Nonylphenol Polyethoxylate Surfactants Research Articles

Change of microbial community composition in anaerobic digesters during the degradation of nonylphenol diethoxylate

Nonylphenol polyethoxylate (NPnEO) surfactants, ubiquitous contaminants in sewage processing facilities, continue to receive attention due to their recalcitrance and diverse toxicity concerns. How the addition of nonylphenol diethoxylate (NP2EO) and its biodegradation products affect microbial community structure in anaerobic semi-continuous digesters was investigated by molecular techniques. Fluorescence in situ hybridization (FISH) and quantitative PCR (qPCR) were used in parallel to monitor total Bacteria, four classes of Proteobacteria, total Archaea, and two genera of acetoclastic methanogens (Methanosarcina and Methanosaeta). Beta- and Gammaproteobacteria were the dominant phyla and the relative abundances of both groups were roughly doubled following NP2EO addition. While Methanosaeta was dominant over Methanosarcina throughout, NP2EO addition and accumulation of NP nearly doubled the relative abundance of Methanosarcina. While digester performance was not affected, this study revealed that relative abundances of the key players in anaerobic digestion were altered by the addition of NP2EO.

Determination of nonylphenol isomers in landfill leachate and municipal wastewater using steam distillation extraction coupled with comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry

4-Nonylphenols (4-NPs) are known endocrine disruptors and by-products of the microbial degradation of nonylphenol polyethoxylate surfactants. One of the challenges to understanding the toxic effects of nonylphenols is the large number of isomers that may exist in environmental samples. In order to attribute toxic effects to specific compounds, a method is needed for the separation and quantitation of individual nonylphenol isomers. The pre-concentration methods of solvent sublimation, solid-phase extraction or liquid–liquid extraction prior to chromatographic analysis can be problematic because of co-extraction of thousands of compounds typically found in complex matrices such as municipal wastewater or landfill leachate. In the present study, steam distillation extraction (SDE) was found to be an effective pre-concentration method for extraction of 4-NPs from leachate and wastewater, and comprehensive two-dimensional gas chromatography (GC×GC) coupled with fast mass spectral data acquisition by time-of-flight mass spectrometry (ToFMS) enhanced the resolution and identification of 4-NP isomers. Concentrations of eight 4-NP isomers were determined in leachate from landfill cells of different age and wastewater influent and effluent samples. 4-NP isomers were about 3 times more abundant in leachate from the younger cell than the older one, whereas concentrations in wastewater effluent were either below detection limits or <1% of influent concentrations. 4-NP isomer distribution patterns were found to have been altered following release to the environment. This is believed to reflect isomer-specific degradation and accumulation of 4-NPs in the aquatic environment.

Isomer-Specific Determination of 4-Nonylphenols Using Comprehensive Two-Dimensional Gas Chromatography/Time-of-Flight Mass Spectrometry

Technical nonylphenol (tNP), used for industrial production of nonylphenol polyethoxylate surfactants, is a complex mixture of C(3-10)-phenols. The major components, 4-nonylphenols, are weak endocrine disruptors whose estrogenicities vary according to the structure of the branched nonyl group. Thus, accurate risk assessment requires isomer-specific determination of 4-NPs. Comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GC x GC/ToFMS) was used to characterize tNP samples obtained from seven commercial suppliers. Under optimal chromatographic conditions, 153-204 alkylphenol peaks, 59-66 of which were identified as 4-NPs, were detected. The 4-NPs comprised approximately 86-94% of tNP, with 2-NPs and decylphenols making up approximately 2-9% and approximately 2-5%, respectively. The tNP products were analyzed for eight synthetic 4-NP isomers, and results were compared with published data based on GC/MS analysis. Significant differences were found among the products and between two samples from a single supplier. The enhanced resolution of GC x GC coupled with fast mass spectral data acquisition by ToFMS facilitated identification of all major 4-NP isomers and a number of previously unrecognized components. Analysis of tNP altered by the bacterium, Sphingobium xenophagum Bayram, revealed several persistent 4-NPs whose structures and estrogenicities are presently unknown. The potential of this technology for isomer-specific determination of 4-NP isomers in environmental matrices is demonstrated using samples of wastewater-contaminated groundwater and municipal wastewater.

