Mineralization Potential for Phenol in Subsurface Soils

The mineralization of 14 C‐phenol to 14 CO 2 was determined in each horizon of four contrasting soil profiles using a modification of the approach used to determine heterotrophic potential in aquatic environments. Short‐term mineralization rates were determined at 12 concentrations ranging from 5 to 10 000 µg phenol kg −1 dry soil and the data were reduced using a hyperbolic saturation model similar to that used for describing enzyme kinetics. The kinetic terms V max and K ′ were estimated using nonlinear regression. Phenol was mineralized in all soil samples at each concentration examined. The V max values ranged from 0.018 to 22.4 ng phenol kg −1 dry soil s −1 ; K ′ values ranged from 20 to 2355 µg phenol kg −1 dry soil. Generally within each soil profile, V max tended to decline with increasing depth; however, the magnitude and pattern of this decline varied widely according to soil type. The V max in the Ap horizons (3–15 cm) ranged from 2.49 to 13.8 ng kg −1 dry soil s −1 . The V max in the B22t horizons (30–101 cm) ranged from 0.839 to 2.65 ng kg −1 s −1 , and V max in the deepest horizons (81–187 cm) ranged from 0.145 to 4.75 ng kg −1 dry soil s −1 . This study indicates that soil horizon and soil type are important determinants of the biodegradation of phenol, a potential groundwater pollutant, as it passes through the soil column.