Micellar partitioning and its effects on Henry's law constants of chlorinated solvents in anionic and nonionic surfactant solutions

Micellar partitioning of volatile chlorinated hydrocarbons in surfactant solutions and its effects on vapor-liquid equilibrium is fundamental to the overall design and implementation of surfactant-enhanced aquifer remediation. Surfactant micelles greatly enhance contaminant recovery from the subsurface; however, the reduced volatility of organic compounds compromises the aboveground treatment of surfactant-laden wastewaters using air-stripping process. Batch equilibrium tests were performed to acquire micellar partition coefficients (Km) and apparent Henry's law constants (H*) of three prominent groundwater contaminants (tetrachloroethylene, trichloroethylene, cis-dichlorethylene) in the presence of two anionic surfactants (sodium dodecyl sulfate, SDS; sodium dodecylbenzene sulfonate, SDBS) and two nonionic surfactants (Triton X-100 and Tween 80). The H* values were significantly reduced in the presence of all four surfactants over their critical micelle concentrations (cmc's). On a cmc basis, the anionic surfactant SDS had the greatest effect on H*, followed by SDBS, Triton X-100, and Tween 80. Anionic surfactants decreased H* to an order of magnitude lower than nonionic surfactants, although nonionic surfactants decreased the H* at concentrations significantly lower than the anionic surfactants due to their lower cmc's. Nonionic surfactants present higher Km and molar solubilization ratio than anionic surfactants. Tetrachloroethylene has the highest Km values among three chlorinated solvents, which agrees well with the hydrophobicity (Kow) of these chemicals. An empirical correlation between log Km and log Kow is developed on the basis of data from this study and the Km values reported for a number of chlorinated and nonchlorinated hydrocarbons. Equilibrium data were also tested against three sets of models that describe the partitioning of volatile compounds in vapor-water-micelle phases. Applications of these models in experimentally determining Km from batch vapor-water equilibrium data are discussed.     

Selective solubilization of polycyclic aromatic hydrocarbons from multicomponent nonaqueous-phase liquids into nonionic surfactant micelles

This research investigates the equilibrium solubilization behavior of naphthalene and phenanthrene from multicomponent nonaqueous-phase liquids (NAPLs) by five different polyoxyethylene nonionic surfactants. The overall goal of the study was to achieve an improved understanding of surfactant-aided dissolution of polycyclic aromatic hydrocarbons (PAHs) from multicomponent NAPLs in the context of surfactant-enhanced remediation of contaminated sites. The extent of solubilization of the PAHs in the surfactant micelles increased linearly with the PAH mole fraction in the NAPL. The solubilization extent and micelle-water equilibrium partition coefficient of the PAHs increased with the size of the polar shell region of the micelles rather than the size of the hydrophobic core of the micelle. The presence of both PAHs in the shell region of the micelles was confirmed by 1H NMR analysis. This is an important observation because it is commonly assumed that in multi-solute systems the solutes with relatively greater hydrophobicity are solubilized only in the micellar core. A comparison of the 1H NMR spectra of pure surfactant solutions and solutions contacted with various NAPLs demonstrated that the distribution of PAHs between the shell and the core changed with the concentration of PAHs in the micelles and in the NAPL. Competitive solubilization of the PAHs was observed when both PAHs were present in the NAPL. For example, in surfactant solutions of Brij 35 and Tween 80, the solubilization of phenanthrene was decreased in the presence of naphthalene as compared to systems that contained phenanthrene as the only solute. In contrast, with micellar solutions of Tergitol NP-10 and Triton X-100, phenanthrene solubilization was enhanced in the presence of naphthalene. The activity coefficients of the PAHs in the micellar phase were generally found to increase with PAH concentrations in the micelle.     

Optimization of gellan gum production by Sphingomonas paucimobilis ATCC 31461 with nonionic surfactants using central composite design