The impact of co-contaminants and septic system effluent quality on the transport of estrogens and nonylphenols through soil

The impact that varying qualities of wastewater may have on the movement of steroid estrogens through soils into groundwater is little understood. In this study, the steroid estrogens 17β-estradiol (E2) and estrone (E1) were followed through batch and column studies to examine the impact that organic wastewater constituents from on-site wastewater treatment systems (i.e., septic systems or decentralized systems) may have on influencing the rate of transport of estrogens through soils. Total organic carbon (TOC) content (as a surrogate indicator of overall wastewater quality) and the presence of nonyl-phenol polyethoxylate surfactants (NPEO) at concentrations well below the critical micelle concentration were independently shown to be indicative of earlier breakthrough and less partitioning to soil in batch and column experiments. Both NPEO and wastewater with increasing TOC concentrations led to shifts in the equilibrium of E1 and E2 towards the aqueous phase and caused the analytes to have an earlier breakthrough than in control experiments. The presence of nonylphenols, on the other hand, did not appreciably impact partitioning of E1 or E2. Biodegradation of the steroids in soil was also lower in the presence of septic tank effluents than in an organic-free control water. Furthermore, the data indicate that the rate of movement of E1 and E2 present in septic tank effluent through soils and into groundwater can be decreased by removing the NPEOs and TOC through wastewater treatment prior to sub-surface disposal. This study offers some insights into mechanisms which impact degradation, transformation, and retardation, and shows that TOC and NPEO surfactants play a role in estrogen transport.

Environmental fate of phenolic endocrine disruptors: field and laboratory studies

Alkylphenolic compounds derived from microbial degradation of non-ionic surfactants became a major focus of environmental research in the early 1980s. More toxic than the parent compounds and weakly oestrogenic, certain metabolites of nonylphenol polyethoxylate (NPnEO) surfactants, especially nonylphenol (NP), raised sustained concern over the risk they pose to the environment and triggered legal measures as well as partly voluntary actions by the manufacturing industry. Continuous progress in the development of analytical techniques is crucial to understand how these alkylphenolic compounds behave in wastewater treatment, the aquatic environment and in laboratory experiments. Measured concentrations and mass flows of phenolic endocrine disruptors, particularly nonylphenolic compounds, bisphenol A and parabens in municipal wastewater effluents and in the Glatt River, Switzerland, show that rain events leading to discharges of untreated wastewater into rivers have a great impact on the riverine mass flows of contaminants. Biotransformation experiments in our laboratory with nonylphenoxyacetic acid and individual NP isomers enabled the elucidation of degradation pathways of these compounds. The finding that nonylphenoxyacetic acid is metabolized via NP further underscores the role of NP as the most relevant metabolite in the degradation of NPnEO. Several Sphingomonadaceae bacterial strains were found to degrade alpha-quaternary 4-NP isomers by an ipso-substitution mechanism, and to use only the aromatic part of the molecule. These reactions turned out to be isomer specific, meaning that rate and extent of transformation depend on constitution, and possibly also on the absolute configuration of the alkyl side chain of a specific isomer. The observation that NP isomers with distinct oestrogenic activities are differentially degraded has significant implications for risk assessment.

Analysis of Nonylphenol Isomers in a Technical Mixture and in Water by Comprehensive Two-Dimensional Gas Chromatography−Mass Spectrometry

Nonylphenol (NP) is a degradation product of nonylphenol polyethoxylate surfactants and has been reported to occur in water and sediments from urban areas. Technical NP is composed of several structural isomers, and conventional gas chromatography-mass spectrometry techniques have tentatively identified up to 22 components. Isolation and characterization of individual isomers in a technical NP mixture is important, because of the differences in estrogenic and bioaccumulation potential among the isomers. In this study, comprehensive two-dimensional gas chromatography (GC x GC) combined with mass spectrometry (MS) enabled tentative identification of 102 components of NP from a technical mixture. GC x GC-MS was also used to quantify two NP isomers in river water samples. This is the first study to use GC x GC-MS to characterize NP isomers in technical mixtures and for quantitative analysis of NP in river waters.

