Occurrence of Fluorescent Whitening Agents in Sewage and River

Environ. Sci. Technol. 1996, 30, 2220-2226

Occurrence of Fluorescent Whitening Agents in Sewage and River Water Determined by Solid-Phase Extraction and High-Performance Liquid Chromatography THOMAS POIGER,† JENNIFER A. FIELD,‡ THOMAS M. FIELD, AND WALTER GIGER* Swiss Federal Institute for Environmental Science and Technology (EAWAG), CH-8600 Du ¨ bendorf, Switzerland

Fluorescent whitening agents (FWAs) used in laundry detergents were determined in aqueous samples from sewage treatment plants and rivers using solidphase extraction (SPE) and high-performance liquid chromatography (HPLC) with post-column UV irradiation and fluorescence detection. FWAs were extracted from 10-200-mL water samples with C18 bondedphase silica extraction disks and eluted with methanolcontaining tetrabutylammonium ion-pairing reagent. No further sample cleanup steps were necessary due to the sensitive and selective fluorescence detection. Recovery of FWAs from raw sewage, primary effluent, secondary effluent, and river water ranged from 76 to 96%. The overall precision of the method, indicated by the relative standard deviation, ranged from 1 to 11%. The limit of quantification was less than 30 ng/L. The concentrations of the two most frequently used FWAs ranged from 7 to 21 µg/L in primary effluent, from 2.6 to 8.9 µg/L in secondary effluent, and from 0.04 to 0.57 µg/L in river water. FWA mass flows calculated from river water concentrations ranged from 0.45 to 1.2 mg day-1 person-1. If calculated on the basis of the consumed amount of FWAs, 1.45.6% was found in surface water. Light-induced isomerization and liquid-solid partitioning of FWA isomers were studied in samples of raw sewage and primary and secondary effluent. Isomers formed during the exposure to sunlight were found to have lower affinity for the suspended solids in sewage than the parent FWAs.

Introduction Cleaning products are used in very large quantities and contribute a significant portion of the load of synthetic chemicals in sewage treatment plants and the aquatic environment. The environmental fate of major detergent

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components such as surfactants and builders is therefore the subject of extensive research. Considerably less attention has been paid to the environmental fate of minor detergent components such as fluorescent whitening agents (FWAs), which on the average contribute only 0.15% of the total mass of laundry detergents. According to a recent review (1), little environmental data on FWAs are available in the open literature and most of it pre-dates 1975. Detergent FWAs are highly fluorescent, moderately water-soluble organic compounds with a high affinity for cellulosic material. Structures and properties of FWAs resemble those of dyes that are used for the direct dyeing of cotton fabrics. When bound to the fabrics, the intense blue fluorescence of FWAs compensates for the slight yellowish cast of cotton. The purpose of the FWAs contained in detergents is to adsorb to laundry and to improve or restore its whiteness during washing. Among the variety of detergent FWAs available on the market (2), two FWAs strongly dominate (FWA 1 and FWA 2, Figure 1). Worldwide production of FWAs 1 and 2 was estimated at 3000 and 14 000 t/yr in 1990 (3). Although these FWAs are partly bound to fabrics during the washing process, a considerable fraction (5-80%) remains in the washing liquor and is discharged to the sewers (4). Several studies have shown that FWAs are not easily biodegradable. No evidence of biodegradability was found in tests whereby the oxygen demand of bacterial cultures fed with FWAs was measured over a period of 5 days (BOD5) (5, 6). In cultures with activated sludge, two FWAs were shown to be slowly biodegraded after an adaptation period of 10-15 days (7). This relatively long adaptation period may be the reason why FWAs were not biodegraded in tests using laboratory-scale activated sludge treatment facilities. In these tests, FWAs were partially removed from wastewater by adsorption to sludge (6). Removal rates for FWAs in different sewage treatment plants ranging from 55 to 99%, based on influent concentrations, were reported (8). Relatively high FWA concentrations of 85-169 mg/kg dry matter in anaerobically-digested sewage sludges in Switzerland also indicate that adsorption to sludge is an important removal process for FWAs (16). In contrast to their resistance toward biodegradation, FWAs are readily degraded photochemically (6, 7, 9). Photochemical degradation is preceded by a fast reversible E,Z-isomerization reaction of the stilbene moiety. FWAs are produced in their (E)- and (E,E)-isomeric forms because only these isomers have fluorescent properties. When in dilute solution, FWAs isomerize upon irradiation with UV light to yield non-fluorescent (Z)- or (E,Z)-isomers. Halflives for isomerization are in the range of a few minutes whereas photochemical degradation takes several hours (9, 10). Reversible isomerization of FWAs complicates their determination in environmental samples. While the (E)and (E,E)-FWA isomers are easily determined by thin-layer * Author for correspondence; telephone: +41 1 823 5475; fax: +41 1 823 5028; e-mail address: [email protected]. † Present address: National Research Council, c/o U.S. Environmental Protection Agency, Athens, GA 30605. ‡ Present address: Department of Agricultural Chemistry, Oregon State University, Corvallis, OR 97331.

