Microplastics are steadily increasing in freshwater environments

As plastic pollution reaches alarming levels in ecosystems worldwide, a new study traces this crisis back to decades of industrial growth.

The research, led by an interdisciplinary team of Penn State researchers, explores the rise of microplastics in freshwater environments and links it to a global increase in plastic production since the 1950s.

Tracking freshwater microplastics

The exports tracked microplastic levels in freshwater sediment back to the mid-20th century. They uncovered a clear link between rising microplastic concentrations and the global surge in plastic manufacturing.

“Ours is one of the first to track microplastic levels in freshwater sediment from before the 1950s to today, showing that concentrations rise in line with plastic production,” said Nathaniel Warner, associate professor of civil and environmental engineering at Penn State.

Focus of the research

Microplastics are minute particles of plastic that range from one hundredth the width of a human hair to roughly the size of a pencil eraser.

The study was primarily focused on sediment cores from four watersheds in Pennsylvania: Kiskiminetas River, Blacklick Creek, Raystown Lake, and Darby Creek.

Interestingly, the team discovered that regardless of the population density or land use, high levels of microplastics could be found.

The recycling landscape and plastic build-up

Lisa Emili, associate professor of physical geography and environmental studies at Penn State Altoona, explained how the findings differed from previous studies.

“Based on other findings in the literature, what we thought would be important turned out not to be driving forces in microplastic variation across sites, notably the percentage of microplastics related to developed area and population density,” said Emili.

The researchers found a decrease in microplastic accumulation from 2010 to 2020, a timeline that seems to align with increased recycling efforts.

Observations from the U.S. Environmental Protection Agency support this finding. The agency reported substantial expansion in plastic recycling efforts from 1980 to 2010.

The mystery of missing plastic

Raymond Najjar, professor of oceanography at Penn State, believes this study can clarify the “missing plastics” paradox. This refers to the disparity between the estimated amounts of plastic waste entering the ocean annually and the visible amount that can be found floating on the ocean’s surface.

Professor Najjar suggested that estuaries, particularly tidal marshes, could be trapping river-borne plastics preventing them from reaching the ocean.

“This could explain why there is far less plastic floating around in the surface ocean compared to how much is expected to be there given the input to the ocean from rivers,” said Professor Najjar.

Need to reduce plastic consumption

The research team predicts continued growth of microplastic concentrations in both water and sediment.

“Humans are ingesting plastic when they eat and drink and inhaling it when they breathe, and the long-term impacts are just beginning to be studied,” said Warner.

“However, we need to figure out how to release less plastic into the environment and how to reduce consumption and exposure.”

Study implications and future research directions

Bringing together an interdisciplinary team from three campuses, five colleges, and five disciplines, Emili highlighted the significance of this collaboration.

“We brought together complementary skillsets from our fields of chemistry, engineering, hydrology, oceanography and soil science.”

Emili also mentioned that the research project was initially funded with an Institute of Energy and the Environment seed grant, which “served as an ‘incubator’ for a continuation and expansion of our work exploring the fate and transport of microplastics in freshwater environments, with a particular focus on coastal locations.”

Going forward, Professor Warner hopes to investigate how the composition and types of microplastics have evolved over time. He also wants to assess how the associated health risks have unfolded.

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

Ultimately, the study aims to expand our understanding of the land-to-sea pathway of microplastics and inspire long-term solutions to reduce pollution and its associated health risks.

The study is published in the journal Science of The Total Environment.

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