Sorption Experiments: Diuron (>99% purity) was purchased from
Sigma–Aldrich (Sydney, Australia). High performance liquid chromatography
(HPLC) grade solvents and calcium chloride were
obtained from Merck Pty Limited (Victoria, Australia). A stock solution
of 1000 mg L1 diuron was prepared in methanol. Sorption
experiments were carried out using a batch equilibration technique
at ambient laboratory temperature (25 ± 3 C), as reported
previously (Liyanage et al., 2006). For single point measurements
on whole soil, an aliquot of soil (5 g) was equilibrated with
10 mL diuron solution (1.0 mg L1
) by end-over-end shaking for
16 h, based on a preliminary kinetics experiment (Liyanage et al.,
2006). For HF-treated soils only 50 mg of the sorbent was equilibrated
with 5 mL diuron solution (1.0 mg L1
). At the end of the
equilibration period, suspensions were centrifuged at 3000 g
for 20 min and 1 mL aliquots of the supernatant were filtered
through 0.45 lm Teflon filters and analysed. Blanks without diuron
and without sorbent were analysed and appropriate corrections
were applied. Sorbed concentrations were calculated from the difference
between the initial solution concentration and equilibrium
solution concentration.