Kinetic interactions of EDDS with soils. 2. Metal-EDDS complexes in uncontaminated and metal-contaminated soils

The effectiveness of biodegradable EDDS has aroused substantial interest over the past few years, yet there has been little information on the fate of metal-EDDS complexes that, prior to biodegradation, stay in contact with the soils. This study conducted 7-day batch experiments to investigate the kinetic interactions of CuEDDS2, ZnEDDS2, PbEDDS2, and AIEDDS, which are newly formed during EDDS application, with uncontaminated and metal-contaminated soils at pH 5.5 and 8. In uncontaminated soils, metal-EDDS complexes were adsorbed and induced mineral dissolution. In contaminated soils, on the contrary, significant metal exchange with sorbed metals on the soil surfaces (i.e., Cu, Zn, and Pb) resulted in a greater extent of metal resorption of the metal-EDDS complexes. The interactions of metal-EDDS complexes, moreover, are influenced by the characteristics of the metal center. Compared with ZnEDDS2- and PbEDDS2-, CuEDDS2- was least adsorbed or exchanged, which may be attributed to higher ionic potential and the electron configuration of Cu. In addition, AIEDDS- was partially exchanged on the soil surfaces at low pH while entirely dissociated in solution at high pH. Therefore, the fate of individual metal-EDDS complexes in the subsurface depends on the metal center, other sorbed metals and mineral cations on soils, and solution pH.