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Diabetes drug found in freshwater potential cause of intersex fish

Scientist looking at fish in tanks

UWM School of Freshwater Sciences researcher Nicholas Niemuth studies minnows that are being raised in water heavy with pharmaceuticals to measure the drugs’ effects.

A medication commonly taken for Type II diabetes, which is being found in freshwater systems worldwide, has been shown to cause intersex in fish –or male fish that produce eggs. The study determined exposure to the diabetes medicine metformin causes physical changes in male fish exposed to doses similar to the amount in wastewater effluent.

“In addition to intersex conditions, fish exposed to metformin were smaller in size than those not exposed,” Rebecca Klaper, a professor in UWM’s School of Freshwater Sciences, said. 

“Because intersex fish are particularly prevalent downstream from wastewater treatment plants, many studies have investigated the effect of hormones from birth control pills,” Klaper said.

Initially, the results of her study seemed surprising since metformin is not a hormone and it targets blood sugar regulation. However, it is also prescribed to women with a common hormonal disease called polycystic ovary syndrome. The research in her lab indicates metformin could be a potential endocrine disruptor — a chemical that confuses the body’s complicated hormonal messaging system, interrupting a range of normal activities, including reproduction.

“Of the chemicals she has detected in water samples collected from Lake Michigan, metformin stands out,” Klaper said.

“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.

The prevalence of the chemical in samples led the researchers to investigate what effects the medication may have in the environment.

In a previous study, the team exposed mature fish to metformin, and although there were no physical changes, they found the genes related to hormones for egg production were being expressed in males as well as females – an indication of endocrine disruption.

For the current study, the researchers monitored fish that had continuous exposure to metformin from birth to adulthood. The next step is to determine the corresponding changes in the genome, which Klaper is doing at UWM’s Great Lakes Genomic Center.

“We’re now working on a paper that investigates the metabolic pathways at various points in the fishes’ life to see what is changing,” Klaper said.

It’s strange to think that something so benign could be the cause of the problem. However, this highlights a different set of issues far more complex than the fish. We as a species are flushing away a multitude of chemicals that pass through our urine naturally — this is not even including the drugs that people mistakenly think can be flushed down the toilet.

Drugs like painkillers, caffeine, and even birth control can be found in drinking water (in low doses) and there is little we can do to filter them out. At the end of the day, we can do better and we should do better.

Niemuth, N., & Klaper, R. (2015). Emerging wastewater contaminant metformin causes intersex and reduced fecundity in fish Chemosphere, 135, 38-45 DOI: 10.1016/j.chemosphere.2015.03.060

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