EFFECT OF THE SIDEROPHORE DESFERRIOXAMINE B ON THE MOBILITY OF PALLADIUM

For over 20 years, catalytic converters have used platinum-group-elements (PGE’s) such as Pt, Pd and Rh to reduce the extent to which automobile exhaust pollutes the air. However, emission of PGE’s from the converters and their presence in roadside dust is causing a growing environmental concern. Recent studies show an increased abundance of these metals over preindustrial levels in ice cores from several locations in the northern hemisphere. Studies also indicate that PGE’s from roadside dust are bioavailable for uptake by both plants and animals. The mobility of PGE’s in the environment may be increased by the presence the siderophore chelating agents such as desferrioxamine B (DFB) secreted by bacteria to capture ferric iron. Estimates in the literature based on linear free energy relationships involving hydrolysis constants suggest that DFB may form very strong complexes with Pd. To determine the extent to which naturally-occurring DFB may elevate the aqueous solubility and thus the environmental mobility of Pd, samples containing amorphous solid Pd(OH)₂ in water were prepared at an ionic strength of 0.1 m with DFB concentrations ranging from 0 to 1000 µm. Experiments were conducted at ambient temperature and a pH of 8 was maintained for all samples. Although equilibrium was not attained even after approximately 400 hours, preliminary ICP-AES analysis shows that concentration of Pd in solution increased substantially with concentration of DFB. Between 70 and 400 hours, the concentration of Pd in solution increased approximately linearly with time at all concentrations of DFB. At 404.5 hours, Pd concentration in a solution with 1000 µm DFB was 236 ppb, more than twenty times the previously determined value in the absence of DFB at pH=8 and I=0.1 at ambient temperature. Although a final conclusion can only be made after all experiments have been shown to reach equilibrium, these preliminary results suggest that complexation of DFB with the Pd emitted from catalytic converters may increase the mobility of the metal into the environment. Further research is necessary to determine the ultimate fate of Pd in the environment.