Water solubility enhancement effects of some polychlorinated organic pollutants by dissolved organic carbon from a soil with a higher organic carbon content.

To elucidate the role of a soil humic acid (HA) in the transport of polychlorinated organic pollutants (PCOPs), such as polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and coplanar-polychlorinated biphenyls, their partition coefficients (Kdoc) into an HA were compared with their adsorption coefficients (KOC) for a soil with a higher organic carbon (OC) content. The soil sample (ando soil) used in the present study was collected in the same location as the HA. The log Kdoc values were positively correlated with logarithm of octanol-water partition coefficients (log KOW) of the PCOPs, indicating that the partitioning of PCOPs into the HA was mainly due to hydrophobic interactions. However, the correlation between log Kdoc and log KOC was negative. This can be attributed to the enhanced water solubility of the PCOPs as the result of the dissolved organic matter from the soil. That is, when the more hydrophobic PCOPs with higher log KOW values are partitioned into the HA, then the larger quantities of PCOPs that are partitioned into the HA are able to dissolve in the aqueous phase. These results suggest that, in a soil with a higher OC content, the HA can serve as more effective carrier of PCOPs from the soil to an aquatic environment.