Abstract
Elevated cadmium (Cd) concentrations in cacao and cocoa-based products (e.g., chocolate) present a potentially serious human health risk. While recent regulatory changes have established a threshold of 0.8 mg kg-1 for Cd content of cocoa-based products, the biophysical factors (e.g., climatic or edaphic conditions) that determine the amount of soil-derived Cd in the cacao bean are poorly understood and have yet to be quantitatively assessed across diverse production contexts. To determine the primary drivers of cacao bean Cd, we used the scientific literature to systematically compile a database of climatic, edaphic, and plant data from across the Cacao Belt, which is approximately 20 degrees latitude on either side of the equator. From this compiled dataset, we then used boosted regression trees to quantitatively synthesize and evaluate these drivers of cacao bean Cd. Total soil Cd concentration, soil pH, and leaf Cd were the best predictors of bean Cd content. Notably, we found that both available soil Cd and soil organic carbon (SOC) content had negligible effects on bean Cd. However, soil pH and SOC decreased the degree of bioconcentration of total soil Cd in the bean Cd concentration. Thus, given the difficulty in remediating soil Cd enriched soils, our results suggest that Cd mitigation strategies targeting plant physiology-based approaches (e.g., breeding, rootstocks) have a higher probability of success than soil-based strategies (e.g., remediation).
Highlights
Cadmium (Cd) is a trace metal element of human health concern [1] that can cause a variety of adverse health outcomes, including endocrine disruption, osteoporosis [2], and has been classified as a carcinogen, especially in the context of Western diets [3]
It is possible that the disproportionate number of studies in Central and South America reflects the differences between higher grade Ecuadorian “fine” cacao and West African “bulk” cacao, as fine cacao is used for dark chocolates with high cacao solid contents and more stringent regulatory limits on Cd concentrations [56, 57]
The general influence of organic matter on metal element bioavailability [72] in soils is mediated by ligand exchange with carboxylate moieties, which has been well detailed for Cd [19, 62]. Though this partitioning between soluble and organically-associated Cd does not appear to inform cacao bean Cd content, our model provides some evidence of its occurrence: at lower concentrations (~1%), soil organic carbon (SOC) had a positive effect on bean Cd (S3 Fig in S1 File), but this effect was negligible at 2.5–3% SOC
Summary
Cadmium (Cd) is a trace metal element of human health concern [1] that can cause a variety of adverse health outcomes, including endocrine disruption, osteoporosis [2], and has been classified as a carcinogen, especially in the context of Western diets [3]. Cadmium enters the anthropogenic trophic chain via soil-plant transfers [4,5,6]. Drivers of cadmium accumulation in Theobroma cacao L. beans
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