I very much doubt that heavy metals such as mercury or lead are used to make tyres. I've only ever heard of steel belted tyres.
It used to be that wheels were balanced with small lead weights, but the use of lead for this has been banned in pretty much every western country, and wasn't contributing to road dust even when they were allowed.
It used to be that wheels were balanced with small lead weights, but the use of lead for this has been banned in pretty much every western country, and wasn't contributing to road dust even when they were allowed.