Biodegradation of polyaromatic hydrocarbons by marine bacteria: effect of solid phase on degradation kinetics

Biodegradation kinetics for phenanthrene and fluoranthene, as a function of their dissolved concentrations, were determined for a marine PAH-degrading enrichment. Biodegradation rates in the presence of artificial (Celite coated with humic acid) or Puget Sound sediments with sorbed PAH were then determined. These rates were expected to be slower than for the tests without sediment, because of limited PAH in the soluble phase due to desorption limitations of PAH from the solid to liquid phases. Due to the low aqueous PAH concentrations that exist for PAH compounds, radiolabeled PAH compounds were used to follow the fate of the PAH compounds in batch degradation test. The radiolabeled compounds were followed as evolved CO2, unreacted PAH in the dissolved phase or sorbed to sediment, and as non-polar intermediate products. Epifluorescence microscopy was used to determine if the marine enrichment bacteria could attach to sediment during PAH degradation. Without sediment, first-order degradation rate coefficients with respect to PAH concentration for phenanthrene ranged from 0.033 to 0.139 L/mg-d, depending on when the marine enrichment was tested. Fluoranthene first-order degradation rate coefficients without sediment were 0.132 and 0.162 L/mg-d. With sediment present, degradation rates for phenanthrene and fluoranthene were 2.1 to 3.5 and 2.1 to 5.3 times faster, respectively, than the degradation rates at the same aqueous PAH and biomass concentrations without sediment. With phenanthrene present about 50% of the biomass added to test samples was attached to the sediment. The results suggest that biomass interactions with sorbed PAH at the sediment particle surfaces account for increased PAH degradation rates in the presence of a solid phase material.