Synergistic Effects of Organic Contaminants and Soil Organic Matter on the Soil-Water Partitioning and Effectiveness of a Nonionic Surfactant (Triton X-100)

Napthalene- and decane-contaminated soils were treated with Triton X-100 (a nonionic surfactant) to characterize the soil-water partitioning behavior of the surfactant in soils with different organic content. Soil samples with different organic content were prepared by mixing sand-mulch mixtures at different proportions. The experimental results indicated that the amount of surfactant sorbed onto soil increased with increasing soil organic content and increasing surfactant concentration. The effective critical micelle concentration (CMC) also increased with increasing organic content in soil. The CMC of Triton X-100 in aqueous systems without soil was about 0.3 mM and the effective CMC values measured for soil-water-surfactant systems (approximately 1:19 soil/water ratio) with 25%, 50%, and 75% mulch content were 0.9, 1.0, and 1.7 mM, respectively. Sub-CMC surfactant sorption was modeled accurately with both the Freundlich and the linear isotherm. The maximum surfactant sorption onto soil varied from 66% to 82% of added surfactant in the absence of contaminant. The effective CMC values for Triton X-100 increased to some extent in the presence of contaminants, as did the maximum surfactant sorption. The maximum surfactant sorbed onto the soil with 75% mulch content increased from 82% for clean soils, to 95% and 96% for soils samples contaminated with naphthalene and decane, respectively.     

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.     

Biodegradation of naphthalene in aqueous nonionic surfactant systems.

The principal objective of this study was to quantify the bioavailability of micelle-solubilized naphthalene to naphthalene-degrading microorganisms comprising a mixed population isolated from contaminated waste and soils. Two nonionic surfactants were used, an alkylethoxylate, Brij 30 (C12E4), and an alkylphenol ethoxylate, Triton X-100 (C8PE9.5). Batch experiments were used to evaluate the effects of aqueous, micellized nonionic surfactants on the microbial mineralization of naphthalene and salicylic acid, an intermediate compound formed in the pathway of microbial degradation of naphthalene. The extent of solubilization and biodegradation under aerobic conditions was monitored by radiotracer and spectrophotometric techniques. Experimental results showed that surfactant concentrations above the critical micelle concentration were not toxic to the naphthalene-degrading bacteria and that the presence of surfactant micelles did not inhibit mineralization of naphthalene. Naphthalene solubilized by micelles of Brij 30 or Triton X-100 in liquid media was bioavailable and degradable by the mixed culture of bacteria.     

Assessing bioavailability of the solubilization of organic compound in nonionic surfactant micelles by dose–response analysis

It is uncertain in some extent that organic compounds solubilized in micelles of a nonionic surfactant aqueous solution are bioavailable directly by the microbes in an extractive microbial transformation or biodegradation process. In this work, a dose–response method, where a bioequivalence concept is introduced to evaluate the synergic toxicity of the nonionic surfactants and the organic compounds, was applied to analyze the inhibition effect of organic compounds (naphthalene, phenyl ether, 2-phenylethanol, and 1-butanol) in nonionic surfactant Triton X-100 micelle aqueous solutions and Triton X-114 in aqueous solutions forming cloud point systems. Based on the result, a mole solubilization ratio of organic compounds in micelle was also determined, which consisted very well with those of classic semi-equilibrium dialysis experiments. The results exhibit that bioavailability of organic compounds solubilized in micelles to microbial cells is negligible, which provides a guideline for application of nonionic surfactant micelle aqueous solutions or cloud point systems as novel media for microbial transformations or biodegradations.     

Low surfactant concentration increases fungal mineralization of a polychlorinated biphenyl congener but has no effect on overall metabolism

Three white rot fungi were compared for their ability to attack polychlorinated biphenyl (PCB) congeners in the presence and absence of the non-ionic Triton X-100 or the anionic Dowfax 8390 surfactants at half their critical micelle concentrations. Neither surfactant affected PCB biodegradation monitored by gas chromatography but the release of 14CO2 from 2,4',5-[U-14C]trichlorobiphenyl by Trametes versicolor was stimulated 12% by Triton X-100. Since mineralization is the complete metabolism of the congener and biodegradation was measured as substrate disappearance, Triton X-100 is proposed to aid intracellular solubilization of 2,4',5-trichlorobiphenyl for complete oxidation by T. versicolor.     

