Dissolved Elemental Mercury [Hg(0)aq] Reactions and Purgeability in the Presence of Organic and Inorganic Particulates

Dissolved elemental mercury [Hg(0)aq] widely exists in natural waters, but its reactivity and purgeability in the presence of suspended particulate matter (SPM) remain controversial. This study investigated reactions between Hg(0)aq and various types of organic and inorganic SPM and found that Hg(0)aq reacted weakly with the inorganic mineral SPM (i.e., kaolinite, montmorillonite, and hematite) but strongly with organic matter (OM) or OM-coated minerals in water. Nearly 100% of Hg(0)aq could be recovered as purgeable gaseous Hg(0) after reactions with mineral SPM, irrespective of the mineral types, concentrations, and reaction time. However, incomplete Hg(0)aq recoveries were observed in the presence of OM or OM-coated minerals and in natural water containing OM and SPM, but the addition of borohydride, a reducing agent, immediately restored the Hg(0)aq purgeability and recovery. The results suggest that Hg(0)aq was oxidized and then retained by OM or OM-coated minerals. These findings clarify previous observations of so-called particulate Hg(0)aq in water and have important implications for understanding the role of Hg(0)aq in affecting Hg transformation and bioavailability in the aquatic environment.