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(P786) Methyl Substitution Effects on Biodegradation Kinetics of Naphthalene Compounds.
Harris, Benjamin*,1,2, Dimitriou-Christidis, Petros2, McDonald, Thomas3, Reese, Erica2, Bonner, James3, Autenrieth, Robin2, 1 Environmental Resources Management, Houston, TX, USA2 Texas A&M University, College Station, TX, USA3 Conrad Blucher Institute for Surveying and Science, Corpus Christi, TX, USA
ABSTRACT- Polycyclic Aromatic Hydrocarbons (PAHs) are common constituents associated with petroleum sources that predominately occur in complex mixtures containing numerous compounds with various conformations and substitutions. Estimating the rates of biodegradation are often limited to composites of compounds or parent compounds, due to the lack of information regarding substituted family members. Performing laboratory analyses on each of the compounds is not currently feasible because of the number of compounds involved. However, quantitative structural activity relationships (QSARs) hold promise in understanding the structural parameters responsible for biodegradation rate differences. A series of experiments were conducted with naphthalene and methyl-substituted naphthalenes to relate the number and position of methyl substituents to their biodegradation rates. Pseudomonas putida ATCC 17484, a known naphthalene degrader, was cultured for extant kinetic experiments. Individual naphthalene family compounds ranging from naphthalene to tetramethylnaphthalene were monitored by GC/MS analysis for compound disappearance over time. Grouped by the number of methyl groups, the average adjusted first-order decay coefficients were 103, 17.7, 2.01, 0.27 and 0.25 (day-1) for naphthalene, methylnaphthalene, dimethylnaphthalene, trimethylnaphthalene and tetramethylnaphthalene, respectively. Degradation rates were more rapid with fewer methyl substitutions and when the alpha positions were open. A QSAR model based on three descriptors and an intercept was fit to 18 different naphthalene containing compounds yielding a r2 of 0.976. These results indicate that both the number and position of the methyl substitutions affect their biodegradation rates. Also, the QSAR results suggest that chemical structure can be used to estimate biodegradation rates for PAH compounds within families. Further research into the processes involved may yield QSAR equations capable of estimating biodegradation rates of PAHs associated with complex mixtures.
Key words: Biodegradation, Naphthalene, QSARs, Kinetics
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