Bacterial decolorization of acid orange 7 in the presence of ionic and non-ionic surfactants

The effects of the non-ionic surfactant Triton X-100, the cationic surfactant cetyltri-methylammonium bromide (CTAB) and the anionic surfactant sodium N-lauroyl sarcosinate (SLS) on the decolorization of the reaction medium containing the monoazo dye Acid Orange 7 (AO7) by Alcaligenes faecalis and Rhodococcus erythropolis were studied. It was found that the surfactants influenced in different ways the rate of decolorization. At all concentrations tested the non-ionic surfactant Triton X-100 decreased the decolorization rate of R. erythropolis. At concentrations above the critical micelle concentration (CMC) Triton X-100 upset the usually observed exponential decay of the dye with A. faecalis due probably to the existence of an outer membrane in this organism. In concentrations above the CMC the anionic surfactant SLS inhibited the decolorization and, at prolonged incubation, caused partial release of the bound dye. The cationic surfactant CTAB in concentrations above and below the CMC accelerated drastically the binding of AO7 to the cells causing a rapid staining of the biomass and complete decolorization of the reaction medium. An attempt was made for explanation of the observed differences by the negative electrostatic charge of the living bacterial cell.     

Molecular characterization of surfactant-driven microbial community changes in anaerobic phenanthrene-degrading cultures under methanogenic conditions

SDS and Triton X-100 added at their critical micelle concentrations (CMCs), increased phenanthrene solubility in the presence of sediments and inhibited phenanthrene biodegradation. Triton X-100 caused more inhibition than SDS. 16S rDNA analyses revealed that both surfactants changed the microbial communities of phenanthrene-degrading cultures. Further, after the surfactant additions, parts of the microbial populations were not detected and methane production decreased. Surfactant applications, necessary to achieve actual CMCs, alter microbial community structure and diminish methanogenic activity under anaerobic conditions. We propose that this change may be related to the inhibitory effects of SDS and Triton X-100 on phenanthrene biodegradation under methanogenic conditions.     

Effect of calcium on the surfactant tolerance of a fluoranthene degrading bacterium

Surfactants are known to increase the apparent aqueous solubility of polycyclic aromatic hydrocarbons (PAHs) and may thus be used to enhance the bioavailability and thereby to stimulate the biodegradation of these hydrophobic compounds. However, surfactants may in some cases reduce or inhibit biodegradation because of toxicity to the bacteria. In this study, toxicity of surfactants on Sphingomonas paucimobilis strain EPA505 and the effect on fluoranthene mineralization were investigated using Triton X-100 as model surfactant. The data showed that amendment with 0.48 mM (0.3 g l-1) of Triton X-100 completely inhibited fluoranthene and glucose mineralization and reduced cell culturability by 100% in 24 h. Electron micrographs indicate that Triton X-100 adversely affects the functioning of the cytoplasmic membrane. However, in the presence of 4.13 mM Ca2+-ions, Triton X-100 more than doubled the maximum fluoranthene mineralization rate and cell culturability was reduced by only 10%. In liquid cultures divalent ions, Ca2+ in particular and Mg2+ to a lesser extent, were thus shown to be essential for the surfactant-enhanced biodegradation of fluoranthene. Most likely the Ca2+-ions stabilized the cell membrane, making the cell less sensitive to Triton X-100. This is the first report on a specific factor which is important for successful surfactant-enhanced biodegradation of PAHs.     

Determination of surfactant critical micelle concentration by a novel fluorescence depolarization technique

A novel method using fluorescence depolarization to determine the critical micelle concentrations (CMC) of surfactants was developed. Fluorescence anisotropies of Triton X-100, sodium dodecyl sulfate, and sodium cholate were measured using 1,6-diphenyl-1,3,5-hexatriene as a fluorescence probe. Fluorescence anisotropy decreased with increasing surfactant concentrations below the CMC and leveled off above the CMC. The depolarization method does not depend on the concentration of DPH and is largely immune to light-scattering problems encountered in turbid aqueous systems.     

