PARTITIONING OF POLYCYCLIC AROMATIC-HYDROCARBONS TO DISSOLVED ORGANIC-MATTER FROM DIFFERENT SOILS

Dissolved organic matter (DOM) in the soil solution or groundwater can have a considerable effect on the dissipation of hydrophobic organic pollutants. We used the fluorescence quenching technique as well as th e reversed-phase separation technique to determine the partition coeff icient of 3- to 5-ring PAH to dissolved organic matter from agricultur al soils and forest floor materials. Several techniques (centrifugatio n, pressure filtration, and percolation) are compared for obtaining DO M solution most representative of the DOM in the natural soil solution to use for the sorption experiments. Centrifugation was shown to be t he most suitable procedure to obtain DOM solutions in large quantities with a composition most similar to the field soil solution. PAH bindi ng to DOM from mineral soil was found to be considerably lower compare d to DOM from acid forest floor materials. These differences can partl y be explained by compositional differences with respect to hydrophobi c and hydrophilic components of DOM. Binding capacity of DOM was only slightly affected by changes in pH and electrical conductivity of the soil solution. The partition coefficients for DOM from soils are rathe r different to the data given for model DOM solutions, such as humic a cids, fulvic acids, or Aldrich humic acid. To obtain realistic estimat es for the effect of DOM on the mobility of hydrophobic organic chemic als in soils, it is essential to use DOM solutions representative of t he dissolved organic matter in the soil solution. (C) 1997 Elsevier Sc ience Ltd.