Assessment of metal contamination in topsoil and leachate at an open dumpsite: pollution indices and geostatistical methods in a mining region of southwestern Tunisia

Waste causes environmental harm, when improperly managed. This study investigates topsoil contamination at the Gafsa dumpsite. Geostatistical analysis were applied to evaluate the spatial distribution of chromium (Cr), nickel (Ni), copper (Cu), cadmium (Cd), and zinc (Zn). Cr exhibited the lowest contamination levels, while Cu and Zn were enriched by anthropogenic activities. Contamination factor (CF) values ranging from 0.75 to 0.77 for Cu and 3.87 to 4.43 for Zn. The leachate pollution index (LPI) reaches a value of 24.98. To achieve optimal prediction accuracy, variogram models were tested with ordinary kriging. In comparison, cokriging provided improved Root Mean Square (RMS) and Mean Error (ME) results for Ni, and Cd when using pH and fine fraction as covariates. The trace elements spatial distribution reflected various mechanisms. Predominantly influence contamination of Traffic activities in roadside areas, particularly for Zn and Cu. The domestic waste has a greater effect on the internal areas of the dumpsite. Cd and Ni emerged as the most concerning pollutants comparing to standard values. The study highlights a complex distribution of trace metals driven by inherent properties of soil and external anthropogenic factors, with phosphate mining activities being a key contributor when compared to other landfills in Tunisia.