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Rivers retain plastic for decades

Published on
March 22, 2022

‘Between one and four million plastic items flow through Dutch rivers every year’, says researcher Tim van Emmerik. And not just that: contrary to the general assumption, the plastic is not carried to the sea, it stays in the rivers.

Tim van Emmerik, assistant professor with the Hydrology and Quantitative Water Management group, has been studying plastic in rivers for over a decade. He was awarded a Veni grant for his River Plastic Monitoring Project in 2020. Wageningen World covered the study, through which Emmerik aimed to prove that most of the plastic is not carried to the oceans, as was speculated in many studies, but stayed in the rivers. If this was the case, it would mean that cleaning efforts should focus more on river ecosystems rather than on plastic in the oceans.

Rivers retain plastic for years, decades, potentially even for centuries
Tim van Emmerik, universitair docent bij de leerstoelgroep Hydrologie en Kwantitatief Waterbeheer

Rhine and Meuse severely polluted

Van Emmerik’s hypothesis was supported. ‘We just published an article as a synthesis of our research on river plastic across the globe. We conclude that river plastic is, indeed, seldomly carried to sea’, the researcher states. ‘Rivers retain plastic for years, decades, potentially even for centuries.’ The scientist stresses that this calls for a smarter monitoring system and more intelligent solutions for this issue.

The project may be considered successful. ‘Here in the Netherlands, we can conclude two things. Our rivers are reasonably polluted. Some 1 to 4 million plastic objects travel through the rivers every year. The Rhine and the Meuse are among the most severely polluted rivers in the world.’

More plastics in rivers during high river flow

‘Moreover, we discovered that the plastic content in rivers increases when the water rises. That plastic originates from the banks and flood plains, but trash discarded on the streets also makes its way into the rivers through the sewage system if the system is unable to cope with heavy downpours. Flooding such as that which occurred in Limburg last year even adds plastic that has not been discarded to the rivers. In this respect, pollution of rivers is related to climate change, as this exacerbates such weather effects.’