The capacity of several additives, i.e., lime, Thomas phosphate basic slag (TBS), hydrous iron oxides (HFO), hydrous manganese oxides (HMO), and Beringite, added to soil to fix Cd or Pb, was evaluated using two pot experiments in tandem with soil extractions. Three soils from France with metal contents ranging from 0.17 to 108 mg Cd kg−1 soil dry weight (DW) and 47 to 1112 mg Pb kg−1 soil DW were studied. Metal sources were: sludge‐borne metals (Soil A), fallout from a smelter (Soil B), and emission from a tetraethyl Pb production facility (Soil C). Ryegrass (Lolium spp.) or tobacco (Nicotiana tabacum L.) shoots were harvested. The addition of HMO decreased to a maximum extent Cd in ryegrass and tobacco for Soils A and B, but did not suppress the differences in Cd uptake between the two plant species. Use of HMO reduced Pb concentrations only in ryegrass shoots. Thomas phosphate basic slag lowered Pb bioavailability in Soils B and C. The addition of HMO into Soils A and B reduced Cd concentrations in water, 0.1 M Ca(NO3)2, or 0.43 M acetic acid (HOAc) extracts, but not in 0.05 M EDTA pH 7 extracts. Water and sequential extractions were employed on Soil C: HMO caused the most reduction in Pb water‐soluble and HOAc‐extractable fractions, and rendered Pb less extractable with H2O2 and more with HONH3Cl. The decrease of Cd‐ and Pb‐soluble fractions was reflected in their suppressed bioavailability. Among the screened additives, HMO exhibited a most promising potential to reduce either Cd or Pb transfer from soil to soil solution or their entry into the food chain via plant uptake. This material would be promising for in‐situ remediation technologies geared to restore Cd‐ and Pb‐contaminated soils. However, little is known about the kinetics and persistence of this chemical under field conditions.
Humic substances are known to play a key role in the immobilisation of metals in soils. The main complexing ligands that are supposed to interact with metals are carboxylic and phenolic. The complexation mechanism of zinc by two natural humic acids (T and F) was studied by EXAFS spectroscopy at the Zn-K edge over a wide range of zinc concentration. The ligation mechanism of Zn was found to vary with the metal concentration and the nature of the humic acid. As Zn concentration is raised, the amplitude of EXAFS spectra decreases, which is interpreted as an increased distribution of Iigand sites. At low Zn concentration (300-5000 mgKg), zinc forms inner sphere complexes in octahedral coordination for T humic acid, and in octahedral and tetrahedral coordinations for F humic acid. At intermediate Zn concentration (32 gKg), a large number of different sites are observed and only octahedral coordination is detected. At high Zn concentration (500 glKg), most Zn forms outer sphere complexes. The difference of complexation mechanisms between humic acids F and T can be related to differences in their structure as indicated by 1 3~-~~~ spectroscopy.
The astronomical and geodetic observatory OCA, located on the karst plateau of Calern (Caussols, France), has been monitoring earth deformation for several years. Two long baseline tiltmeters have been installed in a shaft in 2007, along with classical hydrogeological monitoring tools in order to investigate the relationship between current karst deformation and hydrology. Dye tests have shown that the plateau is drained towards the East, to the spring of Bramafam, except for its Western third. Karst tilting, as recorded by the tiltmeters, is linked to rainfall events. These instruments bring additional information to characterize different reservoirs: the deep karst aquifer of Bramafan with high amplitude oscillations of its water table, up to 100 m, the perched aquifer of Moustiques shaft whose response is attenuated, and several slope aquifers with reduced oscillations (Fontaniers, Castel Bon Pré). Tilt deformation reaches 8 µrad with a definite orientation between N90°E and N100°E. The best correlation between hydrology and tilts is observed for the deep aquifers. If the first autumn rainfall is ineffective on tilt, it recharges the epikarst and refills the reserves. The winter rains cause the water to flush towards the eastern deep aquifer and provokes a quick tilting of the plateau. Finally, the long term variations in tilt and water table show a very good correlation The relationship between current hydrological deformations and tectonics is also analyzed; broken and shifted speleothems in the shafts indicate a general shift of the plateau towards the south.
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