The distribution of cadmium in soil and cacao beans in Peru

Peru is the eighth largest producer of cacao beans globally, but high cadmium contents are constraining access to international markets which have set upper thresholds for permitted concentrations in chocolate and derivatives. Preliminary data have suggested that high cadmium concentrations in cacao beans are restricted to specific regions in the country, but to date no reliable maps exist of expected cadmium concentrations in soils and cacao beans. Drawing on >2000 representative samples of cacao beans and soils we developed multiple national and regional random forest models to develop predictive maps of cadmium in soil and cacao beans across the area suitable for cacao cultivation. Our model projections show that elevated concentrations of cadmium in cacao soils and beans are largely restricted to the northern parts of the country in the departments of Tumbes, Piura, Amazonas and Loreto, as well as some very localized pockets in the central departments of Huanuco and San Martin. Unsurprisingly, soil cadmium was the by far most important predictor of bean cadmium. Aside from the south-eastern to north-western spatial trend of increasing cadmium values in soils and beans, the most important predictors of both variables in nation-wide models were geology, rainfall seasonality, soil pH and rainfall. At regional level, alluvial deposits and mining operations were also

Automated summary

Peru is the eighth largest producer of cacao beans globally, but high cadmium contents are restricting access to international markets. To develop predictive maps of cadmium in soil and cacao beans, representative samples of cacao beans and soils were collected and multiple random forest models were developed. The models showed that elevated concentrations of cadmium in cacao soils and beans are mainly found in specific regions in the country, such as Tumbes, Piura, Amazonas, Loreto, Huanuco, and San Martin.