Heavy metals contamination of soil irrigated with treated waste water in a semi-arid region, case of Sfax, Tunisia

Abstract In arid and semi-arid regions, the use of unconventional water such treated domestic waste water as an alternative water resource in crop irrigation became a common practice. This study investigates the effect of using treated waste water (TWW) for irrigation on Heavy metal (HM) soil contamination. In the other hand, face to the growing concern about contamination risks, the present study aims to quantify the effect of irrigation, for a long time period, with TWW on heavy metals accumulation in soil. The HDRUS-1D model is applied to simulate the transport of Cr, Cu, Ni, Zn and Fe in two soils types irrigated with TWW in Sfax, Tunisia as a case study. The prediction of HM concentrations in the Calcisol over 30 years shows that, over time, the amount of metals propagates more and more in depth. The enrichment is more notable in the surface layer in the case of Cr, Cu and Ni and it affects the entire soil profile in the case of Zn and Fe. In the case of Fluvisol, the HM enrichment is located in the deep sandy layers. A greater growth of the amount of metals in Fluvisol than Calcisol is observed. Even though the TWW content of HM is below Tunisian standard for irrigation, their accumulation in soil need continuous monitoring. The choice of irrigation by TWW will not considers only the water quality but also the type of soil and its ability to accumulate metals.