Is it true that 80 percent of the plastic in the oceans comes from land, and 20 percent from the sea?

This claim is uncertain. We could find no credible scientific source to back it up. The percentage of land- and sea-based plastic inputs into the ocean has not yet been calculated on a global level and therefore remains unknown. Scientific studies show that the ratio of land- versus ocean-based plastics can differ widely depending on the specific location and the scientific metric used.