Differentiation between the role of organic matter-mineral interactions and organic matter chemistry on the sorption of polycyclic aromatic hydrocarbons

Even though it is well documented that the amount of soil organic matter is the most important determinant of the sorption affinity of soils for non-ionic compounds, it is also clear that organic carbon-normalized sorption coefficients (KOC) vary considerably between soils. KOC variability can be affected by two factors, variations in the chemistry of organic matter between soils and interactions between organic matter and soil minerals, especially clay minerals. Here, we quantify both of these effects for phenanthrene. The effect of organic matter- mineral interactions was gauged by comparing KOC for HF-treated soils, which have had their clay minerals removed, with KOC for the corresponding whole soils. The average ratio of KOC of the HF-treated soils to KOC of the whole soils was 2.3, indicating a substantial depression of KOC due to the presence of minerals in the whole soils. The effect of organic matter chemistry was gauged by correlating KOC against distributions of C types determined using solid-state 13C NMR spectroscopy. KOC was positively correlated with aryl C and negatively correlated with O-alkyl C, for HF-treated soils but not for whole soil. We suggest that the lack of a clear effect of organic matter chemistry on whole soil KOC for phenanthrene is due to an over-riding influence of organic matter-mineral interactions in this case. This hypothesis is supported by a correlation between the increase in KOC on HF-treatment and the soil clay content.

کلیدواژه ها:

sorption ، phenanthrene ، NMR spectroscopy