Marion Rabiet

Transmetallation of Gd-DTPA by Fe3+, Cu2+ and Zn2+ in water: Batch experiments and coagulation–flocculation simulations

The study investigates the stability of gadolinium-DTPA complex in presence of competing metallic ions, Fe(3+), Cu(2+) and Zn(2+) using batch experiments and coagulation-flocculation simulations. High performance liquid chromatography with fluorescence detection was used for simultaneous analysis of chelate gadolinium (Gd-DTPA) and free Gd(III) ion in water. It was shown that Cu(2+) has a strong affinity for DTPA and could lead to a complete release of Gd(3+). Fe(3+) appeared also to compete strongly with Gd(3+) for DTPA binding since up to 80% of Gd-complex was dissociated under iron excess condition. Finally, zinc had a lower influence on Gd speciation: only 15% of Gd(3+) was released with addition of a 5-fold excess of Zn(2+). During coagulation-flocculation simulation, Fe(3+) was able to displace about 27% of Gd-DTPA, and no adsorption was observed onto flocs.

Role of microbial reducing activity in antimony and arsenic release from an unpolluted wetland soil: a lab scale study using sodium azide as a microbial inhibiting agent

Environmental context Antimony and arsenic are toxic elements occurring naturally in the environment. We found that arsenic release to water from an unpolluted wetland soil is related to microbial reducing activity only, whereas antimony can still be released when this activity is inhibited, suggesting the involvement of additional processes. The findings show that microbial/non-microbial mechanisms control arsenic and antimony release and can thereby impact water quality at wetland outlets. Abstract In wetland soils, the mobility of geogenic metal(loid)s is usually associated with direct or indirect microbial-induced processes (solubilisation of mineral and organic components, pH induced desorption, competition effects, dissimilatory reduction). To identify the role of microbial reducing activity in As and Sb release, we conducted two series of soil incubations (sodium azide-treated (NaN3-T) and non-treated (NT)) in closed batches for 36 days. During the incubation period, we monitored the evolution of dissolved As, Sb, Mn, FeII, organic carbon (DOC), humic substances (HS) and proteins (PN) with their apparent molecular weight distribution (aMW) as well as pH, reduction potential (Eh) and alkalinity. Results showed that the release of As and Sb occurred when microbially reducing conditions prevailed (NT soil Eh ~0mV and FeII>40mg L–1) and was inhibited for As in the absence of microbial reducing activity (NaN3-T soil; Eh>250mV and Fe<1mg L–1). In contrast, Sb behaved differently since its release was only slowed down when microbially reducing conditions were inhibited. We concluded that soil microbial reducing activity fully controls the release of As and to a lesser extent that of Sb when NaN3 is used as a microbial inhibiting agent. Since Sb release and dissolved organic matter (DOM) solubilisation (NaN3-induced artefact) occurred simultaneously in the absence of microbially reducing conditions, we concluded that organic matter could be one key factor controlling Sb mobilisation in the given conditions, which is not the case for As.

Waterlogging and soil reduction affect the amount and apparent molecular weight distribution of dissolved organic matter in wetland soil: a laboratory study

The release of dissolved organic matter (DOM) from wetland soils is an important pathway for the input of organic compounds into adjacent aquatic environments. In the present study we investigated, under controlled laboratory conditions, the quantity and quality of DOM released from a wetland soil subject to waterlogging and reducing conditions. Three soil redox conditions (oxic, moderately reducing and advanced reducing) were distinguished based on nitrate, ferrous ions and sulfate concentrations in soil solution. Under each redox condition, the quantity (dissolved organic carbon (DOC), humic substances and peptides plus proteins (P-PN) and quality (aromaticity; specific ultraviolet absorbance at 254 nm (SUVA254nm)) and apparent molecular weight (aMW) distribution) of DOM were investigated. The results showed that soil redox condition affects the amount and properties of mobilised DOM. The rate of DOM release and SUVA254 values were highest during the transition from oxic to moderately reducing conditions, whereas both stabilised during progression to advanced reducing conditions. In addition, the mobilised DOM is expected to be more reactive because of an increase in polar substituents in aromatic structures between oxic and moderately reducing conditions. During the development of moderately reducing conditions, dissolved humic substances increased significantly, whereas their aMW distribution (between 500 and 6000 ) remained constant for each of the three different redox conditions. In contrast, the quantity of dissolved P-PN remained low and steady under the three redox conditions, whereas the aMW distribution of protein-like and microbial by-product-like compounds decreased during the development of reducing conditions (aMW of compounds between 100 and >100 000).

Molecular fingerprint of soil organic matter as an indicator of pedogenesis processes in Technosols

PurposeTechnosol management is one of the greatest challenges for the future, more specifically as regards supporting and/or restoring ecosystems. The understanding of natural soil organic matter (SOM) dynamic from Technosol may give important information about soil functioning and Technosol evolution.Materials and methodsAccording to this, SOM from three French old mine Technosols, (an old tin mine, a lead and zinc, and a gold one which is arsenic-rich), were studied and characterized using thermochemolysis coupled with gas chromatography and mass spectrometry (GC-MS) with tetramethyl ammonium hydroxide (TMAH) as reagent and FTIR. The characterization and quantification of some specific biomacromolecules, used as biomarkers, indicate the specific level of incorporation relative to various subgroups. Global parameters of soils (pH, total organic matter, cation exchange capacity…) were also evaluated.Results and discussionResults on bulk samples show that lipids are the most reactive group and therefore play the most important role in young soil pedogenesis. All of the results show that the behavior of SOM of the Technosol is similar to homolog non-anthropized soil and depends on vegetation type.ConclusionsA slight inhibition of bacterial activity is observed which underlines a protective effect of Technosols on SOM degradation due to the low pH, the high clay content, and the presence of Al3+ and metal(loid)s. In fine, lipid fraction of SOM may act as a well-done fingerprint of pedogenesis processes in Technosols.