Linking desorption kinetics to phenanthrene biodegradation in soil

The desorption of polycyclic aromatic hydrocarbons (PAHs) often exhibits a biphasic profile similar to that observed for biodegradation whereby an initial rapid phase of degradation or desorption is followed by a phase of much slower transformation or release. Most investigations to-date have utilised a polymeric sorbent, such as Tenax, to characterise desorption, which is methodologically unsuitable for the analysis of soil. In this study, desorption kinetics of ¹⁴C-phenanthrene were measured by consecutive extraction using aqueous solutions of hydroxypropyl-β-cyclodextrin (HPCD). The data indicate that the fraction extracted after 24 h generally approximated the linearly sorbed, rapidly desorbing fraction (F_rap), calculated using a three-compartment model. A good linear correlation between phenanthrene mineralised and F_rap was observed (r² = 0.89; gradient = 0.85; intercept = 8.20). Hence HPCD extraction (24 h) and first-order three-compartment modelling appear to provide an operationally straightforward tool for estimating mass-transfer limited biodegradation in soil.     

Electrokinetic enhancement of phenanthrene biodegradation in creosote-polluted clay soil

Given the difficulties caused by low-permeable soils in bioremediation, a new electrokinetic technology is proposed, based on laboratory results with phenanthrene, to afford bioremediation of polycyclic aromatic hydrocarbons (PAH) in clay soils. Microbial activity in a clay soil historically polluted with creosote was promoted using a specially designed electrokinetic cell with a permanent anode-to-cathode flow and controlled pH. The rates of phenanthrene losses during treatment were tenfold higher in soil treated with an electric field than in the control cells without current or microbial activity. Results from experiments with Tenax-assisted desorption and mineralization of 14C-labeled phenanthrene indicated that phenanthrene biodegradation was limited by mass-transfer of the chemical. We suggest that the enhancement effect of the applied electric field on phenanthrene biodegradation resulted from mobilization of the PAH and nutrients dissolved in the soil fluids.     

Biodegradability of aged pyrene and phenanthrene in a natural soil

A study was conducted to evaluate the biodegradability of pyrene (PYR) and phenanthrene (PHE) aged in a natural soil. Both the single and binary systems were either biostimulated via a nutrient amendment or bioaugmented via an inoculation of the enriched bacteria and nutrients. Aging resulted in higher concentration of both compounds and smaller bacterial activity in the solution-phase. Surprisingly, the total biodegraded extent was greater in the aged soil system than in the freshly spiked system. As anticipated, biostimulation was not appropriate to attain an effective biodegradation in this study, and bioaugmentation achieved a substantial increase the total biodegradation extent. The above findings were attributed to indigenous Pseudomonas aeruginosa entering a stationary-phase during the 200-day aging and producing rhamnolipid biosurfactants. In addition, a different sampling technique (i.e., after vigorous hand-shaking) revealed a 15 times higher microbial population than the normal sampling from the stagnant solution. Therefore, PAH bioavailability in the aged soils can be underestimated when the microbial activity is determined only from the stagnant solution. Furthermore, cometabolism enhanced PYR degradation when PHE was present as a primary substrate.     

Use of reporter-gene based bacteria to quantify phenanthrene biodegradation and toxicity in soil

A phenanthrene-degrading bacterium, Sphingomonas paucimobilis EPA505 was used to construct two fluorescence-based reporter strains. Strain D harboring gfp gene was constructed to generate green fluorescence when the strain started to biodegrade phenanthrene. Strain S possessing gef gene was designed to die once phenanthrene biodegradation was initiated and thus to lose green fluorescence when visualized by a live/dead cell staining. Confocal laser scanning microscopic observation followed by image analysis demonstrates that the fluorescence intensity generated by strain D increased and the intensity by strain S decreased linearly at the phenanthrene concentration of up to 200 mg/L. Such quantitative increase and decrease of fluorescence intensity in strain D (i.e., from 1 to 11.90 ± 0.72) and strain S (from 1 to 0.40 ± 0.07) were also evident in the presence of Ottawa sand spiked with the phenanthrene up to 1000 mg/kg. The potential use of the reporter strains in quantitatively determining biodegradable or toxic phenanthrene was discussed.     

