Funding was also obtained from the University of Wisconsin Sea Grant College Program under grants from the Office of Sea Grant, NOAA, U.S. Department of Commerce, and the State of Wisconsin (Federal Grant NA84AA-D-00065).

No abstract

A pH-dependent, continuous, multlllgand model Is described. It Is based on the Gaussian distribution model, which has been used to describe both proton binding by humic substances as well as metal binding by humic substances. However, the Gaussian distribution model has never been used to describe the competitive binding of the metalated and protonated ligand species. The Inclusion of pH dependence should allow one to predict metal binding constants that are more representative of the true thermodynamic binding constants rather than curve-fitting parameters with no chemical significance.

No abstract

The acidic functional groups of humic materials are an abundant source of metal binding sites in the natural environment. Studies of metal binding to humics are of great environmental interest because the biological and physicochemical properties of metals are often changed dramatically as a result of complexation with humics. In order to understand how these heterogeneous organic macromolecules bind metals with such a large range of binding energies, lanthanide ion probe spectroscopy (LIPS) has been used to study changes in the fluorescence lifetime of the europium probe metal as it binds to these substances. A method developed by Horrocks and Sudnick for the determination of the number of water molecules bound to Eu3+ was used to calculate the coordination number of humic-bound Eu3+ from the fluorescence data. The peak shift of the Eu3+ hypersensitive emission band (616 nm) was used to calculate the change in charge of the complex. Equations based on Horrocks and Sudnick's method were also developed to calculate the distribution of metal associated with the different types of binding sites on humic substances by computer modeling of the fluorescence lifetime data.