Differences in polarity of soil organic matter can explain the variation of Koc for hydrophobic organic contaminant. A fluorescence spectrum investigation method has been developed for organic matter characterization which does not require harsh extraction. On the basis of the changes of the pyrene fluorescence spectrum related to the polarity of the solvents, the technique has been applied to heterogeneous samples: aqueous soil suspension and activated sludge. Pyrene sorption in organic particles leads to a modification in the observed ratio of the intensity of the first (I1) and the third (I3) peaks of its fluorescence spectrum (Robs = I1/I3). The polarity estimation of the systems tested is expressed by the Rp value (derived from Robs), which is the calculated I1/I3 ratio of the organic matter. This value appears to be negatively correlated to the pyrene Koc value which varies from 24 × 103 to 109 × 103 L kg-1. These results suggest that the Rp values could be used to correct the Koc for non ionic hyd...