A staggering 10,000 metric tonnes of plastic debris enter the Great Lakes every year from the US and Canada, accounting for about 80 per cent of the litter on their shorelines, according to a new study.
The study that tracked high concentrations of plastic in the Great Lakes - series of interconnected freshwater lakes located at the Canada-US border - could help inform cleanup efforts and target pollution prevention.
"This study is the first picture of the true scale of plastic pollution in the Great Lakes," said Matthew Hoffman, assistant professor at Rochester Institute of Technology (RIT) in the US.
Hoffman used computer simulations to follow the volume of plastic debris moving across state and international boundaries - from Illinois to Michigan and from Canada to the US.
Earlier studies estimate 40,000 to 110,000 metric tonnes of plastics enter the oceans along the US coastline, he said.
Researchers report that half of the plastic pollution entering the Great Lakes - 5,000 metrics tonnes per year - goes into Lake Michigan, followed by Lake Erie with 2,500 metric tonnes and Lake Ontario with 1,400 metric tonnes.
Lake Huron receives 600 metric tonnes of plastic and Lake Superior, 32 metric tonnes per year.
Estimates of surface microplastics entering the lakes each year show 4.41 metric tonnes in Lake Erie, 1.44 metric tonnes in Lake Huron and 0.0211 metric tonnes in Lake Superior.
Plastic pollution in Lake Michigan is about the equivalent of 100 Olympic-sized pools full of plastic bottles dumped into the lake every year, whereas the yearly amount of plastic in Lake Ontario equates to 28 Olympic-sized pools full of plastic bottles, said Eric Hittinger from RIT.
Prior observational studies measured localised concentrations of plastic pollution in the open water, tributaries and along the shorelines.
The new study applied mathematical modelling for the first
time to extend the scope of the problem over time and spatial scales.
The inventory gives full mass estimates on the entire connected lake system and maps plastic debris moving between lakes and across interstate and international borders.
The results provide environmentally realistic concentrations of plastic in the Great Lakes.
The study show debris travels differently in the Great Lakes than in the ocean.
Instead of the floating "garbage patches" found in the ocean, plastic in the Great Lakes are carried by persistent winds and lake currents to the shore - often washing up in another state or country, Hoffman said.
Plastic accounts for about 80 per cent of the litter on the shorelines of the Great Lakes.
The study quantifies dense plastic that quickly sinks and surface plastics like microbeads, fragments and pellets, plastic line and Styrofoam, which could be consumed by wildlife and potentially enter the food chain.
The study appears in the journal Marine Pollution Bulletin.
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