The use of treated wastewater in irrigation is increasing in Tunisia. However. it is imperative to study the impact of this water category on soil. Since 1995, the Zaouit Sousse perimeter (Tunisia) has been irrigated by treated wastewater. So, this sector is an excellent case study to evaluate the impact of the use of treated wastewater in irrigation on geochemical properties of isohumic soils Treated wastewater is characterized by high salinity. The Cd, Cr, Fe, Zn, Pb, Cu, Ni and Al concentrations of treated water range from 10 to 25 10 mu g L-1 In Zaouit Sousse, we examine seven irrigated sub-perimeters and seven profiles which differ by soil composition. texture and structure and irrigation periods (from zero to 14 years). The present results showed that soil salinization is caused by high wastewater salinity and increases in irrigation period. The heavy metal content increases with irrigation period, especially for Pb (1010-1890 mu g kg(-1)) and Cd (2-20 mu g kg(-1)). The pH values of the water and soil are slightly basic The metals' migration will especially depend on the concentration of organic carbon and of the soil nature (C) 2009 Elsevier BV All rights reserved.