The effect of nonionic surfactants on gellan production by Sphingomonas paucimobilis was studied by the addition of 0.5, 0.75, 1.0, 1.25 and 1.5 g/l surfactants to shake flask culture. The nonionic surfactants Tween 80, Tween 40 and Triton X-100 improved gellan production by S. paucimobilis, and the maximum yield (10.44 g/l) was obtained with Triton X-100 at 0.75 g/l compared with that of the control fermentation (8.63 g/l) without surfactant. The DO profiles associated with gellan production in a 5-l laboratory fermentor showed higher oxygen and mass transfers during fermentation with surfactant than during control fermentation without surfactant. The addition of surfactant also resulted in a polymer with high viscosity as manifested by its lower acetyl content, than that obtained by control fermentation. A central composite design (CCD) was used to determine the maximum gellan production at optimum values for three process parameters (Triton X-100 concentration, pH, and temperature) each at five levels in a laboratory fermentor. The maximum gellan yield (14.62 g/l) was obtained in a 5-l laboratory fermentor with 1.0 g/l Triton X-100 and at pH 6.0 and temperature 29.6 degrees C. Further studies on the effects of agitation and DOT level demonstrated that the surfactants enhanced oxygen transfer resulting in higher gellan production (27.86 g/l) at higher agitation speed (1000 rpm) and 100% DOT level.     

Influence of rhamnolipids and triton X-100 on the desorption of pesticides from soils

A rhamnolipid biosurfactant mixture produced by P. aeruginosa UG2 and the surfactant Triton X-100 were tested for their effectiveness of enhancing the desorption of trifluralin, atrazine, and coumaphos from soils. Sorption of both surfactants by the soils was significant and adequately described by the Langmuir-type isotherm. Values of maximum sorption capacity (Qmax) and Langmuir constant (Klang) did not correlate with the amount of soil organic matter. Our results indicate that clay surfaces play an important role in the sorption of surfactants. When surfactant dosages were high enough to reach soil saturation and maintain an aqueous micellar phase, pesticide desorption was only enhanced. At dosages below soil saturation, surfactants sorbed onto soil, increasing its hydrophobicity and enhancing the sorption of the pesticides by a factor of 2. Similar values of water-soil partition coefficients (Ksol*) for aged and fresh added pesticides to soils indicate that the aging process used did not significantly after the capability of either surfactant to desorb the pesticides. A model able to estimate equilibrium distributions of organic compounds in soil-aqueous-micellar systems was tested against experimental results. The determined organic carbon partition coefficients, Koc values, indicate that, on a carbon normalized basis, sorbed Rh-mix is a much better sorbent of pesticides than TX-100 or soil organic matter. These results have significant implications on determining the effectiveness of surfactants to aid soil remediation technologies.     

Effects of linear alkylbenzene sulfonate on the sorption of Brij 30 and Brij 35 onto aquifer sand

Surfactant sorption is of considerable importance to environmental applications, including surfactant flushing to mobilize hydrophobic contaminants; effects of surfactants on the transport of dissolved contaminants, microorganisms, and colloids through porous media; and bioremediation of hydrophobic organic compounds, as well as understanding the fate and transport of surfactants as environmental contaminants themselves. Although most sorption studies consider pure surfactants, commercial detergent formulations typically consist of mixtures of nonionic and anionic surfactants. In this study, the effects of varying concentrations of the anionic surfactant linear alkylbenzene sulfonate (LAS) on micelle formation and sorption behavior of the two commonly used nonionic surfactants Brij 30 and Brij 35 onto aquifer sand were examined. A strong linear relationship was observed between the critical micelle concentration (CMC) of the Brij surfactants and the concentration of LAS in the mixture, with the CMC decreasing with increasing concentration of LAS. The relative change in CMC as a function of the LAS concentration was identical forthe two Brij surfactants, indicating that LAS interacted with their common alkyl chains. Sorption isotherms were developed for Brij 30 and Brij 35 present as single surfactants in an aqueous solution as well as when present with LAS. Although LAS had minor effects on the maximum sorption plateaus of the Brij surfactants, Brij sorption at was significantly enhanced as a function of the LAS concentration for Brij aqueous concentrations below the CMC. Application of a multi-interaction isotherm model indicated that the formation of surface aggregates (e.g., hemimicelles) decreased with increasing LAS concentration. Overall, these results provide insight into the complex sorption behavior of surfactant mixtures.     