S0013-936X(95)00593-1 CCC: $12.00

 1996 American Chemical Society

This paper describes a method for the determination of FWAs in sewage and river water samples. Sample pretreatment is accomplished using C18 SPE disks for simultaneous sample filtration and solid-phase extraction. The method is not only suitable for the determination of total concentrations of FWAs but also for the study of the behavior of their individual isomers at the low micrograms per liter level. The method presented here together with a method for FWA determination in sewage sludges reported earlier (16) is a prerequisite for a study on the behavior of FWAs during sewage treatment.

Experimental Section

FIGURE 1. Structures of FWAs investigated in this study, all shown in their (E)- and (E,E)-isomeric forms.

chromatography (11, 12) or high-performance liquid chromatography and fluorescence detection (13-15), the nonfluorescent isomers must be detected by UV absorbance. This change of detection method is accompanied by a loss in both selectivity and sensitivity and increases the need for more effective preconcentration and cleanup steps. These problems have recently been overcome by the use of HPLC in combination with post-column UV irradiation where nonfluorescent isomers are partially reconverted to their fluorescent forms prior to fluorescence detection (16). Solid-phase extraction (SPE) has become a widely accepted technique for sample preparation in environmental analytical chemistry for the analysis of nonpolar, polar, and ionic compounds such as FWAs (17, 18). In recent years, SPE materials have become available in the form of disks. Due to their large surface area, SPE disks are much less prone to clogging by suspended particulate matter than regular SPE cartridges. Using SPE disks, sample concentration can be accomplished without prior filtration, thus eliminating one step in sample pretreatment. Special care must be given, however, to compounds that bind to particulate matter and must be eluted together with the fraction that is bound to the SPE material.

Reagents and Materials. Reference compounds of (E)- and (E,E)-FWAs 1-4 (technical grade with 30-90% active substance content, data provided by the manufacturer) as well as (E,Z)- and (Z,Z)-FWA 2, (Z)-FWA 3, and FWA 5, all as sodium salts, were provided by Ciba-Geigy AG. All results presented here are based on the known amount of active substance. FWA 5 is a research compound with no commercial applications, and it was selected as an internal standard because it can easily be separated from FWAs 1-4 in reverse-phase chromatography. Reagent-grade extraction solvents, N,N′-dimethylformamide (DMF), ammonium acetate, and tetrabutylammonium hydrogen sulfate (TBA), were purchased from Fluka AG (Buchs, Switzerland). Solvents for HPLC were purchased from Riedel de Hae¨n (Seelze, Germany) and were used as received. Empore C18 bonded-phase silica disks with a diameter of 25 mm were a gift from the 3M Co. (Minneapolis, MN). The disks have a nominal pore size of 1 µm and are composed of 8-µm particles, which make up 90% of the disk weight. Samples. Samples of raw sewage, primary effluent, and secondary effluent were collected as 24-h composites (flowbased) in August 1992 from four municipal sewage treatment plants in the region of Zu ¨ rich, Switzerland. Brown glass sample bottles containing 1% (v/v) formalin (37% formaldehyde) were used to collect and preserve samples. Samples were stored at 4 °C. River water samples were obtained as 2-week composite samples (flow-based) from automatic sampling stations of the NADUF program (Nationales Forschungsprogramm zur Analytischen Daueruntersuchung von Fliessgewa¨ssern), a monitoring program designed to survey several chemical and physical parameters of important rivers in Switzerland (19). During collection and storage, samples were maintained at 4 °C; no preservatives were added. All samples were analyzed within 2-3 days of collection. In addition, unspiked sewage and river water samples were periodically analyzed over a period of 4 weeks to determine if any change in FWA concentrations occurred during sample storage. However, no changes in total FWA concentration or isomeric composition greater than the standard deviation of the method were observed during this time period. Solid-Phase Extraction. Polypropylene filter assemblies (Millipore, Bedford, MA) attached to a vacuum manifold (Supelco, Bellafonte, PA) were used to support the C18 Empore disks. The disks were preconditioned using 5 mL of methanol followed by 20 mL of distilled water and were not allowed to go to dryness prior to sample application. Water samples were homogenized for 4 min using a stainless steel auger. Except where noted, water samples were not filtered prior to extraction so that the total

