"Large particles are carried from the road by rain into rivers, where they may leach toxic chemicals into the environment, whilst smaller particles become airborne and breathed in. They are small enough to reach into the deep lung.
These particles may contain a range of toxic chemicals including polyaromatic hydrocarbons, benzothiazoles, isoprene, and heavy metals like zinc and lead. "
https://www.imperial.ac.uk/news/243
https://www.theatlantic.com/technol