Biodegradability of dispersed crude oil at two different temperatures

Laboratory experiments were initiated to study the biodegradability of oil after dispersants were applied. Two experiments were conducted, one at 20 degrees C and the other at 5 degrees C. In both experiments, only the dispersed oil fraction was investigated. Each experiment required treatment flasks containing 3.5% artificial seawater and crude oil previously dispersed by either Corexit 9500 or JD2000 at a dispersant-to-oil ratio of 1:25. Two different concentrations of dispersed oil were prepared, the dispersed oil then transferred to shake flasks, which were inoculated with a bacterial culture and shaken on a rotary shaker at 200 rpm for several weeks. Periodically, triplicate flasks were removed and sacrificed to determine the residual oil concentration remaining at that time. Oil compositional analysis was performed by gas chromatography/mass spectrometry (GC/MS) to quantify the biodegradability. Dispersed oil biodegraded rapidly at 20 degrees C and less rapidly at 5 degrees C, in line with the hypothesis that the ultimate fate of dispersed oil in the sea is rapid loss by biodegradation.     

Effect of environmental factors on photodegradation of polycyclic aromatic hydrocarbons (PAHs) in the water-soluble fraction of Kuwait crude oil in seawater

Photodegradation of PAHs in the water-soluble fraction of Kuwait crude oil in seawater was investigated under various environmental factors (temperature, light intensity, oxygen levels and presence of a sensitizer) in laboratory conditions. All factors investigated had significant effect on the degradation rates of PAHs. At 15 °C almost all PAHs optimally degraded at an oxygen level of 4 ppm. For lower molecular weight PAHs a light intensity of 500 W/m² in the presence of the sensitizer worked well. Higher molecular weight PAHs degraded at faster rates at a light intensity 750 W/m². At 30 °C, most of the PAHs degraded optimally at an oxygen level of 0 ppm and light intensity of 500 or 750 W/m² in presence of the sensitizer. At 40 °C, most of PAHs degraded optimally at low oxygen concentrations (0 and 4 ppm) and a light intensity of 500 W/m² in the presence of the sensitizer. Linear regression indicated that for most of the compounds, light intensity had the greatest effect on degradation rates.     

Estimation of hydrocarbon biodegradation rates in marine environments: A critical review of the Q10 approach

Offshore oil & gas industry is moving exploration and production activities into Arctic and deep water regions. Governmental regulations require environmental impact assessments before operations to evaluate the possible effects of accidental oil releases. These are often performed by numerical fate models, like the Oil Spill Contingency and Response (OSCAR) model, which has become an industry standard in Norway. In this model, biodegradation rates are adjusted to local conditions by temperature compensation according to a Q₁₀ approach. Q₁₀ is the multiplier by which rates of enzymatic reactions increase at a 10 °C temperature rise. Herein, this Q₁₀ approach implemented in the OSCAR model is investigated based on published data and novel obtained results. Overall, biodegradation rate predictions calculated by temperature compensation are found to be questionable, and choosing one universal Q₁₀ value is considered not feasible. The high variation in Q₁₀ values is herein attributed to indirect effects of temperature.     

Seasonal nutritive value of native grasses of Argentine Calden Forest Range

This study assessed the nutritive value of the most important forage species of the Calden forest (central semi-arid La Pampa, Argentina), for samples collected in fall, winter and spring, under grazing conditions and during two successive years, for ranges of good and fair conditions. The crude protein concentration (CP) of short-winter grasses (Piptochaetium napostaense, Poa ligularis, Stipa clarazii and Hordeum stenostachys) was about 10%. Mid-winter grasses (S. tenuissima and S. gynerioides) never reached 6% CP. Summer grasses (Digitaria californica and Trichloris crinita) ranged from 7% to 9% CP. In vitro dry matter digestibility (IVDMD) was similar among short-winter and summer grasses (40–50%). Mid-winter grasses had the lowest IVDMD for all seasons (<40%). Effects of sampling year and range condition on CP were consistently significant only for short-winter grasses. Good condition ranges provide a more acceptable forage supply than fair condition ranges.     

天然盐渍土冻融循环时水盐迁移规律及强度变化试验研究

通过对新疆喀什地区12处天然盐渍土室内基本性质试验分析,选取典型天然盐渍土,在开放系统中进行反复冻融循环条件下的试验研究。研究了天然盐渍土在多次冻融循环时的水分和盐分迁移规律及强度变化特征。试验结果表明:经多次冻融循环,低液限粘土试样水分重分布与盐分重分布有很大的一致性,水分和盐分自下而上迁移;试样粘聚力自下而上线形减小,内摩擦角呈s形分布。含砂低液限粘土试样冻融循环过程中,易溶盐均随水分向冷端面迁移,离子剖面呈现中间大两端小的趋势;试样粘聚力呈反s形分布,内摩擦角均呈s形分布。     

Effects of oil dispersants on settling of marine sediment particles and particle-facilitated distribution and transport of oil components

This work investigated effects of three model oil dispersants (Corexit EC9527A, Corexit EC9500A and SPC1000) on settling of fine sediment particles and particle-facilitated distribution and transport of oil components in sediment-seawater systems. All three dispersants enhanced settling of sediment particles. The nonionic surfactants (Tween 80 and Tween 85) play key roles in promoting particle aggregation. Yet, the effects varied with environmental factors (pH, salinity, DOM, and temperature). Strongest dispersant effect was observed at neutral or alkaline pH and in salinity range of 0–3.5 wt%. The presence of water accommodated oil and dispersed oil accelerated settling of the particles. Total petroleum hydrocarbons in the sediment phase were increased from 6.9% to 90.1% in the presence of Corexit EC9527A, and from 11.4% to 86.7% for PAHs. The information is useful for understanding roles of oil dispersants in formation of oil-sediment aggregates and in sediment-facilitated transport of oil and PAHs in marine eco-systems.     

