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Mercury species transformations in marine and biological systems studied by isotope dilution mass spectrometry and stable isotope tracers
Umeå University, Faculty of Science and Technology, Chemistry.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Umeå: Kemi , 2005. , 38 p.
Keyword [en]
Analytical chemistry, Mercury, methylmercury, ethylmercury, Thimerosal, speciation, methylation, demethylation, brackish water sediment, natural waters, GC-ICP-MS, species-specific isotope dilution, isotope enriched tracers
Keyword [sv]
Analytisk kemi
National Category
Analytical Chemistry
Research subject
Analytical Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-467ISBN: 91-7305-838-6 (print)OAI: oai:DiVA.org:umu-467DiVA: diva2:143518
Public defence
2005-04-01, KB3A9, Kemiskt Biologiskt Centrum (KBC), Umeå Universitet 90187, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2005-03-09 Created: 2005-03-09 Last updated: 2009-05-25Bibliographically approved
List of papers
1. Applications of enriched stable isotope tracers in combination with isotope dilution GC-ICP-MS to study mercury species tranformation in sea sediments during in-situ ethylation and determination
Open this publication in new window or tab >>Applications of enriched stable isotope tracers in combination with isotope dilution GC-ICP-MS to study mercury species tranformation in sea sediments during in-situ ethylation and determination
2001 In: Journal of Analytical Atomic Spectrometry, Vol. 16, 1296-1301 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-4414 (URN)
Available from: 2005-03-09 Created: 2005-03-09Bibliographically approved
2. Organic Material:  The Primary Control on Mercury Methylation and Ambient Methyl Mercury Concentrations in Estuarine Sediments
Open this publication in new window or tab >>Organic Material:  The Primary Control on Mercury Methylation and Ambient Methyl Mercury Concentrations in Estuarine Sediments
2006 (English)In: Environmental Science & Technology, Vol. 40, no 6, 1822-9 p.Article in journal (Refereed) Published
Abstract [en]

Estuarine environments that have no direct sources of mercury (Hg) pollution may have sediment concentrations of methylmercury (MeHg) as high as those of polluted marine environments. In this study we examined the biogeochemical factors affecting net methylation and sediment MeHg concentrations in an unpolluted estuarine environment, the Öre River estuary, which discharges into the Bothnian Bay (20-120 ng total Hg g-1 dry sediment, salinity 3-5‰). We analyzed the spatial and temporal differences in surface sediment profiles of MeHg concentration, Hg methylation, MeHg demethylation, and concentrations of sulfide and oxygen between accumulation and erosion type bottoms. The main difference between the bottoms studied was in the proportion of organic material (OM) in the sediment, ranging between 0.8% and 10.8%. The pore water sulfide concentration profiles also differed considerably between sites and seasons, from 0 to 20 μM, with 100 μM as the extreme maximum. The sediment MeHg concentration profiles (0-10 cm) mostly varied between 0.1 and 7 ng g-1 dry weight (dw, as Hg). The MeHg demethylation rates were relatively low and the depth profiles of the rates were relatively constant over season, site, and depth. In contrast, both rates and depths of maximum Hg methylation differed between the bottoms. The results indicate that the amount of OM accumulated at the bottoms was the main factor affecting net MeHg production, while the total amount of Hg had little or no influence on the amount of MeHg in the sediment.

Place, publisher, year, edition, pages
ACS Publications, 2006
Identifiers
urn:nbn:se:umu:diva-22984 (URN)10.1021/es051785h (DOI)
Available from: 2009-05-25 Created: 2009-05-25 Last updated: 2017-10-24Bibliographically approved
3. Determination of Methylmercury, Ethylmercury, and Inorganic Mercury in Mouse Tissues, Following Administration of Thimerosal, by Species-Specific Isotope Dilution GC-Inductively Coupled Plasma-MS
Open this publication in new window or tab >>Determination of Methylmercury, Ethylmercury, and Inorganic Mercury in Mouse Tissues, Following Administration of Thimerosal, by Species-Specific Isotope Dilution GC-Inductively Coupled Plasma-MS
Show others...
2003 (English)In: Analytical Chemistry, Vol. 75, no 16, 4120-4 p.Article in journal (Refereed) Published
Abstract [en]

Isotopically enriched HgO standards were used to synthesize CH3200Hg+ and C2H5199Hg+ using Grignard reagents. These species were employed for isotope dilution GC-ICPMS to study uptake and biotransformation of ethylmercury in mice treated with thimerosal, (sodium ethylmercurithiosalicylate) 10 mg L-1 in drinking water ad libitum for 1, 2.5, 6, or 14 days. Prior to analysis, samples were spiked with aqueous solutions of CH3200Hg+, C2H5199Hg+, and 201Hg2+ and then digested in 20% tetramethylammonium hydroxide and extracted at pH 9 with DDTC/toluene. Extracted mercury species were reacted with butylmagnesium chloride to form butylated derivatives. Absolute detection limits for CH3Hg+, C2H5Hg+, and Hg2+ were 0.4, 0.2, and 0.6 pg on the basis of 3 of five separate blanks. Up to 9% of the C2H5Hg+ was decomposed to Hg2+ during sample preparation, and it is therefore crucial to use a species-specific internal standard when determining ethylmercury. No demethylation, methylation, or ethylation during sample preparation was detected. The ethylmercury component of thimerosal was rapidly taken up in the organs of the mice (kidney, liver, and mesenterial lymph nodes), and concentrations of C2H5Hg+ as well as Hg2+ increased over the 14 days of thimerosal treatment. This shows that C2H5Hg+ in mice to a large degree is degraded to Hg2+. Increased concentrations of CH3Hg+ were also observed, which was found to be due to impurities in the thimerosal.

