Remnants of your beauty products could be making their way into your gut via a rather circuitous route.

Over the past several years scientists have documented the existence of giant gyres of plastic trash swirling around the world’s oceans; the Pacific garbage patch is twice the size of Texas. Now scientists have measured the extent of plastic pollution in the Great Lakes of the US. And unlike the bottles, toothbrushes and other detritus in the oceans, much of the garbage researchers gathered in Lake Erie, Lake Huron and Lake Superior takes the form of micro-particles measuring less than 1 millimeter (0.04 inches).

That includes tiny bits of plastic called microbeads, barely visible to the eye, that are found in face scrubs, shower gels and other beauty products. Scientists who spent three weeks last year trawling the three lakes have now published the results of their research (paywall), and found that microbeads are more concentrated in the lakes than in most of the oceans.

The study by the 5 Gyres Institute, a nonprofit that researches ocean plastic pollution, and the State University of New York at Fredonia, suggests that when beauty products are washed down the drain, microbeads aren’t getting caught by sewage treatment, and instead are washing into the lakes and into rivers that drain into the Atlantic Ocean. The microbeads “were of similar size, shape, texture and composition to plastic micro-beads found in many consumer products used as exfoliants,” said Marcus Eriksen, head of 5 Gyres and the lead author of the study.

Concentrations of micro-plastics ranged from 450 to 450,000 pieces per square kilometer (0.39 sq miles) with an average of 43,157 per square kilometer. Like other plastics, microbeads get eaten by fish and other marine life, accumulating as they in turn are eaten by larger fish, some of which may end up on people’s dinner plates.

As well as the microbeads, researchers also found significant concentrations of aluminum silicate, a byproduct of pollution from coal-burning power plants. According to the paper, there are 144 coal-fired power plants in the eight states that border the Great Lakes.

The highest concentration of micro-plastics was found in Lake Erie. “All the Great Lakes empty through Erie and concentrations go up as you move through them,” Stiv Wilson, the 5 Gyres Institute’s policy director, told Quartz.

The Institute has used the data it has gathered to lobby several big Western cosmetics companies to phase out their use of microbeads. Wilson said most have pledged to do so by 2015 and the institute is now turning its attention to Asian brands.

It’s also trying to get consumers to exert their influence. The Beat the Microbead smartphone app lets you scan products to see if they contain the tiny pollutants.