iii.) Cadmium uptake mitigation

Some cocoa-growing areas, particularly in certain regions of countries in Latin America and the Caribbean, have soils which naturally contain high levels of cadmium (Cd). 

However, levels in the cocoa beans produced in such areas are not necessarily highly correlated with total soil Cd levels as Cd availability in soil and its uptake by cacao plants depends on a number of factors including soil pH and organic matter (low soil pH and low organic matter increase Cd availability), salinity/chlorinity, availability of other nutrients such as zinc (Zn) and manganese (Mn), the variety of cocoa grown, and post-harvest treatments.

Codex Alimentarius adopted a code of practice for the prevention and reduction of cadmium contamination (CAC CXC 81-2022) which provides details on a various measures, though a nuanced approach is recommended to take account of local soil conditions and varieties grown.

However, guidance will continue to be adapted to take account of results from the research currently underway (see for example “Mitigation of Cadmium Bioaccumulation” project on https://jointcocoaresearchfund.eu/ and the Clima-LoCa project https://climaloca.org.

The following suggestions and recommendations for further research are made based on current knowledge of Cd uptake in cocoa and experience from other crops (See the Further Reading: Cadmium section for further information).

• Carry out a physical-chemical analysis of the soil to include assessment of levels of Cd and micro-nutrients, organic matter content, CEC, pH and chlorinity
• Analyse levels of Cd and micronutrients in leaves and cacao beans, when available
• Avoid flooded soils if the water sources are contaminated with Cd, and ensure water used for irrigation is not contaminated
• Where soils are low in Zn, application of foliar or soil micronutrients may be beneficial 
• In some situations where soil conditions are acidic (pH < 5.5), increase soil pH, for example by liming, to reduce the availability of Cd (but take care to ensure that the availability of essential micronutrients such as Zn does not become a problem);
• Addition of biochar and other sources of organic carbon such as compost may reduce the availability of Cd though the effectiveness will depend on the type of amendment and application method used
• Only use phosphate fertilizers and/or manure which has been checked to ensure it meets national norms for Cd content. In Europe, only products with less than 20 mg kg−1 P2O5 can be labelled as “low cadmium content” (EU Reg 2019/1009).
• In areas where foliar levels of Cd are high, removing pruned material and decaying pod husks from the ground may reduce recycling of Cd back into plant biomass. However, it should be noted that this will also reduce the recycling of nutrients and have a negative impact on soil organic matter content unless another nutrient-rich organic amendment is added, which has been tested to ensure it has low Cd. Moreover, it may be difficult to ensure the safe disposal of the pruned material/husks elsewhere. In most cases this is unlikely to be an effective strategy.
• Avoid post-harvest contamination, particularly by protecting drying/stored beans from dust and traffic fumes.

Key research areas include:
 

• Development of post-harvest procedures to reduce Cd in cocoa nibs. Fine-tuning of fermentation conditions, possibly including pulp drainage and addition of cultures to enhance populations of certain microbes, show promise in reducing Cd in beans whilst maintaining flavour quality attributes.
• Development of cocoa varieties, and/or root stocks, with low accumulation levels.
• Development of improved application methods for soil amendments to ensure they are efficient, practical and economical for farmers to implement.