Alton Lake in northeastern Minnesota in May 2012. A new study of Minnesota lakes finds more evidence that water across the state contains a wide range of chemicals. Derek Montgomery for MPR

A new study of Minnesota lakes finds more evidence that water across the state contains a wide range of chemicals.

The largest study of its kind ever done in Minnesota shows chemicals from household products, prescription drugs and illegal drugs are common in Minnesota lakes. (Full study here.)

"It's confirming what we found in our other studies, but it also showed us some new things that we didn't see before and that are new to us," said Minnesota Pollution Control Agency researcher Mark Ferrey.

Evidence shows some of these chemicals are harmful to fish, but scientists are just starting to understand the environmental effects of products we use every day.

DEET MOST COMMON CHEMICAL

MPCA scientists sampled 50 randomly chosen lakes across Minnesota last year. They tested the water for 125 chemicals.

At least one chemical was found in 47 of the 50 lakes; one lake contained 13 different chemicals.

The common insect repellent DEET was found in 76 percent of lakes.

Bisphenol A, a chemical used in plastics, showed up in more than 40 percent of the lakes sampled.

This map shows the location of the 50 randomly selected lakes the MPCA sampled for 125 chemicals. Courtesy MPCA

New findings include one of the most commonly prescribed anti-depressants Amitriptyline in nearly 30 percent of lakes.

The veterinary antibiotic Carbadox was found in about 30 percent of lakes. Carbadox can only be used in hog production in the U.S. It's been banned in Canada and Europe because it can cause cancer.

And the illegal drug cocaine showed up in one third of the lakes sampled. The MPCA didn't plan to test for cocaine, but it was included in a test that looked for a variety of chemicals.

It's not unusual to find cocaine in water leaving sewage treatment plants. European scientists have found cocaine in air samples.

Ferrey, the MPCA researcher, said government estimates put U.S. cocaine consumption at 156 tons a year. He said that's about the same volume as one commonly used pharmaceutical.

"Maybe we shouldn't be too surprised that we're seeing cocaine in our environment like we see some of the other pharmaceuticals as well," Ferrey said.

This is the largest in a series of lake studies done in Minnesota. Ferrey said the test of 50 lakes is large enough to reflect the condition of all Minnesota lakes.

"These studies, probably for the first time, are giving us the data that we can statistically extrapolate to say, 'well, this is the condition of the lakes in our state,' " Ferrey said.

HOW DO THE CHEMICALS GET TO THE WATER?

The study identifies an expanding list of chemicals in the water. But it doesn't answer the question how the chemicals get into lakes. Sewage treatment plants and septic systems are often a source of pharmaceuticals and other chemicals.

But chemicals were found even in remote lakes with no roads nearby.

Scientists suspect some chemicals, like cocaine, are in the air and settle into lakes. Some chemicals might be falling with the rain. Ferrey said that's an area that needs more research.

All of these chemicals are found at very low levels, often a few parts per trillion.

What's a part per trillion? think of a football field-sized swimming pool four stories deep. Add one drop of water. That's one part per trillion.

Most common chemicals

"The concentrations that we're seeing, at parts per trillion level are vanishingly small," Ferrey said. "But there are more and more pieces of the puzzle coming together to show that yes they can affect organisms in our environment in ways that are very unsettling."

Ferrey points to recent research in Minnesota that found low levels of contamination cause behavioral changes in baby fish that make them less likely to survive.

And studies in mice found genetic damage for four generations after pregnant mice were exposed to bisphenol A, the plastics chemical.

The research on trace amounts of chemicals and pharmaceuticals is still very early, Ferrey said. He said 60,000 to 80,000 chemicals are in use, but only 91 are regulated by the Federal Clean Water Act.

Ferrey said there's a parallel to the 1970s when scientists began to understand the damage from industrial pollution.

"The emphasis in the 1970s was 'well here's this pipe spewing out waste into our river and we've got to put a stop to it.' And we did," Ferrey said. "Now what we need to do a little bit is look in the mirror. What are the products I use that are ending up in the waste stream and ending up in our surface water?"

Ferrey said the MPCA plans to continue testing lakes and streams to see if the level of chemicals increases or decreases over time.

A related study in 2010 tested 50 river locations around the state for 18 chemicals. Among the most commonly found chemicals in that study were food preservatives, a corrosion inhibitor found in de-icing solutions and dishwasher detergent, and anti-depressant pharmaceuticals. Previous studies have found endocrine-disrupting chemicals to be common in Minnesota waters.

Correction (Oct. 26, 2015): An earlier version of this story incorrectly reported the number of river locations tested for chemicals as part of a 2010 study.