Influence of the nonionic surfactant Brij 35 on the bioavailability of solid and sorbed dibenzofuran

The effect of the nonionic surfactant Brij 35 on the bioavailability of solid and Teflon-sorbed dibenzofuran for Sphingomonas sp. strain HH19k was studied in simple model systems. Growth with dibenzofuran and dibenzofuran-specific oxygen uptake in surfactant-free media and with Brij 35 above the critical micelle concentration (cmc) were compared with dissolution and desorption in the absence of bacteria. Brij 35 accelerated dissolution and biodegradation of solid dibenzofuran by a factor of 2. It also enhanced the initial desorption rate of dibenzofuran from Teflon by this factor. Continuously decreasing desorption rates were attributed to slow diffusion of dibenzofuran inside Teflon, leading to depletion of dibenzofuran in the exterior of the Teflon particles. Surprisingly, Brij 35 slowed the initial biodegradation of desorbing dibenzofuran. We propose two processes that led to low bioavailability of sorbed dibenzofuran in the presence of surfactant. First, desorbing dibenzofuran rapidly accumulated in surfactant micelles, leading to reduced truly water-dissolved dibenzofuran concentration as the factor controlling the biodegradation rate. Second, Brij 35 suppressed the contact between bacteria and Teflon. This increased the average diffusion distance of dibenzofuran to the bacteria, which in turn flattened the gradient of the dissolved dibenzofuran concentration between the sorbent and the cells as the driving force for desorption.     

Relative effects of surfactants and humidity on soil/air desorption of chloroacetanilide and dinitroaniline herbicides

Herbicides are typically applied as formulation mixtures in order to ensure uniform application and improve biocide performance, but little is known about the effects of formulated surfactants on herbicide exchange between soil and the atmosphere. Desorption experiments were performed for seven herbicides from the chloroacetanilide and dinitroaniline families with model anionic-nonionic surfactant mixtures under a range of relative humidity (RH) conditions (3-66%) on two soils. Enhanced desorption of herbicides from soil to the gas phase was observed asthe concentration of surfactant mixture or the RH increased. Multiple linear regression models developed to summarize the soil/air desorption behavior of these herbicides revealed that surfactant concentration, relative humidity, and herbicide properties (i.e., K(H), K(OA)) all have significant contributions to herbicide desorption. However, the ANOVA results indicated that surfactant concentration only accounted for 1.4% of the variance in desorption, RH accounted for 40-60%, and herbicide properties, logK(H) or logK(OA), accounted for 20-40%. The study results predict that less than a 20% increase (study range 1.5-21.0%) in surfactant concentration could double the atmospheric losses of herbicide from their soil application sites, and about a 60% increase in ambient RH (3-66%) elevated the losses by 10-40 times.     

Surfactants differentially impact p,p'-DDE accumulation by plant and earthworm species

The effect of four surfactants (Triton X-100, Tween-80, rhamnolipids, cyclodextrin) at 100-1000 mg/L on p,p'-DDE phytoextraction by Cucurbita pepo (zucchini) under field conditions and p,p'-DDE bioaccumulation by earthworm species (Eisenia fetida, Lumbricus terrestris) under laboratory conditions was investigated. Abiotically, surfactants (except cyclodextrin) increased contaminant desorption from soil by 4-fold, with higher concentrations generally promoting greater release. Cyclodextrin had no effect on DDE desorption. DDE concentrations in unamended zucchini roots and stems were 30- and 7.8-fold greater than soil levels, respectively, and 1.6% of the contaminant was extracted from the soil. The surfactant effects were cultivar specific. Triton X-100 increased DDE uptake in "Costata" by 2.6-fold, yielding 5% contaminant phytoextraction. In "Goldrush", DDE accumulation decreased by 69% across all surfactants. Surfactants significantly increased DDE bioaccumulation by earthworms. For E. fetida with all surfactants and L. terrestriswith Triton X-100 and cyclodextrin, DDE accumulation increased 2.5-7.2-fold, paralleling abiotic desorption. However, Tween-80 and rhamnolipids increased DDE accumulation in L. terrestris by 74 and 36 fold, respectively. These dramatic increases in contaminant bioaccumulation do not correlate with the increased availability observed abiotically. Surfactant-mediated increases in contaminant bioavailability are an unexpectedly complex process and clearly present unanticipated concerns over pollutant exposure to nontarget organisms.     

