Cation-Induced Aggregation in Aquatic Humus and Its Relationship to Organic Contaminant Transport

摘要

The specific objectives were to test the hypotheses that: (1) the presence of multivalent cations in natural waters, under environmental pH, DOC concentrations, etc., will cause the formation of colloidal-sized aquatic-humus aggregates; and (2) aggregation induced by the presence of multivalent cations forms aquatic humus colloids show an enhanced ability to solubilize hydrophobic organic contaminants. This study has shown, using gel-filtration chromatography and small-angle x-ray scattering, that the alkaline earth cations will induce significant aggregation in humic samples at cation concentrations typical of natural waters. This phenomenon displays a periodic relationship, with the smaller alkali-earth cations forming larger aggregates than the larger cations. Presumably, this is due to the higher charge density of the former allowing them to interact with a greater number of humic ligands. The colloids formed by this aggregation process do have the ability so solubilize hydrophobic organic contaminants but not under conditions that are likely to be encountered in most natural environments. Similarly, it has been shown in this study that concentration-induced aggregation in humic acid will form micelles. However, this phenomenon occurs at humic acid concentrations that are orders of magnitude higher than those encountered in natural environments. Consequently, these two mechanisms are unlikely to control the solubility of hydrophobic organic contaminants present in a natural system.