Plastic is believed to be the main contaminant in the huge garbage gyres that pollute the oceans. Now researchers, led by Sherri Mason of the State University of New York at Fredonia, have found a stunning amount of plastic in the largest freshwater ecosystem on earth, the Great Lakes. And an increasing amount of it consists of the tiny plastic orbs used as abrasives in products like toothpaste and anti-acne lotions.

The particles are called microbeads, and consumers can avoid them by checking to see if plastic — maybe polyethylene or polypropylene — is on the product’s ingredient list. Once these virtually indestructible beads enter the water, they attract toxic substances, like PCBs. They become part of the aquatic food chain, soon eaten by fish and then, too often, by humans.

When Great Lakes fish are dissected, “they are festooned with microbeads,” said Henry Henderson, director of the Natural Resources Defense Council’s Midwest office, in Chicago. Besides carrying toxins, the beads can cause internal abrasions and can stunt growth of the fish.

Image Scientists are studying the impact of microbeads on the ecosystem. Credit... Lloyd DeGrane/Alliance for the Great Lakes

The studies done at Fredonia in 2012 and 2013 estimated that in Lakes Superior and Huron there were about 7,000 plastic particles per square kilometer. Lake Michigan had 17,000, Lake Erie had 46,000 and Lake Ontario had a whopping 248,000. Asked what amount of plastic pollution would be acceptable in the lakes, Dr. Mason said, “There shouldn’t be any plastic in our water, period.”