Molecular Markers in Environmental Geochemistry - ACS Publications

Chapter 19

Downloaded by UNIV MASSACHUSETTS AMHERST on October 6, 2012 | http://pubs.acs.org Publication Date: July 1, 1997 | doi: 10.1021/bk-1997-0671.ch019

2-(4-Morpholinyl)benzothiazole as an Indicator of Tire-Wear Particles and Road Dust in the Urban Environment Hidetoshi Kumata, Hideshige Takada, and Norio Ogura Laboratory of Aquatic Environment Conservation, Faculty of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai, Fuchu, Tokyo 183, Japan As an indicator of tire wear debris and road dust, 2-(4-morpholinyl)benzothiazole (24MoBT) was determined in environmental samples collected from urban Tokyo in 1989 and 1993/94. 24MoBT existed in tire tread rubber, road dust, runoff particles, river water particles, river sediment and aerosols in the widely varying concentrations(~ngg to~μg g ). Comparison of 24MoBT concentrations in tire tread with those in environmental samples showed that tire debris were a significant com ponent of ambient particulate matter. The contribution of tire debris to runoff was greatest during the early and middle stages of storms. Comparison of 24MoBT concentrations in road dust samples and river samples collected in 1993/94 showed that road dust may comprise as much as 28-65% of suspended river particles during storm-flow and 5.5-41% of river sediments. -1

-1

Various pollutants (e.g., heavy metals and polycyclic aromatic hydrocarbons) are present in road dust on urban road surfaces. These pollutants are derived from weathered materials of the road surface, various types of vehicle emissions (e.g., exhaust, crank case oil, uncombusted fuel, abraded tire tread debris, brake linings, etc.) and atmospheric deposition (1-4). Road dust is washed off road surfaces during heavy rain storms and transported torivers,wastewater treatment plants, and estuaries (5-11). Consequently, road dust and road runoff are considered a major source of various pollutants in aquatic environments (6,12-16). It is often difficult to differentiate and to quantify the magnitude and the contributions from runoff and/or road dust to aquatic environments. A molecular marker would greatly aid in the assessment of the relative importance of this source. We focused on 2-(4-morpholinyl)benzothiazole (24MoBT) as a molecular marker of road dust and/or runoff (Figure la). 24MoBT is a minor component of a commercially used vulcanization accelerator, OBS. OBS consists mainly of 2-morpholinothiobenzothiazole (Figure lb), aud was one of the most widely used vulcanization accelerators, © 1997 American Chemical Society

In Molecular Markers in Environmental Geochemistry; Eganhouse, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.

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MOLECULAR MARKERS IN ENVIRONMENTAL GEOCHEMISTRY

used predominantly in tire tread rubber. Because 24MoBT is contained in tire tread rubber, it is deposited on road surfaces as vehicle tire abrasion debris (referred to as tire wear particles). Hence, it is primarily a marker of tire particles, which finds its way into various media (road dust, runoff particles,riversediments, aerosols, etc.) as part of the transport process. Measuring 24MoBT in such media would allow us to trace not only the process of tire wear particle transportation, but also of road dust transpor tation as tire wear particles are primarily accumulated on road surfaces. Tire particles have attracted attention as a possible source of atmospheric aerosols (17-25). Recently, Rogge et al. (4) investigated high molecular weight n-alkanes as molecular markers of tire wear particles in aerosols. However, thus far no studies have demonstrated the utility of tire wear particles to differentiate sources of pollutants in aquatic environ ments. Spies et al. (26) demonstrated 24MoBT's existence in a vulcanization ac celerator, roadside soils, and estuarine sediments. They also showed the persistent nature of 24MoBT relative to the parent compound (i.e., 2-morpholinothiobenzothiazole) and proposed that 24MoBT might be used as a molecular marker of road dust and/or road runoff. Since that work, however, there have been few papers on the environmental distribution and fate of 24MoBT, and its utility as an indicator has not been evaluated (26, 27). This is due in part to the lack of a quantitative analytical method for determination of 24MoBT concentration in environmental samples. In a previous publication, we presented a quantitative method for analyzing 24MoBT concentrations (28). In the present study, we present 24MoBT concentrations in a wider variety of environmental samples as well as intiretread rubber, and then relate the abundance of the marker in the source material to that in environmental samples. The purpose of this study is (1) to examine the distribution of 24MoBT in the urban environment of Tokyo, and (2) to apply 24MoBT as an indicator of tire wear particles and of road dust to estimate their contributions to ambient particulate matter (i.e., road dust, runoff particles,riverwater particles, river sediment and aerosols). Experimental. Sample Collection. The study was conducted in the Tokyo metropolitan area. Sampling locations are shown in Figure 2. Tokyo, with a population of nearly twelve million, is the largest city in Japan and it has high traffic density. Consequently, the adjoining aquatic environments are expected to receive a significant amount of pollution related to motor vehicles and/or road dust delivered via urban runoff. Road dust was collected from heavily traveled roads in Tokyo carrying > 10,000 vehicles day . To examine the contributions from atmospheric fallout and soil, road dust samples were collected from both inside and outside tunnels. Samples from outside tunnels were taken in 1989 and in 1994, and from inside tunnels in 1989 (Yaesu Tunnel) and 1994 (Shinjukugyoen-shita Tunnel and Yaesu Tunnel). All road dust samples were collected on prebaked (400 °C, 3 hours) glass fiber filters (ADVANTEC GB100R or Whatman GF/C: >1 pirn) by vacuuming the road surface. The filters and particles were stored at -20 °C until analysis. Details of the sampling locations for the 1989 samples are given elsewhere (2). 1



