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International audience; A novel two-step strategy to prepare amorphous oxyfluorides, containing both divalent and trivalent 3d-metals, as cathode materials for lithium batteries is presented. The first step involves the preparation of hydrated fluorides M2+M3+2F8(H2O)2 (M2+ = Mn, Fe, Co, Ni, Cu; M3+ = V, Fe) by microwave-assisted solvothermal synthesis. Besides the MnFe2F8(H2O)2 and CuFe2F8(H2O)2 phases, three new compounds, Fe1.3V1.7F8(H2O)2, CoFe2 F8(H2O)2, and Ni- Fe2F8(H2O)2, which are isostructural with Fe3F8(H2O)2, have been unraveled. The second step consists in the decomposition of M2+M3+2F8(H2O)2 into amorphous oxyfluorides M2+M3+2F8−2xOx via suitable thermal treatments.. The amorphous materials show a greater electrochemical activity toward Li than their parent phases, among them being CuFe2F6O, which displays the best performance as a cathode material with a first discharge capacity of 310 mAh·g−1. We show that such a large capacity results from cumulative insertion and displacement reactions.

International audience; Metal fluorides with 3D open structures, pyrochlore (pyr) or hexagonal tungsten bronze (HTB), are promising materials as positive electrodes for rechargeable batteries or catalysts. Herein, we have developed a two-step synthesis procedure to obtain new anhydrous mixed-metal-cation fluorides crystallizing in the pyrochlore structure. The first step consists of preparing mixed-metal ammonium fluorides (NH4)M2+Fe3+F6 (M = Mn, Fe, Co Ni) using different synthesis strategies. For M = Mn, three allotropic varieties of (NH4)Mn2+Fe3+F6 are obtained; two phases adopt the expected pyrochlore network with either the cubic Fm3̅m or the orthorhombic Pnma space group, and the third phase exhibits a 3D network with narrow pseudotriangular cavities. 57Fe Mössbauer spectrometry indicates that the crystal structures are governed by the Fe3+/Mn2+ cationic order or disorder. The second step is a topotactic oxidation of pyr-(NH4)M2+Fe3+F6 under a molecular F2 flow. To better understand the reaction mechanism, the topotactic oxidation was followed by thermogravimetry, XRD, FTIR, and Mössbauer spectrometry. The successful synthesis of the first anhydrous pyr-M3+0.5Fe0.5F3 provides a new route to prepare anhydrous mixed-metal fluorides pyrochlore with empty cavities of the open framework.

International audience; In our search for novel insertion compounds for Li-based batteries, we have identified a new mixed iron vanadium based Hexagonal Tungsten Bronze (HTB) type phase. Its synthesis involves two steps which consist first of preparing mixed metal hydrated fluoride Fe1.64V1.36F8(H2O)2 by a microwave assisted thermal process, followed by thermal treatment under air to obtain metastable HTB–(Fe0.55V0.45)F2.67(OH)0.33 hydroxyfluoride. 57Fe Mössbauer spectrometry demonstrates the presence of oxidation states Fe2+ and Fe3+ in Fe1.64V1.36F8(H2O)2 as opposed to only Fe3+ in HTB–(Fe0.55V0.47)F2.67(OH)0.33. Moreover, the Mössbauer spectra recorded at 77 K reveal that none of the compounds shows magnetic ordering owing to the presence of V3+ distributed over the crystallographic sites of Fe3+. Complementary X-ray spectroscopy and Rietveld refinement further confirm the successful synthesis of HTB–(Fe0.55V0.45)F2.67(OH)0.33. Electrochemically, the new HTB–(Fe0.55V0.45)F2.67(OH)0.33 shows a first discharge capacity of 181 mA h g−1 with 67% of this capacity remaining upon cycling. Unlike HTB–FeF2.66(OH)0.34, the structure remains stable after the first discharge confirming the positive effect of vanadium in the HTB network.

International audience; The synthesis and the electrochemical properties of iron hydroxyfluorides with an open structure, prepared from the thermal decomposition of Fe2+Fe3+F5(H2O)2 and Fe2+Fe23+F8(H2O)2 under ambient air, are reported. The combination of thermogravimetric analyses, X-ray thermodiffraction (XRD), and infrared spectroscopy has evidenced two unstable lacunar oxyfluorides that transform rapidly into hydroxyfluorides under ambient air. Their formulations and structural features have been determined from powder XRD, Mössbauer spectrometry, and pair distribution function, leading to Fe3+F2.5(OH)0.5 with the pyrochlore network and to Fe3+F2.66(OH)0.34 with the hexagonal tungsten bronze (HTB) structure. The electrochemistry of these hydroxyfluorides indicates excellent and similar capacities with a significant decrease after the first cycle to reach sustained values of ∼110 mAh g–1 upon cycling. In situ XRD measurements reveal that the pyrochlore network undergoes amorphization (xLi+ > 0.5) while the HTB phase transforms into the ReO3-type phase (xLi+ > 0.33).

International audience; The mixture ZnF2/HFaq./Hamtetraz (Hamtetraz = 5-aminotetrazole) with the molar ratio 10/80/10 reacts at 160 °C in different solvents (methanol/water and water respectively) to give two new 3D compounds: (Zn4F4(amtetraz)4)∙H2O (1) and (Zn4F4(H2O)(amtetraz)4)·H2O (2). The structures, determined by single crystal X-ray diffraction, exhibit neutral 3D-frameworks with narrow cavities that contain water molecules. Each network is built up from two types of parallel chains connected by aminotetrazolate ligands. The comparison of 1 and 2 with literature compounds shows that the nature of the polar solvent, aprotic or protic, influences the network characteristics, as well as the condensation of inorganic species or the bridging mode of the organic moieties. The luminescence properties of the zinc fluoro-aminotetrazolates are discussed.

