The sand, rocks, and pebbles of Lake Superior’s beaches appear to have a new component: plastic particles. Scientists earlier this fall found numerous tiny pieces of plastic in every single sample they collected from three different beaches in Duluth and Two Harbors. Almost all of the particles came from textiles. 

As the production of polyester fabric has increased, and awareness of its pollution problem has grown, scientists are studying where the material found on the shores of Lake Superior comes from, what its risks are, how it moves through the natural world, and what humans can do to protect ourselves and our environment.

 A beach being sampled

Researchers from the University of Wisconsin at Madison, UW-Superior, UW-Eau Claire, and the Lake Superior National Estuarine Research Reserve recently published their findings in the Journal of Great Lakes Research. Their study has provided new insights into the scale of the problem and more about how synthetic fibers get from far-flung factories to Lake Superior’s beloved beaches.

“Plastic pollution in freshwater lakes, including the Laurentian Great Lakes, is a critical issue to understand,” the researchers wrote. “Such waters are an important freshwater resource and fishery ecosystem, and thus the impacts of plastic pollution are far-reaching but not yet well understood.”

Macro-problem

Microplastics are a broad term that encompasses any type of plastic particle smaller than 5 millimeters. They originate in many ways, from tiny particles used in manufacturing, to the breaking down of larger plastic items like bags or packaging, and from clothes. 

While litter on a beach is easy to see, microplastics are basically invisible and potentially more harmful.

Despite plastic only being popularized about 60 years ago, microplastics are now ubiquitous in the environment across much of Earth. The Environmental Protection Agency says Americans throw away 30 million tons of plastic each year. Some scientists have suggested the presence of microplastics in sediment could be a marker to identify a new era in geologic time.

In other words, these puny pollutants are a big problem.

 Ben Davidson, lead researcher, on the right taking a core sample and undergraduate researcher Kallyn Batista (and co-author on the paper) on the left taking a surface sample

Beachcombing

To understand where microplastics on Lake Superior’s beaches originate, and which parts of the beach are most contaminated, the team chose sites with different characteristics and proximity to potential microplastic sources. They took several samples from Minnesota and Wisconsin Points in Duluth, and Burlington Bay beach in Two Harbors. The Duluth sites are just outside the St. Louis River estuary and the Two Harbors site is a short distance from the municipal wastewater treatment plant, which treats about 1.2 million gallons per day.

Fanning out across the beaches, the teams collected samples of sand and sediment from the “wrack line,” the high water mark where waves deposit the most material, as well as in the “swash zone,” where churning waters can stir up sediment and bury material. They took the material back to the lab.

 Then they used a 50x microscope to identify and count up the number of microplastic particles in each sample. In total, they found 3,981 particles, or 65 particles per kilogram (2.2 pounds), of sediment. Every single sample had some.

They expected to see more plastic closer to wastewater treatment plants and the St. Louis River estuary, but it wasn’t that simple. “It appears that predicting microplastic concentration on a given beach is more complex than proximity to these potential sources,” they wrote.

One reason for that could be the role of the wind. How much microplastic pollution is carried in the atmosphere and deposited across land and water is still poorly understood.

 An individual microscope image of microplastics found

Polyester pollution

While they were looking for any and all microplastics, the researchers found almost entirely polyester fibers.  This dominant form of microplastics comprised 3,763 of the 3,981 microplastic particles identified (almost 95%). These fibers mostly come from textiles, including fleece and other polyester fabrics. When apparel items are washed in a washing machine, thousands of fibers can go down the drain and straight to wastewater treatment facilities, which can’t currently remove all such tiny plastics before discharging their effluent. 

Polyester fabric is currently essential to keeping people clothed around the world. It is the largest type of synthetic fabric produced on Earth, having grown from about 3.5 million tons per year in 1973 to 61 million tons in 2021. Fibers are not a unique problem in Lake Superior; they have been found from the depths of the Mariana Trench to a glacier high in the Himalayas.

“Because the use of synthetic textiles continues to increase and the world production of synthetic fibers (e.g. polyester) has surpassed the demand of natural fibers, the problem of microfibers released in the environment may be exacerbated in the future,” according to a 2021 review of the problem in the Textile Research Journal.

Tracking the types and sources of plastics found on Superior’s beaches helps target pollution prevention where it will be most effective.

  An individual microscope image of microplastics found. Microplastics can often cause harm to eco-systems due to their small size

Fish food

Preventing this pollution is a high priority. While microplastics are generally invisible to the naked eye, they can cause significant harm to the ecosystem. 

As reported by Boreal Community Media’s Laura Durenberger-Grunow last year, these plastic particles are known to collect toxic chemicals and other pollutants as they move around the environment, like a “sponge”, according to one National Park Service scientist. Then, small organisms consume the particles, loaded with toxins, and then larger creatures eat those organisms, and so on. The plastic and its pollutants accumulate as it moves up the food chain. 

This all makes it very easy for humans to unknowingly consume significant amounts of the plastics and the chemicals they carry. Fish are also increasingly being found contaminated with high levels of plastic. A scientist cited by Boreal last year says about half the fish from Lake Superior that her team has studied have had microplastics in them. A meal of Lake Superior whitefish or trout may include a side salad of fleece fibers.