Is bimolecular reduction of Hg(II) complexes possible in aqueous systems of environmental importance

One-electron reduction potentials for Hg(II) complexes were calculated from experimental data obtained from pulse radiolysis experiments in order to investigate the importance of some reducing agents in the environment, i.e., HO2. and/or O-2(.-). Knowledge on such potentials is valuable to foresee reduction pathways for mercury species in different environmental surroundings. The behavior of an aqueous system containing different proportions of Hg2+/H2C2O4/Cl- in the presence of actinic light was also investigated. The one-electron reduction potentials for the Hg(II) species during the experimental conditions in this study were found to be below -0.45 V. Consequently, Hg(II) should not be reduced by HO2. or O-2(.-) under ambient conditions. Hence, the proposed aqueous phase reduction of Hg(II) species by O-2(.-)/HO2. should not be included in models describing the atmospheric transport and transformation of mercury. Results from the photolytical experiments show that reduction of Hg(II) may occur via photo fragmentation of an organic ligand, such as oxalate, bound to the metal.