Research indicates that lead and cadmium get into cocoa in different ways. For cadmium, it appears that the cocoa plant takes it up from the soil. Lead, however, can be deposited on the cocoa beans after harvest, potentially from dust and soil as beans dry outdoors.
Sounds like this potentially affects nearly all chocolate.
To determine the risk posed by the chocolates in CR’s test, we used California's maximum allowable dose level (MADL) for lead (0.5 micrograms) and cadmium (4.1mcg).
CR’s scientists measured heavy metal content against California’s standard levels because there are no federal limits for the amount of lead and cadmium most foods can contain, and they believe that California’s standard levels are the most protective available.