Environ. Sci. Technol. 2000, 34, 3914-3919
Occurrence and Abundance of Dicarboxylated Metabolites of Nonylphenol Polyethoxylate Surfactants in Treated Sewages ANTONIO DI CORCIA,* ROMINA CAVALLO, CARLO CRESCENZI, AND MANUELA NAZZARI Dipartimento di Chimica, Universita` “La Sapienza”, Piazza Aldo Moro 5, 00185 Roma, Italy
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.
Introduction Alkylphenol polyethoxylates (APEs) are one of the most widely used surfactant classes. Worldwide, about 500 ktons are produced for domestic, agricultural, and industrial uses (1). Among APEs, nonylphenol ethoxylates (A9PEs) are by far the most commonly used, encompassing more than 80% of the world market (2). Commercial A9PEs are complex mixtures of isomers and oligomers, as the multibranched alkyl side chain can take many different structural configurations, and the hydrophilic chain mainly consists of 3-20 ethoxy units. It was estimated that more than 35% of A9PEs are released in the aquatic environment (3). Initial biodegradation of A9PEs occurs rather rapidly with shortening of the ethoxy chain to form mainly A9PE1 and A9PE2. The short ethoxy chains of these breakdown products may then be oxidized with production of carboxylated A9PEs (A9PECs). Under anaerobic conditions, fully de-ethoxylated product nonylphenol (NP) is also produced (4). Figure 1 visualizes general structures of A9PEs and their major degradation products that can be formed under aerobic conditions. In this report, according * Corresponding author phone: +39-06-49913752; fax: +39-06490631; e-mail:
[email protected]. 3914
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FIGURE 1. Structures and acronyms of nonylphenol polyethoxylates and their breakdown products under aerobic conditions. to a consolidated convention, the number following the letter E in acronyms of carboxylated species indicates the number of ethoxy units plus a terminal CH2COOH unit. So, for instance, a compound like A9PE2C contains actually only one ethoxy unit. Recent evidences (5, 6) that some of the A9PE biotransformation products are weakly estrogenic in nature has raised concern over their environmental and healthy effects to the point that some European countries have restricted or banned the use of A9PE surfactants (7). In those countries where this surfactant class is still in use, recent research has focused on monitoring concentration levels of A9PE breakdown products in various aquatic compartments and determining their fate during wastewater treatment and upon entering the environment. Target compounds of these monitoring campaigns are A9PEs and their metabolites cited above, while A9PE breakdown products having both chains oxidized (CAPECs) have received little attention (8-10). This oversight is mainly due to the general belief that bacteria are scarcely able to catabolize the multibranched alkyl side chain of A9PE breakdown products. A laboratory biodegradation test of A9PE has shown that, after several days from the beginning of the experiment, abundant amounts of CAPECs with 3-8 carbons in the residual alkyl chain appeared in the test liquor (11). Components of this metabolite class were extremely recalcitrant to further biotransformation, as they persisted in the test liquor even more than 5 months after their generation. Analysis of a sewage treatment plant (STP) effluent showed CAPECs as a total accounted for 63% of the total A9PE breakdown products leaving the plant (11). The object of this work has been that of following the fate of A9PE species at the five major activated sludge STPs of Rome and assessing concentration levels of CAPECs and the other A9PE metabolites leaving the plants.
