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

Dissolved elemental mercury [Hg(0)(aq)] widelyexistsin natural waters, but its reactivity and purgeability in the presenceof suspended particulate matter (SPM) remain controversial. This studyinvestigated reactions between Hg(0)(aq) and various typesof organic and inorganic SPM and found that Hg(0)(aq) reactedweakly with the inorganic mineral SPM (i.e., kaolinite, montmorillonite,and hematite) but strongly with organic matter (OM) or OM-coated mineralsin water. Nearly 100% of Hg(0)(aq) could be recovered aspurgeable gaseous Hg(0) after reactions with mineral SPM, irrespectiveof the mineral types, concentrations, and reaction time. However,incomplete Hg(0)(aq) recoveries were observed in the presenceof OM or OM-coated minerals and in natural water containing OM andSPM, but the addition of borohydride, a reducing agent, immediatelyrestored the Hg(0)(aq) purgeability and recovery. The resultssuggest that Hg(0)(aq) was oxidized and then retained byOM or OM-coated minerals. These findings clarify previous observationsof so-called particulate Hg(0)(aq) in water and have importantimplications for understanding the role of Hg(0)(aq) in affectingHg transformation and bioavailability in the aquatic environment.

Automated summary

This study found that Hg(0)(aq) reacted strongly with organic matter or organic matter-coated minerals in water, but weakly with inorganic mineral suspended particulate matter (SPM). Almost 100% of Hg(0)(aq) could be recovered as purgeable gaseous Hg(0) after reactions with mineral SPM, regardless of the mineral types, concentrations, and reaction time. However, incomplete recoveries were observed in the presence of organic matter or organic matter-coated minerals, but the addition of borohydride immediately restored the purgeability and recovery of Hg(0)(aq).