Source: Martin, J. M., Bertram, M. G., Saaristo, M., Fursdon, J. B., et. Al. Environ. Sci. Technol. 2019, 53, 6035-6043. https://dx.doi.org/10.1021/acs.est.9b00944
The burden of pharmaceutical pollution
Pharmaceutical pollution is a growing environmental problem, with traces of drugs (including antibiotics) being found in surface and ground waters all over the globe. Most pharmaceutical pollutants enter the environment through wastewater discharge from sewage treatment plants. These plants, designed to remove more traditional contaminants (like oils, solids, and bacteria), have a hard time removing pharmaceuticals. The burden on these treatment plants is only going to increase, due to human population growth and the continuous development of new drugs. The resulting release of active pharmaceuticals into the environment has the potential to adversely impact wildlife, and determining if and how specific species are affected is an open area of research.
Can antidepressants in the water impact fish?
In a recent study, Jake Martin, along with an international team of scientists, sought to determine if a common antidepressant, fluoxetine, could alter the behavior of fish at concentrations that have been detected in the field. They used eastern mosquitofish, small fish that resemble guppies and eat (among other things) mosquito larvae, as model organisms to investigate the effects of fluoxetine on anxiety-related behavior and sociability in fish.
Mosquitofish were separated by gender, and then divided into three fluoxetine exposure groups: control (no dose), low-dose, and high-dose (Figure 3, left panel). The low-dose represented concentrations of fluoxetine that might be found in surface waters, while the high-dose corresponded to concentrations in effluent-dominated systems (ie. near discharges from wastewater treatment plants).
In order to test for changes in anxiety-related behavior, fish were placed in a tank that was half black and half white (Figure 3, upper central panel). Most animals will naturally avoid brightly lit (white) environments, so measuring the time it took fish to enter the white side of the tank gave the scientists insight into their anxiety levels. Entering the white area faster indicated a decrease in anxiety, while hesitating to enter the white area indicated an increase in anxiety.
Martin and coworkers found that exposure to fluoxetine impacted the anxiety-related behavior of mosquitofish. Interestingly, female and male mosquitofish responded differently: females were less anxious at the low dose of fluoxetine and unaffected at the high dose, while males were unaffected at the low dose and more anxious at the high dose. The scientists suggested that this difference in response to antidepressants between male and female fish might be due to differences in their natural behavior: female fish in the control (unexposed group) were more anxious than males. Females could be naturally more anxious because they are bigger and are a more valuable food source for predators, while males are naturally less anxious because they need to take more risks in mating.
Sociability was tested by placing fish in a tank with a group of fish in a subsection (Figure 3, lower central panel). The amount of time the fish spent close to the group of fish vs away from the group of fish determined its sociability. For example, fish that stayed closer to the group for longer amounts of time had higher sociability (more social). Fluoxetine exposure did not seem to impact sociability in any of the fish.
Finally, the researchers investigated the buildup of fluoxetine in mosquitofish tissue and found that it was at higher concentrations in smaller fish than larger fish. This indicated that more bio-accumulation was occurring in the smaller fish, potentially due to these fish having higher metabolism (Figure 3, bottom right panel). It is important to note that pharmaceuticals impact fish in a variety of ways, and different responses have been found when testing different fish species, fish ages, drugs, etc.
Why does this matter?
Fish (and other animals) rely on anxiety-related behaviors to survive. For example, being more anxious can make prey fish more alert and therefore better able to escape from predators. However, it could also make them less likely to take the risks required to forage for food and mate. Therefore, a fine balance is required. Artificially altering this anxiety-related behavior and their natural instincts can have major consequences on the food web. Plus, mosquitofish have an important role to play in controlling the population of mosquitos, which has implications for the spread of mosquito-borne diseases.
What can we do?
We can help reduce the burden on our infrastructure and release of pharmaceuticals into the environment by making sure that we dispose of unused pharmaceuticals properly. The U. S. Food and Drug Administration (FDA) provides a helpful guide to the safe disposal of medicines. So, what is the best course of action for proper drug disposal? If they are available: take-back programs. Controlled substance take-back programs allow professionals to properly dispose of drugs. Drug Enforcement Administration (DEA)-sponsored disposal locations are more common than one might think, and you can also check with your local drugstore or police station for programs. If one of these locations is not convenient, many medicines can be disposed of in household trash. However, in some limited cases, when drugs are particularly dangerous to keep in the household and takeback programs are not available, the best disposal method is flushing them down the toilet (a list of these drugs is found here). Flushing pills down the drain unnecessarily has far-reaching repercussions for wildlife, and in disposing of them properly we can do our part to protect the environment.