Globally, dissolved inorganic carbon (DIC) accounts for more than half the annual flux of carbon exported from terrestrial ecosystems via rivers. Here, we assess the relative influences of biogeochemical and hydrological processes on DIC fluxes exported from a tropical river catchment characterized by distinct land cover, climate and geology transition from the wet tropical mountains to the low-lying savanna plains. Processes controlling changes in river DIC were investigated using dissolved organic carbon, particulate organic carbon and DIC concentrations and stable isotope ratios of DIC (δ13CDIC) at two time scales: seasonal and diel. The recently developed Isotopic Continuous Dissolved Inorganic Carbon Analyser was used to measure diel DIC concentration and δ13CDIC changes at a 15-min temporal resolution. Results highlight the predominance of biologically mediated processes (photosynthesis and respiration) controlling diel changes in DIC. These resulted in DIC concentrations varying between 3.55 and 3.82 mg/l and δ13CDIC values ranging from −19.7 ± 0.31‰ to −17.1 ± 0.08‰. In contrast, at the seasonal scale, we observed wet season DIC variations predominantly from mixing processes and dry season DIC variations due to both mixing processes and biological processes. The observed wet season increases in DIC concentrations (by 6.81 mg/l) and δ13CDIC values of river water (by 5.4‰) largely result from proportional increases in subsurface inflows from the savanna plains (C4 vegetation) region relative to inflows from the rainforest (C3 vegetation) highlands. The high DIC river load during the wet season resulted in the transfer of 97% of the annual river carbon load. Therefore, in this gaining river, there are significant seasonal variations in both the hydrological and carbon cycles, and there is evidence of substantial coupling between the carbon cycles of the terrestrial and the fluvial environments. Recent identification of a substantial carbon sink in the savannas of northern Australia during wetter years in the recent past does not take into account the possibility of a substantial, rapid, lateral flux of carbon to rivers and back to the atmosphere.

The title compound, (H3O)2NaAl3F12 [dihydronium sodium trialuminum(III) dodecafluoride], was obtained by solvothermal synthesis from the reaction of aluminium hydroxide, sodium hydroxide, 1,2,4-triazole and aqueous HF in ethanol at 463 K for 48 h. The structure consists of AlF6 octahedra organized in [AlF4 −] n HTB-type sheets (HTB is hexagonal tungsten bronze) separated by H3O+ and Na+ cations.

Utilising newly available instrumentation, the carbon balance in two small tropical catchments was measured during two discharge events at high temporal resolution. Catchments share similar climatic conditions, but differ in land use with one draining a pristine rainforest catchment, the other a fully cleared and cultivated catchment. The necessity of high resolution sampling in small catchments was illustrated in each catchment, where significant chemical changes occurred in the space of a few hours or less. Dissolved and particulate carbon transport dominated carbon export from the rainforest catchment during high flow, but was surpassed by degassing of CO2 less than 4 h after the discharge peak. In contrast, particulate organic carbon dominated export from the cleared catchment, in all flow conditions with CO2 evasion accounting for 5–23% of total carbon flux. Stable isotopes of dissolved inorganic carbon (DIC) in the ephemeral rainforest catchment decreased quickly from ~1.5 ‰ to ~ −16 ‰ in 5 h from the flood beginning. A two-point mixing model revealed that in the initial pulse, over 90% of the DIC was of rainwater origin, decreasing to below 30% in low flow. In the cultivated catchment, δ13CDIC values varied significantly less (−11.0 to −12.2 ‰) but revealed a complex interaction between surface runoff and groundwater sources, with groundwater DIC becoming proportionally more important in high flow, due to activation of macropores downstream. This work adds to an increasing body of work that recognises the importance of rapid, short-lived hydrological events in low-order catchments to global carbon dynamics. Copyright © 2013 John Wiley & Sons, Ltd.

The tetragonal tungsten bronze (TTB) structure multiferroic fluoride K0.58FeF3 (alternatively K3–xFe5F15 (x ≈ 0.1)) has been studied using variable temperature high-resolution synchrotron powder X-ray diffraction. The as-made sample occurs as a mixture of two closely related TTB phases, one tetragonal (aTTB ≈ 12.68 A, cTTB ≈ 3.98 A) and one orthorhombic (a ≈ 12.70 A, b ≈ 12.66 A, c ≈ 3.98 A). Heating above 340 K produces a single metrically tetragonal phase, but the phase separation reproducibly reappears on cooling. Below 300 K the tetragonal phase undergoes a structural phase transition to a second orthorhombic phase (with a ≈ b ≈ √2 aTTB) and these two different orthorhombic phases continue to coexist down to at least 125 K. These results are discussed in the context of previous studies, which sometimes suggest conflicting structural details within this system.

International audience; Four new [H(3)tren](3+) or [H(4)tren](4+) fluoride zirconates and two new [H(3)tren](3+) fluoride tantalates are evidenced in the (ZrF4 or Ta2O5)-tren-HFaq.-ethanol systems at 190 degrees C: the structurally related phases [H(4)tren]center dot(Zr2F12)center dot H2O and alpha-[H(4)tren](center dot)(Zr2F12) (P2(1)2(1)2(1)). beta-[H(4)tren]center dot(Zr2F12) (P2(1/c)), [H(3)tren](4)center dot(ZrF8)(3)center dot 4H(2)O (123). beta-[H(3)tren](2)center dot(Ta3O2F16)center dot(F) (R32) and its monoclinic distortion alpha-[H(3)rren](2)center dot(Ta3O2F16)center dot(F) (C2/m). alpha and beta-[H(4)tren]center dot(Zr2F12) and [H(4)tren]center dot(Zr2F12)center dot H2O are built up from (Zr2F12) dimers of edge sharing ZrF7 polyhedra while isolated ZrF8 dodecahedra are found in [H(3)tren](4)center dot(ZrF8)(3)center dot 4H(2)O. Linear (Ta3O2F16) trimers build et and beta-[H(3)tren](2)center dot(Ta3O2F16)center dot(F); they consist of two (TaOF6) pentagonal bipyramids that are linked to two opposite oxygen atoms of one central (TaO2F4) octahedron. A disorder affects the equatorial fluorine atoms of the trimers and eventually carbon or nitrogen atoms of [H(3)tren](3+) cations. (C) 2011 Elsevier B.V. All rights reserved.

Two new zirconium (IV) fluorides, [H 2 dap ]·(Zr 2 F 10 )·H 2 O ( I ) and [H meam ] 2 ·(Zr 2 F 10 )·H 2 O ( II), are synthesized and characterized by X-ray diffraction, thermal techniques and NMR spectroscopy. I is triclinic ( P 1 ¯ ) with a = 6.805 (1) A, b = 8.361(1) A, and c = 11.853 (2) A, α = 94.54(1)°, β = 105.44(1)°, γ = 108.75(1)°. II is monoclinic ( C 2 /m ) with a = 10.340(6) A, b = 6.624(4) A, c = 8.758(6) A and β = 110.57(3)°. The structure determinations, performed from single crystal X-ray diffraction data, lead to the R/R w reliability factors 0.041/0.113 for I and 0.057/0.177 for II . The structures are built up from ZrF 7 and ZrF 8 units in I and only ZrF 8 units in II . The polyhedra share common edges in order to form two different ZrF 5 layers that are also found in [H 2 C 2 H 10 N 2 ]·(Zr 2 F 10 )·H 2 O and (H 3 O) 2 ·(Zr 2 F 10 )·H 2 O. On heating at 145 °C, [H 2 dap ]·(Zr 2 F 10 )·H 2 O decomposes to give the anhydrous form [H 2 dap ]·(Zr 2 F 10 ) that undergoes two successive phase transformations at 220 °C and 290 °C. 19 F NMR spectroscopy confirms the structural features of [H 2 dap ]·(Zr 2 F 10 )·H 2 O ( I ): two sets of three lines with a relative intensity 1:2:2 are attributed to five bridging fluorine atoms and to five nonbridging fluorine atoms. This spectroscopy demonstrates that a noticeable substitution of F − anions by hydroxyl OH − groups is excluded, together with the eventual substitution of H 2 O by HF molecules.

