I'd gonna guess "worse"

Brake dust is mostly some iron, carbon, silica. Not great to ingest but very much recyclable by the environment, unlike rubber.

And possibly much easier to greatly reduce (just build some shielding around the brake to catch most of the dust) than the tyre

Unfortunately it's also copper and asbestos :(. (Yes, they're banned, but nobody is checking aftermarket brake pads...)

But tire dust is definitely now the worst of the two, by far. 6-PPD alone.

	▲	potato3732842 2 days ago \| parent [-]
		>Yes, they're banned, but nobody is checking aftermarket brake pads.. On one hand you've got the people who insisted on regulating all of our manufacturing out of the country on environmental and safety grounds. On the other hand you've got the people who want to band asbestos and lead and all manner of other dangerous chemicals in consumer products. Both these people are dressed like Spiderman and they're pointing at each other. <facepalm>