A new model for assessing the risk of pharmaceuticals to fish
From Puget Sound to the Great Lakes and beyond to oceans and seas throughout the world, water quality tests show that our water bodies contain many types of pharmaceuticals. These pharmaceuticals, or medicinal drugs, commonly enter the environment through wastewater discharge. Medications pass through our bodies after we take them, and with every toilet flush these substances flow into sewer systems that connect to wastewater treatment plants. These medications are not broken down or removed by most water treatment plants, so they are discharged with treated wastewater that is released into rivers, lakes and other water bodies. In Western Washington, that often means medications in wastewater are released directly into Puget Sound and its many tributaries.
Given the sheer volume of lakes, sounds, and seas, it may seem difficult to believe that a small pill could cause much harm to fish.
Now, a newly published study describes a method for assessing the potential risks posed to fish by commonly prescribed medications. The study utilized data on the concentrations of pharmaceuticals in global surface waters along with data on pharmaceutical efficacy (the minimum concentrations in the blood that cause a therapeutic effect in people) to identify and rank pharmaceuticals most likely to be harmful to fish. The work also builds on previous research in Puget Sound, where studies on juvenile Chinook salmon highlighted high-priority pharmaceuticals, including hormones and antidepressants, in urbanized watersheds.
Many medications can cause biological effects at very low concentrations. Of the medications included in the study — authored by James Meador, environmental toxicologist at the University of Washington, and research scientist Molly Shuman-Goodier of WDFW’s Toxics Biological Observation System team — more than half may affect fish health and behavior at even very low concentrations. Some medications are so strong that they can affect fish at levels below current detection limits in water.
Why medications in water are a threat to fish
How these pharmaceuticals end up in our waters in amounts significant enough to affect fish is no mystery. In Washington, the human population around Puget Sound is about 4.5 million and continues to increase. According to the National Institute of Health, nearly two in three people take at least one prescription medication regularly, and one in four take at least three prescription medications. In a year, that can add up to hundreds of millions of doses — some still at or near full strength — being flushed into toilets that ultimately drain into streams, rivers, and nearshore marine waters.
Wastewater treatment plants are good at removing harmful bacteria and viruses, and can also remove some chemicals before releasing treated water into the environment. However, many medications are designed to remain stable in extreme conditions, so they do not break down easily. Medications that are taken by mouth, for example, are designed to withstand the harsh acidity of the stomach. This means that typical wastewater treatments do not affect many pharmaceuticals.
But can these medications in the water really affect fish? While humans and fish might have things like eyes, a mouth, a heart, and a backbone in common, we physically appear more different than alike. Logically, it seems medications designed for humans who walk on land and breathe with lungs wouldn’t work on fish.
This is where things get interesting. Human cells and fish cells actually do have a lot in common, including sharing up to 85% of the same types of cell receptors targeted by pharmaceuticals. This means that a medication designed to lower your cholesterol can, in fact, have a similar effect on an Endangered Species Act-listed Chinook salmon — or any fish. As Meador describes, a salmon may appear physically healthy, but if exposed to a high enough amount of a human cholesterol medication, it will struggle to retain enough body fat to sustain it during periods of low food availability. This means, affected fish may not be able to successfully grow or reproduce, further threatening an already imperiled population.
In some cases fish may also be affected by exposure to lower doses of medication than people. Also, depending on the medication, some pharmaceuticals could stay in a fish’s body longer, resulting in extended period for harmful effects to potentially occur.
Assessing risks of medications to fish
Because the medications found in water bodies were not intended for use on fish, there is often no data on what is considered a “safe” level of exposure. The fish plasma model is a way to calculate relative pharmaceutical risk to fish without needing to perform tests with each medication. Using established techniques, it is possible to measure directly, or predict, concentration of a medication in a fish’s blood using the known water concentrations.
By using lists of commonly prescribed medications and water quality data from the United States as well as other countries, risks to fish can be assessed for global waters, and applied regionally to predict potential effects to fish in Puget Sound. This study identified the groups of pharmaceuticals that are likely to pose the greatest threat to fish, which include hormones, antidepressants, blood pressure medications, and allergy medications. In Puget Sound, other substances found at levels of concern to fish included caffeine and over-the-counter pain relievers, as noted by other authors.
Out of 345 pharmaceuticals included in the new study, 57 were rated as a high priority due to their high potency, elevated surface water concentrations, and potential to harm fish.
While this study focuses on the risks posed by individual pharmaceuticals, the real threat to fish is likely far greater. There are many different medications designed to provide the same effect, so even if each one is not individually found at a level of concern in the water, six types of similar medications may add up to a harmful amount. Some medications can interact with one another, increasing the effects. And finally, being exposed to multiple types of medications that affect different body systems could overwhelm a fish’s ability to maintain healthy function.
Ways to reduce medications in water
This study shows the need for monitoring surface water levels of commonly used medications, especially those that can be harmful in very small amounts.
The situation may seem bleak, but there is some good news: wastewater treatment plants are exploring options for integrating low-cost, efficient, and effective ways to remove pharmaceuticals from water.
You can do your part by returning unused medications to your pharmacy or other take-back program rather than flushing them down the drain.
