Enhanced desorption of phenanthrene from contaminated soil using anionic/nonionic mixed surfactant

A new approach using an anionic/nonionic mixed surfactant, sodium dodecyl sulphate (SDS) with Triton X-100 (TX100), was utilized for the desorption of phenanthrene from an artificial contaminated natural soil in an aim to improve the efficiency of surfactant remediation technology. The experimental results showed that the presence of SDS not only reduced the sorption of TX100 onto the natural soil, but also enhanced the solubilization of TX100 for phenanthrene, both of which resulted in the distribution of phenanthrene in soil-water systems decreasing with increasing mole fraction of SDS in surfactant solutions. These results can be attributed to the formation of mixed micelles in surfactant solution and the corresponding decrease in the critical micelle concentration of TX100 in mixed solution. The batch desorption experiments showed that the desorption percentage of phenanthrene from the contaminated soil with mixed solution was greater than that with single TX100 solution and appeared to be positively related to the mole fraction of SDS in surfactant solution. Thus, the anionic/nonionic mixed surfactants are more effective for the desorption of phenanthrene from the contaminated soil than a single nonionic surfactant.     

Enhanced desorption of RDX from granular activated carbon.

Several methods (cosolvents, surfactants, and cyclodextrins) were compared for improving desorption of a high explosive, RDX, from granular activated carbon (GAC). In batch desorption tests, 3% of the adsorbed RDX (initially 71.1 mg RDX/g GAC) was desorbed by water over 11 days, compared to 92.6% desorption by 100% ethanol. Solutions of ethanol or methanol in water also effectively desorbed RDX, although methanol was somewhat less effective than ethanol. Sodium dodecyl sulfate desorbed as much as 70% of the adsorbed RDX, while the non-ionic surfactants Tween 80, Triton X-100, and Brij 30 desorbed as much as 42 to 51% of the RDX. In continuous flow column tests, GAC was partially regenerated. One-half of the adsorbed RDX was desorbed by 2100 bed volumes (BV) of 10% ethanol, compared to the 22 500 BV of buffered water. Column modeling indicated that competitive adsorption and altered equilibrium conditions combined to enhance RDX desorption.     

Selective adsorption of phenanthrene dissolved in surfactant solution using activated carbon

Selective adsorption of a hazardous hydrophobic organic compound (HOC) by activated carbon as a means of recovering surfactants after a soil washing process was investigated. As a model system, phenanthrene was selected as a representative HOC and Triton X-100 as a nonionic surfactant. Three activated carbons that differed in size (Darco 20–40 (D20), 12–20 (D12) and 4–12 (D4) mesh sizes) were used in adsorption experiments. Adsorption of surfactant onto activated carbon showed a constant maximum above the critical micelle concentration, which were 0.30, 0.23, 0.15 g g⁻¹ for D20, D12, and D4, respectively. Selectivity for phenanthrene to Triton X-100 was much higher than 1 over a wide range of activated carbon doses (0–6 g l⁻¹) and initial phenanthrene concentrations (10–110 mg l⁻¹). Selectivity generally increased with decreasing particle size, increasing activated carbon dose, and decreasing initial concentration of phenanthrene. The highest selectivity was 74.9, 57.3, and 38.3 for D20, D12, and D4, respectively, at the initial conditions of 10 mg l⁻¹ phenanthrene, 5 g l⁻¹ Triton X-100 and 1 g l⁻¹ activated carbon. In the case of D20 at the same conditions, 86.5% of the initial phenanthrene was removed by sorption and 93.6% of the initial Triton X-100 remained in the solution following the selective adsorption process. The results suggest that the selective adsorption by activated carbon is a good alternative for surfactant recovery in a soil washing process.     

