Bindungsformen von Quecksilber in Auenböden von Wupper und Saale/Elbe

In Auenböden von Wupper und Saale/Elbe haben sich in den letzten Jahrhunderten große Mengen Quecksilber (Hg) aus anthropogenen und geogenen Quellen akkumuliert. Hieraus ergibt sich ein hohes Gefährdungspotential, da Quecksilber hochgradig toxisch auf Organismen wirkt. Das Ziel dieser Studie ist es, die Bindungsformen von Quecksilber mittels eines sequentiellen Extraktionsverfahrens horizontspezifisch an jeweils einem Bodenprofil von Wupper- und Saale-/Elbeaue zu bestimmen, um das Gefährdungspotential der hohen Hg-Belastung evaluieren zu können. Die Ergebnisse zeigen, dass die Löslichkeit des Quecksilbers in Auenböden von Wupper und Saale/Elbe gering ist, wodurch ist ein geringer Transport in Gewässer zu erwarten ist. Es ist jedoch eine Oxidation von Hg-Sulfiden zu leichter löslichen Formen möglich, so dass bei Sauerstoffeintrag die Gefahr der Hg-Remobilisierung in den Böden besteht. Außerdem ist eine Ausgasung durch den hohen Anteil von elementarem Hg besonders in den oberen Horizonten möglich. Zur Gefahrenabschätzung an den Standorten Wupper und Saale/Elbe ist zu empfehlen, die Hg-Quantität in der Bodenlösung und im Grundwasser sowie den Transfer in Pflanzen zukünftig zu ermitteln

Uticaj različitih redoks uslova na (i)mobilizaciju talijuma u zemljište (Srbija)

Thallium (Tl) is a highly toxic element, even in small concentrations, to a range of organisms and in different environments. Therefore, our aim was to study (i) Tl geochemical fractionation by the means of the modified BCR sequential extraction procedure and (ii) the impact of redox potential (EH) alteration and principal factors such as iron (Fe), manganese (Mn), dissolved organic carbon (DOC), chlorides (Cl) and sulfates (SO4 2) on Tl (im)mobilization in periodically flooded arable soil (Serbia). Flooding was simulated using an automated biogeochemical microcosm system that allows systematical control of pre-defined redox-windows. Afterwards, EH was increased stepwise for approximately 100 mV from reducing (-205 mV) to oxidizing (530 mV) conditions. EH was automatically monitored at 10 minutes intervals. Total duration of the experiment was 914 hours. The sequential extraction revealed majority of pseudo-total soil Tl (0.15 mg kg-1 ) in the residual fraction (85.5 %), following by reducible (10.2 %), oxidable (3.8 %) and acid soluble (exchangeable) (0.5 %) fraction. The soluble Tl concentrations (0.024-0.116 μg l-1 ) were significantly affected by EH, having an increase with EH increase (r=0.75, p lt 0.01, n=30). Concentrations of soluble Fe, Mn, and Doc showed significant negative correlations with soluble Tl (r=-0.78, r=-0.73 and r=-0.91, respectively, p lt 0.01, n=30), whereas Tl correlated significant positive with SO42and Cl(r=0.89, r=0.81, respectively, p lt 0.01, n=30). Thallium mobilization was attributed to several simultaneous processes, involving the reductive dissolution of Fe-Mn oxides and gradual oxidation of Tl-bearing metallic sulfides. Our results imply that soluble Tl concentrations might increase when soil redox status evolves from reducing to oxidizing conditions. Due to high Tl toxicity at low doses, and increasing flooding events, our findings suggest that Tl should be included in future monitoring of plants and groundwater on the site or on similar sites.Talijum je veoma toksičan element i u niskim koncentracijama za razne organizme u okviru različitih delova životne sredine. Cilj rada bio je da se ispita (i) sadržaj talijuma u hemijskim frakcijama u zemljištu po modifikovanoj BCR proceduri i (ii) uticaj redoks potencijala (EH) i glavnih faktora, kao što su gvožđe (Fe), mangan (Mn), rastvorljiv organski ugljenik (DOC), hloridi (Cl -) i sulfati (SO4 2-) na (i)mobilizaciju talijuma u povremeno plavljenom obradivom zemljište (Srbija). Plavljenje zemljište je simulirano u laboratorijskim uslovima, uz korišćenje automatskog biogeohemijskog zatvorenog sistema koji dozvoljava sistematsku kontrolu definisanih redoks uslova. Nakon toga, redoks potencijal zemljište je postepeno povećavan u okvirima od po 100 mV od redukcionih (-205 mV) do oksidacionih (530 mV) uslova. Redoks potencijal je automatski meren u intervalima od 10 minuta. Ukupno vreme trajanja ogleda je bilo 914 sati. Hemijska frakcionacija je pokazala da se najveći deo ukupnog talijuma (0,15 mg kg -1) nalazi u rezidualnoj frakciji (85,5 %), a zatim u redukujućoj (10,2 %), oksidujućoj (3,8 %) i frakciji izmenljivo adsorbovanih elemenata (0,5 %). Redoks potencijal je značajno uticao na sadržaj rastvorljivog talijuma (0.024-0.116 μg l -1), koji se povećavao sa njegovim povećanjem (r=0.75, p lt 0.01, n=30). Rastvorljivi sadržaji Fe, Mn, i Doc su pokazali značajnu negativnu korelaciju sa rastvorljivim sadržajem Tl (r=-0.78, r=-0.73 i r=-0.91, redom, p lt 0.01, n=30), dok su utvržene značajne pozitivne korelacije između Tl i sulfata i hlorida (r=0.89, r=0.81, p lt 0.01, n=30). Mobilizacija talijuma može se dovesti u vezu sa nekoliko procesa koji se istovremeno odvijaju, a to su, između ostalih, rastvaranje Fe-i Mn-oksida u oksidacionim uslovima i postepena oksidacija metalnih sulfida koji sadrže Tl. Naša istraživanja ukazuju da sadržaji rastvorljivog Tl mogu da se povećavaju u kada se redoks potencijal menja od redukcionih ka oksidacionim uslovima. Naša istraživanja upućuju na neophodnost sistematskog praćenja sadržaja Tl u biljkama i podzemnim vodama, s obzirom na njegovu visoku toksičnost u niskim dozama, kao i učestalu pojavu plavljenja obradivih zemljišta

