Efficacy of commercial products in enhancing oil biodegradation in closed laboratory reactors

Summary A laboratory screening protocol was designed and conducted to test the efficacy of eight commercial bacterial cultures and two non-bacterial products in enhancing the biodegradation of weathered Alaska North Slope crude oil in closed flasks. Three lines of evidence were used to support the decision to progress to field testing in Prince William Sound: rapid onset and high rate of oxygen uptake, substantial growth of oil degraders, and significant degradation of the aliphatic and aromatic hydrocarbon fractions of the weathered Alaska North Slope crude oil. A product had to enhance biodegradation greater than that achieved with excess mineral nutrients. Experiments were conducted in closed respirometer flasks and shake flasks, using seawater from Prince William Sound and weathered crude oil from a contaminated beach. Analysis of the data resulted in selection of two of the ten products for field testing. Both were bacterial products. Findings suggested that the indigenous Alaskan microorganisms were primarily responsible for the biodegradation in the closed flasks and respirometer vessels.     

Effect of inoculation on the biodegradation of wathered Prudhoe Bay crude oil

Summary Enrichment cultures from oil-contaminated beach material from Prince William Sound, Alaska, generated both a mixed bacterial community of indigenous, oil-degrading marine microorganisms and a pure culture oil-degrader, strain EI2V. The mixed and axenic cultures were used in comparative shake flask studies of inoculation on biodegradation of Prudhoe Bay crude oil. Within 12 h following inoculation of homogenized, oiled beach material with the mixed culture, total CO₂ production was increased 2-fold relative to a noninoculated control. Moreover, measurements of phenanthrene degradation (as determined by the release of¹⁴CO₂ from [9-¹⁴C]phenanthrene) showed a 2-or 3-fold greater degradation when inoculated with either strain EI2V or with the mixed culture, respectively. However, as medium was replaced by a simulated tidal cycle, the observed stimulation of CO₂ production decreased, and the addition of strain EI2V had no greater effect on total CO₂ production than the addition of inorganic nutrients alone. Chemical analysis of oil recovered after 7 days incubation also suggested that, while these cultures are capable of efficient biodegradation of Prudhoe Bay crude in liquid culture, inoculation of beach material with high numbers of these microorganisms had little effect on the rate and extent of biodegradation of weathered crude oil. Overall, the sustained stimulatory effect was no greater than that observed with the addition of inorganic nutrients alone.     

Oil spill bioremediation: experiences,lessons and results from the Exxon Valdez oil spill in Alaska

The use of bioremediation as a supplemental cleanup technology in the Exxon Valdez oil spill, in Prince William Sound, Alaska, has proven to be a good example of the problems and successes associated with the practical application of this technology. Field studies conducted by scientists from the U.S. Environmental Protection Agency have demonstrated that oil degradation by indigenous microflora on the beaches of Prince William Sound was accelerated by adding fertilizer directly to the surfaces of oil-contaminated beaches. Although several types of fertilizers were used in the studies, only the results from the application of an oleophilic fertilizer are presented. The fertilizer enhanced biodegradation of the oil, as measured by changes in hydrocarbon composition and bulk oil weight per unit of beach material, by approximately two-fold relative to untreated controls. Laboratory studies verified the usefulness of the oleophilic fertilizer as a nutrient source, but the contribution of its oleophilic components towards enhancing biodegradation is still unclear.These studies supported bioremediation as a useful cleanup strategy that was subsequently used by Exxon on a large scale. The Exxon Valdez experience has also provided a number of informative lessons that have significant relevance to future oil bioremediation efforts. This paper discusses these lessons and the difficulties in assessing the effectiveness of bioremediation in the field.     

Microbial populations and hydrocarbon biodegradation potentials in fertilized shoreline sediments affected by the T/V Exxon Valdez oil spill.

