INFLUENCE OF ORIGIN AND PROPERTIES OF DISSOLVED ORGANIC-MATTER ON THEPARTITION OF POLYCYCLIC AROMATIC-HYDROCARBONS (PAHS)

We investigated dissolved organic matter (DOM) from soil, sewage sludg es, water from waste disposal sites, and composts as sorbents and pote ntial carriers for hydrophobic polycyclic aromatic hydrocarbons (PAHs) in soil. Partition coefficients (expressed log K-DOC) for two 5-ring compounds were 4.8-4.9 for DOM from soil, 4.5-4.7 from composts, and 4 .3-4.4 from sewage sludges. The DOM from compost and sewage sludge can influence the transport of non-ionic organic contaminants because of the large concentrations of dissolved organic carbon (DOG) released fr om these materials. Leachates from waste disposal sites did not sorb P AHs. The DOM from compost contained a large percentage of organic mole cules >14 000 Da (32-46%), whereas DOM from waste disposal leachates c ontained only 7-10%, and so bound less PAHs. The percentage of total h ydrophobic components, as characterized by XAD-X chromatography, was 5 0 +/- 9% for most of the DOM solutions and did not express the differe nces in affinity of the organic sorbents to PAHs in the same way as th e K-DOC values. Isolated molecular-weight fractions of DOM from compos ts sorbed benzo(k)fluoranthene in each fraction. The log K-DOC values were 4.1-4.3 for both fractions, < 1000 and 1000-14 000 Da, and 4.8-5. 0 for the fraction > 14 000 Da. The interaction of PAHs with DOM < 100 0 Da cannot be explained by partitioning within intramolecular nonpola r environments of dissolved macromolecules; rather it seems to be due to the amphoteric properties of DOM. This type of interaction of PAHs with small DOM molecules might affect the mobility of hydrophobic orga nic chemicals in soils.