The role of microbial populations in the containment of aromatic hydrocarbons in the subsurface

A survey of soil gases associated with gasoline stations on theSwan Coastal Plain of Western Australia has shown that 20% leak detectable amountsof petroleum. The fates of volatile hydrocarbons in the vadose zone at one contaminatedsite, and dissolved hydrocarbons in groundwater at another site were followed in anumber of studies which are herein reviewed. Geochemical evidence from a plume ofhydrocarbon-contaminated groundwater has shown that sulfate reduction rapidly developedas the terminal electron accepting process. Toluene degradation but not benzene degradationwas linked to sulfate reduction. The sulfate-reducing bacteria isolated from the plumerepresented a new species, Desulfosporosinus meridiei. Strains of the speciesdo not mineralise ¹⁴C-toluene in pure culture. The addition of large numbersof cells and sulfate to microcosms did stimulate toluene mineralisation but not benzenemineralisation. Attempts to follow populations of sulfate-reducing bacteria byphospholipid signatures, or Desulfosporosinus meridiei by FISH in the plume were unsuccessful, but fluorescently-labeled polyclonal antibodies were successfully used.In the vadose zone at a different site, volatile hydrocarbons were consumed in thetop 0.5 m of the soil profile. The fastest measured rate of mineralisation of ¹⁴C-benzenein soils collected from the most active zone (6.5 mg kg^-1 day^-1) could accountfor the majority of the flux of hydrocarbon vapour towards the surface. The studiesconcluded that intrinsic remediation by subsurface microbial populations in groundwateron the Swan Coastal Plain can control transport of aromatic hydrocarbon contamination,except for the transport of benzene in groundwater. In the vadose zone, intrinsicremediation by the microbial populations in the soil profile can contain the transportof aromatic hydrocarbons, provided the physical transport of gases, inparticular oxygen from the atmosphere, is not impeded by structures.