How Do Lead and Cadmium Get into Dark Chocolate?
Growers collect cocoa pods from plants to make chocolate. The wet, sticky beans are removed from the pods, then covered and left to ferment and develop flavor for several days. The beans are then dried – typically in the sun – before being transported to a manufacturing facility where they are sorted, cleaned and roasted.
When examining the source of the contamination, DiBartolomeis and other researchers discovered that cadmium was typically already in the beans when they were harvested. This is because cocoa plants take up cadmium from the soil and it builds up in the beans as the trees grow, similar to how heavy metals contaminate some other crops.
However, lead seems to enter cocoa after the beans are harvested. Researchers examining the contamination found that lead levels were low when the beans were first collected, but increased as the beans were left to dry for days in the sun, where lead-filled dust and dirt could stick to the outside of the beans. Lead is found in dust and dirt near industrial areas and where leaded gasoline is used.
DiBartolomeis says that to lower cadmium levels, growers will need to take a series of steps that can take years. Chocolate producers can start by studying the soil in cocoa-growing areas and choosing plants from lower-level regions. If necessary, nuclei from regions containing more cadmium can be mixed with nuclei from other regions; this is something some manufacturers tell CR they are already doing. Because cadmium levels tend to rise with tree age, older trees can be replaced with younger ones. In some places, contaminated soil can be worked or replaced. And eventually, it may be possible to grow or genetically engineer cocoa plants that are less likely to absorb cadmium in the first place.
Danielle Fugere, president of As You Sow, says fixing lead can be faster because doing so first requires altering harvesting and production processes. Growers and chocolate producers can take steps to minimize ground contact with dried beans and dry them on tables or tarps away from roads, including protective covers to keep contaminated dust away. And in some cases, it may be possible to remove more lead during the cleaning process after the cores reach the factory.
“Lead reductions can be expected in the first year of implementation of new processing practices,” according to the National Confectioners’ Association, which funded research into heavy metals in chocolate as part of the As You Sow agreement. Lower cadmium levels may take longer, but should still be possible, according to both NCA and DiBartolomeis.