Role of loosely bound humic substances and humin in the bioavailability of phenanthrene aged in soil

A study was conducted to determine a possible role of loosely bound humic substances (i.e., humic and fulvic acids) in bioavailability of aged phenanthrene with time. In this study, long-term residence of phenanthrene in soil is defined as aging or sequestration, and the effect was determined by the declined bioavailability to bacteria of the polycyclic aromatic hydrocarbon with increased residence time. After 1, 7, and 100 days of aging of phenanthrene in Lima loam, about 90-93% of initial phenanthrene was recovered from the humin-mineral fraction of Lima loam whereas less than 12% was found in humic and fulvic acids of the same soil. Mineralization rates of phenanthrene aged in the humin-mineral fraction significantly decreased with time by the test bacterium P5-2. In terms of extents of mineralization, the difference with time was not appreciable, but still significant at P<0.05. Additional decreases in the rates and extents of mineralization were observed with the whole soil (i.e. Lima loam) to which phenanthrene had been aged. Data suggest that major sequestration sites for phenanthrene may reside in the humin-mineral fraction, and probably humic and fulvic acids may act as a physico-chemical barrier to bacterial degradation so that the compound's bioavailability may be limited.     

Effect of surfactants, dispersion and temperature on solubility and biodegradation of phenanthrene in aqueous media

In the present study surfactant addition with the help of either a mechanical dispersion or a thermal treatment was applied in order to increase the solubility and the bioavailability of phenanthrene in aqueous media, and therefore to promote its biodegradation. Among four tested surfactants (Tween 80, Brij 30, sodium dodecyl sulphate and rhamnolipids), Brij 30 (0.5 gL(-1)) showed the best results allowing us to attain about 20 mgL(-1) of soluble phenanthrene. An additional thermal treatment at 60°C for 24h, 200 rpm permitted to increase the solubility of phenanthrene in the presence of Brij 30 (0.5 gL(-1)) to about 30 mgL(-1). Higher dispersions of phenanthrene particles as well as the reduction of their size were obtained using Ultra-Turrax and French press. The biodegradation of phenanthrene by Pseudomonas putida was then investigated. The reduction of size of phenanthrene particles by mechanical dispersion did not influence its biodegradation, suggesting that P. putida consumed only soluble phenanthrene. The addition of Brij 30 (0.5 gL(-1)) permitted to obtain more phenanthrene metabolized. The use of Brij 30 coupled with a transitory heating of phenanthrene-containing medium at 60°C led to an even more complete biodegradation. This might be a promising way to enhance biodegradation of PAHs.     

Effect of soil properties on bioavailability and extractability of phenanthrene and atrazine sequestered in soil

Sixteen soils with markedly different properties were analyzed to determine their porosity in the range of 7 nm-10 microm, cation-exchange capacity (CEC), surface area and clay mineralogy. The extent of sequestration of phenanthrene and atrazine has been shown to differ markedly among these soils. Correlations were sought between soil characteristics and four methods of measuring sequestration. Simple correlation analysis showed that some but not all measures of phenanthrene and atrazine sequestration were highly correlated with organic C content, nanoporosity or CEC but not other properties of the soils. Multiple linear-regression analysis suggested an interaction of organic C content with soil texture, CEC or surface area in determining the extent of atrazine or phenanthrene sequestration. We conclude that organic C content, CEC and other properties of soil may be useful predictors of sequestration of some compounds.     

Effect of physical forms of soil organic matter on phenanthrene sorption

The sorption coefficient, K(OC), of phenanthrene (PHE) has been reported to vary with different types of organic matter, leading to uncertainties in predicting the environmental behavior of PHE. Among the studies that relate organic matter properties to their sorption characteristics, physical conformation of organic matter is often neglected. In this work, organic matter samples of different physical forms were examined for their sorption characteristics. Dissolved humic acids (DHA) showed significantly higher K(OC) than the corresponding solid humic acids (SHA) from which the DHAs were made. The K(OC) of DHAs was found to be related to polarity, whereas K(OC) of SHAs increased with aliphatic carbon content. Soil particles were treated with H(2)O(2) to remove organic matter, and humic acid was coated on H(2)O(2)-treated soil particles to make organo-mineral complexes at pH 4, 7 and 10. Although the nonlinear sorption was apparent for SHAs and H(2)O(2)-treated soil particles, the organo-mineral complexes formed using these two components at pH 4, 7 and 10 exhibited relatively linear sorption at organic carbon content, f(OC)>0.5%. These results indicate that organic matter of the same composition may have different sorption properties due to different physical forms (or conformations). Nonlinear sorption for the complexes formed at pH 4 with lower f(OC) (<0.5%) was also discussed.     