The effort of clean up the T/V Exxon Valdez oil spill in Prince William Sound, Alaska, included the use of fertilizers to accelerate natural microbial degradation of stranded oil. A program to monitor various environmental parameters associated with this technique took place during the summer of 1990. Microbiological assays for numbers of heterotrophic and oil-degrading microbes and their hydrocarbon mineralization potentials were performed in support of this program. Fertilizer addition resulted in higher hexadecane and phenanthrene mineralization potentials on treated plots than on untreated reference plots. Microbial numbers in treated and reference surface sediments were not significantly different immediately after the first nutrient application in May 1990. However, subsurface sediments from treated plots had higher numbers of hydrocarbon degraders than did reference sediments shortly after treatment. The second application of fertilizer, later in summer, resulted in surface and subsurface increases in numbers of hydrocarbon degraders with respect to reference sediments at two of the three study sites. Elevated mineralization potentials, coupled with increased numbers of hydrocarbon degraders, indicated that natural hydrocarbon biodegradation was enhanced. However, these microbiological measurements alone are not sufficient to determine in situ rates of crude oil biodegradation.     

Microbial populations and hydrocarbon biodegradation potentials in fertilized shoreline sediments affected by the T/V Exxon Valdez oil spill.

The effort of clean up the T/V Exxon Valdez oil spill in Prince William Sound, Alaska, included the use of fertilizers to accelerate natural microbial degradation of stranded oil. A program to monitor various environmental parameters associated with this technique took place during the summer of 1990. Microbiological assays for numbers of heterotrophic and oil-degrading microbes and their hydrocarbon mineralization potentials were performed in support of this program. Fertilizer addition resulted in higher hexadecane and phenanthrene mineralization potentials on treated plots than on untreated reference plots. Microbial numbers in treated and reference surface sediments were not significantly different immediately after the first nutrient application in May 1990. However, subsurface sediments from treated plots had higher numbers of hydrocarbon degraders than did reference sediments shortly after treatment. The second application of fertilizer, later in summer, resulted in surface and subsurface increases in numbers of hydrocarbon degraders with respect to reference sediments at two of the three study sites. Elevated mineralization potentials, coupled with increased numbers of hydrocarbon degraders, indicated that natural hydrocarbon biodegradation was enhanced. However, these microbiological measurements alone are not sufficient to determine in situ rates of crude oil biodegradation.     

Laboratory evaluation of oil spill bioremediation products in salt and freshwater systems

Ten oil spill bioremediation products were tested in the laboratory for their ability to enhance biodegradation of weathered Alaskan North Slope crude oil in both freshwater and saltwater media. The products included nutrients to stimulate inoculated microorganisms, nutrients plus an oil-degrading inoculum, nutrients plus compounds intended to stimulate oil-degrading activity, or other compounds intended to enhance microbial activity. The product tests were undertaken to evaluate significant modifications in the existing official United States Environmental Protection Agency (EPA) protocol used for qualifying commercial bioremediation agents for use in oil spills. The EPA protocol was modified to include defined formulas for the exposure waters (freshwater, saltwater), a positive control using a known inoculum and nutrients, two negative controls (one sterile, the other inoculated but nutrient-limited), and simplified oil chemical analysis. Three analysts conducted the product test independently in each type of exposure water in round-robin fashion. Statistical tests were performed on analyst variability, reproducibility, and repeatability, and the performance of the various products was quantified in both exposure media. Analysis of variance showed that the analyst error at each time-point was highly significant (P values ranged from 0.0001 to 0.008, depending on water type and oil fraction). In the saltwater tests, six products demonstrated various degrees of biodegradative activity against the alkane fraction of the crude oil and three degraded the aromatic hydrocarbons by >10%. In the freshwater tests, eight products caused >20% loss of alkane hydrocarbons, of which five degraded the alkanes by >50%. Only four products were able to degrade polycyclic aromatic hydrocarbons (PAHs) by >20%, one of which caused 88% removal. However, when the variability of the analysts was taken into consideration, only one of the ten products was found to yield significant percent removals of the PAH fraction and only in freshwater. Viable microorganism population analysis (most-probable-number method) was also performed on every sample by each operator to measure the changes in aromatic and alkane hydrocarbon-degrading organism numbers. In general, little evidence of significant growth of either alkane- or PAH-degraders occurred among any of the ten products in either the saltwater or freshwater testing.     

