A new study by Rochester Institute of Technology estimates that nearly 22 million pounds of plastics enter the Great Lakes every year.
Scientists at the university worked to track and inventory where and how much plastic enters the lakes and where it goes then, with their results now published in the journal Marine Pollution Bulletin.
"This study is the first picture of the true scale of plastic pollution in the Great Lakes," said Matthew Hoffman, assistant professor in RIT's School of Mathematical Sciences and an author of the report.
The authors say they hope their work will help focus efforts to get plastic out of the environment on key areas where the plastic enters the lake's ecosystems - namely cities and developed areas.
The findings show debris travels differently in the Great Lakes than in the ocean. Instead of the floating "garbage patches" found in the ocean, plastics in the Great Lakes are carried by persistent winds and lake currents to shore, often in another state or even across the U.S. Canada border, Hoffman said.
Hoffman used population data and formulas developed by ocean garbage trackers to determine how much plastic waste is generated in each area and how much of it is likely to get into the water. Researchers then used computer simulations to follow the volume of plastic debris moving on currents in the lake.
"You can look at the lakes and see where the people are and then develop a pretty good model to know where the plastic ends up,'' Hoffman told the News Tribune Wednesday.
On Lake Superior, for example, much of the plastic likely comes from the Twin Ports and Thunder Bay areas, but it is probably ending up along Wisconsin's South Shore and even Isle Royale thanks to prevailing winds and currents.
Hoffman and co-author Eric Hittinger, assistant professor of public policy at RIT, report that half of all the plastic pollution entering the Great Lakes, some 11 million pounds per year, goes into Lake Michigan, followed by Lake Erie with 5.5 million pounds, Lake Ontario with 3 million pounds and Lake Huron at 1.3 million pounds of plastic. Lake Superior, the cleanest and most remote of the lakes with the fewest urban area on its shores, sees far less - about 70,000 pounds per year.
The study estimates that the amount of tiny microplastics actually floating on or suspended in the lakes each year ranged from nearly 10,000 pounds in Lake Erie to 436 pounds in Lake Superior.
"We know some of the plastic sinks. But when we input the numbers, this is the amount that's floating near the surface,'' Hoffman told the News Tribune, noting that's the type of plastic most likely to end up in parts of the ecosystem such as fish. "But we also don't know a lot about what happens to the plastic that doesn't float and where it ends up."
While Lake Superior receives less plastic than other Great Lakes, Hoffman noted, it also holds its water far longer than other Great Lakes, offering more time for the plastics to add up.
In the past, regulators and researchers guessed at the amount of plastic in the lakes by observing local concentrations found in rivers and along lakeshores. The new study applied mathematical modeling for the first time to extend the scope of the problem over time and across the region.
Plastic accounts for approximately 80 percent of the litter on the shorelines of the Great Lakes. Major population centers are the primary sources of plastic pollution in the Great Lakes system, with Chicago, Toronto, Cleveland and Detroit among the largest sources. The study found that most of the plastics from those cities that enter the lake float away and end up on distant shores.
"Most of the particles from Chicago and Milwaukee end up accumulating on the eastern shores of Lake Michigan, while the particles from Detroit and Cleveland end up along the southern coast of the eastern basin of Lake Erie," Hoffman said.
Data from the National Oceanic and Atmospheric Administration Great Lakes Coastal Forecast System were used to simulate currents transporting plastic debris throughout the lake system.
Much of the plastic Hoffman calculated is trash, but other plastics come through our drains.
The report comes after many states and the governments of the U.S. and Canada have taken recent action to eventually stop the production and sale of personal care products containing tiny plastic beads - beads there were ending up in fish and other organisms in the lake. Researchers at the University of Wisconsin-Superior reported as early as 2013 that microplastics were a serious issue in the lakes.
More recent reports suggest the beads are just part of the problem - that plastic fibers, many from synthetic "fleece'' clothing, are as big or even bigger issue, showing up in fish and water across the lakes. It's believed the fibers are shed from garments while being washed and then pass through sewage treatment plants.