Solubilization of nitrotoluenes in micellar nonionic surfactant solutions

A key factor in selecting surfactants to enhance chemical or biological transformation or physical removal of an organic pollutant from contaminated soil is knowledge of the pollutant's solubility behavior in the surfactant solution. This study investigated the influence of nonionic surfactant structure on the solubility of 4-nitrotoluene (NT), 2,3-dinitrotoluene, 2,4-dinitrotoluene, 2,6-dinitrotoluene, and 2,4,6-trinitrotoluene (TNT) at room temperature. For a series of alkyl phenol ethoxylates (Tergitol NP-8 to NP-40), decreasing the ethoxylate chain length increased the solubility of these nitrotoluenes by a factor of two or less in 10 g l(-1) surfactant solutions, but did not significantly change their molar solubilization ratios (MSR, e.g. 0.02 for TNT) or their micelle-water partition coefficients (K(m), e.g. 3.4 for TNT). For Tergitol NP-8 solutions ranging from 1.0 to 12.4 g l(-1), no enhancement in NT solubility was found, suggesting that the cloud point was reached. The MSRs for Tween 80 were higher than those of Tween 20 and the MSRs of Brij-58 were higher than those for Brij-35. When comparing solutes, NT had the highest solubility and MSR (0.28-0.41), while TNT had the lowest solubility and MSR (0.02-0.03). A linear relationship between K(m) values and octanol-water partition coefficients based on Triton X-100 predicted the logK(m) values within 0.5 of their measured values. A linear solvation free energy correlation for K(m) suggested the importance of solute volume and effective hydrogen bond basicity in the partitioning process while implying that the nitrotoluenes are solubilized in a polar portion of the micelle.     

Effects of SOM, surfactant and pH on the sorption-desorption and mobility of prometryne in soils

Sorption and desorption of the herbicide prometryne in two types of soil subjected to the changes of pH and soil organic matter and surfactant were investigated. The sorption and desorption isotherms were expressed by the Freundlich equation. Freundlich K_f and n values indicate that soil organic matter was the major factor affecting prometryne behavior in the test soils. We also quantified the prometryne sorption and desorption behavior in soils, which arose from the application of Triton X-100 (TX100), a nonionic surfactant and change in pH. Application of TX100 led to a general decrease in prometryne sorption to the soils and an increase in desorption from the soils when applied in dosages of the critical micella concentration (CMC) 0.5, 1 and 2. At the concentration below the CMC, the non-ionic surfactant showed a tendency to decrease prometryne sorption and desorption. It appeared that TX100 dosages above CMC were required to effectively mobilize prometryne. Results indicate that the maximum prometryne sorption and minimum prometryne desorption in soils were achieved when the solution pH was near its pK_a. Finally, the influence of TX100 on the mobility of prometryne in soils using soil thin-layer chromatography was examined.     

A comparative study of adsorption of an anionic and a non-ionic surfactant by soils based on physicochemical and mineralogical properties of soils

In the present work we performed a comparative study on the adsorption of the surfactants sodium dodecyl sulphate (SDS) (anionic), and octylphenoxypolyethoxyethanol (Triton X-100) (non-ionic) to 18 soils with organic matter (OM) and clay fraction contents varying over a broad range. The objective of the study was to gain further insight into the influence of the physicochemical and mineralogical properties of soils on the adsorption of surfactants by soils. Adsorption isotherms were obtained using concentrations below the critical micellar concentration (cmc) of the surfactants. The adsorption coefficients, Kf, determined from the Freundlich equation were lower for SDS (range 1.77-82.1, mean value 36.3) than for Triton X-100 (range 0.01-913, mean value 257). Simple and multiple correlation coefficients were obtained between Kf values and soil characteristics. The results obtained indicate the influence of the OM content on the adsorption of SDS (r=0.64, p<0.01) and of the clay fraction content on that of Triton X-100 (r=0.83, p<0.001). Additionally, we observed a preferential adsorption of SDS by the 1:1 mineral kaolinite (r=0.54, p<0.05), while Triton X-100 was adsorbed mainly by the 2:1 minerals, montmorillonite (r=0.66, p<0.01) and illite (r=0.87, p<0.001). According to the influence of different soil parameters on adsorption, different mechanisms of adsorption are proposed for each surfactant. Our findings point to the interest of considering the physicochemical properties of soils and also the mineralogy of the soil clay fraction when selecting a surfactant in technologies involving enhanced solubilization and removal of contaminants from soils and sediments.     