19.

KUMATA ET AL.

24MoBT as an Indicator of Tire-Wear Particles

CXK> OCHO (a)

(b)

Figure 1. Molecular structures of (a) 2-(4-Morpholinyl)-benzothiazole (24MoBT) (MW = 220.30; CAS: 4225-26-7), an impurity of the vulcanization accelerator, OBS, and (b) 2-Morpholinothiobenzothiazole (MW = 252.36; CAS: 102-77-2), a major component of the vulcanization accelerator, OBS. OBS are name of vulcanization accelerators defined in the Japan Industrial Standard (JIS K 6202-1979).

Figure 2. Sampling locations in the Tokyo metropolitan area.


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Street runoff was collected in 1989 from a storm drain discharging into the Nogawa River, a tributary of the Tamagawa River. The hydrograph of this drain is illustrated in Figure 3, and it shows the variation of rain intensity and water flow as functions of elapsed time for the runoff event, as well as the variation of suspended solid concentration. The event lasted more than 9 hours, and 10 water samples were collected during the storm at 0.5- to 2-hour intervals. There were two distinctive peaks in flow rate: 3.5 and 6.5 hours from the beginning of this storm event. Suspended solid concentration showed its largest peak at the beginning of the storm in spite of the weak drain flow, and two subsequent distinctive peaks associated with flow rate. Some other aspects of these samples have been given elsewhere (9). The first, fifth and ninth samples (referred to as the initial, middle and final stages, respectively) were analyzed for 24MoBT. During the period June 1993 to September 1994, river water samples were collected at the Chofu dam located just above the upper limit of the tidal zone of the Tamagawa River. They are categorized into two groups: normal-flow samples, collected at water flows less than 20 m3 s-1, and storm-flow samples, collected at water flows greater than 20 m3 s . Samples were transported to the laboratory and immediately filtered through prebaked glass fiber filters (GF/C). The filters containing particles were wrapped in aluminum foil and then stored at -20 °C until analysis. River sediments were taken from the Tamagawa and Sumidagawa Rivers in 1993 using an Ekman-Birge grab sampler (15 X 15 X 15 cm) and the thickness of sediment samples were 0.1 pirn) using a high volume air sampler (Shibata HVC-1000) at a flow rate of 1.28 m3 min-i for 48 hours. Used automobile tires of four different tire manufacturers, representative of the market share in Japan, were collected in 1989 to provide tire tread samples. Tire tread rubber samples were collected by abrading the tire tread surface using a metal rasp, and stored at -20°C until analysis. The rasp was rinsed with solvents before use. 1

Analytical Procedure. 24MoBT was analyzed using the previously reported procedure (28). Because 24MoBT is not commercially available, we extracted it from a vulcanization accelerator by liquid-liquid extraction with dilute sulfuric acid. The vulcanization accelerator, OBS (trade name; MSA), was kindly offered by Ohuchi Shinko Kagaku Inc. (Fukushima, Japan). Its purity was confirmed by GC/MS (gas chromatography/mass spectrometry) analysis. The 24MoBT in this solution was quantified by comparing its peak area on an FID chromatogram to that of benzothiazole (BT). Therefore, the concentrations of 24MoBT are presented as BT concentration in this study, and this stock solution was used as the 24MoBT standard. A dried sample was Soxhlet-extracted with a 6:4 (v/v) mixture of benzene and



KUMATA ET AL.


0

100

200

300

400

500

600

0

100

200 300 400 500 elapsed time (min)

600

Figure 3. Variation of urban runoff parameters as a function of elapsed time for the storm of Oct 19, 1989. (a) Rain intensity and drain flow, (b) suspended solids.


