Ecotoxicological Assessment of Mixtures of Ether Carboxylic Derivative and Amine-Oxide-Based Non-ionic Surfactants on the Aquatic Environment

The purpose of this study was to discuss the effect of the chemical structure of anionic and non-ionic surfactants and surface activity on toxicity. Single and binary mixtures of three ether carboxylic derivative surfactants and three amine-oxide-based non-ionic surfactants were used. Toxicity was determined using three test organisms: freshwater crustaceans (Daphnia magna), luminescent bacteria (Vibrio fischeri), and microalgae (Selenastrum capricornutum). The toxicity of surfactants is related to the hydrophobic alkyl chain, the degree of ethoxylation, and the critical micelle concentration of surfactants. Relationships found agreed with the fact that the lower toxicity is shown by the shorter alkyl chain. There is a strong relation between surface activity and toxicity: the toxicity increased as the CMC of the surfactant or mixtures of surfactants decreased. Commercial products are formulated using surfactants mixtures, so it is important to know their behavior using an easily measured property: the least toxic mixtures were formed by the surfactants having lower individual toxicity. Around the CMC, our data show a synergism for the binary mixtures. The results have given rise to a classification of the different surfactants and their mixtures according to the organism test, as safe, harmful or toxic. V. fischeri was in general the most sensitive microorganism to the toxic effect of the surfactants, followed by Daphnia magna, while Selenastrum capricornutum was more tolerant. These results can be useful for selecting technically efficient surfactants and their mixtures with a lower ecotoxicity on the aquatic environment.     

Aquatic toxicity and biodegradability of advanced cationic surfactant APA-22 compatible with the aquatic environment

Cationic surfactant is a chemical substance used in hair conditioner, fabric softener and other household products. By investigating the relationship between the aquatic toxicity and the chemical structures of two types of mono alkyl cationic surfactants, alkyl trimethylammonium salts and alkyl dimethylamine salts, we have found that the C22 alkyl chain length is effective to reduce the toxicity. Besides, we have recognized that the amidopropyl functional group contributes to the enhanced biodegradability by investigating the biodegradation trend of (alkylamidopropyl)dimethylamine salt (alkyl chain length: C18). Based on these findings, we have developed mono alkyl cationic surfactant called APA-22, N-[3-(dimethylamino)propyl]docosanamide salt. APA-22 is formed by the C22 alkyl chain, amidopropyl functional group and di-methyltertiary amine group. We evaluated the aerobic and anaerobic biodegradability of APA-22 by two standard methods (OECD Test Guideline 301B and ECETOC technical document No.28) and found that this substance was degraded rapidly in both conditions. The toxicity to algae, invertebrate and fish of this substance are evaluated by using OECD Test Guideline 201, 202 and 203, respectively. All acute toxicity values are >1 mg/L, which indicates that environmental toxicity of this substance is relatively less toxic to aquatic organism. In addition, we estimated the biodegradation pathway of APA-22 and observed the complete disappearance of APA-22 and its intermediates during the test periods. Based on the environmental data provided above, we concluded that APA22 is more compatible with the aquatic environment compared to other cationic surfactants with mono long alkyl chain.     

Biodegradability and aquatic toxicity of glycoside surfactants and a nonionic alcohol ethoxylate

The environmental properties of three glycoside surfactants and one alcohol ethoxylate were examined by standardized laboratory methods. All of the surfactants biodegraded extensively in aerobic screening tests and may be assumed to approach 100% removal in aerobic wastewater treatment plants, except in cases of high loadings or otherwise exceptional conditions. Anaerobic biodegradability tests showed that an ethyl glycoside monoester (EGE) and a linear alkyl polyglycoside (APG) were both mineralized (>70%) under methanogenic conditions. In contrast, a branched APG resisted anaerobic degradation, while the alcohol ethoxylate was partially mineralized by anaerobic bacteria. The EGE surfactant was most rapidly mineralized in aerobic and anaerobic biodegradability tests. None of the surfactants inhibited respiration in activated sludge at the highest concentration tested (200 mg/L). Tests with aquatic organisms showed increasing toxicity in the following order: branched APG<EGE<linear APG<alcohol ethoxylate. Negligible aquatic toxicity was observed for the branched APG, while the alcohol ethoxylate was highly toxic to examined organisms. This evaluation demonstrates that considerable variation in biodegradability and toxicity responses can be seen within structurally related glucose-based surfactants.     

