Marc Leblanc

The potential of Thlaspi caerulescens for phytoremediation of contaminated soils

Uptake of Cd, Zn, Pb and Mn by the hyperaccumulator Thlaspi caerulescens was studied by pot trials in plant growth units and in populations of wild plants growing over Pb/Zn base-metal mine wastes at Les Malines in the south of France. The pot trials utilised metal-contaminated soils from Auby in the Lille area. Zinc and Cd concentrations in wild plants averaged 1.16% and 0.16% (dry weight) respectively. The unfertilised biomass of the plants was 2.6 t/ha. A single fertilised crop with the above metal content could remove 60 kg of Zn and 8.4 kg Cd per hectare. Experiments with pot-grown and wild plants showed that metal concentrations (dry weight basis) were up to 1% Zn (4% Zn in the soil) and just over 0.1% Cd (0.02% Cd in the soil). The metal content of the plants was correlated strongly with the plant-available fraction in the soils as measured by extraction with ammonium acetate and was inversely correlated with pH. Bioaccumulation coefficients (plant/soil metal concentration quotients) were in general higher for Cd than for Zn except at low metal concentrations in the soil. There was a tendency for these coefficients to increase with decreasing metal concentrations in the soil. It is proposed that phytoremediation using Thlaspi caerulescens would be entirely feasible for low levels of Cd where only a single crop would be needed to halve a Cd content of 10 μg/g in the soil. It will never be possible to remediate elevated Zn concentrations within an economic time frame (<10 yr) because of the lower bioaccumulation coefficient for this element coupled with the much higher Zn content of the soils.

Phytomining for nickel, thallium and gold

The technique of phytomining involves growing a crop of a metal-hyperaccumulating plant species, harvesting the biomass and burning it to produce a bio-ore. The first phytomining experiments were carried out in California using the Ni-hyperaccumulator Streptanthus polygaloides and it was found that a yield of 100 kg=ha of sulphur-free Ni could be produced. We have used the same technique to test the phytomining potential of the Ni-hyperaccumulators Alyssum bertolonii from Italy and Berkheya coddii from South Africa. The effect of different fertiliser treatments on growth of Alyssum bertolonii was established in situ in Tuscany and showed that the biomass of the plant could be increased by a factor of nearly 3 (4.5 t=ha to 12 t=ha) without significant loss of the Ni concentration (7600 mg=kg) in the plant. Analogous experiments have been carried out on Berkheya coddii where a biomass yield of over 20 t=ha can readily be achieved though the Ni concentration is not as high as in A. bertolonii. The total yield is, however, much greater. We have also been able to induce plants to hyperaccumulate Au by adding ammonium thiocyanate to the substrate. Up to 57 mg=kg Au (dry mass) could be accumulated by Indian mustard (Brassica juncea). Unusual hyperaccumulation (>500 mg=kg dry mass) of Tl has been determined in Iberis intermedia and Biscutella laevigata (Brassicaceae) from southern France. The Iberis contained up to 0.4% Tl (4000 mg=kg) in the whole-plant dry matter and the Biscutella over 1.5%. This unusually high accumulation of Tl has significance for animal and human health, phytoremediation of contaminated soils, and phytomining for Tl. We calculate that using Iberis, a net return of

Bacterial immobilization and oxidation of arsenic in acid mine drainage (Carnoulès creek, France).

US 1200=ha (twice the return from a crop of wheat) would be possible with a biomass yield of 10 t=ha containing 0.08% Tl in dry matter. The break-even point (net yield of

Metal biogeochemistry in the Tinto-Odiel rivers (Southern Spain) and in the Gulf of Cadiz: A synthesis of the results of TOROS project

US 500=ha) would require 170 mg=kg (0.017%) Tl in dry matter. A model of a phytomining operation and its economics is presented and its advantages and disadvantages discussed.

Chromite crystallization in a multicellular magma flow : Evidence, from a chromitite dike in the Oman ophiolite

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.

Immobilization of Arsenite and Ferric Iron by Acidithiobacillus ferrooxidans and Its Relevance to Acid Mine Drainage

TOROS (Tinto-Odiel-River-Ocean Study) has been studying the biogeochemical processes which control metals and nutrients cycling in the mixing zone of the Tinto and Odiel rivers (SW Spain) and has established the fate of metals in the Gulf of Cadiz in relation to hydrodynamics and biological activity. The Tinto and Odiel rivers are small, with a combined mean discharge of 18m 3/s. They drain the largest sulphide mineralisation in the world. Predominantly, Zn-Cu-Pb mineralisation has been worked since 2500yr BC. The estuarine zone includes both an extensive area of salt marsh and an intensively industrialised urban area. As a consequence of pyrite oxidation, the Tinto and Odiel rivers are strongly acidic (pH<3) with extremely high and variable metal concentrations. Transition metals are poorly removed from the water column in the mixing zone. Moreover, drainage from large phosphogypsum waste deposits contributes to As, Hg, U and phosphate contamination of the estuary. The collapse of the tailing reservoir at los Frailes in 1998 had not impacted the chemistry of the coastal waters up to 6 months later. A large plume of metal-rich waters due to the Tinto and Odiel discharges occurs along the coast of the Gulf of Cadiz. This plume affects seasonally the Atlantic inflow through the Strait of Gibraltar. The dispersion of the metal discharges has been simulated by injection of a tracer in the 3-D hydrodynamical model. Both model and field study clearly show the inflow of metal contaminated Spanish Shelf Water through the Strait of Gibraltar.