Soil remediation: humic acids as natural surfactants in the washings of highly contaminated soils

The remediation of the highly contaminated site around the former chemical plant of ACNA (near Savona) in Northern Italy is a top priority in Italy. The aim of the present work was to contribute in finding innovative and environmental-friendly technology to remediate soils from the ACNA contaminated site. Two soils sampled from the ACNA site (A and B), differing in texture and amount and type of organic contaminants, were subjected to soil washings by comparing the removal efficiency of water, two synthetic surfactants, sodium dodecylsulphate (SDS) and Triton X-100 (TX100), and a solution of a natural surfactant, a humic acid (HA) at its critical micelle concentration (CMC). The extraction of pollutants by sonication and soxhlet was conducted before and after the soil washings. Soil A was richer in polycyclic aromatic hydrocarbons, whereas soil B had a larger content of thiophenes. Sonication resulted more analytically efficient in the fine-textured soil B. The coarse-textured soil A was extracted with a general equal efficiency also by soxhlet. Clean-up by water was unable to exhaustively remove contaminants from the two soils, whereas all the organic surfactants revealed very similar efficiencies (up to 90%) in the removal of the contaminants from the soils. Hence, the use of solutions of natural HAs appears as a better choice for soil washings of highly polluted soils due to their additional capacity to promote microbial activity, in contrast to synthetic surfactants, for a further natural attenuation in washed soils.     

Surfactant-enhanced release of carbaryl and ethion from two long-term contaminated soils

The potential of five nonionic surfactants, Triton X-100, Brij35, Ethylan GE08, Ethylan CD127, and Ethylan CPG660 for enhancing release of carbaryl and ethion from two long-term contaminated soils was evaluated using the batch method. Incorporation of the surfactants into soils enhanced the release of both pesticides to various extents, which could be related to the type of pesticides and type and the amount of surfactants added. Release of ethion was dramatically enhanced by aqueous concentrations of surfactants above their critical micelle concentration values. This was attributed to solubility enhancement through incorporation of the highly hydrophobic compound within surfactant micelles. A concentration of 10 g L(-1) of various surfactants released >70% of the total ethion from the soil irrespective of the surfactant. For carbaryl, the surfactants were effective at low concentrations and dependence on concentration was lower than in the case of ethion. The ethylan surfactants (GE08, CD127, and CPG660) had a higher potential than Triton X-100 and Brij35 for releasing the pesticides. However, there was still a significant portion of carbaryl (11% of the total) and ethion (17% of the total) left in the soil. Our study also showed that there must be an optimal concentration of each surfactant to maximize the mass transfer of pesticides. At some threshold concentration level, additional surfactant started to inhibit the mass transfer of solute from the soil into the water. The results suggested that surfactants could help remediation of soils polluted by pesticides. The choice of surfactant should be made based on the properties of pesticides.     

DDT uptake by arbuscular mycorrhizal alfalfa and depletion in soil as influenced by soil application of a non-ionic surfactant

A greenhouse pot experiment was conducted to investigate the colonization of alfalfa roots by the arbuscular mycorrhizal (AM) fungus Glomus etunicatum and application of the non-ionic surfactant Triton X-100 on DDT uptake by alfalfa and depletion in soil. Mycorrhizal colonization led to an increase in the accumulation of DDT in roots but a decrease in shoots. The combination of AM inoculation and Triton X-100 application enhanced DDT uptake by both the roots and shoots. Application of Triton X-100 gave much lower residual concentrations of DDT in the bulk soil than in the rhizosphere soil or in the bulk soil without Triton X-100. AM colonization significantly increased bacterial and fungal counts and dehydrogenase activity in the rhizosphere soil. The combined AM inoculation of plants and soil application of surfactant may have potential as a biotechnological approach for the decontamination of soil polluted with DDT.     