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concentration of FWAs could be determined. Samples of homogenized raw sewage (10 mL), primary effluent (10 mL), secondary effluent (50 mL), and river water (200 mL) were passed through a 25-mm C18 disk by vacuum. Air was pulled through the disk for 2 min after the enrichment to remove excess water from the disk. Elution of the C18 disk was performed by adding 1 mL of 0.05 M TBA in methanol to the disk and allowing it to soak for 2 min after which the vacuum was applied. The procedure was repeated five additional times, and all six extracts were collected in a single vial. The extract was dried under a stream of nitrogen and mild heating (40 °C). Approximately 1 mL of a mixture of water and DMF (1:1) was added and spiked with 10 µL of the internal standard solution (10 µg/mL FWA 5 in methanol). To determine the fraction of FWAs in particulate and dissolved phases, a glass fiber filter with a nominal pore size of 0.45 µm (Gelman Sciences, Ann Arbor, MI) was stacked on top of the C18 disk. Water samples were extracted through the filter and disk as described above. After sample application, disk and filter were separated and eluted individually. The particulate bound FWA fraction was operationally defined as the fraction of FWAs eluted from the glass fiber filter. The dissolved FWA fraction was operationally defined as the fraction of FWAs eluted from the C18 disk. Different filter materials were tested for their potential to retain dissolved FWAs. Primary effluent, secondary effluent, and river water were filtered through a 0.2-µm cellulose ester membrane filter (Millipore, Bedford, MA) and spiked with FWA standard solution containing all photoisomers. The membrane filters to be tested were placed in filter assemblies and preconditioned like C18 disks. Spiked, filtered water samples were passed through the filters and the filters were then eluted like C18 disks. The FWA concentration in these extracts was compared to FWAs extracted by C18 disks. To test the possibility of FWA breakthrough during sample enrichment, experiments were conducted by stacking two C18 disks together. Breakthrough was investigated with primary effluent (20 mL), secondary effluent (50 mL), and river water (200 mL). After sample concentration, the two disks were separated and processed individually. For the investigation of the behavior of individual FWA isomers, it was essential to prevent exposure of samples to UV or blue visible light emitted by normal laboratory light sources. For these studies, all sample preparation steps were conducted in a windowless room equipped with special lamps (Philips TLD 36W/16 Yellow), and the extracts were stored in amber glass vials. However, if only the total FWA concentrations were determined, all procedures were carried out in normal laboratory light. High-Performance Liquid Chromatography. All analyses were performed using a Hewlett-Packard Model 1090L Series II HPLC equipped with an autosampler, a ternary solvent delivery system, and a heated column compartment. Separations were performed using a narrow-bore column (Hypersil ODS, 5 µm, 200 × 4.6 mm i.d. with pre-column, Hewlett Packard) operated at room temperature with an eluent flow rate of 1 mL/min. The mobile-phase solvents were acetonitrile/methanol (1:1) (eluent A) and 0.1 M aqueous ammonium acetate buffer of pH 6.5 (eluent B). A 25-min linear gradient from 30% A/70% B to 70% A/30% B was used for analysis. Initial eluent composition was

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re-established by a 2-min linear gradient, followed by an equilibration time of 5 min. Detection and Quantitation. The outlet of the HPLC column was connected to a post-column UV irradiation apparatus (BeamBoost, ict AG, Basel, Switzerland) equipped with a UV lamp with a maximum intensity at 254 nm and a 0.3 mm i.d. × 1-m Teflon capillary, resulting in a 5-s irradiation time of the column effluent prior to detection. This irradiation time was sufficient to achieve photostationary conditions, e.g., a constant ratio of (E)- and (Z)isomers. The irradiated column effluent was then monitored with a Hewlett Packard Model 1046A fluorescence detector at an excitation wavelength of 350 nm and an emission wavelength of 430 nm. Due to the way FWAs are detected, response factors for (E)- and (Z)-isomers are the same (16). Thus, in principle (Z)-isomers could be quantified using standards containing only (E)-isomers and vice versa. However, for control of the separation performance and for spike/recovery experiments it was desirable to have standards containing all isomers. Standard solutions of (E)- and (E,E)-FWAs were prepared in DMF/water (1:1) at 0.5 mg/mL. These solutions were exposed to direct sunlight for 1 min in order to obtain standard solutions containing also (Z)- and (E,Z)-isomers of FWAs. Concentration series for external calibration curves were prepared by dilution of the standard solutions in 1-mL portions of 0.3 M TBA in DMF/water (1:1) and spiked with 10 µL of the internal standard solution. Calibration curves were linear over a concentration range of 10-1000 ng/mL with r2 typically better than 0.999. To determine the steady-state isomeric composition for FWAs 1 and 2, filtered secondary effluent was spiked with pure (E)- or (Z)-FWA 1 and (E,E)-FWA 2. The spiked effluent was exposed to direct sunlight for several minutes, and samples were taken for analysis periodically until no further change in isomeric composition could be observed.