The partitioning of alkylphenolic surfactants and polybrominated diphenyl ether flame retardants in activated sludge batch tests

Polybrominated diphenyl ethers and nonylphenol polyethoxylates have been reported to be estrogenic and may enter the aquatic environment through the discharge of treated sewage effluent. Therefore, their fate during wastewater treatment processes is an important factor in determining their environmental impact. Batch tests with activated sludge from a Husmann apparatus were used to determine the effects of physico-chemical properties and sludge characteristics on the partitioning of polybrominated diphenyl ether flame retardants and nonylphenol polyethoxylate surfactants during biological wastewater treatment. Hydrophobic compounds, those with high log K ow values, were sorbed more rapidly and to a greater extent to the solid phase than more soluble compounds. For these hydrophobic compounds sorption may become an increasingly important removal mechanism as sludge age and therefore solids content increase. The initial rate of partitioning was greatest for the most hydrophobic compounds but all rates diminished with time as a result of progressive saturation of sorbent binding sites, a reduction of sorbate availability and as a consequence of the system reaching equilibrium. The sorption of polybrominated diphenyl ethers fit Freundlich adsorption isotherms demonstrating generally increasing adsorption capacity and efficiency with increasing hydrophobic nature. A correlation between increasing log K ow and increasing organic matter content was also observed for both polybrominated diphenyl ethers and nonylphenol polyethoxylates indicating the organic content of mixed liquor will also be influential in removing compounds during wastewater treatment.

Trophodynamic Behavior of 4-Nonylphenol and Nonylphenol Polyethoxylate in a Marine Aquatic Food Web from Bohai Bay, North China: Comparison to DDTs

4-Nonylphenol (4-NP) is of particular concern because of its ubiquity in aquatic environment and its endocrine-disrupting effects in aquatic organisms. On the basis of its octanol-water partition coefficient (104.6), it has a potential to bioaccumulate in aquatic food webs. However, there are no reported field studies on the trophodynamics of 4-NP and its precursor, nonylphenol polyethoxylate (NPEOs) surfactants, in aquatic food webs. This study reports the trophodynamics of 4-NP and NPEOs (4 < s < 16) in a marine aquatic food web from Bohai Bay, North China. 4-NP and NPEOs (4 < s < 16) were determined in 14 marine species including plankton, benthic invertebrates, fish, and marine birds. This paper provides the first report on the occurrence of NPEOs with s > 5 in marine biota. Co-analysis of DDTs in all samples allowed a direct comparison of the bioaccumulation behavior of DDTs with that of NP and NPEOs. The lipid equivalent concentration of DDE and 2,2-bis(chlorophenyl)-1-chloroethylene (DDMU) increased with increasing trophic level, and the trophic level was determined by stable isotope ratios. The trophic magnification factors (TMFs) of DDE and DDMU were 3.26 and 3.7, respectively. Lipid equivalent concentrations of 4-NP and of all NPEOs did not exhibit a statistically significant correlation with trophic levels in the food web, and the TMF of NP was 0.83, which was similar to those of all NPEOs (0.45-1.22). These results show that in the studied aquatic food web, there was no trophic magnification for 4-NP and NPEOs, whereas DDE and DDMU biomagnified.

Degradation of nonylphenolic surfactants in activated sludge batch tests

The fate of nonylphenol polyethoxylate surfactants in the activated sludge wastewater treatment process is a concern due to the formation of estrogenic nonlyphenols on degradation and due to the large amounts discharged to the aquatic environment through sewage treatment works. Batch tests using activated sludge from a Husmann apparatus were used to determine the effects of these compounds physico-chemical properties and biological sludge characteristics on biodegradation. Degradation of nonylphenol polyethoxylates with up to 12 ethoxy groups was observed in unacclimated sludge with a concomitant production of nonylphenol and short chain nonylphenol polyethoxylate compounds. Degradation was determined to be a biotic process involving intracellular enzyme activity, which resulted in sludge age being an influential parameter. With increasing sludge age there is an increase in mixed liquor solids concentration in activated sludge which results in greater bacterial numbers and the potential for greater species diversity which therefore increases compound degradation. However, increased degradation of long chain compounds resulted in an accumulation of shorter chain compounds and nonylphenol, which are more resistant to degradation.

