Occurrence, Sources, and Fate ofBenzothiazoles in MunicipalWastewater Treatment PlantsA C H I M K L O E P F E R , M A R T I N J E K E L , A N DT H O R S T E N R E E M T S M A *

Technical University of Berlin, Department of WaterQuality Control, Sekr KF 4, Strasse des 17 Juni 135,D-10623 Berlin, Germany

A set of six benzothiazoles was determined in effluents ofthree municipal wastewater treatment plants. Totalconcentrations of benzothiazoles ranged from 1.9 to 6.7 µg/L, with benzothiazole-2-sulfonate (BTSA) being mostprominent (35-70%), followed by benzothiazole, 2-hydroxy-benzothiazole, and 2-methylthiobenzothiazole (MTBT).The removal of benzothiazoles in tertiary municipal wastewatertreatment was investigated in more detail in one of theplants during two sampling periods of several weeks. Totalbenzothiazole concentration decreased by 5-28% only.This very limited removal was primarily due to BTSA andMTBT that were either hardly removed or even increased inconcentration. In street runoff benzothiazoles exceededthe wastewater concentrations by 1 order of magnitude,showing that surface runoff can be a significant source ofbenzothiazole emission. In household wastewater totalconcentrations were in the range of 50-80% of that foundin municipal wastewater. These investigations outlinethat benzothiazoles, a class of polar and biologically activeindustrial chemicals, are regularly released with treatedmunicipal wastewater and exhibit a considerable lifetime insurface waters.

IntroductionBenzothiazoles are a class of high production volumechemicals with various applications in industry. The largestamounts of benzothiazoles are used as vulcanization ac-celerators, such as 2-morpholinothiobenzothiazole (MoTBT)in rubber production, where they are added in amounts ofup to 1%. In the 1980s the total production of benzothiazolederivatives for rubber production was about 38 000 tons peryear in Western Europe (1). 2-Mercaptobenzothiazole (MBT)is used in paper production as corrosion inhibitor (2), and2-thiocyanomethylthiobenzothiazole (TCMTB) is used as asubstitute for chlorophenols in wood preservation (3-5) andleather production (6). Due to their corrosion-inhibitingproperties, benzothiazoles are also added to antifreeze andcooling liquids (7). The herbicide methabenzthiazuron isanother derivative of benzothiazole. In recent years ben-zothiazoles have gained attention as part of the structure ofvarious antitumor agents (8).

Many of the above-mentioned applications indicate thebiological activity of benzothiazoles. Additionally, MBT, theproduction intermediate and hydrolysis product of manybenzothiazole derivatives, was shown to be acutely toxic tofish (2) and bacteria (6, 9), probably due to its metal-chelating

properties or interferences with membrane-linked proteins.Benzothiazole (BT) and 2-methylthiobenzothiazole (MTBT)also show acute aquatic toxicity in various test systems, butat a lower level than MBT (6).

Owing to the wide application of benzothiazoles in opensystems, several benzothiazoles have previously been de-tected in surface waters. However, the initially applied parentcompounds 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) weredetected. These detections were often only qualitative orsemiquantitative and most studies on the occurrence ofbenzothiazoles in wastewater or surface water were limitedto isolated samples. Industrial wastewater has been shownto be a significant source of discharge of MBT, BT, MTBT,2-hydroxybenzothiazole (OHBT), or benzothiazole-2-sul-fonate (BTSA) (6, 15-17). Another route of benzothiazoledischarge into receiving waters is runoff from imperviousurban surface, especially of tire abrasion from roads (7, 14).

Industrial discharge and surface runoff may also bedirected to municipal wastewater treatment plants, givingrise to elevated concentrations of benzothiazoles in municipalwastewater. To date, only one other comprehensive studywas published on the occurrence of benzothiazoles inmunicipal wastewater (18). Polar benzothiazoles were regu-larly detected in influent and effluent in total concentrationsof 2-6 µg/L. However, these data came from only onetreatment plant and did, thus, not allow assessment ofwhether benzothiazole discharge into surface waters bytreated municipal wastewater is a more general phenomenon.

