Headlines decrying tiny particles in our drinking water and swirling masses like the Great Pacific Garbage Patch have centered plastic waste as the modern scourge of marine ecosystems. But Michiganders may be surprised to learn that this threat hits particularly close to home: recent studies show that at times, the Great Lakes contain the highest concentration of plastics anywhere on the planet.
Plastics were initially pioneered to preserve natural resources during the mid-century production boom. But unlike lumber, glass, and other naturally-derived materials, plastics do not biodegrade, which means that much of the plastic ever produced is still with us in some form. Among the most insidious relics of this history are “microplastics” less than five millimeters long, often formed when larger plastic objects break down. The Ghost of Plastics Past is visiting us now – and its warnings include the corrupted bodies of animals who mistook colorful bits for food, hazardous chemicals leached from plastic shrapnel, and the potential for frightening metabolic, neurotoxic, and carcinogenic human health effects. Still, the trajectory and long-term consequences of plastic waste remain relatively unknown.
Dr. Melissa Duhaime - Assistant Professor in the U-M Ecology and Evolutionary Biology (EEB) department and UMBS “Microbes in the Wild” instructor - is set on addressing that critical knowledge gap. This past summer, she and her research team initiated an experiment to determine the individual and combined role that factors like solar radiation and the growth of slimy microbial blankets called “biofilms” play in the breakdown and movement of environmental plastics. The project - like Duhaime’s summer undergraduate course - is based out of UMBS and its aquatic headquarters, Douglas Lake.
“Biofilm growth influences plastic in a few ways,” says Duhaime. “First, the film’s biomass will change the size, shape, and overall density of plastic particles in water, which will impact where they go in the water column. We have very little empirical data to inform the hydrodynamic models that predict the movement of plastic through water bodies. The data we are collecting on the extent and rate of biofilm growth will be used to improve these models.”
In addition to altering flow patterns, the specific makeup of these slimy coatings govern the destiny of collateral plastic pollutants. Biofilms are made of microbes, and certain microbes are endowed with the rare ability to break down plastic.
“We study the composition -- who is there -- and activity -- what are they doing -- of the biofilm microbes to better understand the potential for naturally-occurring microbes in Douglas Lake (and other freshwater lakes) to degrade plastic,” says Duhaime.
Late last summer, Duhaime and EEB graduate student Rachel Cable deployed three different types of plastics under various age conditions at three different depths in Douglas Lake. The plastics were attached to cross-shaped frames along a line connected to a buoy and anchored to the lake bottom. Two such lines were deployed simultaneously; one was collected after two months and the other will remain in place for fifteen months. Following their stay in the watery depths of Douglas Lake, the plastics are analyzed for microbial activity, composition, and function in the Duhaime Lab, as well as chemical and physical changes in the closely collaborating Department of Chemistry lab. As part of these analyses, enrichment cultures using retrieved plastic as bait to isolate and identify naturally occurring plastic-degrading microbes are established at UMBS before making their way to Ann Arbor for further testing.
On a chilly day in late November, Duhaime and Cable fired up the UMBS pontoon boat and retrieved the first batch of Douglas Lake deployments at 1.5 meters, 15 meters, and 20 meters.
“You can see the differences in the three frames brought up,” explains Duhaime. “The first one is from the surface frame [1.5 m], the next from 15 meters, and the one that’s pretty much ‘clean’ is from 20 meters.”
According to Duhaime, these visible differences are a consequence of differing levels of primary productivity – how living things use sunlight to build biomass.
“The fact that the surface ones have so much growth reflects that primary productivity is important in determining how much biofilm grows. More sun energy, more biofilm growth.”
The methods of the Douglas Lake microplastics project mirror those of other Duhaime-led experiments in the Great Lakes. She has been studying the interplay between microbes and plastic pollution in freshwater and oceans for over a decade, making her a recognized leader in this increasingly hot field.
Duhaime’s research also helps inform the project-based Microbes in the Wild course she teaches at UMBS. In this summer field class, undergraduates work alongside local environmental agencies to study microbes in the context of real-world sustainability issues in Northern Michigan. The alarming rise of microplastics looms particularly large in a local community that hangs its hat on tourism, sport fishing, and the pristine beauty of its natural surroundings.
Back on campus, Duhaime, post-doc Jessica Choi (an expert in isolating hard-to-grow environmental microbes important for bioremediation), lab scientist (and UMBS alumna) Lizy Michaelson, and undergraduate researchers are working to develop an extensive “library” of plastic-degrading bacteria and fungi.
“We are growing [these microbes] to learn which are the degradation champions in realistic environmental conditions,” says Duhaime.
Ultimately, Duhaime and collaborators hope their findings will contribute to remediation plans and school curricula by better defining the ecological and environmental health risks of plastics in aquatic systems, improving predictive models on movement of plastics, and exploring the specific dynamics of plastic-dwelling microbial communities.
The Ghost of Plastics Past is knocking. But Duhaime believes there is still time to answer - with research, with action, and with an eye toward microorganisms whose natural abilities may hold the key to remediating the pollution haunting our waters. The silver lining in this story might turn out to be coated in green slime.
For more information on Duhaime's "Microbes in the Wild" course running this summer 2022 at UMBS, visit the course page.