Determination of the kinetics for ligand exchange reactions of mercury complexes with thiols in natural organic matter using HPLC-ICP-MSPuhar, Gregor (Avtor) Björn, Erik (Mentor) Kolar, Mitja (Komentor) mercuryICP-MSkineticsnatural organic mattercoordination compoundsPollution and bioaccumulation of mercury poses a threat to environment and human health due to the high toxicity of different Hg species. By far the most dangerous form of Hg is formed when certain types of anaerobic bacteria transform dissolved Hg$^{2+}$ ions to methylmercury. The ability of Hg to undergo methylation is influenced by its speciation in aquatic environment. Hg found in nature binds mostly to thiol group containing species. One such type of compounds abundant especially in natural waters is natural organic matter (NOM), a complex mixture of organic compounds with a significant concentration of thiol containing molecules. The goal of this thesis was to explore kinetics of ligand exchange reactions of mercury complexes with thiols in NOM and cysteine (cys). High performance liquid chromatography coupled with inductively coupled plasma mass spectrometry was used to separate and determine the concentration of Hg(cys)$_2$ complex. Three different size fractions of NOM were studied, <1 kDa, 3−5 kDa and 5−10 kDa, with two distinct types of reactions. The first type involved adding NOM to Hg(cys)$_2$ complex and the second involved adding cys to equilibrated Hg-NOM complex. The exchange kinetics between Hg(cys)$_2$ and NOM was very slow for 5−10 kDa and 3−5 kDa fractions and not measurable for < 1kDa fraction. The results implicate that Hg$^{2+}$ preferably binds to higher molecular mass NOM. Conversely the exchange in the reactions where cys was added to Hg-NOM was much faster. The study also confirms that NOM reduces dissolved Hg$^{2+}$ ions in a no complexed form with thiols, while Hg$^{2+}$ bound to cys is protected from reduction.20242024-04-10 09:10:01Magistrsko delo/naloga155657VisID: 22920COBISS_ID: 192362755sl