TRAVERSE CITY, Mich. - Already ravaged by toxic algae, invasive mussels and industrial pollution, the Great Lakes now confront another potential threat that few had even imagined until recently: untold millions of plastic litter bits, some visible only through a microscope.
Scientists who have studied gigantic masses of floating plastic in the world's oceans are now reporting similar discoveries in the lakes that make up nearly one-fifth of the world's fresh water. They retrieved the particles from Lakes Superior, Huron and Erie last year. This summer, they're widening the search to Lakes Michigan and Ontario, skimming the surface with finely meshed netting dragged behind sailing vessels.
"If you're out boating in the Great Lakes, you're not going to see large islands of plastic," said Sherri Mason, a chemist with State University of New York at Fredonia and one of the project leaders. "But all these bits of plastic are out there."
Experts say it's unclear how long "microplastic" pollution has been in the lakes or how it is affecting the environment. Studies are underway to determine whether fish are eating the particles.
The newly identified hazard is the latest of many for a Great Lakes fish population that has been hammered by natural enemies like the parasitic sea lamprey, which nearly wiped out lake trout, and man-made contamination. Through it all, the fishing industry remains a pillar of the region's tourist economy. Until the research is completed, it won't be clear whether the pollution will affect fishing guidelines, the use of certain plastics or cities that discharge treated wastewater into the lakes.
Scientists have already made a couple of startling finds. The sheer number of plastic specks in some samples hauled from Lake Erie, the shallowest and smallest by volume, were higher than in comparable samples taken in the oceans.
They're so minuscule that they flow through screens at waste treatment plants and wind up in the lakes, said Lorena Rios Mendoza, a chemist with the University of Wisconsin-Superior. At the urging of scientists and advocates, some big companies have agreed to phase them out.
During a meeting of the American Chemical Society in April, Rios reported the team had collected up to 1.7 million tiny particles last year in Lake Erie, which acts as something of a "sink" because it receives the outflow from the three lakes to the north - Superior, Michigan and Huron.
The Great Lakes are no stranger to ecological calamity. Zebra and quagga mussels have destabilized food chains, and ravenous Asian carp are poised to invade. Runaway algae blooms that had been stamped out a generation ago have returned. Dozens of harbors and river mouths are fouled with toxic waste. Now, researchers are stepping up efforts to determine how much damage the plastic could do.
While it's unknown where the ocean plastic came from, microscopic examination of Great Lakes samples has produced a smoking gun: many particles are perfectly round pellets. The scientists suspect they are abrasive "micro beads" used in personal care products such as facial and body washes and toothpaste.