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About 80 per cent of human-made debris found in the Great Lakes is plastic, ranging from tiny micro-beads found in cosmetics and clothing fibers to bottles and plastic wrap, scientists said Thursday during a meeting of Great Lakes scientists being held at the University of Vermont.

While the big pieces can be ugly, the smaller pieces can attract dangerous chemicals, such as pesticides or herbicides, which can then be eaten by plankton, mussels, fish or birds, the scientists said.

"The concern is ... these plastics act as a means to move ... toxic compounds into the food web and into us," said Sherri Mason, a chemist who led a Thursday session on micro-plastics at the 58th Annual Conference on Great Lakes Research.

The danger of plastic pollution in the world's oceans has been around for some time. However, the scientific awareness of the threat to the Great Lakes is relatively new, only coming to the attention of scientists in the last several years, said Mason, who works at the State University of New York at Fredonia.

During the past couple of years, Mason and her colleagues have documented micro-plastic litter — some too small to see with the naked eye — in the Great Lakes. Some of the particles are abrasive beads used in personal care products such as facial and body washes and toothpastes. Others are more traditional litter that don't decompose and only gets broken into smaller pieces.

Some states are making efforts to control the microbeads. Earlier this week, Michigan's two Democratic U.S. Senators, Debbie Stabenow and Gary Peters, introduced legislation to phase out the manufacture and sale of microbeads found in household products. Similar legislation has been introduced in the U.S. House.

Thursday's sessions were for scientists to bring each other up to speed on what is being done in different parts of the Great Lakes to confront the problem. They heard of efforts to count how much plastic is washing up on beaches in the U.S. and Canada. They also heard of efforts to count plastic pieces floating in the water of the lakes and their tributaries and in the sediment on the bottom.

The meeting also gave the scientists the opportunity to trade techniques and tips as detailed as the size of mesh that's most effective when used to skim for tiny plastics.

"The goal of all of this ... is creating a framework for assessing the risk of these plastics in the environment," said Melissa Duhaime of the University of Michigan. "So (we're) thinking about the risk of exposure to plastics and potentially to toxins, potentially to microbes and what the implications might be."