The scale of tire tread that just gets washed down into waterways seems staggering. It's probably no more egregious than other pollution sources though.
Anyway, the napkin math is 20 million tons of tires manufactured per year. If 1% of that is lost as worn down tread (or sidewalls depending on the driver), then that is 200,000 tons of tire compound particles dispersed into the environment per year.
That… actually doesn’t seem as bad as I thought it would be. Obviously it’s not going to be evenly spread across the globe, but that’s about (napkin math) 350μg/m^2/year. Even over a century that’s barely a light dusting (to be fair, of toxic/carcinogenic/etc microplastics that are likely much more highly concentrated around major highways and population centres, and their waterways).
I always assumed it was orders of magnitude more than that. But that seems like an amount that, if it were to exist, some sort of bacteria/fungus/algae could actually probably handle.
Anyway, the napkin math is 20 million tons of tires manufactured per year. If 1% of that is lost as worn down tread (or sidewalls depending on the driver), then that is 200,000 tons of tire compound particles dispersed into the environment per year.