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 (KOC) 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 KOC was inversely related to the polarity of the conditioning solvent (i.e. greater increases in KOC 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 KOC on solvent-conditioning. On the contrary, the lipid-extracted soil exhibited very similar increases in KOC as the whole soil. This demonstrated that lipid removal and solvent-conditioning, which both increased KOC for this soil, are quite separate phenomena.