Given the high polarity of several benzothiazoles thatshould render them highly mobile in aquatic systems andthe biological effects determined for some of these groupmembers, it would be important to know whether ben-zothiazoles are regularly released into surface waters byeffluents of municipal wastewater. The present work providesdata on the occurrence of six benzothiazoles in effluents ofthree municipal wastewater treatment plants, investigatesthe extent of removal of benzothiazoles in wastewatertreatment, examines street runoff and household wastewateras emission sources of benzothiazoles, and provides data onthe stability of benzothiazoles after their release into surfacewater.

Materials and MethodsAnalytical Method. A set of six benzothiazoles was analyzedas described in detail elsewhere (19). Briefly, water sampleswere filtered over 0.45 µm membrane filters after arrival inthe lab and stored frozen in glass bottles if not processedimmediately. Before solid phase extraction (SPE) with WatersOasis HLB cartridges, a glutathione solution (GSH) was addedto protect the thiol group of MBT from oxidation. A samplevolume of 100 mL was extracted by SPE and the extractsubjected to reversed-phase liquid chromatography-elec-trospray ionization tandem mass spectrometry (LC-ESI-MS/MS) in the positive and negative ion mode. A T-piece splittingdevice was placed directly before the ESI source to reducethe flow entering the electrospray interface as this has beenshown to reduce matrix effects (20). Quantification wasperformed by standard addition of the analytes into severalsamples of each series.

Dissolved organic carbon (DOC) was determined afterfiltration over 0.45 µm membrane filters using a high TOCanalyzer (Elementar, Hanau, Germany) and borate was

* Corresponding author phone: +49-30-31426429; fax: +49-30-31423850; e-mail: thorsten.reemtsma@tu-berlin.de.

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determined photometrically. Statistical analyses (t-tests,linear correlation analyses) were performed with the SPSSfor Windows 10.0 statistical package (SPSS, Chicago, IL).

Investigation Sites. Wastewater Treatment Plants. Theeffluents of three municipal wastewater treatment plants(WWTP) were investigated. Two of the plants were locatedin Berlin, Germany (Berlin I and Berlin II) and one was locatedin Beijing, China (Beijing). Berlin I received mainly domesticwastewater from a combined sewage system with someindustrial input (approximately 30%). The plant capacity is240 000 m3/day at dry weather flow, and an activated sludgetreatment with nitrification and denitrification and biologicalphosphorus removal is performed. This WWTP was sampledover a period of 13 weeks from March to June 2002 (BerlinIa, 20 samplings, mean water temperature 15-21 °C) andagain from October to November 2003 (Berlin Ib, 9 samplings,mean water temperature 19-16 °C). Twenty-four-hourcomposite samples were taken after degritting (influent) andafter the final sedimentation basin (effluent), and samplingaccounted for the hydraulic retention time in the plant. BerlinII is an activated sludge treatment plant with a throughputof 100 000 m3/day from a separate sewer system. Also in thisplant nitrification and denitrification and biological phos-phorus removal is performed. One grab sample of the finaleffluent was taken on October 9, 2003. The WWTP Beijing isthe largest treatment plant of Beijing City, China, with a plantcapacity of 1 000 000 m3/day, employing a secondary acti-vated sludge treatment without denitrification. According tothe operator, the plant receives up to 50% industrialwastewater. Mixed samples from four parallel sedimentationtanks were taken at four samplings on October 16, 17, 21,and 23, 2003. The samples from Beijing were filtered andextracted on-site. The loaded cartridges were sealed, stored,and transported cooled to Berlin, where they were extracteda few days later.

