What Mussels Can Tell Us About Microplastics

On a cold day in February, chemistry professor Jeffrey Ashley, PhD, and the students in his lab headed to the Delaware Inland Bays, a series of inlets spanning the coast of southern Delaware. There, they trekked through 12 different salt marsh habitats and searched for Atlantic ribbed mussels, scraping them off the tidal shorelines and bringing them back to Dr. Ashley’s lab on Jefferson’s East Falls campus.

After processing the tissue within those mussels, Connor Ogden, a former undergraduate in Ashley’s lab and now a student at Sidney Kimmel Medical College, examined the remains of the animals. As he looked into the microscope, he saw the same thing, again and again: rainbow-colored tangles of plastic fibers.

Their study found microplastics — tiny fragments of plastic smaller than 5 millimeters — in every sample of mussels they analyzed, no matter how urban or rural the site that the mussels came from. Amidst a growing body of research that finds microplastics all around us, their results weren’t necessarily a surprise — but they do shed more light on the type of microplastics plaguing aquatic ecosystems on the east coast, and they may begin to provide some direction on what to do about it.

In recent years, a battery of studies has confirmed that microplastics are in our soil, our oceans, our tap water, and even in the snow of Antarctica. While it was clear that microplastics are already abundant in the environment, Dr. Ashley wanted to investigate the extent to which microplastics had infiltrated filter-feeder organisms like mussels. These animals process gallons of water through their bodies every day, so he believed they were likely taking in microplastics as well.

“These microplastics are suspended in the water column, so the mussels are both getting exposed to them and accumulating them in their bodies,” explains Dr. Ashley.

Ogden, and other undergraduate students within Ashley’s research group, laboriously prepared and analyzed mussels over months. Their analysis confirmed another trend in microplastic research: most of the fibers they identified had come from synthetic fabrics such as polyester and nylon. 

“Our study observed what many other researchers are finding: microplastics are dominated by microfibers,” Dr. Ashley said. “And the primary source of these are textiles and apparel.”

In fact, a 2016 study found that a single fleece jacket emits about a gram of microplastic fibers every time it’s washed. In 2020, France became the first country to mandate that new washing machines must be manufactured with filters for microplastics to reduce their release into the environment, and organisms living within it. But in the U.S., there’s no sign of any laws on the horizon aimed to regulate how much microplastics are emitted from washing machines — and municipal water authorities aren’t sure how to deal with the problem, either.

“Right now, there's not really a good way to regulate the filtration of microplastics,” says Tanisha Rutledge, a master’s student working in the lab of Radika Bhaskar, PhD. Separate from Dr. Ashley’s lab and as part of her undergraduate senior design project, Rutledge and other students worked with the Philadelphia water department to understand the city’s current filtration systems — which don’t address microplastics — and develop an improved version.

In small-scale experiments, she found that adding a layer of hemp fibers to a water filtration system similar to the one used by the city helped filter the majority of the microplastics.

Rutledge admits scaling up projects like hers will take a long time, but the work is an important first step. Likewise, Dr. Ashley and Ogden say there’s still a lot to learn about what exactly it means for microplastics to be present in mussels — for instance, how these organisms’ health is affected, and what that means for the overall ecosystem. Atlantic ribbed mussels play a key role in regulating erosion around the east coast, and are also an important part of the food chain for larger estuarine predators.

And Dr. Ashley says if there are microplastics in one type of filter-feeder organism, it’s likely that they’re in others. “If we had studied oysters instead of mussels, we would probably find the same thing,” he explains — opening up another route for humans to ingest microplastics in our diet.

“These are invisible, ubiquitous environmental pollutants that potentially could harm all the organisms in an ecosystem,” says Dr. Ashley.