Apparent Adsorption and Microbial Degradation of Phenol by Soil

The adsorption of labile organic chemicals by soil and sediment surfaces may be influenced by degradation of the parent molecule. The objective of this study was to determine effects of pretreatment, equilibrium time, and concentration on adsorption of the labile organic chemical phenol by two soils: Captina silt loam (Typie Fragiudult) and Palouse silt loam (Ultic Haploxeroll). Adsorption of phenol by soil was determined by radioassay using the “batch” technique. Since loss from solution is equated with adsorption with the batch method, degradation of phenol is also recorded as adsorption. Therefore, the term “apparent adsorption” was used to describe the total disappearance from solution, which included adsorption plus decomposition. The apparent adsorption of phenol was influenced by pretreatment, equilibration time, and concentration applied. Adsorption of phenol was low, as evidenced by Freundlich K values of 0.57 and 1.19 for the sterile Captina and Palouse soils, respectively. The addition of water, glucose, or nutrient broth to the non-sterile soil increased the apparent adsorption by reducing the phenol concentration in the solution phase. As equilibration time increased, the apparent adsorption of phenol by the non-sterile soil also increased. When compared with the sterilized soil, this increase suggested that the loss of phenol from solution was largely due to microbial decomposition. As the concentration of phenol increased, there was a corresponding increase in the lag phase and a decrease in the degradation rate constant indicating inhibition and microbial activity by phenol at higher concentrations. The length of time in the lag phase was linearly related to the log of the phenol concentration. At a given concentration, the lag phase of the Captina soil was longer and more sensitive to changes in phenol concentration than was the lag phase in the Palouse soil. This was attributed to its lower phenol adsorption, organic matter content, and initial microbial population.