Evaluation of soil organic matter polarity by pyrene fluorescence spectrum variations

Differences in polarity of soil organic matter can explain the variation of K-oc 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 (I-1) and the third (I-3) peaks of its fluorescence spectrum (R-obs = I-1/I-3) The polarity estimation of the systems tested is expressed by the R-p value (derived from R-obs), which is the calculated I-1/I-3 ratio of the organic matter. This value appears to be negatively correlated to the pyrene K-oc value which varies from 24 x 10(3) to 109 x 10(3) L kg(-1). These results suggest that the R-p values could be used to correct the K-oc for non ionic hydrophobic organic compounds in soils. The practical uses of this methods are (i) the correction of K-oc values calculated from literature based on their K-ow or solubility values and (ii) the prediction of K-oc for different sorbents and non polar organic compounds.