INVESTIGATION OF KINETICS AND METABOLITES OF PHENANTHRENE IN SOIL AT DIFFERENT MOISTURE CONTENTS
|B. Liu, M. K. Banks, and A.P. Schwab, Civil Engineering, Agronomy, Kansas State University, Manhattan, KS 66506||
It has long been understood that change in the soil water content has profound effects on microbial activity and bioremediation of organic contaminants. Relationships between biodegradation rates and soil water content depend not only on the type of substrates, temperature, pH, and texture of soil, but also on the microorganism's ability to decompose the contaminants.
In order to compare the degradation rates for different chemicals and to assess the influence of water potential, it is necessary to quantify degradation kinetics at different water potentials. Polycyclic aromatic hydrocarbons (PAHs), such as phenanthrene, are commonly found in contaminated soil. Several studies have demonstrated bacteria and fungi can metabolize phenanthrene and efforts have been made to identify phenanthrene metabolites and propose possible pathways for explanation of the metabolism process.
However, all of these studies were conducted in pure cultures. The objectives of the study are to develop biodegradation kinetics for 14C-labeled phenanthrene which represents PAHs in soil, assess the effect of water content on degradation, and characterize metabolites from phenanthrene degradation by native microorganisms in soil using a High Pressure Liquid Chromatograph (HPLC) connected with a scintillation counter.
Clay soil and sand will be placed in amber Septa-Wide-Mouth bottles (95OmL). De-ionized water will be added in the soil to reach four water contents (11%, 22%, 33%, and 44% for clay and 2.3%, 7%, 12%, and 18% for sand). Besides the four water potentials, there will be an air-dried control. Phenanthrene concentration will be 450 ppm (g/g dry soil) and radioactivity will be 0.071 mCi per gram dry soil. The bottles will be sealed and incubated at the room temperature.
After 5, 10, 15, 20, 25, and 30 days of incubation, the air in the headspace of the bottles will be first bubbled through two sequential traps containing modified Bray's solution to trap l4C-parent and organic metabolites. A third trap will contain carbosorb to trap 14CO2. Radioactivity of 14CO2, metabolites, and 14C-phenanthrene will be measured using a scintillation counter.
After the air phase trapping, the contaminants remaining in the soil will be extracted. The filtrate will be analyzed for 14C-labeled phenanthrene by an HPLC and total radioactivity by a scintillation counter. By the end of the incubation, by-products containing 14C in soil will be identified.
Key words: bioremediation, phenanthrene, water contents, kinetics, metabolites
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