The increase in microplastics in fresh water is directly related to the production of plastic

The work is available online and will be published in the December issue Science of the general environment.

“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 the pre-1950s to today, showing that concentrations increase in line with plastic production.”

Microplastics are tiny plastic particles ranging in size from one micrometer, or 1/100 the width of a human hair, to five millimeters, roughly the size of a pencil eraser. They can consist of larger plastic that breaks down into smaller pieces, or they can be made directly by manufacturers. For this study, the team examined freshwater sediment cores from four watersheds in Pennsylvania: the Kiskimetas 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 the driver of change in microplastics across sites, particularly the percentage of microplastics associated with built-up area and population density,” said Lisa Emily, associate professor of physics. in Geography and Environmental Studies at Penn State Altoona and co-authored the paper.

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

“Although these are preliminary findings that require further study, this decrease may be due to increased recycling efforts,” Emily said.

According to the US Environmental Protection Agency, plastic recycling efforts increased significantly between 1980 and 2010. Although plastic production has also increased, the percentage of recycled plastic has increased from less than 0.3% in 1980 to nearly 8% in 2010.

Additionally, Raymond Najjar, professor of oceanography and co-author of the paper, said the study could shed light on the “missing plastic” paradox. This paradox challenges researchers’ understanding of plastic waste in the ocean, because while estimates show 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 plastics before they reach the ocean,” said Najjar, who previously published modeling of filtering estuaries in Frontiers in Marine Science. “This may explain why there is much less plastic floating on the surface of the ocean compared to the amount expected, given the amount entering the ocean from rivers.”

Warner said the findings suggest that the amount of microplastics in both water and sediment will 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 throw less plastic into the environment and how to reduce consumption and impact.”

According to Emily, it takes a multidisciplinary team to make this kind of research successful.

“This research 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 skill sets from our fields of chemistry, engineering, hydrology, oceanography and soil science.”

This research project was originally funded by a grant from the Institute of Energy and Environment.

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

Najjar agreed and said he would like to see a more complete assessment of river plastic uptake in estuaries.

“We’ve known for a long time that estuaries extensively recycle river materials such as carbon, sediment and nutrients, and this recycling has a big impact on what eventually reaches the ocean,” Najjar said. “I think estuaries can function in a similar way for plastics, but we need more than just modeling studies and a single core. We need to consider the likely sources and sinks of plastic for a given system, such as rivers, the atmosphere, estuarine sediments and marshes.”

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 changed.

In addition to Emily, Najjar and Warner, other Penn researchers who contributed to the study include Juthamas 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 of geography; John Sweetman, Associate Professor, Department of Ecosystem Sciences and Management; Patrick Drohan, Professor, Department of Ecosystem Sciences and Management; Jill Arriola, Associate Professor of Meteorology and Atmospheric Studies; and Katarina Pankratz, who received her doctorate in civil and environmental engineering earlier this year.

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