PROVIDENCE — It’s safe to say Rhode Islanders have a symbiotic relationship with Narragansett Bay.

Its status as New England’s tidal estuary helps define Rhode Island as the Ocean State. For hundreds of years people have fished, swam, and built homes, lives and businesses using the 147-square mile bay.

But for better or for worse, that relationship is very much a two-way street, especially when it comes to microplastics.

New research from scientists at the University of Rhode Island suggests that microplastics are more likely to accumulate in the northern parts of Narragansett Bay, closer to where the state’s biggest population clusters live.

“Our results suggest that freshwater rivers flowing through urban areas are likely accumulating microplastics and then depositing them into the bay,” said Sarah Davis, a postdoctoral research fellow at URI, during a virtual talk earlier this month.

The study, authored by Davis and fellow URI researcher Victoria Fulfer from the 5 Gyres Institute, shows that southern Narragansett Bay tends to have lower amounts of microplastics. Fewer Rhode Islanders live along that part of the bay, using less products that contain or turn into microplastics. The southern reaches of the bay also have the added advantage of being closer to the ocean, therefore getting regularly flushed out.

Davis and Fulfer’s virtual presentation of their results was part of Rhode Island Sea Grant’s Coastal State Series, a discussion and lecture series dedicated to spotlighting current research on marine issues impacting Rhode Island.

Davis said the researchers used surface water travel to collect samples during three seasons: winter, spring, and a combined fall and summer season. Over two years they collected two replicate samples from each site, leading to a total of 72 unique trawls throughout the bay.

Microplastic pollution has been steadily increasing in the bay since the 1950s, according to Fulfer, tracking with the nationwide trend of plastic product production and consumption.

Not all environmental features of the bay capture microplastics evenly, she said. According to the research, the state’s marshes trap 10 to 50 times more microplastics than the nearby seabed.

Fulfer said they sampled marshes close to Providence, and two more on Conanicut Island, which hosts the town of Jamestown. While the marsh closer to Providence had much higher concentrations of microplastics, the pair of marshes in Jamestown still had higher concentrations of microplastics than the nearby seafloor.

“Microplastic accumulation in Narragansett Bay still varies through space from north to south, but that variation has persisted throughout the last 70 years,” Fulfer said. “It’s exponentially increasing over time, and it varies based on the environment type.”

Fulfer was one of the researchers who published a study in 2023 showing the top 2 inches of Narragansett Bay’s seafloor contained more than 1,000 tons of microplastics.

Microplastics, defined as tiny pieces of plastic smaller than 5 millimeters in length, have rapidly become the defining ocean pollutant of the century. Over the past few years scientists around the globe have discovered microplastics in just about everything, including the human body. Their exact impact on human health isn’t yet clear.

Research shows microplastics have a negative impact on the environment. They’re easily ingested by organisms, leading to digestive blockages, reduced efficiency during feedings, and hindering nutrient absorption. They can also act as vectors, magnifying the impacts of natural pollutants on organisms.

Davis said the study’s results would help organizations attempting to abate and manage a lot of the runoff and other pollution in Narragansett Bay.

“Targeted efforts to reduce urban runoff into freshwater rivers and to improve wastewater management during high river flow periods could be really effective in mitigating microplastic inputs into the bay,” Davis said.