The enrichment of the phosphates by a humid process can be accompanied with rejects of mud poured in hydrographic network of the region of Gafsa-Metlaoui to Chott El Gharsa. These releases are rich in phosphate and trace elements; the average is around these values: P₂O₅: 10.96 %, Cd: 25.83 ppm, Zn: 260.91 ppm, Cr: 387.7 ppm, Cu: 16 ppm, Ni: 26 ppm and Sr: 717.15 ppm. Soils adjoining these rejects present total concentrations in Cd, Zn and Cr higher to the maximal contents tolerated in soils. A two step sequential extraction showed that heavy metals (Cd, Cr, Cu and Ni) were poorly labile (i.e. not soluble in diluted CaCl₂), indicating that their leaching under natural conditions is probably very low. However, extraction with DTPA, CaCl₂ and TEA generated significant amounts of metals (mainly Cd and Cu), suggesting that they were potentially mobilizable. However, zinc and strontium are more concentrated in the mobile phase, indicating that the Zn-Sr-solutions are possible in natural conditions.
This study evaluates the potential for phytoremediation of 30 species collected from six localities, growing on a contaminated site of the study area. Plants and the associated soil samples were collected and analyzed for total metals concentrations. While total metals concentrations in soils vary from 1 to 36 ppm Cd, 1.6 to 2463 ppm Zn, 8.5 to 442 ppm Cr, 2.8 to 38.5 ppm Cu, 1 to 31.7 ppm Ni and 144.6 to 1310 ppm Sr, while those in the plants ranged from 0.11 to 82 ppm Cd, 0.5 to 567 ppm Zn, 0.04 to 174.7 ppm Cr, 0.95 to 51.73 ppm Cu, 0.17 to 6.9 ppm Ni and 6 ppm to 2858 ppm Sr. None of the plants were suitable for phytoextraction because no hyperaccumulator was identified. However, plants with a high bioconcentration factor (BCF, metal concentration ratio of plant roots to soil) and low translocation factor (TF, metal concentration ratio of plant leaves to roots) have the potential for phytostabilization. The plants most effective in the accumulation of metals in leaves are Malva aegyptiaca (TF=30.7) for Cd, Frankenia thymifolia (TF=8.55) for Zn, Peganum harmala (TF=29.14) for Cu and Citrulus sp (TF=10.42) for Sr.