Results and Discussion Solid-Phase Extraction and Quantitation. Enrichment of multiply charged compounds on hydrophobic extraction materials often requires the addition of salt or ion-pair reagents to the water samples to increase the solutesorbent interaction (20, 21). However, retention of disulfonated FWAs by the C18 SPE disks was quantitative without additives. This was confirmed in experiments where sewage and river water samples containing (E)-FWAs as well as (Z)-FWAs were extracted through two stacked C18 disks to determine whether any FWAs would break through. All analytes were retained by the first disk so that no FWAs were detected in the extract of the second disk. Thus, the interaction between the C18 SPE disk and the FWAs seems to be sufficiently strong for quantitative isolation. A variety of solvents was evaluated for the elution of FWAs from the C18 SPE disks. Acetonitrile and methanol were found to be suitable elution solvents. However, large volumes (10-15 mL) were required for both solvents to elute FWAs from the disks, and recoveries of 50-70% were achieved for the determination of FWAs in primary effluent samples. With the addition of 0.05 M TBA to the methanol, FWAs could be recovered from the C18 SPE disk in only 6 mL, and recoveries improved to 75-90%. This may be explained, in part, by a more efficient extraction of TBAFWA ion pairs from the suspended particulate matter in the samples. A similar improvement of extraction efficiency was previously shown for the methanolic extraction of FWAs

TABLE 1

Precision and Recovery of FWA Determination in Sewage and River Watera sample

FWA

background concn (µg/L)

raw sewaged (10 mL)

1 2 3 1 2 3 1 2 3 1 2 3

18 23 1.2 14 12 0.4 6 3 0.05 0.8 0.4 0.01

primary effluentd (10 mL) secondary effluentd (50 mL) river watere (200 mL)

RSDb (%)

spiked level (µg/L)

recoveryc (%)

5 6 8 3 2 4 1 5 10 2 3 11

25-100 25-100 2.5-10 11-44 11-44 1-4 5-15 5-15 0.5-1.5 1-5 1-5 0.1-0.5

89 86 77 88 89 76 93 91 82 96 84 88

a Total FWAs (sum of all isomers). b Relative standard deviation (n ) 4). c n ) 6. d Zu¨ rich-Glatt municipal sewage treatment plant. e Glatt River at Opfikon.

from sewage sludge (16). To confirm that the elution of FWAs was indeed complete, several SPE disks and glass fiber filters that had been previously eluted with methanol/ TBA were subjected to a more rigorous extraction procedure reported for sewage sludges (16) using repeated extractions with methanol/TBA and sonication. In all cases, the residual amount of FWAs extracted by this procedure was less than 5% relative to the amount eluted previously. To determine the precision of the method, replicate analyses were performed using samples of raw sewage, primary effluent, secondary effluent, and river water (Table 1). For FWAs 1 and 2, the precision represented by the relative standard deviation (RSD) is 1-6 %. The precision for determination of FWA 3 was generally lower with RSDs of 4-11%. This may be explained by the much lower concentrations of FWA 3 as compared to FWAs 1 and 2. Recoveries of spiked FWAs were 84-96% for FWAs 1 and 2 and 76-88% for FWA 3 (Table 1). The spiked samples were allowed to equilibrate for 15 h, to allow for partitioning of FWAs to the suspended particles. This precaution was used to assure that FWAs could also be recovered from the particulate matter. All standards used for spiking were previously exposed to sunlight and therefore contained all FWA isomers that are formed in sunlight. Recoveries were determined under normal laboratory light. Thus, isomeric composition changed during sample preparation, and recoveries can only be given for total FWA and not for individual isomers. However, as recoveries for FWAs 1 and 2 are high (84-96%), the method can be considered quantitative for all isomers. Combining filtration and trace enrichment into one step was the main reason for the use of SPE disks instead of cartridges. In some cases, however, it was necessary to determine the dissolved and particulate FWA fractions separately. Several different types of membrane filters were tested in order to find one that would retain particles but not the fraction of FWAs in the dissolved phase. Among the filter materials tested were regenerated cellulose, cellulose esters, nylon, and Teflon. All of these membrane filters adsorbed significant amounts of dissolved FWAs. The fraction of the dissolved FWAs retained by the filters was 20-50% in raw sewage and increased to 80-100% in river water. Consequently, these materials were not suitable for

FIGURE 2. Typical chromatograms of extracts of raw sewage (A) and secondary effluent (B) from the sewage treatment plant at Bu1 lach, Switzerland, and of river water, Glatt River, Switzerland (C). Peaks 1, (E,Z)-FWA 1; 2, (E,E)-FWA 1; 3, (E)-FWA 2; 4, (E,Z)- and (E,E)-FWA 3; 5, (Z)-FWA 2; 6, FWA 5; 7, (Z)-FWA 4; 8, (E)-FWA 4.