The environment of H 3 O + , H 2 O, HF and F − species (non-bonded to metals) is considered in fluoride metalates which crystallise from the (Al(OH) 3 , Cr(OH) 3 , FeF 3 , ZrF 4 , Ta 2 O 5 )- tren -HF aq· –ethanol systems (microwave heating at 190 °C during 1 h). The presence of (H 3 O)(H 2 O) 6 + clusters or H 3 O + cations, of isolated or associated H 2 O molecules, of (HF 2 ) − and F − anions is evidenced. The thermal stability of the solids depends strongly on the nature of the hydrogen-bonded species associated with the preceding cations or anions and on the formation of water ribbons or layers.

International audience; Pure tysonite La1-xBaxF3-x solid solutions for x < 0.15 were prepared by solid state synthesis in a platinum tube under an azote atmosphere with subsequent quenching for 0.07 ≤x < 0.15. The solid solutions were studied by X-ray, electron and neutron diffractions and by (19)F NMR and impedance spectroscopy. The evolution of the cell parameters obeying Vegard's rule was determined for 0 < x≤ 0.15 and atomic position parameters were accurately refined for x = 0.03, 0.07 and 0.10. The chemical pressure induced by large Ba(2+) cations leads to an increase of the unit cell parameters. Fluorine environment and mobilities are discussed on the basis of the results of neutron diffraction and (19)F solid state NMR. The F1 subnetwork is lacunar; fluorine exchange occurs according to the order: F1-F1 and F1-F2,3. 2D EXSY NMR spectra of La0.97Ba0.03F2.97 reveal, for the first time, a chemical exchange between F2 and F3 sites that requires two successive jumps. The ionic conductivity was evaluated from sintered pellets and different shaping methods were compared. The only structural features which could explain the conductivity maximum are a crossover together with a smaller dispersion of F1-F1,2,3 distances at x = 0.05-0.07.

A new organic–inorganic zirconium (IV) fluoride, [C6N2H14]⋅(Zr2F10)⋅1.5H2O, is prepared by slow evaporation at 45 °C from a solution of Zr4+ and of 1,4-diazabicyclo[2.2.2]-octane (DABCO) in 40% aqueous HF. The structure, determined from single-crystal X-ray diffraction, is monoclinic, space group C 2 / m , a = 19.598 ( 8 ) A , b = 6.658 ( 3 ) A , c = 10.891 ( 3 ) A , β = 101.25 ( 4 ) ° and Z = 4 . Previously unknown ∞(Zr2F10)2− double chains, built up from edge-sharing ZrF7 pentagonal bipyramids and ZrF8 trigonal dodecahedra, are observed. The diprotonated organic cations, water molecules and the ∞(Zr2F10)2− chains are linked by hydrogen bonds.

A new guanidinium fluoride tantalate, [CN3H6]⋅(TaF6), crystallises at 50 °C from a solution of Ta2O5 in 40% aqueous HF and of guanidinium chloride. The structure is rhombohedral, R 3 ¯ m space group, with the equivalent hexagonal cell a H = 8.647 ( 1 ) A , c H = 8.507 ( 2 ) A , Z = 3 and R = 0.029 , R w = 0.077 for 312 reflections. The three-dimensional network is built up from parallel (0001)H layers ∞([CN3H6]F6)5− between which tantalum atoms are inserted. These tantalum atoms, in 3a sites, adopt an octahedral coordination with 〈 d Ta F 〉 = 1.894 ( 7 ) A . (TaF6)− anions are disordered over (0001)H mirror plane related positions while guanidinium cations are disordered over centrosymmetric positions; site occupancy of fluoride and nitrogen sites is fifty per cent.

Tren amine cations [(C2H4NH3)3N]3+ and zirconate or tantalate anions adopt a ternary symmetry in two hydrates, [H3tren]2·(ZrF7)2·9H2O and [H3tren]6·(ZrF7)2·(TaOF6)4·3H2O, which crystallise in R32 space group with aH = 8.871 (2) A, cH = 38.16 (1) A and aH = 8.758 (2) A, cH = 30.112 (9) A, respectively. Similar [H3tren]2·(MX7)2·H2O (M = Zr, Ta; X = F, O) sheets are found in both structures; they are separated by a water layer (Ow(2)–Ow(3)) in [H3tren]2·(ZrF7)2·9H2O. Dehydration of [H3tren]2·(ZrF7)2·9H2O starts at room temperature and ends at 90 °C to give [H3tren]2·(ZrF7)2·H2O. [H3tren]2·(ZrF7)2·H2O layers remain probably unchanged during this dehydration and the existence of one intermediate [H3tren]2·(ZrF7)2·3H2O hydrate is assumed. Ow(1) molecules are tightly hydrogen bonded with –NH3+ groups and decomposition of [H3tren]2·(ZrF7)2·H2O occurs from 210 °C to 500 °C to give successively [H3tren]2·(ZrF6)·(Zr2F12) (285 °C), an intermediate unknown phase (320 °C) and ZrF4.

