Anaerobic, Sulfate-Dependent Degradation of Polycyclic Aromatic Hydrocarbons in Petroleum-Contaminated Harbor Sediment

Abstract

It has previously been demonstrated that [14C]-labeled polycyclic aromatic hydrocarbons (PAHs) can be oxidized to 14CO2 in anoxic, PAH-contaminated, marine harbor sediments in which sulfate reduction is the terminal electron-accepting process. However, it has not previously been determined whether this degradation of [14C]-PAHs accurately reflects the degradation of the in situ pools of contaminant PAHs. In coal tar-contaminated sediments from Boston Harbor, [14C]-naphthalene was readily oxidized to 14CO2, but, after 95 d of incubation under anaerobic conditions, there was no significant decrease in the detectable pool of in situ naphthalene in these sediments. Therefore, to better evaluate the anaerobic biodegradation of the in situ PAH pools, the concentrations of these contaminants were monitored for ca. 1 year during which the sediments were incubated under conditions that mimicked those found in situ. There was loss of all of the PAHs that were monitored (2-5 ring congeners), including high molecular weight PAHs, such as benzo[a]pyrene, that have not previously been shown to be degraded under anaerobic conditions. There was no significant change in the PAH levels in the sediments amended with molybdate to inhibit sulfate-reducing bacteria or in sediments in which all microorganisms had been killed with glutaraldehyde. In some instances, over half of the detectable pools of in situ 2-3 ring PAHs were degraded. In general, the smaller PAHs were degraded more rapidly than the larger PAHs. A distinct exception in the Boston Harbor sediment was naphthalene which was degraded very slowly at a rate comparable to the larger PAHs. In a similar in situ-like study of fuel-contaminated sediments from Liepaja Harbor, Latvia, there was no decline in PAH levels in samples that were sulfate-depleted. However, when the Latvia sediments were supplemented with sufficient sodium sulfate or gypsum to elevate pore water levels of sulfate to approximately 14-25 mM there was a 90% decline in the naphthalene and a 60% decline in the 2-methylnaphthalene pool within 90 days. These studies demonstrate for the first time that degradation by anaerobic microorganisms can significantly impact the in situ pools of PAHs in petroleum-contaminated, anoxic, sulfate-reducing harbor sediments and suggest that the self-purification capacity of contaminated harbor sediments is greater than previously considered.

Relative importance of macrofaunal burrows for the microbial mineralization of pyrene in marine sediments: impact of macrofaunal species and organic matter quality

“…Anaerobic mineralization of PAHs (nitrateand sulfate-reducing conditions) is generally regarded as slow or incomplete compared to aerobic mineralization (Cerniglia 1993, Rockne & Strand 1998. Complete and highly efficient mineralization of several high and low molecular weight PAHs has, however, recently been observed under strict sulfate-reducing conditions in marine sediment collected from extreme sites with a history of heavy PAH contamination (Coates et al 1997, Rothermich et al 2002. Contaminant exposure, thus, also appears critical for microbial mineralization processes in anaerobic environments.…”

Anaerobic degradation of phenanthrene by a newly isolated humus-reducing bacterium, Pseudomonas aeruginosa strain PAH-1

“…However, the PAHs-contaminated sites are usually anaerobic, and anaerobic degradation may make a more important contribution to PAHs natural attenuation. Previous literatures have widely studied the anaerobic biodegradation of PAHs by mixed cultures under sulfate- (Rothermich et al 2002), nitrate- (Coates et al 2001), Fe(III)-, or humic substances (HS)- (Ramsay et al 2005) reducing conditions and methanogenic conditions (Chang et al 2008) in subsurface soils, sediments, and waste disposal sites, but the reports on PAHs degradation by pure bacterial strains is relatively rare. Only a few pure anaerobic bacteria were isolated, which have the capability to degrade PAHs with nitrate, sulfate, or CO 2 serving as the terminal electron acceptors (McNally et al 1998;Galushko et al 1999;Rockne et al 2000;Yuan and Chang 2007;Chang et al 2008).…”

Anaerobic phenanthrene mineralization by a carboxylating sulfate-reducing bacterial enrichment

“…As frequent environmental contaminants, however, they can be susceptible to biodegradation, even under anaerobic conditions. Indeed, the anaerobic degradation of 2-5-ringed PAHs has been demonstrated in soil and sediment incubations under various electron-accepting conditions (Coates et al, 1996(Coates et al, , 1997Rockne and Strand, 1998;Rothermich et al, 2002;Meckenstock et al, 2004). Studies with the two-ring PAHs naphthalene and 2-methylnaphthalene yielded pure cultures and enrichments that have shed light on the metabolic pathways for the degradation of these compounds.…”