Migration Models of Cu, Zn, and Cd in Soils Under Irrigation With Urban Wastewater

Abstract

A notable migration of Cu, Zn, and Cd has been revealed in the soils used under irrigation for a long period of time in Egypt. To describe the distribution of these elements throughout the soil profiles, mathematical models of migration (diffusion and convective-diffusion models) have been tested, their adequacy has been shown, and their parameters have been estimated. The coefficients of diffusion (D) and convective diffusion (Dc) were 10−7–10−5 cm2/c for Cd and 10−7–10−6 cm2/c for Cu and Zn. The value for Cd is equal to the diffusion rate in water solutions, which indicates that its fixation in soil layers is almost absent. Changes in the fractional compositions of these elements in the soils caused by irrigation with different-quality water agree with those in the parameters of migration models for Zn and Cd.