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UW Crest with engineering background
April 21, 2022

What happens when microbes hitch a ride on microplastics in lakes

Written By: Alex Holloway

As the climate changes, dangerous algal blooms become more common in our lakes, threatening not only humans, but entire freshwater ecosystems.

Nimish Pujara, an assistant professor of civil and environmental engineering, is studying how tiny plastic pieces might play a role in encouraging these blooms.

Nimish Pujara
Nimish Pujara

Pujara has received Wisconsin Idea Grant funding for a collaborative project with Erica Majumder, an assistant professor of bacteriology at UW-Madison. They’ll work with UW Extension Lake Superior outreach specialists Erin Burkett and Chad Cook to study how microorganisms and microplastics influence algal bloom growth on Lake Superior.

Microplastics are plastic fragments smaller than 5 millimeters across. They can come in all sorts of densities and chemical compositions and are ubiquitous in the environment, including sources of drinking water, according to the World Health Organization.

Pujara’s research focuses on fluid mechanics, and he’s leveraging that expertise for the project. He says microbes might latch onto microplastics, which allows them to spread further in lakes than would otherwise be possible.

“Our hypothesis is that there might be a yo-yo effect,” Pujara says. “A biofilm forms around the plastic, which makes it heavier so that it starts sinking. From field data we know that we recover a lot of heavy plastics from the surface of the water. So some biological process on the surface of that plastic—maybe some kind of gas formation—is making it buoyant so that it rises to the top again.”

Pujara’s team will work with the nearshore monitoring workgroup, part of the UW Extension’s Lake Superior Collective, to collect water samples. Once the project begins in spring 2022, Purjara’s team will join the workgroup in collecting lake water samples for analysis.

Because microplastics are so widespread in the environment and because algal blooms are so common (they’re a serious problem in all 50 states, according to the U.S. Environmental Protection Agency), the project has potential for big impact. Algal blooms can sicken or kill humans and wildlife, create “dead zones” in water, make water treatment more expensive, and damage industries that rely on clean water. Pujara says scientific communities are increasingly seeing microplastics as an urgent area of focus as we learn more about just how common they are in the world.

“This is a pollutant that we don’t really know the full impacts of,” he says. “So it’s important to continue encouraging further studies so we can gain a better understanding of how it moves within and impacts our environment.”