Where does the plastic in our oceans come from?

Which countries and rivers emit the most plastic to the ocean? What does this mean for solutions to tackle plastic pollution?

SUMMARY

80% of the world’s ocean plastics enter the ocean via rivers and coastlines. The other 20% come from marine sources such as fishing nets, ropes, and fleets. To tackle plastic pollution we need to know where these plastics are coming from. Previous studies suggested that a very small number of rivers were responsible for the vast majority of ocean plastics: 60% to 90% of plastics came from only ten rivers. 

Higher-resolution mapping and consideration for factors such as climate, terrain, land use, and distance to the ocean suggests that many smaller rivers play a bigger role than we thought. It takes 1,600 of the biggest emitting rivers to account for 80% of plastic inputs to the ocean.

It is estimated that 81% of ocean plastics come from Asian rivers. The Philippines alone contribute around one-third of the global total. Since the number of contributing rivers is much higher than previously thought, we will need global efforts to improve waste management and plastic collection rather than targeting only a few of the largest rivers.

Most of the plastic in our oceans comes from land-based sources: by weight, 70% to 80% is plastic that is transported from land to the sea via rivers or coastlines.1 The other 20% to 30% comes from marine sources such as fishing nets, lines, ropes, and abandoned vessels.2

If we want to tackle plastic pollution we need to stop it from entering the ocean from our rivers. The problem is that we have hundreds of thousands of river outlets through which plastics reach the oceans. To prioritize mitigation efforts we need to understand which of these rivers transport plastic to the sea, and which ones contribute the most.

In this article we look at the distribution of plastics across the world’s rivers; why some rivers carry a lot of plastics while others have very little; and which countries account for the largest share of plastic pollution.

Previous studies suggested that most plastics come from only a few of the world’s rivers: one study estimated that the top ten rivers were responsible for 50% to 60%; another for more than 90%.3

The latest research, which was just published in Science Advances, updates our understanding of how these plastics are distributed.4 Lourens Meijer et al. (2021) developed higher-resolution modeling of global riverine plastics. They found that rivers emitted around 1 million tonnes of plastics into the oceans in 2015 (with an uncertainty ranging from 0.8 to 2.7 million tonnes). Around one-third of the 100,000 river outlets that they modeled contributed to this. The other two-thirds emitted almost no plastic to the ocean. It’s an important point because we might think that most, if not all, rivers are contributing to the problem. This is not the case.

But, importantly, the latest research suggests that smaller rivers play a much larger role than previously thought. In the chart we see the comparison of the latest research (in red) with the two earlier studies which mapped global riverine inputs. This chart shows how many of the top-emitting rivers (on the x-axis) make up a given percentage of [ … ]

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