Development and application of kinetic models for the primary biodegradation of non-ionic surfactants

The growing concern for the environment is promoting the use of surfactant products from renewable sources such as fatty alcohol ethoxylates. The high production and use of these products implies the need to develop models that enable predictions of their behaviour in biodegradation processes. The biodegradation tests were carried out according to the OECD 301 E test for ready biodegradability. In this work, kinetic models of general application to surfactant biodegradation are developed, both for substrates that do not support growth and for those that do, considering a residual substrate concentration as not being biodegraded. The models were applied to three commercial non-ionic surfactants, fatty alcohol ethoxylates with different carbon-chain lengths and degrees of ethoxylation, also analysing the initial surfactant concentration.     

Primary Biodegradation of Commercial Fatty-Alcohol Ethoxylate Surfactants: Characteristic Parameters

This paper concerns the primary biodegradation of different commercial fatty-alcohol ethoxylate surfactants (FAEs), applying the OECD 301 E test for ready biodegradability. Changes were made both in the carbon-chain length of the surfactants as well as in the number of units of ethylene oxide (EO) in its molecule. The biodegradation were monitored, analysing the colony-forming units (CFU) formed during this process. From the biodegradation profiles drawn for the FAEs, parameters characteristic of the biodegradation process were defined: latency time (t _L), biodegradability at 50 h of assay (B), half-life (t _1/2), mean biodegradation rate until reaching biodegradability of 85% (V _M), and the residual concentration of the surfactant (S _R). The analysis of these parameters enabled the establishment of the influence of surfactant concentration and structure during the biodegradation process. The increase in the surfactant concentration lowered the rate of the biodegradation process and the biodegradability of the surfactant in addition to the half-life and residual concentration of the surfactant. The mean biodegradation rate, V _M, for fatty-alcohol ethoxylates increased with the number of EO units and molecular weight of the surfactant. At low initial test concentrations (less than 25 mg/L), the concentration of the residual surfactant rapidly diminished with biodegradation time. For higher concentrations, after an adaptation period of the microorganisms, the surfactant concentration declined exponentially and the biodegradation rate became far slower for all the surfactants. The parameters characteristic of the growth curves: specific growth-rate, k, and the yield of biomass production per gram of surfactant, Y _ap, made possible the quantification and corroboration of the results during the biodegradation process.

Biodegradation of different carboxylate types of cleavable surfactants bearing a 1,3-dioxolane ring

The biodegradability of new carboxylate types of “acid-sensitive” cleavable surfactants bearing a 1,3-dioxolane ring was measured by the biochemical oxygen demand (BOD) method in the presence of activated sludge. The result for sodium dodecanoate, measured under the same conditions, was used as a standard for evaluating the biodegradability of these cleavable surfactants. For cleavable surfactants derived from epoxides and oxocarboxylates, the biodegradation was considerably influenced by the length of the lipophilic alkyl chain, the presence of the oxymethyl moiety in the lipophilic group, and the number of methylene units between the dioxolane ring and the carboxylate group. For another type of cleavable surfactant, 2-(long-chain alkyl)-1,3-dioxolane-4,5-dicarboxylate, the biodegradation rate for the compound, bearing a proton at position 2 in the dioxolane ring, is faster than that for the corresponding compound bearing a methyl group at position 2.     

Biodegradation of sodium alkyl poly(oxyalkylene)sulfates

The biodegradability of sodium alkylpoly(oxyalkylene)sulfates was studied under aerobic conditions by oxygen consumption, total organic corbon (TOC) and methylene blue active substance (MBAS) measurements. MBAS of linear alkylpoly(oxyalkylene)sulfates with propylene oxide (APS) or ethylene oxide (AES) disappeared within 5 days, whereas AES with branched alkyl chains were degraded less than linear AES. APS with propylene oxide from 1 to 3 mol showed BOD/ThOD values of more than 40% after 6 days. Therefore, these surfactants are considered to be readily biodegradable. In comparison to the biodegradability of APS and AES, the existence of propylene oxide groups resulted in a slight decreasing in oxygen consumption and TOC removal. Linear APS with PO of 1~3 mol were degraded according to Swisher's distance principle up to a C₁₆ alkyl chain length. That is, increasing distance principle up to a C₁₆ alkyl chain length. That is, increasing distance between sulfate and chain end increased the rate of biodegradation of these surfactants. Furthermore, from the biodegradation test of³⁵S-C₁₂E₃S, it is suggested that the initial step of biodegradation is attack on the terminal methyl group.     