Shoreline Bioremediation Following the Exxon Valdez Oil Spill in Alaska

Bioremediation played an important role in the cleanup following the oil spill from the Exxon Valdez in Prince William Sound, Alaska. The initial spill response included washing the beaches and collecting the oil with skimmers, but while this was in progress a joint program between Exxon and the United States Environmental Protection Agency investigated the feasibility of using bioremediation to remove residual oil. Early experiments demonstrated that oil biodegradation on affected shorelines was nutrient-limited, and several fertilizer application strategies were tested to overcome this limitation. Two fertilizers, the liquid oleophilic Inipol EAP22 and the solid slow-release Customblen™, were chosen for wide-scale application. Field monitoring convincingly demonstrated that the fertilizer strategy effectively stimulated oil biodegradation severalfold, with no adverse environmental impacts.     

Genetic structuring among Alaskan Pacific herring populations identified using microsatellite variation

Five highly variable microsatellite loci were used to investigate population structuring in Pacific herring Clupea pallasi collected from Kodiak Island, two sites in the Bering Sea and four sites within Prince William Sound, Alaska. All loci revealed high levels of variability with heterozygosity estimates ranging from 86 to 97% (mean heterozygosity: 89%). The variation was structured significantly among sites suggesting that the samples investigated were genetically distinct from each other. Genetic divergence was greatest between populations from the Bering Sea and those from Prince William Sound. The Kodiak Island and Point Chalmers samples appeared to be distinct from the Prince William Sound and Bering Sea populations. The observed genetic distance relationships among samples could be explained largely in terms of geographical separation.     

MORTALITY OF SEA OTTERS IN PRINCE WILLIAM SOUND FOLLOWING THE EXXON VALDEZ OIL SPILL

Abstract: This paper presents an estimate of the total number of sea otters that died as a direct consequence of the oil spill that occurred when the T/V Exxon Valdez grounded in Prince William Sound, Alaska on 24 March 1989. We compared sea otter counts conducted from small boats throughout the Sound during the summers of 1984 and 1985 to counts made after the spill during the summer of 1989. We used ratio estimators, corrected for sighting probability, to calculate otter densities and population estimates for portions of the Sound affected by the oil spill. We estimated the otter population in the portion of Prince William Sound affected by the oil was 6,546 at the time of the spill and that the post-spill population in the summer of 1989 was 3,898, yielding a loss estimate of approximately 2,650. Bootstrapping techniques were used to approximate confidence limits on the loss estimate of about 500–5,000 otters. The wide confidence limits are a result of the complex scheme required to estimate losses and limitations of the data. Despite the uncertainty of the loss estimate it is clear that a significant fraction of the otters in the spill zone survived. We observed otters persisting in relatively clean embayments throughout the oil spill zone suggesting that the highly convoluted coastline of Prince William Sound produced refuges that allowed some sea otters in the oil spill area to survive.     

The Macrobenthos of Sites within Prince William Sound,Alaska, Prior to the Exxon Valdez Oil Spill

Benthic fauna within three bays (Rocky and Zaikof Bays, and Port Etches) of outer Prince William Sound, Alaska are examined. The data represent the only detailed benthic faunal information available for the period prior to a major oil spill by the tanker Exxon Valdez within the Sound. The spatial distribution of fauna determined by classification and ordination resulted in eight station groups. Stepwise multiple discriminant analysis demonstrated a relationship between station groups, sediment grain size and nitrogen. Major faunal differences were observed within Rocky and Zaikof Bays between 1982 and 1990. The faunal differences between the two time periods demonstrate the extreme temporal variability that might be expected within Prince William Sound. The study serves as a cautionary note to avoid conclusions about the effects of disturbance to the benthos on a single data set. An explanation for temporal differences within the bays is presented.     

