Natural and Anthropogenic Sources of Cadmium in Cacao Crop Soils in Santander, Colombia

Abstract

Cadmium (Cd) levels in cacao products from Santander, the main producing area in Colombia, are well above those permitted for export of cocoa products and may pose a potential health hazard. High Cd in cacao is related to the high content of the metal in beans, which in turn is linked to high concentrations of Cd in soils. Geochemical and petrographic analyses of fertilizer, soil and rock samples from three farms were carried out to determine the sources of Cd and soil characteristics that can affect its bioavailability, in order to identify strategies that may reduce Cd in cocoa. Autochthonous natural sources determine the Cd concentration in soils, with a high correlation between elevated Cd in sedimentary parental rocks and soil metal levels. While no industrial or mining inputs were present, an organic fertilizer was identified as a great allochthonous source of Cd in soils. High levels in the fertilizer were probably due to bioaccumulation of the element, since it was sourced from animals in the same area. The addition of crop waste to fertilize the soil may further contribute bioavailable Cd. Even though the pH range, high OM content and presence of Mn and K all diminish bioavailability, the high metal content in the farm soils still results in significant uptake by the cocoa plants and accumulation in the beans. We suggest that phytoremediation and biological amendments, as well as testing of fertilizers before application, could all be cost-effective solutions to reduce Cd levels in the final product.