Measurements of naturally occurring stable isotopic compositions of mercury provide additional information to mercury concentrations, thus, potentially allow us to gain more detailed information for source and processing identification of mercury found in natural environment. In this presentation we introduce our recent researches on the development of sampling and analytical techniques, the source studies for gaseous mercury from biomass burning and commercially available mercury-contained products (potentially important source from waste), and laboratory studies for the isotope fractionation during a chemical reaction of gaseous mercury. Measurements of total gaseous mercury from open grass field burning in the Aso region, Japan showed the increase of atmospheric concentrations of total gaseous mercury by factor or three or more during the grass field burning, evidence of mercury emission to the air. The stable isotope ratios showed lighter compositions in Δ199Hg and δ200Hg than 0 ‰, and the observations approximately coincided to the isotope ratios of mercury in plants reported to date. Stable isotope ratio measurements of mercury in thermometers showed that very similar isotopic compositions to the reported isotope ratios of mercury for cinnabar ores and elemental mercury, and the differences were insignificant. Meanwhile, the stable isotope ratios of gaseous and adsorbed mercury in fluorescent tubes showed very unique values, and the stable isotope ratios can fingerprint the mercury from fluorescent tubes. Preliminary results from the laboratory studies for isotope fractionation during the reaction of gaseous elemental mercury with OH radical exhibited very unique mass independent isotope fractionation; In the remaining gaseous mercury odd mass and the mass 204 isotopes were prone to be enriched, while the mass 200 isotope was significantly depleted. The results of the series of studies here are currently limited, however, the stable isotope ratio measurements demonstrated a promising tool for the mercury cycle studies in the natural environment.

Studies for atmospheric mercury using stable isotope ratio measurement

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ACS Fall 2022

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