> Seventy-eight percent of ocean microplastics are synthetic tire rubber, according to one estimate.

https://e360.yale.edu/features/tire-pollution-toxic-chemical...

> About 34% of the emitted coarse TWPs (tire wear particles) and 30% of the emitted coarse BWPs (brake wear particles) (100 kt yr−1 and 40 kt yr−1 respectively) were deposited in the World Ocean. These amounts are of similar magnitude as the total estimated direct and riverine transport of TWPs and fibres to the ocean (64 kt yr−1).

https://www.nature.com/articles/s41467-020-17201-9

Water pollution from brake and tire dust, (and oil drippings,) is well proven. If you build infrastructure to handle runoff from roads, you need to mitigate pollution in that runoff too.

> Most microplastic in water comes from washing machines. Synthetic fibers from clothes.

I know less about that but from what I've skimmed it appears to be true too.