MICROORGANIZATION IN DISSOLVED HUMIC ACIDS

The proposed pseudomicellar character of five dissolved humic acids has been investigated by monitoring the fluorescence behavior of a pyrene probe added to the solutions. Fluorescence quenching by bromide in the presence of these humic acids was found to be consistent with a hydrophobic microenvironnent. The presence of metal ions, with either quenching 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 mechanism involves enhanced shielding of the probe rather than its expulsion into the aqueous bulk as has been suggested previously. The humic acids that show this micelle-like microorganization also display increased pyrene fluorescence upon heating, which can work in conjunction with metal ion interactions. The observations suggest that a series of events take place that are comparable to the clouding behavior of nonionic detergent solutions. The microorganization progresses through the equivalent of ''intramolecular clouding'' to the customary intermolecular analogue, leading to a separate humic acid phase.