Cadmium distribution in soils, soil litter and cacao beans: a case study from Colombia

Cadmium is a toxic non-essential metal for almost all living systems. It is one of the biggest challenges for farmlands and the food chain because of its toxic effect on human health. This research aims to determine the Cd content in soils, litter and cacao beans, following the Cd fluxes within each cacao system using the two-dimensional electrical resistivity tomography technique. The study was carried out in four farms located in the Magdalena basin in Antioquia, Colombia. The farms showed a heterogeneity in relation to cacao cultivars, altitude, topography and geology. The soil cation electrical capacity, pH and soil organic matter levels, as well as the Al, Al3+H+, Ca, K, Mg and P contents were measured at different depths. Moreover, the Cd content was correlated to the resistivity values of samples taken in situ using ERT. Soil Al3+H+ and the altitude of the farms fitted as the best predictors of the beans’ Cd content. Furthermore, the Cd content in soils from the assessed farms ranged between 1.22 and 2.03 mg kg−1. The Cd content in cocoa beans ranged from 0.07 to 1.44 mg kg−1, with a value of 0.40 mg kg−1 on average. The resistivity values obtained in field showed a high correlation with the soil Cd content determined (R2 = 0.82). The predictive tomography plots highlighted topsoil Cd dynamics between litter, amendments and fertilizers. Therefore, these results underlie the utility of the combined geophysical techniques and soil chemical properties including the analysis of fertilizer amendments to improve the understanding of Cd dynamic.