Two zinc phosphates (ZnPO), [H2(N2C9H20)]·[Zn(H2PO4)4] (I) and [H2(N2C9H20)]2·[Zn2(HPO4)3(H2PO4)2]·H2O (II), are synthesized under hydrothermal conditions using 4-amino-2.2.6.6-tetramethylpiperidine as organic template. I crystallizes in P 1 ¯ space group with a = 8.7398 ( 3 ) A , b = 9.0417 ( 3 ) A , c = 15.3822 ( 1 ) A , α = 92.57 ( 1 ) ° , β = 89.76 ( 1 ) ° , γ = 102.16 ( 2 ) ° , V = 1187.1 ( 1 ) A 3 and Z = 2 . Its structure, refined to R = 0.029 and R w = 0.076 for 4279 independent reflections, consists of [Zn(H2PO4)4]2− clusters held together through strong hydrogen bonds to form pseudo-layers between which the doubly protonated amine molecules are inserted. II is monoclinic, C2, with a = 27.57 ( 2 ) A , b = 9.745 ( 5 ) A , c = 14.08 ( 1 ) A , β = 103.72 ( 5 ) ° , V = 3675 ( 4 ) A 3 and Z = 4 ( R = 0.079 , R w = 0.268 , 2477 independent reflections). The structure of II consists of ∞[Zn2(HPO4)3(H2PO4)2]4− inorganic (2D) layers built up from vertex-sharing [ZnO4] and [(H2/H)PO4] tetrahedra. Organic cations and water molecules ensure the connection between these layers via hydrogen bonds. It is shown that numerous (1D), (2D), e.g., [H2(N2C9H20)]2·[Zn2(HPO4)3(H2PO4)2]·H2O, and (3D) (ZnPO) result from the condensation of the [Zn(H2PO4)4]2− clusters.

Crystalline samples of Na2M2(BO3)2O ( M = Al , Ga ), Na1.5Ca0.25Ga2(BO3)2O and NaCa0.5Ga2(BO3)2O are prepared by conventional high temperature solid state synthesis technique. Temperature dependent impedance spectroscopy measurements are performed. For Na2Al2(BO3)2O and Na2Ga2(BO3)2O, high and low temperature regimes have to be distinguished. Only one regime is observed for the calcium-substituted samples Na1.5Ca0.25Ga2(BO3)2O and NaCa0.5Ga2(BO3)2O.

International audience; The distribution of arsenic (As(III), As(V)) and iron (Fe(II), Fe(III)) species was monitored during 1 year in a borehole drilled in the Carnoulès tailings impoundment which contains As-rich pyrite. The concentrations of total As and Fe in subsurface waters exhibited strong variations over one year, which were controlled by dissolved oxygen concentrations. At high oxygen levels, extremely high As (up to 162 mM) and Fe (up to 364 mM) concentrations were reached in the borehole, with the oxidised species predominant. As and Fe concentrations decreased 10-fold under oxygen-deficient conditions, as a result of pH increase and subsequent precipitation of As(V) and Fe(III). From drill core sections, it appeared that at low dissolved oxygen levels, As(III) was primarily released into water by the oxidation of As-rich pyrite in the unsaturated zone. Subsequent As and Fe precipitation was promoted during transport to the saturated zone; this reaction resulted in As enrichments in the sediment below the water table compared to the original content in pyrite, together with the formation of As-rich (up to 35 wt% As) ferruginous material in the unsaturated zone. High amounts of As(V) were released from these secondary phases during leaching experiments with oxygenated acid sulfate-rich waters; this process is believed to contribute to As(V) enrichment in the subsurface waters of the Carnoulès tailings during periods of high dissolved oxygen level.

The oxidation of Fe(II) in acid mine drainage (AMD) leads to the precipitation of Fe(III) compounds which may incorporate toxic elements, such as arsenic (As), within their structure or adsorb them at their surface, thus limiting their mobility. The present work provides evidence for spatial and seasonal variations of microbial activity that influence arsenite oxidation and As immobilization in the heavily contaminated AMD from the Carnoulès mine, Gard, France ([As III] = 80 to 280 mg x L(-1) in the acidic spring draining the waste-pile). In the first tens of meters of the AMD, the rapid oxidation of Fe(II) leads to the coprecipitation of large amounts of As with Fe(III) in bacterial mats. XRD, XANES, and SEM analyses of sediments and stromatolite samples revealed the unusual formation of As(III)-rich compounds, especially nanocrystalline tooeleite, Fe6(AsO3)4(SO4)(OH)4 x 4H2O, a rare ferric arsenite sulfate oxy-hydroxide mineral, together with XRD-amorphous mixed As(III)/As(V)-Fe(III) oxy-hydroxide compounds. In the wet season, the suspended sediments of the upstream zone essentially consist of tooeleite associated with am-As(III)-Fe(III) oxy-hydroxides, while am-As(V)-Fe(III) oxy-hydroxides, having As:Fe molar ratios as high as 0.6-0.8, dominate in the dry season. Comparing natural and bioassay samples revealed that the formation of As(III)-rich compounds in the wet season may be related to the metabolic activity of bacterial strains able to oxidize Fe(II) but not As(III). One of these strains, having an Acidithiobacillus ferrooxidans genotype, has been isolated from the Carnoulès AMD. In contrast, the formation of As(V)-rich compounds in the dry season can be related to both biotic and abiotic oxidation of As(III) to As(V). Some Thiomonas strains isolated from the Carnoulès AMD were shown to be able to catalyze the oxidation of As(III) to As(V) in solution. Therefore, they can promote the formation of mixed As(V)-Fe(III) oxy-hydroxides, provided enough Fe(II) oxidizes. These results yield a better understanding of natural processes at this site and may help in designing efficient As-removal processes.

The crystal structure of Zn 2 (BO 3 )(OH) 0.75 F 0.25 is determined ab initio from X-ray and neutron powder data. The unit cell is monoclinic, space group P2 1 (no. 4), Z =2, with a =6.8738(4) A, b =4.9178(2) A, c =5.7018(3) A, β =98.829(3) °, V =190.46(3) A 3 (neutron powder data). Alternating up and down ZnO 3 (OH,F) tetrahedra and triangular BO 3 3− groups built corrugated layers. Their connection by hydroxyl ions gives a 3D network similar to that of tridymite. The statistical distribution of fluorine and hydroxyl in infinite chains is evidenced by magical angle spinning-NMR spectroscopy.

Parts of the recent advances in the search of new fluorides or fluoride salts, at the Laboratoire des Fluorures in Le Mans, are presented. Hydrothermal synthesis in sub-critical or super-critical conditions is mainly used to obtain rare earth (RE), Al, Ga, In or 3d transition fluorides or fluoride salts (borates, carbonates, phosphates or silicates). Open structures are obtained by low temperature crystallisation from solutions (δ-(H 3 O)RE 3 F 10 · x H 2 O) and, probably, by decomposition of hybrid organic–inorganic fluorides D·MF 5 (D=diprotonated aliphatic diamine), prepared by micro-wave heating of the solutions. Non-centrosymmetric phases are evidenced in fluoride carbonates and fluoride borates: K 4 RE 2 (CO 3 ) 3 F 4 and M 2 (BO 3 )(OH) 0.75 F 0.25 ; the magnetic properties of several iron fluoride phosphates are found to be governed by super or super-superexchange interactions.

