The book is available online now and will be published in the December issue of Total Environmental Science.

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

Microplastics are tiny plastic particles that range in size from one micrometer, or 1/100 the width of a human hair, to five millimeters, or roughly the size of a pencil eraser. They can come from larger plastics that break down into smaller pieces or be made directly by manufacturers. For this study, the team examined freshwater sediment cores from four Pennsylvania watersheds: the Kiskiminetas 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 not to be a driver of variation in microplastics between sites, including the percentage of microplastics related to developed area and density of population,” said Lisa Emili, associate professor of physics. geography and environmental studies at Penn State Altoona and co-author of the paper.

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

“Although this is a preliminary result that requires further study, this decrease could be linked to increased recycling efforts,” Emili said.

According to the U.S. Environmental Protection Agency, plastic recycling efforts increased significantly between 1980 and 2010. Although plastic production also increased, the percentage of plastic recycled increased from less than 0.3 percent. 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 plastics” paradox. This paradox challenges researchers’ understanding of plastic waste in the ocean because, while estimates suggest that 7,000 to 25,000 kilotons of plastic enter the ocean each year, only about 250 kilotons are thought to float to the surface.

“This suggests that estuaries, particularly tidal marshes, can trap river-borne plastics before they reach the ocean,” said Najjar, who previously published in Frontiers in Marine Science on the simulations of filtered estuaries. “This could explain why there is much less plastic floating on the ocean surface compared to the amount expected given the input of rivers into the ocean.”

Warner said these results suggest there will continue to be increasing amounts of microplastics in water and sediment as people use more plastic.

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

According to Emili, the success of a study like this requires an interdisciplinary team.

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

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

“This funded project has truly served as an ‘incubator’ for the continuation and expansion of our work on the fate and transport of microplastics in freshwater environments, with a particular focus on coastal areas,” said Emili.

Najjar agreed and said he would like to get a more comprehensive assessment of the trapping of river-borne plastics in estuaries.

“We have known for a long time that estuaries massively process materials carried by rivers, like carbon, sediment and nutrients, and this processing has a big impact on what ultimately reaches the ocean,” Najjar said. “I think estuaries could work the same way for plastics, but we need more than just a modeling study and a single core. We need to consider the likely sources and sinks of plastics for a system given, such as rivers, atmosphere, estuarine sediments and marshes.

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

In addition to Emili, Najjar and Warner, other Penn State researchers who contributed to the study include Jutamas Bussarakum, lead author and doctoral student in the Department of Civil and Environmental Engineering; William Burgos, professor in the Department of Civil and Environmental Engineering; Samuel Cohen, who received his master’s degree in geography earlier this year; Kimberly Van Meter, assistant professor in the Department of Geography; Jon Sweetman, assistant research professor in the Department of Ecosystem Science and Management; Patrick Drohan, professor in the Department of Ecosystem Science and Management; Jill Arriola, assistant research professor in the Department of Meteorology and Atmospheric Sciences; and Katharina Pankratz, who earned her doctorate in civil and environmental engineering earlier this year.

The U.S. National Science Foundation, Penn State’s Commonwealth Campus Center Nodes (C3N) program, and the Energy and Environment Institute supported this research.