A recent inventory of plastics pollution in the Great Lakes will help prevent continued pollution and provide a baseline for those working to clean the lakes, which supply local residents with drinking water.
The Great Lakes Basin is a system of five bodies of water and their tributaries along the northernmost tier of the United States, four of which border Canada. They include Lake Superior, Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario. In 2012, the system was supplying water to more than 30 million Americans.
Scientists from the Rochester Institute of Technology found that almost 10,000 metric tons — 22 million pounds — of plastic debris enters the Great Lakes annually from both the United States and Canada. The estimate varies significantly from prior estimates, which put the figure at between 40,000 and 110,000 metric tons of plastics.
‘True Scale of Plastic Pollution’
Matthew Hoffman, an assistant professor in the university’s School of Mathematical Sciences and the lead author of the study, said their survey is the first to provide a “true scale of plastic pollution in the Great Lakes.” The researchers used computer simulations to follow plastic debris moving across state and international boundaries.
The RIT researchers have expressed the extent of the pollution in terms the public can readily grasp. Half of the plastic pollution in the Great Lakes is concentrated in Lake Michigan. Enough plastic bottles to fill 100 Olympic-sized pools — 5,000 metric tons — are dumped into this one lake every year. The amount of plastic dumped into Lake Ontario — 1,400 metric tons a year — equals 28 Olympic-sized pools full.
The researchers also estimated the amount of surface microplastics that enter the lakes each year: Lake Erie, 4.41 metric tons; Lake Huron, 1.44 metric tons; and Lake Superior, .0211 metric tons.
Tracking Movement of Plastics Pollution
How the plastic travels in the Great Lakes varies in comparison to the movement patterns observed in the ocean. The debris travels to the shore via persistent winds and lake currents.
Plastic accounts for approximately 80 percent of the litter on the shorelines of the Great Lakes, according to the researchers, who were able to quantify both the dense plastic that quickly sinks as well as microplastics waste such as microbeads, plastic line, and Styrofoam.
Major cities — Chicago, Toronto, Cleveland and Detroit — release more plastic than the amount that accumulates on their shorelines. Hoffman explains:
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. […] Particles released from Toronto appear to accumulate on the southern coast of Lake Ontario, including around Rochester and Sodus Bay.
Where Does It Come From?
Plastic of all types and sizes enters the water from various sources. Some scientists estimate that only around 20 percent of oceanic microplastics are dumped straight into the sea. They believe the remaining 80 percent comes from waste dumps, litter, sewage, and other land-based sources.
Microplastics are a particular concern. These bits of polyethylene or polypropylene less than 5 millimeters in size have been found in bodies of fresh and salt water worldwide. Their precise effect on human health is not yet fully known, but the concern is that they could contaminate drinking water supplies via freshwater sources.
Little is known about microplastics’ on freshwater ecosystems, but there is a growing body of research on the topic. A study published in early 2016 examined urban rivers in Illinois. Scientists discovered that wastewater treatment plants were a source of microplastics in 80 percent of the rivers. Roughly 15,000 to 4.5 million microplastics particles are being released each day from a single treatment plant, according to the Loyola University Chicago scientists.
The RIT researchers used population and hydrodynamics models to simulate the distribution of plastic debris throughout the Great Lakes between 2009 and 2014. Data from the National Oceanic and Atmospheric Administration Great Lakes Coastal Forecast System was used to simulate currents responsible for moving the plastic throughout the lakes.
The full findings — “Inventory and transport of plastic debris in the Laurentian Great Lakes” — were published in the journal Marine Pollution Bulletin.