One thousand rivers account for nearly 80 percent of plastic carried into oceans: Study

A new study has found nearly 80 percent of the plastic pollution in the oceans come from 1,000 rivers around the world. While it was first thought that a handful of large continental rivers were the main culprits, contributing the most in terms of plastic emissions, a new model has shown a mix of small- and medium-sized rivers play the most significant role in polluting the oceans. The study was conducted by The Ocean Cleanup, and the results have been published in the journal Science Advances.

Only one percent of the world's rivers are responsible for about 80 percent of the plastic that makes it way into the oceans.

The Ocean Cleanup is a non-profit organisation involved in developing advanced technologies to remove plastic from the ocean. It has a two-pronged approach - sealing the source of the plastic pollution and also cleaning up what is already in the ocean.

Two previous studies released in 2017 had different conclusions: one said "five rivers account for 80 percent" of the plastic pollution coming from a river, while the other pegged that figure at 47 rivers. However, neither study used enough data. Now, a new model developed by the Ocean Cleanup, added data collected over three years (from 2017-2020) using 136 field measurements, representing 67 rivers in 14 countries across three continents.

According to a statement, this updated model suggests "1,000 rivers account for nearly 80 percent of global annual emissions, ranging between 0.8 million and 2.7 million metric tons per year, with small urban rivers among the most polluting."

Researchers found that while 1,000 rivers is a large number, they only make up one percent of the world's rivers. To put this information into perspective, only one percent of the world's rivers are responsible for about 80 percent of the plastic that makes it way into the oceans.

Types of rivers and their contribution to plastic emissions
The study says 454 'very small' rivers contribute 25 percent of emissions, while 360 small rivers make up 24 percent of emissions. 162 medium rivers are responsible for 22 percent of emissions, while 18 large and six 'very large' rivers contribute to two percent and one percent of plastic emissions respectively. Other rivers of varying sizes contribute to 26 percent of the pollution.

Riverine plastic emission into the ocean per river class. Image credit: the ocean cleanup

Another revelation from this study was the probability of plastic entering the ocean – produced and used in a coastal or island nation – is higher than from a land-locked country. It is all about proximity to the rivers.

The top five plastic-emitting countries are all located in Asia - the Philippines, India, Malaysia, China, and Indonesia. They are also responsible for 79.7 percent of the plastic that finds its way into the oceans.

With Asia accounting for around 60 percent of the world's population and many Asian countries having long coastlines, they have a higher probability of emitting plastic into the ocean.

For example, plastic waste generated in the Philippines is less than that generated in China. However, China is a landlocked nation, while the Philippines is an archipelago. According to the statement, "the chances that plastic will reach the ocean is greater in the Philippines than in China, so the fraction of mismanaged plastic waste that enters the ocean is higher in the Philippines."

The factors behind this unfairness is related to the geography of the region (distance to the nearest river/ocean and size of river), population density and the climate of the archipelago (rainfall rates).

It is easier to nip this plastic pollution in the bud by employing a mix of various technologies such as Ocean Cleanup's Interceptor and land-based solutions including improved regulatory frameworks, sustainable product design, circular consumption patterns and more advanced waste management.



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