Cocoa and Coffee By-Products for Cadmium Remediation: An Approach to Sustainable Cocoa Cultivation in Colombian Soils

For the successful commercialization of cocoa in the global market, ensuring product quality and compliance with regulations—such as EU regulation, which established maximum cadmium (Cd) levels for cocoa products—is essential. Moreover, cocoa cultivation in Colombian soils, an alternative to coca cultivation, is in many cases an unsustainable practice due to soil degradation, which is accompanied by a drastic decrease in soil organic carbon content. This study evaluated the use of a nature-based solution for cadmium remediation in cocoa cultivation soils by applying three organic amendments: biochar derived from cocoa pod shells (Cocoachar), spent coffee grounds (SCGs), and SCG-derived biochar (SCGchar). The effects of these organic amendments, applied at rates of 5, 10, and 15% (w/w), were evaluated in an in vitro incubation experiment (climate chamber) using soil samples collected from Zulia (mountain soils) and Tibú (alluvial soils), located in the Catatumbo region of Norte de Santander (Colombia). Soil analyses included available Cd concentrations (by atomic absorption spectroscopy), physicochemical properties (pH, organic matter, electrical conductivity), and other mineral elements. The results showed that Cocoachar significantly reduced Cd concentrations while enhancing soil quality, particularly by increasing pH and improving soil organic matter content. The application of 15% Cocoachar reduced Cd levels from 0.056 to 0.012 mg kg−1 and increased soil pH from 6.3 to 7.0 in Zulia. In Tibú, the addition of 15% Cocoachar lowered Cd levels from 0.12 to 0.05 mg kg−1 and raised the pH from 5.0 to 6.1. SCGchar primarily enhanced soil organic carbon, increasing its content from 1.87% to 2.35% in Zulia and from 0.66% to 1.53% in Tibú, thereby supporting ecological balance and sustainable soil fertility. Overall, the recycling of cocoa and coffee by-products into biochar offers a solution within the circular economy and a sustainable way to cultivate cocoa. This in vitro exploratory study must be confirmed with field trials and Cd analyses in cocoa beans.