生物与化学表面活性剂协同洗脱土壤中PCBs的研究

通过序批实验和土柱淋洗实验研究了由生物表面活性剂鼠李糖脂(RL)与非离子化学表面活性剂十二烷基醇聚氧乙烯(6)醚(POE(6))混合得到的复配试剂洗脱污染土壤中多氯联苯(PCBs)的作用效果及其作用机理。结果表明,同一土样中,从批实验得到的PCBs洗脱率略高于土柱淋洗实验。RL与POE(6)两种单一试剂对人工污染土样中的PCBs洗脱率均大于60%,而对陈化土样中的洗脱率均不到20%,且土壤中的TOC含量越高,PCBs的洗脱率越低。在质量浓度为301 mg/L(10 CMC)及1 505 mg/L(50 CMC)的RL-POE(6)复配试剂中,RL与POE(6)对人工污染土壤中PCBs的洗脱具有一定的协同作用。当复配试剂的浓度为301 mg/L时,RL与POE(6)对陈化土样中PCBs的洗脱没有协同作用;但当RL-POE(6)的浓度增加到1 505 mg/L时,RL与POE(6)对陈化土样中PCBs的洗脱具有明显的协同作用。     

Synergistic solubilization of polycyclic aromatic hydrocarbons by mixed anionic-nonionic surfactants

Water solubility enhancements of naphthalene (Naph), acenaphthylene (Acen), anthracene (An), phenanthrene (Phen) and pyrene (Py) by micellar solutions of single and mixed anionic-nonionic surfactants were measured and compared. Effects of typical inorganic ions, such as NH(4)(+), Na(+) and Mg(2+) coexisted with the organic pollutants (in soils) on water solubilities of polycyclic aromatic hydrocarbons (PAHs) in the presence of single and mixed surfactants were also investigated. Solubilities of PAHs in water are greatly enhanced in a linear fashion by each of Triton X-100 (TX100), Triton X-305 (TX305), Brij 35, and sodium dodecyl sulfate (SDS). Solubility enhancement efficiencies of surfactants above the critical micelle concentration (CMC) follow the order of TX100>Brij 35>TX305>SDS. PAHs are solubilized synergistically in mixed anionic-nonionic surfactant solutions, especially at low surfactant concentrations. The synergistic power of the mixed surfactants is SDS-TX305>SDS-Brij 35>SDS-TX100. Synergistic effect of a given mixed-surfactant solution on different PAHs also appears to be linearly related to the solute logK(ow). The noted synergism for the mixed surfactants is attributed to the formation of mixed micelles, the lower CMC of the mixed-surfactant solutions, and the increase of the solute's molar solubilization ratio or micellar partition coefficients (K(mc)) because of the lower polarity of the mixed micelles. Suitable quantity of inorganic cations can enhance the solubilization capacities of anionic-nonionic mixed surfactants, the effect being Mg(2+)>NH(4)(+)>Na(+). The water solubility of pyrene was slightly increased by anthracene and significantly increased by 1,2,3-TCB in the presence of SDS-Brij 35. Mixed surfactants may improve the performance of surfactant-enhanced remediation of soils and sediments by decreasing the applied surfactant level and thus the remediation cost.     

Soil- and surfactant-enhanced reductive dechlorination of carbon tetrachloride in the presence of Shewanella putrefaciens 200

Sorption of organic contaminants to soils has been shown to limit bioavailability and biodegradation in some systems. Use of surfactants has been proposed to reverse this effect. In this study, the effects of a high organic carbon content soil and a nonionic surfactant (Triton X-100) on the reductive dechlorination of carbon tetrachloride (CCl₄) were examined in anaerobic systems containing Shewanella putrefaciens. Although more than 70% of the added CCl₄ was sorbed to the soil phase in these systems, the reductive dechlorination of CCl₄ was not diminished. Rather, rates of CCl₄ dechlorination in systems containing soil were enhanced relative to systems containing non-sorptive sand slurries. This enhancement was also observed in sterile soil slurries to which a chemical reductant, dithiothreitol was added. It appears that the organic soil used in these experiments contains some catalytic factor capable of transforming CCl₄ in the presence of an appropriate chemical or microbial reductant. The addition of Triton X-100 to sand and soil slurries containing S. putrefaciens resulted in increased CCl₄ degradation in both systems. The effect of Triton could not be explained by: (i) surfactant induced changes in the distribution of CCl₄, (i.e. decreased sorption) or the rate of CCl₄ desorption; (ii) a direct reaction between Triton and CCl₄; or (iii) increased cell numbers resulting from use of the surfactant as a substrate. Rather, it appears that Triton X-100 addition resulted in lysis of bacterial cells, a release of biochemical reductant, and enhanced reductive transformation of CCl₄. These results provide insights to guide the development of more effective direct or indirect bioremediation strategies.     