Surface Water. The discharge of the WWTP Berlin II isdiverted via a trench of 19 km in length (BlankenfelderGraben/Nordgraben) toward Lake Tegel. The travel timethrough this trench is about 18 h. In this channel the behaviorof benzothiazoles after release into receiving waters wasstudied. Five samples were taken along the channel, ac-counting for the travel time of the water. Sampling wasperformed on October 9, 2003 between 02:00 and 17:00 ona dry day with 3.8 h of sunshine and air temperatures between6.4 and 13.0 °C. Water temperature was 14-16 °C and theaverage water flux in the trench system was 1.2 m3/s.

Street Runoff. Samples from street runoff were taken froma runoff drainage pipe that collected the runoff from about63 000 m2 of an inner-city motorway in Berlin. About 200 000cars pass this part of the motorway daily. A rainfall event onAugust 29, 2003 lasting for 3.5 h after a dry period of severaldays was investigated with a total precipitation of 8.2 mm(8.2 L/m2). About 90% of the water was collected in the streetrunoff sewer system that discharged the water into a nearbylake. Samples were taken from the sewer in 10-min intervalsfor the first 2 h and in 20 min intervals during the following2.5 h.

Domestic/Sanitary Wastewater. Samples of householdwastewater were collected in a sewer pumping station froma separate sewer system in a purely residential area of Berlin.Three grab samples were taken over 30 min on a Mondaymorning (January 12, 2004) and another five grab sampleswere taken over 60 min on August 23, 2004 during dry weatherconditions. Samples were directly brought to the laboratory,filtered, and processed as described above.

Results and DiscussionOccurrence in Treated Municipal Wastewater. Six ben-zothiazoles (Scheme 1) were analyzed in the effluents of threemunicipal wastewater treatment plants, two performing

tertiary treatment with enhanced nutrient removal (Berlin Iand II) and one performing secondary treatment (Beijing).Concentrations of total benzothiazoles in the effluents ofthese municipal wastewater treatment plants ranged from1.9 µg/L (Berlin Ib) to 6.7 µg/L (Beijing) on average (Table1). In all effluents, benzothiazole sulfonate (BTSA) is thedominant compound with average concentrations between1 µg/L (Berlin Ib) and 2.3 µg/L (Beijing). Benzothiazole (BT),2-methylthiobenzothiazole (MTBT), and 2-hydroxybenzo-thiazole (OHBT) also occur in relevant concentrationsbetween 2.3 µg/L (BT in Beijing) and 0.1 µg/L (BT in BerlinII; Table 1). Concentrations of 2-mercaptobenzothiazole(MBT) and 2-aminobenzothiazole (ABT) were analyzed inall effluent samples but remained below the LOQs (50 ng/LMBT, 30 ng/L ABT). Since ABT concentrations never ex-ceeded the LOQ in any sample analyzed in this study, thiscompound can be considered as not environmentally relevantand is, therefore, excluded from the further discussion.

The average composition of the benzothiazole fraction inthe effluent of the three wastewater treatment plants differsto some extent (Figure 1), with a high portion of BT (33% oftotal concentration) and OHBT (23%) in the Beijing effluentand a comparatively low contribution of BT (<3%) in theBerlin II effluent. These differences may reflect inputs fromdifferent sources into the sewer systems of the three plantsas well as differences in removal of benzothiazoles in therespective activated sludge treatments. Furthermore, differentsampling frequencies (n ) 20 for Berlin Ia, n ) 1 for BerlinII) limited the comparability in quantitative terms. Anyhow,it is obvious from these data that benzothiazoles regularlyoccur in low microgram/liter quantities in the effluents ofdifferent municipal wastewater treatment plants with sec-ondary (Beijing) or even tertiary (Berlin) treatment. Thesedata outline that previous findings of benzothiazoles in onemunicipal wastewater treatment effluent (Berlin Ia (18)) werenot limited to this one plant or one observation period butthat benzothiazoles are continuously released with treatedmunicipal wastewater in microgram/liter concentrations.Besides this one previous report (18), literature providedevidence for the occurrence of only two of these benzothia-zoles, BT and MTBT. First findings in the US date back to the1980s (12), more recent but still isolated reports came fromSweden (11) and, very recently, from four treatment plantsin California, where BT (0.05-0.1 µg/L) and MTBT (0.1-0.3µg/L) were detected (13). These concentrations are consistentwith a generally more diluted wastewater due to higher percapita water consumption in the US as compared to WesternEuropean countries. No report on the occurrence of any otherbenzothiazoles found in this study is available. This maypartly be due to the exclusive use of GC-MS in screeninginvestigations, as BTSA and MBT are not amenable to GCanalysis. Only by using LC-MS has this become possible(17, 19). Since BTSA is the dominant benzothiazole com-pound released from wastewater treatment plants (Figure1), the discharge of benzothiazoles has been systematicallyunderestimated in previous investigations.

