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Study: MN Rivers that flow into Lake Superior are polluted, but not as polluted as other areas

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Two tributaries in Northern Minnesota that feed into Lake Superior were part of a recent study that looked at how much plastic flows into the Great Lakes.

The study came out this week in the Environmental Science & Technology Journal. Scientists from the U.S. Geological Survey in Wisconsin and from the State University of New York at Fredonia contributed to the research.

Scientists have known for awhile that microplastics – microscopic plastic particles that come from bottles, clothing fibers and personal care products – are prevalent in the Great Lakes.

However, this study showed that the tributaries are even more polluted than the lakes themselves.

"The concentrations that we saw in the tributaries were 10 to 1,000 times higher than in the Great Lakes," said Austin Baldwin, U.S. Geological Survey Hydrologist and the lead author of the study, according to Wisconsin Public Radio.

He is now studying the bottoms of Lakes Erie and Michigan to understand how much of these microplastics are sinking versus floating.

How Minnesota compared

The two sample areas that were studied in Minnesota – the St. Louis and Nemadji Rivers which flow into Lake Superior – were some of the least polluted out of the 29 rivers studied across six different states.

The Huron River at Ann Arbor, Michigan, Buffalo River at Buffalo, New York, and the Ashtabula River near Ashtabula, Ohio contained the highest concentration of microplastics.

This is partly because those tributaries are in urban areas, not forested areas like the rivers analyzed in Minnesota. However, the setting also makes the source of microplastics in the Minnesota rivers more mysterious, as Baldwin explains to MPR. 

More on microplastics

Synthetic fibers from fleece clothes, cigarette butts and diapers were most prevalent in the waters samples of the study, making up for 71 percent of the microplastics, explains PlasticNews.

Baldwin told MPR that other studies have shown that a few thousand to several hundred thousand microfibers can get flushed away when a single fleece jacket is washed. That's "kind of staggering," he said.

Microplastics can be harmful to the health of wildlife as well as humans, says the U.S. Geological Survey.

Congress passed a law last year that banned certain microplastics from being in cosmetic products. The law doesn't go into effect until 2018.

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