Depth-dependent bioremediation efficiency in crude oil-impacted soils: the Evrona oil spill

Plain Language Summary A field experiment in the Evrona Nature Reserve in southern Israel tested how well different bioremediation treatments could clean up soil contaminated with crude oil. The site had very shallow, rocky soil and was heavily polluted, with oil soaked up to 10 cm deep. On March 15, 2015, the area was treated with a commercial product (OSE II) containing oil-degrading bacteria and nutrients, followed by daily watering. Two smaller plots received additional treatments: one with PRP (a beeswax-based powder) and another with OB (beeswax plus corn cob chips). Soil samples were collected in April and tested for total petroleum hydrocarbons (TPH) and bacteria levels. The results showed a significant decrease in TPH over time and with soil depth, but no significant change in total organic carbon. While OSE II alone did not increase helpful bacteria, the combinations of OSE II with PRP or OB did. However, none of the treatments showed a significantly better oil reduction than the others.