Role of environmental factors and microorganisms in determining the fate of polycyclic aromatic hydrocarbons in the marine environment

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are widespread in marine ecosystems and originate from natural sources and anthropogenic activities. PAHs enter the marine environment in two main ways, corresponding to chronic pollution or acute pollution by oil spills. The global PAH fluxes in marine environments are controlled by the microbial degradation and the biological pump, which plays a role in particle settling and in sequestration through bioaccumulation. Due to their low water solubility and hydrophobic nature, PAHs tightly adhere to sediments leading to accumulation in coastal and deep sediments. Microbial assemblages play an important role in determining the fate of PAHs in water and sediments, supporting the functioning of biogeochemical cycles and the microbial loop. This review summarises the knowledge recently acquired in terms of both chronic and acute PAH pollution. The importance of the microbial ecology in PAH-polluted marine ecosystems is highlighted as well as the importance of gaining further in-depth knowledge of the environmental services provided by microorganisms.

Salt Marsh Bacterial Communities before and after the Deepwater Horizon Oil Spill

“…However, TPH measurements, bulk PAHs, and especially bulk n-alkane concentrations, capture non-petroleum hydrocarbon source contributions, such as from terrestrial plant leaf epicuticular waxes (62,67,121). Therefore, although total n-alkane concentrations were determined by summing all measured compounds from the marsh sediment samples (nC 10 to nC 35 ), distinction among the different size and size ranges of n-alkanes was also done because specific NOM sources are linked to these sizes and size ranges. For example, nC 14 to nC 20 can be attributed to microbial biosynthesis (122,123).…”

“…However, although microorganisms are known to regulate marsh biogeochemical reactions (6,23,24), predicting whether and how marsh microbial communities would respond to the DWH oil spill was a challenge because diversity had been understudied (8,16,25,26), and almost nothing was known about community functional redundancy that could enhance response and resistance (20,21,(27)(28)(29)(30). Initially, some DWH spill researchers proposed a swift microbial response (16,17) because microbes have the capacity to degrade constituent carbon compounds in oil (31)(32)(33)(34)(35) and earlier nutrient enrichment, metal exposure, and oiling experiments provided evidence that marsh communities could withstand low levels of disturbance from an oil spill (25,36). Short-duration studies based on research conducted during one sampling time or from Ͻ6 to 9 months of sampling events in 2010 and 2011 confirmed that the relative abundances and species richness for bacterial communities exposed to weathered oil residues changed through time and recognized a greater diversity among known hydrocarbon-degrading bacteria as the amount of petroleum hydrocarbon concentrations increased (37)(38)(39)(40).…”

“…We expected that the PAH compound concentrations would generally decrease as the molecular weight increased because the half-lives for LMW PAH compounds, which have higher volatility and enhanced bioavailability, range from ϳ10 to 120 days, and the half-lives for high-molecular-weight (HMW) compounds, like BaP, range from 200 to Ͼ1,400 days (71). We also expected that biodegradation should have decreased PAH levels from the time of initial oiling (35,37,72). However, the concentration of PAH compounds increased over time, and the molecular ratios of key PAHs indicated that the source(s) also changed (see Fig.…”

“…Although the highest PAH concentrations, in total or as individual PAH compounds, were below the concentrations thought to induce toxic effects (76), this PAH source transition likely impacted the microbial communities because petrogenic PAHs are generally more bioavailable than pyrogenic compounds (32). However, the impact of PAHs on marsh sediment microbial communities, as well as to marsh plants and the ecosystem at large, are still being realized (see, for example, references 35,77,78).…”

Metagenomics and stable isotope probing offer insights into metabolism of polycyclic aromatic hydrocarbons degraders in chronically polluted seawater

“…As there is tidal mixing across the San Pedro Channel, we would expect some potential for degradation at those sites by bacteria advected from the port. A possible explanation for the non-detectable rates at SPOT and CAT is that diminishing PAH inputs offshore [56] can support a very limited degrader seed community, and that the PAH degraders are out-competed for nutrients at those sites by microbes that are better adapted to oligotrophic conditions, and lose viability or are otherwise removed by processes like grazing and viruses at rates faster than they are replenished by mixing or growth. Tag-SIP results at SPOT indicated that only three OTUs were significantly enriched and others presented a bimodal distribution which may imply PAH incorporation only by a sub-population of the OTU.…”