Cadmium in fertilisers used for cacao production: a case study in Colombia

The cacao crop is important for Colombia due to its high economic impact. One concern is the presence of cadmium (Cd) in beans, which can enter the soil from various sources, including fertilisers. However, to date, no studies have been carried out to identify Cd in these inputs. Therefore, this study seeks to determine Cd concentrations in (i) organic matter, (ii) chemical fertilisers and (iii) lime, together with the available fraction accessible to the cacao tree. A total of 133 fertilisers used in eight departments of Colombia were assessed. For 10 of these fertilisers a sequential extraction of Cd was carried out in five categories: water-soluble, exchangeable, reducible, oxidizable and residual fractions. Likewise, the mobility of available Cd from the fertiliser to the soil was assessed with an incubation experiment. This study showed that organic fertilisers had the highest total Cd content of all those studied, and increased the Cd retained in the soils. In contrast, the mobile fraction and bioavailable Cd were higher in chemical fertilisers. These findings show a need to raise awareness about the rational use of fertilisers, as well as greater monitoring by local government authorities and elaboration of new regulations for maximum limits.