Solubilization and biodegradation of phenanthrene in mixed anionic-nonionic surfactant solutions

The effects of mixed anionic-nonionic surfactants, sodium dodecyl sulfate (SDS) mixed with Tween80 (TW80), Triton X-100 (TX100) and Brij35 respectively on the solubility enhancement and biodegradation of phenanthrene in the aqueous phase were investigated. The efficiency of solubilization and biodegradation of phenanthrene in single-, and mixed-surfactant solutions were also compared. The critical micellar concentrations (CMCs) of mixed surfactants were sharply lower than that of sole SDS. The degree of solubility enhancements by the mixed surfactants followed the order of SDS-TW80>SDS-Brij35>SDS-TX100. Synergistic solubilization was observed in the mixed surfactant solutions, in which the molar ratios of SDS to nonionic surfactant were 1:0, 9:1, 7:3, 5:5, 3:7, 1:9 and 0:1 while the total concentration of surfactants was kept at 5.0 and 10.0 mM, respectively. SDS-Brij35 exhibited more significant degree of synergistic solubility enhancement for phenanthrene. The mixed surfactants exhibited no inhibitory effect on biodegradation of phenanthrene. Substantial amounts of the solubilized phenanthrene by mixed surfactants were completely degraded by phenanthrene-degrading microorganisms within 96 h. The results suggested that anionic-nonionic surfactants would improve the performance of remediation of PAH-contaminated soils.     

非离子型表面活性剂吐温80增溶条件下菲的生物降解

本实验的目的是研究非离子型表面活性剂吐温 80 (Tween 80 )对菲的溶解及生物降解过程的影响。结果表明 ,通过吐温 80促溶 ,菲在水中的溶解度有明显的提高。在与菲共同降解的过程中 ,吐温 80亦能作为碳源被降解微生物利用。但是 ,高浓度的吐温 80对菲的降解有一定的抑制作用 ,同时在菲的降解完成后造成较高的残留表面活性剂量和微生物量     

一株菲降解菌的筛选及降解动力学分析

从克拉玛依油田附近稠油污染土壤中筛选出能以菲为唯一碳源的菲降解菌y-8,通过形态观察、生理生化特性及16SrDNA比对序列分析对该菌株进行了鉴定,确定菲降解菌y-8属于弯曲假单胞菌(Pseudomonas geniculata)。菲降解菌y-8在30℃、接种量2%(体积分数)、pH=7.0、170r/min的条件下振荡培养72h,对初始质量浓度为100mg/L菲的降解率达到93.7%,同时可耐受较高质量浓度的菲(3 000mg/L)。同时,对不同初始浓度菲降解动力学曲线进行分析,建立菌降解的指数模型,得到一级反应动力学方程:lnc=-0.045 1t+A(其中,c为菲质量浓度,mg/L;t为降解时间,h;A为常数),半减期为91.01h。     

Biodegradation of phenanthrene in soil.

We investigated the potential of an aerobic polycyclic aromatic hydrocarbon (PAH)-adapted consortium to degrade phenanthrene in soil. Optimal degradation conditions were determined as pH7.0 and 30 degrees C with a water content of 100% wt soil/wt water (w/w). At a concentration of 5 microg/g, phenanthrene degradation (k1) was measured at 0.0269 l/hr with a half-life (t(1/2)) of 25.8 hrs. Our results show that the higher the phenanthrene concentration, the slower the degradation rates. Phenanthrene degradation was enhanced by treatment with yeast extract, glucose, or pyruvate, but was not significantly improved by the addition of acetate. Degradation was delayed by the addition of either compost or potassium nitrate and enhanced by the addition of nonionic surfactants (Brij30, Brij35, Triton X100 or Triton N101) at critical micelle concentration (CMC). Phenanthrene degradation was delayed at levels above CMC.     

Effect of sludge-amendment or nutrient addition on the biodegradation of the herbicide isoproturon in soil

Adding sludge to agricultural soil results in added organic matter, nutrients and metallic and/or organic pollutants. These components may modify the behaviour of pesticides in the soil. We monitored possible changes in the degradation of the herbicide isoproturon (production of CO2 and degradation products) in soil amended with sludge, heavy metals or nitrogen and phosphorus. The treated and control soils were incubated under controlled conditions for 60 days. The nitrogen and phosphorus had the greatest effect on isoproturon degradation, independent of the presence of pollutants. Mineralisation of the herbicide to CO2 was slow and seemed to be linked to a fast degradation and to the accumulation of a complex degradation product that was neither catabolized nor adsorbed, 4,4'-diisopropylazobenzene. This degradation pathway also produced smaller amounts of non-extractable residues. Sewage sludge had no significant effect on isoproturon degradation, despite a large increase of organic matter mineralisation (factor 2).     

