Tidal marshes — where crabs and fish feed their way toward adulthood — are the lifeblood of estuarine systems like the Chesapeake Bay. They’re also where a lot of our microplastics end up.
A study by Penn State researchers confirms earlier assumptions that tidal marshes are a hotspot not only for ecological life but also for the detritus of what some scientists now call the Earth’s Plasticene era. This study also went a step further to identify which plastics are most prevalent in tidal marshes and which are most toxic to humans and the environment.
“It’s a lot of single-use stuff,” said Nathaniel Warner, an associate professor in civil and environmental engineering at Penn State. “And the potential toxicity associated with that is increasing. Some of those plastics are more toxic than others.”
Microplastics are defined as plastic particles 5 millimeters or less in size that are left behind when larger plastic objects break down. The Chesapeake Bay Program, the state-federal partnership that leads the Bay restoration effort, identified microplastics as a contaminant of mounting concern in 2019 and has called for more studies on the presence and potential dangers of ubiquitous plastic bits.
Since then, researchers globally have found microplastics and their smaller counterparts, nanoplastics, everywhere they’ve looked. They’re in the air we breathe and the food we eat, and they are found in human brains and in mothers’ placentas. While these findings are troubling, scientists are still working to understand exactly how plastics harm the ecosystems where they’re found and the humans that unwittingly absorb or consume them.
One of the big questions of recent microplastics research has been why the volume of plastic particles entering the ocean appears to be considerably less than what is known to run off the landscape. Where do the plastics that break down into smaller and smaller pieces end up (besides our brains)?
A 2021 modeling exercise also conducted by Penn State researchers found that about 94% of microplastics running into the Chesapeake Bay and its tributaries never leave the system for the ocean. The Bay, it seems, is a catch basin for these tiny plastic particles.
This latest study, which will be published in the Marine Pollution Bulletin in December, aimed to explore those findings by digging in the mud of a specific ecosystem: tidal marshes. This time, the team wanted to understand what types of plastics were present and whether they were becoming more prevalent — and more toxic to ecological life — over time.
Conducted with the help of Penn State’s Institute of Energy and the Environment and a National Science Foundation grant, the research involved an interdisciplinary team including soil scientists, sedimentologists, wetland ecologists and chemists.
Building on existing work, the researchers collected core samples from the Darby Creek watershed in the John Heinz National Wildlife Refuge at Tinicum, PA. Jutamas “Judy” Bussarakum, a Penn State graduate student at the time of the work, had already collected data about microplastics building up in the sediments of that tributary to the Delaware River.
Stable sediments there allowed the team to collect core samples dating to pre-1950 — before plastics proliferated — to understand how their presence in tidal marshes has changed over time.
That presence increased exponentially over each decade from the 1950s through the 2010s at rates corresponding to the increase in global plastic production. There was, however, no increase from 2000 to 2010, which could possibly be attributed to recycling efforts.
The concentrations found in the most recent sediment cores also were similar to those found by studies in estuaries across five continents.
Previous research has shown that microplastics can fill the guts of oysters and impact the reproductive potential of aquatic species. But this study also considered the toxicity established by other studies that is now associated with six common polymers (such as polyethylene). The effort found that both the presence and toxicity of plastics increased in recent decades largely due to an ongoing increase in single-use plastics.
“The field of microplastics is a Catch-22,” said Lisa Emili, an associate professor of physical geography and environmental studies at Penn State Altoona.
On one hand, she said, she hoped they wouldn’t find as many plastics as they did. On the other hand, it’s exciting to see how new technologies and methods can help researchers make helpful generalizations. Her takeaway?
“There are plastics, and they are accumulating, and they are largely single use,” Emili said. “There are implications for toxicology and environmental and human health. I guess we’re sounding the alarm.”
The researchers acknowledged the many modern uses of plastics in fields such as medicine and construction. But they found that the most prevalent and most toxic plastics were those used only once and then tossed away, leading them to emphasize “the need for stricter waste management and reduction efforts aimed at disposable plastics.”
Warner said that if the trajectory of plastic production — and microplastics in marshes — persists, society will continue to see a “skyrocketing amount of plastic in the environment.”
Raymond Najjar, a professor of oceanography at Penn State, said he has replaced much of his plastic food containers with glass ones after working on the study. But individual efforts, he said, can only do so much.
“We don’t need our study to make the point that the management of plastics has to be done holistically,” Najjar said. “It’s not a cleanup thing. If you don’t turn off the tap, the problem is going to get worse.”