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TECHNICAL REPORTS

Organic Compounds in the Environment

The Role of Lipids on Sorption Characteristics of Freshwater- and Wastewater-Irrigated Soils

^a Department of Soil and Water Sciences, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel
^b Casali Institute of Applied Chemistry and The Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
^c Department of Physical and Environmental Science, The University of Toronto at Scarborough, 1265 Military Trail, Toronto, Ontario, MIC 1A4 Canada

^* Corresponding author (chefetz{at}agri.huji.ac.il)

Received for publication January 8, 2006. The soil lipid fraction can play an important role in the sorption of organic compounds. In this study, the impact of the lipid fraction of freshwater- and wastewater-irrigated soils on the sorption of non- and relatively polar compounds was assessed. Lipid analyses revealed a clear difference between the two lipid fractions. The lipid extract from the wastewater-irrigated soil was consistent with mainly straight paraffinic chain materials; the lipid extract from freshwater-irrigated soil, on the other hand, exhibited stronger signals of aromatics, double bonds, ester, ether, and methyl, in addition to a smaller contribution from methylene protons. Our data suggest that lipid removal induced a stronger increase in the soil's sorption affinity for solutes capable of polar interactions such as atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) and chlorotoluron (N'-(3-chloro-4-methylphenyl)-N,N-dimethylurea) as compared to phenanthrene. Moreover, the level of increase in sorption affinities due to lipid removal was much higher for the freshwater-irrigated soil than for its wastewater-irrigated counterpart, even though the level of lipids in the freshwater-irrigated soil was half that in the wastewater-irrigated one (6 vs. 11% of the total organic C). The higher level of polar functionalities, such as ether and ester moieties, in the lipid fraction from the freshwater-irrigated soil suggests that these extractable compounds compete successfully with the polar solutes (atrazine and chlorotoluron) for specific binding sites in the soil organic matter (SOM). It appears that the composition of the lipid fraction may be a key consideration in unraveling the sorption of organic molecules in soils.

Abbreviations: Cr, reduced concentrations • GC/MS, gas chromatograph/mass spectrometer • HOC, hydrophobic organic compound • K_F, Freundlich distribution coefficient • K_OC, carbon-normalized distribution coefficient • NMR, nuclear magnetic resonance • SOM, soil organic matter • UCM, unresolved-complex mixture