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Faculty for Biology, Chemistry, and Earth Sciences

Environmental Geochemistry Group - Prof. Dr. Britta Planer-Friedrich

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Bachelor Thesis

Measuring volatile metal(loid)s by AgNO3 traps at the fumarolic field of Vulcano, Italy

Benedikt Ehrenfels (11/2012-09/2013)

Support: Britta Planer-Friedrich, Julia Arndt

Volatile metalloids are poorly examined and a new approach for their investigation in geothermal environments was tested in this study. Metalloids were sampled by AgNO3-traps along a transect at the fumarolic field of La Fossa crater, Vulcano, Italy. Filters were added before the traps to separate particular-bound and volatile metalloids. Both, traps and filters were analyzed. Total element concentrations were determined by HNO3/H2O2-microwave extraction and ICP-MS analysis. Arsenic speciation was identified by 1 % HNO3-microwave extraction and HPLC-ICP-MS analysis. Arsenic was found on filters in concentrations of 8.8 µg*m-3 within the fumarolic field, whereas Se, Sb, Te, and Tl concentrations were ranging from 0.22 to 0.51 µg*m-3 . Only Se and Sb were found in the traps in concentrations of 0.083 and 2.7 µg*g-1*m-3 , respectively. Interactions with S from the fumarolic gases could explain the low trapping of metalloids in the traps. However, more likely, preferential sorption on the filters was caused by the high water vapor content of fumaroles forming a water film that induced complete metalloid dissolution. Concentration profiles along the transect identified the fumaroles as the source of emission for all volatile metalloids. An exponential decrease of concentrations with increasing distance to the fumaroles indicates wind-borne transport. Comparison of total element concentrations with those determined by moss-bag monitoring in a separate study showed a significant linear correlation, confirming the suitability of the applied method. Arsenic speciation on the filters indicated a dominance of inorganic arsine emission. However, the validity of filters for species conservation has to be further tested. Further investigations must focus on identifying the processes, which caused preferential trapping on filters versus traps in geothermal environments.

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