Experimental Section Reagents and Chemicals. Marlophen 810 (Chemische Werke Hu ¨ ls AG, Marl, Germany) contains A9PE chain isomers and oligomers with an average of 10 and a range of 2-20 ethoxy units. Imbentin-N/7A, a mixture composed of mainly A9PE1 and A9PE2 with little amounts of also A9PE3, was received from W. Kolb, Hedingen, Switzerland. Nonylphenoxyacetic acid (A9PE1C), nonylphenoxyethoxyacetic acid (A9PE2C), and nonylphenoxydiethoxyacetic acid (A9PE3C) with purity of 8590% were synthesized from Imbentin-N/7A following a previously reported procedure (12) and characterized by the LC-MS instrumentation herein described. A linear alcohol ethoxylate with an n-C10 alkyl chain and six ethoxy units (A10E6) and n-C8 linear alkylbenzene sulfonate (C8-LAS) were purchased from Fluka Bucks, Switzerland. These latter two compounds were used as internal standards. Stock solutions 10.1021/es001208n CCC: $19.00
2000 American Chemical Society Published on Web 08/08/2000
of the individual standards and standard mixtures were prepared by dissolving known amounts of them in methanol to obtain concentrations of 1 mg/mL. Working standard solutions were obtained by further diluting stock solutions with methanol to obtain final concentrations of 1 µg/mL. For LC analysis, distilled water was further purified by passing it through a Milli-Q Plus apparatus (Millipore, Bedford, MA). Acetonitrile “Plus” of gradient grade was obtained from Carlo Erba, Milan, Italy. Other solvents were of analytical grade (Carlo Erba), and they were used as supplied. Analytes were extracted from aqueous samples by solidphase extraction (SPE) cartridges filled with 0.5 g of Carbograph 4 (Lara, Rome, Italy). This sorbent material is a recently introduced form of graphitized carbon black (GCB) with a surface area of 210 m2/g. After fitting the SPE cartridge into a sidearm filtering flask, it was washed sequentially with 10 mL of CH2Cl2/CH3OH (80:20, v/v) acidified with formic acid, 50 mmol/L, 5 mL of methanol, 20 mL of water acidified with HCl (pH 2), and 5 mL of distilled water. Liquids were forced to pass through the cartridge by the aid of vacuum from a water pump. Sample Collection. All types of aqueous samples were collected in glass bottles. Twenty 4-h composite samples of raw and treated sewages were obtained by using flow proportional samplers. Influents and effluents of five STPs were collected once a month for 4 months. All plants use activated sludge treatment and are located in the area of Rome. Sample Preparation. Analytes were extracted from 25 mL of raw sewages and 250 mL of treated sewages. Before processing samples, suspended particulate matter was removed by filtration with a 1.5-µm pore size Whatman GF/C glass fiber pad (Maidstone, U.K.) to avoid SPE cartridge plugging. Analytes eventually adsorbed on these particles were quantitatively removed by washing with 3 mL of methanol, and these extracts were added to the aqueous samples. After passage of the aqueous samples through the SPE cartridge, this was washed with 50 mL of distilled water. Water remaining in the cartridge was partially removed by drawing room air through the cartridge for 1 min. Residual water was eliminated by slowly passing through the trap 0.5 mL of methanol. After the passage of methanol, the cartridge was again air-dried. By exploiting the singular feature of the GCB materials of adsorbing anionic organics by electrostatic interactions (13, 14), a stepwise desorption procedure was performed to isolate neutral analytes from acidic ones extracted from treated sewages. A9PEs were re-extracted from the cartridge by passing 1.5 mL of methanol through it followed by 10 mL of CH2Cl2/CH3OH (80:20, v/v), at a flow rate of about 4 mL/min. The eluate was collected in a 1.4 cm i.d. glass vial with a conical bottom. The last drops of this solvent mixture were collected by further decreasing the pressure inside the vacuum flask. Acidic A9PE metabolites were subsequently removed from the sorbent bed and collected in a second vial by elution with 10 mL of CH2Cl2/ CH3OH (80:20, v/v) acidified with formic acid, 50 mmol/L. Before solvent removal, 200 µL of the methanolic solutions containing the two internal standards, that is A10E6 and C8LAS, were added respectively to the neutral and acidic extracts. Both neutral and acidic extracts were taken to dryness in a water bath at 40 °C, under a gentle stream of nitrogen. Both residues were reconstituted with 200 µL of a water/methanol solution (40:60, v/v), and one-fourth of the final extracts were then injected into the LC column. LC-ES-MS Analysis. The LC apparatus was a Model 9010 (Varian, Walnut Creek, CA) equipped with a Rheodyne Model 7125 injector having a 50 µL loop. Neutral analytes were chromatographed on an “Alltima” 25 cm × 4.6 mm i.d. column filled with 5-µm C-18 reversed phase packing (Alltech,