Environmental Engineering and Endocrine Disrupting Chemicals

Endocrine disruptors are a class of chemicals of growing interest to the environmental community. The U.S. Environmental Protection Agency’s ~EPA! Risk Assessment Forum defined an endocrine disrupting chemical ~EDC! as ‘‘an exogenous agent that interferes with the synthesis, secretion, transport, binding, action, or elimination of natural hormones in the body that are responsible for the maintenance of homeostasis, reproduction, development, and/or behavior’’ ~EPA 1997!. Most of us are more familiar with chemicals of concern that have a specific health outcome such as lung cancer. However, EDCs are a class of chemicals defined by their mode of action and can result in a variety of health outcomes. For example, an EDC can initiate a health-related outcome in humans or wildlife by binding to and stimulating estrogen or androgen receptors. Gaining a thorough understanding of the endocrine-related effects of chemicals on humans and wildlife is the goal of domestic and international research that will continue far into the future. The Global Endocrine Disruptor Research Inventory ~EPA 2001a! indicates over 600 human and wildlife health effects studies currently underway. The Food Quality Protection Act requires the U.S. EPA to build a screening and testing program to identify those industrial chemicals that cause endocrine-related effects to human and wildlife health ~see http://www.epa.gov/scipoly/ oscpendo/index.htm!. To obtain results for existing industrial chemicals will likely take most of this decade. However, the literature already points to some chemicals as likely endocrine disruptors including certain phthalate esters, particular biodegradation products of octylphenol and nonylphenol polyethoxylate surfactants, several specific PCBs, some chlorinated dioxins, DDT and DDE, bisphenol A, tributyltin, the pesticides methoxychlor and endosulfan, and exogenous steroid hormones, among others. Studies are also underway, worldwide, to characterize the levels of suspected endocrine disruptors to which humans and wildlife are exposed ~EPA 2001a!. Once adequate effects and exposure information are collected, the risk of individual or mixtures of endocrine disruptors can be assessed. Some political bodies have begun to implement risk management strategies for EDCs. For example, the European Union and some individual European nations have banned or are phasing out the use of some endocrine disruptor-related chemicals such as nonylphenol polyethoxylate surfactants and certain phthalate esters. Decisions on how and when to begin actively managing or reducing unacceptable risks posed by EDCs must be determined by stakeholder organizations. Whether or not to apply risk management tools to an EDC-related environmental problem depends on currently available risk information, available management technologies, their economic impact, and social and political factors. Some level of uncertainty is always associated with risk management decision making. The earlier risk management tools are applied to reduce exposure to a chemical of concern, the greater the level of uncertainty. However, early application of risk management tools can reduce exposure of humans and wildlife while additional and more detailed information is acquired. As more information about the chemical of concern is obtained ~e.g., levels in the environment, effects on human and ecosystem health, specific sources, etc.!, risk management decisions are made with less uncertainty. Our role as research and development environmental engineers is to provide engineering information to stakeholders so that decisions on the application of risk management tools or processes can be made with minimal uncertainty. The input we can provide regarding EDCs includes the following: ~1! identification of currently available tools that can be adapted to lower exposure of humans and wildlife to EDCs; and ~2! development of new approaches to reduce exposure if adequate tools are not readily available. Environmental engineering research on managing exposure to EDCs has begun in the last several years. This initial work is an international effort addressing, among others, the following questions:

Photocurrent enhancement from an active hybrid TiO2film electrode fabricated by a sol–gel method: photocurrent generation during the photooxidation of 4-nonylphenol and 4-nonylphenol polyethoxylate on TiO2/OTE electrodes

Photocurrent is generated during the photooxidation of nonylphenol polyethoxylate surfactants (NPE-n; n = 1, 5, 7, 9 and 10), precursors of 4-nonylphenol (NP), on illuminated TiO2/OTE electrodes on which TiO2 semiconductor particles were immobilized by a pasting (PA), a sol–gel (SG), or both techniques (HY). The photooxidative process of NP and NPEs was examined by absorption spectroscopic methods monitoring the cleavage of the benzene ring moiety, and by the evolution of CO2 gas. The kinetics of photooxidation and the magnitude of the generated photocurrent scaled with the length of the ethoxyl side-chain for NPEs where n = 0, 1, 5, 7 and 10. The relative order of adsorption of NPEs on the positive TiO2 surface was predicted from calculated partial negative point charges of all the C and O atoms in the NPEs using molecular orbital methods. Both photodegradation and photocurrent generation were enhanced for the NPE-9 substrate using the HY TiO2/OTE electrode compared to the PA and SG electrodes. Although, biodegradation of NPEs yields NP in rivers, no formation of NP was observed during the photooxidation of NPE-9 because of predominant opening of the benzene ring. Photooxidation of NPEs is facilitated under an applied bias of +0.3 V and scales with the number of ethoxylate groups.

