Annals of Occupational Hygiene Advance Access originally published online on February 24, 2006
Annals of Occupational Hygiene 2006 50(5):459-468; doi:10.1093/annhyg/mel001
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Vapours and Aerosols of Bitumen: Exposure Data obtained by the German Bitumen Forum
1 BG BAU – Berufsgenossenschaft der Bauwirtschaft, An der Festeburg 27–29 D-60389 Frankfurt am Main, Germany
2 Steinbruchs-Berufsgenossenschaft, Theodor-Heuss-Straße 160 D-30853 Langenhagen, Germany
3 Berufsgenossenschaft der Chemischen Industrie, Brosteler Chaussee 51 D-22453 Hamburg, Germany
4 BG BAU – Berufsgenossenschaft der Bauwirtschaft, Landsbergerstraße 309 D-80687 München, Germany
5 Berufsgenossenschaftliches Institut für Arbeitsschutz, Alte Heerstraße 111 D-53757 Sankt Augustin, Germany
*Author to whom correspondence should be addressed. Tel: +49 69 4705 213; Fax: +49 69 4705 299; E-mail: reinhold.ruehl{at}bgbau.de
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ABSTRACT |
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In a large project of the German Bitumen Forum, almost all branches of industry in Germany that use bitumen have been examined with regard to bitumen exposure. A total of 1272 samples were gathered between 1991 and 2005. The measuring method includes vapours and aerosols emitted from hot bitumen; the proportions of these two components and their dependency on bitumen temperature are described. Whereas in most branches a value of 10 mg m–3 for the sum of vapours and aerosols is not exceeded, much higher values have been observed for work with mastic asphalt. Polycyclic aromatic hydrocarbons have been analysed in some cases, but exposure is several orders of magnitudes lower than with the earlier use of tar.
Keywords: bitumen • asphalt • construction • polyaromatic hydrocarbons
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INTRODUCTION |
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Since mid-1990s, the German Bitumen Forum (Rühl and Musanke, 2006) has worked on a comprehensive programme on the safety and health at work of bitumen. [In Europe, asphalt refers to a mixture of organic binder (bitumen) and filler (sand, gravel); this paper adheres to European nomenclature.] Determining the concentration of emissions arising from handling hot bituminous substances has been one of the main priorities of the Forum's work up to now. With the results of these measurements it is possible to show how exposures to vapours and aerosols of bitumen vary with production and use, e.g. rolled asphalt, mastic asphalt, bitumen sheeting, joint fillers and others. This paper summarizes the results of the Forum's measurements. New developments in the production of rolled asphalt and mastic asphalt (so-called ‘low-temperature asphalt’) allow production and laying at lower temperatures. The data on these ‘new materials’ will be published in a separate article (Musanke et al., 2006).
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MEASURING EMISSIONS OF HOT BITUMEN |
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The German method for measuring emissions from working with hot bitumen uses the GGP (Fig. 1). The GGP is a modification of the GSP sampler for inhalable aerosols with an additional cartridge for vapour sampling. The aerosols are collected on a 37 mm glass fibre filter and the vapour is adsorbed on 3 g AmberliteTM XAD-2. The flow rate is 3.5 litre min–1. Filter and XAD-2 are extracted with tetrachloroethylene and analysed by infrared spectroscopy (calibration with mineral oil for spectroscopy) (BGIA, 1997; Kenny et al., 1997).
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RESULTS AND DISCUSSION |
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The Bitumen Forum determined the concentration of vapours and aerosols at all workplaces where hot bitumen is handled in Germany. Even jobs which used warm rather than hot bitumen were considered.
The results of the measurements for the various job tasks of the different uses of bitumen are listed inTable 1, distinguished between aerosols and the sum of vapours and aerosols, and summarized in Fig. 2. Usually, sampling duration was 2 h. The tasks often lasted for a full 8-h shift, and the sampling period was assumed to be representative of shift-length exposure, without correction for time-weighting. There were two exceptions, the ‘reload’ exposure in the production of bitumen, and the ‘inside asphalt plant’ exposure in the production and transport of asphalt. These lasted for 2 h and 1 h per shift, respectively, and the measured exposures were time-weighted by dividing by four and eight, respectively (Table 1).
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Throughout this article, a value of half the detection limit is applied for measurements with below detection limit values.
During the measurements a large variety of parameters possibly influencing level of exposure has been collected such as date, location, performed job, product/bitumen name, bitumen/asphalt temperature, amount and machines used. In addition, environmental conditions such as weather conditions (e.g. temperature, direction and force of wind, and type of weather), room measures and conditions, exposure control measures, etc. have been documented.
