Cadmium is a heavy metal which exists naturally in low concentrations in all soils. It is spread by air and water and is absorbed by many plants. Fertilisers may also be a source of cadmium in plants. It is difficult to assess the source of cadmium content in a plant because it exists everywhere. But some research has shown that for Central American cocoa high cadmium content is related to the specific local constituency of the soil.
Volcanic soils have an above average cadmium content.
Lead is a heavy metal which also exists naturally in soil and therefore lead levels in cocoa beans may be related to the type of soil. Fertilisers may also be a source of lead in plants. Cocoa makes little contribution to the total level of lead consumption. In 1987 Prugarova and Kovac studied heavy metals in cocoa and found levels of lead and cadmium to be variable, but within acceptable levels. Copper has been studied more recently as its deficiency has been associated with cardiovascular disease.