**1. Introduction**

The constant increase in the production of sludge from wastewater treatment plants presents a major environmental problem. Compared to traditional means such as landfill or incineration, agricultural sludge spreading appears to be the most cost-effective option for sludge disposal [1]. The use of sludge in agriculture appears among the most sustainable environmental solutions in their disposal. In fact, sludge potential fertilizer and the high cost of mineral fertilizers promote sludge use in agriculture. Nevertheless, their metallic trace elements content (ETM) presents a real disadvantage in their use. Actually, metallic elements retained by the sludge during

wastewater treatment can cause high metallic charges accumulation in soil [2]. Metals can be found in the form of sulphites, oxides, hydroxides, silicates, phosphates, carbonates and insoluble salts. They can also be adsorbed or associated with the organic matter of the sludge. The amount of metals in the sludge depends on the origin of the wastewater and the treatments it has undergone [3, 4]. It is, therefore, necessary to try to understand the mechanisms and factors involved in the transfer of these elements into the soil and their effects on the plant following the addition of sludge. The behavior of heavy metals in soils and their absorption by plants depend on the quality of the sludge, the nature of the metal, the physico-chemical properties of the soils and the plant species. Plants differ in their ability to absorb and accumulate metals [2, 3]. From the perspective of an agricultural recovery of sludge, we have tried to contribute to the study of the impact of sludge on the transfer of metallic trace elements in the sludge-soil–plant system. Therefore, a field experiment was carried out in Oued Souhil (Tunisia). In this context, we propose to study the effect of two types of urban and industrial sludge on the distribution and compartmentalization of metallic trace elements in the different organs of two species (durum wheat and rapeseed) chosen according to their absorption capacity.