On construction sites exposure naturally depends very strongly on wind force and direction as well as on the local conditions. Nevertheless, representative exposure data were received by performing a large number of measurements on different building sites. This is reflected by the number of measurements for each area, which is much higher for work on changing building sites than for work in stationary plants, as indicated in Fig. 2.
The following ranges and/or activities were examined:
(i) Production and transport of bitumen (BP in Fig. 2): Bitumen is produced in closed plants and exposure could only occur at some jobs, e.g. sample collection or bitumen loading of the truck. The exposures are very low. A comment has to be made about the exposure value of about 10 mg m–3 (vapours and aerosols) for reloads, that here work with bitumen exposure takes 2 h per shift at most. Therefore, in contrast to the job task exposure a time weighted shift exposure would be about 2.5 mg m–3, as shown in Fig. 2.
(ii) Production of bitumen sheetings (BSP): Bitumen sheetings are produced in partially enclosed plants with bitumen temperatures of 
160°C. The monitoring data show also that during this work relatively low concentrations of vapours and aerosols of bitumen are present. Most samples were taken stationary near to the control stand close to the bitumen soak, they are considered to be representative for the workplace. All plants were supplied with a local exhaust ventilation system.
(iii) Production of car body sound deadening systems (SDSP): Production takes place in partially enclosed plants with a temperature of the bitumen between 160 and 190°C. The situation is comparable with production of bitumen sheeting and therefore the measurements revealed only low concentrations.
(iv) Production and transport of asphalt (APT): Asphalt is usually produced in closed plants from which vapours and aerosols of bitumen could only be emitted at negligible concentrations. Vapours and aerosols of bitumen are emitted during top loading of the open trucks for the transport of rolled asphalt. Additional monitoring took place in the asphalt mixing plant. However, workers tend to stay in this area only very rarely and for only short periods (less than 1 h per shift). In the external area, where wheel loaders handle gravel and sand, and in the control room area, monitoring data show negligible vapours and aerosols of bitumen. The maximum production temperatures of the bitumen are 190°C for rolled asphalt and 250°C for mastic asphalt, respectively. For the transportation of asphalt low exposures could occur during filling or emptying (the latter for mastic asphalt) the truck. In particular, exposure takes place while workers cover or recover the loading space for rolled asphalt with tarpaulin. However, the exposure duration commonly does not exceed 2 h per shift.
(v) Paving of rolled asphalt (RA): Paving with rolled asphalt (Fig. 3) happens with asphalt temperatures between 140 and 180°C. Commonly, the paver operator, screed operator and to a lesser extent the roller driver are exposed to vapours and aerosols of bitumen. The paver operator constantly stays above the hot asphalt and the screed operator works closely to the fresh paved asphalt with a continuously new surface. Both are more or less strongly exposed depending upon wind direction. The roller driver commonly works with more or less cooled asphalt and is therefore less exposed.
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(vi) Mechanical laying of mastic asphalt (MMA): Works with mastic asphalt show the highest overall exposure compared to the other tasks. The screed is included in the mastic asphalt at temperatures of about 250°C because hard grade bitumen is used. For mechanical laying of mastic asphalt, the highest exposures are for the charger on the mixer, sometimes above 50 mg m–3 for vapours and aerosols of bitumen. The charger on the mixer stays between the truck which lets the hot asphalt fall on the ground and the screed inserted into the asphalt. The screed operator gets about half of this exposure. The smoother, who works around the edge of the new asphalt, and even more the gritter, who works usually with colder asphalt, show much lower exposure. Finally, it should be stated that indoor mechanical laying of mastic asphalt is quite rare and the method is only used in large halls, e.g. exhibition halls.
(vii) Manual work with mastic asphalt (HMA): Mastic asphalt may be fitted manually (Fig. 4). The temperature of the mastic asphalt is very high, 250°C or more, because hard grade bitumen is used. The transportation at the construction site occurs with dumpers, barrows or buckets when laying mastic asphalt manually. It can be seen that the transportation with barrows, smoothing and charging on the mixer are the highest exposed tasks for manual work. As expected, indoor bituminous emissions are significantly higher than outdoor emissions. Transportation with buckets shows lower concentrations than with barrows, probably because the buckets have a smaller surface area. The gritter works in the same area as the smoothers and therefore shows nearly the same exposure.
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(viii) Working with joint fillers (JF): These activities make use of small quantities of hot bitumen that is used to fill joints on roads. Therefore, the personal monitoring data for charging the kettle with bitumen and for pouring of the hot filler are relatively low, as well as the stationary monitoring data at the kettle.
