Occurrence, Sources, and Fate of Benzothiazoles in Municipal

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Environ. Sci. Technol. 2005, 39, 3792-3798

Occurrence, Sources, and Fate of Benzothiazoles in Municipal Wastewater Treatment Plants ACHIM KLOEPFER, MARTIN JEKEL, AND THORSTEN REEMTSMA* Technical University of Berlin, Department of Water Quality Control, Sekr KF 4, Strasse des 17 Juni 135, D-10623 Berlin, Germany

A set of six benzothiazoles was determined in effluents of three municipal wastewater treatment plants. Total concentrations of benzothiazoles ranged from 1.9 to 6.7 µg/ L, with benzothiazole-2-sulfonate (BTSA) being most prominent (35-70%), followed by benzothiazole, 2-hydroxybenzothiazole, and 2-methylthiobenzothiazole (MTBT). The removal of benzothiazoles in tertiary municipal wastewater treatment was investigated in more detail in one of the plants during two sampling periods of several weeks. Total benzothiazole concentration decreased by 5-28% only. This very limited removal was primarily due to BTSA and MTBT that were either hardly removed or even increased in concentration. In street runoff benzothiazoles exceeded the wastewater concentrations by 1 order of magnitude, showing that surface runoff can be a significant source of benzothiazole emission. In household wastewater total concentrations were in the range of 50-80% of that found in municipal wastewater. These investigations outline that benzothiazoles, a class of polar and biologically active industrial chemicals, are regularly released with treated municipal wastewater and exhibit a considerable lifetime in surface waters.

Introduction Benzothiazoles are a class of high production volume chemicals with various applications in industry. The largest amounts of benzothiazoles are used as vulcanization accelerators, such as 2-morpholinothiobenzothiazole (MoTBT) in rubber production, where they are added in amounts of up to 1%. In the 1980s the total production of benzothiazole derivatives for rubber production was about 38 000 tons per year in Western Europe (1). 2-Mercaptobenzothiazole (MBT) is used in paper production as corrosion inhibitor (2), and 2-thiocyanomethylthiobenzothiazole (TCMTB) is used as a substitute for chlorophenols in wood preservation (3-5) and leather production (6). Due to their corrosion-inhibiting properties, benzothiazoles are also added to antifreeze and cooling liquids (7). The herbicide methabenzthiazuron is another derivative of benzothiazole. In recent years benzothiazoles have gained attention as part of the structure of various antitumor agents (8). Many of the above-mentioned applications indicate the biological activity of benzothiazoles. Additionally, MBT, the production intermediate and hydrolysis product of many benzothiazole derivatives, was shown to be acutely toxic to fish (2) and bacteria (6, 9), probably due to its metal-chelating * Corresponding author phone: +49-30-31426429; fax: +49-3031423850; e-mail: [email protected]. 3792

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properties or interferences with membrane-linked proteins. Benzothiazole (BT) and 2-methylthiobenzothiazole (MTBT) also show acute aquatic toxicity in various test systems, but at a lower level than MBT (6). Owing to the wide application of benzothiazoles in open systems, several benzothiazoles have previously been detected in surface waters. However, the initially applied parent compounds such as TCMTB or MoTBT were not detected, as these undergo quick transformation (6, 10). Instead, putative transformation products such as BT and MTBT (5, 7, 11-13) or stable byproducts such as 2-(4-morpholinyl)benzothiazole or N-cyclohexyl-2-benzothiazole (14) were detected. These detections were often only qualitative or semiquantitative and most studies on the occurrence of benzothiazoles in wastewater or surface water were limited to isolated samples. Industrial wastewater has been shown to be a significant source of discharge of MBT, BT, MTBT, 2-hydroxybenzothiazole (OHBT), or benzothiazole-2-sulfonate (BTSA) (6, 15-17). Another route of benzothiazole discharge into receiving waters is runoff from impervious urban surface, especially of tire abrasion from roads (7, 14). Industrial discharge and surface runoff may also be directed to municipal wastewater treatment plants, giving rise to elevated concentrations of benzothiazoles in municipal wastewater. To date, only one other comprehensive study was published on the occurrence of benzothiazoles in municipal wastewater (18). Polar benzothiazoles were regularly detected in influent and effluent in total concentrations of 2-6 µg/L. However, these data came from only one treatment plant and did, thus, not allow assessment of whether benzothiazole discharge into surface waters by treated municipal wastewater is a more general phenomenon. Given the high polarity of several benzothiazoles that should render them highly mobile in aquatic systems and the biological effects determined for some of these group members, it would be important to know whether benzothiazoles are regularly released into surface waters by effluents of municipal wastewater. The present work provides data on the occurrence of six benzothiazoles in effluents of three municipal wastewater treatment plants, investigates the extent of removal of benzothiazoles in wastewater treatment, examines street runoff and household wastewater as emission sources of benzothiazoles, and provides data on the stability of benzothiazoles after their release into surface water.