Structural elucidation of dicarboxylated metabolites of nonylphenol polyethoxylate surfactants in surface waters by gas chromatography/tandem mass spectrometry

AbstractPersistent dicarboxylated metabolites of nonylphenol polyethoxylates (NPEOs), carboxyalkylphenoxy ethoxy carboxylates (CAPECs), have periodically been detected during gas chromatography/mass spectrometry (GC/MS) characterization of NPEO metabolites in samples of surface water and sewage effluent. An electron impact ionization (EI) MS study was conducted on two esterified CAPEC metabolites, CA4P1EC isomers (where A4 denotes a 4‐carbonalkyl group plus one carboxylic group (C)). The most abundant characteristic ions were produced by benzylic cleavages to yield [M−87]+ and [M−101]+ ions, corresponding to ions of m/z 249 and 235, each of which is formed from one of two isomeric dipropyl esters CA4P1EC. These two base‐peak ions were selected as precursor ions to help elucidate the fragmentation mechanisms and support the proposed structures via tandem mass spectrometric (MS/MS) experiments. The two isomers have been tentatively identified as 4‐(2‐ethyl‐2‐methylacetic acid)phenoxyacetic acid and 4‐(3,3‐dimethylpropionic acid)phenoxy acetic acid, which give rise to the fragments at m/z 249 and 235, respectively. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Separation of isomers of nonylphenol and select nonylphenol polyethoxylates by high-performance liquid chromatography on a graphitic carbon column

p-Nonylphenol (NP) is a ubiquitous degradation product of nonylphenol polyethoxylate (NPE) surfactants and has been reported to be an endocrine disrupter. It is composed of numerous structural isomers resulting from the various branching patterns of the C-9 group. Twenty-two isomers in a technical mix of NP have been identified with high-resolution capillary GC–MS. In most HPLC analyses, nonylphenol elutes as a single, broad peak. In the method described here, HPLC using a graphite carbon column resulted in the resolution of a technical mixture of NP into 12 peaks or groups of isomers. This method was also applied to select NPEs with one to 10 ethoxy units with similar results. Separation was achieved by gradient elution with 1% acetic acid in water and acetonitrile. Elution of individual isomers 4-butylphenol and 4-propylphenol under the same gradient conditions indicate that increased branching of an alkyl group results in shorter retention times than for the less substituted alkyl groups. This method can be used to fractionate NP based on structure and assess the potential for different isomers (or groups of structurally similar isomers) to act as endocrine disrupters.

Occurrence and Abundance of Dicarboxylated Metabolites of Nonylphenol Polyethoxylate Surfactants in Treated Sewages

Very little is known on the occurrence and abundance in the environment of dicarboxylated metabolites (CAPECs) of A9PE surfactants. We have monitored monthly CAPECs and the other A9PE metabolites in effluents of five activated sludge sewage treatment plants (STPs) for 4 months. The analytical procedure is based on solid-phase extraction with a Carbograph 4 cartridge and liquid chromatography−mass spectrometry (MS) with an electrospray (ES) interface. On extracting 25 and 250 mL of respectively untreated and treated sewage samples, analyte recoveries ranged between 87 and 93% with RSDs no larger than 10%. Unexpectedly, data averaged on 20 samples of treated sewages showed that CAPECs were the dominant products of the A9PE biotransformation, accounting for 66% of all the metabolites leaving the plants. As a total, CA8PEC and CA6PEC represented 87% of the CAPEC class. On the average, CAPEC amounts having one ethoxy unit (CAPE2Cs) were almost double those of species having only a phenoxy acid moiety (CAPE1Cs). CAPEC species having more than four ethoxy units were never detected during our survey.

