Humans have spiked ecosystems with a flood of active pharmaceuticals. The drugs are feminizing male fish, confusing birds, and worrying scientists.
In the fall of 2012, PhD student Hendrik Wolschke leaned over the side of a boat on the Elbe River in Northern Germany and lifted a stainless steel bucket from the water’s depths. Pulling it aboard, he set the sloshing bucket next to a pile of empty plastic bottles.
Once he’d filled them with the river water, Wolschke packed the bottles into coolers for transport southeast to the chemistry laboratory of his doctoral advisor, Klaus Kümmerer, at Leuphana University of Lüneburg. There, the bottles joined water samples collected from all around Germany: the North Sea, drainage streams from wastewater treatment plants, even drinking water straight from municipal taps.
Each sample was tested for the most widely prescribed antidiabetic drug in the world—metformin, which treats high blood sugar by suppressing glucose production in the liver. Humans do not metabolize the drug, so within 24 hours of being swallowed, metformin is excreted from the body essentially unchanged.
Because of its high prescription rate—the U.S. alone dispensed 76.9 million metformin prescriptions in 2014—it’s not surprising that the drug is abundant in the environment. Metformin was present in every water sample Kümmerer’s team tested, including tap water, at concentrations exceeding environmental safety levels proposed by an international Rhine River Basin agency by 50 percent. When publishing the results in 2014, Kümmerer and his coauthors concluded that the drug is likely “distributed over a large fraction of the world’s potable water sources and oceans.”1
That sounds melodramatic, but he may be right, and the problem is not limited to metformin. Rebecca Klaper and colleagues at the University of Wisconsin–Milwaukee recently measured concentrations of pharmaceuticals in Lake Michigan, where researchers had speculated that any drugs that were present would be highly dilute and not detectable.
On the contrary, Klaper’s team found evidence of 32 pharmaceuticals and personal care products in the water and 30 in the lake’s sediment. Fourteen of these were measured at concentrations considered to be of medium or high risk to the ecosystem, based on data from the US Environmental Protection Agency (EPA) and other researchers.2 Metformin topped the list, at concentrations of concern even 3 kilometers off the shores of Milwaukee.
Ecologists have long recognized that pharmaceuticals, both unmetabolized drugs like metformin and others that break down into various metabolites, are polluting the environment, but researchers have traditionally focused on just two classes: antibiotics and endocrine-disrupting compounds such as the birth control hormone estradiol. Antibiotics in the environment promote antibiotic resistance in a range of bacterial species, and endocrine disruptors are known to affect development and reproduction in animals.
Metformin was not thought to have either of those effects on animals. But in lab experiments conducted earlier this year, Klaper’s team discovered that male minnows exposed to metformin at concentrations comparable to those of wastewater treatment plants produce proteins typically found only in female fish, develop feminized gonads, weigh less, and have fewer offspring.3 The antidiabetic is now one of a growing list of drugs that researchers are realizing pose major ecological problems.
“All [pharmaceuticals], by design, are meant to elicit a biological response,” says the US Geological Survey’s Dana Kolpin, chief of the organization’s Emerging Contaminants Project. “We need to know what the environmental consequences are.”
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