SCHEME 1. Structures and Acronyms of the Benzothiazolesunder Investigation

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Removal in Municipal Wastewater Treatment. Thecontinuous and widespread occurrence of four of thebenzothiazoles in treated effluents initiated a study on theremoval of benzothiazoles in one of these activated sludgemunicipal wastewater treatment plants during two periodsin early summer 2002 (Berlin Ia) and fall 2003 (Berlin Ib).Total average influent concentrations of the six benzothia-zoles amounted to 3.4 and 2.6 µg/L during the two periods(Table 1). As for the effluent, BTSA was the most prominentbenzothiazole also in the influents (1.7 and 1.2 µg/L onaverage) and accounted for 45-50% of the total influentconcentration. BT was also quite prominent (25% in bothseries), followed by OHBT (6-15%) and MTBT. MBT ac-counted for 5 and 3% of the total benzothiazole concentrationonly.

On one hand, the low concentration of MBT in the influentwas astonishing, as MBT is the benzothiazole most frequentlymentioned in the literature and it is the major productionintermediate as well as hydrolysis product of many com-mercial benzothiazole compounds. On the other hand, noneof the other four benzothiazoles that are regularly found inmunicipal wastewaters in this study is known to be acommercial product used in either household or industry.Thus, their sources of emission are largely unknown.

A comparison of the influent data with the respectiveeffluent data indicates that the overall removal of benzothia-zoles in activated sludge municipal wastewater treatment islimited (5-28%, Figure 2). This finding contrasts previousresults for an industrial wastewater treatment, in which anaverage elimination of 87% was observed for the same setof benzothiazoles (21). However, influent concentrations inthat study were more than 2 orders of magnitude higher(about 700 µg/L) than in municipal wastewater and theywere dominated by MBT, which is hardly present here. Thefive benzothiazoles showed quite different behavior in theactivated 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 laboratoryexperiments with different setups and experimental condi-tions, in which BT has been shown to be readily biodegradable(5, 6, 22). A part of the BT elimination may also be due tostripping, as BT is quite volatile.

For BTSA an increase of 23% was recorded during thefirst period (Berlin Ia), whereas the average elimination of20% in the second period was not statistically significant(Figure 2). Increasing concentrations of BTSA have previouslybeen reported for an industrial wastewater treatment (21).

TABLE 1. Mean Concentrations (µg/L) of the Analytes and Their Mean Total Concentration in Wastewater Treatment PlantInfluents and Effluents and in Household Wastewaters

concentration (µg/L)