Sedriano, Italy). For fractionating both neutral and acidic analytes, the phase A was acetonitrile and the phase B was water. Both solvents were acidified with formic acid, 1 mmol/ L. For analyzing A9PE species entering and leaving STPs, the initial mobile phase composition was 60% A, which was linearly increased to 100% in 20 min. Acidic A9PE metabolites in treated sewages were analyzed by setting the initial mobile phase composition at 25% A and then increasing it linearly to 100% within 50 min. In both cases, the flow rate of the mobile phase was 1 mL/min, and 0.5 mL/min of the column effluent was diverted to the ES source. A Finnigan AQA benchtop mass spectrometer (Thermoquest, Manchester, U.K.) consisting of a pneumatically assisted ES interface and a single quadrupole was used for detecting and quantifying target compounds (except for A9PE1, see below) in the LC column effluent. The probe temperature was maintained at 300 °C. Ions were generated using highly pure nitrogen as drying and nebulizing gases at flow rates of 150 L/h and 15 mL/min. Full-scan mass chromatograms of A9PE species were obtained by acquiring in the positive ionization (PI) mode after applying to the capillary a voltage of 4 kV and scanning the quadrupole from 300 to 900 with a 3-s scan. The skimmer cone voltage was set at 20 V. Full-scan mass chromatograms of acidic A9PE breakdown products were obtained by acquiring in the negative ionization (NI) mode under the same instrumental conditions reported above with the exception that the capillary voltage was decreased to 3.0 kV. The quadrupole was scanned from 90 to 600 with a 3-s scan, while the skimmer cone voltage was switched over continuously to 20 and 55 V during the chromatographic run. With the lowest cone voltage used, only molecular ions were formed, while the highest cone voltage provoked decomposition of the molecular ions with production of diagnostic fragment ions. The former instrumental condition was exploited to quantify in a simple way the analytes, while the latter condition served to confirm molecular structures of the analytes. LC-Fluorometry Analysis. Under the instrumental conditions reported above for analyzing neutral analytes, A9PE1 gave a very weak ion signal that precluded its quantification in treated sewages. Therefore, concentration levels of this compound were estimated by normal-phase LC with fluorometric detection, following a method developed by Kvestak and Ahel (15). Analyte Quantitation. Quantitation of A9PE species was performed following a procedure reported elsewhere (16). Concentrations of A9PECs for which standards were available (see above) were measured by external calibration. Calibration curves were constructed for each compound by adding 20-2000 ng of them to 200 µL of a water/methanol solution (40:60, v/v) containing 1 ng/µL of the C8-LAS internal standard and injecting three times one-fourth of each solution in the LC column. Interestingly, the three A9PECs exhibited very similar molar response factors. This effect is usually encountered when gas-phase ions are generated from preformed ions in the electrosprayed solution (17). On this basis, measurement of A9PE>3Cs concentrations in water samples was performed by assigning to each of them a molar response factor such as that of A9PE3C. CAPEC quantitation in aqueous environmental samples was made more difficult because of the lack of any standard and could suffer from some inaccuracy. Following a previously reported procedure (11), CAPECs were generated by submitting to biodegradation the A9PE mixture (Marlophen). Dicarboxylated A9PE metabolites were then characterized and quantified in the biodegradation solution as reported elsewhere (11). Thereafter, molar response factors of the various CAPEC homologues relative to that of the internal standard were calculated by analyzing a known aliquot of the biodegradation solution under the same conditions used VOL. 34, NO. 18, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 2. Typical total ion current chromatogram (cone voltage 20 V) and ion current profiles of dicarboxylated metabolites (see Figure 1 for acronym explanation) of nonylphenol polyethoxylate surfactants on analyzing the acidic extract of a STP effluent. to analyze extracts of STP effluents. These relative response factors were then used to quantify CAPECs in STP effluents. The response of the ES/MS detector in the NI mode was linearly related to amounts of injected acidic APE metabolites up to 1 µg, while the linearity of the response in the PI mode was maintained on injecting no more than 50 ng of each individual A9PE oligomer. The mass spectrometry data handling system used was the Mass-Lab software from Thermoquest.
