The Great Lakes, which hold a fifth of Earth's freshwater, have seen their share of ecological adversity. Yet on top of the invasive species, algae blooms and toxic chemicals they've endured over the years, an even subtler scourge is now lurking in their waters: billions of tiny plastic specks, including a horde of microscopic beads.

The problem is coming to light as scientists learn more about plastic pollution in water, from giant gyres like the Pacific Ocean "garbage patch" to freshwater systems like the Great Lakes. Ocean plastic comes from all over the world — including plastic bags, fishing nets and industrial pellets — and gradually breaks into smaller pieces without truly decomposing. But according to nascent research in the Great Lakes, much of that region's aquatic plastic may have been microscopic to begin with.

Initial samples from several Great Lakes are teeming with abrasive "microbeads," or tiny bits of polyethylene plastic commonly used as exfoliants in face soaps, body washes, toothpastes and other personal care products. Scientists found huge amounts of the beads — broadly known as microplastics — during a Great Lakes research cruise last summer, and they plan to publish a peer-reviewed study about them later this year.

Some of the preliminary findings have already been reported, though, and deemed "disturbing" by researchers with the 5 Gyres Institute. The cruise pulled in 1.7 million tiny plastic particles from Lake Erie alone, for example, an even higher density than most ocean samples contain. And preliminary data suggest "Lake Ontario is as contaminated as Lake Erie, if not more so," one of the project's leaders tells the Associated Press.

"These beads wash straight down your drain after washing your face, and directly into your watershed," according to 5 Gyres. "No sewage treatment system can capture them."

After establishing the prevalence of microplastics, the next step is to see if they're being ingested by wildlife — and if so, what kind of damage they can do. Eating larger pieces of plastic sickens and kills some marine creatures, but the main danger of microbeads is their ability to absorb toxins from the water, a distinct possibility in the Great Lakes thanks to decades of industrial dumping, spilling and leaking. Researchers have already found polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in Lake Erie's plastic debris, two industrial chemicals that can cause cancer and birth defects.

Sick wildlife is bad enough for the Great Lakes' ecology, but it could also hurt their commercial and sport fishing industries, which generate about $1 billion and $4 billion per year, respectively. Aside from harming animals directly, PCBs and many other toxins can "biomagnify" as they move up the food web, potentially threatening humans.

5 Gyres and other environmental groups have successfully pushed many big companies to stop using microbeads, albeit slowly. Unilever, the Body Shop and Johnson & Johnson have pledged to phase out microbeads by 2015, according to Treehugger, while Procter & Gamble plans to do so by 2017. In the meantime, though, 5 Gyres co-founder Anna Cummins says "there are no prospects" for removing microbeads from lakes or oceans.

For more about Great Lakes microplastics, check out this video from 5 Gyres:

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