Protocol for laboratory testing of crude-oil bioremediation products in freshwater conditions

In 1993, the Environmental Protection Agency, National Risk Management Research Laboratory (EPA, NRMRL), with the National Environmental Technology Application Center (NETAC), developed a protocol for evaluation of bioremediation products in marine environments [18]. The marine protocol was adapted for application in freshwater environments by using a chemically defined medium and an oil-degrading consortium as a positive control. Four products were tested using the modified protocol: two with nutrients and an oleophilic component; one with nutrients, sorbent, and organisms; and one microbial stimulant. A separate experiment evaluated the use of HEPES and MOPSO buffers as replacements for phosphate buffer. The oleophilic nutrient products yielded oil degradation similar to the positive control, with an average alkane removal of 97.1±2.3% and an aromatic hydrocarbon removal of 64.8±1.2%. The positive control, which received inoculum plus nutrients, demonstrated alkane degradation of 98.9±0.1% and aromatic degradation of 52.9±0.1%. The sorbent-based product with inoculum failed to demonstrate oil degradation, while the microbial stimulant showed less oil degradation than the positive control. Replacement of phosphate buffer with other buffers had no significant effect on one product's performance. Differences in product performance were easily distinguishable using the protocol, and performance targets for alkane and aromatic hydrocarbon degradation are suggested. Electronic Publication     

Recolonization and restoration of upper intertidal Fucus gardneri (Fucales,Phaeophyta) following the Exxon Valdez oil spill

The Exxon Valdez oil spill in March 1989 and subsequent cleanup caused injury to intertidal Fucus gardneri populations especially in the upper intertidal. A survey in 1994 in Prince William Sound, Alaska showed that the upper boundary of Fucus populations at oiled sites was still an average of 0.4 m lower than the upper boundary at unoiled sites.Restoration of severely damaged Fucus populations was started on a small-scale at a heavily oiled rocky site in Herring Bay, Prince William Sound. Experiments employed mats of biodegradable erosion control fabric to act as a substratum for Fucus germlings and to protect germlings from heat and desiccation stress. A series of plots was covered with mats made from a resilient coconut-fiber fabric in June 1993. Half of the mats were inoculated with Fucus zygotes. A series of uncovered control plots was also monitored. There was no enhancement of Fucus recruitment on the rock surfaces under the mats. Dense populations of Fucus developed on the surface of all of the mats by the summer of 1994. The natural rock surfaces in the control plots, both inoculated and not, were barren of macroscopic algal cover. By September 1994, the juvenile thalli on the mats were approximately 2 cm in length. Inoculating the mats had an effect only in the upper region of the intertidal. It is expected that the thalli will become fertile during the 1995 season. These thalli may serve as a source of embryos to enhance the recovery of new Fucus populations in this high intertidal area.     

Use of hopane as a conservative biomarker for monitoring the bioremediation effectiveness of crude oil contaminating a sandy beach

Much of the variability inherent in crude oil bioremediation field studies can be eliminated by normalizing analyte concentrations to the concentration of a nonbiodegradable biomarker such as hopane. This was demonstrated with data from a field study in which crude oil was intentionally released onto experimental plots on the Delaware shoreline. Five independent replicates of three treatments were examined: no nutrient addition, addition of inorganic mineral nutrients alone, and nutrient addition plus indigenous oil-degrading microorganisms from the site. Samples collected biweekly were analyzed for the Most Probable Numbers (MPNs) of alkane and aromatic degraders and oil component analysis by GC/MS. The data were normalized to either the mass of sand that was extracted or to the concentration of hopane that was measured. Hopane normalization enabled detection of significant treatment differences in hydrocarbon biodegradation that were not detected when the data were normalized to sand mass. First-order loss rates for the hopane-normalized data were lower than those for the sand-normalized data because hopane normalization accounts only for loss due to biodegradation whereas sand normalization includes all loss mechanisms. Plots amended with nutrients alone and nutrients plus the inoculum showed enhanced removal of hydrocarbons compared to unamended control plots. However, no differences were detected between the nutrient-amended plots and the nutrient/inoculum-amended plots. Received 06 November 1995/ Accepted in revised form 26 June 1996     

