Oxidation of elemental mercury by aqueous bromine: atmospheric implications

The special characteristics of mercury, such as, its long-range atmospheric transport, its transformation between various species, biomagnification and its role as a neurotoxin, make it a pollutant of global concern. The chemical processes that take place in the atmosphere and water systems are closely linked and affect the transport of mercury. The kinetics of aqueous elemental mercury oxidation by aqueous bromine species detected by Dithizone–Hg(II) complexation-UV–VIS spectroscopy was extensively investigated in this study. The second-order oxidation rate constants at room temperature (294–296 K) for the Hg(aq)0–Br2, Hg(aq)0–HOBr and Hg(aq)0−OBr− are determined to be 0.20±0.03, 0.28±0.02 and 0.27±0.04 M−1 s−1, respectively. Such small oxidation rate constants also mean that the important atmospheric “sink” for mercury, which was discovered in the Arctic and sub-Arctic regions, is not caused by aqueous bromine, but other oxidizing bromine species (e.g., gaseous-phase bromine species).