Long-term transformation and redistribution of continually added mobile heavy metals and evaluation of their environmental risk: Case study of Khlédia soils (North Tunisia)

Abstract

The fractional redistribution index of the element i (Utf), whole hole soil redistribution (Uts) and reduced partitioning (binding intensity) (IR) indexes were proposed to quantify the metal transformation and redistribution processes in amended soils with fix quantity of salt metal solutions and incubated for long period. By definition, the initial soil is at equilibrium state the “equilibrium’ parameters (Uts and IR) are equal 1. First, Uts and IR of added heavy metals were high. With time incubation, the Uts and IR must converge towards 1. However, the mobile heavy metal forms could continuously added to agricultural (active) soils. As nay equation was suggested to follow the evolution of the heavy metals transformation and distribution in active soil, the objective of this work is to test if the applied equilibrium parameters in amended soil are useful in this different context. The results showed that (i) the evolution of the equilibrium parameter are sensitive to soil redox, pH, salinity and dissolved organic matter (DOM) concentrations variations, (ii) the continuous toxic metals quantities loading highly increased the Uts and the relative bending intensity (IR) indexes that couldn't never return to quasi-equilibrium state of control soil, and (iii) to predict the environmental risks of added toxic trace elements, the IR is a valid assessor. Therefore, after adopting some new terms definition, the equilibrium parameter could be designed to assess the long-term transformation and redistribution of the continuous input of toxic elements in soil and sediment.