Biodegradation of PAH Mixtures by a Marine Sediment Enrichment

Aerobic polycyclic aromatic hydrocarbon (PAH) degrading bacteria were enriched from creosote contaminated marine sediments (Puget Sound, Washington, USA) using a continuous-flow fluidized-bed reactor. Artificial seawater media and a mixture of seven 2 to 3-ring PAHs were used as enrichment substrates. The biodegradability of PAH mixtures by the enrichment was determined in batch vial assays. The tested PAH mixtures included alkyl substituted naphthalenes, phenanthrene, anthracene, fluoranthene, and pyrene. Co-occurring PAHs significantly affected the degradation rates of individual compounds. Degradation was generally slower in mixtures than with individual compounds indicating competition. Degradation of some recalcitrant PAHs, on the other hand, was enhanced in mixtures. Phenanthrene degraded rapidly but pyrene degradation was insignificant when present alone. In pyrene-phenanthrene mixtures, pyrene was nearly completely removed indicating enzyme induction or cometabolism.