Evaluation of solubilizing ability of humic aggregate basing on the phase-separation model

Solubilizing abilities of aggregates of humic acid (HA) to chlorinated benzenes (CBs) were investigated by means of the apparent water solubility enhancement. Both the water solubilities of 1,4-dichlorobenzene (DCB) and 1,2,4,5-tetrachlorobenzene (TeCB) linearly increased with increasing concentration of HA above the critical micelle concentration (CMC). Such solubilization behavior of CBs for HA was compatible with those for sodium dodecyl sulfate (SDS). These results indicate that the solubilization of CBs in the aqueous solution of HA above the CMC can be interpreted on the basis of the phase-separation model. Thus, the partition coefficients (Kmic) of CBs between water and HA aggregate phases were calculated by assuming this model. The fact that the Kmic value increased with increasing Kow of CBs supported the partition into the HA aggregate phase by hydrophobic interaction. The estimated Kmic values of DCB were not dependent on the solution pH. Both Kmic values of DCB and TeCB for the HA aggregate were found to be 4–5-fold lower than those of SDS.