A new oxyborate Na2Ga2(BO3)2O is evidenced. The mean crystal structure, determined by X-ray diffraction, is trigonal, space group P-31c (n°163), Z=2, with a=4.855(2) A, c=15.441(7) A, V=315.2(4) A3, R1=0.047, wR2=0.123. The three-dimensional network is built up from the stacking, along the c axis, of infinite [NaGa2B2O7]∞ sheets, separated by sodium layers. Na2Al2(BO3)2O is isostructural with Na2Ga2(BO3)2O. Ionic conductivity is expected.

The optical behavior of europium fluoride borate Eu3(BO3)2F3 and barium fluoride carbonates Ba2Eu(CO3)2F3 is investigated with Eu3+ as a local structural probe. Tentative correlation between the optical and structural data are discussed. Unexpected broad emission lines are observed for Eu3+ in fluoride borate and the separation of two crystallographic sites, predicted from the structure determination, is impossible. It is assumed that deviation from the ideal stoichiometry Eu3(BO3)2F3 occurs and is due to the substitution BO3−3↔3F−, leading to the formulation Eu3(BO3)2+xF3−3x. Crystal field analysis is performed on the 7FJ basis of the 4f6 configuration of Eu3+. The crystal field parameters (cfp) and crystal field strength parameter NV are similar for both compounds though slightly larger for Eu3(BO3)2F3 This difference is especially significant for two rank (cfp), indicative of a larger electrostatic field in Eu3(BO3)2F3.

The luminescence of Eu 3+ in sodium europium hydroxyfluoride carbonate, Na 2 Eu(CO 3 )F 2.5 (OH) 0.5 , synthesized by hydrothermal growth at low temperature, is presented. The structure is orthorhombic and is built up from EuO 3 (F, OH) 6 polyhedra linked by triangular faces and edges. The emission spectrum consists of groups of sharp lines attributed to 5 D 0 → 7 F 0–4 transitions of one low symmetry site for Eu 3+ in agreement with the crystallographic analysis. 23 from 25 expected electronic levels for 7 F J ( J =0–4) manifolds are fitted by the phenomenological crystal field parameters in the approaching C 2v point symmetry. The simulation is achieved with very good root mean square ( rms ) deviation of 5.3 cm −1 . The crystal field strength parameter, N v , is weak ( N v =1652). Satellite vibronics of carbonate groups coupled to electronic transitions are also observed.

Biscutella laevigata and Iberis intermedia were sampled from sites near St Laurent le Minier, Southern France, and B. laevigata was also sampled from Rocca San Silvestro, Tuscany, Italy. Soils associated with the rhizosphere of each plant were also sampled. Both Biscutella laevigata and Iberis intermedia accumulate inordinately high concentrations of thallium (1.94 and 0.4%, respectively) in their above-ground dry tissue. The levels of thallium accumulated by both species were strongly correlated with both the total and extractable concentrations of thallium in the soils. Concentrations of zinc, cadmium, and lead were below the threshold for hyperaccumulation. It is proposed that B. laevigata and/or I. intermedia could be used for phytoremediation or phytomining of thallium-contaminated soils. Such an operation would involve the repeated cropping of either species, until an acceptable level of thallium in the soils was reached. Additionally, the harvested plant material could be burnt and the res...

Unusual hyperaccumulation (>500 mu g/g dry mass) of toxic Tl has been determined in Iberis intermedia (Brassicaceae) from southern France. This species contained up to 3,070 mu g/g (0.31%) Tl in the whole-plant dry matter. Pot trails with Iberis showed that it could tolerate nearly 2,000 mu g/g available Tl in the substrate compared with about 20 mu g/g for the metal-tolerant grass Arrhenatherum elatius. This unusually high accumulation of Tl has significance for animal and human health, phytoremediation of contaminated soils, and phytomining for Tl. It was determined that three crops of Iberis would be sufficient to phytoremediate to a non-toxic level, a soil containing 10 mu g/g Tl, and the production of a saleable plant ash (bio-ore) would probably pay for the cost of the operation. Phytomining (growing a "crop" of a metal over ores subeconomic for conventional mining) could be a viable option since it has been calculated that a net return of $1,200/ha (twice the return from a crop of wheat) would be possible with a biomass yield of 10 t/ha containing 0.08 percent Tl in dry matter. The break-even point (net yield of $500/ha) would require 170 mu g/g (0.017%) Tl in dry matter. Such a project would, however, require a large area to be able to afford economies of scale.

The optical study of the trivalent europium ion in polycrystalline K 4 Eu 2 (CO 3 ) 3 F 4 is reported. Three main low symmetry sites for Eu 3+ are deduced from the emission spectra at 4.2 K. Extra lines are also present at low temperature, which may be assigned to a fourth site. When the temperature increases, these extra lines disappear without energy change of other lines. This reversible phenomenon is not yet explained. Above 8 K, site to site energy transfer becomes effective. The electrostatic crystal field effects on the 7 F multiplet are also evaluated on the basis of the phenomenological crystal field theory.

The crystal structure and the luminescence properties of a new carbonate, Na3Eu(CO3)3, are presented. Na3Eu(CO3)3is orthorhombic, acentric,Ama2,Z=4;a=9.942(2) A,b=11.024(3) A,c=7.147(2) A;R=0.019,RW=0.051, 2374 unique reflections. The anionic subnetwork is built up from the stacking of “standing on edge” and “flat lying” carbonate layers into which Na+and Eu3+ions are inserted. The symmetry of the EuO9polyhedra isCs. The Eu3+luminescence technique confirms the presence of a unique low symmetry site for the rare earth atom. The electrostatic crystal field (cf) effects on the7Fmultiplet are evaluated on the basis of the phenomenological cf theory. The simulation usingC2vsymmetry for the rare earth atom gives good agreement between the calculated and experimental7F0–6energy level schemes (r.m.s. standard deviation 8.9 cm−1). Out of 49 theoretical7FJMStark components, 39 observed components are deduced from the absorption and emission spectra.