an accurate determination of the dissolved FWA fraction in water samples. Glass fiber filters gave much less retention of dissolved FWAs than membrane filters, typically less than 5 %. Thus, glass fiber filters were used throughout this study. Filters and C18 SPE disks were stacked during sample concentration but separated before the elution step, providing a simple and rapid method for the determination of the dissolved and particle-bound FWA fractions. High-Performance Liquid Chromatography. Separation of FWAs was achieved using a reverse-phase column and a gradient of aqueous ammonium acetate and a 1:1 mixture of acetonitrile and methanol (Figure 2). Individual photoisomers of FWAs 1, 2, and 4 could be separated while (E,Z)- and (E,E)-FWA 3 coeluted under all tested conditions. The internal standard (FWA 5) does not isomerize and always yields one peak. Despite the complexity of the samples analyzed, the chromatograms obtained for sewage and river water extracts are simple and easy to interpret. The instrumental detection limit (s/n ) 10) was 50 pg FWA injected into the HPLC, resulting in a detection limit of 2.5 ng/L in river water samples. Concentrations of FWAs 1 and 2 in blank samples were 3-12 ng/L, resulting in a limit of quantification (LOQ) of 20-30 ng/L. Thus, detection was limited by blanks rather than instrumental sensitivity. The selected approach for the detection of FWAs using post-column UV irradiation is described in more detail elsewhere (16). It takes advantage of the fact that photoisomerization is a reversible process. The separated FWA


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TABLE 2 a

Concentrations of FWAs Found in Wastewaters FWA 1 (µg/L)

2 (µg/L)

3 (µg/L)

Zu¨ rich Glatt Opfikon Bu¨ lach Niederglattb

Primary Effluent 14.0 ( 0.4 11.4 ( 0.3 21.3 ( 0.6 9.8 ( 0.2 9.0 ( 0.3 11.3 ( 0.2 6.9 ( 0.3 7.1 ( 0.1

0.38 ( 0.02 2.40 ( 0.11 0.37 ( 0.04 0.27 ( 0.03

Zu¨ rich Glatt Opfikon Bu¨ lach Niederglatt

Secondary Effluent 5.6 ( 0.1 2.6 ( 0.1 8.9 ( 0.1 2.8 ( 0.1 6.6 ( 0.2 4.5 ( 0.1 3.3 ( 0.1 3.5 ( 0.1

0.051 ( 0.005 0.15 ( 0.01 0.033 ( 0.002 0.014 ( 0.002

Opfikon

Tertiary Effluentc 8.7 ( 0.1 2.5 ( 0.2

0.009 ( 0.001

a

Total FWA (sum of all isomers), 24-h composite samples from municipal sewage treatment plants located near Zu¨ rich, Switzerland. b Raw influent, Niederglatt had no primary clarification. c Effluent of sand filter.

isomers are irradiated through a transparent capillary wrapped around a UV lamp connected in-line between the HPLC column outlet and the fluorescence detector. By this irradiation, nonfluorescent (Z)- and (E,Z)-isomers are partially reconverted into fluorescent (E)- and (E,E)-isomers and can thus be detected by fluorescence detection. Since the irradiation is long enough (5 s) to reach a constant isomer ratio, the response factors are different for every FWA, but are identical for their (E)- and (Z)- or (E,E)- and (E,Z)-isomers, respectively. Fluorescence detection is especially advantageous for FWAs due to their high fluorescence quantum yields and the relatively high wavelength of the maximum fluorescence, which sets them apart from most naturally-occurring compounds. Combined with a baseline separation of the respective photoisomers of FWAs 1 and 2, studies of the occurrence and behavior of FWA isomers are possible at low micrograms per liter levels. Application to Sewage Samples. A survey of FWA concentrations in wastewaters from four municipal sewage treatment plants in the region of Zu ¨ rich, Switzerland (Table 2) indicated that FWAs are present in sewage in the low micrograms per liter range. There is a remarkable variability in the relative levels of individual FWAs. This variability should not be expected from compounds that are mainly incorporated in consumer products, e.g., FWAs 1 and 2. On the other hand, FWA 3 and to a lesser extent also FWAs 1 and 2 are used in large-scale commercial laundry facilities. The ratios of FWA 1 to FWA 2 found in primary effluent samples were typically around 1:1, the exception being Opfikon, where the ratio was about 2:1. This result is consistent with a survey of FWA concentrations in sewage sludges where the highest ratio of FWA 1 to FWA 2 was found in sludge from Opfikon (16). The highest concentration of FWA 3 was also found in Opfikon, indicating that the sewage treatment plant receives effluent from large-scale commercial laundry facilities. Although not checked in detail, it is very likely that Opfikon with its proximity to the Zu ¨ rich airport and to many big hotels has such facilities. Concentrations of FWAs in primary effluent (e.g., influent to the activated sludge facility) and secondary effluent are very similar, indicating that FWAs are only moderately removed from wastewater during activated sludge treatment

