(AREA) -- Already ravaged by invasive species and industrial pollution, the Great Lakes now confront a newly discovered threat: untold millions of tiny plastic bits, some visible only through a microscope. Scientists discovered masses of floating plastic particles in Lakes Superior, Huron and Erie last year. This summer, they're widening the search to Lakes Michigan and Ontario. It's unclear how long the pollution has been in the lakes or how it is affecting the environment. Studies are under way to determine whether fish are eating the particles and passing them up the food chain. Scientists suspect the particles are abrasive "micro beads" used in personal care products such as facial and body washes. They're so minuscule that they flow through screens at waste treatment plants and wind up in the lakes.