Results and Discussion Optimization of the Experimental Conditions. In a previous work (11), acidic catabolic products of A9PE surfactants formed by a laboratory biodegradation experiment were analyzed by LC-ES-MS in the PI mode after derivatization to their methyl esters. The relative spectra obtained by the insource collision-induced dissociation (CID) process displayed several signals for fragment ions that provided detailed information on the structure of the various CAPEC homologues. In this work, we modified the previous procedure in that the derivatization step was omitted and acidic metabolites were detected as intact species by acquisition in the NI mode. Besides simplifying the analytical protocol and shortening the analysis time, the present procedure offers two additional advantages over the previous one. One is that the linear dynamic range of the ES-MS detector is expanded by more than 1 order of magnitude, as already experienced in previous works (16, 18). When unexpectedly large amounts of analytes are present in water samples, a wide linearity range of the response of the detection device can avoid analyte underestimation. The other advantage is that also A9PE1C could be detected and quantified in the NI mode together with the other acidic metabolites. When the ES-MS system was operated in the PI mode, the methyl ester of A9PE1C gave no appreciable response, as this molecule does not have any moiety sufficiently able to pick up protons or cations. Characterization of CAPEC Species in the NI Mode. Figure 2 shows a typical total ion current mass chromatogram as well as ion current profiles of various CAPEC homologues in a STP effluent. By itself, the ES source in the NI mode is capable of producing only gas-phase (quasi) molecular ions. 3916
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This permits assignment of the molecular weight to a certain compound, but structural information is precluded. Yet, structure-significant fragment ions can be obtained by collision between molecular ions and residual drying gas molecules in the desolvation chamber. So-called in-source CID spectra can be easily obtained by increasing the potential difference between sample and skimmer cones. Providing the analyte is chromatographically separated from any other compound, these in source CID spectra closely resemble those obtained by the MS-MS technique (19, 20). Figure 3 visualizes two exemplary spectra obtained at two different cone voltages and taken from the chromatographic peak at 33.5 min (see Figure 2). With the cone voltage at the lowest value, that is 20 V, no CID process was possible, and the spectrum displayed only signals at 323 and 345 Da/e that were tentatively assigned to the [M - H]- and [MNa - 2H]molecular ions of the CA6PE2C compound. Structural confirmation of this species was achieved by observing that at a cone voltage of 55 V the spectrum displayed two intense signals at 221 and 161 Da/e. The former fragment ion could be produced after loss of the carboxylated ethoxy chain with formation of the [OOC-(CH2)6-C6H4-OH]- fragment ion, while the latter ion could result from loss of acetic acid from the ion 221. The least abundant ion at 93 Da/e was postulated to be originated by the loss of both carboxylated side chains of CA6PE2C with formation of the phenate ion. Analogously to CA6PE2C, CID spectra of any other CAPEC compound displayed invariably an intense ion signal relative to a fragment ion coming from neutral loss of the carboxylated ethoxy chain. CAPECs having a different number of ethoxy units could be identified by neutral loss of the acetate moiety (58 amu) from the molecular ions of CAxPE1C species (an example is given in Figure 4) and 58 + n44 amu (n ) 1-4) for oligomers with one to four intact ethoxy units. Higher CAPEC oligomers were never detected in STP effluents during our survey. Recovery Studies. In the past, we used the Carbograph material for extracting A9PE species (13, 16) from both raw and treated sewages. More recently, CAPECs were efficiently extracted from a small volume of a A9PE biodegradation test solution by a Carbograph 4 SPE cartridge (11). In this study,
FIGURE 3. Spectra of the CA6PE2C dicarboxylated metabolite of nonylphenol polyethoxylate surfactants taken at two different cone voltages and from the chromatographic peak at 33.5 min (see Figure 2). Tentative structures of fragment ions at 93, 161, and 221 Da/e are also shown.