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compared to removal rates for well biodegradable compounds. Removal rates for FWAs 1, 2, and 3 for a given sampling day vary between 27-60%, 51-77%, and 8796%, respectively. The low removal rates for FWAs 1 and 2 are consistent with laboratory experiments on FWA removal by activated sludge (6) and with biodegradation tests (5, 7), which indicate that FWAs are to a varying degree eliminated from sewage by adsorption to sewage sludge but not biodegraded. Rather high concentrations of FWAs (30-100 mg/kg dry matter) found in sewage sludges support this hypothesis (16). However, the data presented here reflects only a 1-day period, and because FWA concentrations may vary significantly from day to day, the removal rates should only be interpreted in a qualitative way. Concentrations of FWAs in sewage were also determined over a longer time period as part of a mass flow study, which will be reported elsewhere. Isomerization and Solid-Liquid Partitioning. Detergents contain FWAs in their fluorescent (E)- or (E,E)-forms. Neither during the washing process nor in the sewers do FWAs come in contact with light. Once the raw sewage reaches a sewage treatment plant, FWAs are exposed to sunlight and gradually undergo photoisomerization. In initial laboratory experiments, a steady state between the respective isomers of FWAs 1 and 2 was reached after 3-5 min of irradiation with sunlight. The steady-state isomeric composition determined in filtered sewage effluent was 14% (E,Z)- to 86% (E,E)-FWA 1 and 75% (Z)- to 25% (E)FWA 2, respectively, indicating that FWA 1 isomerizes less readily to the (Z)-form than does FWA 2. It should be noted here that (Z,Z)-FWA 1 was not formed in detectable quantities under sunlight irradiation. The change in the fraction of individual FWA isomers between raw sewage and primary and secondary effluent is illustrated in Figure 3. The samples were obtained during a summer day with cloudless sky. Raw sewage was sampled right at the point where it enters the sewage treatment plant and was only exposed to sunlight for a few seconds; thus, no steady state was achieved at this point. During primary clarification, FWAs were exposed to sunlight for more than 1 h. However, at this stage, sewage contains a lot of particulate matter so that light cannot penetrate the water column very far, and thus the average exposure of FWAs to light is much shorter than 1 h. Consequently, the isomeric composition in primary effluent is still quite different from steady-state conditions. Finally, in secondary effluent the isomeric composition was very close to steadystate conditions due to extensive exposure (>2 h) of the FWAs to sunlight, especially during secondary clarification. The fraction of FWA isomers adsorbed to suspended solids indicated in Figure 3 decreases with decreasing solids content from raw sewage (63 mg/L) to primary effluent (30 mg/L) to secondary effluent (5.1 mg/L). There is a difference in the behavior of FWAs 1 and 2 in that FWA 2 exhibits a stronger tendency to adsorb onto suspended solids. Additionally, different isomers were found to have different affinities for suspended particles, particularly FWA 2 (Figure 3). Solid-liquid distribution ratios calculated from the data for primary effluent are 720 and 3600 L/kg for (E,Z)- and (E,E)-FWA 1 and 1600 and 37 000 L/kg for (Z)- and (E)-FWA 2. The finding of different partitioning behavior for different FWA isomers is consistent with the present knowledge on stilbene FWAs with respect to whitening applications. Upon isomerization from the (E)- to the (Z)-form, stilbene FWAs

FIGURE 3. Isomeric composition of FWAs 1 and 2 in grab samples of raw sewage, primary effluent, and secondary effluent from the treatment plant Zu1 rich-Glatt, Switzerland.

lose their affinity for cellulose as well as their fluorescence properties (22). Sunlight thus potentially influences the fate of FWAs during sewage treatment by transforming FWAs into isomeric forms that have lower affinities for suspended solids. In the case of FWA 1, the influence of photoisomerization is not substantial due to the small fraction of the (E,Z)-isomer formed. The fate of FWA 2 might be influenced more strongly by photoisomerization. Removal due to adsorption onto suspended solids can occur during mechanical treatment (primary sludge) and during activated sludge treatment. During both treatment stages, light does not penetrate the water column very far, as the concentration of particulate matter is high. Consequently, the