Methylierung von Arsen sowie Freisetzungskinetiken von Schwermetallen unter definierten Redoxbedingungen

Auenböden sind häufig stark mit Arsen (As), Schwermetallen und anderen Schadstoffen belastet. Die Mobilität dieser Schadstoffe wird erheblich durch das Redoxpotenzial (EH) beeinflusst. In Auenböden können Schwankungen des Wasserspiegels zu variierenden Redoxbedingungen führen. Diese EH-Veränderungen wurden systematisch unter definierten Bedingungen im Labor mit Hilfe eines automatischen biogeochemischen Mikrokosmensystems simuliert. Dabei erfolgte der Versuchsverlauf von reduzierenden zu oxidierenden Verhältnissen. Ziel dieser Untersuchung ist es, die Auswirkungen eines gezielt gesteuerten EH auf die Freisetzungskinetik von Schwermetallen und die Methylierung von Arsen (As) in einem kontaminierten, leicht sauren Auenboden der Wupper zu determinieren. Die Ergebnisse zeigen, die die Konzentrationen von Cd, Cu, Mn, Ni und Zn in der Bodenlösung bei niedrigem EH gering waren und sich mit steigendem EH erhöhten. Dies könnte auf Interaktionen der Metalle mit gelöstem organischem Kohlenstoff (DOC) und die Fällung als Sulfide zurückzuführen sein. Die Konzentrationen von anorganischem As, Monomethylarsen und Dimethylarsen in der Lösung sanken mit steigendem EH. Reduzierende Bedingungen erhöhen die Mobilität und Verfügbarkeit dieser Verbindungen. Sanierungstechniken, die mit einer Belüftung des Bodens einhergehen, könnten zu einer Remobilisierung der Schwermetalle führen. Im Gegensatz dazu sollten mit As kontaminierte Böden möglichst nicht zusätzlich überflutet werden, um eine erhöhte Mobilität und Verfügbarkeit dieser Verbindungen als Folge reduzierender Bedingungen zu vermeiden