Materials and Methods Analytical Method. A set of six benzothiazoles was analyzed as described in detail elsewhere (19). Briefly, water samples were filtered over 0.45 µm membrane filters after arrival in the lab and stored frozen in glass bottles if not processed immediately. Before solid phase extraction (SPE) with Waters Oasis HLB cartridges, a glutathione solution (GSH) was added to protect the thiol group of MBT from oxidation. A sample volume of 100 mL was extracted by SPE and the extract subjected to reversed-phase liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/ MS) in the positive and negative ion mode. A T-piece splitting device was placed directly before the ESI source to reduce the flow entering the electrospray interface as this has been shown to reduce matrix effects (20). Quantification was performed by standard addition of the analytes into several samples of each series. Dissolved organic carbon (DOC) was determined after filtration over 0.45 µm membrane filters using a high TOC analyzer (Elementar, Hanau, Germany) and borate was 10.1021/es048141e CCC: $30.25

 2005 American Chemical Society Published on Web 04/02/2005

determined photometrically. Statistical analyses (t-tests, linear correlation analyses) were performed with the SPSS for Windows 10.0 statistical package (SPSS, Chicago, IL). Investigation Sites. Wastewater Treatment Plants. The effluents of three municipal wastewater treatment plants (WWTP) were investigated. Two of the plants were located in Berlin, Germany (Berlin I and Berlin II) and one was located in Beijing, China (Beijing). Berlin I received mainly domestic wastewater from a combined sewage system with some industrial input (approximately 30%). The plant capacity is 240 000 m3/day at dry weather flow, and an activated sludge treatment with nitrification and denitrification and biological phosphorus removal is performed. This WWTP was sampled over a period of 13 weeks from March to June 2002 (Berlin Ia, 20 samplings, mean water temperature 15-21 °C) and again from October to November 2003 (Berlin Ib, 9 samplings, mean water temperature 19-16 °C). Twenty-four-hour composite samples were taken after degritting (influent) and after the final sedimentation basin (effluent), and sampling accounted for the hydraulic retention time in the plant. Berlin II is an activated sludge treatment plant with a throughput of 100 000 m3/day from a separate sewer system. Also in this plant nitrification and denitrification and biological phosphorus removal is performed. One grab sample of the final effluent was taken on October 9, 2003. The WWTP Beijing is the largest treatment plant of Beijing City, China, with a plant capacity of 1 000 000 m3/day, employing a secondary activated sludge treatment without denitrification. According to the operator, the plant receives up to 50% industrial wastewater. Mixed samples from four parallel sedimentation tanks were taken at four samplings on October 16, 17, 21, and 23, 2003. The samples from Beijing were filtered and extracted on-site. The loaded cartridges were sealed, stored, and transported cooled to Berlin, where they were extracted a few days later. Surface Water. The discharge of the WWTP Berlin II is diverted via a trench of 19 km in length (Blankenfelder Graben/Nordgraben) toward Lake Tegel. The travel time through this trench is about 18 h. In this channel the behavior of benzothiazoles after release into receiving waters was studied. Five samples were taken along the channel, accounting for the travel time of the water. Sampling was performed on October 9, 2003 between 02:00 and 17:00 on a dry day with 3.8 h of sunshine and air temperatures between 6.4 and 13.0 °C. Water temperature was 14-16 °C and the average water flux in the trench system was 1.2 m3/s. Street Runoff. Samples from street runoff were taken from a runoff drainage pipe that collected the runoff from about 63 000 m2 of an inner-city motorway in Berlin. About 200 000 cars pass this part of the motorway daily. A rainfall event on August 29, 2003 lasting for 3.5 h after a dry period of several days was investigated with a total precipitation of 8.2 mm (8.2 L/m2). About 90% of the water was collected in the street runoff sewer system that discharged the water into a nearby lake. Samples were taken from the sewer in 10-min intervals for the first 2 h and in 20 min intervals during the following 2.5 h. Domestic/Sanitary Wastewater. Samples of household wastewater were collected in a sewer pumping station from a separate sewer system in a purely residential area of Berlin. Three grab samples were taken over 30 min on a Monday morning (January 12, 2004) and another five grab samples were taken over 60 min on August 23, 2004 during dry weather conditions. Samples were directly brought to the laboratory, filtered, and processed as described above.