(ix) Roofing work (RW): Torching of bitumen sheeting: In this application, the bituminous sheets are torched with a propane/butane gas burner and as such the bitumen is liquefied while the bituminous sheet is unrolled slowly (Fig. 5). The exposure is below 10 mg m–3 and depends particularly on the ventilation situation at the workplace (e.g. work on free-standing roofs or on sheltered position as on balconies or loggias) and on the distance between the respiratory tract and the heated sheet (e.g. when working in kneeling position at corners and edges it is higher than in a standing position when working in the area). Pouring of hot bitumen: In order to lay bitumen sheetings or foam glass insulation hot bitumen is used as an adhesive. The bitumen is heated up to about 200–260°C in digesters at the construction site and carried with buckets or cans to the workplace. For this activity the bitumen temperature must be kept as low as possible in order to reduce exposure. Further the environmental conditions during the activities have effects on the exposure. It is obvious that the torching process in comparison to the pouring process shows only a quarter of the values for aerosols whereas the sum of vapours and aerosols are nearly identical.
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Until the end of 2004 in Germany there was a technically-based threshold limit value for vapours and aerosols of bitumen of 10 mg m–3, which had been coupled to the measuring method. It was—like all technical limit values—invalidated by the new German legislation on hazardous substances. Apart from work with mastic asphalt, at all other uses of bitumen total concentrations of vapours and aerosols are in part less than 10 mg m–3. The high values for asphalt production are found inside the plant where the workers stay only for a short time period. The significant effect of working temperature, especially for mastic asphalt work, becomes apparent. In road paving with rolled asphalt—with a maximum laying temperature of
180°C—the highest exposures (95% value) are about 10 mg m–3 for the sum of vapours and aerosols of bitumen. But for mastic asphalt work—with a laying temperature of 250°C—the exposures are more than 50 mg m–3. The Bitumen Forum has compiled exposure descriptions (downloadable at: www.gisbau.de/bitumen.html), which relate to the working situation and the associated exposures of the workers. By publishing the exposure descriptions, companies have the opportunity to predict concentrations of vapours and aerosols from hot bitumen without having to carry out measurements by themselves (Rühl et al., 2002). In these descriptions, additional information on certain parameters (e.g. temperature restrictions, details to the ventilation of the machines, etc.) is available. In these exposure descriptions, the extent of exposure is taken as the 95-percentile value of the data collected and reported here.
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EFFECT OF TEMPERATURE |
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Bitumen temperature (or process temperature) has a great influence on the level of emissions. It should be mentioned that bitumen temperature while working with hot bituminous products on building sites might vary over time by several degrees. Thus, the temperature values are to be observed as a representative temperature values for the working period with smaller or larger ranges of several degrees. Therefore, we constructed temperature classes to identify the distribution within the data.
In Fig. 6 the distribution of the sum of vapours and aerosols is shown for three classes of bitumen temperature. The figure shows a shift to higher emission levels with increasing temperature. The number of data, N, for the second class 200–230°C is 99, which is approximately for a quarter that of the other classes. This temperature zone is quite unusual, since production of bituminous products mostly happens at lower temperatures and laying of mastic asphalt with higher ones. The values for torching of bitumen sheeting cannot be used in temperature discussions. Since the liquefied bitumen layer of the sheeting passes through the burner flame and is directly covered by the rest of the sheeting, there is no possibility of measuring the temperature at building site conditions.
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A more detailed classification, especially for the temperature range below 200°C, causes problems, since the differences in other parameters which influence exposure besides temperature get more important. E.g. the high exposure values inside the asphalt mixing plant at relatively low temperatures, or low exposure values for bitumen sheeting production plants with exhaust ventilation, even at temperatures above 170°C, complicate a comparison.
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PROPORTION OF VAPOURS AND AEROSOLS |
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As reported in the previous section, the exposures are to a very large degree influenced by the working temperature of the bitumen. In this context it is noteworthy that there is a variation in the proportion of vapour to aerosol with increased laying temperature (Figs 7 and 8). Looking at these figures it should be mentioned that the low aerosol concentration values for rolled asphalt and pouring of hot bitumen in many instances are below the detection limit.
