Three independent speciation techniques, the free liquid/moving boundary electrophoresis, ultrafiltration, and equilibrium dialysis, combined with the radiotracer method (using 152Eu) have been compared at the study of Eu interaction with humic acid (HA). The degree of complexation of Eu in 10 mg/l Aldrich HA solutions was determined within a broad range of metal loading (Eu total concentration 10-8-10-4 mol . l-1), at pH 4 and 6, ionic strength of 0.01 and 0.1 (NaClO4). From the anodic electrophoretic mobilities determined, additional information on the charge of the Eu-HA complexes was obtained. Uncertainty of the determination given by sorption losses of Eu on the walls and membranes of the experimental devices, and the effect of kinetic lability of the Eu-HA complexes are estimated. Based on the ultrafiltration experiments, the existence of an unknown, labile, high-molecular non-humic Eu species is discussed.
Authors:A. Johnsson, A. Ödegaard-Jensen, A. Jakobsson, C. Ekberg, and K. Pedersen
The aqueous-phase partitioning of 59Fe, 147Pm, 234Th and 241Am by complexing compounds from subsurface bacteria has previously been studied in the presence of quartz sand. In this study
the aqueous-phase partitioning of pico-to submicromolar amounts of 59Fe, 147Pm, 234Th and 241Am was analyzed in the presence of TiO2 and exudates from three species of subsurface bacteria: Pseudomonas fluorescens, Pseudomonas stutzeri, and Shewanella putrefaciens. All were grown under aerobic conditions and P. stutzeri and S. putrefaciens were grown under anaerobic conditions as well. The supernatants of the aerobic and anaerobic cultures were collected and
radionuclide was added. TiO2, with BET surface area of 49.9 m2·g−1, was added to the supernatant radionuclide mix, and the pH was adjusted to approximately 8. After incubation, the amount
of radionuclide in the liquid phase of the samples and controls was analyzed using scintillation method. Two types of values
were calculated: solution% = the activity maintained in solution relative to the total activity, and Q-values = the quotient between the activity in samples and the activity in controls. Aerobic supernatants had solution% values
between 89% and 100% for 59Fe and between 18 and 43% for 234Th. The solution% values for 241Am and 147Pm were less than 2% overall, but the Q-values were between 34 and 115 times more 241Am in bacterial supernatants than in controls. The corresponding values for 147Pm ranged from 6 to 20 times more than in the control. The solution% values for all elements in the presence of anaerobic
supernatants were below 2%, but the Q-values clustered around 7 for 59Fe and ranging from 2 to 29 for 234Th, indicated that anaerobic supernatants partitioned these elements to the aqueous phase. Both aerobic and anaerobic supernatants
tested positive for complexing compounds when analyzed, using the Chrome Azurol S assay. Complexation with excreted organic
ligands is most likely the reason for the higher amounts of metals in samples than in the controls. Hence, aerobically and
anaerobically excreted organic ligands seem able to influence the mobility of radionuclides in aerobic and anaerobic environments
contaminated with these compounds.