Brakes are iron and copper, the latter is an environmental contaminant. But tires pollute zinc and a hundred other petrochemicals. One is causing big problems with fish - 6PPD, but there are likely others causing yet unseen damage. Between the two brake dust seems more manageable in stormwater.

Yay! Thank you! Adding it to the archive. I keep my car in the level 3 regeneration, so mostly "coast" up to the stop. I'm glad to see such significant reduction. Also because I breath a lot of that dust when I'm cycling, less particulates = better.

Edit: Some key findings from the paper:

Key finding #3.8: As the level of electrification of a vehicle rises, the dependence on regenerative braking also increases, thus lowering PM emissions from brake wear. Based on recent evidence [30], regenerative braking can reduce, in the worst- case scenario (i.e. highest usage of mechanical brakes or equivalently lowest usage of regenerative braking), brake wear emissions by 10-48% for hybrid electric vehicles (HEVs), 66% for plug-in hybrid electric vehicles (PHEVs), and 83% for battery electric vehicles (BEVs)

Key finding #3.13: Vehicle weight is directly proportional to tyre wear emissions. For example, a car with a 20% higher mass demonstrated a 20% increase in tyre wear [13]. Electric cars are around 20% heavier than the equivalent conventional cars, so they emit around 20% more tyre wear [40], [42], [43].

That and the increased road wear which grows exponentially (with the fourth power of axle weight) with the weight of the vehicle. That means a 2 ton car does 16 times more road damage than a 1 ton car. And before someone takes this to mean I prefer to not have EVs on the road, NO, I mean that this is a fact and we have to deal with it somehow while eliminating ICE. For example by making lower range EVs more attractive, since they already are acceptable in practice for a large proportion of road users. Going from ICE cars to ICE trucks, a common trend, is even worse in this regard since it adds significant emissions on top.

The additional weight, yes, as posted by @avidamoeba. Tho' those are different things, apples to oranges - brake dust and tire dust are not the same. With the power that some EVs have it's really easy to accelerate rapidly leading to faster tire wear. That is a choice made by the driver. I put my EV in eco mode, and gently accelerate. And try to ride my bike as much as possible, instead of my car. On the bike, I often try to accelerate as fast as possible, for cardiovascular and other health reasons, including just plain having fun!