土壤中高环多环芳烃微生物降解的研究进展

微生物修复是去除土壤中多环芳烃(PAHs)的主要措施。本文以微生物修复PAHs污染土壤的理论基础及其难点为主线,全面综述了土壤中高环PAHs的微生物降解机理。近年来,富集分离得到的以高环PAHs为唯一碳源和能源的优势降解菌逐渐增多,其中,主要是代谢降解四环PAHs的单株降解菌,一些降解菌还能以共代谢方式利用五环PAHs。高环PAHs污染土壤修复的一个难点是其低生物可利用性,微生物通过释放生物表面活性剂、形成生物膜以及分泌胞外多糖提高高环PAHs的生物可利用性,从而加速其降解。真菌和细菌联合作用能增强污染土壤实地修复的效果。因此,通过微生物修复技术来去除土壤中PAHs具有环境友好性、经济适用性以及可持续应用性。     

Microbial Factors Rather Than Bioavailability Limit the Rate and Extent of PAH Biodegradation in Aged Crude Oil Contaminated Model Soils

The rate and extent of polynuclear aromatic hydrocarbons (PAH) biodegradation in a set of aged model soils that had been contaminated with crude oil at the high concentrations (i.e.,>20,000?mg/kg) normally found in the environment were measured in 90-week slurry bioremediation experiments. Soil properties such as organic matter content, mineral type, particle diameter, surface area, and porosity did not significantly influence the PAH biodegradation kinetics among the 10 different model soils. A comparison of aged and freshly spiked soils indicates that aging affects the biodegradation rate and extent only for higher-molecular-weight PAHs, while the effects of aging are insignificant for 4-ring PAHs and total PAHs. In all model soils with the exception of kaolinite clay, the rate of abiotic desorption was faster than the rate of biodegradation during the initial phase of bioremediation treatment, indicating that PAH biodegradation was limited by microbial factors. Similarly, any of the higher-molecular-weight PAHs that were still present after 90 weeks of treatment were released rapidly during abiotic desorption tests, which demonstrates that bioavailability limitations were not responsible for the recalcitrance of these hydrocarbons. Indeed, an analysis of microbial counts indicates that a severe reduction in hydrocarbon degrader populations may be responsible for the observed incomplete PAH biodegradation. Therefore, it can be concluded that the recalcitrance of PAHs during bioremediation is not necessarily due to bioavailability limitations and that these residual contaminants therefore might pose a greater risk to environmental receptors than previously thought.     

Effects of humic substances and soya lecithin on the aerobic bioremediation of a soil historically contaminated by polycyclic aromatic hydrocarbons (PAHs)

The high hydrophobicity of polycyclic aromatic hydrocarbons (PAHs) strongly reduces their bioavailability in aged contaminated soils, thus limiting their bioremediation. The biodegradation of PAHs in soils can be enhanced by employing surface-active agents. However, chemical surfactants are often recalcitrant and exert toxic effects in the amended soils. The effects of two biogenic materials as pollutant-mobilizing agents on the aerobic bioremediation of an aged-contaminated soil were investigated here. A soil historically contaminated by about 13 g kg(-1) of a large variety of PAHs, was amended with soya lecithin (SL) or humic substances (HS) at 1.5% w/w and incubated in aerobic solid-phase and slurry-phase reactors for 150 days. A slow and only partial biodegradation of low-molecular weight PAHs, along with a moderate depletion of the initial soil ecotoxicity, was observed in the control reactors. The overall removal of PAHs in the presence of SL or HS was faster and more extensive and accompanied by a larger soil detoxification, especially under slurry-phase conditions. The SL and HS could be metabolized by soil aerobic microorganisms and enhanced the occurrence of both soil PAHs and indigenous aerobic PAH-degrading bacteria in the reactor water phase. These results indicate that SL and HS are biodegradable and efficiently enhance PAH bioavailability in soil. These natural surfactants significantly intensified the aerobic bioremediation of a historically PAH-contaminated soil under treatment conditions similar to those commonly employed in large-scale soil bioremediation.     

