Youtube essay on the Tonga Trench, only 100 yards shallower than the Mariana Trench.
https://m.youtube.com/watch?v=XEzEW8VUmMMOn neat take away, on human time scales, plastic in the ocean is rather bad, but on the planet's time scale, it'll all be eaten up and recycled same as everything else. Plastic floating in the ocean gets colonized by algea and bacteria to the point it loses bouyancy and sinks to the bottom with all the other dead algea mass that eventually falls into the subduction zones. May drive some critter extinct, but the survivors will surely adapt to fill the new open niches.