Bioremediation of soils contaminated with the herbicide 2-sec-butyl-4,6-dinitrophenol (dinoseb).

A novel soil treatment method for achieving the removal of dinoseb (2-sec-butyl-4,6-dinitrophenol) from contaminated soils was investigated. One soil contained dinoseb as the major contaminant, although several other hazardous compounds were also present. A second soil was highly contaminated with dinoseb. Dinoseb was not degraded in these soils under the aerobic conditions at each site. Pretreatment of the soils by the addition of a starchy potato-processing by-product and flooding with phosphate buffer stimulated the consumption of oxygen and nitrate from the soils, thereby lowering the redox potential and creating anaerobic conditions. Anaerobiosis (Eh less than -200 mV) promoted the establishment of an anaerobic microbial consortium that degraded dinoseb completely, without the formation of the polymerization products seen under aerobic or microaerophilic conditions. When dinoseb was present at low concentrations in a chronically contaminated soil, the natural microflora was capable of establishing anaerobic conditions and degrading dinoseb as a result of starch degradation. Inoculation of this soil with an aerobic starch-degrading microorganism and then an acclimated, anaerobic, dinoseb-degrading consortium did not improve dinoseb degradation. In a second acutely contaminated soil, these inoculations improved dinoseb degradation rates over those of uninoculated controls.     

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.     

Bioremediation of soils contaminated with the herbicide 2-sec-butyl-4,6-dinitrophenol (dinoseb).

A novel soil treatment method for achieving the removal of dinoseb (2-sec-butyl-4,6-dinitrophenol) from contaminated soils was investigated. One soil contained dinoseb as the major contaminant, although several other hazardous compounds were also present. A second soil was highly contaminated with dinoseb. Dinoseb was not degraded in these soils under the aerobic conditions at each site. Pretreatment of the soils by the addition of a starchy potato-processing by-product and flooding with phosphate buffer stimulated the consumption of oxygen and nitrate from the soils, thereby lowering the redox potential and creating anaerobic conditions. Anaerobiosis (Eh less than -200 mV) promoted the establishment of an anaerobic microbial consortium that degraded dinoseb completely, without the formation of the polymerization products seen under aerobic or microaerophilic conditions. When dinoseb was present at low concentrations in a chronically contaminated soil, the natural microflora was capable of establishing anaerobic conditions and degrading dinoseb as a result of starch degradation. Inoculation of this soil with an aerobic starch-degrading microorganism and then an acclimated, anaerobic, dinoseb-degrading consortium did not improve dinoseb degradation. In a second acutely contaminated soil, these inoculations improved dinoseb degradation rates over those of uninoculated controls.     

Effects of oxygen,nitrogen, and temperature on gasoline biodegradation in soil

Biodegradation was considered to be a feasible approach to remediate petroleum hydrocarbon-contaminated soil from a site at the University of Idaho. Before a full-scale treatment process was designed, the biodegradative capacity of the soil's indigenous microorganisms was tested. Gas chromatography was used to measure gasoline vapor components in the headspace above the contaminated soils held in closed containers. In a study of biodegradation kinetics, gasoline degradation rates under various conditions (different soil cores, temperatures, oxygen concentrations, and nutrient concentrations) were tested. It was found that gasoline hydrocarbons could be biodegraded at relatively high rates after appropriate nutrient additions. An unexpected observation was that the optimal concentration of oxygen for the gasoline-degrading microorganisms in these soils was only 10%.Publication No. 94505 of the Idaho Agricultural Experiment Station.     

Toluene biodegradation rates in unsaturated soil systems versus liquid batches and their relevance to field conditions

Contaminant biodegradation in unsaturated soils may reduce the risks of vapor intrusion. However, the reported rates show large variability and are often derived from slurry experiments that are not representative of unsaturated conditions. Here, different laboratory setups are used to derive the biodegradation capacity of an unsaturated soil layer through which gaseous toluene migrates from the water table upwards. Experiments in static unsaturated soil microcosms at 6–30 % water-filled porosity (WFP) and unsaturated soil columns at 9, 14, and 27 % WFP were compared with liquid batches containing the same culture of Alicycliphilus denitrificans. The biodegradation rates for the liquid batches were orders of magnitude lower than for the other setups. Hence, liquid batches do not necessarily reflect optimal conditions for bacteria; either oxygen or toluene mass transfer at the cell scale or the absence of soil–water–air interfaces seemed to be limiting bacterial activity. For the column setup, the rates were limited by mass supply. The microcosm results could be described by apparent first-order biodegradation constants that increased with WFP or through a numerical model that included biodegradation as a first-order process taking place in the liquid phase only. The model liquid phase first-order rates varied between 6.25 and 20 h^?1 and were not related to the water content. Substrate availability was the primary factor limiting bioactivity, with evidence for physiological stress at the lowest water-filled porosity. The presented approach is useful to derive liquid phase biodegradation rates from experimental data and to include biodegradation in vapor intrusion models.     

