But there isn't lead or other heavy metal in the cast iron itself. If there are heavy metals, they are found in the glazing, so the best thing to do is buy pure cast iron, not glazed cast iron. The same goes for ceramics, but you can't really buy ceramics without glazing, because the ceramic itself is porous - I personally replaced all ceramics with glass and stainless.

Just as a single data point, all our kitchenware today is:

glass, borosilicate glass, pyrex(the US made ones are not borosilicate),

stainless, titanium, cast iron (that we season ourselves),

wood (but not bamboo -- too much glue in there), silicone (for mats and mittens).

Almost no plastic anywhere.