Microplastic pollution linger in rivers for years before entering oceans

The Severn River is directly downstream from the city of Birmingham, England. The credit is given by the University ofNorthwestern.

A new study has found that microplastics can linger in riverbeds for as long as seven years before washing into the ocean.

Researchers assumed lightweight microplastics flowed quickly through the rivers because they are in constant motion.

Hyporheic exchange, a process in which surface water mixes with water in the riverbed, can trap lightweight microplastics that otherwise might be expected to float.

The study was published in the journal Science Advances. It is the first assessment of plastic pollution in the entire water stream. The model describes processes that affect particles, including hyporheic exchange, and focuses on microplastics at 100 micrometers in size and smaller.

The study's senior authors said that most of the pollution they know about is from the oceans. Small plastic particles, fragments and fibers can be found everywhere. We don't know what happens to the particles that are discharged into the water. Most of the work thus far has been to document how much plastic is in the ocean.

A lot of microplastics from urban wastewater end up near the river's source and take a long time to be transported downstream to oceans.

Packman is the director of the Northwestern Center for Water Research. He is a member of the Program on Plastics, Ecosystems and Public Health at the Institute for Sustainability and Energy. The study's first author is a research fellow at the University of Birmingham, and a former student of Packman's.

Microplastic movement is modeled.

Packman, Drummond and their teams created a new model to model how individual particles enter and settle in freshwater systems.

Hyporheic exchange processes play a significant role in retaining microplastics within rivers. The hyporheic exchange process is known to affect how natural organic particles move and flow through freshwater systems, but it is rarely considered microplasticAccumulation.

Packman said that the retention of microplastics was not a surprise because they already knew this happened with natural organic particles. Natural particles biodegrade, whereas a lot of plastic just accumulate. Because plastic doesn't degrade, they stay in the freshwater environment for a long time.

Global data on urban wastewater discharges and river flow conditions were used to run the model.

They were trapped in the water.

Microplastic pollution is the longest at the source of a river or stream. Microplastic particles moved at an average rate of five hours per kilometer. The movement took up to seven years to move just one kilometer during low-flow conditions. Microplastics are more likely to be found in the water in these areas.

The residence time went down as microplastics moved further downstream. The residence times were shortest in large creeks.

Packman hopes that researchers will be able to better assess and understand the long-term impacts of microplastic pollution on freshwater systems.

It will take a long time for all of the microplastics to be washed out of the freshwater environment. This information shows us whether we need solutions to remove the plastic from the water.

Science Advances has more information about MicroplasticAccumulation in riverbed sediment via hyporheic exchange from headwaters to mainstems. Science.org has a DOI of/10.1126/sciadv.abi9305.

Science Advances has journal information.

Microplastic pollution linger in rivers for years before entering oceans.

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