Zebra mussels could be increasing mercury levels in fish, U of M study shows

A new University of Minnesota study shows that zebra mussels are increasing mercury levels in fish. 

Since they were first found in Minnesota lakes, countless studies have been done to find out how zebra mussels impact fish and other wildlife. But the study shows they can impact people too. 

"Mercury is a neurotoxin and really affects developing fetuses and children when they are developing," said Denver Link, U of M research scientist. 

Link and other university researchers looked at mercury concentrations in more than 350 Minnesota lakes, 90 of which have zebra mussels in them.

Link said what they found in those lakes was eye-opening. 

"They are making conditions more favorable for mercury to make its way into the food web," said Link. 

Walleyes, northern pike, bluegills, and black crappies are among the fish species who have seen increased levels of mercury.

Link said how zebra mussels contribute to higher mercury levels isn't entirely known. But one theory is that when the mussels take plankton from the water, they deposit an organic material, and that material creates conditions that allow mercury to thrive. 

"When those results came back it was astonishing to see the difference between zebra mussel lakes to un-invaded lakes," said Link. 

As studies continue, researchers said people who regularly eat fish may consider eating slightly fewer meals per month to stay below recommended mercury exposure levels.

"I think this study kind of gives a yellow flag of, if a lake is invaded with zebra mussels, maybe we should take a closer look at what is going on in the system. And monitor the system more closely for fish consumption," said Link. 

The study was funded by the University of Minnesota's Aquatic Invasive Species Research Center. 

The Minnesota Department of Health has a "fish consumption advisory page" that offers guidelines for fish species caught in Minnesota lakes and rivers.