Mixing of dissolved organic matter from distinct sources: using fluorescent pyrene as a probe

Binary mixtures of humic substances (HSs) from three distinct sources (two soil humic acids and one natural organic matter) were used to investigate the mixing behavior of dissolved organic matters in the aquatic environment. Much longer time was required for equilibration of a solution of mixed HSs with pyrene as a probe, than for a solution comprising a single HS. Restructuring processes were responsible for the difference in equilibration kinetics and included conformational changes and aggregation. A major factor found controlling these processes was intermolecular interactions between components of HSs, although the concentration and hydrophobicity of the HSs were also important. In addition, the fluorescence quenching method yielded the binding constant (K DOC) of the HSs with pyrene. The K DOC of pyrene with binary humic mixtures was found to follow the conservative mixing rule. The findings of this study are applicable to studies of other hydrophobic organic pollutants and HSs and, will assist in modeling of the transport and fate of pollutants in aquatic environments.