From UPI :

MILWAUKEE, April 24 (UPI) — As the rate of diabetes skyrockets in the United States, so too are prescriptions for the drugs that treat the blood sugar disorder. One of the most common Type II diabetes medication is metformin.

But metformin isn’t just being found on pharmacy shelves and private medicine cabinets. It’s also increasingly showing up in freshwater systems. Now, new research suggests it could be to blame for intersex fish.

Rebecca Klaper, a researcher at the University of Wisconsin-Milwaukee, has been looking to the drug’s prevalence in watersheds, as well as exploring its potential effects on wildlife.

“It is the chemical we found in almost every sample and in the highest concentrations compared to other emerging contaminants — even higher than caffeine,” she said in a recent press release.

Fish expressing combinations of male and female sex organs are increasingly common in waters downstream from water treatment plants. The phenomenon has mostly been blamed on hormone-related drugs like birth control and beauty products such as acne medicine.

Metformin isn’t a hormone. Like other diabetes drugs, it targets blood-sugar regulation. But it’s also been occasionally used to treat a hormonal disease, common in women, called polycystic ovary syndrome. Klaper believes metformin may act as an endocrine disruptor.

When Klaper exposed fish to metformin in her lab, their growth or physical appearance was not altered, but eggs produced by the females showed signs of male and female morphology — suggesting metformin is indeed disrupting hormone-related reproductive processes.


From Emerging wastewater contaminant metformin causes intersex and reduced fecundity in fish:

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.



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