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TECHNICAL REPORTS

Organic Compounds in the Environment

Physicochemical Study of the Sorption of Pesticides by Wood Components

^a Inst. of Natural Resources and Agrobiology of Salamanca (IRNASA-CSIC). P.O. Box 257, 37071 Salamanca, Spain
^b Dep. of Inorganic Chemistry, Univ. of Salamanca. Plaza de la Merced s/n. 37008 Salamanca, Spain

^* Corresponding author (mjesus.sanchez{at}irnasa.csic.es).

Received for publication March 31, 2008. The sorption–desorption and interaction mechanisms of three non-ionic (linuron, alachlor, and metalaxyl) and two ionic (paraquat and dicamba) pesticides by three commercial lignins (hydrophobic macromolecule) and cellulose (hydrophilic macromolecule) as wood components were studied. Wood is a low-cost and environmentally friendly material proposed in recent years to immobilize pesticides in soils. The influence of sorbent and pesticide properties and the identification of the functional groups of the organic molecules involved in sorption were evaluated by a statistical approach and by Fourier transform infrared spectroscopy. The sorption isotherms of non-ionic pesticides by the lignins and cellulose fit the Freundlich model, and those of the ionic pesticides also fit the Langmuir model. The sorption constants of pesticides by cellulose were 62-, 9-, 24-, 119-, and 3-fold lower than those for the sorption by lignins. A predictive model of pesticide sorption indicated that 88.5% of the variability in the sorption coefficient normalized to the organic carbon content could be explained in terms of the variability of the polarity index and the octanol–water partition coefficient of sorbent and sorbate. The greater irreversibility observed for ionic pesticides was attributed to the involvement of simultaneous interaction mechanisms. The results obtained contribute the knowledge of sorption capacity of pesticides by lignin/cellulose, the main components of woods and ubiquitous materials in the environment.

Abbreviations: CEL, cellulose • dpm, disintegrations per minute • FTIR, Fourier transform infrared spectroscopy • HA, humic acid • HPLC, high-performance liquid chromatography • K_f, sorption coefficients calculated from Freundlich equation • K_fd, desorption coefficients calculated from Freundlich equation • K_foc, sorption coefficient normalized to the organic carbon content • K_ow, octanol-water partition coefficient • L1, lignin 1 • L2, lignin 2 • L3, lignin 3 • OC, organic carbon • OM, organic matter • PI, polarity index