Effect of remediation strategies on biological activity of oil-contaminated soil - A field study

The effects of oil contamination and different remediation strategies (natural attenuation, biostimulation, and bioaugmentation) on physico-chemical and biological parameters of podzolic soil were studied. The relationships between petroleum hydrocarbons, total organic carbon, nutrients, basal respiration and enzymatic activity (dehydrogenase, catalase and urease) were evaluated in soil over a 9-year period. The principal component analysis indicated that hydrocarbons were mainly responsible for changing metabolic activity for all treatments. Dehydrogenase activity was the most sensitive biological indicator with greater levels in unpolluted soil than those recorded in contaminated soil under all remediation strategies. The activity of urease was not directly correlated with oil degradation, while the relationships of catalase and respiration rate with petroleum hydrocarbons were dependent on method of remediation. Although both biostimulation and bioaugmentation had a positive influence on the biological activity of soil and its physicochemical properties, the considerable part of decontamination could be attributed to degradation activities of indigenous microorganisms. The addition of oil degrading bacteria (bioaugmentation) enhanced biodegradation rates only temporarily indicating that biostimulation is a better remediation strategy for podzolic soil in the field.