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.
"Hundreds of other ingredients, including steel, fillers, and heavy metals — including copper, cadmium, lead, and zinc — make up the rest, many of them added to enhance performance, improve durability, and reduce the possibility of fires."
They didn't reference a source, and the claim is rather outlandish.
Cadmium and Lead are both quite toxic, and I'd be absolutely shocked if any tyre company in the western world used either of them anywhere near their products, let alone mixed into the rubber, which is insane.
"The low cadmium levels in their tyres was due to the efficacy of the zinc oxide purification process. In the nearly 50 years since the David and Williams study, Zn, S, and Cd refining has improved and this may contribute to low levels of cadmium being detected" from: https://www.sciencedirect.com/science/article/pii/S016041202...
So... it looks like tyres contain some Zinc, which many decades ago wasn't purified very well, which resulted in Cadmium and Lead being included as impurities in the Zinc. The industrial processes have improved and this is no longer a problem, but people are quoting tyre compound issues from the 1950s like they're still issues today.
Whoever wrote the article you linked couldn't be bothered to run a quick Google search to see if the problem still exists. That's unfathomably lazy.
PS: Not to mention that the lead added to fuel was a vastly bigger problem than any trace lead impurities that got into 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.