influence of sunlight on the removal by adsorption to sludge is very limited. Only in the secondary clarifier are FWAs exposed to sunlight long enough to make isomerization an important process. Some treatment plants apply filtration for further removal of suspended solids from secondary effluent. Filtration of secondary effluent thus potentially also contributes to the removal of FWAs. However, in secondary effluent the concentration of suspended particles is low (5 mg/L) compared to raw sewage (63 mg/L) or activated sludge (typically 3000 mg/L) so that the fraction of adsorbed FWAs is small even for isomers with high affinities for suspended particles. Among the treatment plants investigated, only Opfikon applies filtration to secondary effluent. As is shown in Table 2, filtration has little effect on the removal of FWA 1 or FWA 2. Application to River Water Samples. In addition to the typical detergent-derived FWAs 1-3, which were expected to be present in river water, more hydrophilic FWAs were observed in chromatograms of some river waters (Figure 2C). By comparison to reference compounds, two peaks were identified as the two isomers of FWA 4, whereas the others probably originate from other tetra-sulfonated stilbene FWAs; however, they were not identified. Highly sulfonated FWAs are used in textile finishing and in the production of paper. In contrast to detergent-derived FWAs, highly sulfonated FWAs mainly are discharged from point sources. None of the highly sulfonated FWAs were observed in the municipal sewage treatment plants investigated in this study, indicating that there was no textile or paper industry discharging to these particular plants. On the other hand, the rivers investigated in this study receive wastewaters from many sewage treatment plants and are more likely to receive wastewater from textile or paper industry. Concentrations of FWAs 1 and 2 in samples of river water from several rivers in Switzerland are reported in Table 3. The rivers selected for this study vary in terms of the size of their catchment areas and in terms of their associated population densities and levels of pollution. As a result, the range of FWA concentrations found in river water is rather large (36-574 ng/L). The FWA concentrations found in this study are consistent with FWA concentrations reported for several rivers in Japan of a few nanograms per liter up to 45 000 ng/L, and in the United States of 16-1500 ng/L (17, 18, 23-28). The FWA mass flows and per capita mass flows in Table 3 were calculated from measured FWA concentrations, hydraulic flows, and population discharging sewage in the particular catchment areas. With one exception, all per capita mass flows lie within a very narrow range of 0.51-

TABLE 3

Concentrations and Mass Flows of FWAs in Swiss Riversa river

sampling location

catchment areab (km2)

Limmat Rhein

Gebenstorf Rekingen Village-Neuf Brugg Chancy Rheinsfelden

2 415 14 718 36 472 11 750 10 294 416

Aare Rhoˆ ne Glatt

populationb (× 1000) 843 2 451 6 903 1 941 1 426 341

FWA concn ((SD)c (ng/L) FWA 1 FWA 2 155 ( 10 41 ( 6 142 ( 8 107 ( 13 59 ( 2 574 ( 23

67 ( 29 36 ( 8 -e 94 ( 6 63 ( 10 439 ( 24

hydraulic flowd (m3/s) 68 352 699 191 248 6.3

mass flow (kg/d) FWA 1 FWA 2 0.91 1.25 8.58 1.77 1.26 0.31

0.39 1.09 1.55 1.35 0.24

per capita mass flow (mg day-1 person-1) FWA 1 FWA 2 1.08 0.51 1.24 0.91 0.89 0.91

0.47 0.45 0.80 0.95 0.70

a Total FWA (sum of all isomers), 2-week composite samples. b Ref 19. c Standard deviation (n ) 3). d Data supplied by Landeshydrologie und -geologie, Bern, Switzerland. e Chromatographic signals for FWA 2 overlapped with signals from an unknown compound.


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1.2 and 0.45-0.95 mg per day and person FWAs 1 and 2, respectively. These mass flows can be compared to the amount of FWAs consumed with laundry detergents to estimate the fraction of FWAs that ends up in the aquatic environment. In Switzerland, approximately 16 and 49 mg per day and person FWAs 1 and 2, respectively, are used in laundry operations (3). In river water on average 0.92 and 0.67 mg per day and person (Table 3) or 5.6 % and 1.4%, respectively, of the consumed FWAs 1 and 2 were found. Based on a FWA mass flow study in a sewage treatment plant and a survey of FWA concentrations in sewage sludges, we estimated that about 23% and 2%, respectively, of the consumed FWAs 1 and 2 are discharged to Swiss rivers associated with sewage effluent (16, 29). While the data for discharge of FWA 2 corresponds well with the amount of FWA 2 found in river water, a rather large discrepancy becomes obvious for FWA 1, suggesting the potential further elimination of FWA 1 in the aquatic environment through either photochemical degradation (10) or sorption to sediments.

Acknowledgments As partners in the Rhine Basin Program, we gratefully acknowledge the donation of the HPLC/FLD equipment by Hewlett Packard Co. We thank Ciba-Geigy AG for providing FWA samples. We thank A. Alder, M. Berg, J. B. Kramer, S. Mu ¨ ller, and J.-M. Stoll for critically reviewing the manuscript.