Preferential surfactant utilization by a PAH-degrading strain: effects on micellar solubilization phenomena

Biodegradable nonionic Tween series surfactants were employed to assess the effects of synthetic surfactants on the bioavailability of a target polycyclic aromatic hydrocarbon (PAH), phenanthrene, in soil/sediment-free micellar solutions. Dosages of surfactants in excess of their respective critical micelle concentrations (CMCs) dramatically enhanced solubilization of phenanthrene, but the micellar-solubilized phenanthrene was neither directly nor readily bioavailable to the PAH-degrading strain, Sphingomonas paucimobilis EPA 505, used in these bioavailability experiments. The microorganism preferred instead to utilize hydrophobic fractions of the Tween surfactants as a carbon source, resulting in an imbalance of amphiphilic moieties in surfactant molecules and associated destabilization of micelles. This effect was assessed by measurements of surface tension, CMCs, weight-based PAH solubilization ratios, and by characterizations of the surfactants via HPLC separation and emulsification behavior. The observations and analyses lead to a conclusion that preferential biological destabilization of surfactant micelles effects an associated release of phenanthrene to the aqueous phase. The phenanthrene so released then apparently reverts to a crystallized form that appears to be bioavailable only through normal re-dissolution to the aqueous phase. This is, to our knowledge, the first attempt to characterize and quantify changes in the properties and solubilization behaviors of surfactant micelles resulting from their partial and preferential biodegradation. The associated re-deposition of previously micellar-solubilized PAHs observed and the loss of solubilization capacity of recovered surfactants have significant implications for applications of surfactant-enhanced bioremediation of contaminated soils and sediments.     

Sorption behavior of nonylphenol in terrestrial soils

Nonylphenol (NP) as an intermediate from anaerobic degradation of widely used nonionic surfactants occurs widespread in the environment. Partition behavior of this toxic and endocrine-disrupting chemical between soil and water was not examined until yet. The objective of this investigation was to quantify sorption and desorption behavior of 4-nonyl[14C]phenol in a set of 51 soils using the batch equilibrium approach. Kinetic studies indicated apparent equilibrium within 20 h. Sorption was influenced by sorbate structure as could be shown with branched 4-nonyl[14C]phenol and the linear 4-n-NP, respectively. Linear 4-n-NP behaves differently from the branched isomers of 4-NP. Sorption of 4-nonyl[14C]phenol tested with five different initial concentrations resulted in linearly fitted isotherms that provided calculation of sorption partition coefficients (KP). Desorption partition coefficients (KP-des) revealed hysteresis independent of soil properties but decreasing with decreasing initial NP concentrations. KP values were correlated with organic carbon content of the soils yielding a log KOC of 3.97.     

Interactions of organic contaminants with mineral-adsorbed surfactants

Sorption of organic contaminants (phenol, p-nitrophenol, and naphthalene) to natural solids (soils and bentonite) with and without myristylpyridinium bromide (MPB) cationic surfactant was studied to provide novel insightto interactions of contaminants with the mineral-adsorbed surfactant. Contaminant sorption coefficients with mineral-adsorbed surfactants, Kss, show a strong dependence on surfactant loading in the solid. At low surfactant levels, the Kss values increased with increasing sorbed surfactant mass, reached a maximum, and then decreased with increasing surfactant loading. The Kss values for contaminants were always higher than respective partition coefficients with surfactant micelles (Kmc) and natural organic matter (Koc). At examined MPB concentrations in water the three organic contaminants showed little solubility enhancement by MPB. At low sorbed-surfactant levels, the resulting mineral-adsorbed surfactant via the cation-exchange process appears to form a thin organic film, which effectively "adsorbs" the contaminants, resulting in very high Kss values. At high surfactant levels, the sorbed surfactant on minerals appears to form a bulklike medium that behaves essentially as a partition phase (rather than an adsorptive surface), with the resulting Kss being significantly decreased and less dependent on the MPB loading. The results provide a reference to the use of surfactants for remediation of contaminated soils/sediments or groundwater in engineered surfactant-enhanced washing.     

表面活性剂对大肠杆菌产L-鸟氨酸的影响

系统研究了表面活性剂种类(Tween-40、Tween-60、Tween-80、曲通-X-100(Triton X-100)、十二烷基硫酸钠(SDS)、十六烷基三甲基溴化胺(CTAB))、表面活性剂添加浓度以及表面活性剂添加时间对大肠杆菌BW25113生长和发酵产L-鸟氨酸的影响。研究结果表明,发酵0h添加浓度范围为0.1g/L 2g/L的表面活性剂时,Tween-40、Tween-60、Tween-80、Triton X-100和SDS对大肠杆菌BW25113的生长和L-鸟氨酸的产量均无影响,而CTAB对L-鸟氨酸生物合成有一定的促进作用。CTAB的作用效果因CTAB的添加浓度和添加时间的不同而有所差异。发酵8h添加与0.1g/L为CTAB最适添加时间和最佳添加浓度。在该条件下,添加CTAB对大肠杆菌BW25113发酵产L-鸟氨酸的促进作用最大,L-鸟氨酸产量可达743mg/L并且几乎不影响大肠杆菌BW25113的生长。与不添加CTAB的对照组相比,L-鸟氨酸产量提高1.25倍,发酵周期也缩短10h。     