The effect of chemical pretreatment on the aerobic microbial degradation of PCB congeners in aqueous systems

A series of experiments was conducted to examine the effects of chemical pretreatment on biodegradation of¹⁴C-labeled PCB congeners in aqueous systems. Fenton's reagent was used to generate hydroxyl radicals (OH) which were successful in partially oxidizing/transforming otherwise recalcitrant molecules of tetrachlorinated PCB, but had little or no impact on the biodegradation of a monochlorinated congener. Application of Fenton's reagent (1% H₂O₂, 1 mM FeSO₄) followed by inoculation with pure culturesPseudomonas sp, strain LB 400 andAlcaligenes eutrophus, strain H850 resulted in the removal of approximately 38% of 2-chlorobiphenyl and 51% of 2,2, 4,4-tetrachlorobiphenyl in the form of¹⁴CO₂. Comparison of the rate and extent of biodegradation of 2,2, 4,4-tetrachlorobiphenyl after the application of Fenton's reagent with the dynamic and final level of radioactivity in the aqueous phase of experimental system suggests two possible means of microbial utilization of tetrachlorinated PCB congener altered by chemical oxidation: (a) consumption of the partially oxidized chemical dissolved in the aqueous phase, and (b) direct microbial attack on the transformed compound, which may still be adhered to the solid surface.     

Seasonal foraging movements and migratory patterns of female Lamna ditropis tagged in Prince William Sound, Alaska

Conventional and electronic tags were used to investigate social segregation, distribution, movements and migrations of salmon sharks Lamna ditropis in Prince William Sound, Alaska. Sixteen salmon sharks were tagged with satellite transmitters and 246 with conventional tags following capture, and were then released in Prince William Sound during summer 1999 to 2001. Most salmon sharks sexed during the study were female (95%), suggesting a high degree of sexual segregation in the region. Salmon sharks congregated at adult Pacific salmon Oncorhynchus spp. migration routes and in bays near Pacific salmon spawning grounds in Prince William Sound during July and August. Adult Pacific salmon were the principal prey in 51 salmon shark stomachs collected during summer months in Prince William Sound, but the fish appeared to be opportunistic predators and consumed sablefish Anoplopoma fimbria, gadids, Pacific herring Clupea pallasi, rockfish Sebastes spp. and squid (Teuthoidea) even when adult Pacific salmon were locally abundant. As Pacific salmon migrations declined in late summer, the salmon sharks dispersed; some continued to forage in Prince William Sound and the Gulf of Alaska into autumn and winter months, while others rapidly moved south‐east thousands of kilometres toward the west coasts of Canada and the U.S. Three movement modes are proposed to explain the movement patterns observed in the Gulf of Alaska and eastern North Pacific Ocean: ‘focal foraging’ movements, ‘foraging dispersals’ and ‘direct migrations’. Patterns of salmon shark movement are possibly explained by spatio‐temporal changes in prey quality and density, an energetic trade‐off between prey availability and water temperature, intra‐specific competition for food and reproductive success. Transmissions from the electronic tags also provided data on depth and water temperatures experienced by the salmon sharks. The fish ranged from the surface to a depth of 668 m, encountered water temperatures from 4·0 to 16·8° C and generally spent the most time above 40 m depth and between 6 and 14° C (60 and 73%, respectively).     