FIGURE 4. In-source CID spectrum of the CA5PE1C dicarboxylated metabolite of nonylphenol polyethoxylate surfactants taken at 55 V and from the chromatographic peak at 29.6 min (see Figure 2). Tentative structures of fragment ions at 149 and 207 Da/e are also shown. we assessed whether matrix effects and percolation of relatively large water volumes through the SPE cartridge could negatively affect extraction of acidic metabolites of A9PE surfactants from treated sewages. Recovery studies of A9PECs were conducted in a conventional way by adding suitable volumes of the working standard solution containing A9PE1-3Cs to a previously analyzed pooled treated sewage sample and reanalyzing. As no standard of CAPECs were available, recovery studies of these compounds were performed by adding suitable volumes of the CAPEC-containing A9PE biodegradation solution (see the Experimental Section). In any case, analyte addition was made with the criterion of approximately tripling the original concentrations. Five replicate measurements of both not spiked and spiked 250mL aliquots of the treated sewage sample were performed. For all the analytes considered, recoveries ranged between
87 and 93% with relative standard deviations no larger than 10%. Analysis of Raw and Treated Sewages. A recent OECD biodegradation test performed by us showed that, after 20 days of incubation, CAPECs were the most relevant breakdown products of A9PE surfactants (11). The aims of this extensive survey were those of knowing the fate of A9PEs in activated sludge STPs and ascertaining the extent at which CAPECs are generated during sewage treatment. Species having the alkyl side chain carboxylated and the ethoxy chain shortened but not carboxylated were present in treated sewages at very low concentration levels, so that they were not considered in this study. Moreover, A9PE1, A9PE2, A9PECs, and CAPECs amounts in STP effluents were considered to be formed exclusively during sewage treatment, as these compounds were contained in negligible amounts or absent VOL. 34, NO. 18, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Inlet Concentrations of A9PE Surfactants (in Parentheses) and Outlet Concentrations of A9PEs and Their Breakdown Products at Five Roman Activated Sludge Sewage Treatment Plants (September-December 1999) concentration, µg/L STP Nord
Ostia
Fregene
Est
Cobis
month
A9PEs
A9PECs
CA8PECs
CA7PECs
CA6PECs
CA5PECs
CA4PECs
CA3PECs
Sep Oct Nov Dec Sep Oct Nov Dec Sep Oct Nov Dec Sep Oct Nov Dec Sep Oct Nov Dec
3.2 (83) 4.7 (58) 3.8 (120) 4.5 (130) 5.1 (80) 5.3 (92) 6.6 (110) 4.5 (145) 2.4 (29) 4.1 (34) 4.5 (37) 5.7 (43) 1.7 (77) 2.9 (58) 4.1 (54) 3.6 (120) 6.3 (82) 3.8 (35) 5.9 (67) 5.7 (60)
4.2 5.4 4.5 11 6.5 15 3.3 3.9 2.2 5.3 5.8 11 8.6 7.4 10 11 11 0.6 7.8 8.6
4.1 8.5 9.8 11 19 21 22 15 4.7 5.2 4.4 7.4 8.9 12 19 20 15 3.6 24 2.5
0.29 0.8 0.74 1.0 1.6 0.9 1.0 0.8 0.44 0.39 0.62 0.96 1.2 1.3 1.8 1.6 1.7 0.4 2.0 0.8
3.2 9.6 8.7 8.7 16 15 16 12 3.2 3.9 3.8 6.3 7.9 9.3 11 14 13 2.3 12 3.3
0.3 1.2 0.91 0.78 2.0 1.1 0.95 1.4 0.54 0.57 0.55 0.90 1.3 1.1 1.3 1.3 2.1 0.45 1.9 0.68
0.14 0.39 0.4 0.31 0.87 1.4 1.0 0.67 0.26 0.37 0.18 0.41 0.07 0.25 0.22 0.32 1.1 0.41 0.54 0.4
0.23 0.23 0.11 0.18 0.43 0.60 0.65 0.15 0.05 0.24 0.08 0.14 0.10 0.09 0.13 0.21 0.6 0.16 0.12 0.21
TABLE 2. Relative Abundance of A9PE Metabolites in Effluents of Five Roman Activated Sludge Sewage Treatment Plants Averaged over 4 Months (September-December 1999) relative abundance,b % (SD,c %) STP Nord Ostia Fregene Est Cobis a
A9PE1
-2a
10 (1) 8 (1) 11 (3) 6 (1) 11 (5)
A9PECs
CA8PECs
CA7PECs
CA6PECs
CA5PECs
CA4PECs
CA3PECs
24 (7) 14 (8) 29 (8) 24 (4) 22 (15)
31 (3) 40 (5) 29 (7) 36 (4) 32 (14)
3 (0.4) 2 (1) 3 (1) 4 (1) 4 (0.3)
28 (5) 30 (4) 23 (2) 26 (2) 23 (4)
3 (1) 3 (1) 3 (1) 3 (1) 4 (0.4)
1 (0.4) 2 (0.3) 2 (0.4) 1 (1) 2 (1)
1 (1) 1 (0.3) 1 (0.4) 0.3 (0.1) 1 (1)
Sum of the A9PE1 and A9PE2 concentrations.
