Jeq60013 1..8

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 freshwaterand wastewater-irrigated soils on the sorption of nonand 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 (N9-(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. SOIL ORGANIC MATTER consists mainly of plant residues, materials derived from them via decomposition processes, microbial tissues, and humic substances (Zech et al., 1997). In agricultural soils, lipids make up between 0.2 and 5% of the total SOM (Stevenson, 1994). The soil lipid fraction is defined as the water-insoluble organic matter that can be solubilized and extracted from soils using nonpolar organic solvents such as hexane, benzene, chloroform, ether, and others. The lipid fraction of SOM is derived from degradation products of plant materials (mainly from aerial and subaerial cuticular matter) and microorganisms (Bull et al., 2000; Naafsa et al., 2004) and includes fatty acids, sterols, terpenes, long-chain hydrocarbons, chlorophyll, fats, waxes, and resins (Stevenson, 1994; Jandi et al., 2002). The molecular fingerprint or “profile” in the lipid extract (e.g., C-chain length, dominant C, and the distribution of odd and even C chains) is used to reveal the origin of lipids in the soil. Strong odd-to-even C ratios of n-alkanes are usually assigned to plant-derived epicuticular waxes, whereas n-alkanes from bacterial and fungal activities typically exhibit similar levels of odd and even C chain (Stevenson, 1994; Nguyen et al., 2003). Therefore, a higher even/odd ratio of C4–C26 fatty acids suggests microbial origin, whereas fatty acids exhibiting a dominant fraction of C26–C38 originate from vascular plants (Schnitzer et al., 1986). Due to the strong hydrophobic nature of the soil lipids, these materials have been shown to affect the sorption–desorption behavior of hydrophobic organic compounds (HOCs) in soils and sediments. Free extractable lipids can compete with HOCs for hydrophobic sorption sites within the SOM and affect their sorption affinity (Tremblay et al., 2005). On the other hand, Grathwohl (1990) suggested that due to the high hydrophobicity of this fraction, it could also behave as a partitioning domain in soil and sorb HOCs. In addition, Kohl and Rice (1999) and Kohl et al. (2000) suggested that soil lipids are responsible for the linear sorption of polycyclic aromatic hydrocarbons by SOM. Long-term irrigation with reclaimed wastewater can affect the physical and chemical properties of the soil, as well as the amount and properties of SOM (Guichet et al., 1991; Gonzalez-Vila et al., 1995; Tarchitzky et al., 1999; Friedel et al., 2000). The chemical alteration of the SOM due to long-term irrigation with reclaimed wastewater is influenced mainly by the nature of the applied dissolved organic matter. Guichet et al. (1991) reported that irrigation with wastewater enriched with low-molecular-weight dissolved organic matter significantly increases the amount of SOM. In addition, a relative enrichment of lipids, polysaccharides, and plant residues was observed in the wastewater-irrigated plots. In another report, changes in the chemical properties of fulvic acid were obtained after irrigation with wastewater (Boyd and Sommers, 1990). Gonzalez-Vila et al. (1995) reported that irrigation with olive-mill effluents increases and alters the composition of the soil lipid fraction. Oleic acid (the major component of olive oil) and its oxidation derivates dominated the free and bound lipid fractions in the soil, after 3 yr of oil-mill effluent application. In a previous study (Drori et al., 2005), we reported higher sorption potential and lower desorption ability of atrazine with freshwatervs. Y. Drori and B. Chefetz, 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. Z. Aizenshtat, Casali Institute of Applied Chemistry and The Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel. B. Lam and A. Simpson, Department of Physical and Environmental Science, The University of Toronto at Scarborough, 1265 Military Trail, Toronto, Ontario, MIC 1A4 Canada. Received 8 Jan. 2006. *Corresponding author ([email protected]). Published in J. Environ. Qual. j:j–j (2006). Technical Reports: Organic Compounds in the Environment doi:10.2134/jeq2006.0013 a ASA, CSSA, SSSA 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: Cr, reduced concentrations; GC/MS, gas chromatograph/mass spectrometer; HOC, hydrophobic organic compound; KF, Freundlich distribution coefficient; KOC, carbon-normalized distribution coefficient; NMR, nuclear magnetic resonance; SOM, soil organic matter; UCM, unresolved-complex mixture. R e p ro d u c e d fr o m J o u rn a l o f E n v ir o n m e n ta l Q u a lit y . P u b lis h e d b y A S A , C S S A , a n d S S S A . A ll c o p y ri g h ts re s e rv e d .