Consumer Reports published a list of the safest and most dangerous dark chocolate bars containing the heavy metals lead and cadmium.

Lead and cadmium are metals found in soils, so cacao beans naturally take up these toxins. But most of the lead issue seems to occur after harvesting while the beans are drying in the open air or during the manufacturing process.

A quick check of medical journals found high cadmium and lead exposure and levels increase the risk of lung, kidney, breast, prostate, colon, pancreas cancers.

A low zinc level increases the risk of dying from higher cadmium levels. [i] It seems zinc helps balance the cancer risks for several toxic metals including cadmium. If you can’t get a blood test for zinc, ask your local compounding pharmacy for a zinc taste test. An example is https://flourishrx.com/test-kit-products/zinc-taste-test?rq=zinc 

Consumer Reports used California's maximum allowable dose level (MADL) for lead (0.5 micrograms)...