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Why do oceans receive so much plastic waste generated on land?

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Ubiquitous plastics — plastic pollution A volunteer collecting plastic nurdles (pellets less than 0.2 inch [0.5 centimeter] in diameter) at Barreiras Beach, Corrubedo, Spain.

The ocean acts as the ultimate receiving body for plastic waste because it is geographically downstream from nearly every terrestrial location. Millions of tons of plastic enter marine environments annually through a variety of pathways, driven by both intentional and accidental factors.12

Much of this pollution stems from improper disposal, where single-use plastics are discarded as litter rather than being sent to landfills or recycling centers. Once on the ground, this waste is transported to aquatic systems via several diffuse sources:3

Environmental Transport: Wind, stormwater runoff, and rainfall carry discarded plastic from urban and rural landscapes into rivers, which eventually transport the debris to the ocean.12
Infrastructure Limitations: In many regions, inadequate waste management infrastructure or overflowing containment structures lead to plastic entering waterways.32
Direct Inputs: In some instances, solid waste is intentionally dumped into bodies of water or originates from industrial facilities and wastewater outfalls.12

Because synthetic plastics are largely nonbiodegradable, they persist in the environment, accumulating in subtropical gyres and breaking down into microplastics that circulate throughout global ecosystems.132