The Great Lakes are swimming with tiny specks of floating plastic, posing threats to both wildlife and human health.
Adding to years of research that have already documented gyres of plastic pieces swirling in the oceans, the new study is the first to officially add the world's largest freshwater ecosystem to the list of natural places affected by plastic pollution.
As scientists continue to investigate how much plastic is out there, where it's coming from and how it's moving between lakes and from lakes to sea, the findings may eventually offer strategies for mitigating the problem.
"The reality is that all the plastic we see in the environment makes its way into the water, which means it's making its way ultimately into us," said Sherri Mason, an environmental chemist at SUNY Fredonia. "What we find in the lakes is coming from us, so we're the problem but we're also the solution.
"I always want to encourage people to be thinking about their own lives and what they can do," she added. "If they're not going to go out and clean up the beach, they can find ways to reduce plastic in their own lives, especially single-use plastics. Forgo the straw. Stop buying disposable plastic bottles. Bring reusable bags so you don't need to take plastic bags home."
For decades, scientists have been documenting patches of plastic in the oceans that often congregate where circulation patterns push them together. Most of the bulk of that plastic, according to recent work, is made of tiny bits that are often invisible to the naked eye but can end up accumulating in the food chain.
While teaching a course on a boat in the Great Lakes last summer, Mason stared at the water and wondered if the same might be true there. When she returned to land, she searched the scientific literature for studies on plastic in the big lakes -- and turned up nothing.
To begin to fill the knowledge gap, she and colleagues used a manta ray-shaped trawl to collect 21 water samples from near the surface of three lakes: Superior, Erie and Huron. The trawl held a mesh net that caught anything larger than a third of a millimeter in diameter. Each sample filtered water along a distance of two miles.
The researchers did their best to free the many water bugs that landed in the net. Back in the lab, they removed seaweed, fish and other non-plastic items. Then they separated plastic bits by size. And they counted and weighed their stash.
From sample to sample, they found a huge variety in concentrations of plastic, ranging from an extrapolated 600 to 650,000 plastic pieces per square kilometer. Two samples yielded particularly high counts. Both were in areas where the topography of the lakes caused water to converge into river-like currents.
She and her team are currently writing up their findings for submission to scientific journals.
Some headlines about the new research have suggested that the Great Lakes plastic counts exceed anything that's been found in the oceans, but that's not necessarily accurate. Research cruises have found the equivalent of 12 million pieces per square kilometer in a few samples in both the Pacific and the Atlantic, said Kara Lavender Law, a physical oceanographer at the Sea Education Association in Woods Hole, Mass. Only with more comprehensive surveys will it become clear how extensive the problem is.
Expecting to pick up lots of large objects, Mason was surprised to find that the majority of plastics in her samples were tiny. It's not yet clear where all that microplastic is coming from, but Mason's theory includes broken down bits of things like bottle caps that get weathered on beaches, fragments of boats that chip off during washing, and polyethylene microbeads that appear in lots of commercial facial cleansers and slide right through wastewater treatment plants.
Once microplastic gets into the lakes, it can enter the food chain at any level, including phytoplankton, fish and people. Adding to both environmental and public health concerns, plastic readily absorbs toxic chemicals from the water, including DDT and other persistent organic pollutants that have circulated in the lakes for decades.
More than 35 million people live around the Great Lakes. Documenting loads of plastic there might do better at grabbing people's attention compared to studies of remote regions in the ocean, where people generally don't go, Law said.
"The problem of plastic pollution is so widespread, I'm not surprised they found plastic in the Great Lakes," she said. "It raises an alarm. You realize the impact of your everyday habits is expanding way beyond your local influence."