BTSA MTBT BT OHBT MBT total

mean SD n>LOQa mean SD n>LOQ

a mean SD n>LOQa mean SD n>LOQ

a mean SD n>LOQa mean SD

Berlin Ia influent 1.70 0.75 20 0.17 0.06 20 0.85 0.20 20 0.50d 0.16 5 0.19 0.07 17 3.44 0.92n ) 20 effluent 2.10 0.48 20 0.44 0.09 20 0.55 0.19 20 0.14d 0.08 4 0.02d 0.03 2 3.27 0.56Berlin Ib influent 1.21 0.20 9 0.44 0.39 9 0.74 0.24 8 0.16d 0 0.02d 0 2.60 0.46n ) 9 effluent 0.99 0.48 9 0.36 0.06 9 0.28 0.08 9 0.20d 0.06 3 0.01d 0.01 3 1.86 0.32Berlin IIn ) 1

effluent 1.76 0.40 0.07d 0.27 0.01d 2.54

Beijingn ) 4

effluent 2.25 1.16 4 0.55 0.13 4 2.26 0.27 4 1.54 0.66 4 0.04d 0.01 1 6.66 2.28

household Jan, n ) 3 0.76 0.09 3 0.10 0.07 2 0.48 0.32 3 0.32d 0 nde 1.71 0.67wastewater Aug, n ) 5 0.92 0.38 5 0.07d 1 0.79 0.35 5 0.37d 1 nde 2.21 1.05

LOQ in raw wastewater b 0.14 0.08 0.42 0.62 0.12LOQ in treated wastewaterc 0.09 0.04 0.10 0.20 0.05

a Number of samples with concentration above LOQ. b For WWTP influent and household wastewater. c For WWTP effluent. d Concentrationbetween LOD and LOQ. e nd, below LOD.

FIGURE 1. Mean contribution (%) of individual benzothiazoles tototal benzothiazole concentration in the effluent of municipalwastewater treatment plants. ABT was not detected in relevantamounts. Numbers on the column top denote mean total concentra-tion of benzothiazoles in each sample series.

FIGURE 2. Change in concentration of individual benzothiazolesand total benzothiazole concentration (% of influent) in municipalwastewater treatments Berlin Ia and Ib. Negative values indicateremoval, and positive values indicate formation of the benzothiazolecompound. *Statistical significance e 0.05; **statistical significancee 0.005.

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As for BT, previous laboratory studies implied that BTSA wasbiodegradable by aerobic bacteria, but these findings werebased on the use of the pure substrate (23, 24).

The source from which BTSA was formed in this activatedsludge treatment (Berlin Ia) is still unknown. In a previousstudy on industrial wastewater treatment with extremely highMBT concentrations in the influent, MBT was assumed tobe the precursor substance (21), but this can be excludedhere, as influent MBT concentrations were too low. Moreover,another transformation pathway is favored for MBT fromthese data sets (see below). Some hydrophobic benzothia-zoles such as MoTBT from rubber may enter the sewagetreatment plant sorbed onto fine particulate matter that isnot removed in primary treatment. In secondary treatmenta part of the sorbed MoTBT may then be oxidized andsuccessively released into the dissolved phase as the polarBTSA. However, no samples of the activated sludge wereanalyzed 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). Thiselimination is likely due to mineralization, since OHBT hasbeen shown to be readily degradable in laboratory degrada-tion tests with activated sludge (22) and also with isolatedstrains (25). But as for the readily degradable BT, the removalin full scale activated sludge treatment remains incomplete.OHBT may also be formed as a biodegradation intermediatefrom BT, as shown with pure cultures (26, 27).

The behavior of MBT and MTBT in this activated sludgetreatment appears to be linked to each other. During thefirst investigation period (Berlin Ia) the average amount ofMTBT formed during the treatment (+1.5 nmol/L) roughlycorresponds to the average amount of MBT being removed(-1.0 nmol/L). This first impression was substantiated by acomparison of MBT removal and MTBT formation for eachpair of influent and effluent samples (Figure 3). A clear andstatistically significant trend is visible, showing that anincreasing removal of MBT is accompanied by increasingformation of MTBT (r2 ) 0.45, p e 0.002, after removal of oneoutlier). Microbial methylation of thiols has been shown tobe mediated by an S-methyltransferase and was interpretedas being a detoxification strategy (28, 29). Methylation ofMBT to form MTBT has been observed in laboratoryexperiments under variable conditions (5, 6), and it was alsoshown that the acute aquatic toxicity of MBT substantiallydecreased upon methylation to MTBT (6). Though methy-lation of MBT to form MTBT seems a reasonable strategy to