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methanol for 24 h. The cycling rate for the extraction was 8 min/cycle. (Caution: Because benzene is a known carcinogen, all handling procedures should be done in a fume hood.) The extract was concentrated and subjected to liquid-liquid extraction with sulfuric acid (4 X 10 mL of 0.18 M H2SO4: pH12), back-extracted with dichloromethane ( 4 X 5 mL), and then purified through a 5% H2O deactivated silica gel column (1 cm i.d. X 9 cm). The 24MoBT fraction was concentrated to just dryness and redissolved in an appropri ate volume of benzene for injection into the gas chromatograph. Concentrations of 24MoBT were determined using a Hewlett Packard 5890 series II GC with a flame photometric detector (FPD). The detection limit of the method was 0.08 ng of injected 24MoBT. Reproducibility and recovery were 1.5% and 85.4 ± 5.2%, respectively (n=4). Identifications of 24MoBT in the stock solution and ambient samples (i.e., road dust, runoff particles,riverparticles,riversediments, aerosols) were carried out with a Hewlett Packard 5972A mass spectrometer interfaced to a Hewlett Packard 5890 series II plus GC. The obtained mass spectra, which are presented in Figure 4, are essential ly identical. The four major fragments, m/z 108, 135, 163 and 220, are the same as reported in the database (NIST/EPA Library) and in the literature (26, 29). However, the mass spectrum for the aerosol sample (Figure 4f) has many additional peaks probably because of the low concentration of 24MoBT. Results and Discussion. Environmental Distribution. As shown in Tables I, II and III, we found 24MoBT intiretread rubber and in a variety of environmental samples. Concentrations varied widely (-ng g-i to ~/*g g-i). However, our data reveal large differences in the 24MoBT concentrations found in samples collected during 1989 and 1994.

Table I. 24MoBT Concentrations in Tire Tread Rubber no. of samples

brand

% market share in 1989°

1

g"

Tire#l

1

2.77

50

Tire#2

1

2.27

18

Tire#3

1

2.23

12

Tire#4

1

1.00

15

weighted mean: a

»Z

2.3* b

market share in Japan (1989) from ref. 8. calculated by weighting individual concentration by fractional market share.

Table I indicates the 24MoBT concentrations in tire tread rubber as well as the market share of each brand (Tire#l - #4) in Japan (30). Because thetiresamples were


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163

6000

220

135


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150

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m/z

Figure 4. Electron impact ionization mass spectra of 24MoBT in the stock solution prepared from a vulcanization accelerator (a) and extracts of environmen tal samples; (b) road dust, (c) runoff particles, (d)riverwater particles, (e) river sediment, (f) aerosol.


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obtained in 1989, the 24MoBT concentrations in the tire tread (Table I) are only representative oftiresproduced and sold in 1989. The weighted mean concentration of 24MoBT in tire tread rubber was calculated as 2.3 pig g by weighting individual concentrations by fractional market share. In the calculation, 24MoBT concentrations intireswhich occupy the remaining 5% of the market share were assumed to be in the range shown in Table I. The concentrations of 24MoBT in road dust collected in 1989 ranged from 12 to 490 ng g-i (Table II) and were at approximately the same level as that reported for roadside soil of a highway in San Francisco (273 ng g ; ref. 26). The concentrations are an order of magnitude lower than that oftiretread rubber mainly because of the dilution of tire wear particles by other particles (e.g., sand, soil, finely ground plant tissue, road surface material, and atmospheric fallout), and partly because of environ mental alteration (i.e., degradation, desorption, and leaching). 24MoBT existed at higher concentrations (293 ± 155 ng g ) in dust from inside tunnels than those from outside tunnels (84 ± 108 ng g-i). The difference between the inside- and outside-tunnel samples may be due to increased "dilution" of tire wear particles by soils and sand in outside tunnels, and/or to environmental alteration. 1


1

1

Table II. 24MoBT Concentrations in Road Dusts and Runoff Particles Collected in 1989 ^ ~ , concentration no. of samples range r

average ± s.d.

road dust* inside tunnel

5

60-491

293 ±155 ngg-

outside tunnel

6

12-289

84± 108 n g g

1

1

runoff particles* 1

initial stage

1

215 ngg(29 n g L ) '

middle stage

1

150 ng g i (13 n g L ) '

final stage

1

1.2 ng g (0.73 ngL-i^

1

1

1

a c

b

collected by Takada et al. (ref. 2) collected by Ito et al. (ref. 9) numbers in parentheses are concentrations on a volume basis.

