supernatant solution was then subjected to HPLC analysis. No
detectable traces of pesticides were observed in the supernatant
solutions obtained in the blank samples. The sorbed amounts were
calculated by the difference between the initial solute concentration
and the solution concentration at equilibrium and reported
per unit dry weight of the sorbent. The solute losses in the controls
did not exceed 4% thus indicating the relative constancy of concentrations
of organic compounds during the time allotted for sorption
experiments. The pH values of the aqueous supernatants were
between 6.9 and 7.8 and did not change substantially for any given
solute/sorbent pair within the range of examined solute concentrations.
No ionization is expected for simazine and diuron in this pH
range due to the reported pKa values of their conjugated acids,
which are 1.62