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Plastic Microfibers Found in the Food Web of Three Lake Michigan Rivers

By: Irene Miles, originally posted by Illinois-Indiana Sea Grant

As you dine on locally-caught fish, you probably aren’t thinking of that old acrylic sweater or fleece jacket that you wear and wash frequently. But it turns out that they may be on your plate. Illinois-Indiana Sea Grant-funded researchers have found microplastic fibers that come from clothing and other sources in the water, sediment and fish of three major rivers that flow into Lake Michigan.

Loyola University Chicago biologists John Kelly, Tim Hoellein and Rachel McNeish are assessing levels of microplastic using a range of measures. As part of a larger study, they collected samples from the mouths of the Muskegon, Milwaukee and St. Joseph rivers seasonally over the course of 2016 and into 2017.

“We found that 99 percent of the microplastic is fibers, and microfibers are everywhere,” said McNeish, a post-doctoral fellow who implemented the project. “Much of what we found is acrylic, polyester, and polyethylene, which comes from plastic bags.” These plastics break down to microscopic size in the water due to physical abrasion, sunlight and freezing.

While water sampling is typically done using nets, the Loyola team also sampled water directly. “We started doing these grab samples – we just fill up a liter container and bring it back and filter it, and we found particles smaller than 300 microns, the pore size of the nets,” said Kelly. “The smaller you go, the more numerous the pieces of plastic there are.”

A key goal of this project is to understand how the different ways in which we use land affect how much microplastic is in the environment.

The most northern river, the Muskegon, flows through a landcape dominated by forests and had less microplastic than the other two rivers. The two rivers in the more populated and developed southern region, the St. Joseph, which drains a farm-rich region, and the Milwaukee, which sits in a mixed urban and agricultural region, both had higher numbers of microplastics.

“Ultimately what we really want to do is predict what aspects of our development or features of the landscape pose bigger problems when it comes to contributing microplastic to the landscape,” said Hoellein. “And we need to understand where microplastic accumulates the most, because if we don’t answer those questions, we’re not really in a good position to come up with a solution or even address the problem.”

The researchers also sampled 74 fish from these three rivers and found that 85 percent of them, including bass and other sportfish, contained microplastic in their digestive tract, with each individual fish containing an average of 13 particles. They found that the amount of microplastic in individual fish was not a reflection of how much plastic was in the water—fish from all three sites had similar numbers of microplastics in their digestive system.

How much microplastic shows up in one fish versus another can better be explained by looking at the food web. The researchers found fish which eat insects and other invertebrates (that is, food that may already contain microplastics) have more fibers than those fish that eat plants.

“Microplastic is interacting with aquatic wildlife,” said McNeish. “Fish are consuming it—either actively eating it thinking its food, eating insects with microplastic in them or maybe just through drinking water with microplastic. Or they may consume it through contact with sediment. In any case, microplastic is entering the food web.”

“And as these three rivers drain into Lake Michigan,” she explained, “the movement of microplastic can happen with the rivers’ currents, but also through the migration of animals.”

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