24MoBT was also found in urban runoff (Table II). The concentration of 24MoBT in runoff varied considerably with time during the runoff event (29 ng L for the initial stage to 0.73 ng L for the final stage). The presence of 24MoBT in runoff demonstrates that urban runoff can transport tire wear particles and road dust into aquatic environments. 1

1



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The road dust samples collected in 1994 (Table III) contained less 24MoBT than those collected in 1989. The concentrations for the 1994 samples were about a 0.1 (inside tunnels) to 0.2 (outside tunnels) times those observed in the 1989 samples. This decrease in 24MoBT concentrations in 1994 road dust may be attributed predominantly to the decreased usage of the vulcanization accelerator OBS. Production of OBS in 1994 was less than 10% of that in 1989 (Figure 5). This change probably occurred because of toxicological concerns. In 1987, the West German authorities regulated the concentration of certain N-nitrosamines in work area atmospheres (57). Because 2-morpholinothiobenzothiazole, a major constituent of OBS, was suspected to be a source of a regulated nitrosamine (32), most tire manufacturers in Japan shifted from OBS to other accelerators. Some of the differences may be due to variability of road dust compositions because of the differences in sampling locations. 24MoBT was also found at significant concentrations in other samples collected in 1993 and 1994 (Table III), even though the vulcanization accelerator, OBS, is no longer used intiremanufacturing as described above. It is assumed, however, that significant numbers of vehicles in Tokyo were still equipped with tires containing 24MoBT which were probably manufactured in or before 1989. In river water, 24MoBT was detected only in the storm-flow samples (0.55-1.0 ng L-i) and not in the normal-flow samples (Table III), suggesting that tire wear particles and road dust are transported to theriverprimarily during and after heavy rain storms. 24MoBT was measured in river sediment samples in the ng g-i range for both the Tamagawa and Sumidagawa Rivers. These concentrations are one to two orders of magnitude lower than those reported for San Francisco Bay sediments (26). This difference may be due to the decrease in overall usage of the vulcanization accelerator OBS and the subsequent decrease in 24MoBT contents in road dust. The 24MoBT concentrations are higher in the Sumidagawa River (5.1 ± 1.7 ng g^dry) than in the Tamagawa River (2.5 ± 1.5 ng g^dry). This may be due to the proximity of the Tokyo Expressway to the Sumidagawa River. 24MoBT was also detected in aerosol samples. It has been reported that most tire wear particles are deposited near roads and that only a small fraction is available for a long range transport (78, 33). The TUAT station is in an area with roads of high traffic density, while the station HEF is in a forest of 22,000 which is more than 500 m from the nearest road (which has little traffic). Thus, it is reasonable to expect higher 24MoBT concentrations at the TUAT station (15-18 pg m-3) than at the HEF station (5.6-6.2 pg m-3). These results demonstrate that tire particles and/or road dust contribute significantly to atmospheric aerosols as previously reported by Hildemann et al. (34). On a unit weight basis (ng g-i), 24MoBT concentrations inriverwater particles (5.2-12 ng g-i) are between those in road dust (12-82 ng g ) and river sediments (1.0-7.6 ng g-i). These results are reasonable considering that both road dust and river sediment contributes toriverwater particles. At the sametime,the difference between sediment and suspended-particle concentrations may also reflect differences in the distribution of tire wear particles among different particle sizes, and differences between suspended-particle and sediment-particle size distributions. Furthermore, the 1


300


Table III. 24MoBT Concentrations in Various Environmental Samples Collected in 1993 and 1994 no. of samples

concentration range

average ± s.d.

road dust

18-82

30 ±22 ngg-

12-30

19±7.0 ngg-

2

nd*

4

5.2-12 (0.55-1.0)*

nd* 7.0 ±3.4 ngg(0.76 ± 0.24 ngL )*

Sumidagawa River

7

2.0-7.6

5.1 ±1.7 ngg-

Tamagawa River

7

1.0-5.4

2.5 ±1.5 ngg"

HEF

2

91-114 (5.6-6.2)*

103 ±16 ngg" (5.9 ± 0.4 pg m-3)*

2

180-210 (15-18)*

195 ±21 ngg-

TUAT

outside tunnel Downloaded by UNIV MASSACHUSETTS AMHERST on October 6, 2012 | http://pubs.acs.org Publication Date: July 1, 1997 | doi: 10.1021/bk-1997-0671.ch019

1

8 10

inside tunnel

1

river particles a

normal-flow c

storm-flow

1

1

river sediments 1

1

aerosols 1

1

(17 ± 2 pg m-3)rf

River sediment samples and some river particle samples were taken in 1993. All other samples were collected in 1994.

Molecular Markers in Environmental Geochemistry - ACS Publications

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