The mechanism of action of mitochondrial ATPase (ATP synthase)

The F₁ part of the ATP synthase contains 6 nucleotide binding sites, four of which can be occupied and covalently labeled with 8-azido-adenine nucleotides. The other two sites contain tightly bound nucleotides that cannot be replaced by 8-azido-adenine nucleotides. Of the four exchangeable sites two are directly ivolved in catalysis and these are located on -subunits, while the other two are located at - interfaces and have probably a regulatory role by influencing the affinity of the catalytic sites for substrate and product. When only one catalytic site contains substrate the affinity is very high, the rate of hydrolysis is slow, and the dissociation of products is even slower (single-site catalysis). When the second site also becomes occupied, the affinity decreases enormously, and the rate of hydrolysis and dissociation of products increases several orders of magnitude. When, however, the second site is occupied by substrate in such a way that turnover is not possible at this site (e.g., covalent linkage of nitreno-ATP), the first site is no longer active, apart from the very slow single-site catalysis. The two nonexchangeable, tightly bound nucleotides that cannot be replaced by 8-azido-nucleotides, can be replaced by 2-azido-nucleotides, due to their anticonfiguration. This anticonfiguration of the substrate is also required for binding with high affinity to a catalytic site. A picture emerges in which one of the three - pairs of F₁ contains tightly bound, nonexchangeable nucleotides, while the other two contain both one catalytic site (on ) and one regulatory site (at the - interface). Cooperativity exists both between the two catalytic sites and between the catalytic and the regulatory sites.     

Synthesis and anti-phlogistic potency of some new non-proteinogenic amino acid conjugates of “Diclofenac”

Summary In search for more potent, particularly less ulcerogenic gastritis that hopefully replace the universal NSAID Diclofenac, (2-[(2,6-di-chlorophenyl)amino]-phenylacetic acid, C.A.S. 15307-86-5), twelve new non-proteinogenic amino acid conjugates of the drug, namely that of sarcosine,-alanine, D-leucine and D-phenylalanine, were synthesized and biologically screened for their anti-inflammatory, analgesic and ulcerogenic activity in rats.Diclofenac amino acid esters (IIa-d), were synthesizedvia the corresponding HOSu or HOBt active esters. Alkaline hydrolysis (NaOH) followed by acidification (KHSO₄) or thioamide formation (Lawsson's Reagent, C.A.S. 19172-47-5), afforded the corresponding free acids IIIa-d or the thioamides IVa-d respectively.Interestingly, in contrary to the parent Diclofenac, the synthesized candidates (except IIId), were entirly nonulcerogenic in rats. Further, they considerably retained a generelized anti-phlogistic activity. The major Diclofenac irritating gastric side effect was thus eliminated.Particularly, the sarcosine conjugate IIa and its thiomimic IVa exhibit promising therapeutic perspectives.Preliminary results were presented and discussed at the 5^th International Congress on Amino Acids, August 25–29, 1997, Chalkidiki, Greece and abstracted in Amino Acids (1997) 15/1: 75.     

Enhanced Biodegradation of Diesel Oil in Seawater Supplemented with Nutrients

The imbalance of C, N, and P caused by the spilled oil could be regulated by the addition of nitrogen and phosphorous. Moreover, different kinds of N and P sources were used in order to stimulate oil biodegradation under laboratory and field conditions, but the results were conflicting. To evaluate the effectiveness of nutrient supplementation, N sources (NO₃‐N and NH₄‐N) and P sources (PO₄‐P) were applied to the simulated diesel‐polluted seawater in the N/P ratio of 10:1 and 20:1, respectively. The results showed that the addition of nutrients increased the oil biodegradation rate and the counts of petroleum degrading bacteria (PDB) and heterotrophic bacteria (HB). A strongly positive correlation existed (the interrelated coefficient was nearly 0.9) between the percentage ratio of PDB/HB and the oil biodegradation rates, and therefore the percentage ratio of PDB/HB could be used as a good indicator to predict oil biodegradation. Among the four samples treated with nutrients, the biodegradation efficiency of the group amended with NO₃‐N and PO₄‐P in the ratio of 10:1 (10NO₃‐P group) was as much as 75.8 %, while in the 10NH₄‐P, 20NO₃‐P and 20NH₄‐P groups this value was 61.3 %, 52.4 % and 40.5, respectively. It would take natural degradation without nutrient supplementation about 78 days to achieve the result obtained within 14 days with 10NO₃‐P amendment . Chemical and microbiological analyses confirmed that the addition of nutrients in the same N/P ratio remarkably enhanced the biodegradation rate and the counts of microorganisms in the NO₃‐N treated groups, indicating that the microorganisms tend to utilize NO₃‐N rather than NH₄‐N as their growth N source. When the same kind of N source was added to the system, the promoted efficiency in the 10:1 (N/P ratio) groups was notable compared to the 20:1 groups, i.e., adding nutrients in the ratio of 10:1 is superior in the stimulation of oil biodegradation to the ratio of 20:1.     

