Benzene exposure and the effect of traffic pollution in Copenhagen, Denmark

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Abstract

Benzene is a carcinogenic compound, which is emitted from petrol-fuelled cars and thus is found ubiquitous in all cities. As part of the project Monitoring of Atmospheric Concentrations of Benzene in European Towns and Homes (MACBETH) six campaigns were carried out in the Municipality of Copenhagen, Denmark. The campaigns were distributed over 1 year. In each campaign, the personal exposure to benzene of 50 volunteers (non-smokers living in non-smoking families) living and working in Copenhagen was measured. Simultaneously, benzene was measured in their homes and in an urban network distributed over the municipality. The Radiello diffusive sampler was applied to sample 5 days averages of benzene and other hydrocarbons. Comparison of the results with those from a BTX-monitor showed excellent agreement. The exposure and the concentrations in homes and in the urban area were found to be close to log-normal distribution. The annual averages of the geometrical mean values were 5.22, 4.30 and 2.90 μg m−3 for personal exposure, home concentrations and urban concentrations, respectively. Two main parameters are controlling the general level of benzene in Copenhagen: firstly, the emission from traffic and secondly, dispersion due to wind speed. The general level of exposure to benzene and home concentrations of benzene were strongly correlated with the outdoor level of benzene, which indicated that traffic is an important source for indoor concentrations of benzene and for the exposure to benzene.

Introduction

Benzene is a carcinogenic compound of which it is well documented that exposure in the ppmv range causes leukaemia (WHO, 1996). The risk assessment is more uncertain for concentration ranges typical for ambient levels. However, WHO has estimated that a lifetime exposure of 0.17 μg m−3 gives rise to an excess risk of developing leukaemia of 1 per 1,000,000 inhabitants based on toxic-kinetic models (WHO, 1996).

The main source of benzene in the atmosphere is the emission from petrol-fuelled cars. In Denmark, petrol contained about 30% aromatics and about 3.5% benzene in 1994 (Christensen et al., 1999; Palmgren et al., 2000). In recent years, the content of benzene in petrol has gradually been reduced in Denmark and the level e.g. in Copenhagen, was reduced from 2 to 1% during the summer 1998.

In Europe, the annual average concentrations of benzene in the atmosphere in cities are between a few μg m−3 up to about 50 μg m−3 at hot spots e.g. in busy streets with high traffic density (Cocheo et al., 2000). Urban background concentrations are typically 5 times lower.

Though the potential toxicity of benzene and its presence in cities throughout the world are well known, few studies have quantified the connection between ambient concentrations and exposure (Raaschou-Nielsen et al., 1997; Wallace, 1996; Leung and Harrison, 1998; Hoffmann et al., 2000).

Though people in the western world, in general, spend 90% of their time indoors, outdoor air accounts for 40% of the exposure and indoor air for 31%. The rest of the exposure was attributed to time spent during personal transportation by car (19%) and to environmental tobacco smoke (10%) (Wallace, 1996). While in outdoor air, traffic is the main source, see above; in indoor air there are several potential sources. Wolkoff et al. (1991) studied the emissions of volatile organic compounds (VOC) from different building materials. They measured the emission of a wide range of aromatic compounds (e.g. toluene) but benzene was not observed to be among those emitted. In addition, they measured the concentration levels of VOC in two identical apartments with the only difference that one of the apartments was vacant and the other was occupied. Human activity was in this way shown to increase the concentration level of benzene by a factor of 8 in the apartment. In a different study Hoffmann et al. (2000) carried out a study of the exposure to volatile organic compounds (VOC) on a cohort of 113 persons. They analysed their data with regression analysis. Environmental tobacco smoke (ETS) accounted for 20% of the exposure, traffic and refuelling together accounted for 12%. The linear model could explain 39% of the variance.

The objective of this study is to investigate the possible connection between traffic emissions and human exposure to benzene, using Copenhagen, Denmark as a study domain. A group of 50 volunteers living and working in Copenhagen participated in this project. The volunteers were mainly non-smokers, living alone or together with other non-smokers, so that ETS should be of minor importance in this study. Six campaigns of 5 days duration each and equally distributed over 1 year were carried out. In these campaigns, the exposure of the volunteers was measured together with the concentration in their homes. Furthermore, the urban concentrations at about 70 locations distributed around in the Municipality of Copenhagen were measured. Benzene and other aromatics were measured by diffusive sampling using a high uptake diffusive sampler, the Radiello diffusive sampler (Cocheo et al., 1996). In addition, the volunteers filled in a diary describing their activities during the campaigns. Interpretation of the observed benzene levels was based on toluene levels, meteorological data and on information available from the diaries.

The work presented here is part of a larger project, Monitoring of Atmospheric Concentrations in European Towns and Homes (MACBETH), where benzene exposure was measured in six European cities (Cocheo et al., 2000).

Section snippets

Methodology

About 250,000 inhabitants live in the municipality of Copenhagen; if the suburbs are included the number is about 1 million inhabitants. The present study focuses on the municipality of Copenhagen. Since traffic is the major source of benzene (Christensen et al., 1999; Palmgren et al., 2000), benzene concentrations are highest in cities; therefore, urban inhabitants represent a high-risk group for benzene exposure in Denmark. In this project, 50 volunteers living and working in Copenhagen

Validation of method

The performance of the entire method of sampling and analysis was intensively investigated during the MACBETH project and the results are presented elsewhere (Baldan et al., 1999; Pérez Ballesta et al., 1999). Only some of the main features are presented here. During the MACBETH project, central quality control and quality assurance were carried out by the participating laboratories. Samples exposed in a test atmosphere with known concentrations were distributed among the participants before

Discard of outliers

A few measurements of human exposure to benzene were identified where the volunteer left Copenhagen and thus these volunteers did not represent the exposure in Copenhagen. For example, a volunteer had been on a 2 days trip by car out of the city and the exposure was thus discarded. This particular measured exposure was the highest observed in the study (62 μg m−3) and was more than 10 times higher than the geometrical mean value. The exposure to toluene was also elevated (toluene 301 μg m−3). The

Conclusion

In this study, Radiello diffusive sampler has been used to study the relation between traffic emitted pollution of benzene and personal exposure to benzene. Comparison of the results obtained by the Radiello technique was compared to those using a BTX monitor at a Monitoring station at Jagtvej. The agreement was better than 12% for benzene.

The distributions of personal exposure to benzene and home as well as outdoor benzene concentrations were found to be close to a log-normal distribution. The

Acknowledgments

The EU-LIFE programme is acknowledged for financial support. Vincenzo Cocheo is acknowledged for excellent co-ordination of the MACBETH project and the rest of the members of the MACBETH group for good co-operation. The (Danish) National Research Programme (SMP) and Danish Ministry of transportation are acknowledged for financial support to carry out BTEX measurements at the national station at Jagtvej.

A special thanks is given to the volunteers for their participation and to Christina Falk

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