Mutual effects of crude oil and plants in contaminated soil: a field study

The effect of oil contamination on growth of mono- and dicotyledonous plants (clover and ryegrass), on the one hand, and the effect of plants on oil biodegradation in soil, on the other hand, were studied in a long-term field experiment. It was found that plants respond differently to oil contamination of soddy-podzolic soil. Clover was more resistant to oil than ryegrass. Biosynthesis of photosynthetic pigments (chlorophylls and carotenoids) was not disturbed in clover, and the plant yield was fully restored by the end of the third growing season. The content of oxidative enzymes in clover leaves was 2-10 times higher than in ryegrass. Biological activity of soil planted with clover was 1.5-2 times higher correlating with the biochemical parameters of plants. Higher basal respiration in soil planted with clover corresponded to the enhanced oil biodegradation. The differences in the carbon of oil products between soils planted with clover and ryegrass appeared at the end of the third growing season at high doses of oil (5 and 10 L m^-2).

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.