, when pharmaceutical companies discharge tainted water into a river, or someone throws unused drugs in a sewer.  But a portion of drug pollution also comes from the mere use of pharmaceuticals that pass through the body, are discharged in urine and then enter sewage systems. 

Current sewage treatment facilities don’t do a very good job of removing drugs, whether intentionally flushed or naturally introduced, from wastewater.  About 93% of drug compounds that enter a waste treatment facility pass through and are discharged into the ecosystem.  Technology exists that could reduce that percentage, but it is not cheap.

Scientists are now learning that as expensive as enhanced wastewater treatment might be, it can also be costly to allow pharmaceutical pollution to continue unabated, for such pollution can have an array of adverse impacts on aquatic life.

Many different sorts of pharmaceuticals have been found in inland and coastal waters.  One paper, “A review of the pharmaceutical exposome in aquatic fauna,” published in Science Direct in 2018, surveyed the existing research on the topic published through 2016.  If revealed that 631 different pharmaceuticals were reported found in the waters of 71 separate nations; of those, only 16 seemed to occur worldwide.  Relatively few published papers reported on pharmaceuticals appearing in fish or aquatic invertebrates, with only 43 articles, addressing occurrences in 18 different nations, discovered; the majority of such pharmaceuticals were either antibiotics or antidepressants.

Scientists are beginning to understand the impacts of pharmaceutical pollutants on aquatic animals, performing studies both in the laboratory and in the wild.  Such impacts appear to be diverse, and may depend not only on the drug involved, but also on the environment.

For example, researchers in the Czech Republic found that brown trout could become addicted to methamphetamine.  They split 120 trout into two groups; one group was placed in water laced with methamphetamine for eight weeks, the other remained in amphetamine-free water.  The fish from the amphetamine-laced environment were then moved to clean water for a ten-day period, in a simulation of drug withdrawal; after two days when no fish were exposed to methamphetamine, the trout were exposed to two flows of water, one clean, one laced with meth.

The trout that had spent eight weeks exposed to methamphetamine demonstrated evidence of addiction, favoring the meth-laced flow of water over the meth-free flow; the trout that were kept in clean water showed no such propensity.

While such experiment might seem almost frivolous, significant concentrations of methamphetamine have been found in rivers, usually concurrent with music festivals or similar events, where researchers say that addiction presents a real risk.

“Drug reward cravings by fish, as was documented in our results, could overshadow natural rewards like foraging or mating that provision homeostatic and reproductive success.  The elicitation of drug addiction in wild fish could represent another example of unexpected evolutionary selection pressure for species living in urban environments, along with ecological side effects of human societal problems within aquatic ecosystems.”

Another laboratory study, performed on guppies, suggested that exposure to the drug fluoxetine, better known as the antidepressant Prozac, made it more difficult for fish to adapt to changing environmental conditions.

Such study, “Psychoactive pollution suppresses individual differences in fish behaviour,” was published in the Proceedings of the Royal Society B in 2021.   The study notes that

“Different behavioural strategies among individuals…are ubiquitous in the animal kingdom and essential for animal populations to thrive.  A common view is that such variation increases the power of selection through ecological and evolutionary processes, ranging from intra-species competition to anti-predatory responses and mate choice.  For example, more active and risk-prone individuals have been found to secure more resources and enjoy more reproductive success relative to less active and more risk-averse conspecifics, but at the cost of higher mortality.  Such behavioural specialization is a major driver of reproductive isolation within lineages and precedes changes in gene frequency.  As a result, intra-species behavioural variation fuels resilience, providing the adaptive potential for animal populations to survive in a changing and increasingly polluted world...populations with higher degrees of behavioural variation have higher population growth and persist longer than less diverse populations in the face of environmental change.  Conversely, the risk of extinction rises with reduced behavioural differences between individuals…”

Researchers found that exposure to even very low concentrations of fluoxetine reduced behavioral variation between individuals.  Given the importance of such variation to a species’ ability to adapt to environmental changes, exposure to such pharmaceutical pollution could negatively impact fishes’ ability to survive in a changing world.

Such findings are not limited to laboratory environments.

Atlantic salmon smolts exposed to anti-anxiety medications such as Valium and Xanax in their natal rivers begin their first migration into the ocean sooner than unexposed smolts, often reaching the sea before their bodies have completely changed to suit a life in the ocean, and before ocean conditions change to best support a successful migration.

A very different category of chemicals, synthetic estrogens and other “endocrine disruptors,” are blamed for creating “intersex fish,” most notably smallmouth bass in the Potomac River, where male fish possess female features, and can even produce eggs.

In Florida, researchers have found signs that pharmaceutical pollution may be adversely affecting one of salt water anglers’ most storied, and most valued, inshore species—the bonefish.

Hakai Magazine recently told the story of two scientists from Florida International University, who are trying to determine why there are far fewer bonefish in the Florida Keys and Bahamas than there were three or four decades ago, why the size of the remaining fish has declined, and why the sex ratio has fallen out of balance, with males far outnumbering females.

After taking blood and tissue samples from more than 90 bonefish, the researchers have found high levels of 58 different pharmaceuticals to be present, including antibiotics, anti-depressants, and heart medicines.  Every fish sampled had at least one such drug in its blood; many had more, with some bonefish having as many as 17 different drugs in their systems.  An abundance of pharmaceutical pollutants was also found in the crabs and other invertebrates upon  which bonefish feed.

One of the scientists opined that

“There is compelling evidence linking drug pollution to bonefish decline.”

It’s not yet clear which drugs might be harming the bonefish, or how such harm might be caused.  As described above, some drugs can change fish behaviors, while others affect their ability to spawn successfully.  Bonefish might be impacted in either—or both—ways.

It’s not completely clear what can be done to limit pharmaceutical pollution.  Expanding wastewater treatment facilities, and rerouting home waste disposal from septic tanks to such treatment facilities would reduce, but not eliminate, the problem.

In the meantime, it seems that many of the drugs that people take, in an attempt to stay healthy, are threatening the health of both inland and coastal fish stocks.