Substrate interactions in the biodegradation kinetics of PAH mixtures

Ten PAH (naphthalene (NPH), 1-methylnaphthalene, 2-methylnaphthalene, acenaphthene (ACE), 2-ethylnapthalene, fluorene (FLR), phenanthrene (PHN), anthracene, fluoranthene, and pyrene (PYR)) were studied. Biodegradation rate parameters and yield coefficients were estimated for each of the PAH in sole-substrate experiments. NPH had the faster degradation rate, followed by PYR. Aside from ACE, the slowest compound to degrade was FLR. The remaining six PAH had biodegradation rates that were comparable in value. The lack of a trend of decreasing biodegradation rate with increasing molecular size was contrary to that in the literature for biodegradation rates of PAH in soils. The differences in biodegradation rates observed in field samples were largely due to differences in the physical-chemical properties that govern bioavailability, e.g., hydrophobicity, which for PAH was closely correlated to molecular weight. The differences in biodegradation rates observed could be explained by differences in molecular structure features that govern reactivity and binding affinity for the enzyme. Substrate interactions were most noticeable for PHN, which shows a significant deviation from the sole substrate model. Substrate interactions were observed in biodegradation kinetics of PAH mixtures and that the best model to describe these interactions was the multi-substrate model with competitive inhibition.