The effect of solvent-conditioning on soil organic matter sorption affinity for diuron and phenanthrene

The effect of solvent-conditioning on the sorption of diuron and phenanthrene was investigated. The organic carbon-normalized sorption coefficients (K-OC) for diuron and phenanthrene (determined from single initial concentrations of 0.8 mg L-1 and 1.5 mg L-1, respectively) were consistently higher following solvent-conditioning of a whole soil with five organic solvents (acetonitrile, acetone, methanol, chloroform and dichloromethane). The relative increase in K-OC was inversely related to the polarity of the conditioning solvent (i.e. greater increases in K-OC were observed for the least polar solvents: chloroform and dichloromethane). The effect of solvent-conditioning on the sorption properties of the same soil that had been lipid-extracted using accelerated solvent extraction (ASE) was also investigated. Since lipid extraction involves treatment with a non-polar solvent (95:5 dichloromethane: methanol) one may have expected no further increase in K-OC on solvent-conditioning. On the contrary, the lipid-extracted soil exhibited very similar increases in K-OC as the whole soil. This demonstrated that lipid removal and solvent-conditioning, which both increased K-OC for this soil, are quite separate phenomena. (C) 2009 Elsevier Ltd. All rights reserved.