Pharmaceuticals in Minnesota Lakes

The MN Pollution Control Agency has found pharmaceuticals even in remote lakes in the Boundary Waters Canoe Area Wilderness.

With Minnesota’s population hovering around 5.4 million people, it’s no wonder that many of our 10,000 lakes are beginning to feel the stress of too much love. Boaters and anglers leave traces of their visits behind – a little engine oil here, a broken fishing line there. Pollution also washes into lakes from nearby farms and neighborhoods – fertilizer, sediment, road salt and litter. Perhaps most troubling of all, however, is the discovery that even medicines and drugs are ending up in our waterways. How did these chemicals get into the water and what will the impacts be for fish and other wildlife?

In a study conducted by the Minnesota Pollution Control Agency (MPCA) in 2012, Pharmaceuticals and Endocrine Active Chemicals in Minnesota Lakes, researchers randomly selected 50 lakes in Minnesota and then tested water samples from these lakes for 125 chemicals, including common medications, personal care products, and endocrine active chemicals. Forty-seven of the fifty lakes sampled contained at least one chemical. The insect repellent DEET was found in 76 percent of the lakes, making this chemical the most frequently discovered. Bisphenol A (BPA), a chemical in packaging that the Food and Drug Administration has recently banned from baby bottles due to health concerns, was found in 43 percent of the lakes. Chemicals not previously analyzed – cocaine, the antidepressant amitriptyline, and the veterinary antibiotic carbadox – were all often detected in lakes as well.

Though the chemicals tested by the MPCA were only found at very low concentrations in lake water, it is disturbing to see how widespread these chemicals are in Minnesota. Also disturbing are results from a 2008 research project, which found evidence of endocrine disruption in fish collected from eleven Minnesota lakes, even though the lakes had only very low concentrations of chemicals[i].  

Wastewater is the most obvious source of drugs and medications in our waterways. When we take medications, trace amounts end up in our urine, which gets flushed down the toilet and then ends up in municipal wastewater (or an individual septic system). Treatment plants remove gross solids, bacteria and pathogens before discharging the water to lakes and rivers, but they aren’t equipped to remove pharmaceutical chemicals. Of the 50 lakes tested by the MPCA, one currently receives wastewater from a treatment plant and four used to prior to 1990. The researchers were perplexed, however, to also find pharmaceuticals and endocrine active chemicals even in remote, undeveloped lakes with no septic systems or wastewater treatment plants nearby. It is not entirely clear how the chemicals have become so pervasive, though evidence suggests that at least some of the contamination is coming from atmospheric deposition. In other words, trace amounts of cocaine that is smoked in southern Minnesota could eventually end up in a lake in the Boundary Waters.

Prescription Drug “Take-Back” Programs are one tool to help keep medications out of our lakes and rivers. People used to think it was safest to flush old and unused drugs down the toilet, but now we realize that isn’t the case. For example, Washington County has year-round drop boxes and holds special collection events so that old and unused medications can be disposed of safely, without harming fish and wildlife. “Take-Back” events are scheduled for April 26, 10am-2pm, at the County Government Building in Stillwater and June 14, 10am-2pm, at the County South Service Center in Cottage Grove. During the events, people are encouraged to drop off prescription, over-the-counter, and even pet medications, including pills and capsules, blister packs, creams and gels, unused Epipens, inhalers, IV bags, liquids, patches, powders, sprays, and vials. Drop off is free and anonymous and no ID is required. There are also year-round drop boxes for old and unused medications at the county government centers in Forest Lake, Stillwater and Cottage Grove. For more information, go to

In addition, researchers at the MPCA, University of Minnesota, and other institutions are continuing research to learn more about how pharmaceuticals are getting into our lakes, what impacts these chemicals might be causing, and what can be done to remove more chemicals from wastewater treatment plants.

[i] Writer, J. H., L. B. Barber, G. K. Brown, H. E. Taylor, R. L. Kiesling, M. L. Ferrey, N. D. Jahns, S. E. Bartell, and H. L. Schoenfuss. 2010. Anthropogenic tracers, endocrine disrupting chemicals, and endocrine disruption in Minnesota lakes. Sci. Total Environ. 409, 100-111.