URI Team Studying Microplastics in Local Waters


A fragment of plastic litter caught in the wrack line at Quonochontaug Salt Pond in Charlestown. A team of researchers from the University of Rhode Island is collecting samples of salt and fresh water to determine the extent of plastic pollution and its impacts on aquatic life. (Cynthia Drummond/ecoRI News photos)

CHARLESTOWN, R.I. — Researchers from the University of Rhode Island are collecting and analyzing microplastics in Narragansett Bay, coastal ponds, Worden and Roger Williams Park freshwater ponds, and the Blackstone River, to determine which types of plastics are most prevalent and where most of it can be found.

At an Aug. 15 presentation in Charlestown to members of the Salt Ponds Coalition, Ph.D. candidate Sarah Davis said plastic debris, which is present in almost every waterbody, is an environmental problem because so little plastic is recycled.

“It is estimated that 13 million tons of plastic enter our oceans every year,” she said. “You may have also heard the recent estimates that less than 10% of plastic is actually recycled, when it does make its way into our global waste systems. Also, our waste systems really just aren’t effective at handling really small plastic debris.”

Plastic waste can be divided into two broad categories: macroplastics, such as water bottles, that are larger than 5 millimeters, and microplastics, which measure from 5 millimeters to 1 micrometer.

Davis described several sources of plastics entering Narragansett Bay and freshwater bodies. One source, which might come as a surprise to many people, is clothing.

“Sewage-related debris … is a major source of microplastic fibers from clothing and microbeads from cosmetics,” she said. “Much of our clothing is made of plastic. Polyester is one of the main woven plastic materials that we use as a textile, and every time we wash our clothes, we actually release thousands of fibers into the wastewater that flows out of our washing machines, and if we’re attached to local sewer systems, most wastewater treatment plants can’t filter out these tiny fibers and they’re released at outflow points into our waterways.”

Litter is an obvious source of plastic pollution, as is industrial waste from plastic refineries. Some plastics also end up in the ocean during shipping, when tiny, pre-production plastic beads, called nurdles, are lost in transit.

Marine industries and recreation also produce plastic waste.

“Lost or abandoned equipment, such as nets and ropes, which are made of bundled plastic fibers such as polypropylene or nylon, break down very quickly into tiny plastic fragments,” Davis said. “Cut or abandoned fishing line might also be a familiar plastic danger to wildlife.”

Depending on their densities, plastics will either float on the surface or sink. This in turn determines which organisms might ingest them, Davis said.

Quonochontaug Pond in Charlestown. Researchers at the University of Rhode Island are assessing the extent of plastics pollution in Narragansett Bay, as well as in fresh and saltwater ponds.

“Organisms that live down in the sediment, like clams, might be more impacted by things like nylon or polyester that are sinking to the bottom, whereas seabirds and fish, who are hanging out toward the top of the water column, might be more impacted by polyethylene or polypropylene fragments,” she said.

Plastics enter organisms when they are eaten or absorbed, usually through the gills. Ingested plastics disrupt hormone regulation and create what Davis described as “a false sense of fullness” in which the organism feels like it has eaten, when in fact it hasn’t consumed any nutrients. Microplastics can also act as vectors for invasive species and diseases, which are transported on the fragments.

Davis is part of a research team that is involved in three plastics projects: a seasonal assessment of plastic debris in surface water in Narragansett Bay; an assessment of plastic pollutants in fresh water; and a study of the ways in which marine organisms interact with microplastics through the food web.

Using a net called a manta trawl, researchers have been sampling Narragansett Bay waters at several locations for two seasons. Save The Bay is also manta trawling for plastics in Narragansett Bay.

“We want to produce a really robust, technically sound approximation of what’s happening in the bay, which is why our sites are spaced the way they are,” Davis said. “We start up by Providence, so really urbanized, [a] kind of urban-to-rural gradient, which is great, not only adjacent to different levels of urbanization, but also different influences from things like currents, wind, ship traffic, rainfall runoff — all the things that might influence the spread of microplastics.”

Wearing bright-orange jumpsuits — so fibers from their clothing can be differentiated from plastic fragments found in the water — researchers deploy a manta trawl that is towed behind a URI research vessel for 10 minutes at each site.

In the laboratory, ocean water is removed from the sample and a hyper-saline solution, which is denser than regular seawater, is added to help the plastic fragments float.

“Then,” Davis said, “myself and our wonderful undergraduate assistants sit under the microscope and we hand pick out all the suspected microplastics.”

The pieces are affixed to slides and high-resolution photographs are taken of them. The last step to confirm they are plastics involves a hot needle inserted into each fragment. The non-plastic pieces burn, but the plastic fragments melt.

The process is laborious, Davis said, because much of the work must be done by hand.

“We’ve characterized over 3,000 particles from the bay so far, so it’s a lot of poking,” she said.

The final step utilizes Raman spectroscopy, a type of analysis that uses laser light to create molecular vibrations that the spectrometer reads. It then produces a spectrograph that enables researchers to identify specific plastic polymer types.

The Results

The research team has not found any clear seasonal patterns in microplastics abundance, but preliminary results show more microplastics were recovered in Narragansett Bay near Providence.

Overall, however, compared with other waterbodies, the bay is about in the middle of the plastics pollution scale, with an average concentration of 0.3 microplastics per cubic meter.

Plastic litter quickly breaks down into smaller pieces. These fragments, called macroplastics because they are larger than 5 millimeters, washed up in the seaweed at Quonochontaug Pond in Charlestown.

“I think that’s pretty good,” Davis said, “and it also is pretty good when we compare it to some other places. … The Monterey Bay Marine Sanctuary, in 2021, using manta trawl methods, found an average concentration of 1.32 microplastics per cubic meter. So, we’re definitely sitting lower than that, but we’re also sitting a little bit higher than some other places. The Chesapeake Bay found 0.16. So, we’re kind of in the middle.”

There is also a relationship between tides and microplastic abundance, with more plastics found at low tide.

Researchers are still collecting samples of fresh water, but the lack of rain this summer has meant there has been no stormwater to analyze.

There are several measures Rhode Islanders can take to reduce the prevalence of microplastics in salt and fresh waters.

Davis suggested people wear natural fibers when they are on the water, handle vinyl and PVC-coated traps with care so the coating doesn’t come off, replace old marine ropes with ropes made from natural fibers, and use reusable tarps instead of shrink wrap to protect boats during winter storage.

Davis said boaters should also try to recycle the shrink wrap they do use.

Woods Hole actually offers a recycling program every summer, and has yielded thousands of tons of shrink wrap recycling,” she said.

Local shrink wrap recycling is available through Clean Ocean Access.


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  1. Nice article. Thank you, Sarah Davis for your work. My son and I helped this project a little this summer with a water collection in RWP. I’m glad my son had a chance to learn that people can pick up litter for educational reasons, not just as a community service.

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