In the acidic stream (pH 2.2–4) of the Carnoules Pb-(Zn) mine, Gard, France, very high As contents (from 9 to 20%) can be accumulated as ferric arsenate and arsenate-sulphate precipitates in rapidly growing bacteria-made structures. The main bacterial forms are rod-shaped and sheathed, their sheath is made of Fe-As-rich material and is coated with ferric arsenate colloidal particles or may be partially included in authigenic crystals. Living forms ofThiobacillus-type bacteria have been recognized in the precipitates. The cyclic development of bacterial colonies alternating with sand deposition and erosive episodes results in the formation of As-rich ferruginous accretions. These laminated and dome-shaped bacterial constructions are similar to those of stromatolites. The extremely high contents of solute As in upstream flow (250 mg/1) are lowered by 2–3 order of magnitude downstream. Lead is also precipitated and concentrated in this FeAs-rich bacterial stromatolite (2500 ppm Pb). This accumulation and concentration of As and heavy metals via direct or induced microbial action limits pollution downflow. But seasonal storms could erode these FeAsPb-rich deposits and drastically increase pollution. The accumulation of ferric arsenate by bacterial stromatolites suggests that possible microbial remediation strategies may be used in acid mine drainage environments.

The luminescent properties of trivalent europium are analyzed in Na{sub 3}La{sub 2}(CO{sub 3}){sub 4}F:Eu{sup 3+} at 77 and 9 K and in BaEu(CO{sub 3}){sub 2}F at 77 K. In BaEu(CO{sub 3}){sub 2}F, the C{sub 3v} symmetry of the rare earth, deduced from the X ray diffraction study, is confirmed. In Na{sub 3}La{sub 2}(CO{sub 3}){sub 4}F, the spectroscopic technique shows that the order which appears at low temperature implies a single site for the rare earth with a C{sub 3v} or a C{sub 3} symmetry. For both compounds, the energy level scheme of the {sup 7}J{sub J} (J = 0-4) levels is well reproduced (weak RMS standard deviation) from six crystal field (cf) parameters consistent with the C{sub 3v} site symmetry.

The title compound, (C10H28N4)[AlF5(H2O)]2·2H2O, obtained solvothermally at 473 K and isostructural with the iron analogue, consists of isolated [AlF5(H2O)] octahedral anions and centrosymmetric tetraprotonated 1,4,8,11-tetra­aza­cyclo­decane (cyclamH44+) moieties connected by a network of N—H⋯X (X = O,F) hydrogen bonds. One water mol­ecule participates in the aluminium coordination, whereas the second water mol­ecule connects two neighbouring [AlF5(H2O)] octahedra via F1⋯H2WB—O2—H2WA⋯F3 bridges.

Dipotassium trizirconium oxide dodecafluoride, K2Zr3OF12, obtained by microwave-assisted hydro­thermal synthesis, crystallizes in the trigonal space group R\overline 3m (No. 166) and is isostructural with Tl2Zr3OF12. The structure was determined from X-ray powder diffraction data and is described in terms of fluorine- or oxy­gen-centered cation polyhedra and consists of [F12O2KZr6]∞ and [F12K3Zr6]∞ layers connected by Zr4+ cations.

The mixed fluoride series Fe1−xCrxF3 (0 ⩽ x ⩽ 1), synthesized by solid state reaction, crystallizes in space group R 3 c, identical to that of r-FeF3 and r-CrF3. Mossbauer spectroscopy gives clear evidence for six-fold coordinated trivalent high-spin iron ions and magnetic susceptibility for antiferromagnetic interactions. Both Mossbauer and susceptibility measurements have clearly revealed reentrance phenomena and magnetic spin-cluster structures; these properties which result from the presence of short-range spin correlations, are strongly dependent on the chromium content and on the synthesis conditions. By accounting for magnetic studies previously discussed on the Fe1−xGaxF3 series, we can confirm the paramagnetic Curie temperature value θp of r-FeF3 from the literature. In addition, one can conclude in favour of nonnegligible antiferromagnetic interactions between second next nearest neighbours: such a phenomenon agrees well with the presence of magnetic frustration in these compounds, experimentally observed through the values of | θp/TN |.

A new generation UV absorber is obtained by microwave-heating-assisted hydrothermal synthesis: [Hgua](2)·(Ti(5)O(5)F(12)). The structure of this hybrid titanium(IV) oxyfluoride is ab initio determined from powder X-ray data by combining a direct space method, Rietveld refinement [orthorhombic, Cmm2, a = 22.410(1) A, b = 11.191(1) A, c = 3.802(1) A], and density functional theory geometry optimization. The three-dimensional network is built up from infinite inorganic layers (∞)(Ti(5)O(5)F(12)) separated by guanidinium cations. The theoretical optical gap (3.2 eV) estimated from density of state calculations is in good agreement with the experimental gap (3.3 eV) obtained by UV-vis diffuse reflectivity. The optical absorption is mainly due to O(2p) → Ti(3d) and F(2p) → Ti(3d) transitions at higher energies. The refraction index is low in the visible range (n ≈ 1.9) compared to that of TiO(2) and, consequently, [Hgua](2)·(Ti(5)O(5)F(12)) shows a good transparency adapted to UV shielding. Under UV irradiation at 254 nm for 40 h, the white microcrystalline powder turns to light purple-gray. This color change is caused by the reduction of Ti(IV) to Ti(III), confirmed by magnetic measurements.

Two new zirconium (IV) fluorides, [H 2 dap ]·(Zr 2 F 10 )·H 2 O ( I ) and [H meam ] 2 ·(Zr 2 F 10 )·H 2 O ( II), are synthesized and characterized by X-ray diffraction, thermal techniques and NMR spectroscopy. I is triclinic ( P 1 ¯ ) with a = 6.805 (1) A, b = 8.361(1) A, and c = 11.853 (2) A, α = 94.54(1)°, β = 105.44(1)°, γ = 108.75(1)°. II is monoclinic ( C 2 /m ) with a = 10.340(6) A, b = 6.624(4) A, c = 8.758(6) A and β = 110.57(3)°. The structure determinations, performed from single crystal X-ray diffraction data, lead to the R/R w reliability factors 0.041/0.113 for I and 0.057/0.177 for II . The structures are built up from ZrF 7 and ZrF 8 units in I and only ZrF 8 units in II . The polyhedra share common edges in order to form two different ZrF 5 layers that are also found in [H 2 C 2 H 10 N 2 ]·(Zr 2 F 10 )·H 2 O and (H 3 O) 2 ·(Zr 2 F 10 )·H 2 O. On heating at 145 °C, [H 2 dap ]·(Zr 2 F 10 )·H 2 O decomposes to give the anhydrous form [H 2 dap ]·(Zr 2 F 10 ) that undergoes two successive phase transformations at 220 °C and 290 °C. 19 F NMR spectroscopy confirms the structural features of [H 2 dap ]·(Zr 2 F 10 )·H 2 O ( I ): two sets of three lines with a relative intensity 1:2:2 are attributed to five bridging fluorine atoms and to five nonbridging fluorine atoms. This spectroscopy demonstrates that a noticeable substitution of F − anions by hydroxyl OH − groups is excluded, together with the eventual substitution of H 2 O by HF molecules.

