INTRODUCTION EXPERIMENTAL ACKNOWLEDGEMENT ...
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A modified constrained sediment probe [4] packed with agarose based resin and diffusive gels were exposed to uranium spiked sediment core to obtain high resolution profiles of manganese, iron and uranium to show its performance The diffusive equilibrium in thin films technique (DET) was used to obtain complementary high resolution pore water profiles of total concentrations of dissolved metals species Sediment sample was taken at a sampling site of Krencak pond, Netin, Czech Massif, Czech Republic, GPS-coordinates: 49°24'41.87"N, 15°56'19.129"E) during spring 2011 remediation period, homogenized, incubated before and after spiking of sediment core by depleted uranium (DU) standard solution Segmented sediment DGT and DET probes were deployed in sediment core for one week, and pH and redox potential depth profiles were also measured Mobile metals species were taken up by the Spheron-Oxin® based resin gel: Pseudo steady-state concentration gradient in the diffusive gel was established, and thus metal flux to the resin gel was governed by interfacial metal concentration C a Metals were eluted from the strips of resin and diffusive gels by 1 M nitric acid, and subsequently determined by ICP MS (Agilent 7700 Series) NEW MODIFICATION OF DIFFUSIVE GRADIENT IN THIN FILM TECHNIQUE (DGT) FOR DETERMINATION OF METALS IN SEDIMENTS M. Gregušová, B. Dočekal Institute of Analytical Chemistry of the ASCR, v. v. i., Veveří 97, 602 00 Brno, Czech Republic [email protected] INTRODUCTION EXPERIMENTAL The diffusive gradient in thin film (DGT) technique has been used for measurement of concentrations and fluxes of labile metal species in environmental systems, in characterization of waters, soils and sediments. When DGT probes are exposed to aquatic systems over a certain time period, metal species diffuse through the well-defined diffusion layer into the binding resin gel and provide in situ time averaged concentrations of mobile metal species [1]. In sediments, the probes disturb local sediment/pore water equilibrium under well-defined conditions, so that the sediment response, metal re-supply fluxes can be monitored in situ [2-3]. The scope of the work was to investigate performance of a modified DGT probe for sediment characterization. dt t C t C t t i a DGT i 0 1 DGT technique is widely used to asses fluxes of metals in sediment pore waters. High resolution of a modified probe and the preconcentration capability of DGT technique provides direct information on remobilization processes of metals in sediments. The interference free determination of manganese, iron and uranium by the Spheron-Oxin based resin gel can give additional data on uranium reactions that are driven by redox processes. Combination of DGT technique with ICP MS analysis can also potentially provide information on sources of uranium in sediments and related environmental systems. ACKNOWLEDGEMENT CONCLUSION This work was performed within the Institutional research plan AVO Z40310501 and the project No. P503/10/2002 of the Czech Science Foundation. RESULTS & DISCUSSION 2 2 x c D t c x c D F x t x t , ) , ( DET DGT Modified probe The DGT technique can provide information on geochemical cycling and fluxes of metals. As documented in graphs, the modified segmented probe enables to obtain sediment depth profiles of metals with the resolution down to the millimeter level. The depth profile of redox potential exhibits significant changes to negative values close to the water-sediment interface, and it remains fairly constant in deeper horizons of the sediment core. This indicates that the pond sediment was anoxic under laboratory model conditions. Manganese and iron depth profiles show changes in metal speciation, i.e. the reductive mobilization in accordance with the redox profile of the model sediment. Uranium data show a good correlation between the uptake of uranium by the DGT probe and the amount of uranium spikes in the sediment core. Transport of uranium from spiked zones into upper sediment horizons, even though into overlaying water was significantly hindered by the redox conditions, which indicates reductive immobilization of uranium in deeper horizons of sediment core. Determination of 238 U and 235 U isotopes by DET and DGT technique showed that the isotopic composition of uranium varies within both depth profiles. Uranium DET profile reflects final equilibrium concentration of uranium isotopes in sediment pore water at the end of one week deployment period. In contrary, DGT profile shows averaged record of uranium isotopes taken up over the whole deployment period. Consequently, comparison of both types of profiles can give an information on kinetics of transport and changes in metal speciation. The sediment sample exhibited natural uranium isotope abundance with a 238 U/ 235 U ratio of 140. The spikes were based on a depleted uranium standard solution with the isotopic ratio of 281. Consequently, the DET measured isotope ratio decreases stepwise in the depth profile due to isotopic dilution by natural abundant uranium isotopes (sediment contained 0.49 ± 0.01 mg/kg U), i.e. upwards the profile according to spike locations from the value of 280 to a value of approximately 260 at the water/sediment interface. Evidently, this effect of isotopic dilution is more pronounced in the DGT profile, in which natural isotopic ratio of 145 was found in the overlaying aqueous phase. [1] H.Zhang, W.Davison, Anal.Chem. 67 (1995) 3391. [2] H.Zhang, W.Davison, B. Knight, S. McGrath, Environ.Sci.Technol. 32 (1998) 704. [3] M.P.Harper, W.Davison, H.Zhang, W.Tych, Geochim.Cosmochim.Acta 62 (1998) 2757. [4] B.Dočekal, M.Gregušová, Analyst, 137 (2012), 502 – 507. REFERENCES
Transcript of INTRODUCTION EXPERIMENTAL ACKNOWLEDGEMENT ...
