The effect of lipids on the sorption of diuron and phenanthrene in soils.

The influence of lipids on the sorption of diuron and phenanthrene to soils was investigated. Accelerated solvent extraction (ASE) was used to extract lipids from twelve soil horizons. Extractable lipids accounted for 3-13% of organic C. The organic carbon-normalized sorption coefficients (K(OC)) for diuron and phenanthrene were consistently higher for the lipid-extracted soils than for the whole soils (average of 31% for diuron and 29% for phenanthrene), indicating that lipids compete for or block sorption sites on the organic matter. Sorption experiments on one pair of HF-treated soils indicated that the blocking effects of minerals and lipids are independent, since lipid extraction and HF-treatment combined increased K(OC) by more than either treatment alone. Lipids extracted from whole and HF-treated soils were very similar in composition, consisting predominantly of long-chain polymethylene structures. K(OC) of the lipid itself was lower than for any of the whole soils and soil fractions (lipid extracted and HF-treated) for diuron, but higher for phenanthrene. Solid-state (13)C NMR spectra of the HF-treated soils before and after lipid extraction indicated that 15-20% of alkyl C was removed by ASE and that no other structures were affected.