Results and Discussion Occurrence in Treated Municipal Wastewater. Six benzothiazoles (Scheme 1) were analyzed in the effluents of three municipal wastewater treatment plants, two performing

SCHEME 1. Structures and Acronyms of the Benzothiazoles under Investigation

tertiary treatment with enhanced nutrient removal (Berlin I and II) and one performing secondary treatment (Beijing). Concentrations of total benzothiazoles in the effluents of these municipal wastewater treatment plants ranged from 1.9 µg/L (Berlin Ib) to 6.7 µg/L (Beijing) on average (Table 1). In all effluents, benzothiazole sulfonate (BTSA) is the dominant compound with average concentrations between 1 µg/L (Berlin Ib) and 2.3 µg/L (Beijing). Benzothiazole (BT), 2-methylthiobenzothiazole (MTBT), and 2-hydroxybenzothiazole (OHBT) also occur in relevant concentrations between 2.3 µg/L (BT in Beijing) and 0.1 µg/L (BT in Berlin II; Table 1). Concentrations of 2-mercaptobenzothiazole (MBT) and 2-aminobenzothiazole (ABT) were analyzed in all effluent samples but remained below the LOQs (50 ng/L MBT, 30 ng/L ABT). Since ABT concentrations never exceeded the LOQ in any sample analyzed in this study, this compound can be considered as not environmentally relevant and is, therefore, excluded from the further discussion. The average composition of the benzothiazole fraction in the effluent of the three wastewater treatment plants differs to some extent (Figure 1), with a high portion of BT (33% of total concentration) and OHBT (23%) in the Beijing effluent and a comparatively low contribution of BT (LOQa mean

SD

BT

n>LOQa mean

1.70 2.10 1.21 0.99 1.76

0.75 0.48 0.20 0.48

20 20 9 9

0.17 0.44 0.44 0.36 0.40

0.06 0.09 0.39 0.06

20 20 9 9

0.85 0.55 0.74 0.28 0.07d

0.20 0.19 0.24 0.08

20 20 8 9

effluent

2.25 1.16

4

0.55

0.13

4

2.26

0.27

Jan, n ) 3 Aug, n ) 5

0.76 0.09 0.92 0.38 0.14 0.09

3 5

0.10 0.07 0.07d

2 1

0.08 0.04

a Number of samples with concentration above LOQ. between LOD and LOQ. e nd, below LOD.