Reduction of Perchlorate and Nitrate by Microbial Communities in Vadose Soil

Perchlorate contamination is a concern because of the increasing frequency of its detection in soils and groundwater and its presumed inhibitory effect on human thyroid hormone production. Although significant perchlorate contamination occurs in the vadose (unsaturated) zone, little is known about perchlorate biodegradation potential by indigenous microorganisms in these soils. We measured the effects of electron donor (acetate and hydrogen) and nitrate addition on perchlorate reduction rates and microbial community composition in microcosm incubations of vadose soil. Acetate and hydrogen addition enhanced perchlorate reduction, and a longer lag period was observed for hydrogen (41 days) than for acetate (14 days). Initially, nitrate suppressed perchlorate reduction, but once perchlorate started to be degraded, the process was stimulated by nitrate. Changes in the bacterial community composition were observed in microcosms enriched with perchlorate and either acetate or hydrogen. Denaturing gradient gel electrophoresis analysis and partial sequencing of 16S rRNA genes recovered from these microcosms indicated that formerly reported perchlorate-reducing bacteria were present in the soil and that microbial community compositions were different between acetate- and hydrogen-amended microcosms. These results indicate that there is potential for perchlorate bioremediation by native microbial communities in vadose soil.     

Reduction of perchlorate and nitrate by microbial communities in vadose soil

Perchlorate contamination is a concern because of the increasing frequency of its detection in soils and groundwater and its presumed inhibitory effect on human thyroid hormone production. Although significant perchlorate contamination occurs in the vadose (unsaturated) zone, little is known about perchlorate biodegradation potential by indigenous microorganisms in these soils. We measured the effects of electron donor (acetate and hydrogen) and nitrate addition on perchlorate reduction rates and microbial community composition in microcosm incubations of vadose soil. Acetate and hydrogen addition enhanced perchlorate reduction, and a longer lag period was observed for hydrogen (41 days) than for acetate (14 days). Initially, nitrate suppressed perchlorate reduction, but once perchlorate started to be degraded, the process was stimulated by nitrate. Changes in the bacterial community composition were observed in microcosms enriched with perchlorate and either acetate or hydrogen. Denaturing gradient gel electrophoresis analysis and partial sequencing of 16S rRNA genes recovered from these microcosms indicated that formerly reported perchlorate-reducing bacteria were present in the soil and that microbial community compositions were different between acetate- and hydrogen-amended microcosms. These results indicate that there is potential for perchlorate bioremediation by native microbial communities in vadose soil.     

Aerobic biodegradation of biphenyl and polychlorinated biphenyls by Arctic soil microorganisms.

We examined the degradation of biphenyl and the commercial polychlorinated biphenyl (PCB) mixture Aroclor 1221 by indigenous Arctic soil microorganisms to assess both the response of the soil microflora to PCB pollution and the potential of the microflora for bioremediation. In soil slurries, Arctic soil microflora and temperate-soil microflora had similar potentials to mineralize [14C]biphenyl. Mineralization began sooner and was more extensive in slurries of PCB-contaminated Arctic soils than in slurries of uncontaminated Arctic soils. The maximum mineralization rates at 30 and 7 degrees C were typically 1.2 to 1.4 and 0.52 to 1.0 mg of biphenyl g of dry soil-1 day-1, respectively. Slurries of PCB-contaminated Arctic soils degraded Aroclor 1221 more extensively at 30 degrees C (71 to 76% removal) than at 7 degrees C (14 to 40% removal). We isolated from Arctic soils organisms that were capable of psychrotolerant (growing at 7 to 30 degrees C) or psychrophilic (growing at 7 to 15 degrees C) growth on biphenyl. Two psychrotolerant isolates extensively degraded Aroclor 1221 at 7 degrees C (54 to 60% removal). The soil microflora and psychrotolerant isolates degraded all mono-, most di-, and some trichlorobiphenyl congeners. The results suggest that PCB pollution selected for biphenyl-mineralizing microorganisms in Arctic soils. While low temperatures severely limited Aroclor 1221 removal in slurries of Arctic soils, results with pure cultures suggest that more effective PCB biodegradation is possible under appropriate conditions.     