Primary aerobic biodegradation of cationic and amphoteric surfactants

The primary aerobic biodegradation of several cationic and amphoteric surfactants has been studied by using the shaking-flask degradation test and orange II spectrophotometric analysis. The results show that cationic and amphoteric surfactants can be readily biodegraded, with their degradation exceeding 94%. The degradation kinetics can be accurately described by the Boltzmann model. The relationship between structure and biodegradability is discussed. The presence of hydrophobic groups has a strong effect on the biodegradability of these surfactants. Biodegradability decreases with increasing chain length. The presence of hydrophilic groups mainly affects the degradation rate of these surfactants, but not their ultimate biodegradeability. Bio-degradability is deterred and degradation is slowed as steric hindrance increases. Degradation rates increase markedly when hydrophilic groups containing an amide bond are pres-ent.     

A molecular‐thermodynamic approach to predict the micellization of binary surfactant mixtures containing amino sulfonate amphoteric surfactant and nonionic surfactant

A molecular‐thermodynamic approach was adopted to predict the value of mixed critical micelle concentration (cmc) for the binary surfactant mixtures constituted by an amino sulfonate amphoteric surfactant, sodium 3‐(N‐dodecyl ethylenediamino)‐2‐hydropropyl sulfonate (abbr. C12AS), and a nonionic surfactant, octylphenol polyethylene ether (OP‐n, where n denotes the average number of oxyethylene glycol ether). In this investigation, considering two positive charges on the hydrophilic group of C12AS, which is unlike to conventional zwitterionic surfactants having one positive charge (such as, alkylbetaine, etc.), three schemes were designed to obtain the geometric parameter describing the dipole structure of C12AS. According to the selected optimum scheme, four cases corresponding to the different conformations of both the headgroup and the hydrocarbon chain of surfactant were discussed. The results show that the predicted value of mixed cmc for the C12AS/OP‐n mixtures agrees well with the experiment value. The deviation of the predicted value from the experimental value can be explained by the effect of the hydrophilicity of OP‐n on the process of micellization. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Synergism and Performance for Systems Containing Binary Mixtures of Anionic/Cationic Surfactants for Enhanced Oil Recovery

The surfactant structure–performance relationship and application properties in enhanced oil recovery (EOR) for binary mixtures of anionic and cationic surfactants are presented and discussed. A polyoxyethylene ether carboxylate anionic surfactant was blended with a quaternary ammonium chloride cationic surfactant and tested for a high-temperature, low-salinity, and high-hardness condition as found in an oil reservoir. These mixtures were tailored by phase behavior tests to form optimal microemulsions with normal octane (n-C8) and crude oil having an API gravity of 48.05°. The ethoxy number of the polyoxyethylene carboxylate anionic surfactant and the chain length of the cationic surfactant were tuned to find an optimal surfactant blend. Interfacial tensions with n-C8 and with crude oil were measured. Synergism between anionic and cationic surfactants was indicated by surface tension measurement, CMC determination, calculation of surface excess concentrations and area per molecule of individual surfactants and their mixtures. Molecular interactions of anionic and cationic surfactants in mixed monolayers and aggregates were calculated by using regular solution theory to find molecular interaction parameters β ^σ and β ^M . Morphologies of surfactant solutions were studied by cryogenic TEM. The use of binary mixtures of anionic/cationic surfactants significantly broadens the scope of application for conventional chemical EOR methods.     

Sugar fatty acid ester surfactants: Biodegradation pathways

In previous work, we found that the presence of a sulfonyl or alkyl group adjacent to the ester bond of sugar ester surfactants is associated with a dramatic reduction in the rate of biodegradation relative to that of unsubstituted esters. In this study, we investigated the pathways followed during the biodegradation of sucrose laurate, sucrose α-sulfonyl laurate, and sucrose α-ethyl laurate to determine the reasons for their different biodegradation rates. Through the use of high-performance liquid chromatography and proton nuclear magnetic resonance spectroscopy, the nature of the intermediates formed during the biodegradation of these three key sugar esters was determined. It was found that sucrose laurate biodegradation occurs via initial ester hydrolysis. In contrast, sucrose α-sulfonyl laurate degrades by initial alkyl chain oxidation. This indicates that the ester hydrolysis pathway is blocked by the sulfonyl group adjacent to the ester bond so that biodegradation is forced to proceed via the slower alkyl chain oxidation pathway. Sucrose α-ethyl laurate was degraded at least in part by alkyl chain oxidation, indicating that ester hydrolysis was also inhibited by the presence of an ethyl group. It is therefore concluded that previously observed relationships between structure and biodegradability arise because of the influence that different structural elements have on the pathways followed during biodegradation.     

