Fate and transport of metal trace elements from phosphogypsum piles in Tunisia and their impact on soil bacteria and wild plants.

The phosphate industry in Tunisia generates large amounts of phosphogypsum (PG) with more than 10⁷ t per year. Environmental impact of this solid waste was studied. Cd, Ce, La, Nd, Sr and Y were analyzed from soils near PG stockpiles (Sfax and M'dhilla) and sediments from marine discharge (Gabes). Their impacts on the bacterial community structure and wild plants were investigated. Metal trace elements (MTE) concentrations (in mg Kg^-1 DM) were much higher in contaminated soil than in the control (at 12 km from PG stockpiles). Highest concentrations were recorded in top soil and decreased with depth. A low bacterial diversity was shown (impacted by plants more than by MTE). The MTE concentrations in aerial parts (AP) and roots varied according to the plant species and were higher in contaminated sites. Sr, La and Cd in the AP ranged 33.10-657.56, 2.22-11.05 and 0.21-14.20 mg Kg^-1 DM respectively. Plants exhibiting the maximal metal concentrations in AP (in mg Kg^-1 DM) were the following: Zygophylum album for Sr (657.56) >Zygophylum album for Cd (14.20) >Zygophylum album (11.05) for La >Conyza canadensis (1.11) for Ce >Conyza canadensis (0.75) for Nd >Arthrocemum inducum (0.72) for Y. Kochia indica showed the highest bioconcentration factor (1.60) for Cd, while Zygophylum album exhibited the highest translocation factor (6.12) for La. Zygophylum album would be the most suitable candidate for MTE phytoextraction. CAPSULE: Phosphogypsum contaminates soils near stockpiles with metal trace elements including rare earth element and selects wild plants able to be used for phytostabilization and phytomining.