Influence of Nonionic Surfactants on Bioavailability and Biodegradation of Polycyclic Aromatic Hydrocarbons

The presence of the synthetic nonionic surfactants Triton X-100, Tergitol NPX, Brij 35, and Igepal CA-720 resulted not only in increased apparent solubilities but also in increased maximal rates of dissolution of crystalline naphthalene and phenanthrene. A model based on the assumption that surfactant micelles are formed and act as a separate phase underestimated the dissolution rates; this led to the conclusion that surfactants present at concentrations higher than the critical micelle concentration affect the dissolution process. This conclusion was confirmed by the results of batch growth experiments, which showed that the rates of biodegradation of naphthalene and phenanthrene in the dissolution-limited growth phase were increased by the addition of surfactant, indicating that the dissolution rates were higher than the rates in the absence of surfactant. In activity and growth experiments, no toxic effects of the surfactants at concentrations up to 10 g liter(sup-1) were observed. Substrate present in the micellar phase was shown to be not readily available for degradation by the microorganisms. This finding has important consequences for the application of (bio)surfactants in biological soil remediation.     

Extractive biodegradation of diphenyl ethers in a cloud point system: Pollutant bioavailability enhancement and surfactant recycling

The biodegradation of diphenyl ethers (DEs) in the environment is limited by their high hydrophobicity. The enhancement of DE bioavailability by a cloud point system (CPS) was investigated in this study. Three CPSs (i.e., Triton X-114, Triton X-114 + Triton X-45, and Brij30 + TMN-3) were tested to promote DE biodegradation. Biocompatibility tests showed that the biodegradation of DE and 4-bromodiphenyl ether (4-BDE) was inhibited by TX-114, unaffected by TX-114 + TX-45, and promoted by Brij30 + TMN-3 over 48 h of cultivation with Cupriavidus basilensis and 4% (w/v) nonionic surfactants. Further optimization with 2% (w/v) Brij30 + TMN-3 yielded residual DE and 4-BDE quantities of 143 and 154 mg/L, respectively, lower than quantities in the control. During degradation, DE content did not decrease in the dilute phase, but sharply decreased in the coacervate phase, indicating that the DEs gradually diffused and transferred from the coacervate phase to the dilute phase for degradation by microbial cells. This behavior also enhanced the bioavailability of DEs in the CPS. By removing the cell-rich dilute phase and adding fresh degradation medium and DE to the coacervate phase, surfactants were successfully recovered and reused twice without affecting DE biodegradation. Results demonstrated that a CPS with 2% (w/v) Brij30 + TMN-3 not only enhanced the bioavailability of DEs, but also decreased the treatment cost through surfactant recycling, which is beneficial for large-scale applications.     

Co-degradation with glucose of four surfactants,CTAB, Triton X-100, SDS and Rhamnolipid,in liquid culture media and compost matrix

Strengthened biodegradation is one of the key means to treat surfactant pollution in environment, and microorganism and surfactant have significant effects on degradation. In this paper, co-degradation of CTAB, Triton X-100, SDS and rhamnolipid with glucose by Pseudomonas aeruginosa, Bacillus subtilis and compost microorganisms in liquid culture media, as well as the degradation of rhamnolipid in compost were investigated. The results showed that CTAB was recalcitrant to degrade by the three microorganisms and it also inhibited microorganisms from utilizing readily degradable carbon source. Non-ionic surfactant Triton X-100 could also hardly be degraded, but it was not toxic to microorganisms and would not inhibit the growth of the microorganisms. Anion surfactant SDS had no toxicity to microorganisms and could be co-degraded as carbon source with glucose. Biosurfactant rhamnolipid was a kind of particular surfactant, which had no toxicity and could be degraded by Bacillus subtilis and compost microorganisms, while it could not be utilized by its producing bacterium Pseudomonas aeruginosa. Among these three bacteria, the compost consortium had the strongest degradation capacity on the tested surfactants due to their microorganisms’ diversity. In compost matrix rhamnolipid could be degraded during composting, but not preferentially utilized.     