Estimation of Toxicity Equivalency and Probabilistic Health Risk on Lifetime Daily Intake of Polycyclic Aromatic Hydrocarbons from Urban Residential Soils

In this study, toxicity equivalents and health risks, based on concentration of 16 priority polycyclic aromatic hydrocarbons (PAHs) in urban residential soils were estimated for the human population in Gwalior, India. Benzo(a)pyrene total potency equivalents (BaP TPE) were estimated for assessment of human health risk from direct contact with PAH-contaminated soil. Potential risk to contaminated groundwater from leaching of carcinogenic PAHs was assessed by estimating the index of additive cancer risk (IACR). On the basis of lifetime average daily intake of 16 PAHs through ingestion of PAH-contaminated soils, lifetime cancer risk to human adults and children was estimated. The concentration of probable human carcinogenic PAHs in soils accounted for 38% of ∑16PAHs. BaP TPE and index of additive cancer risk (IACR) were lower than guideline values of 0.6 mg kg^?1 and <1, respectively. Estimated lifetime average daily intakes of PAHs via soil ingestion were lower than recommended dose. However, the ILCR for human adults was within acceptable limits recommended by regulatory agencies, but may need action for children in Gwalior, India.     

Assessment of Factors Governing Biodegradability of PAHs in Three Soils Aged Under Field Conditions

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants of great environmental concern due to their toxic, mutagenic and carcinogenic properties. This study correlates soil characteristics (i.e. soil organic matter, particle- and pore-size distribution) with extractability and toxicity data (LUMIStox, Ostracod) to investigate factors that govern biodegradability of PAHs in three historically contaminated soils. Desorption of PAHs occurred most readily from soil TA1 (82%), followed by soil AS3.7 (69%) and soil WG2 (20%). This is in line with toxicity data, as the soil in which the greatest contaminant desorption (SFE) was observed exhibited the highest toxicity (TA1). Of the three soils, pronounced biodegradation of 2-4-ring, and slight biodegradation of 5-ring PAHs was observed only in AS3.7, while no decrease of PAHs was reported for soils WG2 and TA1 during the degradation experiment. Strong sorption reduced pollutant bioavailability in WG2 and hence hampered biodegradation. By contrast, pollutant sorption was weak in TA1 and microbial activity was most likely inhibited due to high toxicity in this soil. Based on our results we conclude that biodegradation of PAHs in soils is determined by a number of phenomena with complex interactions between them. Consideration of a single factor will be misleading and may result in false prediction of the biodegradation potential.     

微生物降解多环芳烃(PAHs)的研究进展

从多环芳烃(PAHs)的降解菌株的筛选、降解机制以及PAHs污染的生物修复等方面介绍了微生物降解PAHs的最新研究进展。     

Biodegradation of Aliphatic vs. Aromatic Hydrocarbons in Fertilized Arctic Soils

The objectives of this study were to (1) test a simple bioremediation treatment strategy in the Arctic and (2) examine the effect of fertilization on the degradation of aliphatic and aromatic hydrocarbons. The site is a coarse sand pad that once supported fuel storage tanks. Concentrations of diesel-range organics at the beginning of the study (July 1996) ranged from 250 to 860 mg/kg soil. Replicate field plots treated with fertilizer yielded final concentrations of 0, 50, 100, or 200 mg N/kg soil. Soil samples were collected three times during the thaw season and analyzed for physical and chemical properties, microbial populations and activities, and concentrations of semivolatile hydrocarbons. Soil pH and soil-water potentials declined as a result of fertilizer application. Addition of fertilizer significantly increased soil respiration potentials, but not the populations of microorganisms measured. Fertilizer addition also resulted in ∼50% loss of measured aliphatic and aromatic hydrocarbons in surface and subsurface soils. For fertilized plots, hydrocarbon loss was not related to the amount of fertilizer added. Losses of aliphatic hydrocarbons were attributed to biotic processes, whereas losses of aromatic hydrocarbons likely were a result of both biotic and abiotic processes.     

土壤中多环芳烃的微生物降解及土壤细菌种群多样性

利用室内模拟方法,研究中、低浓度多环芳烃(PAHs)污染土壤的微生物修复效果,阐明土壤微生物（接种和土著）与PAHs降解的关系.结果表明:投加PAHs高效降解菌可以促进土壤中PAHs的降解,2周内效果显著;典型PAHs降解的难易程度依据为：菲<蒽<芘<苯并(a)芘和屈;细菌种群丰度和多样性均与PAHs降解呈负相关关系,同一处理细菌种群结构随时间变化不大.对于中、低浓度PAHs原位污染土壤,增强土著菌的活性是提高土壤PAHs降解率的有效途径之一.     

