Assessment of heavy metals contamination/pollution of phosphogypsum waste of the Mdhilla region (Gafsa, southern Tunisia)

Tunisia is currently faced with the extremely delicate problem of managing the millions of tons of phosphogypsum (PG) discharges which is already causing considerable environmental damage. The research carried out in this work is part of a geochemical assessment of the level of heavy metal contamination in phosphogypsum waste from the Mdhilla region (Gafsa, southern Tunisia). The assessment of ETM contamination/pollution is based on the relatively simple principles of measuring concentrations, calculating indices, and comparing them with established standards, which vary according to the nature of the element, its toxicity, and the receiving environment. Six PG samples are taken from the storage heaps right next to the chemical group’s plant. Our investigations to assess the level of heavy metals contamination focused on: zinc (Zn), chromium (Cr), copper (Cu), nickel (Ni), and cadmium (Cd). These metallic elements are measured by atomic absorption spectrometry. To achieve our objectives, we calculated several indices, such as the geo-accumulation index (Igeo), the contamination factor (FC), the degree of contamination (DC), and the sediment pollution index (IPS). The index approach enables us to predict the extent of heavy metal pollution in these PG discharges from the Mdhilla region. The Mdhilla region’s PG heavy metals contents show the following order of abundance: Zn > Ni > Cr > Cd > Cu. Calculation of contamination/pollution indices reveals in principle polymetallic contamination dominated by three elements: cadmium, nickel, and copper.