How does pharmaceutical pollution affect fish?

The Snake River courses through a boulder field near Keystone. Colorado.
Traces of medicine in freshwater streams have a wide range of impacts on fish.

New study documents wide range of impacts

Staff Report

Fish exposed to remnant traces of medicines, including pain relievers, muscle relaxants and antidepressants, grow more slowly and have a harder time escaping predators, say scientists who carefully studied the effects of pharmaceutical pollutants.

The study analyzed effects from nine individual pharmaceuticals, as well as varying mixtures of these chemicals, on both juvenile and adult fathead minnows. It was conducted by the Aquatic Toxicology Laboratory at St. Cloud State University and the U.S. Geological Survey, with the findings published in a special edition of Environmental Toxicology & Chemistry.

”Exploring the effects of multiple pharmaceuticals in mixtures at concentrations previous measured in the environment provided for immediate relevance of the study,” said St. Cloud State University scientist Heiko Schoenfuss, the lead author of the study. “The pharmaceuticals studied are highly prescribed and have been found in the environment in previous studies,” Schoenfuss said.

Previous USGS research showed there are more releases of pharmaceuticals in areas where medicinal manufacturers, may contribute a disproportionately larger amount of pharmaceuticals to wastewater treatment plants.

Fathead minnows were used as they are a common laboratory model for studies of this kind and are also an ecologically important species that can be found throughout North America. The minnows were exposed to both individual pharmaceuticals and mixtures of these chemicals in a laboratory setting as well as to treated wastewater at a wastewater treatment plant to represent a real world setting.

“Including the field exposures was an important part of this study,” said USGS scientist Dana Kolpin, one of the study’s co-authors. “Our research documented that effects observed in the field are not always easily reconciled by laboratory studies because of the full complexity of real-world conditions. Because of this, it’s crucial to include a wide variety of conditions and organism life stages when assessing the effects of pharmaceuticals on aquatic ecosystem health.”

The scientists looked at a wide range of adverse health effects at different life stages. Juvenile fathead minnows exposed to the pharmaceuticals suffered from reduced growth and altered escape behavior.

Adult females and males were found to react differently to pharmaceutical exposures. Adult females generally experienced an increase in relative liver size compared to control females, suggesting that the liver is reacting to the influx of pharmaceuticals.

Adult males exposed to the pharmaceuticals did not defend their nests as rigorously as those that were not exposed to the pharmaceuticals. The males exposed to wastewater treatment plant effluent in the field component of this research ended up producing a chemical known as plasma vitellogenin, a protein associated with egg production in females and is an indicator of feminization of male fish.

The following pharmaceutical chemicals were studied:

  1. Hydrocodone: an opioid pain reliever
  2. Methadone: an opioid pain reliever
  3. Oxycodone: an opioid pain reliever
  4. Tramadol: an opioid agonist pain reliever
  5. Methocarbamol: a muscle relaxant
  6. Fluoxetine: an antidepressant
  7. Paroxetine: an antidepressant
  8. Venlafaxine: an antidepressant
  9. Temazepam: a sleep aid

The paper describing the results of this study in detail can be found in Environmental Toxicology and Chemistry, and is part of a long-term effort to understand the fate and effects of contaminants of emerging concern and to provide water-resource managers with objective information that assists in the development of effective water management practices.

To learn more about the study, please see this USGS science feature. To learn more about USGS environmental health science, please visit the USGS Environmental Health website and sign up for the GeoHealth Newsletter.


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