A mechanistic understanding of cadmium behavior in tropical cacao soils

Research output: Chapter in Book/Report/Conference proceedingAbstract


Relatively high levels of cadmium in cacao beans threaten the livelihoods of smallholder cacao farmers in Latin America and the Caribbean (LAC), due to strict food safety regulations in chocolate-producing countries. A potential strategy to reduce bean cadmium concentrations is to apply soil amendments to reduce soil cadmium availability. Nevertheless, the design of such strategies is hampered by a limited understanding of the biogeochemical behavior of cadmium in tropical soils. We performed a lab incubation study where soils from farms in Ecuador and Colombia with high bean cadmium levels (1.2-4.5 mg kg-1) and contrasting levels of pH and organic matter were amended with four types of compost (30 t ha-1), with or without the addition of lime (CaCO3; 1.75 t ha-1). The objective was to explain the changes in the bioavailability of cadmium in response to those amendments. We measured the amount of reactive surfaces of organic matter and metal oxides. Applying a geochemical multi-surface model including NICADonnan and CD-MUSIC, we predicted that 60-100% of cadmium is bound to organic matter. Considering that the dissolved (i.e. bioavailable) cadmium concentration constituted only 1-5% of total soil cadmium, adequate quantification of this pool is essential. Hence, we compared the common 1 mM Ca(NO3)2 extraction method with rhizon samplers that directly sample soil pore water. Rhizon cadmium concentrations were up to an order of magnitude larger than the Ca(NO3)2 extraction. Overall, our results offer a mechanistic understanding of how soil amendments could be used to create sustainable low-cadmium cacao in LAC.
Original languageEnglish
Title of host publication2023 Book of Abstracts: Wageningen Soil Conference
Subtitle of host publicationWorking together on solutions for a sustainable world
Place of PublicationWageningen
PublisherWageningen University & Research
Publication statusPublished - 2023
EventWageningen Soil Conference 2023 - Wageningen
Duration: 28 Aug 20231 Sept 2023


ConferenceWageningen Soil Conference 2023
Internet address


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