Nonylphenols in sediments and effluents associated with diverse wastewater outfalls

AbstractNonylphenols (NPs) have been reported to disrupt endocrine function and sexual development in aquatic organisms at low concentrations. Environmental NP burdens are predominantly derived from degradation of nonylphenol polyethoxylate surfactants. We detected NPs in discharge‐associated riverine sediments adjacent to 11 of 20 active sewage treatment plants (STPs) at concentrations up to 12,400 μg/kg. While most previous studies have focused on STPs, nonylphenols were observed in association with a variety of outfall types. The highest sediment burden, 14,100 μg/kg, was detected near a federal facility's stormwater discharge. Of 75 sediments examined from 67 sites, 45% contained NP concentrations &gt;5 μg/kg; median concentration in these NP‐positive sediments was 369 μg/kg. Other surfactant‐derived alkylphenolic compounds, specifically 4‐tert‐octylphenol and 4‐cumylphenol, were observed in two sediments at 8,220 and 70,000 μg/kg, respectively. The maximum NP concentration detected in an effluent, 6,300 μg/L, was from a shipyard oil/water separator. Nonylphenols were detected (&gt; 1.0 μg/L) in 20% of the 59 effluents examined; 10% exceeded 10 μg/L. Sediments sampled near a STP that had ceased treatment operations 20 years prior contained 54,000 μg/kg, indicative of long‐term NP residence. Results indicate that NPs may be released from diverse sources, concentrate in associated sediments, and persist therein for extended periods.

Nonylphenol Polyethoxy Carboxylate Metabolites of Nonionic Surfactants in U.S. Paper Mill Effluents, Municipal Sewage Treatment Plant Effluents, and River Waters

Because of their weakly estrogenic properties, interest in nonylphenol polyethoxylates and their carboxylated metabolites is resurging. To assess their occurrence in surface waters impacted by municipal and industrial effluents, an analytical method was developed for the quantitative determination of nonylphenol polyethoxy carboxylate (NPEC) metabolites of nonylphenol polyethoxylate surfactants in paper mill effluents, municipal sewage treatment plant effluents, and river waters. Strong anion exchange solid phase extraction disks were used for NPEC isolation from aqueous samples, and NPEC elution from the disk is simultaneously combined with derivatization. Extracts were analyzed by gas chro matography and positive mode chemical ionization mass spectrometry. The detection limit of the method ranged from 0.2 μg/L for NP1EC to 2 μg/L for NP4EC. The total concentration of NPECs in a group of paper mill and municipal sewage effluents ranged from below detection to 1300 μg/L. The total concentration of NPECs i...

Behaviour of alkylphenol polyethoxylate surfactants in the aquatic environment—III. Occurrence and elimination of their persistent metabolites during infiltration of river water to groundwater

The behaviour of various persistent metabolites derived from nonylphenol polyethoxylate (NPnEO) surfactants was studied during infiltration of river water to groundwater at two field sites situated in the northern part of Switzerland (Glatt River and Sitter River). Nonylphenol (NP), nonylphenol monoethoxylate (NP1EO), nonylphenol diethoxylate (NP2EO), nonylphenoxy acetic acid (NP1EC) and nonylphenoxy(ethoxy) acetic acid (NP2EC) were observed in the two investigated rivers at relatively high concentrations with average values of the individual types of nonylphenolic compounds ranging from 1.8 to 25 μg/l. The average concentrations of NP, NP1EO and NP2EO in groundwater were significantly lower (range <0.1–1 μg/l) suggesting an efficient elimination of these compounds during infiltration. In contrast, the elimination of nonylphenoxy carboxylic acids was less efficient. Most of the observed elimination occurred in the first 2.5 m of the aquifer, while further decrease in concentration was rather slow. In one sampling period, residual concentrations of nonylphenolic compounds up to 7.2 μg/l were detected in a pumping station used for drinking water supply which is situated 130 m from the Glatt River bed. Concentrations of NP, NP1EO and NP2EO in both river water and groundwater showed a pronounced seasonal variability with higher values observed during winter. The data suggest that low temperatures, which prevail in winter, significantly reduce the elimination efficiency of NP and to a lesser extent of NP1EO, while the behaviour of NP2EO was not affected. Such a behaviour indicates biogical transformation as the responsible elimination process. A comparison of average elimination efficiences of nonylphenolic compounds with those of pentachlorphenol (PCP) and nitrilotriacetate (NTA) gives the following sequence: NTA ≧ NP2EO > NP1EO > NP > PCP > NP1EC = NP2EC.