reduce aquatic toxicity, it is not useful in terms of miner-alization. Laboratory degradation studies prove that MTBTis stable (6). These findings are well-reflected in the behaviorof MTBT and MBT in the activated sludge treatment (Figure3). No indication was found for a mineralization of MBT,which has recently been observed in degradation tests withan isolated strain (30).

During the second investigation period (Berlin Ib), MBTand MTBT behavior in wastewater treatment differed fromthe first period as neither a decrease of MBT was observablenor an increase of the MTBT concentration (Figure 2). Insteada limited (-25%) but statistically insignificant decrease inthe MTBT concentration occurred. The influent concentra-tions of MBT and MTBT during this period provide the keyto understand this difference (Table 1): contrary to the firstperiod (Berlin Ia), the MBT concentration in the influent wasalmost negligible during the second period, whereas theMTBT concentration was already at the level found in theeffluent of the first period (0.4 µg/L). We conclude that duringthis investigation period (October/November) methylationof MBT had already taken place in the sewer system. Theaverage temperature in the sewer system can be expected tobe higher after the summer (Berlin Ib) than before thesummer (Berlin Ia) and this may have allowed for methylationof MBT before the wastewater entered the treatment plant.

Behavior in Surface Water. As this investigation of sewagetreatment plant effluents revealed that benzothiazoles arecontinuously discharged into surface waters, it seems neces-sary to investigate the fate of these compounds in surfacewaters. A first study was conducted along a 19 km trenchsystem in the city of Berlin that discharges the effluent of thetreatment plant Berlin II into the next larger surface water,Lake Tegel. Concentrations of the five benzothiazoles in fivesamples taken on a dry day without precipitation from astanding wave in that trench system are shown in Figure 4.The composition of the benzothiazole fraction reflects theWWTP effluent that is the only source water. During thetravel time of 15 h, some fluctuations in the total concentra-tion 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 arelikely due to problems in repeatedly sampling the same bodyof water over the travel time of 15 h. No significant inflowof water from other sources occurs during the 19 km lengthof the trench system. Neither the DOC nor the borateconcentrations showed any trend along the trench, withaverage values of 9.7 ((0.3 mg/L) and 3.8 ((0.5 mg/L),respectively. Analogously, no clear trend toward decreasingconcentrations is visible for any of the five benzothiazoles

FIGURE 3. Increase in MTBT concentration versus decrease inMBT concentration (nmol/L) for each pair of influent and effluentsamples in municipal wastewater treatment Berlin Ia. X marks oneoutlier that was excluded from linear correlation analysis.

FIGURE 4. Concentrations of individual benzothiazoles (µg/L) alongthe trench system (Blankenfelder Graben/Nordgraben) dischargingthe effluent of WWTP Berlin II. Total observation time 15 h.

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(Figure 4). These first data on benzothiazoles in surface waterssuggest that BT, OHBT, MTBT, and BTSA exhibit a consider-able lifetime in surface water and are not rapidly degradedafter discharge with WWTP effluents.

For surface waters, some literature data on the stabilityof BT and MTBT are available. For BT, 60-90% of theconcentration discharged from a chemical company wasfound several miles downstream of its point of discharge(15). In a different study, decreasing concentrations of BTand stable concentrations of MTBT were found over a traveltime of 8-14 h in a small trench system receiving wastewaterfrom a chemical plant (5). Moreover MTBT was found inlong-term monitoring along the River Elbe (Germany) withaverage concentrations of 0.04 µg/L between 1994 and 1999(31). This concentration matches the average effluent con-centration of MTBT of around 0.4 µg/L found in this study(Table 1), assuming a general dilution factor of 10 forwastewater discharges in surface waters. Other benzothia-zoles were not included in any of the cited studies.