Effect of surfactants on desorption of aldicarb from spiked soil

Surfactant enhanced desorption of aldicarb from spiked soil was investigated in this paper. Anionic (sodium dodecyl benzene sulphonate, SDBS), cationic (hexadecyl trimethyl ammonium bromide, HTAB) and nonionic (octyl polyethylene glycol phenyl ether, OP) surfactants were tested to determine their optimal desorption conditions including desorption time, mixing speed and surfactant concentrations. The results showed that the optimal operating conditions were obtained at 2 h, 150 rpm, and surfactants concentrations were 1000, 100, and 200 mg l(-1) for SDBS, OP, and HTAB, respectively. The paper also investigated the desorption efficiency of mixture of different kinds of surfactants for aldicarb-spiked soil, and found that anionic-nonionic surfactant mixtures gave the best desorption efficiency up to 77%, while anionic-cationic surfactant mixture gave a poor desorption efficiency similar to water, suggesting that mixture of anionic-nonionic surfactants were highly promising on remediation of aldicarb-contaminated soil.     

Surfactant-induced mobilisation of trace metals from estuarine sediment: implications for contaminant bioaccessibility and remediation

The mobilisation of metals (Al, Fe, Cd, Cu, Mn, Ni, Pb, Sn, Zn) from contaminated estuarine sediment has been examined using commercially available surfactants. Metal release by the anionic surfactant, sodium dodecyl sulphate (SDS), increased with increasing amphiphile concentration up to and above its critical micelle concentration (CMC). Metal mobilisation by the bile acid salt, sodium taurocholate, and the nonionic surfactant, Triton X-100, however, did not vary with amphiphile concentration. SDS was the most efficient surfactant in mobilising metals from the sample, and Cd, Cu and Ni were released to the greatest extents (12-18% of total metal at [SDS] > CMC). Metal mobilisation appeared to proceed via complexation with anionic amphiphiles and denudation of hydrophobic host phases. Surfactants may play an important role in the solubilisation of metals in the digestive environment of deposit-feeding animals and, potentially, in the remediation of metal-contaminated soil and sediment.     

Triton X-100在土壤颗粒上的吸附特征研究

采用平衡振荡法，研究了砂土对非离子表面活性剂Triton X-100的吸附特征。结果表明，砂颗粒对Triton X-100的吸附能力总体较低，单位吸附含量均＜1.1 mg/g；砂颗粒吸附Triton X-100过程中存在显著的吸附剂浓度效应，砂颗粒上Triton X-100含量随着固液比（吸附剂浓度）的增大而减小；吸附容量q_m与平衡常数K_L值随固液比变化而变化，Langmuir方程适用范围是起始浓度C₀相对较小的固液吸附体系；0.5～1 mm石英砂的吸附能力略＞0.2～0.5 mm石英砂，0.5～1 mm和0.2～0.5 mm石英砂吸附Triton X-100变化特征具有显著的一致性，采用高斯拟合模型可以反映出石英砂吸附Triton X-100的变化规律，相关系数R²均＞0.98。     

Selection of surfactant in remediation of DDT-contaminated soil by comparison of surfactant effectiveness

With an aim to select the most appropriate surfactant for remediation of DDT-contaminated soil, the performance of nonionic surfactants Tween80, TX-100, and Brij35 and one anionic surfactant sodium dodecyl benzene sulfonate (SDBS) in enhancement of DDT water solubility and desorption of DDT from contaminated soil and their adsorption onto soil and ecotoxicities were investigated in this study. Tween80 had the highest solubilizing and soil-washing ability for DDT among the four experimental surfactants. The adsorption loss of surfactants onto soil followed the order of TX-100 > Tween80 > Brij35 > SDBS. The ecotoxicity of Tween80 to ryegrass (Lolium perenne L.) was lowest. The overall performance considering about the above four aspects suggested that Tween80 should be selected for the remediation of DDT-contaminated soil, because Tween80 had the greatest solubilizing and soil-washing ability for DDT, less adsorption loss onto soil, and the lowest ecotoxicity in this experiment.     