Biodegradation of crude oil and n-alkanes by fungi isolated from Oman

Ten fungal species isolated from tar balls collected from the beaches of Oman were tested for their abilities to grow and degrade n-alkanes and crude oil. The abilities of Aspergillus niger, A. ochraceus and Penicillium chrysogenum to degrade n-alkanes (C13-C18), crude oil were compared and their mycelial biomass was measured. Significant differences were found in the utilization of C15, C16, C17 and C18 by the three fungi. Similarly, significant differences we found in the amount of biomass produced by the three fungi growing on C13, C17, C18 and crude oil. The correlation coefficient of biomass and oil utilization was not statistically significant for Aspergillus niger, significant for Aspergillus terreus and highly significant for P. chrysogenum.     

Effects of chemical dispersants and mineral fines on crude oil dispersion in a wave tank under breaking waves

The interaction of chemical dispersants and suspended sediments with crude oil influences the fate and transport of oil spills in coastal waters. A wave tank study was conducted to investigate the effects of chemical dispersants and mineral fines on the dispersion of oil and the formation of oil-mineral-aggregates (OMAs) in natural seawater. Results of ultraviolet spectrofluorometry and gas chromatography flame ionized detection analysis indicated that dispersants and mineral fines, alone and in combination, enhanced the dispersion of oil into the water column. Measurements taken with a laser in situ scattering and transmissometer (LISST-100X) showed that the presence of mineral fines increased the total concentration of the suspended particles from 4 to 10microl l(-1), whereas the presence of dispersants decreased the particle size (mass mean diameter) of OMAs from 50 to 10microm. Observation with an epifluorescence microscope indicated that the presence of dispersants, mineral fines, or both in combination significantly increased the number of particles dispersed into the water.     

Effect of secondary oil migration distance on composition of acidic NSO compounds in crude oils determined by negative-ion electrospray Fourier transform ion cyclotron resonance mass spectrometry

The acidic and neutral NSO compounds in a series of Duvernay-sourced oils in Canada, which are believed to have migrated extensively over relatively long distances such as along the Rimbey-Meadowbrook reef trends, were characterized by negative-ion electrospray (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Heteroatomic compounds were characterized according to their class (number of nitrogen, oxygen and sulfur heteroatoms), degree of aromaticity [rings plus double bonds (DBE)] and carbon number distribution. The N₁, N₁O₁, N₁O₂, N₁S₁, O₁ and O₂ classes were identified in Duvernay-sourced oils. With increasing migration distance, the relative abundance of O₂, N₁O₁ and N₁O₂ showed a significant decrease, while the O₁ class increased from < 10% to nearly 30% of the total. With increasing migration along the Rimbey-Meadowbrook reef trend, pyrrolic nitrogen compounds (N₁ class) shows an enrichment of alkylcarbazoles (DBE = 9) relative to alkylbenzocarbazoles (DBE = 12), and of higher homologous relative to the lower homologous. O₁ compounds show a relative enrichment of those with low DBE values. Additionally, the N₁O₁ and N₁S₁ compounds show a relative enrichment of those with high DBE values, and of higher homologues compared to the lower homologues, indicating great potential for developing new migration indices.     

Crude oil families in the Euphrates Graben (Syria)

The most petroliferous province in Syria is the Euphrates Graben system in the eastern part of the country. The source of the produced light and heavy oils has been a matter of debate from a petroleum geochemistry perspective as there are several possible source rock and just one proven source rock (R'mah formation). Based on gross composition and oil-oil correlation of biomarker and non-biomarker characteristics, three oil families have here been identified in the study area. Crude oils of Family 1 have been found to be generated from a marine and clay-rich source rock that is older than Jurassic in age based on age-related biomarker parameters (steranes and nordiacholestane ratios). Maturity-related parameters (aliphatic biomarkers and diamondoids) signal that the source of this oil family had a high maturation level. These features fit very well to the Tanf Formation (Abba Group) which is equivalent to Lower Silurian Hot Shales found elsewhere in the Middle East and North Africa. However, the Upper Cretaceous R'mah Formation and Shiranish Formation were found to be responsible for generating the majority of the crude oils studied (Family 2). Compositional and molecular differences between Families 2A and 2B were attributed to facies and subtle maturation variations. Geochemical oil-source rock correlations indicate that Family 2A was most likely sourced from the Shiranish Formation, while Family 2B was sourced from the R'mah Formation. Secondary alteration processes influenced bulk petroleum composition, most notably the depletion of light ends and the lowering of API gravity, particularly in the northwestern part of the graben.