Emerging wastewater contaminant metformin causes intersex and reduced fecundity in fish

Chemosphere. 2015 Sep:135:38-45. doi: 10.1016/j.chemosphere.2015.03.060. Epub 2015 Apr 18.


The occurrence of intersex fish, where male reproductive tissues show evidence of feminization, have been found in freshwater systems around the world, indicating the potential for significant endocrine disruption across species in the ecosystem. Estrogens from birth control medications in wastewater treatment plant effluent have been cited as the likely cause, but research has shown that endocrine disruption is not solely predictable based on hormone receptor interactions. Many other non-hormone pharmaceuticals are found in effluent at concentrations orders of magnitude higher than estrogens, yet there is little data indicating the impacts of these other medications. The widely prescribed anti-diabetic metformin is among the most abundant of pharmaceuticals found in effluent and is structurally dissimilar from hormones. However, we show here that exposing fathead minnows (Pimephales promelas) to a concentration of metformin found in wastewater effluent causes the development of intersex gonads in males, reduced size of treated male fish, and reduction in fecundity for treated pairs. Our results demonstrate that metformin acts as an endocrine disruptor at environmentally relevant concentrations.

Keywords: Contaminants of emerging concern; Diabetes; Endocrine disrupting compounds; Pharmaceuticals and personal care products.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cyprinidae / growth & development
  • Disorders of Sex Development / chemically induced
  • Endocrine Disruptors / toxicity*
  • Environmental Monitoring
  • Estrogens / toxicity
  • Fertility
  • Gonads / drug effects
  • Male
  • Metformin / toxicity*
  • Reproduction / drug effects
  • Wastewater / chemistry
  • Wastewater / toxicity
  • Water Pollutants, Chemical / toxicity*


  • Endocrine Disruptors
  • Estrogens
  • Waste Water
  • Water Pollutants, Chemical
  • Metformin