Integrated Approach for Polycyclic Aromatic Hydrocarbon Solubilization from the Soil Matrix to Enhance Bioremediation

Polycyclic aromatic hydrocarbons (PAHs) are known to be toxic to living organisms and have been identified as carcinogenic. In this study, a pathway of surfactant flushing, chemical oxidation, and biological treatment is proposed to remediate the soils polluted with the hydrophobic PAHs. Different surfactants such as Tween 80, Brij 35, sodium dodecyl sulfate (SDS), and polyethylene glycol (PEG) 6000 were tested in order to increase the PAH solubilization from the soil matrix. The maximum desorption efficiency of naphthalene and anthracene were found to be 56.5% and 59%, respectively, when Brij and SDS were used. The soluble PAH in the aqueous phase was amended with sodium thiosulfate (3%) to oxidize the PAH into a more bioavailable form. The chemical oxidation with subsequent biodegradation by Pseudomonas aeruginosa exhibited the relatively high PAH degradation rate (1.24 times higher) when compared with chemical oxidation alone. These results display the efficiency of chemical pretreatment of PAH-contaminated soil for improved bioremediation.     

微生物降解多环芳烃的研究进展

多环芳烃(PAHs)是具有严重危害的环境污染物质。介绍PAHs的降解菌,降解机理和PAHs的生物修复方面的研究进展。土壤中PAHs的生物修复被认为是解决污染的有效方法,目前,菲的生物降解途径已经比较清楚,但对结构更为复杂的多环芳烃研究较少。文章还对消除环境中多环芳烃的相关生物技术提出展望。     

Incomplete Hydrocarbon Biodegradation in Contaminated Soils: Limitations in Bioavailability or Inherent Recalcitrance?

Bioremediation has been used to treat soils contaminated with complex mixtures of organic compounds such as total petroleum hydrocarbons (TPH), oil and grease (O&G), or polycyclic aromatic hydrocarbons (PAHs). Despite the common use and cost-effectiveness of bioremediation for treating hydrocarbon-contaminated soils, it has been observed that a residual fraction remains undegraded in the soil even when optimal biodegradation conditions have been provided. This paper provides a brief review of the two major conceptual models that have been used to explain why a residual hydrocarbon fraction remains in the soil after bioremediation treatment. The contaminant sequestration model is based on the assumption that a certain fraction of hydrocarbons is “locked up” in small soil pores within soil particles or aggregates. These sorbed hydrocarbons are believed to be inaccessible to soil microorganisms. Consequently, limitations in bioavailability are thought to be the major reason for incomplete hydrocarbon biodegradation, particularly in aged or weathered soils. Alternatively, according to the inherent recalcitrance model, incomplete TPH biodegradation may be caused by the presence of certain hydrocarbons that are inherently recalcitrant to biodegradation or are only extremely slowly degradable even under optimal conditions. Each conceptual model provides different explanations regarding the potential risks of the residual hydrocarbon fraction. If the residual TPH is truly sequestered within the soil pore space, it is unlikely that these compounds will pose any significant risk to human or environmental receptors. By contrast, these risks may be considerably greater if the residual TPH fraction consists of inherently recalcitrant compounds that reside mostly on the surface of soil particles and therefore are much more available to potential receptors. Both conceptual models and their implications for the potential risk of the residual TPH fraction are discussed.     

Phytoremediation of polycyclic aromatic hydrocarbons (PAH) by cv. Crioula: A Brazilian alfalfa cultivar

This work aimed to evaluate the phytoremediation capacity of the alfalfa cultivar Crioula in soils contaminated with polycyclic aromatic hydrocarbons (PAHs), primary pollutants with mutagenic and carcinogenic potential. Alfalfa was grown from seed for 40 days on soil amended with anthracene, pyrene, and phenanthrene. Soil and plant tissue was collected for biometric assay, dry mass analysis, and PAH analysis by liquid chromatography. Increased total PAH concentration was associated with decreases in plant biomass, height, and internode length. The Crioula cultivar had a satisfactory phytoremediation effect, reducing total PAH concentration (300 ppm) in the experimental soil by 85% in 20 days, and by more than 95% in 40 days. The PAH showed a tendency to be removed in the temporal order: phenanthrene before pyrene before anthracene, and the removal ratio was influenced by the initial soil concentration of each PAH.     

Does Bioavailability Limit Biodegradation? A Comparison of Hydrocarbon Biodegradation and Desorption Rates in Aged Soils

In order to determine whether bioavailability limits the biodegradability of petroleum hydrocarbons in aged soils, both the biodegradation and abiotic desorption rates of PAHs and n-alkanes were measured at various time points in six different aged soils undergoing slurry bioremediation treatment. Alkane biodegradation rates were always much greater than the respective desorption rates, indicating that these saturated hydrocarbons apparently do not need to be dissolved into the aqueous phase prior to metabolism by soil microorganisms. The biodegradation of PAHs was generally not mass-transfer rate limited during the initial phase, while it often became so at the end of the treatment period when biodegradation rates equaled abiotic desorption rates. However, in all cases where PAH biodegradation was not observed or PAH removal temporarily stalled, bioavailability limitations were not deemed responsible for this recalcitrance since these PAHs desorbed rapidly from the soil into the aqueous phase. Consequently, aged PAHs that are often thought to be recalcitrant due to bioavailability limitations may not be so and therefore may pose a greater risk to environmental receptors than previously thought.     

