lower solute concentrations; Fig. 1a and d) and the appearance of
the cooperative-like uptake (Fig. 1c and e) seem to be induced by
the added OM. These changes could be associated with the presence
of flexible aliphatic components and oil residues in the
OMW that may more readily swell and accommodate sorbed
organic compounds. The possibility that sorbate-induced changes
in a soil–sorbent matrix might be a reason for sorption cooperativity
is supported by the above-mentioned observation of strong desorption
hysteresis for all of the sorbate–soil systems where it was
tested. This indicates a resistance of the organic compounds to
being released from a sorbed state to aqueous solutions. The
biodegradation of simazine and diuron in the batch sorption experiments
carried out at the presence of a biocide (see Section 2) is not
expected. Also, based on examining the controls containing a
solute (without a sorbent) and NaN3 (at the presence of 0.01 M
CaCl2), no reactions between sodium azide and organic solutes
were anticipated. In addition, the desorption resistance was
observed for two compounds belonging to essentially different
chemical classes, i.e., triazines and ureas, with different chemical
reactivity, that typically do not undergo biotic and abiotic degradation
for time periods much longer than that of the current experiment
(TOXNET-HSDB, 2015). Therefore, ‘‘an irreversible swelling’’
(Braida et al., 2003) of soil components by sorbed simazine and
diuron could contribute to desorption resistance and cooperative
sorption uptake.
4. Conclusions