Effects of Heterogeneity and Experimental Scale on the Biodegradation of Diesel

Biodegradation of petroleum hydrocarbon contamination is a common method forremediating soils and groundwater. Due to complexities with field-scale studies,biodegradation rates are typically evaluated at the bench-scale in laboratory studies.However, important field conditions can be difficult to mimic in the laboratory. Thisstudy investigates three scaling factors that can impact laboratory biodegradation ratesand that are frequently unaccounted for in typical laboratory experimental procedures.These factors are soil heterogeneity, morphology of petroleum hydrocarbon non-aqueous phase liquids (NAPLs) and soil moisture distribution. The effects of these factors on the biodegradation rate of diesel NAPL is tested under a variety of experimental procedures from well-mixed batch studies to four-foot static soil columns. The results indicate that a high degree of variability results from even small-scale heterogeneities. In addition, it appears that as the experimental scale increases, the measured biodegradation rates slow. The results indicate that diesel biodegradation rates derived from small-scale experiments are not necessarily representative of field-scale biodegradation rates.     

Efficiency of Indigenous and Inoculated Cold-Adapted Soil Microorganisms for Biodegradation of Diesel Oil in Alpine Soils

Biodegradation of diesel oil (5 g(middot)kg [soil dry weight](sup-1)) was investigated in five alpine subsoils, differing in soil type and bedrock, in laboratory experiments during 20 days at 10(deg)C. The biodegradation activities of the indigenous soil microorganisms and of a psychrotrophic diesel oil-degrading inoculum and the effect of biostimulation by inorganic fertilization (C/N/P ratio = 100:10:2) were determined. Fertilization significantly enhanced diesel oil biodegradation activity of the indigenous soil microorganisms. Biostimulation by fertilization enhanced diesel oil biodegradation to a significantly greater degree than bioaugmentation with the psychrotrophic inoculum. In none of the five soils did fertilization plus inoculation result in a higher decontamination than fertilization alone. A total of 16 to 23% of the added diesel oil contamination was lost by abiotic processes. Total decontamination without and with fertilization was in the range of 16 to 31 and 27 to 53%, respectively.     

A Correlation to Estimate the Bioventing Degradation Rate Constant

Estimating the biodegradation rate is essential when designing a bioremediation strategy for petroleum-contaminated sites, and when evaluating assessment guidelines. However, estimating the biodegradation rate is difficult as the rate constant varies from site to site due to changing site conditions, which include soil type, biological activity, and type of contaminant. Accordingly, bench-scale biodegradation studies were completed using respirometers to measure first-order biodegradation rate constants for gasoline in several soils over 30 days of incubation. A total of seven soils were tested at various gasoline concentrations with constant nutrient ratios and water content. No microbial inhibition was observed for the range of gasoline concentrations studied. Analysis showed that the statistically significant parameters were the initial population of petroleum-degrading microorganisms and the organic matter content. The developed empirical correlation is a simple tool that practioners can use to estimate the biodegradation rate without conducting lengthy and expensive experiments.     

Site-Specific Limitations of Using Urea as a Nitrogen Source in Biodegradation of Petroleum Wastes in Soil

Nutrient addition is important to achieving the carbon/nitrogen balance and successful biodegradation of petroleum contaminants. Urea has been considered as a preferred nitrogen source in enhancing biodegradation, because of its high nitrogen content and commercial availability. This study investigated urea in the biodegradation of petroleum-contaminated soils collected from an arid and sandy area in Egypt. Ammonium nitrate served as the nitrogen amendment control in this study. Biodegradation of petroleum-contaminated soils from Wyoming was monitored as a comparison. Addition of urea failed to improve the enhancement of biodegradation of petroleum-impacted soil from the Egyptian site; in addition, urea demonstrates an adverse effect on the biodegradation rates. Results indicate that urea or its intermediates may inhibit the microorganisms involved in petroleum degradation. Data from this study suggest that the application of urea in the enhancement of biodegradation of petroleum compounds should consider site specificity, and may not be applicable in geological areas or soils structures similar to those in this study.     