The luminescence of Eu 3+ in sodium europium hydroxyfluoride carbonate, Na 2 Eu(CO 3 )F 2.5 (OH) 0.5 , synthesized by hydrothermal growth at low temperature, is presented. The structure is orthorhombic and is built up from EuO 3 (F, OH) 6 polyhedra linked by triangular faces and edges. The emission spectrum consists of groups of sharp lines attributed to 5 D 0 → 7 F 0–4 transitions of one low symmetry site for Eu 3+ in agreement with the crystallographic analysis. 23 from 25 expected electronic levels for 7 F J ( J =0–4) manifolds are fitted by the phenomenological crystal field parameters in the approaching C 2v point symmetry. The simulation is achieved with very good root mean square ( rms ) deviation of 5.3 cm −1 . The crystal field strength parameter, N v , is weak ( N v =1652). Satellite vibronics of carbonate groups coupled to electronic transitions are also observed.

Nd2Gd2O3F6 was prepared by solid-solid reaction between 1 mol Nd2O3 and 2 mol GdF3 at 1100°C for 3 h in an argon flow. X-ray powder diffraction-Rietveld analysis revealed that the crystal system of Nd2Gd2O3F6 was assigned to the monoclinic structure with the cell parameters; a0=0.3973 nm, b0=1.123 nm, c0=0.5595 nm and β=134.75°. The ionic arrangement was suggested to be slightly disordered in the Nd2Gd2O3F6 crystal lattice in contrast to in the Nd2Eu2O3F6 with the high ordered ionic arrangement. It was assumed that the slightly disordered ionic arrangement in Nd2Gd2O3F6 resulted in the smaller electrical conductivity of Nd2Gd2O3F6 (0.2 S m−1 at 600°C) than that of Nd2Eu2O3F6 (5.4 S m−1 at 600°C). Nd2Gd2O3F6 was confirmed to be stable up to ca. 650°C in air, and converted into NdGdO3 (monoclinic) at ca. 1350°C through the metastable state of NdGdO2F2 (rhombohedral) at ca. 850°C by the pyro-hydrolysis. The rate of pyro-hydrolysis was analyzed as the tarnishing reaction represented by the surface reaction control. The electrical conductivity largely declined with decreasing fluorine content due to the pyro-hydrolysis. This cause was considered due to disappearance of the vacant sites for oxide ion migration according to change in the crystal structure.

The synthesis and the crystal structure of two isostructural fluoride carbonates are presented. BaZn(CO3)F2 and BaMn(CO3)F2, obtained by hydrothermal growth (T=650 °C, P=210 MPa, t=48 h), are hexagonal, P63/m, Z=2, with a=4.8523(8), c=9.854(1) A for BaZn(CO3)F2 and a=4.9120(8), c=9.919(1) A for BaMn(CO3)F2. Their structures are solved by X-ray diffraction; the reliability factors are R/Rw=0.016/0.039 and R/Rw=0.019/0.046 for BaZn(CO3)F2 and BaMn(CO3)F2, respectively. The 3D network is built up from [MO3F2] (M=Zn, Mn) polyhedra and CO2−3 groups, which lie in (0 0 0 1) planes. The structures, which derive from the structure of KPu(CO3)O2, are very similar to the structures of two fluoride borates, BaAl(BO3)F2 and BaGa(BO3)F2, recently published.

Several solid solutions of the mixed fluoride series Fe1−xGaxF3 with 0 ⩽ x ⩽ 1 were synthesized by solid state reaction. They crystallize in space group R3c, identical to that of r-GaF3. The presence of six-fold coordinated trivalent high-spin iron atoms is evidenced by Mossbauer spectroscopy. The magnetic ordering temperatures decrease linearly with increasing gallium content and vanish at the extrapolated value 1 − x = 0.31, close to the theoretical percolation threshold. High field Mossbauer spectroscopy and susceptibility measurements give a clear evidence for antiferromagnetic interactions.

Hydrothermal synthesis starting from Na0.46VOPO4 · 1.58H2O leads to a new mixed-valence sodium vanadium phosphate: Na2.44V4P4O17(OH) (orthorhombic, space group Pnma; Z = 4; a = 13.723(5) A, b = 6.314(2) A, c = 16.139(4) A; R = 0.032 for 2659 reflections). In this phase, the interconnection of three complex types of infinite chains, built from VO6 octahedra and PO4 tetrahedra, sometimes edgeshared, defines tunnels partly occupied by a portion of the sodium atoms.

Phase stability domains in the Na 2 CO 3 YF 3 H 2 O system are investigated in sub-critical hydrothermal conditions with microwave heating in Teflon lined autoclaves. At T = 190 °C , t = 1 h and P = 11 × 10 5 Pa , five phases are obtained for [YF 3 ] ⩽ 1.0 M and [ Na + ] / [ Y 3 + ] 30 : NaY(CO 3 )F 2 , Na 2 Y(CO 3 )F 3 , Na 3 Y(CO 3 ) 2 F 2 , Na 2 Y(CO 3 ) 2 (OH,F), and Na 4 Y(CO 3 ) 2 F 3 ⋅H 2 O. All phases are characterized by powder or single crystal X-ray diffraction, thermogravimetric or chemical analyses. NaY(CO 3 )F 2 is the rare mineral horvathite. Na 2 Y(CO 3 )F 3 , and Na 2 Y(CO 3 ) 2 (OH,F) are isostructural with Na 2 Eu(CO 3 )F 3 and Na 2 Yb(CO 3 ) 2 F, respectively; the Na 3 Y(CO 3 ) 2 F 2 and Na 4 Y(CO 3 ) 2 F 3 ⋅H 2 O phases were still unknown. The average structure of Na 3 Y(CO 3 ) 2 F 2 is determined in the monoclinic P2 1 /n space group with a = 7.047 ( 6 ) A , b = 14.840 ( 3 ) A , c = 7.192 ( 3 ) A , β = 113.32 ( 5 ) ° ; V = 690.7 ( 6 ) A 3 ; Z = 4 ; R = 0.076 and R w = 0.278 (1965 unique reflections). The structure is built up from ∞ [NaY(CO 3 ) 2 F 2 ] layers; Y 3+ and Na + cations are disordered in these (010) layers which are separated by other Na + cations. The structures of Na 3 Yb(CO 3 ) 2 F 2 , previously described, and Na 3 Y(CO 3 ) 2 F 2 are correlated. Disorder between sodium and ytterbium or yttrium occurs and it is shown by transmission electron microscopy that both structures are noncommensurate.

