Mercury species transformations in marine and biological systems studied by isotope dilution mass spectrometry and stable isotope tracers

Abstract: This thesis focuses on the implementation of species-specific isotope dilution (SSID) methodology and stable isotope tracers to determine mercury species occurrence and transformation processes in-situ and during sample treatment. Isotope enriched tracers of methyl-, ethyl- and inorganic mercury were synthesised and applied in different combinations to marine and biological samples. Experimental results were obtained using gas chromatography-inductively coupled plasma-mass spectrometry (GC-ICP-MS).Mercury methylation and methylmercury demethylation processes in surface sediments were studied in the brackish Öre River estuary, Bothnian Bay. Uni- and multivariate data evaluation identified the organic material content and mercury methylation potential in the sediments as important factors controlling incipient methylmercury levels. Mercury species distribution in mice treated with the pharmaceutical preservative Thimerosal (ethylmercurithiosalicylate) was studied. The ethylmercury moiety of Thimerosal was observed to rapidly convert to inorganic mercury in the mice during the treatment period as well as during sample treatment, hence necessitating SSID methodology for accurate ethylmercury determinations in biological samples.To facilitate the introduction of SSID as a routine quantitative method in mercury speciation, a methylmercury isotopic certified reference material (ICRM) was produced. Prior to certification, the stability of the material was examined in conventional and isochronous stability studies spanning 12 months, which permitted uncertainty estimation of the methylmercury amount content for two years of shelf-life.Finally, a field-adapted SSID method for methylmercury determinations in natural water samples was developed. The proposed analytical protocol significantly simplified sample storage- and treatment procedures without sacrifices in analytical accuracy.