土壤电动修复中菲迁移的数值模拟

针对菲污染土壤修复建模的问题,通过对电动力学作用下菲污染土壤的迁移现象的室内模拟实验,确定了影响菲迁移的电渗流、电迁移、对流和弥散4个主要过程,建立了电动力学作用下菲在污染土壤中的迁移模型;运用COMSOL Multiphysics 5.3软件结合迁移模型的各项方程和选取的参数对菲的迁移过程进行了模拟计算。结果表明：当孔隙率分别为0.33、0.38、0.43和0.48时,菲的最大迁移率分别为31.89%、34.78%、37.97%和41.74%;当电压从0.5 V·cm⁻¹增加至2 V·cm⁻¹的过程中,电渗流通量增大,最大迁移率可达到44.35%;修复区域的浓度均呈“碗状”分布,模拟计算得到在中间靠近阳极区域的菲的浓度达到最小值2.14 mol·m⁻³,迁移率最大为38%。模拟计算的菲迁移分布结果与实验所得结果相吻合,证明该模型用于电动修复多环芳烃污染土壤的适用性。     

Influence of diesel concentration on the fate of phenanthrene in soil

The aim of this study was to investigate the influence of diesel on the loss and bioavailability of soil-associated [14C]phenanthrene with time. In addition, the temporal development of phenanthrene catabolic activity and the impact of co-contaminant mixtures on the soil microflora were also assessed. With respect to compound fate, the results suggested that competitive effects between dissimilar co-contaminants did influence [14C]phenanthrene loss. Where diesel was present at a concentration of 0, 20, 200 and 2000 mg kg(-1), increased phenanthrene loss was observed with increasing diesel concentrations. In the 20,000 mg kg(-1) diesel treatment, however, a significantly higher amount of the initial [14C]activity remained after 225 days. Furthermore, initial degradation of phenanthrene in this treatment was retarded as a result of repressed phenanthrene catabolic activity. These results were complemented by a 4-fold increase in total culturable bacterial cell numbers in the 20,000 mg kg(-1) treatment when compared with the 2000 mg kg(-1) after 225 days of incubation time.     

电子受体对深层土壤中石油烃缺氧降解的影响

微生物降解是处理土壤中石油烃 (PHC)污染的有效技术,目前对PHC微生物降解的研究多集中在好氧条件下,对PHC缺氧微生物降解的研究较少,PHC缺氧降解规律尚不清楚。以PHC污染的深层土壤为对象,探究不同质量分数 (500、1 500、5 000 mg·kg⁻¹)的硫酸盐、硝酸盐或混合电子受体对土壤中土著微生物丰度、群落结构以及PHC缺氧降解的影响规律。结果表明,150 d缺氧培养后,添加相同种类电子受体的土壤处理中细菌丰度、潜在PHC降解菌 (变形菌门和厚壁菌门)丰度随电子受体的质量分数增加而增加;添加相同质量分数的不同种类电子受体土壤处理中细菌丰度、潜在PHC降解菌丰度从高到低分别为硝酸盐、混合电子受体、硫酸盐。添加相同种类电子受体的土壤处理中ΣPHC (C₁₀~C₃₀)和C1 (C₁₀~C₁₆)、C2 (C₁₇~C₂₃)、C3 (C₂₄~C₃₀)组分的降解率随着加入电子受体质量分数增加而增加;相同质量分数的不同种类电子受体土壤处理中ΣPHC和C1、C2、C3组分的降解率从高到低分别为硝酸盐、混合电子受体、硫酸盐。土壤中PHC缺氧降解率与细菌丰度、潜在PHC降解菌丰度均存在正相关关系。研究结果可为石油烃污染土壤的修复技术研发提供技术支持。     

Induction of PAH-catabolism in mushroom compost and its use in the biodegradation of soil-associated phenanthrene

