riparian; soil; reduction; oxidation; copper; humic substances
Fulda Beate (2013), Changes in copper and cadmium solubility and speciation induced by soil redox dynamics - competitive metal sulfide formation and interactions with natural organic matter
, Dissertation Nr. 21200, ETH Zürich, Zürich.
Fulda Beate, Voegelin Andreas, Maurer Felix, Christl Iso, Kretzschmar Ruben (2013), Copper redox transformation and complexation by reduced and oxidized soil humic acid. 1. X-ray absorption spectroscopy study., in Environmental science & technology
, 47(19), 10903-11.
Maurer Felix, Christl Iso, Fulda Beate, Voegelin Andreas, Kretzschmar Ruben (2013), Copper redox transformation and complexation by reduced and oxidized soil humic Acid. 2. Potentiometric titrations and dialysis cell experiments., in Environmental science & technology
, 47(19), 10912-21.
Fulda, Voegelin, Ehlert, Kretzschmar (2013), Redox transformation, solid phase speciation and solution dynamics of copper during soil reduction and reoxidation as affected by sulfate availability, in Geochimica et Cosmochimica Acta
, 123, 385-402.
Fulda, Voegelin, Kretzschmar (2013), Redox-controlled changes in cadmium solubility and solid-phase speciation in a paddy soil as affected by reducible sulfate and copper, in Environmental Science and Technology
, 47(22), 12775-12783.
Maurer Felix, Christl Iso, Hoffmann Martin, Kretzschmar Ruben (2012), Reduction and reoxidation of humic acid: influence on speciation of cadmium and silver., in Environmental science & technology
, 46(16), 8808-16.
Copper (Cu) is an essential nutrient, but due to its high toxicity for microorganisms also of concern as a soil contaminant affecting soil fertility and ecosystem functioning. Cu(II) dominates in oxic soils and strongly binds to natural organic matter (NOM). In redox-dynamic environments such as periodically flooded wetland soils, however, reducing conditions may lead to the formation of Cu(I) and Cu(0) exhibiting a biogeochemical reactivity and mobility which strongly differs from that of Cu(II). At the same time, soil reduction also leads to the reduction of redox-active moieties of NOM resulting in the formation of proton-reactive functional groups including phenols and thiols. This may have drastic effects on metal binding by NOM, which may be further affected by electron transfer between NOM and redox-sensitive trace elements like Cu.This proposal relates to an ongoing SNF project involving two PhD students (SNF proposal No. 200021-117933; 1.3.2008-28.2.2011). In this project, we demonstrated that reduction of humic acid affected its protonation behavior by the formation of proton-reactive functional groups . Current work addresses the effect of these changes on cation complexation by NOM. Furthermore, we investigated changes in the solid phase speciation and solubility of Cd in periodically reduced soil over a reduction-reoxidation cycle as affected by sulfate and Cu. The results obtained in the ongoing project suggest that Cu dynamics in periodically flooded soils are strongly affected (i) by changes in the redox states of both Cu and NOM including mutual electron-transfer and (ii) by corresponding changes in Cu complexation by NOM, namely by Cu(I) binding to NOM thiol-groups.The aim of the proposed project continuation is to address metal-NOM interactions in redox dynamic systems in greater detail. We propose (i) to quantify the effect of NOM reduction on the formation of thiol groups having a very high affinity for soft cations (e.g., Cu+ and Ag+), (ii) to study changes in Cu redox state when reacted with oxic and reduced humic acid, and (iii) to characterize the structure of Cu(II) and Cu(I) complexes with oxic and reduced NOM. These results are expected to provide a solid mechanistic basis for the interpretation of our earlier observations in soil microcosms and for the understanding of metal-NOM interactions in redox-dynamic environments. To perform the proposed analyses and to finalize the two PhD theses, we apply for this project continuation for 12 months. Both PhD students involved in the ongoing project are expected to fulfill the requirements for their PhD degree within the timeframe of the proposed project extension. Maurer, F.; Christl, I.; Kretzschmar, R., Reduction and reoxidation of humic acid: Influence on spectroscopic properties and proton binding. Environ. Sci. Technol. 2010, 44, 5787-5792.