Bioremediation (Natural Attenuation and Biostimulation) of Diesel-Oil-Contaminated Soil in an Alpine Glacier Skiing Area

We investigated the feasibility of bioremediation as a treatment option for a chronically diesel-oil-polluted soil in an alpine glacier area at an altitude of 2,875 m above sea level. To examine the efficiencies of natural attenuation and biostimulation, we used field-incubated lysimeters (mesocosms) with unfertilized and fertilized (N-P-K) soil. For three summer seasons (July 1997 to September 1999), we monitored changes in hydrocarbon concentrations in soil and soil leachate and the accompanying changes in soil microbial counts and activity. A significant reduction in the diesel oil level could be achieved. At the end of the third summer season (after 780 days), the initial level of contamination (2,612 ± 70 μg of hydrocarbons g [dry weight] of soil(−1)) was reduced by (50 ± 4)% and (70 ± 2)% in the unfertilized and fertilized soil, respectively. Nonetheless, the residual levels of contamination (1,296 ± 110 and 774 ± 52 μg of hydrocarbons g [dry weight] of soil(−1) in the unfertilized and fertilized soil, respectively) were still high. Most of the hydrocarbon loss occurred during the first summer season ([42 ± 6]% loss) in the fertilized soil and during the second summer season ([41 ± 4]% loss) in the unfertilized soil. In the fertilized soil, all biological parameters (microbial numbers, soil respiration, catalase and lipase activities) were significantly enhanced and correlated significantly with each other, as well as with the residual hydrocarbon concentration, pointing to the importance of biodegradation. The effect of biostimulation of the indigenous soil microorganisms declined with time. The microbial activities in the unfertilized soil fluctuated around background levels during the whole study

Identification of Disulfides from the Biodegradation of Dibenzothiophene

Several investigations have identified benzothiophene-2,3-dione in the organic solvent extracts of acidified cultures degrading dibenzothiophene via the Kodama pathway. In solution at neutral pH, the 2,3-dione exists as 2-mercaptophenylglyoxylate, which cyclizes upon acidification and is extracted as the 2,3-dione. The fate of these compounds in microbial cultures has never been determined. This study investigated the abiotic reactions of 2-mercaptophenylglyoxylate incubated aerobically in mineral salts medium at neutral pH. Oxidation led to the formation of 2-oxo-2-(2-thiophenyl)ethanoic acid disulfide, formed from two molecules of 2-mercaptophenylglyoxylate. Two sequential abiotic, net losses of both a carbon and an oxygen atom produced two additional disulfides, 2-oxo-2-(2-thiophenyl)ethanoic acid 2-benzoic acid disulfide and 2,2′-dithiosalicylic acid. The methods developed to extract and detect these three disulfides were then used for the analysis of a culture of Pseudomonas sp. strain BT1d grown on dibenzothiophene as its sole carbon and energy source. All three of the disulfides were detected, indicating that 2-mercaptophenylglyoxylate is an important, short-lived intermediate in the breakdown of dibenzothiophene via the Kodama pathway. The disulfides eluded previous investigations because of (i) their high polarity, being dicarboxylic acids; (ii) the need to lower the pH of the aqueous medium to <1 to extract them into an organic solvent such as dichloromethane; (iii) their poor solubility in organic solvents, (iv) their removal from organic extracts of cultures during filtration through the commonly used drying agent anhydrous sodium sulfate; and (v) their high molecular masses (362, 334, and 306 Da) compared to that of dibenzothiophene (184 Da)

Just add water and salt: the optimisation of petrogenic hydrocarbon biodegradation in soils from semi-arid Barrow Island, Western Australia

We investigated the potential of soil moisture and nutrient amendments to enhance the biodegradation of oil in the soils from an ecologically unique semi-arid island. This was achieved using a series of controlled laboratory incubations where moisture or nutrient levels were experimentally manipulated. Respired CO2 increased sharply with moisture amendment reflecting the severe moisture limitation of these porous and semi-arid soils. The greatest levels of CO2 respiration were generally obtained with a soil pore water saturation of 50–70%. Biodegradation in these nutrient poor soils was also promoted by the moderate addition of a nitrogen fertiliser. Increased biodegradation was greater at the lowest amendment rate (100 mg N kg−1 soil) than the higher levels (500 or 1,000 mg N kg−1 soil), suggesting the higher application rates may introduce N toxicity. Addition of phosphorous alone had little effect, but a combined 500 mg N and 200 mg P kg−1 soil amendment led to a synergistic increase in CO2 respiration (3.0×), suggesting P can limit the biodegradation of hydrocarbons following exogenous N amendment