Benzene exposures caused by traffic in Munich public transportation systems between 1993 and 1997

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Abstract

Volatile aromatics (benzene, toluene, xylenes, the BTX-aromatics) were measured between 1993 and 1997 in buses and trams in Munich center and along main roads during regular rides. The sampling time was between 07.00 and 00.00 h. A total of 631 probes were sampled and centrally analyzed. In the mean of 5 years we found 15.0 μg benzene/m3, 50% above the limit of the 23. BImSchV and 107.5 μg BTX aromates/m3 along the strongly traffic loaded main streets. Splitting up these mean emissions into single years we observed a trend toward a decline of mean immission of all volatile aromatics (benzene from 23.8 μg/m3 to 7.4 μg/m3) and the sum of BTX aromatics (from 147.5 μg/m3 to 59.4 μg/m3). The measured hydrocarbon concentrations in Munich center were consistent with the long range theoretical calculations concerning the decrease of traffic-caused benzene immissions in cities. If the current trends continue, we can expect benzene concentrations to be below 5 μg/m3 by the year 2001 and below 2.5 μg/m3 by the year 2008. At these levels, the carcinogenic risk from benzene is probably less significant than the risks to public health from other car exhaust components.

Introduction

The mean air pollution in urban centers caused by industry and traffic are controlled at several measuring points by federal agencies in Germany. However, only the emissions which have threshold values (VDI, 1984–1992) have been continuously monitored for approximately 35 years and illustrate a decreasing trend for most inorganic air pollutants emitted by the industry. However, there is very little information about the trend of organic pollutants in the ambient air caused by traffic over the last 20 years, also because these measurements are difficult and expensive to undertake. It is only known that the content of benzene in fuels has doubled since the second stage of the Fuel Lead Act.

Occupational investigations in different industries showed that benzene plays an undoubted and considerable role in cancer risk for humans (Brief et al., 1980, Aksoy, 1985, Invante and White, 1985). In Sweden an association was found between acute myeloid leukemia (AML) and car density (Nordlinder and Järvolm, 1997). The incidence of AML was 5.5 in regions with more than 20 cars/km2 as compared with 3.4 cases per 1 million person years in regions with only five cars per kilometer squared. Although this was an ecological study and some uncontrolled confounding factors may have played a role, low benzene concentrations in ambient air are likely to be dangerous; other authors (Savitz and Feingold, 1989, Wolff, 1994) have also found an association between traffic density and incidence of leukemia in children.

People inside cars (van Wijen et al., 1995), cyclists (Bevan et al., 1991, van Wijen et al., 1995) and pedestrians (van Wijen et al., 1995) along the street or adjoining owners of roads with high traffic density are especially and regularly exposed to high doses of volatile hydrocarbons including carcinogenic benzene.

In Bavaria, 30 years since our first investigation on traffic-emitted fuels in the air near main roads in cities (Römmelt and Dirnagl, 1980), we studied the ‘background’ areas of the drivers cabs and later for safety regulations within the passenger compartments the exposure to volatile fuel hydrocarbons in the immediate vicinity of traffic over a 5-year period (1993–1997) using similar sampling and analytical conditions. Among other air contaminants our main intention was to investigate whether or not the threshold value of 10 μg benzene/m3 established by the new legislative regulations (Verordnung zur Durchführung des Bundes-Immissionsschutzgesetzes, 1994) is exceeded along main roads.

Section snippets

Sampling periods

Sampling took place during regular rides in buses and tramways of the Munich public transportation system. We especially examined traffic lines in the center and along main streets with a high traffic load. Measurements of volatile hydrocarbons were carried out between January 1993 and November 1997. Sampling periods were 2–3 h between 07.00 and 00.00 h during the daytimes in the morning rush hour (07.00–09.00 h) and the evening rush hour (15.00–17.00 h) and the results were compared with the

Analysis

We used a Shimadzu Model GC Mini 3 gas chromatograph with a flame ionization detector (FID). The 3-m column was filled with 10% SP 2100 on 100/120 mesh Supelcoport (Fa. Supelco, Bellefonte, USA). The hydrocarbons were directly desorbed at 330°C on the column of the GC. We started a temperature program after 8 min at 40°C isotherm and then raised the column temperature by 4°C/min until 200°C.

The detection limit was 0.2 μg benzene/m3 in a sample volume of 60 l. The detection limit was 12 ng

Results

More than 200 different hydrocarbons are emitted by car exhaust. As the BTX aromatics (first of all the cancerous benzene) are heavily discussed in public, here we report in detail the results for the aromatics benzene, toluene and xylenes. Between 1993 and 1997 we placed 631 probes in buses and trams; 624 of these probes were taken along routes with high traffic density, eight probes were taken from the outskirts. Table 1 shows the mean concentrations of the BTX aromatics as well as the range

Discussion

Earlier reports (van Wijen et al., 1995) showed that 90% of environmental benzene contamination is emitted by traffic. This amount represents an annual benzene emission of 35 000 t caused by traffic. Approximately 92% of the entire benzene emissions by cars is emitted in exhaust products. The lower fuel consumption of the car engines and, above all, the increased use of three-way catalysts have caused a considerable decrease in benzene emissions by traffic. Table 2 shows the benzene

Acknowledgements

The investigation was funded by the Bavarian State Ministry of Development and Environmental Affairs. We thank the staff of the Munich bus and tramway depots for their support and technical assistance during the sampling period.

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