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Looking over all examined work places a shift in the distributions of the proportion of aerosol to vapour with increasing bitumen temperature can be observed. Figure 8 shows the distributions of these quotients for different temperature classes. With increasing temperature, aerosol values become more and more important. It can be seen from Fig. 8 that for the temperature ranges 170–200°C, 200–230°C and 230–260°C the aerosol concentration exceeds the vapour concentration in approximately 15, 65 and 80% cases, respectively. Below 170°, aerosol concentration hardly ever exceeds vapour concentration. This figure shows only measurements without ‘below-detection-limit-values’ and excludes the values for torching of bitumen sheeting (see above) and for manual work with mastic asphalt, since the latter often are distorted by separating agents like mineral oil or vegetable oil which increase the vapour values. These mineral/vegetable oil adulterations have been included when looking at exposure at the workplace (so the figures represent a ‘worst-case’), but they should be ignored, when the main interest is the real aerosol to vapour ratio.
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INTERNATIONAL COMPARISONS |
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Burstyn et al. (2002) published an overview of exposure levels among Norwegian asphalt workers. As they stated there is a need for a standardized method for measuring bitumen emissions, since there are several methods used in different countries.Table 2 lists limit values for vapours and/or aerosols of bitumen in different countries. Ekström et al. (2001) gave a comparison of different sampling methods for fumes of bitumen based on laboratory examinations. Figure 9 shows the results of parallel measurements with the US and German procedure. Further field measurements comparing the US and the German procedures are planned for 2006 (Emmel, 2005).
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Figure 9 can explain why care must be taken in comparing the US threshold limit of 0.5 mg m–3 with the former German limit. In no way is the US threshold limit 20 times more severe than the former German limit of 10 mg m–3. Whereas the German threshold limit covered vapours and aerosols, without any allowance for the variation of these two components with temperature, the US limit value only relates to the aerosol fraction. Hence, at temperatures below 180°C, only a small proportion of the emissions of bitumen would be registered when applying the analytical methods commonly used in the United States for monitoring air in workplace. At these temperatures the emissions are primarily vapours.
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POLYCYCLIC AROMATIC HYDROCARBONS IN BITUMEN |
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 TOPABSTRACTINTRODUCTIONMEASURING EMISSIONS OF HOT...RESULTS AND DISCUSSIONEFFECT OF TEMPERATUREPROPORTION OF VAPOURS AND...INTERNATIONAL COMPARISONS POLYCYCLIC AROMATIC HYDROCARBONS... GENERAL DISCUSSIONOUTLOOKREFERENCES |
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The debate about possible hazards from vapours and aerosols emitted when working with hot bitumen is often concentrated on the small quantities of polycyclic aromatic hydrocarbons (PAH) that bitumen contains. Therefore, the concentrations of these substances were also determined in some cases.
The results of a study to determine the major constituents of bitumens used in Germany clearly show that there are considerable differences in the content of the ‘PAH leading substance’, benzo[a]pyrene (BaP) in bitumen and in tar (in Germany, all PAHs are evaluated in terms of the leading substance benzo[a]pyrene, for which a technical threshold limit value of 0.002 mg m–3 was valid until end of 2004). However, in bitumen (from petroleum) the BaP content is 2 mg kg–1 and in tars (from coal) it is 5 g kg–1, i.e. a factor of 2500 times greater (Knecht et al., 2006). Obviously for bitumen this is clearly well below the 100 mg kg–1 limit allowed by the European Regulation (Council Directive 67/548/EES).
Moreover, from an occupational health and safety perspective, the content of PAH or rather BaP is less important than the quantity released while working with the material. In the earlier standard practice of using tar as the binding agent in rolled asphalt up to 50 µg m–3 BaP was released (HVBG, 1999).
Using very sensitive measuring systems, BaP maximum concentrations of only 0.1 µg m–3 could be determined for work with rolled asphalt with bitumen as binder. For bitumen workers exposed to the highest levels, those working with mastic asphalt, 0.51 µg m–3 was measured in an extreme case.
Even with milling of bituminous materials, the BaP concentrations in dust are markedly lower than those determined by the removal of substances containing tar (e.g. tar adhesive). On the one hand, when milling of mastic asphalt using diesel vehicles, a concentration of 0.099 µg m–3 BaP was determined. On the other hand, 50 µg m–3 to more than 100 µg m–3 BaP was measured for the manual removal of tar-based parquet adhesive (results not shown).
Air monitoring in context of the ‘Human study Bitumen’ (Raulf-Heimsoth et al., 2005) showed low PAH-exposure values (e.g. for naphthalene, 0.323–1.03 µg m–3; phenanthrene, 0.123–0.401 µg m–1; pyrene, 0.028–0.145 µg m–3; benzo[a]pyrene, 0.008–0.078 µg m–1) (Knecht, 2005).
Overall, it can be maintained that with the current use of bituminous materials the PAH exposure is several magnitude levels lower than the PAH exposure with the earlier use of tar.
