This source article contains the key information that the heavy metals are not contaminants introduced by the processors, they are present in the beans.
> metals are not contaminants introduced by the processors, they are present in the beans.
That’s true of the cadmium, but not the lead:
> … [L]ead seems to get into cacao after beans are harvested. The researchers found that the metal was typically on the outer shell of the cocoa bean, not in the bean itself. Moreover, lead levels were low soon after beans were picked and removed from pods but increased as beans dried in the sun for days. During that time, lead-filled dust and dirt accumulated on the beans. “We collected beans on the ground that were heavily loaded with lead on the outer shell,” DiBartolomeis says.
Calling out for botanists to weigh in here - is there something that makes chocolate uniquely susceptible to this and if so, is it part of a class of other plants we typically eat? And lastly, this is for food chemists, is there a reliable way to remove such things in the manufacturing that can be added?
Not a botanist, but this is not unique to cocoa. Rice, for example, is known to take up arsenic, cadmium, and other nasties from soils. But it varies significantly depending on the rice variety and where it is gown. Basmati rice grown in California, Pakistan, and India is known to have low levels of arsenic compared to most other types of rice.
> For lead, that will mean changes in harvesting and manufacturing practices, says Danielle Fugere, president of As You Sow. Such practices could include minimizing soil contact with beans as they lie in the sun, and drying beans on tables or clean tarps away from roads or with protective covers, so lead-contaminated dust won’t land on them. Another option is finding ways to remove metal contaminants when beans are cleaned at factories, Fugere says.
> Solving for cadmium is trickier, though it is possible, DiBartolomeis says. Carefully breeding or genetically engineering plants to take up less of the heavy metal could help, though that could take several years. Other potential options include replacing older cacao trees with younger ones, because cadmium levels tend to increase as the plants get older, and removing or treating soil known to be contaminated with cadmium.
Generally plants are excellent at removing metals from the environment and concentrating them in different tissues, depending on the species and metal. Poplar trees, for example, have often been used for remediation of Mercury contamination of souls
Not sure about the specifics of cocoa, but not beyond the pale to see cadmium, for example, be concentrated in the beans.
As for removal from food stuffs, it really depends on how the metals are bound to the plant material. Could be as simple as heating up in a vat with agitation, to requiring something so drastic it changes the nature of the chocolate.
Best way is to reduce the amount that can be integrated by the plant, but good luck with that. The farmers would probably have to import heavy-metals reduced soil
This source article contains the key information that the heavy metals are not contaminants introduced by the processors, they are present in the beans.