Bacteria-mediated PAH degradation in soil and sediment

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the natural environment and easily accumulate in soil and sediment due to their low solubility and high hydrophobicity, rendering them less available for biological degradation. However, microbial degradation is a promising mechanism which is responsible for the ecological recovery of PAH-contaminated soil and sediment for removing these recalcitrant compounds compared with chemical degradation of PAHs. The goal of this review is to provide an outline of the current knowledge of biodegradation of PAHs in related aspects. Over 102 publications related to PAH biodegradation in soil and sediment are compiled, discussed, and analyzed. This review aims to discuss PAH degradation under various redox potential conditions, the factors affecting the biodegradation rates, degrading bacteria, the relevant genes in molecular monitoring methods, and some recent-year bioremediation field studies. The comprehensive understanding of the bioremediation kinetics and molecular means will be helpful for optimizing and monitoring the process, and overcoming its limitations in practical projects.     

Release Of Petroleum Hydrocarbons From Bioremediated Soils

This article presents a qualitative evaluation of the extent to which the bioavailability (release) of a chemical is related to the biodegradation of hydrocarbons in a field bioremediation unit. The objectives of this research were to (1) quantify the rate of release of petroleum hydrocarbons from two soils that were bioremediated, (2) explore hydrocarbon release as a process affecting bioremediation; and (3) investigate the impact of bioremediation on chemical release in the two soils. An experimental protocol was used to quantify the rate of release of these hydrocarbons from two soils that had been bioremediated in a field-scale prepared bed land treatment unit. One soil showed little change in hydrocarbon concentration during 55 weeks of prepared bed bioremediation. The field study results indicated that, prior to the bioremediation, this soil had reached an environmentally acceptable endpoint. The second soil showed considerable hydrocarbon loss as a result of the bioremediation. The rate of hydrocarbon release was determined for the first soil and for the second soil at time zero and after 1, 2, and 7 months of prepared bed bioremediation. The results indicated: (1) the fraction (F) of the specific hydrocarbons that were released rapidly from the soil and the rates of release (k₂) of the residual hydrocarbons that were released slowly, (2) that the mass of each chemical of concern that was released from the first soil was very low; and (3) that the hydrocarbon released rapidly from the second soil decreased as treatment progressed. The experiments also verified, qualitatively, that some portion of each chemical evaluated was not able to be released, and thus was unavailable for bioremediation in the prepared bed land treatment unit.     

Nutrient-limited biodegradation of PAH in various soil strata at a creosote contaminated site

The effects of nutrient addition on the in situ biodegradation of polycyclic aromatic hydrocarbons in creosote contaminated soil were studied in soil columns taken from various soil strata at a wood preserving plant in Norway. Three samples were used: one from the topsoil (0–0.5 m), one from an organic rich layer (2–2.5 m) and one from the sandy aquifer (4.5–5 m). The addition of inorganic nitrogen and phosphorous stimulated the degradation of polycyclic aromatic hydrocarbons (PAHs) in the top soil and the aquifer sand. These two soils, which differed strongly in contamination levels, responded similarly to nutrient addition with the corresponding degradation of 4-ring PAHs. The ratio between available nitrogen (N) and phosphorous (P) might explain the degree of degradation observed for the 4-ring PAHs. However, the degree of degradation of 3-ring PAHs did not significantly increase after nutrient addition. An increase in the respiration rate, after nutrient addition, could only be observed in the topsoil. In the aquifer sand, 4-ring PAH degradation was not accompanied by an increase in the respiration rate or the number of heterotrophic micro-organisms. PAH degradation in the organic layer did not respond to nutrient addition. This was probably due to the low availability of the contaminants for micro-organisms, as a result of sorption to the soil organic matter. Our data illustrate the need for a better understanding of the role of nutrients in the degradation of high molecular weight hydrocarbons for the successful application of bioremediation at PAH contaminated sites.     