Response of fluoranthene-degrading bacteria to surfactants

A prerequisite for surfactant-enhanced biodegradation is that the microorganisms survive, take up substrate and degrade it in the presence of the surfactant. Two Mycobacterium and two Sphingomonas strains, degrading fluoranthene, were investigated for their sensitivity towards non-ionic chemical surfactants. The effect of Triton X-100 and Tween 80 above their critical micelle concentration on mineralization of [¹⁴C]-glucose and [¹⁴C]-fluoranthene was measured in shaker cultures. Tween 80 had no toxic effect on any of the tested strains. The surfactant inhibited fluoranthene mineralization by the hydrophobic Mycobacterium spp. slightly, but more than doubled that by the two less hydrophobic Sphingomonas strains. Triton X-100 inhibited fluoranthene mineralization by all strains, yet this was more pronounced for the Sphingomonas spp. Both surfactants caused cell wall permeabilization, as shown by transient colouring of surfactant-containing media. Inhibition of glucose mineralization, indicating non-specific toxic effects of Triton X-100, was observed only for the Sphingomonas strains and the toxicity was caused by micelle-to-cell interactions. These strains, however, appeared to recover from initial Triton X-100 toxicity within 50–500 h of exposure. The ratio of surfactant concentration to initial cell density was found to determine critically the bacterial response to surfactants. For both Sphingomonas and Mycobacterium strains, this work indicates that fluoranthene solubilized in surfactant micelles is only partially available for mineralization by the bacteria tested. However, our results suggest that optimal conditions for polycyclic aromatic hydrocarbon mineralization can be developed by selection of the proper surfactant, bacterial strains, cell density and incubation conditions. Received: 6 February 1998 / Received revision: 19 June 1998 / Accepted: 19 June 1998     

Bacterial Adhesion to Soil Contaminants in the Presence of Surfactants

It has been proposed that addition of surfactants to contaminated soil enhances the solubility of target compounds; however, surfactants may simultaneously reduce the adhesion of bacteria to hydrophobic surfaces. If the latter mechanism is important for the biodegradation of virtually insoluble contaminants, then the use of surfactants may not be beneficial. The adhesion of a Mycobacterium strain and a Pseudomonas strain, isolated from a creosote-contaminated soil, to the surfaces of highly viscous non-aqueous-phase liquids (NAPLs) was measured. The NAPLs were organic material extracted from soils from two creosote-contaminated sites and two petroleum-contaminated sites. Cells suspended in media with and without surfactant were placed in test tubes coated with an NAPL, and the percentages of cells that adhered to the surface of the NAPL in the presence and absence of surfactant were compared by measuring optical density. Test tubes without NAPLs were used as controls. The presence of either Triton X-100 or Dowfax 8390 at a concentration that was one-half the critical micelle concentration (CMC) inhibited adhesion of both species of bacteria to the NAPLs. Both surfactants, when added at concentrations that were one-half the CMCs to test tubes containing previously adhered bacteria, also promoted the removal of the cells from the surfaces of the NAPL-coated test tubes. Neither surfactant was toxic to the bacteria. Further investigation showed that a low concentration of surfactant also inhibited the growth of both species on anthracene, indicating that the presence of a surfactant resulted in a reduction in the uptake of the solid carbon source.     

Release kinetics of ATP in cells exposed to nonionic detergents

We have previously shown that the protein binding of intracellular ATP could be examined by monitoring the ATP release kinetics from Triton X-100 and Brij 58 nonionic detergent permeabilized cells. We have now analysed the protein binding of ATP in an isotonic medium using intact and partially ATP depleted Brij 58 treated human erythrocytes. The effects of Triton X-100 below the critical micelle concentration (CMC) was studied in normal and tumorous tissue culture cells and human red blood cells. Our results showed that the protein association of ATP was altered in the partially ATP depleted erythrocytes. Below the CMC value, but above a critical level Triton X-100 treatment was effective in mobilizing the intracellular ATP in both cell types. The ATP release curves were sigmoidal and an ‘all or none’ type of response was observed, especially in erythrocytes. The use of Triton X-100 (< CMC) delays the detergent-induced cell decomposition time thus providing a new approach to investigating the physical state of intracellular ATP.     

Surfactant mediated enhanced biodegradation of hexachlorocyclohexane (HCH) isomers by Sphingomonas sp. NM05

Environmental biodegradation of several chlorinated pesticides is limited by their low solubility and sorption to soil surfaces. To mitigate this problem we quantified the effect of three biosurfactant viz., rhamnolipid, sophorolipid and trehalose-containing lipid on the dissolution, bioavailability, and biodegradation of HCH-isomers in liquid culture and in contaminated soil. The effect of biosurfactants was evaluated through the critical micelle concentration (CMC) value as determined for each isomer. The surfactant increased the solubilization of HCH isomers by 3-9 folds with rhamnolipid and sophorolipid being more effective and showing maximum solubilization of HCH isomers at 40 μg/mL, compared to trehalose-containing lipid showing peak solubilization at 60 μg/mL. The degradation of HCH isomers by Sphingomonas sp. NM05 in surfactant-amended liquid mineral salts medium showed 30% enhancement in 2 days as compared to degradation in 10 days in the absence of surfactant. HCH-spiked soil slurry incubated with surfactant also showed around 30-50% enhanced degradation of HCH which was comparable to the corresponding batch culture experiments. Among the three surfactants, sophorolipid offered highest solubilization and enhanced degradation of HCH isomers both in liquid medium and soil culture. The results of this study suggest the effectiveness of surfactants in improving HCH degradation by increased bioaccessibility.     

