The Interrelationship of Aggregation and Cation Binding of Fulvic Acid

Abstract

Practical problems associated with metal ions in soil solutions and surface waters have led to the investigation of two related phenomena. They are the effects of dissolved humic materials on metal ion speciation and on the metal ion complexing capacity of the water. Several years of work by Wershaw and coworkers have demonstrated that dissolved humic materials can aggregate (Wershaw et al., 1967, 1970, 1973, 1973). In addition research by Schnitzer (Schnitzer et al,, 1965; Stevenson, 1976) and earlier workers (Broadbent et al., 1952; Coleman et al., 1956; Beckwith, 1959) proved that humic materials make the most important contribution to complexing capacity. A number of authors have suggested that aggregation and cation binding are related (Stevenson, 1976; Senesi et al., 1977; Ghosh et al., 1981). A preliminary report has outlined the application of Rayleigh light scattering to the investigation of this relationship (Underdown et al., 1981). The objective of this review is to determine the extent to which stoichiometricly exact chemistry can be deduced from the available experimental evidence. The Armadale Bh horizon fulvic acid is the only humic sample available to date with which this may be done.