Influence of nonionic surfactant on attached biofilm formation and phenanthrene bioavailability during simulated surfactant enhanced bioremediation

Surfactant effects on preformed attached biofilm formation and the biodegradation of soil-sorbed phenanthrene were monitored using a continuously flowing flowcell system. Thirty-two flowcell reactors were constructed to monitor phenanthrene degradation and biofilm formation under five different surfactant concentrations. Initially, all flowcell reactors were operated without surfactant for 25 days to allow for the formation of an attached bacterial biofilm on phenanthrene spiked soil; after that, a model nonionic surfactant (Triton X-100) was applied to the flowcell reactors at five different concentrations (0, 100, 200, 500, and 1000 mg/L), which represent concentrations below (0 and 100 mg/L) and above (200, 500, and 1000 mg/L) the critical micelle concentration (cmc). The results obtained in this study reveal that bacterial biofilm formation with extracellular polymeric substances was the strategy of bacteria to utilize partially soluble PAHs. However, in the presence of surfactant, this strategy was modified. The presence of surfactant at all concentrations changed the physiological aspects of the attached biofilm, and the bioavailability of the phenanthrene increased with the addition of surfactant above the cmc.     

Enhanced soil washing of phenanthrene by mixed solutions of TX100 and SDBS

Increased desorption of hydrophobic organic compounds (HOCs) from soils and sediments is a key to the remediation of contaminated soils and groundwater. In this study, phenanthrene desorption from a contaminated soil by mixed solutions of a nonionic surfactant(octylphenol polyethoxylate, TX100) and an anionic surfactant (sodium dodecylbenzenesulfonate, SDBS) was investigated. Phenanthrene desorption depended on not only aqueous surfactant concentrations and phenanthrene solubility enhancement but also the soil-sorbed surfactant amount and the corresponding sorption capacity of sorbed surfactants. The added surfactant critical desorption concentrations (CDCs) for phenanthrene from soil depended on both sorbed concentrations of surfactants and their critical micelle concentrations (CMCs). Phenanthrene desorption by mixed solutions was more efficient than individual surfactants due to the low sorption loss of mixed surfactants to soil. Among the tested surfactant systems, mixed TX100 and SDBS with a 1:9 mass ratio exhibited the highest phenanthrene desorption. Mixed micelle formation, showing negative deviation of CMCs from the ones predicted by the ideal mixing theory, was primarily responsible for the significant reduction of soil-sorbed amounts of TX100 and SDBS in their mixed systems. Therefore, mixed anionic-nonionic surfactants had great potential in the area of enhanced soil and groundwater remediation.     

Combined effect of plasticizers and surfactants on the physical properties of starch based edible films

Films made of potato starch were developed and glycerol as plasticizer and Tween 20, Span 80, and soy lecithin as surfactants were included in the formulation. Films were characterized with respect to water vapor permeability (WVP) and mechanical properties. The wettability of the film solutions was quantified by measuring their surface tension.The incorporation of plasticizers resulted in more flexible and manageable films and higher WVP. At low concentration, Tween 20 was the surfactant that reduced surface tension the most, while at high concentration it was lecithin. In the absence of glycerol, surfactants had a significant effect on mechanical properties, but they did not modify significantly WVP of the films. It was observed a synergistic behavior between the plasticizer and the surfactants. Films with glycerol and high level of any of the surfactants behaved as films with larger amount of plasticizer (with lower tensile strength, higher elongation, and higher WVP). Tween 20 was the surfactant that showed the most intense synergistic effect with glycerol.     

Chemicals from wastes: compost-derived humic acid-like matter as surfactant

Compost humic acid-like (cHAL) polymeric matter (MW = 15610), isolated in 12% yield from food and green waste compost, exhibits very good surfactant properties in aqueous solution: i.e., critical micelle concentration (cmc) = 403 mg/L and surface tension at cmc = 36.1 mN/m. Values of cmc are confirmed also by conductivity and phenanthrene solubility measurements. These results, compared with those for other major commercial and research surfactants, propose cHAL as a competitive low-cost biosurfactant.     