b
Values obtained by averaging over 4 months of analyte monitoring. c Standard deviation.
in untreated sewages. Inlet concentrations of A9PEs and outlet concentrations of A9PEs and their breakdown products monitored monthly at the five STPs from September to December 1999 are listed in Table 1. As a general remark, we monitored 8 years ago A9PE concentrations entering the Ostia STP during the same months (13). At that time, we measured an average concentration of A9PE of 160 µg/L which is about 1.5 times larger than that measured in this work. This seems to indicate that the use of A9PEs is slowly declining in Italy. Removal during sewage treatment is used as a term to describe all losses of a given compound or a class of compounds from the aqueous phase, regardless of whether the losses are caused by biological or nonbiological processes (21). By comparing the influent-effluent concentrations, we calculated that A9PE removal from the wastewater after the overall treatment at the five STPs averaged 93 ( 4%. This value is in good agreement with the removal efficiency (94 ( 4%) measured in the past at the Ostia plant (13). Removal of A9PE intermediates (A9PEI) resulting from sewage treatment was also calculated by comparing their “initial” and effluent concentrations. As defined by Trehy et al. (22), the “initial” concentration includes the eventual intermediate amounts in the influent as well as those ones that would be formed if all parent compounds removed from the influent by treatment were converted into intermediates. This index provides an estimation of the mineralization yield of A9PE species as the result of sewage treatment. It has to be pointed out, however, that this calculation gives only an approximate estimation of removal efficiencies by biochemical processes, as it does not consider those fractions of A9PEs and A9PECs 3918
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which are adsorbed on sludges. On this basis and by averaging data relative to the five STPs over 4 months, we calculated that the average A9PEI removal efficiency was 53 ( 19%. By matching this value with that relative to A9PE removal, it can be deduced that this class of compounds undergoes extensive primary biodegradation with loss of the surfactant properties, but only about one-half of the quantities entering an activated sludge STP are mineralized, that is are converted to CO2 and water. Relative concentrations averaged over 4 months of neutral and acidic A9PE metabolites in effluents of the five activated sludge STPs considered are presented in Table 2 (please, note that the abundance of neutral metabolites are reported as the sum of those relative to A9PE1 and A9PE2). By averaging data relative to the five STPs over 4 months, relative abundances of A9PE1-2, A9PECs, and CAPECs were found to be respectively 10 ( 2, 24 ( 5, and 66 ( 7. These figures point out that, among A9PE metabolites leaving activated sludge STPs, dicarboxylated species are by far the most abundant. At the present, A9PECs are still believed to be refractory metabolites of A9PE surfactant biotransformation. On the basis of the results of this survey, this matter should be reexamined, considering that A9PECs are direct precursors of CAPECs (11). Among CAPECs, the dominant homologues were invariably those having carboxylated alkyl chains with six and eight residual reduced carbons. On the average, CA8PECs and CA6PECs represented 87 ( 3% of the total amount of CAPECs in STP effluents. Presumably, the two most abundant CAPEC homologues are generated respectively from the ω and ω/β oxidation mechanisms of the multibranched alkyl side chain of A9PECs. Compared to A9PECs,