0.48 0.79 0.42 0.10

b

0.32 0.35

SD

0.50d

MBT

n>LOQa mean

SD

total

n>LOQa mean

0.16 0.14d 0.08 0.16d 0.20d 0.06 0.27

5 4 0 3

0.19 0.07 0.02d 0.03 0.02d 0.01d 0.01 0.01d

17 2 0 3

4

1.54

4

0.04d 0.01

1

3 5

0.32d

0 1

nde

0.37d 0.62 0.20

0.66

Removal in Municipal Wastewater Treatment. The continuous and widespread occurrence of four of the benzothiazoles in treated effluents initiated a study on the removal of benzothiazoles in one of these activated sludge municipal wastewater treatment plants during two periods in early summer 2002 (Berlin Ia) and fall 2003 (Berlin Ib). Total average influent concentrations of the six benzothiazoles amounted to 3.4 and 2.6 µg/L during the two periods (Table 1). As for the effluent, BTSA was the most prominent benzothiazole also in the influents (1.7 and 1.2 µg/L on average) and accounted for 45-50% of the total influent concentration. BT was also quite prominent (25% in both series), followed by OHBT (6-15%) and MTBT. MBT accounted for 5 and 3% of the total benzothiazole concentration only. On one hand, the low concentration of MBT in the influent was astonishing, as MBT is the benzothiazole most frequently mentioned in the literature and it is the major production intermediate as well as hydrolysis product of many commercial benzothiazole compounds. On the other hand, none of the other four benzothiazoles that are regularly found in municipal wastewaters in this study is known to be a commercial product used in either household or industry. Thus, their sources of emission are largely unknown. ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 10, 2005

3.44 3.27 2.60 1.86 2.54

SD 0.92 0.56 0.46 0.32

6.66 2.28 1.71 0.67 2.21 1.05

nde 0.12 0.05

For WWTP influent and household wastewater. c For WWTP effluent.

FIGURE 1. Mean contribution (%) of individual benzothiazoles to total benzothiazole concentration in the effluent of municipal wastewater treatment plants. ABT was not detected in relevant amounts. Numbers on the column top denote mean total concentration of benzothiazoles in each sample series.

9

OHBT

n>LOQa mean

influent effluent influent effluent effluent

LOQ in raw wastewater b LOQ in treated wastewaterc

3794

SD

d

Concentration

FIGURE 2. Change in concentration of individual benzothiazoles and total benzothiazole concentration (% of influent) in municipal wastewater treatments Berlin Ia and Ib. Negative values indicate removal, and positive values indicate formation of the benzothiazole compound. *Statistical significance e 0.05; **statistical significance e 0.005. A comparison of the influent data with the respective effluent data indicates that the overall removal of benzothiazoles in activated sludge municipal wastewater treatment is limited (5-28%, Figure 2). This finding contrasts previous results for an industrial wastewater treatment, in which an average elimination of 87% was observed for the same set of benzothiazoles (21). However, influent concentrations in that study were more than 2 orders of magnitude higher (about 700 µg/L) than in municipal wastewater and they were dominated by MBT, which is hardly present here. The five benzothiazoles showed quite different behavior in the activated sludge treatment (Figure 2). BT experienced a stable average elimination of 40 to 60% during both periods, but elimination was never complete (Figure 2). This contrasts with results from laboratory experiments with different setups and experimental conditions, in which BT has been shown to be readily biodegradable (5, 6, 22). A part of the BT elimination may also be due to stripping, as BT is quite volatile. For BTSA an increase of 23% was recorded during the first period (Berlin Ia), whereas the average elimination of 20% in the second period was not statistically significant (Figure 2). Increasing concentrations of BTSA have previously been reported for an industrial wastewater treatment (21).

