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Copper isotope fractionation during its interaction with soil

and aquatic microorganisms and metal oxy(hydr)oxides:

Possible structural control

O.S. Pokrovsky a,*, J. Viers a, E.E. Emnova b, E.I. Kompantseva c, R. Freydier a

a Laboratoire de Me´canismes et Transfert en Ge´ologie (LMTG), Universite´ de Toulouse, CNRS, IRD,

OMP, 14 Avenue Edouard Belin, 31400 Toulouse, France

b Institute of Genetics and Plant Physiology, Moldavian Academy of Science, Kishinev, Moldavia

c Institute of Microbiology, Russian Academy of Science, Moscow, Russia

Received 4 June 2007; accepted in revised form 23 January 2008; available online 31 January 2008

Pdf Abastract This work is aimed at quantifying the main environmental factors controlling isotope fractionation of Cu during its adsorption from aqueous solutions onto common organic (bacteria, algae) and inorganic (oxy(hydr)oxide) surfaces. Adsorption of Cu on aerobic rhizospheric (Pseudomonas aureofaciens CNMN PsB-03) and phototrophic aquatic (Rhodobacter sp. f-7bl, Gloeocapsa sp. f-6gl) bacteria, uptake of Cu by marine (Skeletonema costatum) and freshwater (Navicula minima, Achnanthidium minutissimum and Melosira varians) diatoms, and Cu adsorption onto goethite (FeOOH) and gibbsite (AlOOH) were studied using a batch reaction as a function of pH, copper concentration in solution and time of exposure. Stable isotopes of copper in selected filtrates were measured using Neptune multicollector ICP-MS. Irreversible incorporation of Cu in cultured diatom cells at pH 7.5–8.0 did not produce any isotopic shift between the cell and solution (D65/63Cu(solid-solution)) within ±0.2&. Accordingly, no systematic variation was observed during Cu adsorption on anoxygenic phototrophic bacteria (Rhodobacter sp.), cyanobacteria (Gloeocapsa sp.) or soil aerobic exopolysaccharide (EPS)-producing bacteria (P. aureofaciens) in circumneutral pH (4–6.5) and various exposure times (3 min to 48 h): D65Cu(solid-solution) = 0.0 ± 0.4&. In contrast, when Cu was adsorbed at pH 1.8–3.5 on the cell surface of soil the bacterium P. aureofacienshaving abundant or poor EPS depending on medium composition, yielded a significant enrichment of the cell surface in the light isotope (D65Cu (solid-solution) = _1.2 ± 0.5&). Inorganic reactions of Cu adsorption at pH 4–6 produced the opposite isotopic offset: enrichment of the oxy(hydr)oxide surface in the heavy isotope with D65Cu(solid-solution) equals 1.0 ± 0.25& and 0.78 ± 0.2& for gibbsite and goethite, respectively. The last result corroborates the recent works of Mathur et al. [Mathur R., Ruiz J., Titley S., Liermann L., Buss H. and Brantley S. (2005) Cu isotopic fractionation in the supergene environment with and without bacteria. Geochim. Cosmochim. Acta 69, 5233–5246] and Balistrieri et al. [Balistrieri L. S., Borrok D. M., Wanty R. B. and Ridley W. I. (2008) Fractionation of Cu and Zn isotopes during adsorption onto amorhous Fe(III) oxyhydroxide: experimental mixing of acid rock drainage and ambient river water. Geochim. Cosmochim. Acta 72, 311–328] who reported heavy Cu isotope enrichment onto amorphous ferric oxyhydroxide and on metal hydroxide precipitates on the external membranes of Fe-oxidizing bacteria, respectively. Although measured isotopic fractionation does not correlate with the relative thermodynamic stability of surface complexes, it can be related to their structures as found with available EXAFS data. Indeed, strong, bidentate, inner-sphere complexes presented by tetrahedrally coordinated Cu on metal oxide surfaces are likely to result in enrichment of the heavy isotope on the surface compared to aqueous solution. The outer-sphere, monodentate complex, which is likely to form between Cu2+ and surface phosphoryl groups of bacteria in acidic solutions, has a higher number of neighbors and longer bond distances compared to inner-sphere bidentate complexes with carboxyl groups formed on bacterial and diatom surfaces in circumneutral solutions. As a result, in acidic solution, light isotopes become more enriched on bacterial surfaces (as opposed to the surrounding aqueous medium) than they do in neutral solution. Overall, the results of the present study demonstrate important isotopic fractionation of copper in both organic and inorganic systems and provide a firm basis for using Cu isotopes for tracing metal transport in earth-surface aquatic systems. It follows that both adsorption on oxides in a wide range of pH values and adsorption on bacteria in acidic solutions are capable of producing a significant (up to 2.5–3& (±0.1–0.15&)) isotopic offset. At the same time, Cu interaction with common soil and aquatic bacteria, as well as marine and freshwater diatoms, at 4 < pH < 8 yields an isotopic shift of only ±0.2–0.3&, which is not related to Cu concentration in solution, surface loading, the duration of the experiment, or the type of aquatic microorganisms.

Biosorption of Cr(VI) by immobilized biomass of two indigenous

strains of cyanobacteria isolated from metal contaminated soil

Kamra Anjana, Anubha Kaushik , Bala Kiran, Rani Nisha

Department of Environmental Science and Engineering, Guru Jambheshwar

University of Science and Technology, Hisar-125 001, India

Received 16 November 2006; received in revised form 19 February 2007;

accepted 19 February 2007 Available online 23 February 2007

Pdf Abstract Biosorption of Cr(VI) using native strains of cyanobacteria from metal contaminated soil in the premises of textile mill has been reported in this paper. Biosorption was studied as a function of pH (1–5), contact time (5–180 min) and initial chromium ion concentration (5–20 mg/l) to find out the maximum biosorption capacity of alginate immobilized Nostoc calcicola HH-12 and Chroococcus sp. HH-11. The optimum conditions for Cr(VI) biosorption are almost same for the two strains (pH 3–4, contact time 30 min and initial chromium concentration of 20 mg/l) however, the biomass of Chroococcus sp. HH-11 was found to be more suitable for the development of an efficient biosorbent for the removal of Cr(VI) from wastewater, as it showed higher values of qm and Kf, the Langmuir and Freundlich isotherm parameters. Both the isotherm models were suitable for describing the biosorption of Cr(VI) by the cyanobacterial biosorbents.

 

Keywords: Algae; Heavy metal; Adsorption isotherm

 

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