Mercury Species in Environmental Samples Studied by Spectroscopic Methods

Qian, J. 2001. Mercury Species in Environmental Samples Studied by Spectroscopic Methods. Doctor k dissertation. ISSN 1401-6230, ISBN 91-576-6085-9. In this thesis, attention is focused on the determination, stability, reaction, and chemical association of mercury species in various types of environmental samples. Capillary gas chromatography (GC) was coupled to a number of systems for mercury speciation analyses, including microwave-induced plasma atomic emission spectrometry (MIP-AES), inductively coupled plasma-mass spectrometry (ICP-MS), atomic absorption spectrometry (AAS) and mass spectrometry (MS). In addition, synchrotron-based mercury L,-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, sulphur K-edge X-ray absorption near edge structure (XANES) spectroscopy were used to explore the chemical association of monomethyl mercury (CH,Hg (11)) in soil organic matter (SOM). Reactions of mercury species in organic solutions were investigated to determine the stability of mercury species in hydrocarbon products, standards and reference materials. A simple and rapid sample preparation procedure including acid leaching and simultaneous ultrasonicassisted in situ ethylation and extraction was developed for the determination of methyl mercury in biological samples. The efficiency of different solvent extraction and derivatisation methods for the determination of methyl mercury in soils was evaluated. It was found that the binding affmity of Cu2+ to SOM functional groups and affinity of Brfor mercury ions are strong enough to extract in average 93% of the total mercury in the soil samples investigated. The results indicated that the extraction efficiency was related to the oxidation state of sulphur present in the soil. Reactions with Grignard reagent for the derivatisation of mercury species for GC separation were characterised. Evaluation of derivatisation efficiency and species transformation reactions allowed for efficient optimisation of methods to reduce analytical errors. EXAFS analysis provided direct molecular level evidence for the bonding between mercury (in CH,Hg (11)) and sulphur in the first shell at a CH,Hg (II)/Org-Sm, ratio below 0.26 in SOM. Calculated surface complexation constants were in the range of 10163-10167, that was very similar to stability constants for associations between methyl mercury and thiol groups (RSH) in well-defined organic compounds. Concentrations of CH,Hg (11), Hg-tot and sulphur species were determined in soil, soil solutions and streams of a forested catchment. Higher ratios of CH,Hg (II)/Hg-tot were found in stream bank soils and open mire peat soils, indicating that these sites provide favourable conditions for net methylation on a landscape level. Org-SRED made up 50 to 78% of total S in all soil and stream organic samples examined. Model calculations showed that under oxic and slightly reduced conditions nearly all the Hg (11) and CH3Hg (11) were complexed by Org-S,, in soil, soil solution and stream water.