When did zink WW appear

[zomby woof]

I have some old WW. What time period do I need to worry about zink being mixed in?

[Pepe Ray]

I'd "ball park it" at about 12 years.
What's more important is the presence and frequency of foreign imported cars.
Europe and Asia have been using Zinc for much longer than we have. Any area of the nation where the "imports" controlled the highways would be suspect of producing more zinc ww.

I warned of zinc here for more than a year before anyone took notice.
Pepe Ray