Ion-chromatographic characterization of ethoxylated anionic surfactants

Alkyl ether sulfates (AES), analyzed by nonsuppressed or single-column ion chromatography with conductivity detection, generate profiles that are characteristic of the ethoxylate content. Identification of ethoxylation content was accomplished by calculating the slope of the log of the peak area for each homologue vs. the number of ethoxyl groups in the homologue. Quantitation of ethylene oxide content as well as quantitation of mixed alkyl sufates in the presence of AES in mixed surfactant systems is possible. Raw materials require only dilution in mobile phase, while finished products must be subjected to a solid-phase extraction by means of a reverse-phase cartridge and an ion-pair reagent. The chromatogram of the anionic surfactant yields the moles of ethoxylation and the characterization of the ethoxyl chain distribution. Anionic surfactant mixtures in products are identified and quantitated by reference to AES raw materials with a similar slope.     

新型磷酸酯两性表面活性剂的研究 Ⅱ.复配体系分子间相互作用

用二元表面活性剂溶液的热力学,研究了ＲＨＥＰ－ＨＴＭＡＢ、ＲＨＥＰ－ＳＤＳ、ＲＨＥＰ－ＡＥＯｎ３种水溶液的混合体系中表面吸附层及胶束中表面活性剂分子间相互作用参数βｍ、βｓ及吸附层和胶束的组成。结果表明：（１）３种混合体系βｍ、βｓ值分别为：－１１．２１,－１１．２２;－８．２４,－１０．９６;－５．５,－２．０８。（２）随着烷基（Ｒ）碳链增长,βｍ值变小,但｜βｓ｜值出现极大值。（３）表面压越高,βｓ值越大。并对这些结果做了理论解释。     

Study of the efficiency of technical grade nonionic surfactants

Parameters concerning the microemulsion phase behavior of nonionic surfactants of the alkyl polyglycol ether type have extensively been investigated in the last years. By studying these, essential parameters for future applications can be determined. Especially in the field of enhanced oil recovery, lubricants, and cosmetic applications these parameters are of special interest. In this work, the influence of technical grade nonionic surfactants on the phase behavior and the resulting surfactant efficiency has been studied. For this, the alkyl chain length, the degree, type, and order of alkoxylation of the surfactant have been varied. The investigation of these parameters has been conducted by measuring the phase behavior via the Kahlweit fish diagram. It has been found that varying the C-chain length has a great impact on the efficiency, whereas the influence of the ethoxylation degree is minor. By the introduction of propylene oxide, the efficiency has been improved significantly. Additionally, it is important to have the right order of alkoxylation. If the fatty alcohol is first ethoxylated and afterwards propoxylated the efficiency is significantly decreased.     

Polyethoxylated alkyl phenols: Relationship of structure to biodegradation mechanism

Using various isolation procedures and measurement by infrared spectroscopy, the mechanism of biodegradation of the polyethoxylated alkyl phenols (ABE) in the river water die-away test has been ascertained. Degradation is shown to proceed by carboxylation of the alkyl chain and, in certain cases, by degradation of the ethylene oxide chain. Degradation of the ether chain has been found to take place only when the chain contains ten or less units of ethylene oxide. The analytical evidence points to the degradation of the ether chain by a hydrolysis mechanism. The effect of ether chain degradation on the measurement of residual surfactant by ultraviolet spectroscopy and the cobalt thiocyanate procedures has been demonstrated. Ether chain degradation causes the ABE results to be high by ultraviolet measurement and low by the cobalt thiocyanate procedures. Results of this investigation emphasize the necessity of understanding the mechanism by which degradation takes place, and the significant importance of that degradation, in the various biodegradability tests, before the applicability and reliability of any test for measurement of the residual surfactant can be evaluated. Presented at AOCS Meeting in Cincinnati, October 1965.     