The stability of polar organics in surface water is deter-mined by their microbial recalcitrance and their chemicaland photochemical reactivity. Several studies on photolysisof MBT are available (5, 32), but this compound is not relevantin surface waters. For those compounds found in this study(BTSA, MTBT, OHBT, and BT) no information on theirphotolytic transformation is available. Therefore, it remainsunknown by which process the benzothiazoles delivered tosurface water with wastewater discharges may be removedand whether photolysis would contribute significantly.

Sources of Benzothiazoles Release. As outlined in theIntroduction, benzothiazoles are employed in various in-dustrial applications. The occurrence of benzothiazoles inmunicipal wastewater may, thus, indicate indirect dischargesof industrial wastewater into the sewer systems. In the caseof combined sewer systems benzothiazoles may also originatefrom street runoff, in which BT, OHBT, MTBT, and twobyproducts of vulcanization accelerators have previouslybeen found (7, 10, 33). The importance of households as asource of benzothiazoles immission into municipal waste-water is unknown.

Street Runoff. Reports exist on the occurrence of ben-zothiazoles in street runoff and road dust. These studies,however, either focus on nonpolar byproducts of vulcaniza-tion accelerators or were limited as only isolated sampleswere analyzed or only qualitative data were provided.

Surface runoff from a collecting sewer was analyzed forbenzothiazoles during and after a strong rainfall event (8.2mm precipitation) that followed several days of drought.Benzothiazole concentrations summed up to 74 µg/L in thefirst sample (Figure 5). Increasing water flow, then, led todilution of benzothiazole concentrations down to 45 µg/Lduring the peak flow, while the further decrease in totalconcentration reflects the reduced amounts of organics onthe surfaces that are available for washing off with ongoingprecipitation. Nevertheless, this decrease leveled off at totalbenzothiazole concentrations around 20 µg/L. These con-centrations are about 1 order of magnitude higher than thosefound in nontreated municipal wastewater. The compositionof the benzothiazole fraction hardly changed during therainfall, and BTSA was the dominant compound thataccounted for about 60% of the total concentration. OHBT(25-30%) and BT (8-13%) were also of importance, whereasthe contribution of MBT and MTBT was negligible (Figure5).

These data show, for a broader range of compounds andin more detail than previous reports, that surface runoff isa relevant source of benzothiazole discharges into the aquaticenvironment. In previous investigations, concentrations ofBT in the range of 0.1-0.5 and 0.4-1.2 µg/L were reportedin surface runoff (7, 13), as well as OHBT (5-7 µg/L (13)) and

MTBT (0.04-0.2 µg/L (7)). However, the most importantbenzothiazole, BTSA, has not been considered before. ForBT and OHBT, higher concentrations in street runoff werefound here as compared to those previous investigations.This may be due to the unusually high traffic on the highwayin the study area, leaving behind large amounts of tireabrasion.

The flux of benzothiazoles from the study area into surfacewater during this rainfall event adds up to 14 g, correspondingto 152 µg/m2 for BTSA, 54 µg/m2 for OHBT, and 15 µg/m2 forBT. Fluxes of MTBT, ABT, and MBT remained below 5 µg/m2. These data indicate that surface runoff in cities willtransport significant amounts of polar organic compoundsinto surface waters. This discharge would not be reduced bythe preferred pretreatment in settling basins.

If not discharged into surface water, surface runoff maybe collected in a combined sewage system and would, then,increase the total benzothiazole load of municipal waste-water. The treatment plant Berlin I is connected to such acombined sewer system. However, no increasing concentra-tions of benzothiazoles were determined in the influent ofthe treatment plant on those occasions when samplingcoincided with strong rainfalls. This may be due to the largesize of the drainage area (1.6 mio population equivalents),which leads to strong mixing and equalization of peaks ofconcentrations.