FIGURE 3. Increase in MTBT concentration versus decrease in MBT concentration (nmol/L) for each pair of influent and effluent samples in municipal wastewater treatment Berlin Ia. X marks one outlier that was excluded from linear correlation analysis. As for BT, previous laboratory studies implied that BTSA was biodegradable by aerobic bacteria, but these findings were based on the use of the pure substrate (23, 24). The source from which BTSA was formed in this activated sludge treatment (Berlin Ia) is still unknown. In a previous study on industrial wastewater treatment with extremely high MBT concentrations in the influent, MBT was assumed to be the precursor substance (21), but this can be excluded here, as influent MBT concentrations were too low. Moreover, another transformation pathway is favored for MBT from these data sets (see below). Some hydrophobic benzothiazoles such as MoTBT from rubber may enter the sewage treatment plant sorbed onto fine particulate matter that is not removed in primary treatment. In secondary treatment a part of the sorbed MoTBT may then be oxidized and successively released into the dissolved phase as the polar BTSA. However, no samples of the activated sludge were analyzed for such hydrophobic precursors in this study. Elimination of OHBT was similar to that of BT with 70% and 50% removal in the two periods (Figure 2). This elimination is likely due to mineralization, since OHBT has been shown to be readily degradable in laboratory degradation tests with activated sludge (22) and also with isolated strains (25). But as for the readily degradable BT, the removal in full scale activated sludge treatment remains incomplete. OHBT may also be formed as a biodegradation intermediate from BT, as shown with pure cultures (26, 27). The behavior of MBT and MTBT in this activated sludge treatment appears to be linked to each other. During the first investigation period (Berlin Ia) the average amount of MTBT formed during the treatment (+1.5 nmol/L) roughly corresponds to the average amount of MBT being removed (-1.0 nmol/L). This first impression was substantiated by a comparison of MBT removal and MTBT formation for each pair of influent and effluent samples (Figure 3). A clear and statistically significant trend is visible, showing that an increasing removal of MBT is accompanied by increasing formation of MTBT (r2 ) 0.45, p e 0.002, after removal of one outlier). Microbial methylation of thiols has been shown to be mediated by an S-methyltransferase and was interpreted as being a detoxification strategy (28, 29). Methylation of MBT to form MTBT has been observed in laboratory experiments under variable conditions (5, 6), and it was also shown that the acute aquatic toxicity of MBT substantially decreased upon methylation to MTBT (6). Though methylation of MBT to form MTBT seems a reasonable strategy to

