MICROORGANIZATION IN DISSOLVED HUMIC ACIDS

The proposed pseudomicellar character of five dissolved humic acids ha s been investigated by monitoring the fluorescence behavior of a pyren e probe added to the solutions. Fluorescence quenching by bromide in t he presence of these humic acids was found to be consistent with a hyd rophobic microenvironnent. The presence of metal ions, with either que nching or nonquenching counterions, increased the pyrene fluorescence of several of the humic acids. The results indicate that cations have the property of increasing intramolecular micellization in these humic acids, thereby minimizing quenching interactions. The proposed mechan ism involves enhanced shielding of the probe rather than its expulsion into the aqueous bulk as has been suggested previously. The humic aci ds that show this micelle-like microorganization also display increase d pyrene fluorescence upon heating, which can work in conjunction with metal ion interactions. The observations suggest that a series of eve nts take place that are comparable to the clouding behavior of nonioni c detergent solutions. The microorganization progresses through the eq uivalent of ''intramolecular clouding'' to the customary intermolecula r analogue, leading to a separate humic acid phase.