Adrian wrote:
Clot ("Clot" ) gurgled happily, sounding much
like they were saying:

I'm not wishing to enter a dribbling drivel conversation, but Adrian
I have been involved in point source and diffuse inputs of heavy
metals into the environment. Tyres contain zinc. I had expected that
most would have been contributed on motorways and dual carriageways.
A university research project currently ongoing is indicating that
at least higher concentrations are generated in the urban
environment and possibly greater quantities. The work is ongoing.

Are tyres the only source of Zinc?

No, galvanising as mentioned above is also a source.