It was previously thought that only 10 rivers contributed to the vast majority of riverine pollution
| 6 May 2021
A new, three-year study by nonprofit The Ocean Cleanup, published in Science Advances, reveals that 1,000 rivers worldwide are responsible for emitting 80% of the plastic transported by rivers into the ocean – a type of pollution referred to as riverine waste by scientists.
The figure is 100 times larger than a widely reported 2017 study, “Export of Plastic Debris by Rivers into the Sea” by Christian Schmidt at the Helmholtz Centre for Environmental Research in Germany, which found only 10 major rivers were behind 88%-95% of plastic riverine waste.
At the time, Schmidt’s 2017 study was widely misreported by outlets including The Times, Sky and The Sun as concluding that 10 rivers are responsible for generating around 90% of all plastic waste in the oceans.
Schmidt, who co-authored the new study, collaborated with The Ocean Cleanup to map the world’s most polluting rivers using a refined modelling system. The project involved a top-down global modelling framework as well as deploying measuring devices into waterways and observing and categorising pollution in rivers around the world.
The findings were notable not just for highlighting the startling breadth and scale of the problem, but also for establishing the types of rivers that are bringing plastic into the oceans.
The authors concluded that many smaller rivers, passing through cities in developing economies, are among the pollution hotspots of the world. Overall, these 1,000 rivers presented very different characteristics, including river width, flow dynamics, marine traffic, and urbanisation. In other words, strategies for mitigation must be rolled out case-by-case to ensure efficacy.
Factors such as rainfall, high wind rates and a high number of populated waterways all contribute to a country being more likely to be a source of plastic riverine waste, aside from simply the amount of pollution produced overall.
A large number of Asian countries including the Philippines, Malaysia, China, Vietnam and India were among the highest emitters overall.
Efforts must now turn to how to reduce plastic at the source. While riverine plastic accounts for 0.8 – 2.7 million metric tons per year, only 2% of global mismanaged plastic waste ends up in the oceans. The vast majority ends up trapped in river systems and being deposited along riverbanks.
Last month, British chart-toppers Coldplay sponsored an Interceptor vessel, a solar-powered catamaran that will be deployed by The Ocean Cleanup to clean polluted waterways in Malaysia later this year.
The findings of the new study have been made available on an interactive map, which can be explored here: www.theoceancleanup.com/sources/