Identifiers
urn:nbn:se:umu:diva-9948 (URN)10.1021/ac0342370 (DOI)
Available from: 2008-05-29 Created: 2008-05-29 Last updated: 2017-10-24Bibliographically approved
4. Preparation and certification of ERM-AE670, a 202Hg enriched methylmercury isotopic reference material
Open this publication in new window or tab >>Preparation and certification of ERM-AE670, a 202Hg enriched methylmercury isotopic reference material
2004 (English)In: JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, ISSN 0267-9477, Vol. 19, no 10, 1315-24 p.Article in journal (Refereed) Published
Abstract [en]

The need for comparability of methylmercury, noted MeHg, measurement results and for the reduction of their associated uncertainties is hampered by the lack of suitable calibration materials. An isotopic certified reference material, ICRM, of MeHg containing isotopically enriched Hg has the potential to answer these problems, in combination with the isotope dilution mass spectrometry, IDMS, strategy. The objective of this work was to produce such a material, of demonstrated stability and carrying certified values traceable to the SI accompanied by combined uncertainty statements. Mercury oxide enriched in 202Hg was used for the preparation of a solution of 202Hg enriched CH3HgCl. The starting material had previously been employed for the preparation of ERM-AE640; a 202Hg enriched inorganic mercury ICRM. The CH3HgCl was synthesised by reaction with a Grignard reagent and a subsequent comproportionation reaction between (CH3)2Hg and HgCl2. The process was optimised to give a high yield of the product, minimise contamination with naturalHg and additional steps were applied to purify the material from other Hg species and by-products of the synthesis reaction. Aliquots of 5 g of the solution were sealed in quartz ampoules for later distribution as a reference material, named ERM-AE670. Using gas chromatography inductively coupled plasma mass spectrometry, only MeHg and inorganic Hg was detectable in the finished reference material with inorganic Hg in <2% of the total amount. The isotopic composition of Hg in the form of MeHg was confirmed to be identical to that of ERM-AE640, within enlarged uncertainty statements. The Hg amount content in the form of MeHg was obtained by subtraction of the inorganic Hg amount content from the total Hg amount content (determined by IDMS in the digested material). The final uncertainty on the Hg amount content in the form of MeHg (3.5% relative, k= 2) included a contribution covering for potential changes over 2 years of shelf-life. This contribution was estimated from the results of a 1 year isochronous stability study.

Identifiers
urn:nbn:se:umu:diva-14247 (URN)doi:10.1039/b407368a (DOI)
Available from: 2007-05-25 Created: 2007-05-25 Last updated: 2011-01-12Bibliographically approved
5. Validation of a simplified field-adapted procedure for routine determinations of methyl mercury at trace levels in natural water samples using species-specific isotope dilution mass spectrometry
Open this publication in new window or tab >>Validation of a simplified field-adapted procedure for routine determinations of methyl mercury at trace levels in natural water samples using species-specific isotope dilution mass spectrometry
2004 (English)In: Analytical and Bioanalytical Chemistry, ISSN 1618-2642 (Print) 1618-2650 (Online), Vol. 380, no 7-8, 871-5 p.Article in journal (Refereed) Published
Abstract [en]

A field-adapted procedure based on species-specific isotope dilution (SSID) methodology for trace-level determinations of methyl mercury (CH3Hg+) in mire, fresh and sea water samples was developed, validated and applied in a field study. In the field study, mire water samples were filtered, standardised volumetrically with isotopically enriched CH3200Hg+, and frozen on dry ice. The samples were derivatised in the laboratory without further pre-treatment using sodium tetraethyl borate (NaB(C2H5)4) and the ethylated methyl mercury was purge-trapped on Tenax columns. The analyte was thermo-desorbed onto a GC-ICP-MS system for analysis. Investigations preceding field application of the method showed that when using SSID, for all tested matrices, identical results were obtained between samples that were freeze-preserved or analysed unpreserved. For DOC-rich samples (mire water) additional experiments showed no difference in CH3Hg+ concentration between samples that were derivatised without pre-treatment or after liquid extraction. Extractions of samples for matrix–analyte separation prior to derivatisation are therefore not necessary. No formation of CH3Hg+ was observed during sample storage and treatment when spiking samples with 198Hg2+. Total uncertainty budgets for the field application of the method showed that for analyte concentrations higher than 1.5 pg g–1 (as Hg) the relative expanded uncertainty (REU) was approximately 5% and dominated by the uncertainty in the isotope standard concentration. Below 0.5 pg g–1 (as Hg), the REU was >10% and dominated by variations in the field blank. The uncertainty of the method is sufficiently low to accurately determine CH3Hg+ concentrations at trace levels. The detection limit was determined to be 4 fg g–1 (as Hg) based on replicate analyses of laboratory blanks. The described procedure is reliable, considerably faster and simplified compared to non-SSID methods and thereby very suitable for routine applications of CH3Hg+ speciation analysis in a wide range of water samples.

Keyword
Methyl mercury, Speciation, SSID, Species-specific isotope dilution mass spectrometry
Identifiers
urn:nbn:se:umu:diva-14327 (URN)doi:10.1007/s00216-004-2863-z (DOI)
Available from: 2007-05-28 Created: 2007-05-28 Last updated: 2011-01-12Bibliographically approved

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