Influence of adjuvants on physicochemical properties, droplet size spectra and deposit patterns: relevance in pesticide applications

The influence of adjuvants on physicochemical properties, droplet size spectra and deposit patterns of five aqueous spray mixtures was studied under laboratory conditions, using two surfactants, Atlox 3409F and Triton X-114; two humectants, propylene glycol and glycerol; and one polymeric adjuvant, Agrisol FL-100F. For the sake of comparison, two fenitrothion formulations containing polymeric adjuvants, and water were also included in the study. Spray was applied at 25 degrees C and 75 +/- 5% relative humidity, in an enclosure using a twin fluid atomizer. Deposits were collected on Kromekote card/glass plate units. Physicochemical properties studied were: relative viscosity, surface tension, apparent viscosity-shear rate relationship, volatility, pH and conductance. The first four of these properties played significant roles on the droplet and deposit patterns on sampling units. However, the chemical nature of the adjuvants also played some role. Between the two surfactants tested, Triton X-114 provided a pseudoplastic medium, but both surfactant solutions provided similar droplet size spectra and deposit patterns. Between the two humectants, glycerol proved to be more advantageous than propylene glycol. The polymeric adjuvant provided droplet sizes similar to those of the two surfactants, although the recovery of the applied spray volume was higher. Among the two fenitrothion formulations, the one containing lower amounts of polymeric adjuvants showed some advantages, although deposits on the actual biological target should be examined before any definite conclusions can be drawn on the optimum adjuvant concentrations in end-use formulations.     

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.     

应用表面活性剂-生物柴油微乳液去除污染土壤中多环芳烃

针对修复焦化厂高浓度多环芳烃污染土壤高成本的现实,采用以非食用性植物油、生物柴油、表面活性剂及其乳化合成的微乳液为淋洗剂,比较不同淋洗剂的淋洗效果。结果表明乳化合成的微乳液对焦化厂土壤中多环芳烃的总去除率高于单独使用表面活性剂为淋洗剂对土壤中多环芳烃的总去除率,说明生物柴油及植物油与表面活性剂乳化形成的微乳液对原污染土壤中的多环芳烃具有显著的增溶作用。1%TW-80和2.5%TW-80对土壤中多环芳烃总去除率分别为11%和14%;以2.5%TW-80为原料乳化合成的微乳液的淋洗去除率较以1%TW-80为原料乳化合成的微乳液高,总去除率分别为15%～30%和11%～18%;以生物柴油为原料乳化合成的微乳液的淋洗去除率较以植物油为原料乳化合成的微乳液高,分别为17%～30%和15%～23%,且对多环芳烃的去除率与其辛醇水分配系数(logKow)呈线性相关关系。     

Influence of microbial and synthetic surfactant on the biodegradation of atrazine

The present study reports the effect of surfactants (rhamnolipids and triton X-100) on biodegradation of atrazine herbicide by strain A6, belonging to the genus Acinetobacter. The strain A6 was able to degrade nearly 80 % of the 250-ppm atrazine after 6 days of growth. The bacterium degraded atrazine by de-alkylation process. Bacterial cell surface hydrophobicity as well as atrazine solubility increased in the presence of surfactant. However, addition of surfactant to the mineral salt media reduced the rate and extent of atrazine degradation by decreasing the bioavailability of herbicide. On the contrary, addition of surfactant to atrazine-contaminated soil increased the rate and extent of biodegradation by increasing the bioavailability of herbicide. As compared to triton X-100, rhamnolipids were more efficient in enhancing microbial degradation of atrazine as a significant amount of atrazine was removed from the soil by rhamnolipids. Surfactants added for the purpose of hastening microbial degradation may have an unintended inhibitory effect on herbicide degradation depending upon contiguous condition, thus highlighting the fact that surfactant must be judiciously used in bioremediation of herbicides.