Reclamation of oil-induced soil hydrophobicity in the hyper-arid Evrona Nature Reserve, southern Israel

Abstract

Two oil spills occurred in the Evrona Nature Reserve (southern Israel), in 1975 and 2014. This oil contamination induced highly persistent soil hydrophobicity. The objective of this study was to investigate the decrease in oil-induced soil hydrophobicity under different environmental conditions and to assess the relationship between the hydrophobicity and hydrocarbon content. A laboratory incubation experiment was conducted over 1.5 years to monitor the soil hydrophobicity and total hydrocarbon concentration under different environmental conditions. We hypothesized that the addition of water (20% or 50% saturation), nutrients, and biosurfactants can accelerate the reduction in hydrophobicity and decomposition of hydrocarbons. Water drop penetration time and molarity of ethanol droplet tests were used to assess soil hydrophobicity. In parallel, alkane composition and total petroleum hydrocarbons were evaluated to indicate oil attenuation. The addition of water, nutrients, and biosurfactants resulted in a concomitant reduction in hydrophobicity and hydrocarbon concentration of varying degrees, exhibiting enhanced degradation and hydrophobicity reduction observed in treatments to which nutrients and biosurfactants were added. At the end of the incubation, however, soil hydrophobicity in all treatments remained severe, even though total petroleum hydrocarbon removal was fairly high and reached 40%–80% in the treatments to which water with or without nutrients and/or surfactants was added.