Arch Toxicol (2011) 85 (Suppl 1):S21–S28 DOI 10.1007/s00204-011-0677-2
ANALYTICAL TOXICOLOGY
Levels and determinants of exposure to vapours and aerosols of bitumen Anne Spickenheuer • Reinhold Ru¨hl • Dieter Ho¨ber • Monika Raulf-Heimsoth • Boleslaw Marczynski Peter Welge • Dietmar Breuer • Stefan Gabriel • Uwe Musanke • Peter Rode • Evelyn Heinze • Benjamin Kendzia • Rainer Bramer • Udo Knecht • Jens-Uwe Hahn • Thomas Bru¨ning • Beate Pesch
•
Received: 7 January 2011 / Accepted: 10 February 2011 / Published online: 25 February 2011 Ó Springer-Verlag 2011
Abstract Bitumen (referred to as asphalt in the United States) is a widely used construction material, and emissions from hot bitumen applications have been a longstanding health concern. One objective of the Human Bitumen Study was to identify potential determinants of the exposure to bitumen. The study population analysed comprised 259 male mastic asphalt workers recruited between 2003 and 2008. Personal air sampling in the workers’ breathing zone was carried out during the shift to measure exposure to vapours and aerosols of bitumen. The majority of workers were engaged in building construction, where exposure levels were lower than in tunnels but higher than at road construction sites. At building construction sites, exposure levels were influenced by the room size, the processing temperature of the mastic asphalt and A. Spickenheuer (&) M. Raulf-Heimsoth B. Marczynski P. Welge E. Heinze B. Kendzia R. Bramer T. Bru¨ning B. Pesch Institute for Prevention and Occupational Medicine of the German Social Accident Insurance, Institute of the Ruhr University Bochum (IPA), Bu¨rkle-de-la-Camp-Platz 1, 44789 Bochum, Germany e-mail:
[email protected] R. Ru¨hl D. Ho¨ber U. Musanke BG-BAU, An der Festeburg 27–29, Frankfurt/Main, Germany D. Breuer S. Gabriel J.-U. Hahn Institute for Occupational Safety of the German Social Accident Insurance (IFA), Alte Heerstrasse 111, Sankt Augustin, Germany P. Rode Bga, Beratungsstelle fu¨r Gussasphaltanwendung e.V, Dottendorfer Straße 86, Bonn, Germany U. Knecht Institute for Occupational and Social Medicine, University Giessen-Marburg, Giessen-Marburg, Germany
the job task. The results show that protective measures should include a reduction in the processing temperature. Keywords Asphalt Bitumen Exposure assessment Mastic asphalt Paving
Introduction Bitumen is a widely used construction material with an annual production of approximately 20 million metric tons in Europe (Eurobitume 2009). In the present article, we refer to the European nomenclature ‘bitumen’ to describe a binder, which yields asphalt when mixed with mineral matter. Mastic asphalt contains around 7–10% bitumen, whereas rolled asphalt has a bitumen content of about 5%. Mastic asphalt provides a high durability and good waterproofing integrity. The processing temperature of mastic asphalt ranges from 230° to 250°C and is much higher compared with the maximal temperature of 180° C for rolled asphalt. Bitumen is a complex mixture containing polycyclic aromatic hydrocarbons (PAH) in small amounts. Emissions from hot bitumen applications have been a long-standing health concern, and monitoring of PAH exposure in mastic asphalt workers is fully described by Breuer et al. in this issue. Various agencies, such as the US National Institute for Occupational Safety and Health (NIOSH), have assessed the exposure and health risk of bitumen (NIOSH 2000). The International Agency for Research on Cancer (IARC) has classified extracts of steam-refined and air-refined bitumen in Group 2B as possible human carcinogens. The German Committee for Hazardous Substances (AGS) lowered the technology-based occupational exposure limit (OEL) to 10 mg/m3 for vapours and aerosols of bitumen in
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2001, but deferred this threshold for mastic asphalt workers (Raulf-Heimsoth et al. in this issue). On January 1, 2005, a new ordinance on hazardous substances came into effect, regarding German regulation of health-based OELs. For vapours and aerosols of bitumen, a health-based OEL is still to be derived. In order to further reduce the airborne occupational concentrations of fumes of bitumen, it is important to identify the potential determinants of the exposure at the workplaces. For mastic asphalt applications, both mechanic laying and manual laying have to be considered. Several studies have addressed the influencing factors of exposure in mechanic asphalt laying in road construction. The factors reported thus far were the tasks performed within a paving crew; the type of asphalt and the use of recycled or modified asphalt products; the processed amount of asphalt per time; and the application temperature, meteorological conditions and the degree of enclosure at the paving site (Burstyn et al. 2000; Heikkila et al. 2002; McClean et al. 2004). Conversely, less information is currently available on the exposure-predicting factors in manual asphalt laying. In this study, we investigate influencing factors of exposure to vapours and aerosols of bitumen. The German Bitumen Forum was established to assess exposure to bitumen on a broad scale of industrial applications (Ru¨hl et al. 2006) and assigned a cross-shift study among German mastic asphalt workers to assess exposure and health effects. One of the various objectives of the Human Bitumen Study was to investigate the levels and potential determinants of the exposure to bitumen in mastic asphalt workers. Here, we present the analysis of the airborne exposure to vapours and aerosols of bitumen in workers at a variety of construction sites across Germany.