Bioremediation of BTEX Hydrocarbons: Effect of Soil Inoculation with the Toluene-Growing Fungus Cladophialophora Sp. Strain T1

The biodegradation of a mixture of benzene, toluene, ethylbenzene, xylene, (BTEX) and methyl-tert-butyl ether (MTBE) was studied in soil microcosms. Soil inoculation with the toluene-metabolising fungus Cladophialophora sp. strain T1 was evaluated in sterile and non-sterile soil. Induction of biodegradation capacity following BTEX addition was faster in the soil native microflora than in axenic soil cultures of the fungus. Toluene, ethylbenzenes, and the xylenes were metabolized by the fungus but biodegradation of benzene required the activity of the indigenous soil microorganisms. MTBE was not biodegraded under the tested environmental conditions. Biodegradation profiles were also examined under two pH conditions after a long term exposure to BTEX. At neutral conditions the presence of the fungus had little effect on the intrinsic soil biodegradation capacity. At an acidic pH, however, the activity of the indigenous degraders was inhibited and the presence of Cladophialophora sp. increased significantly the biodegradation rates of toluene and ethylbenzene. Comparison of the BTEX biodegradation rates measured in soil batches combining presence and absence of indigenous degraders and the fungal inoculum indicated that no severe antagonism occurred between the indigenous bacteria and Cladophialophora sp. The presence of the fungal inoculum at the end of the experiments was confirmed by PCR-TGGE analysis of small subunits of 18S rDNA.     

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.     

Biodegradation of chemically modified flax fibers in soil and in vitro with selected bacteria

The extent and rate of degradation of flax (Linum usitatissimum) fibers, both in the native state and after surface chemical modification (acetylation or poly(ethylene glycol), PEG, grafting), was investigated under laboratory conditions in two different biodegrading environments. Degradation of the fibers under aerobic conditions by the action of the microorganisms present in soil is assessed with the ASTM 5988-96 method by monitoring carbon dioxide evolution. In vitro biodegradation experiments were carried out by exposing the fibers to a pure culture of Cellvibrio fibrovorans bacteria and measuring the mass loss as a function of time. Despite the complexity of the system, the results of degradation in soil were satisfactorily reproducible, although the absolute rates were found to change in different experiments using the same soil. The degradation rate of acetylated fibers in soil nearly equals that of unmodified fibers, whereas in the pure culture, acetylated fibers biodegrade slower than native fibers. The opposite happens with the PEG-grafted fibers, which degrade slower than unmodified flax in soil and at a comparable rate upon in vitro exposure to the bacterial culture. The different biodegradation kinetics observed in the two biodegrading environments were attributed to differences of biocenoses, abiotic factors, and biodegradation assessing methods. Nevertheless, the final extent of biodegradation was the same for modified and unmodified fibers both in soil and in the pure culture, showing that the surface chemical modifications applied do not significantly affect biodegradability of the flax fibers.     

Microorganisms participating in the biodegradation of modified polyethylene films in different soils under laboratory conditions

The degree of biodegradation of low-density polyethylene (LDPE) films modified with Bionolle^® polyester in different soils under laboratory conditions was evaluated. Films were incubated in soils from waste coal, a forest and an extinct volcano crater. Prior to degradation studies, soils underwent chemical and microbiological analysis. Film weight loss and mechanical properties, as well as the surface of the polymeric samples determined via scanning electron microscopy, were evaluated after 75, 150 and 225 days of biodegradation. Important chemical changes in the polymeric chains were detected by Fourier Transform Infrared Spectroscopy (FTIR). Fungal and bacterial species that were able to grow on the film surfaces were monitored in order to see whether the films were easily colonised by autochthonous microorganisms (i.e., typical to each soil). Identification of microorganisms was based on their cellular fatty acid methyl ester (FAME) profiles. Biodegradation of modified polyethylene films in soils led to significant changes (i.e., elongation at brake of 98%) in their mechanical properties that were caused by biochemical modifications of both polyester and polyethylene. Compared to waste coal soil, films underwent rapid biodegradation in soils that were rich in organic matter. Bacteria belonging to the genus, Bacillus, and the fungi, Gliocladium viride, Aspergillus awamori and Mortierella subtilissima, were easily able to colonise both polyethylene and polyethylene modified with Bionolle^®.     