Effect of a nonionic surfactant on biodegradation of slowly desorbing PAHs in contaminated soils

The influence of the nonionic surfactant Brij 35 on biodegradation of slowly desorbing polycyclic aromatic hydrocarbons (PAHs) was determined in contaminated soils. We employed a soil originated from a creosote-polluted site, and a manufactured gas plant soil that had been treated by bioremediation. The two soils differed in their total content in five indicator 3-, 4-, and 5-ring PAHs (2923 mg kg(-1) and 183 mg kg(-1) in the creosote-polluted and bioremediated soils, respectively) but had a similar content (140 mg kg(-1) vs 156 mg kg(-1)) of slowly desorbing PAHs. The PAHs present in the bioremediated soil were highly recalcitrant. The surfactant at a concentration above its critical micelle concentration enhanced the biodegradation of slowly desorbing PAHs in suspensions of both soils, but it was especially efficient with bioremediated soil, causing a 62% loss of the total PAH content. An inhibition of biodegradation was observed with the high-molecular-weight PAHs pyrene and benzo[a]pyrene in the untreated soil, possibly due to competition effects with other solubilized PAHs present at relatively high concentrations. We suggest that nonionic surfactants may improve bioremediation performance with soils that have previously undergone extensive bioremediation to enrich for a slowly desorbing profile.     

Influence of surfactant hydrophobicity on the detachment of Escherichia coli O157:H7 from lettuce

The influence of surfactant hydrophobicity on detachment of Escherichia coli O157:H7 from lettuce was determined. Lettuce pieces inoculated with the pathogen were rinsed with Tween and Span surfactants of different hydrophobicity. Of the Tweens, only Tween 85, the Tween with the lowest hydrophile/lipophile balance (HLB), significantly detached the pathogen from lettuce surface. Span 85 (the surfactant with the lowest HLB studied) exhibited the greatest ability among surfactants tested to detach cells from lettuce. This surfactant removed cells attached to the leaf cuticle but not to the cut edge, and caused no detectable reduction in viability of cells remaining on the lettuce. Treatment with Span 85 did not detach cells when they were allowed to attach in the presence of calcium ions. The combination of NaCl/NaHCO3 (pH 10) and Span 85 did not detach cells possibly due to reduced hydrophobicity of the Span at this pH. This study suggests that surfactants of low HLB disrupt hydrophobic interactions between E. coli O157:H7 and the lettuce surface but cannot cause release of cells adhering to hydrophilic structures such as cut or damaged tissue.     

Applications of ultrasound in NAPL remediation: sonochemical degradation of TCE in aqueous surfactant solutions

Surfactant-enhanced pump-and-treat technologies increase the efficiency of nonaqueous-phase liquids (NAPLs) removal from soils. However, high concentrations of surfactants in groundwater impose severe limitations to water treatment. In this paper, we explore the applicability of ultrasonic irradiation as an alternative method for surfactant recovery and contaminant degradation. The combined effects of temperature, initial substrate concentration, and concentration of added surfactant (sodium dodecyl sulfate, SDS) were analyzed for the sonolysis of trichloroethylene (TCE) in batch experiments at an ultrasonic frequency of 500 kHz and 77 W/L applied power density. In the range of 5-30 degrees C, TCE sonolysis becomes faster at higher temperatures, both in the absence and in the presence of surfactant. This indicates that gas-phase pyrolysis prevails over other chemical reactions in the liquid phase. Inhibition of TCE sonolysis was observed in the presence of surfactant at all SDS concentrations. Changes in the initial TCE concentration (from 250 microM to 1.2 mM) showed no effect on the degradation rates in the presence of SDS. For surfactant levels below its critical micelle concentration (cmc), the inhibition of TCE sonolysis exhibited a highly nonlinear dependence with increasing SDS concentration. A correlation was observed in this range between the relative inhibition of sonolysis and the decreasing surface tension of the solutions. Above the cmc up to an SDS concentration of 5%, the reaction rate decreased less markedly. Micellar sequestration of the contaminant seems to be the main reason for this additional inhibition. Bubble growth prior to collapse may incorporate some of the TCE dissolved in the micelles through their adsorption in the expanding bubble walls, thus partially overcoming the scavenging effect due to micellar entrapment of the contaminant.