Understanding Cadmium Uptake by Cocoa Plants via Cd Isotope Analyses

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Cadmium (Cd) is a trace metal that is highly toxic even at low concentrations. The relatively high Cd abundances often found in cocoa are a serious problem for the cocoa producers of developing nations, as the European Union plans to implement strict new upper limits for Cd in cocoa products in 2019. This development has recently spurred research into the causes of Cd enrichment in cocoa. Such work has mainly focused on the impact of external factors, such as soil type, pH and cultivation practices, on the Cd content of cocoa but until now, these investigations have failed to provide conclusive results. Hence, it has been suggested that Cd accumulation may vary across different cocoa varieties but this possible link has yet to be investigated. The current project constitutes collaborative research by Prof M Rehkamper, an isotope geochemist at Imperial College London, and Prof J Dunwell, a plant physiologist at the University of Reading. Previous work of Rehkamper has shown that coupled Cd concentration and stable isotope analyses, initially developed for planetary science research, can provide unique insights into Cd uptake and translocation by plants. Furthermore, a 2015 pilot study of Rehkamper and Dunwell revealed that such analyses are also promising for cocoa. In the current 6-month project, the results of the 2015 pilot experiment will be verified, to ensure that coupled Cd concentration and isotope data indeed provide a reliable measure for Cd uptake by and translocation within plants. Furthermore, a suite of different cocoa varieties will be analysed to characterise the overall variability of Cd uptake and accumulation amongst different types of this plant. Together, the results will enable an initial identification of cocoa varieties that are particularly suitable for cultivation because they feature minimal Cd accumulation in beans, due to low uptake of Cd by the plant and reduced transport from the roots to the fruit.As such, the results of this study can make an important contribution to the development of sustainable methods for the production of cocoa beans with safe levels of Cd, thereby ensuring a reliable source of income for cocoa producers in developing nations and boosting the economies of rural communities.