Household Wastewater. It is yet unknown whethersanitary wastewater from private households is a source ofbenzothiazoles in municipal wastewater or whether ben-zothiazoles originate from industrial wastewater and surfacerunoff only. No information was available that indicated theinclusion of benzothiazoles in consumer products used inhouseholds. However, the broad application of benzothia-zoles in industrial processes also suggests that various goodsused in the private environment may contain benzothiazoles.To elucidate this aspect, wastewater of a separate sewersystem (no surface runoff) in a residential area was inves-tigated. The average concentrations of benzothiazoles foundduring two samplings are compiled in Table 1.

The total concentration of benzothiazoles in householdwastewater was 1.7 and 2.2 µg/L on average. These totalconcentrations comprise 50-85% of that found in themunicipal wastewater in Berlin (Table 1), showing for thefirst time that significant emission of benzothiazoles intomunicipal wastewater originates from households. It mustbe mentioned that these samples could not be analyzed forMBT, as MBT turned out to be unstable in these samples,although glutathione had been added to prevent its oxidation.

FIGURE 5. Concentrations of individual benzothiazoles (µg/L) andwater flux (m3/h) in street runoff collected in a sewer after a rainfallevent with 8.2 mm precipitation (8.2 L/m2).

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This instability was recognized by the routinely performedstandard addition experiments. As standard addition wasrepeatedly performed with each kind of samples, it can beexcluded that similar instabilities of MBT occurred forsamples other than sanitary wastewater.

Due to this instability of MBT, the total benzothiazoleconcentration in household wastewater may have even beenhigher. The contribution of the individual compounds differsfrom the wastewater treatment plant influents with a lowerportion of BTSA (42-44%) but a higher portion of BT (28-36%). MTBT occurred in very low concentration (e0.1 µg/L),which was probably due to the instability of MBT in thiswastewater and the very short residence time of thehousehold wastewater in the sewer system before samplingthat did not allow for biomethylation of MBT. The unex-pectedly high concentration of total benzothiazoles inhousehold wastewater suggests that their emission from thehousehold was not only due to the release from aged productscontaining benzothiazoles but that certain consumer prod-ucts regularly used in households are responsible for thisemission. These products are not yet known.

Future Aspects. This first comprehensive investigationon benzothiazoles in municipal wastewater has shown thatfour polar benzothiazoles are regularly found in treatedmunicipal wastewater, with benzothiazole sulfonate beingmost prominent. As their polarity is high and their stabilityconsiderable, it is worthwhile to study the behavior ofbenzothiazoles in surface water and beyond. This appliesespecially to the anionic BTSA, as this compound should bemost mobile and was found in highest concentrations in allsamples yet investigated. Further studies may be directedtoward the potential of improved wastewater treatment,especially of physicochemical oxidation, to remove thesetrace organics. Emissions of benzothiazoles with householdwastewater was shown to be significant, but their field ofapplication in private household is yet unknown. Theoccurrence of benzothiazoles in surface runoff has outlinedthat this kind of water, which is often discharged directlyinto receiving waters, can provide considerable inputs ofpolar organic pollutants into the aqueous environment.

AcknowledgmentsWe are grateful to Thomas Ludwig for providing surface runoffsamples and runoff data and to Jutta Jakobs for laboratoryassistance. We thank Berliner Wasserbetriebe for valuablesupport in the sampling campaigns and the Senate of Berlinfor providing flux data. Funding by the German Ministry forEducation and Research (FKz. 02WA0123) and by theEuropean Union for the project ‘Removal of Persistent PolarPollutants Through Improved Treatment of WastewaterEffluents’ (P-THREE; EVK1-CT-2002-00116) is gratefullyacknowledged.

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Received for review November 25, 2004. Revised manuscriptreceived March 4, 2005. Accepted March 9, 2005.

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