[EDIT: Ugh, this turns out to be wrong -- it's actually 78% of 11%. See page 89 of https://www.systemiq.earth/wp-content/uploads/2020/07/BreakingThePlasticWave_MainReport.pdf -- misleading representation. 8.5% ain't nothing, but it's nothing like a majority. Thanks to those who replied to correct this!]

The good news: The majority of ocean microplastics come from one source, which means we could dramatically reduce their occurrence by focusing on just one solution.

The bad news: It's car tires. https://www.thedrive.com/news/tire-dust-makes-up-the-majority-of-ocean-microplastics-study-finds