Effect of different non-ionic surfactants on the biodegradation of PAHs by diverse aerobic bacteria

The aim of this work was to evaluate the effect of several non-ionic surfactants (Tween-80, Triton X-100 and Tergitol NP-10) on the ability of different bacteria (Enterobacter sp., Pseudomonas sp. and Stenotrophomonas sp.) to degrade polycyclic aromatic hydrocarbons (PAHs). Bacterial cultures were performed at 25 °C in an orbital shaker under dark conditions in BHB medium containing 1% of surfactant and 500 mg l⁻¹ of each PAH. Experiments performed with Tween-80 showed the highest cell density values and maximum specific growth rate because this surfactant was used as a carbon source by all bacteria. High degree of PAHs degradation (>90%) was reached in 15 days in all experiments. Toxicity increased at early times using Tween-80 but decreased to low levels in a short time after the firsts 24 h. On the other hand, Triton X-100 and Tergitol NP-10 were not biodegraded and toxicity kept constant along time. However, PAHs-degradation rate was higher, especially by the action of Enterobacter sp. with Tween-80 or Triton X-100. Control experiments performed without surfactant showed a significant decrease in biomass growth rate with a subsequent loss of biodegradation activity likely due to a reduced solubility and bioavailability of PAHs in absence of surfactant.     

Rapid determination of surfactant critical micelle concentration in aqueous solutions using fiber-optic refractive index sensing

We describe a simple and rapid method for determining the critical micelle concentration (CMC) of surfactants from fiber-optic measurements of refractive index. The refractive index of an aqueous surfactant solution was monitored as the surfactant concentration was increased using an automated dispensing system. On reaching the surfactant’s CMC value, an abrupt change was observed in the rate of increase of the refractive index with increasing concentration. The measurement system provides rapid semiautomatic data collection and analysis, increasing the precision, sensitivity, and range of applicability of the technique while substantially decreasing the amount of manual intervention required. Measurements of CMC for sodium dodecyl sulfate (8.10 mM), cetyltrimethylammonium chloride (1.58 mM), and Triton X-100 (0.21 mM) were in excellent agreement with values previously reported in the literature. The method is applicable to cationic, anionic, and nonionic surfactants, and it offers a facile, in situ, and sensitive means of detecting micelle formation over a broad range of CMC values larger than 10⁻¹ mM.     

Alteration in cell surface properties of <Emphasis Type="Italic">Burkholderia</Emphasis> spp. during surfactant-aided biodegradation of petroleum hydrocarbons

Chemical surfactants may impact microbial cell surface properties, i.e., cell surface hydrophobicity (CSH) and cell surface charge, and may thus affect the uptake of components from non-aqueous phase liquids (NAPLs). This work explored the impact of Triton X-100, Igepal CA 630, and Tween 80 (at twice the critical micelle concentration, CMC) on the cell surface characteristics of Burkholderia cultures, Burkholderia cepacia (ES1, aliphatic degrader) and Burkholderia multivorans (NG1, aromatic degrader), when grown on a six-component model NAPL. In the presence of Triton X-100, NAPL biodegradation was enhanced from 21% to 60% in B. cepacia and from 18% to 53% in B. multivorans. CSH based on water contact angle (50–52°) was in the same range for both strains while zeta potential at neutral pH was −38 and −31 mV for B. cepacia and B. multivorans, respectively. In the presence of Triton X-100, their CSH increased to greater than 75° and the zeta potential decreased. This induced a change in the mode of uptake and initiated aliphatic hydrocarbon degradation by B. multivorans and increased the rate of aliphatic hydrocarbon degradation in B. cepacia. Igepal CA 630 and Tween 80 also altered the cell surface properties. For B. cepacia grown in the presence of Triton X-100 at two and five times its CMC, CSH increased significantly in the log growth phase. Growth in the presence of the chemical surfactants also affected the abundance of chemical functional groups on the cell surface. Cell surface changes had maximum impact on NAPL degradation in the presence of emulsifying surfactants, Triton X-100 and Igepal CA630.