Cadmium accumulation and allocation in different cocoa cultivars

Authors: ENGBERSEN, NADINE - Terrestrial Environmental Research Center; GRAMLICH, ANJA - Terrestrial Environmental Research Center; LOPEZ, MARLON - Honduran Foundation For Agricultural Research (FHIA); SCHWARZ, GUNNAR - University Of Zurich; Gutierrez, Osman; SCHULIN, RAINER - Terrestrial Environmental Research Center

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2019
Publication Date: 5/2/2019
Citation: Engbersen, N., Gramlich, A., Lopez, M., Schwarz, G., Gutierrez, O.A., Schulin, R. 2019. Cadmium accumulation and allocation in different cacao cultivars. Science of the Total Environment. 678, 660-670. https://doi.org/10.1016/j.scitotenv.2019.05.001.
DOI: https://doi.org/10.1016/j.scitotenv.2019.05.001

Interpretive Summary: Cadmium is an inessential heavy metal that produces severe toxic effects in many living organisms, including humans. Cacao beans from production areas in South and Central America present high Cadmium levels that are above the standards to be enforced by European Union in 2019. Therefore, there is critical need to find ways to lower Cadmium accumulation in the beans. An interdisciplinary research team participated in the evaluation of Cadmium uptake, translocation and accumulation in 11 cacao cultivars planted in Northern Honduras. Several plant organs including rootstocks, scions, leaves and beans were collected and analysed. Results indicated that available soil Cadmium concentrations were more closely associated with the Cadmium concentrations of the rootstocks’ scions and leaves but not as much with the bean Cadmium concentrations. Bean Cadmium concentrations were also different among cultivars. Further analysis of three specifically selected cultivars indicated differences in Cadmium uptake between mature beans and immature beans. Results may indicate that the differences in bean Cadmium uptake among cultivars was due to specific cultivars traits. Results indicate the possibility of cultivar selection with lower Cadmium uptake that would be beneficial to human consumption.

Technical Abstract: Cadmium (Cd) is a biologically non-essential heavy metal that can cause toxic effects in plants, animals and humans already at very low concentrations compared to other metals. After Cd concentrations in cocoa beans of various provenances, particularly from Latin America, were found to be so high that their products will not meet the new regulations enforced by the European Union in 2019, there is an urgent need to find measures by which Cd accumulation by cocoa beans can be lowered to acceptable values. In this research, the long-term cocoa cultivar trial CEDEC-JAS in northern Honduras was used to investigate differences between 11 cultivars in Cd uptake and translocation. Sampling of various plant parts, including rootstocks, scions, leaves and beans, from three replicate trees per cultivar and the soil around each tree was conducted at this site. Results indicate that concentrations of available soil Cd were more closely correlated with the Cd concentrations of the rootstocks (R2 = 0.56), scions (R2 = 0.59) and leaves (R2 = 0.46) than with the bean Cd concentrations (R2 = 0.26). In addition, Cd concentrations of rootstocks, scions and leaves showed close relationships to available soil Cd concentrations, with no significant differences between the cultivars. In contrast, bean Cd concentrations showed only weak correlations to available soil Cd and Cd concentrations in the vegetative plant parts, but significant variation among cultivars. Three cultivars (IMC-67, SPA-9 and POUND-7), which were analyzed in more detail, showed significant differences in the Cd concentrations of mature beans, but not of immature beans. These results suggest that the cultivar-related differences in bean Cd concentrations were primarily the result of differences in Cd loading during bean maturation, possibly due to cultivar-specific differences in the xylem-to-phloem transfer of Cd. The results show that selection of cultivars with low Cd transfer from the vegetative parts of the trees into the beans has high potential to keep Cd accumulation in cocoa beans at levels that are safe for consumption.