FIGURE 4. Concentrations of individual benzothiazoles (µg/L) along the trench system (Blankenfelder Graben/Nordgraben) discharging the effluent of WWTP Berlin II. Total observation time 15 h. reduce aquatic toxicity, it is not useful in terms of mineralization. Laboratory degradation studies prove that MTBT is stable (6). These findings are well-reflected in the behavior of MTBT and MBT in the activated sludge treatment (Figure 3). No indication was found for a mineralization of MBT, which has recently been observed in degradation tests with an isolated strain (30). During the second investigation period (Berlin Ib), MBT and MTBT behavior in wastewater treatment differed from the first period as neither a decrease of MBT was observable nor an increase of the MTBT concentration (Figure 2). Instead a limited (-25%) but statistically insignificant decrease in the MTBT concentration occurred. The influent concentrations of MBT and MTBT during this period provide the key to understand this difference (Table 1): contrary to the first period (Berlin Ia), the MBT concentration in the influent was almost negligible during the second period, whereas the MTBT concentration was already at the level found in the effluent of the first period (0.4 µg/L). We conclude that during this investigation period (October/November) methylation of MBT had already taken place in the sewer system. The average temperature in the sewer system can be expected to be higher after the summer (Berlin Ib) than before the summer (Berlin Ia) and this may have allowed for methylation of MBT before the wastewater entered the treatment plant. Behavior in Surface Water. As this investigation of sewage treatment plant effluents revealed that benzothiazoles are continuously discharged into surface waters, it seems necessary to investigate the fate of these compounds in surface waters. A first study was conducted along a 19 km trench system in the city of Berlin that discharges the effluent of the treatment plant Berlin II into the next larger surface water, Lake Tegel. Concentrations of the five benzothiazoles in five samples taken on a dry day without precipitation from a standing wave in that trench system are shown in Figure 4. The composition of the benzothiazole fraction reflects the WWTP effluent that is the only source water. During the travel time of 15 h, some fluctuations in the total concentration of the analytes are visible (between 2.0 and 3.4 µg/L), especially for BTSA (between 1.3 and 2.3 µg/L). These are likely due to problems in repeatedly sampling the same body of water over the travel time of 15 h. No significant inflow of water from other sources occurs during the 19 km length of the trench system. Neither the DOC nor the borate concentrations showed any trend along the trench, with average values of 9.7 ((0.3 mg/L) and 3.8 ((0.5 mg/L), respectively. Analogously, no clear trend toward decreasing concentrations is visible for any of the five benzothiazoles VOL. 39, NO. 10, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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(Figure 4). These first data on benzothiazoles in surface waters suggest that BT, OHBT, MTBT, and BTSA exhibit a considerable lifetime in surface water and are not rapidly degraded after discharge with WWTP effluents. For surface waters, some literature data on the stability of BT and MTBT are available. For BT, 60-90% of the concentration discharged from a chemical company was found several miles downstream of its point of discharge (15). In a different study, decreasing concentrations of BT and stable concentrations of MTBT were found over a travel time of 8-14 h in a small trench system receiving wastewater from a chemical plant (5). Moreover MTBT was found in long-term monitoring along the River Elbe (Germany) with average concentrations of 0.04 µg/L between 1994 and 1999 (31). This concentration matches the average effluent concentration of MTBT of around 0.4 µg/L found in this study (Table 1), assuming a general dilution factor of 10 for wastewater discharges in surface waters. Other benzothiazoles were not included in any of the cited studies. The stability of polar organics in surface water is determined by their microbial recalcitrance and their chemical and photochemical reactivity. Several studies on photolysis of MBT are available (5, 32), but this compound is not relevant in surface waters. For those compounds found in this study (BTSA, MTBT, OHBT, and BT) no information on their photolytic transformation is available. Therefore, it remains unknown by which process the benzothiazoles delivered to surface water with wastewater discharges may be removed and whether photolysis would contribute significantly. Sources of Benzothiazoles Release. As outlined in the Introduction, benzothiazoles are employed in various industrial applications. The occurrence of benzothiazoles in municipal wastewater may, thus, indicate indirect discharges of industrial wastewater into the sewer systems. In the case of combined sewer systems benzothiazoles may also originate from street runoff, in which BT, OHBT, MTBT, and two byproducts of vulcanization accelerators have previously been found (7, 10, 33). The importance of households as a source of benzothiazoles immission into municipal wastewater is unknown. Street Runoff. Reports exist on the occurrence of benzothiazoles in street runoff and road dust. These studies, however, either focus on nonpolar byproducts of vulcanization accelerators or were limited as only isolated samples were analyzed or only qualitative data were provided. Surface runoff from a collecting sewer was analyzed for benzothiazoles during and after a strong rainfall event (8.2 mm precipitation) that followed several days of drought. Benzothiazole concentrations summed up to 74 µg/L in the first sample (Figure 5). Increasing water flow, then, led to dilution of benzothiazole concentrations down to 45 µg/L during the peak flow, while the further decrease in total concentration reflects the reduced amounts of organics on the surfaces that are available for washing off with ongoing precipitation. Nevertheless, this decrease leveled off at total benzothiazole concentrations around 20 µg/L. These concentrations are about 1 order of magnitude higher than those found in nontreated municipal wastewater. The composition of the benzothiazole fraction hardly changed during the rainfall, and BTSA was the dominant compound that accounted for about 60% of the total concentration. OHBT (25-30%) and BT (8-13%) were also of importance, whereas the contribution of MBT and MTBT was negligible (Figure 5). These data show, for a broader range of compounds and in more detail than previous reports, that surface runoff is a relevant source of benzothiazole discharges into the aquatic environment. In previous investigations, concentrations of BT in the range of 0.1-0.5 and 0.4-1.2 µg/L were reported in surface runoff (7, 13), as well as OHBT (5-7 µg/L (13)) and 3796

