Physicochemical and mineralogical characterization of Brazzaville landfill soils: Assessment of mercury (Hg), nickel (Ni) and zinc (Zn) ion contamination

The aim of this study was to characterize in depth the soils from six urban landfill sites in Brazzaville (Diata, Glacière, Kinsoundi, Moukondo, Tsiémé and Mikalou) by assessing their physicochemical properties, mineralogy and metal ion contamination (Hg, Ni, Zn). Using samples taken according to a rigorous methodology, we analysed water content, pH, organic matter, mineralogy via X-ray diffraction (XRD), and metal ion concentration using Inductively Coupled Plasma - Optical Emission Spectroscopy (ICP-OES). The results highlight significant variability in parameters between sites, with concentrations of Hg²⁺, Ni²⁺ and Zn²⁺ systematically exceeding regulatory thresholds, underlining the potential environmental and health impact. Statistical analyses reveal strong correlations between certain physicochemical parameters and the presence of heavy metals, indicating a potential relationship between soil composition and metal contamination. Furthermore, the distribution of parameters and heavy metals is predominantly asymmetrical, except for organic matter in the Tsiémé landfill, where a symmetrical distribution is observed. These results contribute to a better understanding of the dynamics of urban soil contamination, and underline the urgent need for sustainable and appropriate management of these landfill sites.