Microplastics In Freshwater Environments Are Steadily Increasing, Directly Related To Plastic Production

A new study in Comprehensive Environmental Science shows that microplastics in freshwater environments have been steadily increasing for decades, and since the 1950s, microplastics have been directly associated with the rise in global plastic production. The study, led by an interdisciplinary research team at Pennsylvania State University, provides insights into how microplastics move and spread in freshwater environments, helping to develop long-term solutions to reduce pollution.

In this study, the team examined freshwater sediment cores from four river basins in Pennsylvania: the Kiskiminetas River, the Blacklick Creek, the Reston Lake, and the Darby Creek. The author of the paper, Nathaniel Warner, an associate professor of civil and environmental engineering, said, "There are few studies investigating how microplastics change over time. We were one of the first teams to track microplastic levels in freshwater sediments before the 1950s to the present day. Research has shown that microplastic concentrations increase with increasing plastic production.It is worth noting that contrary to the research team's expectations, the study found no correlation between population density or land use and high levels of microplastics.

Floating disposable plastic bottles and fast food packaging boxes on the Chao Phraya River in Bangkok, Thailand

Based on other findings in the literature, we believe that the important factor ultimately is not the driving force behind changes in microplastics in different locations, especially the percentage of microplastics associated with developed regions and population density, "said Lisa Emili, Associate Professor of Natural Geography and Environmental Studies at Pennsylvania State University Altona and co-author of the paper.
The researchers were also surprised to find that although the accumulation of microplastics had been increasing every decade until 2010, the accumulation of microplastics had decreased from 2010 to 2020. But researchers also say that this is only a preliminary finding and further research is needed, but this reduction may be related to increased recycling efforts.

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

Regarding the amount of plastic entering the ocean each year, it is estimated that 7000 to 25000 tons of plastic enter the ocean each year. However, it is believed that only about 25000 tons of plastic are floating on the sea surface. This suggests that estuaries, especially tidal marshes, may capture plastic carried by rivers before it reaches the ocean, which may explain why there is much less plastic floating on the ocean surface compared to the plastic flowing into the ocean by rivers, "said Raymond Najjar, co-author of the paper and professor of oceanography.

These findings suggest that as people use more plastics, the levels of microplastics in water and sediment will continue to increase, "Nathaniel Warner said.

This study incorporates a wide range of professional knowledge from interdisciplinary teams, bringing together experts and their complementary skills in fields such as chemistry, engineering, hydrology, oceanography, and soil science. The researchers stated that they will continue and expand their exploration of the transportation of microplastics in freshwater environments, with a particular focus on coastal areas.

The estuary processes a large amount of substances carried by the river, such as carbon, sediment, and nutrients, which have a significant impact on the substances that ultimately enter the ocean, "said Professor Raymond Najjar." I think the effect of estuaries on plastics may be similar, but what we need is not just a model study and a single core. We need to consider the possible sources and sinks of plastics in specific systems, such as rivers, atmosphere, estuarine sediments, and swamps, in order to conduct a more comprehensive assessment of river plastics captured by estuaries.