Binding to fulvic acid

Data Treatments for Relating Metal-Ion Binding to Fulvic Acid as Measured by Fluorescence Spectroscopy... 

HAYS ET AL. Relating MetaUIon Binding to Fulvic Acid... 

Hays, M.D., Ryan, D.K., Pennell, S. and Ventry-Milenkovic, L. 1996 Data treatments for relating metal ion binding to fulvic acid as measured by fluorescence spectroscopy. Preceding paper in this volume. 

Figure 4.6. Fourier transform infrared spectra of humic acids (HAs) and fulvic acids (FAs) isolated from pig slurry (PS), unamended soil (PSO, and soils amended with 90 and 150m3ha 1yr 1 of PS for 7 years (PS90 and PS150, respectively). Reprinted from Hernandez, D., Plaza, C., Senesi, N., and Polo, A. (2006). Detection of copper(II) and zinc(II) binding to humic acids from pig slurry and amended soils by fluorescence spectroscopy. Environ. Pollut. 143, 212-220, with permission from Elsevier, and from Hernandez, D., Plaza, C., Senesi, N., and Polo, A. (2007). Fluorescence analysis of copper(II) and zinc(II) binding behavior of fulvic acids from pig slurry and amended soils. Eur. J. Soil Sci. 58, 900-908, with permission from Blackwell Publishing.

The accordance of the modeled values of Cd and Zn with the experimentally determined values is sufficient. So the effects of binding of Cd and Zn to fulvic acid in water are quantitatively interpretable. The error of PLS modeling is smaller than that of MLR modeling because the interactions between the analyzed heavy metals have also been taken into consideration. 

The importance of complex formation is exemplified by the binding of Mg, Na, Co, Mn, Fe, Cu, and Zn to fulvic acids (FA), and of Fe to humic acids. The binding capacity of these natural acids for metal ions is within the range of 0.2-0.6 mmol/g, and the order of stability of complex formation (M-FA) with some key metals is Fe2+ > Al3+ > Cu2+ > Ni2+ > Ca2+ > Zn2+ > Mn2+ > Mg2+(see Schnitzer, 1970). Interestingly, some cryptogams (i.e., mosses and lichens) capture part of their essential minerals by secreting... 

Intensity changes in the natural fluorescence of fulvic acid (FA) caused by the binding of metal ions have been well documented. Various quantitative models have been developed relating the measured fluorescence signal to the amount of metal ion bound to fulvic acid. Stem-Volmer, linear, and nonlinear models developed for 1 1 binding between metal ions and fulvic acid ligand sites have been used to calculate concentrations of FA binding sites (CJ, and conditional stability constants (K). However, the ability of these models to describe metal complexation by the polydispersed fulvic acid system is somewhat limited. 

The presence of at least two fluorophores, and possibly a third, associated with metal ion binding in fulvic acid strongly suggests the need for multiple binding site models. Existing linear and nonlinear models will be reviewed for both fluorescence quenching and enhancement. A new modified 1 1 Stem - Volmer model will be introduced as well as two site and multiple site models. Application of the models to Cu binding by fulvic acid and certain well defined model systems are discussed. 

About half of the dissolved organic carbon may appear in humic or fulvic acids. These are high-molecular weight organic compounds of a composition which is somewhat uncertain. They contain aromatic hydroxyl and carboxyl groups which have the ability to bind to metal ions. Rivers and estuaries typically contain 10 mg/liter of acid with an exchange capacity of 5-10 mmol/g, mainly due to carboxylic... 

Another compartmental partitioning issue of major consequence for pesticides is the dissolved versus adsorbed fraction in an aqueous environment. Carter and Suffet (16) present measurements of binding of pesticides to dissolved fulvic acids that-will provide inputs to compartment models. Data from laboratory measurements used in compartment models can often bypass costly field experiments in the screening stage. Thomas, Spillner and Takahashi (1 7) have related the soil mobility of alachlor, butylate and metachlor to physicochemical properties of these compounds. 

We have made quantitative measurements of the binding of organic compounds to dissolved humic and fulvic acids. The extent of binding increases as a compounds octanol/water partition coefficient increases or as its water solubility decreases. Humic acids bind compounds to a greater extend than fulvic acids, but there are large differences between different humic and fulvic acids. 

DePaolis F, Kukkonen J (1997) Binding of organic pollutants to humic and fulvic acids Influence of pH and the structure of humic material. Chemosphere 34 1693-1704... 

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