PARTITIONING OF POLYCYCLIC AROMATIC-HYDROCARBONS (PAH) TO WATER-SOLUBLE SOIL ORGANIC-MATTER

The mobility of polycyclic aromatic hydrocarbons (PAH) in soils can be influenced by the presence of dissolved organic matter. Partition coe fficients of selected polycyclic aromatic hydrocarbons, ranging from 3 -ring to 6-ring compounds, to water-soluble soil organic matter (WSSOM ) were determined. Partition coefficients were determined for WSSOM ob tained from two soils under agricultural use and forest and for commer cially available humic acid (Aldrich), taking advantage of a reversed phase (C-18) separation method. The WSSOM was characterised with regar d to charge and hydrophilic/hydrophobic properties with a dissolved or ganic matter (DOM) fractionation method. No sorption to WSSOM was foun d for the tri- and tetracyclic PAH, whereas the penta- and hexacyclic PAH showed a significant binding to both types of WSSOM and to Aldrich humic acid. The affinity of penta- and hexacyclic PAH to WSSOM was co nsiderably lower compared to the affinity to Aldrich humic acid. This is suggested to be due to the lower amount of hydrophobic fractions, c . 30%, in the natural WSSOM as compared to Aldrich humic acid. Effecti ve partition coefficients (K-OCeff) for the sorption of PAH to bulk so il calculated from K-DOC and DOM in the naturally occurring concentrat ion range were only 60-70% of the K-OC values in pure water. The impac t of DOM on pollutant transport is further influenced by non-equilibri um behaviour of PAH in soils and by sorption of DOM to the solid-soil matrix. Several scenarios are described in which the effect of DOM on pollutant transport may become important.