Bs. Xing, REACTION OF TOLUENE WITH SOIL ORGANIC-MATTER, Journal of environmental science and health. Part B. Pesticides, food contaminants, and agricultural wastes, 33(3), 1998, pp. 293-305
Toluene and a peat soil (93% organic matter content) were used to inve
stigate time-dependence of isotherm nonlinearity and to gain a better
understanding of sorption mechanisms of organic chemicals in soil orga
nic matter (SOM). Isotherms were constructed using batch mixing techni
que at a series of contact time intervals. Toluene analysis was perfor
med using liquid scintillation counting and sorption data were fitted
with the Freundlich model (S = KFCN, where S and C are sorbed and solu
tion concentrations, respectively, K-F and N are constants). Isotherms
at all contact times were nonlinear (N = 0.84 - 0.93), indicating a d
istribution of site energies in SOM. The K-F values increased (from 54
to 75) with contact time. Nonlinearity also increased (i.e., N decrea
sed) with increasing contact time, suggesting that energetic sites and
condensed domains were relatively concentrated within the SOM matrix.
These results are consistent with dual-mode model of sorption in SOM
proposed earlier. In this model both solid-phase dissolution and site-
filling (adsorption-like) mechanisms were shown to take place and the
competition took place only in the site-filling (or condensed) domains
.