表面活性剂的结构与生物降解性的关系

对表面活性剂的生物降解性进行了全面的概述，着重讨论了表面活性剂的降解性能与结构的关系。表面活性剂的生物降解性主要由疏水基团决定，并随着疏水基线性程度的增加而增加，末端季碳原子会显著降低降解度，疏水链长短也影响降解性；表面活性剂的亲水基性质对生物降解度有次要的影响；乙氧基链长影响非离子表面活性剂的生物降解性；增加磺酸基和疏水基末端之间的距离，烷基苯磺酸盐的初级生物降解度增加（距离原则）。最后指出了我国今后表面活性剂生物降解度研究的发展方向。     

Properties of Sodium Methyl Ester Alpha-Sulfo Alkylate/Trimethylammonium Bromide Mixtures

The surface properties of binary mixtures of anionic sodium methyl ester ??-sulfo alkylate (C _m MES) and cationic alkyl trimethylammonium bromide (C _n TAB) of different carbon chain length have been studied in the present work. The critical micelle concentration (CMC) that was obtained from the plots of surface tension (??) versus concentration showed that mixed surfactants have CMC values that were about 10 times lower than their single components. The large negative values for both interaction parameters suggest the existence of strong synergism between the oppositely charged surfactant molecules. The effect of hydrocarbon chain length of either surfactant was also compared and results showed that the effect of cationic surfactant chain length dominated that of the anionic surfactants. It was also discovered that certain mixed surfactant combinations behave differently from the expected trend.     

Sugar fatty acid ester surfactants: Structure and ultimate aerobic biodegradability

Ultimate aerobic biodegradabilities of an array of sugar ester surfactants were determined by International Standards Organisation method 7827, “Water Quality—Evaluation in an Aqueous Medium of the Aerobic Biodegradability of Organic Compounds, Method by Dissolved Organic Carbon” (1984). The surfactants were nonionic sugar esters with different-sized sugar head groups (formed from glucose, sucrose, or raffinose) and different lengths and numbers of alkyl chains [formed from lauric (C₁₂) or palmitic (C₁₆) acid]. Analogous anionic sugar ester surfactants, formed by attaching an α-sulfonyl group adjacent to the ester bond, and sugar esters with α-alkyl substituents were also studied. It was found that variations in sugar head group size or in alkyl chain length and number do not significantly affect biodegradability. In contrast, the biodegradation rate of sugar esters with α-sulfonyl or α-alkyl groups, although sufficient for them to be classified as readily biodegradable, was dramatically reduced compared to that of the unsubstituted sugar esters. An understanding of the relationship between structure and biodegradability provided by the results of this study will aid the targeted design of readily biodegradable sugar ester surfactants for use in consumer products.     

Synergistic Interaction between Nonionic Octylphenol Polyoxyethylene Ethers and Effect of Hydrophilic Chain

The micellization of binary mixture composed of nonionic octylphenol polyoxyethylene ether (OP-n, n is the average number of oxyethylene unit) and its homologues, as well as the effect of hydrophilic chain were investigated. The tensiometry was adopted to determine the critical micelle concentration of binary surfactant mixture. According to the regular solution theory, some thermodynamic models were used to predict the parameters of micellization and the thermodynamic parameters. For all the three binary mixtures of nonionic/nonionic surfactants, each of which shows a nonideal mixing and can behave synergistically in aqueous solution. For both the mixture of OP-10/OP-7 and the mixture of OP-10/OP-4, the positive deviation of the mole fraction of surfactant in mixed micelle from its ideal value coexists with the negative deviation in the entire range of compositions in aqueous solution, while for the mixture of OP-7/OP-4, it only shows a positive deviation. Thermodynamic data indicate that for all the three binary surfactant mixtures, the process of micellization is entropically spontaneous, and the change of hydrophilic chain results in the difference in the stability of mixed micelle. The results can be explained by the steric effect, the hydrogen bonding and the hydration. The work helps with understanding the interaction between molecules and properties for some industrial products constituted by nonionic surfactant and its homologues.     

Ozonation of Anionic and Non-ionic Surfactants in Aqueous Solutions: Impact on Aquatic Toxicity

The objective of this study was to investigate the influence of ozonation of anionic and non-ionic surfactants on their aquatic toxicity. Toxicity values of various commercially important anionic and non-ionic surfactants have been determined using the luminescent bacterium Vibrio fischeri. Surface tension measurements were made to study the interfacial activity. The behavior depends on the chemical structure. Some intermediate ozonation products were found to be more toxic than the base surfactant and others were found to be less. Surfactants with aromatic rings such as linear alkyl benzene sulfonates, or surfactants with glycosidic groups such as alkylpolyglucosides, exhibit a lower toxicity after ozonation. On the other hand, ether groups present in the fatty-alcohol ethoxylates and ether carboxylic derivative surfactants, and carboxylic acid derivates present in the ether carboxylic derivative surfactants lead to increasing toxicity after ozonation. Surfactants with ether groups probably formed short-chain polyethoxylated compounds and carboxylic acids, which are possibly responsible for the surface-tension decrease that promotes the toxicity increase.