Fulvic acids oxide

Klapper, L., D. M. McKnight, J. R. Fulton, E. L. Blunt-Harris, K. P. Nevin, D. R. Lovely, and P. G. Hatcher. 2002. Fulvic acid oxidation state detection using fluorescence spectroscopy. Environmental Science Technology, in press. 

De Haan (1974, 1977) studied the effect of fulvic acids from Tjeukemeer on the growth of Pseudomonas and an Arthrobacter species. He found that fulvic acids in the culture medium had a stimulatory effect on a species of Pseudomonas which was explained in terms of the co-metabolism of fulvic acids. De Haan suggested that the same enzyme system is involved in both the lactic acid and the fulvic acid oxidation. This may be valid if the fulvic acid molecules are largely aliphatic, which has recently been shown for Tjeukemeer fulvic acids (De Haan et al., 1979). 

Klapper, L., Mcknight, D.M., Fulton, J.R., Blunt-Harris, E.L., Nevin, K.P., Lovley, D.R., and Hatcher, RG. (2002). Fulvic acid oxidation state detection using fluorescence spectroscopy. Environ. Sci. TechnoL, 36(14), 3170-3175. 

In this work a novel five-step leaching scheme for HM has been developed addressing exchangeable, acid soluble (carbonate), easily reducible (bound to Mn oxides), easily oxidizable (bound to humic and fulvic acids), and moderately reducible (bound to amorphous Ee oxides) fractions extractable by 0.05 M Ca(N03), 0.43 M CH3COOH, 0.1 M NH,OH-HCl (non-acidified), 0.1 M K/,03 (pH 11), and 0.1 M (NH4),C,04 (pH 3), respectively. The sequence of extractants was chosen according to recent studies on the selectivity of leachants toward dissolved phases of soils. 

The Table shows a great spread in Kd-values even at the same location. This is due to the fact that the environmental conditions influence the partition of plutonium species between different valency states and complexes. For the different actinides, it is found that the Kd-values under otherwise identical conditions (e.g. for the uptake of plutonium on geologic materials or in organisms) decrease in the order Pu>Am>U>Np (15). Because neptunium is usually pentavalent, uranium hexavalent and americium trivalent, while plutonium in natural systems is mainly tetravalent, it is clear from the actinide homologue properties that the oxidation state of plutonium will affect the observed Kd-value. The oxidation state of plutonium depends on the redox potential (Eh-value) of the ground water and its content of oxidants or reductants. It is also found that natural ligands like C032- and fulvic acids, which complex plutonium (see next section), also influence the Kd-value. 

This organism is able to oxidize acetate to CO2 under anaerobic conditions in the presence of Fe(III). A study of the intermediate role of humic and fulvic acids used ESR to detect and quantify free radicals produced from oxidized humic acids by cells of G. metallireducens in the presence of acetate. There was a substantial increase in the radical concentration after incubation with the cells, and it was plausibly suggested that these were semiquinones produced from quinone entities in the humic and fulvic structures (Scott et al. 1998). 

The surfaces of sorbent materials, e.g., oxide particles in soil, are often less complex than the exterior of protein molecules. However, if such particles are (partly) covered with organic materials, e.g., humic acids and/or fulvic acids, their surface chemistry may be very complex as well. Also, surfaces of biological structures, such as those of plant roots, may be heterogeneous. 

So-called "dissolved" iron(III) consists mainly of colloidal Fe(III) oxides stabilized by humic or fulvic acids Soil Colloids... 

Both humic acids and fulvic acids have a strong affinity for particulate and crystalline substances possessing oxygen atoms at their surfaces and they have been reported to bring about the dissolution of iron phosphate, calcium phosphate (61), uranium dioxide (65), hydrated magnesium alumino-silicates (66) and limonite, a complex mixture of hydrated ferric oxides (67). 

Soil anomalies present in the raw element data from a variety of extractions are attributed to the effects of metal scavenging onto the surfaces of either Fe oxides or humic/fulvic acids. These metal... 

Bjorklund et al. (2001) showed with ellipsometry that fulvic acid adsorbed on a thin Fe oxide film (on an Fe substrate) could be photodesorbed into aqueous solution upon illumination with light of wavelengths up to 546 nm. 

In view of its importance, reductive dissolution of Fe oxides has been widely studied. Reductants investigated include dithionite, thioglycolic acid, thiocyanate, hydrazine, ascorbic acid, hydroquinone, H2S, H2, Fe ", tris (picolinato) V", fulvic acid, fructose, sucrose and biomass/bacteria (Tab. 12.3). Under the appropriate conditions, reductive dissolution may also be effected photochemically. As with protonation, the extent of reduction may be strongly influenced by ligand and proton adsorption on the oxide surface. 

Colloid concentrations drop to almost zero at I>0.2mol/L. The same trend is found for humic/fulvic acids represented in Fig. 5b as dissolved organic carbon (DOC). The studies, however, also make clear that the variation of the chemical conditions with the creation of oxidizing conditions by, for example, radiolysis may temporarily generate high colloid populations even under conditions of high ionic strength. 

Faust, B. C., and J. Hoigne, Sensitized photo-oxidation of alkylphenols by fulvic acid and natural water , Environ. Sci. Technol., 21,957-964(1987). 

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