Fulvic acid studies

Saar, R., and Weber, J. H. (1980). Metal-ion complexation of fulvic-acids studied by fluorescence. Abstr. Papers Am. Chem. Soc. 180, 62-envr. 

Ephraim J.H., Mathuthu A.S., Marinsky J.A. (1994), Calcium binding by fulvic acids studied by an ion selective electrode and an ultrafiltration method. Humic Substances in the Global Environment and Implications on Human Health, (Ed. N. Senesi, T.M. hliano), Elsevier Science, 1125-1130. 

To determine mole ratios, it is necessary to know the average molecular weight of fulvic acid. For the fulvic acid studied by Schnitzer the average molecular weight was 670. 

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 availability of aniline has made possible a direct study of the reactions of aniline with humic and fulvic acids (Thom et al. 1996), and the detection of resonances attributed to anilinoquinone, imines, and N-heterocyclic compounds are fully consistent with reactions involving quinone and ketone groups. 

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). 

Evidence for the association of U with humic acids has been documented elsewhere. Dearlove et al. (1991) showed that U concentrated by ultrafiltration techniques from organic-rich groundwater samples were associated with humic colloids. Humic and fulvic acids have been shown to strongly complex U. Lienert et al. (1994) modeled the distribution of U species in the Glatt River and concluded that U-humate complexes become important at pH <6.8. These results reinforce the conclusions in the estuarine studies that U humate and fulvate complexes may account for the association of U with colloids. 

Wilson et al. [2] carried out a compositional and solid state nuclear magnetic resonance (NMR) spectroscopic study of humic and fulvic acid and fractions present in soil organic matter. 

At present, soil derived humic matter and fulvic acids extracted from freshwater are available commercially and are commonly used to test techniques for DOM detection and also used as model compounds for trace metal chelation studies. The results obtained using these model compounds are frequently extrapolated to the natural environment and measurements on "real" samples provide evidence that this DOM is a good model compound. In the past, some investigators also made available organic matter isolated from marine environments using C18 resins. While these compounds come from aquatic sources, this isolation technique is chemically selective and isolates only a small percentage of oceanic DOM. Reference materials are not currently available for these compounds, which inhibits study of the role they play in a variety of oceanographic processes. 

Schnitzer and Hansen (59) have studied the sequestering properties of fulvic acid at low pH and observed the following order ... 

A fractionation procedure has been established and widely applied to studies of humic materials [42-44]. The procedure begins with natural OM (i.e., humus) and uses an aqueous basic solution (e.g., 0.1-0.5 mol/1 NaOH and Na2C03) to solubilize a fraction of the OM. The basic extract is then acidified which causes a precipitate to form, i.e., humic acids (HA). The fraction, which remains in solution, is called fulvic acids (FA). Humin is the name given to the insoluble organic fraction that remains after extraction of humic and fulvic acids. At nearneutral pH (pH 5 - 8), which is characteristic of most natural water, the FA are the most water soluble of these three fractions. HA are somewhat less soluble, with their solubility increasing as the pH increases. Humin is insoluble at all pH values. 

Recently, Burkhard (2000) reviewed contaminant sorption by dissolved organic matter. Using several hundreds of UCC-water partition coefficients (A doc) reported in these studies, he found that UCC-water partition coefficients for naturally occurring DOC (humic and fulvic acids, sediment pore water, soil pore water, groundwater, and surface water) was best described by... 

Using the aforementioned methodology, the electrode reaction of Mo(VI) has been studied in the presence of phenanthrohne and an excess of fulvic acids [105]. Both ligands exhibit a synergetic effect toward adsorption of the mixed complex of... 

Photolytic. Mathew and Khan (1996) studied the photolysis of metolachlor in water in the presence of kaolinite, montmorillonite, and goethite and fulvic acid under neutral and acidic conditions at 22 °C. Metolachlor degraded in all the treatments at both pH conditions. The rate of photolysis and degradation products formed was dependent on the duration of UV exposure, the initial pH of the solution, and the composition of the suspended/dissolved material. The following photoproducts identified included 2-hydroxy-A-(2-ethyl-6-methylphenyl)-A-(2-methoxy-l-meth-ylethyl)acetamide, 4-(2-ethyl-6-methylphenyl)-5-methyl-3-morpholine (major product forming at 74-84% yield), 8-ethyl-3-hydroxy-A-(2-methoxy-l-methylethyl)-2-oxo-l,2,3,4-tetrahydroquino-line, 2-chloro-A -(2-(l-hydroxyethyl)-6-methylphenyl)-7V-(2-hydroxy-l-methylethyl)acetamide, and 2-chloro-A -(2-ethyl-6-hydroxymethylphenyl)-A-(2-methoxy-l-methylethyl)acetamide. 

Kinetics and mechanisms of complex formation have been reviewed, with particular attention to the inherent Fe +aq + L vs. FeOH +aq + HL proton ambiguity. Table 11 contains a selection of rate constants and activation volumes for complex formation reactions from Fe " "aq and from FeOH +aq, illustrating the mechanistic difference between 4 for the former and 4 for the latter. Further kinetic details and discussion may be obtained from earlier publications and from those on reaction with azide, with cysteine, " with octane-and nonane-2,4-diones, with 2-acetylcyclopentanone, with fulvic acid, and with acethydroxamate and with desferrioxamine. For the last two systems the various component forward and reverse reactions were studied, with values given for k and K A/7 and A5, A/7° and A5 ° AF and AF°. Activation volumes are reported and consequences of the proton ambiguity discussed in relation to the reaction with azide. For the reactions of FeOH " aq with the salicylate and oxalate complexes d5-[Co(en)2(NH3)(sal)] ", [Co(tetraen)(sal)] " (tetraen = tetraethylenepentamine), and [Co(NH3)5(C204H)] both formation and dissociation are retarded in anionic micelles. 

The GC/MS study of methylated fulvic acid showed the presence of -hydroxybenzoic acid (ff 166), vanillic acid (Nr " 196), a methyldihydroxybenzoic acid (M " 210), coumaric acid (M+ 192), syringic acid (M" " 226), caffeic acid (fT " 222), ferulic acid (M" " 222), and stearic acid (M" " 298). The same compounds were present in humic acid, along with palmitic acid (M" " 270). The presence of these compounds was confirmed by TLC, using standard compounds. 

In another study, maximum adsorption of fulvic acid from a podzol B horizon by goethite was found to lie at ca. 0.6 0.3 and 0.05 mg m at pH 4 7 and 10, respectively and this was successfully described with the CD-MUSIC model (Films et al.,... 

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. 

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