A modified constrained sediment probe [4] packed with agarose based resin anddiffusive gels were exposed to uranium spiked sediment core to obtain high resolutionprofiles of manganese, iron and uranium to show its performance
The diffusive equilibrium in thin films technique (DET) was used to obtain complementary high resolution pore water profiles of total concentrations of dissolved metals species
Sediment sample was taken at a sampling site of Krencak pond, Netin, Czech Massif,Czech Republic, GPS-coordinates: 49°24'41.87"N, 15°56'19.129"E) during spring 2011remediation period, homogenized, incubated before and after spiking of sediment coreby depleted uranium (DU) standard solution
Segmented sediment DGT and DET probes were deployed in sediment core for one week, and pH and redox potential depth profiles were also measured
Mobile metals species were taken up by the Spheron-Oxin® based resin gel:
Pseudo steady-state concentration gradient in the diffusive gel was established, andthus metal flux to the resin gel was governed by interfacial metal concentration Ca
Metals were eluted from the strips of resin and diffusive gels by 1 M nitric acid, andsubsequently determined by ICP MS (Agilent 7700 Series)
NEW MODIFICATION OF DIFFUSIVE GRADIENT IN THIN FILM TECHNIQUE (DGT) FOR DETERMINATION OF METALS IN SEDIMENTS
M. Gregušová, B. DočekalInstitute of Analytical Chemistry of the ASCR, v. v. i., Veveří 97, 602 00 Brno, Czech Republic
INTRODUCTION EXPERIMENTALThe diffusive gradient in thin film (DGT) technique hasbeen used for measurement of concentrations and fluxesof labile metal species in environmental systems, incharacterization of waters, soils and sediments. When DGTprobes are exposed to aquatic systems over a certain timeperiod, metal species diffuse through the well-defineddiffusion layer into the binding resin gel and provide in situtime averaged concentrations of mobile metal species [1].In sediments, the probes disturb local sediment/pore waterequilibrium under well-defined conditions, so that thesediment response, metal re-supply fluxes can bemonitored in situ [2-3].The scope of the work was to investigate performance of amodified DGT probe for sediment characterization.
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DGT technique is widely used to asses fluxes of metals in sediment porewaters. High resolution of a modified probe and the preconcentrationcapability of DGT technique provides direct information on remobilizationprocesses of metals in sediments. The interference free determination ofmanganese, iron and uranium by the Spheron-Oxin based resin gel can giveadditional data on uranium reactions that are driven by redox processes.Combination of DGT technique with ICP MS analysis can also potentiallyprovide information on sources of uranium in sediments and relatedenvironmental systems.
ACKNOWLEDGEMENTCONCLUSIONThis work was performed within theInstitutional research plan AVO Z40310501and the project No. P503/10/2002 of the CzechScience Foundation.
RESULTS & DISCUSSION
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The DGT technique can provide information on geochemical cycling and fluxes ofmetals. As documented in graphs, the modified segmented probe enables to obtainsediment depth profiles of metals with the resolution down to the millimeter level.The depth profile of redox potential exhibits significant changes to negative valuesclose to the water-sediment interface, and it remains fairly constant in deeper horizonsof the sediment core. This indicates that the pond sediment was anoxic underlaboratory model conditions. Manganese and iron depth profiles show changes inmetal speciation, i.e. the reductive mobilization in accordance with the redox profile ofthe model sediment. Uranium data show a good correlation between the uptake ofuranium by the DGT probe and the amount of uranium spikes in the sediment core.Transport of uranium from spiked zones into upper sediment horizons, even thoughinto overlaying water was significantly hindered by the redox conditions, whichindicates reductive immobilization of uranium in deeper horizons of sediment core.
Determination of 238U and 235U isotopes by DET and DGT technique showed that the isotopiccomposition of uranium varies within both depth profiles. Uranium DET profile reflects finalequilibrium concentration of uranium isotopes in sediment pore water at the end of one weekdeployment period. In contrary, DGT profile shows averaged record of uranium isotopes takenup over the whole deployment period. Consequently, comparison of both types of profiles cangive an information on kinetics of transport and changes in metal speciation. The sedimentsample exhibited natural uranium isotope abundance with a 238U/235U ratio of 140. The spikeswere based on a depleted uranium standard solution with the isotopic ratio of 281.Consequently, the DET measured isotope ratio decreases stepwise in the depth profile due toisotopic dilution by natural abundant uranium isotopes (sediment contained 0.49 ± 0.01 mg/kgU), i.e. upwards the profile according to spike locations from the value of 280 to a value ofapproximately 260 at the water/sediment interface. Evidently, this effect of isotopic dilution ismore pronounced in the DGT profile, in which natural isotopic ratio of 145 was found in theoverlaying aqueous phase.
[1] H.Zhang, W.Davison, Anal.Chem. 67 (1995) 3391.[2] H.Zhang, W.Davison, B. Knight, S. McGrath, Environ.Sci.Technol. 32 (1998) 704.[3] M.P.Harper, W.Davison, H.Zhang, W.Tych, Geochim.Cosmochim.Acta 62 (1998)
2757. [4] B.Dočekal, M.Gregušová, Analyst, 137 (2012), 502 – 507.
REFERENCES