Biogeochemie von Quecksilber in zeitweise überfluteten Böden

We have assessed the effect of various factors on the mobility of total mercury (Hg) as well as on the methylation of Hg in two floodplain soils with different Hg loads using an automated biogeochemical microcosm system allowing controlled variation of redox potential (EH) in soil suspensions. The experiment was conducted under stepwise variation from reducing (approximately -240 mV at pH 5) to oxidizing (approximately 600 mV at pH 5) conditions. Generally it is known that sulphate (SO42-) reduction is mainly catalyzed by sulfate reducing bacteria (SRB) and iron (Fe) reducing bacteria, which promote the Hg methylation. However, the specific linking mechanisms between Hg methylation and microorganisms are still a black box. Analysis of phospholipid fatty acids (PLFA) indicate the occurrence of sulphate reducing bacteria such as Desulfovibrio or Desulfobulbus species, which are considered to promote Hg methylation. A direct impact of EH and pH could not be detected, instead, EH and pH indirectly affected Hg dynamics and methylation rate. Dissolved organic carbon (DOC) is an important factor controlling the dynamics and methylation of Hg. Both, Hg and methyl mercury (MeHg) in the solution increased with raising DOC. The lnMeHg/Hg ratio as the net production of MeHg normalized to the Hg concentration increases with increasing lnDOC/Hg ratio under changing EH

Erfassung und Bewertung der Schwermetallverteilung in Auenoberböden von Ruhr und Wupper

Auf Grund erheblicher räumlicher Heterogenität von stofflichen Bodenbelastungen in Auenböden ist eine flächenhafte Prognose der Schadstoffverteilung in Oberböden, wie sie mit den Methoden der digitalen Bodenbelastungskarten in Nordrhein-Westfalen zur Verfügung steht, in diesen Bereichen bisher nicht befriedigend oder nur mit sehr hohem Aufwand möglich. Es ist notwendig, Methoden zu entwickeln, mit denen die räumliche Verteilung und die Höhe der Schadstoffbelastung in Böden der Überschwemmungsgebiete besser prognostiziert werden können. Die Entwicklung und erste Ergebnisse einer solchen Methode werden vorgestellt. Es zeigt sich, dass die Belastungen in Auenböden über die Höhenlage im Verhältnis zum angrenzenden Fließgewässer zu unterscheiden und abzugrenzen sind

Impact of systematic change of redox potential on the leaching of Ba, Cr, Sr, and V from a riverine soil into water

Floodplain soils are often contaminated with toxic elements such as Ba, Cr, Sr, and V. For an adequate risk assessment of such contaminated sites, the assessment of factors affecting the leaching of those elements from riverine soils into water is fundamental. Since the redox potential (E-H) can be important within this context, we aimed to assess the impact of pre-set redox conditions on the dynamics of Ba, Cr, Sr, and V in a floodplain soil. To achieve this aim, we used an automatic biogeochemical microcosm system allowing computer-controlled regulation of E-H by adapting the supply of N-2 or O-2 to the soil suspension. With this system, the effect of E-H on the dynamics of Ba, Cr, Sr, and V was studied mechanistically. Chromium and V were negatively correlated with E-H possibly due to co-precipitation of these metals with Fe (hydr)oxides at high E-H. Vanadium might additionally be oxidized from more soluble V(IV) to less soluble V(V) with rising E-H. Barium and Sr were positively correlated with E-H, which might be attributed to their association with dissolved organic carbon (DOC). The influence of pH on the dynamics of the studied elements seemed to be of minor importance in our study. A significant negative correlation was observed between the specific UV absorbance at 254 nm (SUVA (254)) and E-H indicating that oxidizing conditions favored the removal of aromatic DOC molecules from solution via binding to Fe (hydr)oxides. Redox potential is important for metal fate in the current study. Results imply an absorption of Cr and V to Fe (hydr)oxides and an interaction with DOC while particularly Ba and Sr dynamics may be influenced by DOC. In the future, different V species in wetland soils under pre-definite redox conditions should be determined and further studies should elucidate the specific role of DOC and sulfur (S) chemistry on the dynamics of the studied metals

Nickel in a serpentine-enriched Fluvisol: Redox affected dynamics and binding forms

