From its humble beginnings as Bakelite, which was used to make colorful items like radios and billiard balls in the early 20th century, plastic has expanded to a nearly ubiquitous presence in the places we live, work, and play. However, the very thing that made plastic so popular and useful, its near indestructability, is now the problem. Plastic doesn’t break down like organic compounds, rather it breaks up into smaller and smaller pieces, called microplastics. These tiny, man-made particles persist in the environment indefinitely, moving through all phases of the water cycle and passing up the food chain through a process called bioaccumulation.
There is a great deal of research on microplastics in marine ecosystems and it seems like nearly everyone is familiar with the Great Pacific Garbage Patch, an area of the ocean roughly 7.7 million square miles in size and filled with a haze of microplastics, 80% of which come from land-based sources. The small, colorful plastics often confuse marine bird species, which ingest them, mistaking them for food. Plastic straws and bags became infamous for their impacts on sea turtles. More recently, researchers found the presence of plastic in a newly discovered species of amphipod in the Mariana Trench, which they appropriately named Eurythenes plasticus.
Just how prolific are microplastics exactly? As Bill Nye used to say, “Consider the following:”
- While eight billion tons of plastic have been produced since the 1950s, less than 10% has been recycled (National Geographic).
- It is estimated that Americans ingest at least 74,000 microplastic particles every year in food and drinks (Washington Post). When intake through air is considered, this number jumps to between 74,000 and 121,000 particles a year (Smithsonian Magazine).
- Cigarette filters contain a plastic called cellulose acetate. Approximately six trillion cigarettes are consumed annually (National Geographic).
- A study in 2016 found that more than 700,000 plastic fibers are released during each cycle of a washing machine and another study in 2019 estimated that there are 1.5 million trillion microfibers in the world’s oceans (UN Environment Programme).
Looking upstream from the oceans to our freshwater rivers and lakes, there is far less research on microplastic pollution. The intersection of microplastics and stormwater is even less traveled, but it is currently an emerging area of focus and concern. A journal article published in Environmental Pollution earlier this year found that microplastic pollution in rivers rises at the transition from rural to urban areas and that storm sewers are important pathways of microplastics from land into urban rivers.
Wishing to investigate microplastics on a local level, the City of Springfield hired an Environmental Intern to conduct a 6-month research project on the prevalence of trash and plastic in urban stormwater. Intern Laiken Cash, a pre-med student at Drury University, conducted a combination of stormwater sampling and laboratory studies to provide a better picture of the composition and quantity of plastic in the urban environment. Stormwater samples were collected at locations with the City’s stormwater Municipal Separate Storm Sewer System (MS4), which includes storm drains, ditches and other drainageways which convey runoff toward the nearest stream. These samples were analyzed using laboratory equipment and AI software to calculate total particles in stormwater samples.
When you look at microplastics under a microscope, it’s like looking into another world. Using the eyes of a scientist, with a smidge of archeologist, you start to see the particles for what they are, some of the tiniest remnants of modern civilization. There are tiny fibers from clothing that has long been discarded, rubber crumbs from tires that may have passed through Springfield traveling the fabled Route 66, particles of a Styrofoam cub used to hold a drink on a hot summer day, and so much more. Microplastics are traditionally considered to be <5mm in size. Behind the easily identified particles, sprinkled like stars in the night sky, are tiny dots. These smaller particles, less than 1 mm in size, are referred to as nano plastics.
Over the course of Laiken’s internship, seven storm events were sampled at four locations and microplastics were found to be present in every sample collected. Both microfibers (from textiles, cigarette filters, etc.) and globular microplastics (tire dust, fragments, foams, etc.) were observed. The study determined that, on average, one liter of urban stormwater runoff contains seven million microplastics. Furthermore, microplastics were found in soil samples collected from detention basins, showing that these structures are effective at removing microplastics from stormwater runoff. Other studies have shown stormwater retention ponds and bioretention facilities such as rain gardens to be effective at filtering microplastics out of stormwater runoff. A study published in 2021 found bioretention facilities to be 84% effective at removing microplastics. The City’s intern completed an encouraging indoor study using five-gallon buckets filled with bioretention mix and found a very similar result, approximately 85% removal.
So, the good news is we already have potential solutions to help address the macro-problem of microplastic pollution! While it’s not going to solve the plastic pollution crisis any time soon, bioretention is certainly one tool in the toolkit, and one that we’ll likely see more of as the City implements use of green infrastructure to improve water quality of streams and lakes in our community.
Sarah Wilkerson, CESSWI
Senior Stormwater Specialist
290 E Central St, Springfield, MO 65802