高黎贡山土壤微生物生态分布及其生化特性的研究

研究了高黎贡山东坡不同海拔高度的自然林、不同海拔高度和人为干扰强度的集体林、不同权属森林和不同土地利用类型土壤微生物数量及某些生化特性。结果表明,在高黎贡山上半部,自然林随海拔降低,土壤微生物数量及活性升高。而下半部,集体林随海拔降低,人为干扰强度和频率增加,土壤微生物数量和活性降低;森林权属从国有集体个人,土壤微生物数量及活性降低;森林被纯林替代后,土壤微生物数量及活性迅速降低,但耕作通常更有利于微生物繁殖。高黎贡山中部(海拔2000m左右)的自然植被下土壤微生物含量丰富且活性较高,但海拔高气温低不利于土壤微生物生长繁殖及进行生物化学变化。另一方面,森林植被的过份砍伐和利用也使土壤微生物数量和活性降至较低水平。     

Estimation of bioavailability and potential risks of naphthalene in soils with solid phase microextraction

A series of batch experiments were conducted to observe the variations of bioavailability of naphthalene in different types of soil with indigenous microorganisms. Solid phase microextraction (SPME) was employed to estimate the bioavailability of naphthalene in the soils. Various soil properties were attained by artificially modifying soil organic matter (SOM) with the addition of bagasse compost and textures with the addition of original silt and clay to determine the correlation between the amount of biodegraded naphthalene after 300 h and the amount of extractable naphthalene by SPME. Experimental results indicated that the biodegradation rate increased from 0.30 (sandy loam) to 0.48 (silty loam) μg g⁻¹ h⁻¹ when soils had more silt/clay. In contrast, the biodegradation rate slightly decreased from 0.30 (1.3% SOM) to 0.20 (5.2% SOM) μg g⁻¹ h⁻¹ when the SOM was high. Distributions of naphthalene in soils after biodegradation were affected by the addition of bagasse compost. It showed that the bioavailability of naphthalene in soils decreased with an increase in SOM. Sequestration as measured by ultrasonic extractability evidently occurred within 4 months in aged soil samples. However, the amounts extracted by sonication after 4 and 16 months of aging did not statistically differ from each other. The SPME measurements correlated well with the amount of biodegraded naphthalene by indigenous microorganisms. Results of this study demonstrate that SPME is a promising method to estimate the bioremediation efficacy of naphthalene-contaminated soils with various properties.     

Microbial degradation of hydrocarbons in the environment.

The ecology of hydrocarbon degradation by microbial populations in the natural environment is reviewed, emphasizing the physical, chemical, and biological factors that contribute to the biodegradation of petroleum and individual hydrocarbons. Rates of biodegradation depend greatly on the composition, state, and concentration of the oil or hydrocarbons, with dispersion and emulsification enhancing rates in aquatic systems and absorption by soil particulates being the key feature of terrestrial ecosystems. Temperature and oxygen and nutrient concentrations are important variables in both types of environments. Salinity and pressure may also affect biodegradation rates in some aquatic environments, and moisture and pH may limit biodegradation in soils. Hydrocarbons are degraded primarily by bacteria and fungi. Adaptation by prior exposure of microbial communities to hydrocarbons increases hydrocarbon degradation rates. Adaptation is brought about by selective enrichment of hydrocarbon-utilizing microorganisms and amplification of the pool of hydrocarbon-catabolizing genes. The latter phenomenon can now be monitored through the use of DNA probes. Increases in plasmid frequency may also be associated with genetic adaptation. Seeding to accelerate rates of biodegradation has been shown to be effective in some cases, particularly when used under controlled conditions, such as in fermentors or chemostats.     

Effects of Zeolite-Containing Material and Ammonium Nitrate on Biodegradation of n-Tridecane in Heavy Clay-Loam Leached Chernozem with High Organic Matter Content

Biostimulation based on usage of soil amendments is growing due to their efficiency in removing different petroleum hydrocarbons (PHC) from contaminated sand or loam-sand soils. However, the research on clay-rich soils with higher organic carbon content, in which PHC biodegradation may proceed differently and which are more difficult to clean up, has been less extensive. In a pot experiment, we studied and compared the effects of two soil amendments, natural zeolite-containing material (ZCM, 50 g kg^?1) as a bulking agent and ammonium nitrate (0.3 g N kg^?1) as a nitrogen fertilizer, on biodegradation of n-tridecane (1 wt.%) in a weakly acidic heavy clay loam leached chernozem with fairly high organic carbon content (3.71%). After 48 days, the nitrogen-amended contaminated soil showed enhancement of both respiratory activity (basal and substrate-induced respiration rates) and the number of n-tridecane- degraders. As a consequence, the extent of n-tridecane biodegradation (86.5%) was essentially higher in the presence of added nitrogen than that in the non-amended soil (73.7%). In contrast, due to the partial retention of n-tridecane molecules in its pores, ZCM retarded biodegradation to 56.0%, showed no significant effect on the number of n-tridecane-degraders and, moreover, enhanced the decomposition of the soil intrinsic organic matter. The obtained data indicate that more precautions should be considered when using porous sorbents such as ZCM for remedial arrangements in PHC-contaminated soils.