Antidepressants in the Water Affect Daphnia and Their Babies… and Their Babies’ Babies!

Selective serotonin reuptake inhibitors - more commonly known as SSRIs - are used to treat depression and anxiety disorders.  They have been widely prescribed for decades and have improved the quality of life for millions of people.

But as the saying goes, what goes in must come out, and SSRIs that are either excreted by humans or improperly disposed of are accumulating in our water, putting the health of aquatic organisms at risk. Now, new research from the Department of Integrative Biology has found even very small amounts of these pharmaceuticals can impact aquatic species and their offspring multiple generations later.

Dr. Andreas Heyland is using a tiny species of freshwater zooplankton called Daphnia magna to demonstrate the weight of this issue. Heyland and his research team analyzed the effects of SRRIs on the life history trade-offs in the life cycle of daphnia exposed to two compounds, fluoxetine and sertraline, the major components of the antidepressants Prozac and Zoloft. The team found that just 72 hours of exposure affected not only the physiology of the exposed daphnia, but also their unexposed offspring up to four generations later.

“We were primarily interested to look at it from a transgenerational perspective,” says Heyland. “Even with chronic exposures, you don’t actually account for how it can affect development and how these effects carry forward through generations, which is why we looked at multiple generations.”

The lab found that SSRI exposure altered the normal balance between the size of the organism’s offspring versus how many offspring it produced, and between current reproduction versus future reproduction. By analysing these reproductive trade-offs over generations, Heyland’s group were able to gain insight as to how daphnia respond to SSRI contamination in the water.

For example, SSRI exposure initially causes an increase in reproduction in exposed daphnia, but this comes at a cost to future generations.

“If they reproduce more now, they can reproduce less in the future, and this can have effects on longevity as well as a number of other reproductive traits,” explains Heyland.

A powerful but troubling aspect of this research is that the lab used physiologically relevant concentrations of these compounds in their experiments, meaning that the daphnia were exposed to concentrations that are 10-100 times lower than what is currently present in our water systems.

“We were able to find consequences of an extremely low exposure, including transgenerational effects that were quite significant,” says Heyland.

One unexpected finding of this study was that SSRI exposure caused daphnia to “switch” their mode of reproduction in subsequent generations.  Under normal conditions, daphnia reproduce by asexual cloning.  But in times of stress or when environmental conditions are harsh, they can produce tough “resting” eggs called ephippia through sexual reproduction.  These ephippia can withstand adverse conditions for long periods of time.

“I would call it a bet hedging strategy” says Heyland. “It looks like these SSRIs can contribute to later generations switching to sexual reproduction, which is a really interesting finding.”

Overall, this work demonstrates the multi-generational impacts of aquatic contamination with common pharmaceuticals. 

“We were able to shine a novel light on how to analyze transgenerational effects using life history theory. From an interpretation perspective, you need to consider the trade-offs or present versus future consequences,” says Heyland. “Here we were able to demonstrate that this very low exposure to SSRIs have very real consequences that are perpetuated through generations.” 

The Heyland lab plans to take this transgenerational model and use it to study the impacts of other environmentally relevant compounds. 

With daphnia occupying an integral role in aquatic food chains, understanding how toxins and other environment stressors can cross generational boundaries will be critical to protecting the health of aquatic ecosystems. 

This study was funded by the Natural Sciences and Engineering Research Council.  

 Read the full study in the journal  of Comparative Biochemistry and Physiology.

 Read about other  CBS Research Highlights.