Factors regulating PAH transformations in disturbed coastal sediments

Important limitations to bacterial transformations of polycyclic aromatic hydrocarbon (PAH) compounds in sediments include compound structure, dissolved concentration and oxygen availability. Here the authors present evidence suggesting that dissolved concentration is as important as structure in controlling degradation in radiolabeled sediments in flow through microcosms. Results from experiments where the mineralization rates of naphthalene phenanthrene and benzo[a]pyrene were related to the degree of oxygenation of suboxic sediments via sediment resuspension, showed that differences between mineralization rates and percent maximum degradation never varied by more than a factor of two between naphthalene and phenanthrene, despite phenanthrene having sixteen-fold greater hydrophobicity. The results also showed that dissolved naphthalene concentrations in the overlying water from frequently resuspended sediments were much farther below equilibrium predictions than dissolved concentrations of phenanthrene and B[a]P. The authors postulate that kinetic limitations to desorption into the aqueous phase limits the biodegradation of naphthalene to a greater extent than for phenanthrene and B[a]P. Results from experiments relating desorption from sediment to mineralization in side-by-side comparisons showed that labeled sediments undergoing resuspension in microcosms desorbed much less naphthalene than phenanthrene, and that the amount desorbed was largely underpredicted by a kinetic radial diffusion model, especially for naphthalene. Desorption rate limitationmore » in the system may help to explain the similar degree of mineralization of naphthalene and phenanthrene seen in the experiments.« less