Using tris(2-aminoethyl)amine [(C 2 H 4 NH 2 ) 3 N] ( tren ) as a template, two new tantalum fluorides are obtained by slow evaporation of solutions: [H 4 tren ](TaF 7 ) 2 · H 2 O ( I ) and [H 4 tren ](TaF 7 ) 2 ( II ). The structure determinations are performed by single crystal X-ray technique. Structures of I and II are built up from isolated TaF 7 distorted monocapped trigonal prisms or pentagonal bipyramids; charge balance is achieved by tetraprotonated [H 4 tren ] 4+ cations which possess a “scorpion” configuration. In I and II , TaF 7 polyhedra, connected by hydrogen bonds with water molecules in I , lie in corrugated layers; hydrogen bond networks ensure the cohesion between these layers and [H 4 tren ] 4+ cations.

Crystalline samples of Na2M2(BO3)2O ( M = Al , Ga ), Na1.5Ca0.25Ga2(BO3)2O and NaCa0.5Ga2(BO3)2O are prepared by conventional high temperature solid state synthesis technique. Temperature dependent impedance spectroscopy measurements are performed. For Na2Al2(BO3)2O and Na2Ga2(BO3)2O, high and low temperature regimes have to be distinguished. Only one regime is observed for the calcium-substituted samples Na1.5Ca0.25Ga2(BO3)2O and NaCa0.5Ga2(BO3)2O.

Weathering of the As-rich pyrite-rich tailings of the abandoned mining site of Carnoulès (southeastern France) results in the formation of acid waters heavily loaded with arsenic. Dissolved arsenic present in the seepage waters precipitates within a few meters from the bottom of the tailing dam in the presence of microorganisms. An Acidithiobacillus ferrooxidans strain, referred to as CC1, was isolated from the effluents. This strain was able to remove arsenic from a defined synthetic medium only when grown on ferrous iron. This A. ferrooxidans strain did not oxidize arsenite to arsenate directly or indirectly. Strain CC1 precipitated arsenic unexpectedly as arsenite but not arsenate, with ferric iron produced by its energy metabolism. Furthermore, arsenite was almost not found adsorbed on jarosite but associated with a poorly ordered schwertmannite. Arsenate is known to efficiently precipitate with ferric iron and sulfate in the form of more or less ordered schwertmannite, depending on the sulfur-to-arsenic ratio. Our data demonstrate that the coprecipitation of arsenite with schwertmannite also appears as a potential mechanism of arsenite removal in heavily contaminated acid waters. The removal of arsenite by coprecipitation with ferric iron appears to be a common property of the A. ferrooxidans species, as such a feature was observed with one private and three collection strains, one of which was the type strain.

International audience; Aims: To isolate, identify, and characterize heterotrophic bacteria in acid-mine drainage that mediate oxidation of As(III). Methods and Results: Samples of acid-mine drainage were collected over a period of 14 months. Heterotrophic and non-obligatory acidophilic bacteria in the samples were cultured on a solid medium (pH 7AE0-7AE2), and three strains were isolated. The three different strains belong to the genus Thiomonas, and have more than 99% homology with the group Ynys1. Culturing in mineral media demonstrated that the isolated strains used thiosulphate as an energy source, and oxidized iron in the presence of thiosulphate. However, none of the strains were able to oxidize arsenic in the presence of thiosulphate, nor could they use iron or arsenic alone as an energy source. In vitro experiments demonstrated that two of the Thiomonas strains were able to oxidize more than 90% of the As(III) present in the acid-mine drainage, whereas no abiotic oxidation of arsenic occurred. Conclusions: Two strains of newly identified Thiomonas sp. found in acid-mine drainage are capable of oxidizing arsenic. Significance and Impact of Study: These results represent the first reported oxidation of arsenic by Thiomonas sp. Biologically mediated oxidation and subsequent immobilization of arsenic is of great interest for the remediation of contaminated mine sites.

International audience; The acid waters (pH=2.73–3.37) originating from the Carnoulès mine tailings contain high dissolved concentrations of arsenic (1–3.5 mmol l−1) and iron (20–40 mmol l−1). At the outlet, arsenite predominates. During the first 30 m of downflow, 20–60% is removed by coprecipitation with Fe(III). This process results from bacterially mediated As- and Fe-oxidation. The precipitation rates in the creek depend on the oxygen concentration in spring water and are lower during the dry summer period when the anoxic character of the spring water inhibits the activity of oxidizing bacteria. Ex situ experiments show that the presence of bacteria-rich precipitates increases the As- and Fe-removal rates. Three strains of bacteria promoting the oxidation of As have been isolated, and two of them have the characteristics of Thiomonas ynys1. The third strain, which is not identified yet, also catalyzes the oxidation of Fe.

International audience; In the acid stream (pH 2.5–4.7) originating from the Carnoulès mine tailings, the acidophilic protozoan Euglena mutabilis grows with extremely high sulfate (1.9–4.9 g/l), iron (0.7–1.7 g/l) and arsenic concentrations (0.08–0.26 g/l). Strong variations in flow rate and high sulfate concentrations (up to 4.9 g/l) have been registered in early winter and might be the reason for the reduction in cell number of the protozoan from October to December 2001. No relation was established between arsenic concentration and/or speciation and abundance of the protozoan in the stream. Arsenite, which is the most toxic form, predominates in water. The oxidation of arsenite to arsenate occurred within a few days in laboratory experiments when E. mutabilis was present in Reigous Creek water and synthetic As(III)-rich culture medium. Methylated compounds (MMA, DMA) were not identified in the culture media. The protozoan bioaccumulated As in the cell (336±112 μg As/g dry wt.) as inorganic arsenite (105±52 μg As/g dry wt.) and arsenate (231±112 μg As/g dry wt.). Adsorption of As at the cell surface reached 57 mg/g dry wt. in the As(V) form for E. mutabilis grown in 250 mg/l As(III) synthetic medium. Both intracellular accumulation and adsorption at the cell surface increased for increasing As(III) concentration in the medium but the concentration factor in the cell relative to soluble As decreased.