This paper describes the induction of phenanthrene-catabolism within Phase II mushroom compost resulting from its incubation with (1) phenanthrene, and (2) PAH-contaminated soil. Respirometers measuring mineralization of freshly added 14C-9-phenanthere were used to evaluate induction of phenanthrene-catabolism. Where pure phenanthrene (spiked at a concentration of 400 mg kg(-1) wet wt.) was used to induce phenanthrene-catabolism in compost, induction was measurable, with maximal mineralization observed after 7 weeks phenanthrene-compost contact time. Where PAH-contaminated soil was used to induce phenanthrene-catabolism in un-induced compost, induction was observed after 5 weeks soil-compost contact time. Microcosm-scale amelioration of soil contaminated with 14C-phenanthrene (aged in soil for 516 days prior to incubation with compost) indicated that both induced (using pure phenanthrene) and uninduced Phase II mushroom composts were equally able to promote degradation of this soil-associated contaminant. After 111 days incubation time, 42.7 +/- 6.3% loss of soil-associated phenanthrene was observed in the induced-compost soil mixture, while 36.7 +/- 2.9% loss of soil-associated phenanthrene was observed in the uninduced-compost soil mixture. These results are notable as they indicate that while pre-induction of phenanthrene-catabolism within compost is possible, it does not significantly increase the extent of degradation when the compost is used to ameliorate phenanthrene-contaminated soil. Thus, compost could be used directly in the amelioration of contaminated land i.e. without pre-induction of catabolism.     

Low impact of phenanthrene dissipation on the bacterial community in grassland soil

The effect of phenanthrene on the bacterial community was studied on permanent grassland soil historically presenting low contamination (i.e. less than 1 mg kg^?1) by polycyclic aromatic hydrocarbons (PAHs). Microcosms of soil were spiked with phenanthrene at 300 mg kg^?1. After 30 days of incubation, the phenanthrene concentration decreased rapidly until its total dissipation within 90 days. During this incubation period, significant changes of the total bacterial community diversity were observed, as assessed by automated-ribosomal intergenic spacer analysis fingerprinting. In order to get a deeper view of the effect of phenanthrene on the bacterial community, the abundances of ten phyla and classes (Actinobacteria, Acidobacteria, Bacteroidetes, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Firmicutes, Verrucomicrobiales, Gemmatimonadetes, and Planctomycetes) were monitored by quantitative polymerase chain reaction performed on soil DNA extracts. Interestingly, abundances of some bacterial taxa significantly changed as compared with controls. Moreover, among these bacterial groups impacted by phenanthrene spiking, some of them presented the potential of phenanthrene degradation, as assessed by PAH-ring hydroxylating dioxygenase (PAH-RHD_α) gene detection. However, neither the abundance nor the diversity of the PAH-RHD_α genes was significantly impacted by phenanthrene spiking, highlighting the low impact of this organic contaminant on the functional bacterial diversities in grassland soil.     

Evaluation of impacts of soil fractions on phenanthrene sorption

Phenanthrene sorption to soils and soil fractions was investigated using two contrasting soils with different clay mineral and organic carbon (OC) contents in an attempt to evaluate the contribution of each soil fraction to phenanthrene sorption and the applicability of the carbon-normalized distribution constant (K(OC)) in soils. Sorbents were characterized using surface analysis, solid-state (13)C NMR analysis, and glass transition temperature (T(g)) analysis to gain a insight into the chemical nature of OC in soils. Dissolved organic carbon (DOC) in the soil solution impeded the phenanthrene sorption, while humins accounted for the predominant phenanthrene sorption in soils. The contribution of OC to phenanthrene sorption in soil would be overestimated if only a K(OC)-approach was adopted, since clay minerals could account for much of the sorption, especially when OC was low in soils. Nitrogen gas was shown to be inappropriate for probing non-polar sorption capacity. The results obtained highlight the importance of clay minerals in governing the sorption of phenanthrene in soil, and emphasize the inapplicability of the carbon-normalized distribution coefficient K(OC) in soils.     

Accumulation of phenanthrene and pyrene in rhizosphere soil

A study was conducted to determine PAH concentrations in the rhizosphere of plants grown in soil containing phenanthrene or pyrene. The rhizosphere of tall fescue and wheat grown in sterile soil contained 4-5-fold higher pyrene concentrations than unplanted soil. The rhizosphere of several plant species grown in non-sterile soil temporarily contained appreciably more phenanthrene or pyrene than unplanted soil, but those PAHs were degraded with time. The data suggest that plants accumulate such hydrophobic compounds in the rhizosphere after facilitating their transport toward the roots.