'From soil to chocolate bar': identifying critical steps in the journey of cadmium in a Colombian cacao plantation.

Regulation of maximum levels of cadmium in chocolate is an issue for cacao exportation from many parts of Latin America, including Colombia. These limits are related to the final product, but buyers often request maximum levels of Cd in the beans. However, to date, there is neither a clear understanding of the relationship between the specified levels of Cd in chocolate and cocoa derivatives and levels in harvested beans or soil nor of the effect of post-harvest processes on the levels of Cd in the final product. To address this, the fate of Cd concentration from soil to chocolate bar was followed in a single farm in Santander district, Colombia. The concentration of Cd in soils was measured using ICP-OES and correlated with soil pH, soil organic matter (SOM), and the use of P-based fertilisers. Cd concentrations were also measured in unfermented seeds, fermented and dried beans, shell, nibs, and chocolate. SOM (2.93-3.78%), soil pH (4.7-4.9), soil P concentration (120-132 mg kg-1) affect Cd availability. However, it is still unclear whether Cd concentration of P-based fertilisers (3-30 mg kg-1) is important or not. While post-harvest treatments did not affect the Cd concentration of beans (4.17 ± 0.8 mg kg-1 on average), the removal of the shell (6.57 mg kg-1) from the nibs (3.28 mg kg-1), as well as the percentage of cocoa mass used contributes to a reduction in Cd concentration in the chocolate bar (1.60 mg kg-1). This study provides clear indications on where research into mitigation measures should be focussed, as well as indicating the importance of carrying out analyses for Cd in the nib or cacao mass, rather than the whole bean, reducing Cd concentration by up to 40%.

The effectiveness of soil amendments, biochar and lime, in mitigating cadmium bioaccumulation in Theobroma cacao L.

Cocoa (Theobroma cacao L.) is an important neotropical tree crop grown for its seeds or beans used in global chocolate and confectionary industries. Following studies showing ill effects of long-term dietary exposure of cadmium (Cd) on human health, a number of countries including the European Union (EU) have developed stringent regulations to protect consumers from exposure to cadmium. Cocoa is capable of bioaccumulating Cd in the cocoa beans when grown in soils high in cadmium and hence livelihood of cocoa farmers can be at risk if methods to mitigate the bioaccumulation of Cd are not developed. In vitro, greenhouse and field experiments were established with four, three and three replications respectively to evaluate the effectiveness of soil amendments, biochar and lime, at various application rates (0, 0.5×, 1×, 1.5× and 2× of the recommended rate), on soil pH, Cd phytoavailability and Cd bioaccumulation in Theobroma cacao L. For the in vitro study, Cd-containing soil was amended with 5 levels of biochar and lime, while for the greenhouse and field study four application rates were tested. The study showed that while lower rates were effective under in vitro conditions as you progressed from in vitro to greenhouse to field conditions the application rates and application frequency had to be increased, as the effectiveness and longevity of the treatments were compromised by environmental factors. Our study implies that the two amendments were complementary in their action and can be used in the recommended rated to reduce Cd bioaccumulation. However further studies are required on the placement of amendments to improve their effectiveness and longevity particularly under field conditions.