TABLE 3. Relative Abundance of Oligomers of CAPECs and A9PECs in Effluents of Five Roman Activated Sludge Sewage Treatment Plants Averaged over Four Months (September-December 1999) relative abundance, % (SD,a %) Nord A9PE1C A9PE2C A9PE3C A9PE>3C
Ostia
41 (13) 39 (8) 46 (7) 43 (4) 7 (3) 7 (3) 7 (5) 11 (7)
Fregene
Est
Cobis
av
A9PECs 41 (5) 42 (5) 9 (4) 9 (5)
38 (7) 38 (1) 10 (2) 14 (6)
35 (7) 39 (2) 41 (9) 42 (3) 8 (3) 8 (1) 17 (13) 12 (4)
Literature Cited
CA8PE1C 27 (5) CA8PE2C 64 (4) CA8PE3C 6 (1) CA8PE4-5C 4 (3)
23 (2) 66 (2) 9 (2) 3 (1)
CA8PECs 34 (8) 54 (6) 7 (2) 5 (3)
17 (3) 68 (9) 10 (1) 5 (5)
43 (11) 29 (10) 45 (10) 60 (10) 9 (4) 8 (2) 4 (4) 4 (1)
CA7PE1C 33 (6) CA7PE2C 67 (9) CA7PE3C 1 (3) CA7PE4-5C ndb
33 (9) 62 (7) 6 (4) ndb
CA7PECs 28 (7) 61 (7) 7 (5) 2 (3)
20 (9) 71 (8) 8 (4) 2 (2)
53 (23) 33 (12) 42 (22) 60 (11) 3 (3) 5 (3) 2 (1) 1 (1)
CA6PE1C 24 (3) CA6PE2C 69 (4) CA6PE3C 5 (1) CA6PE4-5C 3 (1)
19 (4) 73 (2) 6 (2) 3 (1)
CA6PECs 26 (5) 61 (7) 6 (1) 5 (1)
17 (6) 72 (4) 6 (2) 5 (2)
53 (25) 28 (15) 37 (19) 62 (15) 7 (3) 6 (1) 4 (4) 4 (1)
CA5PE1C 34 (8) CA5PE2C 65 (6) CA5PE3C 1 (2) CA5PE4-5C ndb
CA5PECs 19 (6) 38 (9) 71 (13) 58 (5) 6 (7) 3 (4) 2 (2) ndb
23 (6) 66 (8) 9 (7) ndb
57 (27) 34 (15) 37 (21) 59 (13) 5 (6) 5 (3) 2 (3) 1 (1)
CA4PE1C CA4PE2C
26 (3) 74 (3)
10 (3) 90 (3)
CA4PECs 31 (12) 34 (17) 62 (29) 33 (19) 69 (12) 66 (17) 38 (29) 67 (19)
CA3PE1C CA3PE2C
13 (3) 87 (3)
14 (7) 87 (7)
CA3PECs 31 (11) 21 (6) 69 (11) 79 (6)
a
Standard deviation.
b
one exception, A9PE2Cs were by far most abundant than A9PE1Cs. On the contrary, we observed that similar quantities of these two groups of compounds were present in all samples of STP effluents analyzed by us. Interestingly, we calculated that the amounts of CAPEC oligomers with one intact ethoxy unit (CAPE2C) in STP effluents were about double than those having only a phenoxy acid moiety (CAPE1C). Assuming reasonably that the precursors of the above two compounds are respectively A9PE2C and A9PE1C, our data seem to indicate that A9PE2C is more prone than A9PE1C to microbial oxidation of the branched alkyl side chain.
20 (8) 80 (8)
21 (8) 79 (8)
Not detectable, nd.
we observed that STP effluents contained 10-15% of A8PECs. If these species degrade by the same oxidation mechanisms mentioned above, then both CA7PECs and CA5PECs should be completely or in large part produced by A8PEC biotransformation. If this occurs, CA8PECs and CA6PECs are then substantially the only dicarboxylated metabolites formed by degradation of A9PE surfactants. Table 3 lists relative abundances of oligomers of acidic metabolites in effluents of the five STP considered averaged over 4 months of monitoring. If present, oligomers of CA4PECs and CA3PECs having more than one intact ethoxy chain could not be detected by this method. On analyzing samples of effluents of six Swiss STPs, Ahel et al. (23) found that, with
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Received for review April 26, 2000. Revised manuscript received June 16, 2000. Accepted June 21, 2000. ES001208N
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