Literature Cited (1) Kramer, J. B. In The Handbook of Environmental Chemistry, Vol. 3, Part F: Anthropogenic Compounds, Detergents; Hutzinger, O., de Oude, N. T., Eds.; Springer: Berlin, 1992; pp 351-366. (2) Siegrist, A. E.; Eckhardt, C.; Kaschig, J.; Schmidt, E. In Ullmann’s Encyclopedia of Industrial Chemistry; VCH Verlagsgesellschaft mbH: Weinheim, 1991; pp 153-176. (3) Kaschig, J. Ciba-Geigy AG, personal communication, 1992. (4) Bode, K.-D. Tenside Deterg. 1975, 12, 69-70. (5) Zinkernagel, R. In Fluorescent Whitening Agents; Anliker, R., Mu ¨ ller, G., Eds.; Georg Thieme Publishers: Stuttgart, 1975; pp 129-142. (6) Dojlido, J. R. Investigations of Biodegradability and Toxicity of Organic Compounds; EPA-Report 600/2-79-163; U.S. EPA: Springfield, VA, 1979.

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(7) Guglielmetti, L. In Fluorescent Whitening Agents; Anliker, R., Mu ¨ ller, G., Eds.; Georg Thieme Publishers: Stuttgart, 1975; pp 180-190. (8) Ganz, C. R.; Liebert, C.; Schulze, J.; Stensby, P. S. J. Water Pollut. Control Fed. 1975, 47, 2834-2849. (9) Ikuno, H.; Honda, M.; Komaki, M.; Yabe, A. Nippon Kagaku Kaishi 1985, 8, 1603-1608. (10) Kramer, J. B.; Canonica, S.; Hoigne´, J.; Kaschig, J. Environ. Sci. Technol. 1996, 30, 2227-2234. (11) Lepri, L.; Desideri, P.; Coas, W. J. Chromatogr. 1985, 322, 363370. (12) Theidel, H. In Fluorescent Whitening Agents; Anliker, R., Mu ¨ ller, G., Eds.; Georg Thieme Publishers: Stuttgart, 1975; pp 111-114. (13) McPherson, B. P.; Omelczenko, N. J. Am. Oil Chem. Soc. 1980, 57, 388-391. (14) Tsuji, K.; Setsuda, S.; Naito, S.; Abe, A. Bull. Kanagawa Prefect Public Health Lab. 1981, 65-67. (15) Jasperse, J. L.; Steiger, P. H. J. Am. Oil Chem. Soc. 1992, 69, 621625. (16) Poiger, T.; Field, J. A.; Field, T. M.; Giger, W. Anal. Methods Instrum. 1993, 1, 104-113. (17) Abe, A.; Tanaka, K.; Fukaya, K.; Takeshita, S. Suishitsu Odaku Kenkyu 1983, 6, 399-405. (18) Tsuji, K.; Naito, S.; Nakazawa, H. Eisei Kagaku 1988, 34, 501507. (19) Jakob, A.; Zobrist, J.; Davis, J. S.; Liechti, P.; Sigg, L. Gas Wasser Abwasser 1994, 74, 171-186. (20) Zerbatini, O.; Ostacoli, G.; Gastaldi, D.; Zelano, V. J. Chromatogr. 1993, 640, 231-240. (21) Schullerer, S.; Brauch, H. J.; Frimmel, F. H. Vom Wasser 1990, 75, 83-97. (22) Weller, W. T. J. Soc. Dyers Colour. 1979, 95, 187-190. (23) Abe, A.; Yoshimi, H. Water Res. 1979, 13, 1111-1112. (24) Hirayama, N.; Takahashi, A.; Matsuo, K.; Kurosawa, Y.; Oshima, M. Kawasaki-shi Kogai Kenkyusho Nenpo 1983, 10, 67-74. (25) Kato, K.; Mori, H.; Watanabe, N.; Yasuda, Y.; Nakamura, T. Gifuken Kogai Kenkyusho Nenpo 1982, 11, 40-43. (26) Komaki, M.; Yabe, A. Nippon Kagaku Kaishi 1982, 5, 859-867. (27) Uchiyama, M. Water Res. 1979, 13, 847-853. (28) Burg, A. W.; Rohovsky, M. W.; Kensler, C. J. CRC Crit. Rev. Environ. Control 1977, 7, 91-120. (29) Poiger, T. Behavior and fate of detergent-derived fluorescent whitening agents in sewage treatment. Ph.D. Dissertation, Swiss Federal Institute of Technology (ETH), No. 10832, 1994.

Received for review August 10, 1995. Revised manuscript received December 7, 1995. Accepted March 14, 1996.X ES950593R X

Abstract published in Advance ACS Abstracts, May 1, 1996.

Occurrence of Fluorescent Whitening Agents in Sewage and River

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