The effect of resuspension of estuarine sediments on the biodegradation of polynuclear aromatic hydrocarbons

Polynuclear aromatic hydrocarbons (PAHs) are a class of contaminants commonly found in bottom sediments near highly industrialized areas. Resuspension of these sediments can make these contaminants more available for dispersal into the marine environment. The process will also cause the oxidation-reduction characteristics of the sediments to change from anaerobic to aerobic. Bacteria in these sediments have been shown capable of degrading 2 and 3 ring PAHs under aerobic conditions. This research examined the relationship between resuspension and biodegradation of PAHs in laboratory scale slurry reactors. Phenanthrene was used as the model compound. Radiolabeled compound was used to monitor mineralization, and mass balances were performed to determine final partitioning of carbon from degraded phenanthrene. Sediments were kept anaerobic from collection, through the contamination process, and through the loading of test reactors. Aeration of and contaminant release in sediment/water slurries was rapid, within 30 minutes. Mixing was found to be the controlling factor in both contaminant release and compound mineralization. Analysis of the final carbon partitioning indicates that the phenanthrene was being used as a growth substrate by the indigenous bacteria. Complete degradation of the phenanthrene required 5 days, including a 2 day lag period, in all reactors tested. Due to this long degradation period, the mixing and aeration provided solely by dredging cannot be considered a remedial treatment. Nutrient amendment had no effect on rate or extent of mineralization. Augmenting the slurry reactor with an aged slurry (2-3 days) eliminated the lag time before onset of biodegradation. Therefore a system of sequential treatment cells could have potential as a remediation technique