We determined redox-induced (im)mobilization of geogenic nickel (Ni) as well as binding forms of Ni in a Fluvisol at the River Velika Morava valley (Serbia), enriched with serpentine minerals. The selected site is representative for intensive agricultural land use in the area and susceptible to dynamic redox conditions due to periodical flooding. A seven-step sequential extraction, grain-size and light-liquid separation as well as mineralogical analyses were used, first, to assess binding forms of Ni and second, to determine relationships between grain-size fractions, abundance of heavy density minerals, and Ni concentration in the bulk soil. The sequential extraction revealed that the majority of Ni was in the residual fraction, followed by organic matter and Fe oxides. Fine grain-size fraction ( lt 63 mu m) was the major location of accumulation of Ni in the soil. Minerals which are characteristic for serpentine soils such as serpentine, spinels, hematite, and magnetite were found in silt and in the heavy density fraction (>2.9 g ml(-1)) of the medium and fine sand. However, the light minerals quartz, chlorite, micas, and secondary clay minerals dominate the soil mineral composition. Thus, total Ni concentration in the soil is derived from the content of Ni-bearing minerals and diluted by the minerals which are low in Ni. We simulated flooding using an automated biogeochemical microcosm system and determined the release dynamics of Ni at controlled redox potentials (E-H) in soil slurries. Pre-defined redox-windows were systematically created in steps of approximately 100 mV from reducing to oxidizing conditions while E-H and pH were continuously monitored. In parallel, the release dynamics of soluble nickel (Ni), iron (Fe), magnesium (Mg), manganese (Mn), dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and sulfate (SO42-) were measured at each E-H-window. Our results highlighted that geogenic Ni can be mobilized to a considerable amount during low E-H, while elevating E-H from reducing to oxidizing conditions generated an immobilization Ni. We suggested that mobilization of Ni has been primarily affected by formation of Ni DOC complexes at low E-H, whereas Ni seems to be immobilized as a result of formation of Fe/Mn (hydro)oxides and the linked co-precipitation of Ni during oxidation. Factor analysis (FA) as multivariate statistical method explained 85.08% of the variance (67.89% and 17.19% component Nos. 1 and 2, respectively). The FA reveals that soluble Ni, Fe, DOC, Mn, and Mg were clustered in one group which indicate that the combined effect of DOC together with the chemistry of Fe, Mn, and Mg might be linked to the redox-induced release dynamics of Ni. The practical perspective of the study was to draw attention to dynamics of soluble Ni in fluctuating conditions for a better ecological risk assessment of floodplain sites under agricultural use. Nevertheless, similar studies should be conducted with further serpentine soils from various sites world-wide to verify the detected dynamics and processes

Impact of controlled redox conditions on nickel in a serpentine soil

Serpentine soils exist in many regions around the world; they are naturally enriched with nickel (Ni). An adequate understanding of soil processes determining Ni solubility is a special need particularly since less research has been addressed to Ni behavior under dynamic and controlled redox conditions. Our aim was (1) to characterize the properties of a serpentine soil and (2) to determine the impact of predefined redox windows on the mobility and dynamics of Ni in a serpentine soil. A soil with high geogenic Ni concentrations from Serbia was incubated using an automated biogeochemical microcosm system. Redox windows were created from reducing to oxidizing conditions in predefined steps of approximately 100 mV. Three microcosms were used as replicates; redox potential (E-H) and pH were automatically monitored every 10 min. The samples were centrifuged, and the supernatants were immediately filtered under N-2 atmosphere and analyzed for soluble Ni, iron (Fe), manganese (Mn), dissolved organic carbon (DOC), and sulfate (SO (4) (2-) ). X-ray diffraction was performed to assess mineral composition of the soil grain-size fractions. Nickel binding forms in the bulk soil were determined by the sequential extraction according to Tessier et al. (1979). Total Ni concentration in the bulk soil was 550 mg kg(-1). Quartz, chlorite, serpentine minerals, and secondary minerals were the prevalent minerals. The residual fraction contained the most Ni (91.3%). Nickel percentages of the fractions: Fe/Mn oxides, organic matter, carbonate, and exchangeable were low. Soluble Ni concentrations varied in the range 77-166 mu g L-1, showing a linear decrease with increasing E-H. Soluble Ni was positive correlated with Fe, Mn, and DOC and inversely correlated with SO (4) (2-) . Dissolution and precipitation of Fe/Mn oxides, organic matter transformations, and adsorption on solids are important processes controlling the Ni solubility during redox change. Nickel concentrations at definite redox windows were in the same order of magnitude as the exchangeable Ni determined by the sequential extraction procedure. Our study demonstrates that considerable amounts of Ni can be mobilized during low E-H despite a high Ni retention capacity of the soil. The sequential extraction might provide a reliable estimation of the potential mobile Ni under dynamic redox alterations. The interactions of DOC, pH, Fe, and Mn (hydr)oxides are controlling the dynamics of soluble Ni under changing E-H conditions. It is important to verify the detected dynamics at various scales and in other serpentine soils in the future