Long-term effects of oil contamination on soil quality and metabolic function.

Widespread soil contamination with oil and the toxicity of petroleum hydrocarbons to soil biota make it extremely important to study microbial responses to oil stress. Soil metabolites reflect the main metabolic pathways in the soil microbial community. The examination of changes in the soil metabolic profile and metabolic function is essential for a better understanding of the nature of the pollution and restoration of the disturbed soils. The present study aimed to assess the long-term effect of oil on the ecological state of the soil, evaluate quantitative and qualitative differences in metabolite composition between soil contaminated with oil and non-contaminated soil, and reveal biologically active metabolites that are related to oil contamination and can be used for contamination assessment. A long-term field experiment was conducted to examine the effects of various oil concentrations on the biochemical properties and metabolic profile of the soil. Podzolic soil contaminated with oil demonstrated the long-term inhibition of soil biological activity and vegetation. Oil affected the metabolic activity of soil fungi increasing the production of toxic metabolites. A metabolomic approach was employed to determine soil metabolites. The metabolite profile was found to vary greatly between oil-contaminated and non-contaminated soils. Carbohydrates had the largest number of metabolites negatively affected by oil, while the content of organic acids, phenolic compounds, and terpenoids was mainly increased in oil-contaminated soil. The evaluation of the long-term impact of oil on microbial metabolism can make a valuable contribution to the assessment of soil quality and the activity of soil microorganisms being under stress from oil pollution. The results contribute to a further understanding of the role of microorganisms in the ecological functions of contaminated soil, which can be useful in the development of rehabilitation strategies for disturbed sites.

Bioaugmentation: possible scenarios due to application of bacterial preparations for remediation of oil-contaminated soil.

Although bioaugmentation is known as effective and environmentally friendly method increasing removal of hydrocarbons from oil-contaminated soil, it sometimes fails in soil restoration and disturbs the ecological state of soil. We studied possible scenarios of the introduction of oil-degrading bacteria into oil-contaminated podzolic soil assessing the environmental safety of different bacterial preparations in a long-term field experiment. Integral indicators characterizing the state of biocenosis included biological activity of soil and aboveground biomass of grasses. It has been established that bacterial preparations can have both positive and negative effects on the ecological state of soil and oil biodegradation. Of the five bacterial preparations studied, one had a pronounced positive effect on soil biological activity and oil mineralization processes. Two preparations did not accelerate oil biodegradation and were characterized by a weaker positive effect or even a lack of influence. Two more bacterial preparations had a significant negative impact on soil biological properties. These preparations slowed oil mineralization in soil. Both positive and negative effects of bacterial preparations were observed only during the first two years after their application. All preparations were not effective during the latter stages of long-term remediation processes. The results indicate that successful application of bioaugmentation for the restoration of oil-contaminated soil requires testing of environmental safety of bacterial preparations in a long-term field experiments prior to any treatment processes.

The possible role of toxigenic fungi in ecotoxicity of two contrasting oil-contaminated soils - A field study.

Long-term field experiments were performed to evaluate the phytotoxic properties of fungal metabolites in oil-contaminated soil and to assess the impact of contamination on the allelopathic activity of soil mycobiota. Two contrasting soils of Northwest Russia (sandy and loamy podzols) exposed to oil contamination underwent changes in abundance and allelopathic activities of soil fungi. Shifts within the microbial community caused by oil contamination affected not only oil-decomposition rates but also ecotoxicity of contaminated soil. There were significant differences in soil toxicity dynamics between sandy and loamy podzols. Four years after contamination, ecotoxicity of loamy podzol decreased, whereas sandy podzol remained highly toxic even nine years after contamination. The abundance and allelopathic activity of fungi is correlated with hydrocarbon degradation dynamics. The soil fungal community demonstrated high allelopathic activity which decreased over time in fertile loamy podzolic soil, whereas in poor sandy podzolic soil it remained high over the nine-year monitoring period. The results illustrate how oil contamination may influence allelopathic interactions in soil and demonstrate the advantage of using fungal metabolite toxicity test for testing of oil-contaminated soil samples.