>>In the preindustrial world, lead and cadmium were locked away in the earth’s crust
Cacao has always taken up cadmium from the soil - if there is any there. Yes, some industrial ag processes left cadmium behind in the soil, but for parts of Latin America, it's always been there. Not so much in parts of the Amazon basin and most of Africa. I mostly get cacao from the Amazon basin as it's part of a reforestation program (and has been tested) , but I'd guess any African sourced chocolate is fine.
Without getting into the Dutching process and acrylamides...