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GENERAL DISCUSSION |
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The most frequently asked question concerning work with hot bitumen is whether this work is dangerous or not. Apart from the burns risk of working with a hot substance, this question cannot be answered at present. There is a lack of a toxicologically well-founded threshold limit value, especially taking into account whether emissions of bitumen at the workplace can cause cancer. To answer this, several toxicological studies are still going on. Perhaps one day, with the results of these studies, the exposure data determined by the German Bitumen Forum may help to answer the risk question.
With the exception of work with mastic asphalt, all uses of bitumen show a more or less comparable level of exposure to vapours and aerosols of bitumen. Even if some job tasks for roofing work or for paving with rolled asphalt show exposures up to 10 mg m–3 vapours and aerosols of bitumen, in most cases 5 mg m–3 are not exceeded.
The situation for mastic asphalt is entirely different. For mechanical as well as for manual work with mastic asphalt exposure to vapours and—especially—aerosols of bitumen is definitely high. A value of 5 mg m–3 vapours and aerosols of bitumen is exceeded in approximately half of the cases of mechanical use and in nearly 70% of manual use. For single job tasks like charger on the mixer, transporting in a barrow or smoothing or gritting indoors, nearly 50% of each data collective show values above 10 mg m–3 vapours and aerosols of bitumen.
In order to reduce the high exposure of the mastic asphalt workers, there is the possibility to use modified mastic asphalt (‘low temperature mastic asphalt’), which allows lower bitumen temperatures. The results of exposure measurements for these materials up to now create an optimistic impression. Details of this will be published.
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OUTLOOK |
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Determining exposure data for work with bitumen in Germany has been one of the main topics of the Bitumen Forum up to now. For the future it would be desirable to find a possibility for a comparison of these values received with the German measuring method with those methods used in other countries. This work has started now and the results may possibly help to understand bitumen exposure in a better way.
The most important part of the work of the Bitumen Forum will be the future promotion of the low temperature asphalt, which in particular will help to reduce the extreme high exposure of worker with mastic asphalt (Musanke et al., 2006).
Received October 15, 2005; in final form January 4, 2006
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REFERENCES |
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BGIA—Berufsgenossenschaftliches Institut für Arbeitsschutz. (1997) Measurement of Hazardous Substances—BIA-Working folder / Determination of Exposure to Chemical and Biological Agents, Erich Schmidt Verlag, Berlin.
Burstyn I, Randem B, Lien JE, et al. (2002) Bitumen, polycyclic aromatic hydrocarbons, vehicle exhaust: exposure levels and controls among Norwegian asphalt workers. Ann Occup Hyg; 45:79–87.
Ekström LG, Kriech A, Bowen C, et al. (2001) International studies to compare methods for personal sampling of bitumen vapours. J Environ Monit 3:439–45.[CrossRef][Web of Science][Medline]
Emmel Ch, Kriech A, Breuer D, et al. (2006) Parallel methods of measuring bitumen emissions in workplace environments in Europe and North America. International Bitumen Health Symposium 7–8 June 2006, Dresden, Germany. (Poster).
HVBG. (1999) BK Report BaP-Jahre. Hauptverband der gewerblichen Berufsgenossenschaften, St. Augustin, Germany (BaP year-report. Federation of the Industrial Trade Associations) ISBN 3-88383-503-X.
Kenny LC, Aitken R, Chalmers C, et al. (1997) A collaborative European study of personal inhalable aerosol sampler performance. Ann Occup Hyg 41:135–153.
Knecht U. (2005) Justus Liebig Univ., Giessen, personal communication.
Knecht U, Stahl S, Woitowitz H.-J. (2006) Commercially available bitumens: PAH-total content and effect of temperature on emissions under standardized conditions. Ann Occup Hyg (submitted for publication).
Musanke U, Rühl R, Radenberg M, et al. (2006) Low-temperature asphalt—exposure data from the German BITUMEN Forum. (in preparation).
Raulf-Heimsoth M, Pesch B, Schott K, et al. (2005) Irritative effects of fumes and aerosols of bitumen on the airways—results of a cross-shift study. (in preparation).
Rühl R and Musanke U. (2006) Commentary: The German Bitumen Forum. Ann Occup Hyg 50:441–4.
Rühl R, Lechtenberg-Auffarth E, Hamm G. (2002) The development of process-specific risk assessment and control in Germany. Ann Occup Hyg 46:119–25.
Shell G. (2002) Sampling and analysis of personal exposure samples. Report OGMB 2002–03. Study carried out by Shell Global Solutions International BV for Arbit, Germany.
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