Assessment of heavy metals contamination/pollution of phosphate discharge mud in the Metlaoui region (Gafsa, southern Tunisia).

The aim of this study is to evaluate the geochemical and heavy metal contamination degree of phosphate mud in the Metlaoui region (Gafsa, southern Tunisia). These discharges are one of the sources of contamination of the region's hydrographic network to Chott el Gharssa (Tozeur) more to the south. Assessment of heavy metals pollution is based on the relatively simple principles of measuring concentrations, calculating indexes and comparing them with established standards, which vary according to the nature of the element, its toxicity, and the receiving environment. Seven mud samples were taken from the beds of the Thelja, Sebseb, Gouifla, Tarfawi, Melah and Charia wadis. Our investigations to assess the degree of heavy metal contamination focused on: zinc (Zn), chromium (Cr), copper (Cu), nickel (Ni) and cadmium (Cd). These metallic elements are measured by atomic absorption spectrometry. To meet our objectives, we calculated the following contamination/pollution indexes: geo-accumulation index (Igeo), contamination factor (FC), degree of contamination (DC) and sediment pollution index (SPI). The index approach can be used to predict the extent of mud pollution and identify priority polluted sites. Heavy metals content in phosphate mud in the Metlaoui region shows the following order of abundance: Zn > Cr > Ni > Cd > Cu. Calculation of contamination/pollution indexes reveals at first sigt polymetallic contamination dominated by four elements. Cd (FC ranging from 8.42 to 28.75) , Cr (FC = 9.24), Cu (FC = 7.27) and Ni (FC = 5.86) are of greatest concern. Consequently, the mud analyzed is considered hazardous sediment for most of the study area.