Reaction of toluene with soil organic matter

Abstract

Toluene and a peat soil (93% organic matter content) were used to investigate time‐dependence of isotherm nonlinearity and to gain a better understanding of sorption mechanisms of organic chemicals in soil organic matter (SOM). Isotherms were constructed using batch mixing technique at a series of contact time intervals. Toluene analysis was performed using liquid scintillation counting and sorption data were fitted with the Freundlich model (S = K_FC^N, where S and C are sorbed and solution concentrations, respectively, K_F and N are constants). Isotherms at all contact times were nonlinear (N = 0.84–0.93), indicating a distribution of site energies in SOM. The K_F values increased (from 54 to 75) with contact time. Nonlinearity also increased (i.e., N decreased) 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.

Key words:

• Soil organic matter
• toluene
• nonlinearity
• sorption
• dual mode model