EFFECT OF PEROXIDASE ADDITION ON SORPTION, DESORPTION, AND BINDING OF
PHENOLIC MIXTURES IN SOILS
1
Fangxiang Xu and 2Alok Bhandari
1,2
Department of Civil Engineering, Kansas State University, Manhattan KS 66506-2905; 1,2Phone:
(785) 532-7717; 1E-mail: fxu5398@ksu.edu; 2E-mail: bhandari@ksu.edu.
Peroxidase and phenol-oxidase enzymes can catalyze oxidative coupling reactions that result
in the polymerization of phenolic contaminants in aqueous systems. When these enzymes and
necessary cofactors are added to soils, they can enhance the rate and extent of contaminant binding
to soil organic matter in a process analogous to humus formation. The contaminant is immobilized
within the soil matrix and is prevented from transport via surface runoff or leaching into the
subsurface. The strong contaminant-soil interactions result in reduced ecotoxicity and, therefore,
hold the potential to attenuate health risks without necessarily removing the pollutant from the
contaminated media. Another attractive feature of enzyme-based engineered humification is that
this approach can be used to treat soils contaminated with mixtures of phenolic chemicals present in
a wide range of concentrations. The study presented here focused on evaluating the distribution and
binding of phenol-dichlorophenol-naphthol mixtures on two sandy loams belonging to the Haynie
series. One soil was obtained from an agricultural field (1.7% organic matter) while the other was
collected from an adjacent forested area (2.6% organic matter). To reduce the influence of dissolved
organic matter, both soils were washed several times before use in the experiments. U-ring-14Clabeled target chemicals were used to improve detection limits and better track the distribution of
the pollutant among various soil components. Bottle-point adsorption experiments with constant
soil dosage were conducted for a period of 7 days followed by sequential extraction (desorption)
with synthetic groundwater. The strongly adsorbed chemicals were removed by multiple extractions
with methanol. Next, the soil was extracted with alkali under a nitrogen atmosphere to remove
humic and fulvic acids and quantify the contaminant associated with this fraction. Finally, the
phenol remaining on the alkali-extracted soil was quantified by combusting the soil at 925°C and
counting the 14CO2 on a liquid scintillation counter. The effect of the presence of horseradish
peroxidase on the nature and extent of binding was compared to situations when no peroxidase was
added. Results showed a dramatic enhancement in contaminant binding in the presence of the
enzyme.
Key words: soil, phenols, binding, peroxidase, humification