Platinum-Group Elements and Gold in Ophiolitic Complexes: Distribution and Fractionation from Mantle to Oceanic Floor

The investigated chromitite dike is located at the top of an upwelling mantle structure of the Oman ophiolite (Maqsad diapir), in undeformed dunites displaying evidence for magma impregnation and circulation, just below the paleo-ridge axis. The chromitite dike is undeformed, its shape is that of an upward widening tube. It exhibits an internal layering which is roughly perpendicular to the cavity axis and comprises a vertical succession of four main layers showing a graded-bedding. Chromitite magmatic structures are beautifully preserved and result from a progressive crystallization from small euhedral crystals to wide octahedron-shaped nodules; dissolution textures provide evidence for late magmatic desequilibrium; sedimentation structures include flattening of the largest nodules. The silicate matrix comprises poikilitic forsterite and a locally abundant association of primary pargasite and plagioclase and alteration minerals (vesuvianite-chlorite-dolomite); pargasite inclusions are very abundant in the chromite. Chromite composition changes from one layer to the other and from core to rim in the chromite nodules (chromium decreases and titanium increases); Ti contents are generally high (0.4 to 0.8 wt.% TiO2) with respect to podiform chromites. Platinum-group elements are not abundant but they show a strong fractionation at the scale of the orebody and of the main graded-bedded layers (Pd/Ir ratio varies from 0.5 to 11.5). REE patterns of chromitite parallel to those of gabbros and furthermore display a sea water related hydrothermal alteration (Ce negative anomaly). n nThe chromitite dike of Maqsad provides evidence for the crystallization of chromitite bodies in subvertical magma conduits below oceanic ridges; it corroborates the model of Cassard et al. (1981) and Lago et al. (1982) concerning the formation of chromitite pods in ophiolites which were later deformed and transposed into the horizontal plane due to the plastic flow prevailing away from the paleo-axial zone. Layering and chromite compositional variations are ascribed to a multicellular convective system segregating various stocks of chromite particles either in the upwelling flow of fresh magma or in the convective cells of fractionated residual magma in the confined part of the cavity. The estimated life-time for the magma influx is very short (<2 months). The parent-magma was probably of MORB-type and already fractionated (Ti-rich and PGE-poor), which is consistent with the strong evidence of magma-peridotite interactions in the core of the Maqsad diapir. Hydrous fluids were present during chromite crystallization (pargasite inclusions) suggesting that fluid-rich melts occur in the upper mantle.

Impact of Los Frailes mine spill on riverine, estuarine and coastal waters in southern Spain

ABSTRACT 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.

Light Rare Earth Elements enrichment in an acidic mine lake (Lusatia, Germany)

This review paper attempts to discuss the distribution of noble metals in ophiolitic complexes and suggests new targets for exploration.

Biogeochemical studies of metal-tolerant plants from southern Morocco

On April 25, 1998, a spill at the Los Frailes mine in southern Spain resulted in a very high input of metals (including Ag, As, Cd, Cu, Fe, Pb, Tl and Zn) into the river Guadiamar. Calculations indicate that the discharges into the Guadiamar of Cu (5100t), Pb (24,700t), Zn (26,200t) and Ag (138t, based on mud only) were higher than the annual production by the Los Frailes mine for Ag and Pb, and ca. two times less for Cu and Zn. For many metals, the increase in concentration in the affected river (Guadiamar), 2days after the initial discharge, was by several orders of magnitude. However, 6months after the incident, no evidence of the spill could be observed in the plume of the river (Guadalquivir) which discharged the mine waters into the coastal waters of the Gulf of Cadiz. This observation can possibly be explained by low rainfall, natural metal removal processes in the river and estuarine environments and by human interventions. Copyright (C) 1999 Elsevier Science Ltd. On April 25, 1998, a spill at the Los Frailes mine in southern Spain resulted in a very high input of metals (including Ag, As, Cd, Cu, Fe, Pb, Tl and Zn) into the river Guadiamar. Calculations indicate that the discharges into the Guadiamar of Cu (5100 t), Pb (24,700 t), Zn (26,200 t) and Ag (138 t, based on mud only) were higher than the annual production by the Los Frailes mine for Ag and Pb, and ca. two times less for Cu and Zn. For many metals, the increase in concentration in the affected river (Guadiamar), 2 days after the initial discharge, was by several orders of magnitude. However, 6 months after the incident, no evidence of the spill could be observed in the plume of the river (Guadalquivir) which discharged the mine waters into the coastal waters of the Gulf of Cadiz. This observation can possibly be explained by low rainfall, natural metal removal processes in the river and estuarine environments and by human interventions.