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FIGURE 5. Concentrations of individual benzothiazoles (µg/L) and water flux (m3/h) in street runoff collected in a sewer after a rainfall event with 8.2 mm precipitation (8.2 L/m2). MTBT (0.04-0.2 µg/L (7)). However, the most important benzothiazole, BTSA, has not been considered before. For BT and OHBT, higher concentrations in street runoff were found here as compared to those previous investigations. This may be due to the unusually high traffic on the highway in the study area, leaving behind large amounts of tire abrasion. The flux of benzothiazoles from the study area into surface water during this rainfall event adds up to 14 g, corresponding to 152 µg/m2 for BTSA, 54 µg/m2 for OHBT, and 15 µg/m2 for BT. Fluxes of MTBT, ABT, and MBT remained below 5 µg/ m2. These data indicate that surface runoff in cities will transport significant amounts of polar organic compounds into surface waters. This discharge would not be reduced by the preferred pretreatment in settling basins. If not discharged into surface water, surface runoff may be collected in a combined sewage system and would, then, increase the total benzothiazole load of municipal wastewater. The treatment plant Berlin I is connected to such a combined sewer system. However, no increasing concentrations of benzothiazoles were determined in the influent of the treatment plant on those occasions when sampling coincided with strong rainfalls. This may be due to the large size of the drainage area (1.6 mio population equivalents), which leads to strong mixing and equalization of peaks of concentrations. Household Wastewater. It is yet unknown whether sanitary wastewater from private households is a source of benzothiazoles in municipal wastewater or whether benzothiazoles originate from industrial wastewater and surface runoff only. No information was available that indicated the inclusion of benzothiazoles in consumer products used in households. However, the broad application of benzothiazoles in industrial processes also suggests that various goods used in the private environment may contain benzothiazoles. To elucidate this aspect, wastewater of a separate sewer system (no surface runoff) in a residential area was investigated. The average concentrations of benzothiazoles found during two samplings are compiled in Table 1. The total concentration of benzothiazoles in household wastewater was 1.7 and 2.2 µg/L on average. These total concentrations comprise 50-85% of that found in the municipal wastewater in Berlin (Table 1), showing for the first time that significant emission of benzothiazoles into municipal wastewater originates from households. It must be mentioned that these samples could not be analyzed for MBT, as MBT turned out to be unstable in these samples, although glutathione had been added to prevent its oxidation.

This instability was recognized by the routinely performed standard addition experiments. As standard addition was repeatedly performed with each kind of samples, it can be excluded that similar instabilities of MBT occurred for samples other than sanitary wastewater. Due to this instability of MBT, the total benzothiazole concentration in household wastewater may have even been higher. The contribution of the individual compounds differs from the wastewater treatment plant influents with a lower portion of BTSA (42-44%) but a higher portion of BT (2836%). MTBT occurred in very low concentration (e0.1 µg/L), which was probably due to the instability of MBT in this wastewater and the very short residence time of the household wastewater in the sewer system before sampling that did not allow for biomethylation of MBT. The unexpectedly high concentration of total benzothiazoles in household wastewater suggests that their emission from the household was not only due to the release from aged products containing benzothiazoles but that certain consumer products regularly used in households are responsible for this emission. These products are not yet known. Future Aspects. This first comprehensive investigation on benzothiazoles in municipal wastewater has shown that four polar benzothiazoles are regularly found in treated municipal wastewater, with benzothiazole sulfonate being most prominent. As their polarity is high and their stability considerable, it is worthwhile to study the behavior of benzothiazoles in surface water and beyond. This applies especially to the anionic BTSA, as this compound should be most mobile and was found in highest concentrations in all samples yet investigated. Further studies may be directed toward the potential of improved wastewater treatment, especially of physicochemical oxidation, to remove these trace organics. Emissions of benzothiazoles with household wastewater was shown to be significant, but their field of application in private household is yet unknown. The occurrence of benzothiazoles in surface runoff has outlined that this kind of water, which is often discharged directly into receiving waters, can provide considerable inputs of polar organic pollutants into the aqueous environment.

Acknowledgments We are grateful to Thomas Ludwig for providing surface runoff samples and runoff data and to Jutta Jakobs for laboratory assistance. We thank Berliner Wasserbetriebe for valuable support in the sampling campaigns and the Senate of Berlin for providing flux data. Funding by the German Ministry for Education and Research (FKz. 02WA0123) and by the European Union for the project ‘Removal of Persistent Polar Pollutants Through Improved Treatment of Wastewater Effluents’ (P-THREE; EVK1-CT-2002-00116) is gratefully acknowledged.

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Received for review November 25, 2004. Revised manuscript received March 4, 2005. Accepted March 9, 2005. ES048141E