A recent study of 35 national parks found the waters of Lake Superior in Wisconsin's Apostle Islands had the highest concentration of plastic pollution.
The National Park Service, South Carolina's Clemson University and the National Oceanic and Atmospheric Administration Marine Debris Program began working on the two-year study in 2015.
Samples collected from the Apostle Islands National Lakeshore had an average of 170 to 225 pieces of microplastic per kilogram of sand, Wisconsin Public Radio reported. Microplastic fibers are typically from sources such as clothing, deteriorating nets or broken fishing lines.
Local conditions seem to have a larger influence on microplastic concentrations than proximity to highly populated areas, said Stefanie Whitmire, the study's lead author and a research scientist at Clemson.
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"One of the reasons we try to correlate it to urban areas is because we think with higher population densities and more people, more plastic use, you'd think those numbers would be higher," Whitmire said. "But, with this study, I didn't find the correlation between how close these parks were to urban centers or how close they were to the nearest river."
Researchers will continue to study the water around the islands this summer, said Brenda Lafrancois, a regional aquatic ecologist with the Park Service.
"Those will be places ranging from Meyers Beach all the way out to Outer Island in the Apostles, so a real range of beach sites that'll capture currents that might deposit microplastics from many different directions in Lake Superior," said Lafrancois.
Researchers will then study the chemical composition of the microplastic samples. That information can help determine where the fibers came from, said Liz Minor, a professor with the Large Lakes Observatory at the University of Minnesota Duluth.
Despite studies about microplastics and their potential impacts on wildlife and humans, much is still unknown about the fibers' impact on the health of organisms.