The increase in microplastics in fresh water is directly linked to plastic production

The work is already available online and will be published in the December issue of the magazine. General Environment Science.

“Few studies examine how microplastics change over time,” said Nathaniel Warner, assistant professor of civil and environmental engineering and author of the paper. “Our company is one of the first to track microplastic levels in freshwater sediments from the 1950s to today, showing that concentrations are increasing along with plastic production.”

Microplastics are tiny plastic particles that range in size from one micrometre, or 1/100th the width of a human hair, to five millimeters, roughly the size of a pencil eraser. They can be made from larger plastics that break down into smaller pieces, or made directly by manufacturers. For this study, the team examined freshwater sediment cores from four Pennsylvania watersheds: Quiquiminetas River, Blacklick Creek, Raystown Lake and Darby Creek.

Contrary to the team’s expectations, the study found no correlation between population density or land use and high levels of microplastics.

“Based on other findings in the literature, what we thought was important turned out to be not the drivers of variation in microplastics across locations, but rather the percentage of microplastics associated with developed area and population density,” said Lisa Emily, assistant professor of physics. Studies in Geography and the Environment at the University of Pennsylvania at Altoona and co-author of the paper.

The researchers also said they were surprised to find that while microplastic accumulation increased every decade until 2010, it decreased from 2010 to 2020.

“Although this is a preliminary finding that requires further study, this decrease may be due to increased recycling efforts,” Emilie said.

Plastic recycling efforts increased significantly between 1980 and 2010, according to the U.S. Environmental Protection Agency. Although plastic production has also increased, the percentage of recycled plastic has increased from less than 0.3% in 1980 to almost 8% in 2010.

Additionally, Raymond Najjar, professor of oceanography and co-author of the paper, said this study could shed light on the “missing plastic” paradox. This paradox challenges researchers’ understanding of plastic waste in the ocean, because while estimates indicate that between 7,000 and 25,000 kilotons of plastic enter the ocean each year, only about 250 kilotons are thought to float on the surface.

“This suggests that estuaries, especially tidal marshes, can trap river-borne plastic before it reaches the ocean,” said Najjar, who has previously published in the journal Frontiers in Marine Science on modeling estuarine filters. “This may explain why there is far less plastic floating on the surface of the ocean compared to what would be expected there, given rivers entering the ocean.”

Warner said these results suggest the amount of microplastics in both water and sediment will continue to increase as people use more plastic.

“People ingest plastic when they eat and drink, and inhale it when they breathe, and the long-term effects are just beginning to be studied,” Warner said. “However, we need to figure out how to put less plastic into the environment and how to reduce consumption and impact.”

According to Emily, an interdisciplinary team is needed for such research to be successful.

“This study demonstrates Penn State’s breadth of expertise, bringing together a team from three campuses, five colleges and five disciplines,” Emily said. “We have brought together complementary skills from our fields of chemistry, engineering, hydrology, oceanography and soil science.”

This research project was initially funded by a seed grant from the Institute for Energy and the Environment.

“This funded project has really served as an incubator to continue and expand our work studying the fate and transport of microplastics in freshwater environments, with a particular focus on coastal areas,” Emilie said.

Najjar agreed and said he would like to see a more complete assessment of the capture of river-borne plastic in estuaries.

“We have long known that estuaries intensively process river-borne materials such as carbon, sediment and nutrients, and this processing has a large impact on what ultimately reaches the ocean,” Najjar said. “I think estuaries can function similarly in terms of plastic, but we need more than just a modeling study and one core. We need to consider the likely sources and sinks of plastic for a given system, such as rivers, the atmosphere, estuarine sediments and wetlands.”

Warner added that he hopes to study how the composition and types of microplastics have changed over time and assess how the associated health risks have evolved.

In addition to Emily, Najjar and Warner, other Penn State researchers who contributed to the study include Yutamas Bussarakum, lead author and graduate student in the Department of Civil and Environmental Engineering; William Burgos, professor in the Department of Civil and Environmental Engineering; Samuel Cohen, who completed his master’s degree in geography earlier this year; Kimberly Van Meter, assistant professor of geography; John Sweetman, associate professor of ecosystem sciences and management; Patrick Drohan, professor in the Department of Ecosystem Sciences and Management; Jill Arriola, assistant professor of meteorology and atmospheric sciences; and Katharina Pankratz, who received her doctorate in civil and environmental engineering earlier this year.

This research was supported by the U.S. National Science Foundation, Penn State’s Commonwealth Campus Centers (C3N) Program, and the Institute for Energy and the Environment.