SULFUTOPES

Isotope Studies of the Sulfur Cycling using the Four Sulfur Isotopes: Developing Tools to Investigate the Flow of Sulfur through Biogeochemical Systems

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 Obiettivo del progetto (Objective)

'New developments in isotope ratio mass spectrometry have made possible the use of both traditional and rare sulfur isotopes in biogeochemical systems studies and open new ways to explore natural sulfur cycle. The project will focus on the detection of the abundances of four sulfur isotopes in reduced and intermediate sulfur compounds such as sulfide, dispersed particulate elemental sulfur, polysulfides, thiosulfate and polythionates in natural aquatic and sedimentary systems. Quantitative detection of these compounds together with determination of four sulfur isotopes abundances will allow development of the method, which answers the following long-standing questions: a) how to differentiate between the systems, where production of hydrogen sulfide from sulfate is due to sulfate reduction to sulfide, and the systems, where disproportionation of intermediate compounds like sulfur occurs; b) how to differentiate between the systems, where intermediate sulfur compounds, especially dissolved (polysulfidic) and non-soluble (elemental) zero-valent sulfur, are produced by oxidation of hydrogen sulfide by biotic and abiotic routes. Various systems with different rates (from minutes to thousands of years), microbial activities, pH and mechanisms of reduced and intermediate sulfur compounds cycling will be studied. Systems may include: Black Sea, North Sea, salt marshes, meromictic lakes, monomictic lakes, acidic pools (i.e. at Yellowstone National Park) and soda lakes. The samples from both water column and sediment will be analyzed in order to reconstruct the flow of sulfur through the complex biogeochemical system. Bacterial cultures will be studied to explain the role of microbial processes in sulfur isotopes fractionation.'

Introduzione (Teaser)

New developments in analytical techniques have enabled both conventional and rare sulphur isotopes to be used in studying the movement of this essential element through the natural environment. Sulphur can be a pollutant but it is also a key component of many proteins and enzymes essential for life known as cofactors.

Descrizione progetto (Article)

The Sulfutopes project focused on detecting four isotopes of sulphur in natural aquatic and sedimentary systems. Scientists investigated sediment samples and tidal flat sulphide-rich water pool samples from the Wadden Sea, situated off the Dutch coast. Sulphur isotope composition was also conducted on samples from Yellowstone National Park hydrothermal springs and the Delaware Great Marsh groundwater.

New analytical techniques based on mass spectrometry enabled researchers to use both conventional and rare sulphur isotopes in their investigation into the natural sulphur cycle. The aim was to differentiate between natural systems where hydrogen sulphide was produced from sulphate and those systems where sulphur was reduced and oxidised in a process known as disproportionation.

Scientists also distinguished between systems where sulphur compounds were produced by oxidation of hydrogen sulphides and systems that involved a mineral or biological component. This was especially relevant to dissolved (polysulfidic) and non-soluble (elemental) zero-valent sulphur.

High concentrations of hydrogen cyanide and thiocyanate were unexpectedly detected in the groundwater from the Delaware Great Marsh. Additional research showed that the cyanide was produced by the roots of cord grass (Spartina alterniflora). The main sinks of free hydrogen cyanide were found to be complexes with Fe (II), adsorption on sediment and reaction with certain sulphur species. The reaction results in formation of thiocyanate, which is less toxic than hydrogen cyanide.

Data from sediment and water samples taken from the Wadden Sea, Yellowstone and the Delaware Great Marsh enabled researchers to recreate the flow of sulphur through complex biogeochemical systems. This information provided scientists with a greater understanding of the importance of sulphur in the natural environment and to life itself.