Trace Metal Contamination of Cocoa Soils Resulting from Illegal Gold Panning in Central West Côte d'Ivoire

Abstract

Côte d'Ivoire, the world's leading cocoa producer, is facing the challenge of illegal gold washing, which is likely to jeopardise its goal of a sustainable cocoa farming system. This is due to the degradation of soil resources through trace metal contamination (TM). The aim of this study is to determine the levels of copper (Cu), cadmium (Cd), lead (Pb) and arsenic (As) contamination in cocoa growing soils in Bonikro. 70 soil samples were collected using the toposequential method, processed and sent to the laboratory for analysis. The results show that TM levels vary significantly depending on the topographical position and depth of the soil. However, these levels are below tolerable limits, excluding As (9.36 mgkg-1). There are significant correlations between pH and TM, which vary with depth and topographic position. A strong positive correlation was observed at depth between pH and Pb (r = 0.82) and Cd (r = 0.71), whereas at the surface the correlations were negative for the same elements. This indicates that pH plays a crucial role in the evolution of TM concentrations. In conclusion, this study highlights the fact that cocoa-growing soils have TM levels below tolerable thresholds, but with significant variation as a function of depth and topographic position. Soil pH appears to be a determining factor in the mobility of TMs, which has important implications for the sustainable management of soils and the environment. Further research is needed to refine these observations and improve natural resource management.