Polycyclic aromatic hydrocarbons: environmental pollution and bioremediation

Polycyclic aromatic hydrocarbons (PAHs) are widely distributed and relocated in the environment as a result of the incomplete combustion of organic matter. Many PAHs and their epoxides are highly toxic, mutagenic and/or carcinogenic to microorganisms as well as to higher systems including humans. Although various physicochemical methods have been used to remove these compounds from our environment, they have many limitations. Xenobiotic-degrading microorganisms have tremendous potential for bioremediation but new modifications are required to make such microorganisms effective and efficient in removing these compounds, which were once thought to be recalcitrant. Metabolic engineering might help to improve the efficiency of degradation of toxic compounds by microorganisms. However, efficiency of naturally occurring microorganisms for field bioremediation could be significantly improved by optimizing certain factors such as bioavailability, adsorption and mass transfer. Chemotaxis could also have an important role in enhancing biodegradation of pollutants. Here, we discuss the problems of PAH pollution and PAH degradation, and relevant bioremediation efforts.     

Microbe-aliphatic hydrocarbon interactions in soil: implications for biodegradation and bioremediation

Aliphatic hydrocarbons make up a substantial portion of organic contamination in the terrestrial environment. However, most studies have focussed on the fate and behaviour of aromatic contaminants in soil. Despite structural differences between aromatic and aliphatic hydrocarbons, both classes of contaminants are subject to physicochemical processes, which can affect the degree of loss, sequestration and interaction with soil microflora. Given the nature of hydrocarbon contamination of soils and the importance of bioremediation strategies, understanding the fate and behaviour of aliphatic hydrocarbons is imperative, particularly microbe-contaminant interactions. Biodegradation by microbes is the key removal process of hydrocarbons in soils, which is controlled by hydrocarbon physicochemistry, environmental conditions, bioavailability and the presence of catabolically active microbes. Therefore, the aims of this review are (i) to consider the physicochemical properties of aliphatic hydrocarbons and highlight mechanisms controlling their fate and behaviour in soil; (ii) to discuss the bioavailability and bioaccessibility of aliphatic hydrocarbons in soil, with particular attention being paid to biodegradation, and (iii) to briefly consider bioremediation techniques that may be applied to remove aliphatic hydrocarbons from soil.     

Estimating the availability of polycyclic aromatic hydrocarbons for bioremediation of creosote contaminated soils

Bioremediation of soil contaminated by organic compounds can remove the contaminants to a large extent, but residual contamination levels may remain which are not or only slowly biodegraded. Residual levels often exceed existing clean-up guidelines and thereby limit the use of bioremediation in site clean-up. A method for estimating the expected residual levels would be a useful tool in the assessment of the feasability of bioremediation. In this study, three soil types from a creosote-contaminated field site, which had been subjected to 6 months of bioremediation in laboratory column studies, were used to characterize the residual contamination levels and assess their availability for biodegradation. The soils covered a wide range of organic carbon levels and particle size distributions. Results from the biodegradation studies were compared with desorption rate measurements and selective extractability using butanol. Residual levels of polycyclic aromatic hydrocarbons after bioremediation were found to be strongly dependent on soil type. The presence of both soil organic matter and asphaltic compounds in the soil was found to be associated with higher residual levels. Good agreement was found between the biodegradable fraction and the rapidly desorbable fraction in two of the three soils studied. Butanol extraction was found to be a useful method for roughly estimating the biodegradable fraction in the soil samples. The results indicate that both desorption and selective extraction measurements could aid the assessment of the feasability for bioremediation and identifying acceptable end-points. Received: 15 September 1999 / Received revision: 7 February 2000 / Accepted: 13 February 2000     

Enhanced biodegradation of phenanthrene in oil tar-contaminated soils supplemented with Phanerochaete chrysosporium.

In recent years, the white rot fungus Phanerochaete chrysosporium has shown promise as an organism suitable for the breakdown of a broad spectrum of environmental pollutants, including polynuclear aromatic hydrocarbons (PAHs). The focus of this study was to determine whether P. chrysosporium could effectively operate in an actual field sample of oil tar-contaminated soil. The soil was loaded with [14C]phenanthrene to serve as a model compound representative of the PAHs. Soil with the native flora present under static, aerobic conditions with buffering (pH 5.0 to 5.5) displayed full mineralization on the order of 20% in 21 days. The addition of P. chrysosporium was synergistic, with full mineralization on the order of 38% in 21 days. In addition to full mineralization, there was an increase in the proportion of radiolabelled polar extractives, both soluble and bound, in the presence of P. chrysosporium. From this study, it is apparent that the native soil microflora can be prompted into full mineralization of PAHs in some contaminated soils and that this mineralization can be enhanced when supplemented with the white rot fungus P. chrysosporium. With further refinement, this system may prove an effective bioremediation technology for soils contaminated with PAHs.