Biotransformation of nonylphenol polyethoxylate surfactants by estuarine mixed bacterial cultures

Biotransformation of nonylphenol polyethoxylates (NPnEOs), a major class of non-ionic surfactants, was studied under laboratory conditions by using a static die-away method. The experiments were performed with autochthonous bacterial cultures that originated from two essentially different estuarine compartments, i.e., from the brackish water and saline water layers of the highly stratified Krka River estuary, Croatia. Highly specific HPLC methods were applied to study biotransformation kinetics of individual NPnEO oligomers in the range of 1–16 EO units. Mixed bacterial cultures from the brackish water layer exhibited a significantly greater ability to transform NPnEO than that from the saline water layer. The results suggest, however, that this difference should not be interpreted as a salinity effect, but rather as a consequence of a better preadaptation of the brackish water bacteria to NPnEOs in their natural habitat. The biodegradation rates, calculated by presuming first-order kinetics, showed a strong temperature dependence. The estimated overall half-lives of NPnEOs under winter temperature conditions (13°C) ranged from 23–69 days, while the half-lives determined under summer temperature conditions (22.5°C) ranged from 2.5–35 days. Transformation kinetics of larger, more hydrophilic, oligomers of NPnEOs was faster than that of the lower ones. In fact, the elimination of higher NPnEOs was followed by a significant formation of the short-chain NPnEOs (nEO = 1–4). The main lipophilic intermediate formed during the experiments was nonylphenol diethoxylate (NP2EO), whose concentration in the medium increased by a factor of 10–20. Its relatively fast accumulation was followed by a rather slow degradation. Consequently, residual concentrations of NP2EO were detected in the medium even after 30 days.

Behaviour of alkylphenol polyethoxylate surfactants in the aquatic environment—II. Occurrence and transformation in rivers

The behaviour of nonylphenol polyethoxylate surfactants (NP nEO) and their metabolites in the Glatt River, Switzerland was studied. Discharge of secondary effluents from municipal sewage plants into the river was the predominant source of the investigated compounds. The majority of nonylphenolic compounds in the Glatt River were in the form of persistent metabolites, the most abundant being nonylphenoxy carboxylic acids. Distribution of the various classes of nonylphenolic compounds in the river was influenced to differing extents by biological and physico-chemical processes and was dependent on the compound class and the season. Biotransformation appears to be the predominant mechanism determining the fate of nonylphenolic compounds. High concentrations of lipophilic metabolites in river sediments indicate the importance of physico-chemical processes on the distribution of the nonylphenolic chemicals in natural waters.

Input and distribution of alkylphenol polyethoxylates in a stratified estuary

The behaviour and fate of nonylphenol polyethoxylate surfactants (NPnEO) in the Krka River estuary were studied during 1990–1991. The study comprised determination of NPnEO input via municipal wastewaters and their subsequent distribution in the water column of the estuary. All quantitative determinations were performed by high-performance liquid chromatography using both normal-phase and reversed-phase systems. The concentrations of NPnEO in untreated municipal wastewaters varied in a wide range of 70 to 2960 μg/l. The oligomer distribution in all of the analysed wastewater samples was rather uniform characterised by a maximum at NP10EO which indicated heavy-duty detergents as the predominant source of NPnEO in the investigated area. Hydrophobic partitioning between dissolved and solid phase was found to play a significant role in wastewaters, as indicated by a relatively high percentage (6–60%) of NPnEO associated with wastewater suspended solids and by different oligomer distribution patterns in the two phases. The most important features of the NPnEO distribution in the estuary were: (1) exponential decrease of concentrations with increasing distance from sewage outlets, and (2) a rather complex vertical distribution pattern which reflected the basic hydrographic properties of this strongly stratified estuary. An efficient initial dilution was found to be the chief mechanism that was responsible for rather low NPnEO concentrations in estuarine waters. However, significant concentration differences were observed between the brackish water layer (1.1–6 μg/l) and saline water layers (0.1–0.7 μg/l). This suggested that the wastewater plume spreads into the estuary predominantly in the brackish water layer while the underlying saline water layer remains much less affected. However, NPnEO concentration maxima were observed at the two estuarine phase boundaries: air-brackish water (17 μg/l) and brackish water-saline water (9 μg/l). Relatively small changes of the oligomer distribution pattern in the water column, compared to that originally found in wastewaters, indicated that biodegradation played only a limited role as the mass balance determining process in the estuary.