Abstract
Petroleum contaminants are exposed to weathering when released into environment, resulting in the alteration of their chemical composition. Here, we investigated microbial communities through the soil profile at an industrial site, which was exposed to various petroleum products for over 50 years. The petroleum is present as light non-aqueous phase liquid (LNAPL) and is undergoing natural source zone depletion (NSZD). Microbial community composition was compared to the contaminant type, concentration, and its depth of obtained soil cores. A large population of Archaea, particularly Methanomicrobia and Methanobacteria and indication of complex syntrophic relationships of methanogens, methanotrophs and bacteria were found in the contaminated cores. Different families were enriched across the LNAPL types. Results indicate methanogenic or anoxic conditions in the deeper and highly contaminated sections of the soil cores investigated. The contaminant was highly weathered, likely resulting in the formation of recalcitrant polar compounds. This research provides insight into the microorganisms fundamentally associated with LNAPL, throughout a soil depth profile above and below the water table, undergoing NSZD processes at a legacy petroleum site. It advances the potential for integration of microbial community effects on bioremediation and in response to physicochemical partitioning of LNAPL components from different petroleum types.
Highlights
Long-term exposure of hydrocarbon derived contaminants is widely understood to adversely impact environmental ecosystems [1,2]
This study identified the differences in microbial communities established under different weathered petroleum contaminants, when exposed to similar environmental conditions, and suggests potential microbial degraders that might be able to utilize contaminants with a high polar compound content as a food source
gas chromatography–mass spectrometry (GC–MS) analysis of light non-aqueous phase liquid (LNAPL) samples was performed using an Agilent 7890 GC fitted with a vaporizing injector (320 ◦C operating in splitless mode, helium as carrier gas (1 mL min−1 flow), an auto-sampler, and an Agilent 7000B mass spectrometer
Summary
Long-term exposure of hydrocarbon derived contaminants is widely understood to adversely impact environmental ecosystems [1,2]. The similar environmental characteristics across the site and exposure to individual petroleum-derived contaminants at different sections, make this a unique opportunity to directly compare the microbial communities established at different depths and contaminant concentrations, after significant weathering This knowledge adds to the understanding of LNAPL undergoing NSZD, which can support effective management of similar sites. The method used was 16S rRNA metabarcoding, which identified potential degradation scenarios at different locations of the site contaminated with three petroleum products (jet fuel/kerosene, diesel, and crude oil range products) It investigated microorganisms within and associated with the LNAPL itself, and not just the dissolved or volatile phases. This study identified the differences in microbial communities established under different weathered petroleum contaminants, when exposed to similar environmental conditions, and suggests potential microbial degraders that might be able to utilize contaminants with a high polar compound content as a food source. The current work follows, but builds on, a significant body of previous research conducted at this site and adds significantly to our understanding of the processes and difficulties commonly encountered at legacy spill sites, which have a significant impact worldwide
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