Nutrients and Primary Production in the Estuary of the Razdol’naya River (Amur Bay,Sea of Japan)

The behavior of the basic nutrients (NO₃, PO₄, SiO₂) was studied in the estuary of the Razdolnaya River in low and high water, the flow was 4.3 × 10⁶ m³/day and 10.8 × 10⁶ m³/day, respectively. It was shown that within the limits of the euphotic zone the nutrients were characterized by a pronounced nonconservative behavior caused by their removal by phytoplankton in primary production. It was determined that phytoplankton removal of nutrients occurred with ratios C : NO₃ : P : Si = 105 : 18 : 1 : 37 and C : NO₃ : P : Si = 93 : 11 : 1 : 29 at a respective ratio P : NO₃ : Si = 1 : 22 : 140 in low water and P : NO₃ : Si = 1 : 17 : 120 in high water. It was also determined that the maximum rate of nutrient removal was 4 times higher in the high water than in the low water. The maximum value of primary production of phytoplankton was 2.5–4.0 gC/m² day. The estuary area of the Razdolnaya River was specified by rather high production. Such a rate of estuarine primary production, caused by nutrients carried out by the river, being no less than 250 t of dry weight of phytoplankton a day, can provide daily production up to 800 t of biomass in the secondary chain of the ecosystem.Original Russian Text Copyright © 2005 by Biologiya Morya, Zvalinsky, Nedashkovsky, Sagalayev, Tishchenko, Shvetsova.     

Biostimulation of Natural Microbial Assemblages in Oil-Amended Vegetated and Desert Sub-Antarctic Soils

A field study was initiated in December 2000 in two selected soils of The Grande Terre (Kerguelen Archipelago) with the objective of determining the long-term effects of fertilizer addition on the biodegradation rate and the toxicity of oil residues under severe sub-Antarctic conditions. Two soils were selected. The first site supports an abundant vegetal cover; the second one was desert soil, devoid of plant material. These two soils were located in the vicinity of the permanent station of Port-aux-Français (69° 42E; 49° 19S). A series of five experimental plots (0.75 × 0.75 m) were settled firmly into each of the studied soils. Each plot received 500 mL of diesel or Arabian light crude oil, and some of them were treated with a bioremediation agent: slow-release fertilizer Inipol EAP-22 (Elf Atochem). All the plots were sampled on a regular basis over a 1 year period. Heterotrophic and hydrocarbon-degrading microorganisms increased by two orders of magnitude during the first month of the experimentation in all treated enclosures, but differences appeared between the different plots. The microbial response was improved by bioremediation treatments. However, fertilizer addition had a greater impact on the desert soil when compared to the vegetated one. All chemical indices show a reduction of alkanes and light aromatics. Toxicity results show a high variability between treatments and environmental conditions. As a conclusion, it is clear that the microbial response was rapid and efficient in spite of the severe weather conditions, and the rate of degradation was improved by bioremediation treatments. However, after 1 year of treatment, the signal of a relatively high toxicity of oiled residues remained present in the two studied soils.