Rivers transport between 1.15 and 2.41 million tonnes of plastic waste into the world’s oceans each year, according to researchers at The Ocean Cleanup.
The Dutch foundation, which is currently developing technologies to rid the oceans of plastic, has published the ‘first-ever’ estimate of plastic emissions from rivers into the world’s oceans.
Writing in Nature Communications, they calculate that two-thirds of the input comes from the 20 most polluting rivers, most of which are located on the Asian continent.
The orgranisation explained that the distribution of plastic in the oceans can only be mapped if the main sources of plastic pollution are known.
By pinpointing these sources, The Ocean Cleanup said that it can target the best possible locations in the ocean for the deployment of its cleanup systems. Additionally, knowledge about the sources of plastic pollution can aid prevention efforts.
It is commonly accepted that most plastic found in the oceans originates from land-based sources. It is also well known that rivers play a particularly important role in transporting mismanaged plastic waste from land into the ocean.
Until now, however, researchers had quantified neither the total amount of plastic flowing out of the world’s rivers, nor how much plastic is emitted by each individual river.
For this study, a team lead by The Ocean Cleanup researcher Laurent Lebreton created a model from the combined global geospatial information on: population density, waste management, topography, hydrography and the locations of dams.
After calibrating the model against field measurements of plastic flows from various rivers across the world, it was used to obtain a global picture of the annual river plastic emissions into the oceans.
Of the 40,760 ocean-bound rivers studied, just 20 are responsible for two-thirds of the global plastic input. In total, between 1.15 and 2.41 million metric tonnes of plastic are deposited into the oceans by rivers.
The model also shows that plastic input from rivers is highly correlated with drainage of debris from the river banks and creeks leading into main waterways, and that this river-to-ocean input therefore varies per season. Worldwide, three quarters of the plastic released annually enters the oceans between May and October.
“We’re pleased to see how many initiatives have been taken in the past few years to raise awareness of the ocean pollution problem,” commented Boyan Slat, Founder and CEO of The Ocean Cleanup.
“However, for our work in the deep ocean to succeed in the long run, it’s crucial that governments and other organisations speed up their efforts to mitigate the sources of the problem we aim to resolve. The results of this latest study can assist with those efforts,” he concluded.
A video of a recent presentation in which Slat discusses the technology being developed to make use of ocean currents to autonomously clean the oceans can be viewed below.
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