Materials and methods
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2003. The bitumen-exposed group comprised 259 males who worked at building construction sites (239 workers), in road construction (14 workers) and in one tunnel (6 workers). All participants provided written informed consent. The study was approved by the Ethics Committee of the Ruhr University Bochum and was conducted in accordance with the Helsinki Declaration. Characteristics of the construction sites and job tasks The worksite description comprised the method of mastic asphalt laying (mechanical or manual), the room size for indoor applications and other information like the processed amount. Small rooms were defined as indoor construction sites of less than 1,000 m3, large rooms exceeded 1,000 m3. In the few cases where information on the room dimensions was not available, the room size was categorized with the aid of photographs. It should be noted that not all workers at a construction site got the same room description. For example, at one building construction site, the charger on the mixer worked outdoors, whereas his co-workers worked in a small room. The asphalt types were documented from delivery notes. The processing temperatures were measured with a specialized thermometer at intervals of 15 min. For this analysis, we used the arithmetic mean of the temperature data. The job tasks of the participants working in manual asphalt laying were categorized as direct application of asphalt, transport of asphalt and other tasks by expert assessment. Direct asphalt application comprised smoothers and similar job tasks. Persons engaged in transport included those who carried bitumen in buckets or barrows, chargers on the mixer, dumper drivers or those who performed other transport duties. The third group, categorized as those involved in ‘other tasks’, comprised jobs not elsewhere classified such as foremen and persons with alongside work.
Study population Details of the study design and study population were described by Raulf-Heimsoth et al. (2011) in this issue. In brief, the construction sites were independently described by the occupational hygienist in charge of the project and by the technicians that performed the exposure measurements during a working shift. The workplaces were additionally documented by photographs. A structured questionnaire on job tasks, lifestyle and other factors were assessed by in-person interviews. Between 2001 and 2008, 320 eligible workers with exposure to fumes of bitumen were examined, whereby 61 workers were excluded from the analysis of potential predictors of the vapours and aerosols of bitumen due to missing information about the characteristics of the construction sites enroled before
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Air sampling and laboratory analysis of vapours and aerosols of bitumen Details of the personal air sampling and analytical methods for the vapours and aerosols of bitumen were described by Breuer et al. in this issue. In brief, all asphalt workers were equipped with the personal air sampler GGP for the assessment of airborne exposure to aerosols and vapours of bitumen. Air sampling was conducted in the worker’s breathing zone during a working shift. Vapours and aerosols were collected in the inhalable fraction at a flow rate of 3.5 l/min, using a 37-mm glass–fibre filter and a 3-g AmberliteTM XAD-2 sorbent tube to trap particulate matter and volatile compounds. After 2–4 h, the glass–fibre filter and the XAD-2 cartridge were replaced. The samples were
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Table 1 Distribution of the exposure to aerosols of bitumen and vapours and aerosols of bitumen by type of construction site in 259 bitumenexposed workers of the Human Bitumen Study Aerosols of bitumen (mg/m3)
Building construction Road construction
Vapours and aerosols of bitumen (mg/m3) P25–P75b
NLOQa
239
15
1.77
0.90–3.32
7
2.98
1.80–5.01
14
2
1.07
0.34–3.20
0
1.50
0.70–3.95
6
0
5.20
3.15–6.85
0
7.84
5.22–11.49
Tunnel
Median
a
NLOQ, number of measurements below the limit of quantitation
b
P25–P75, interquartile range
transported to the Institute of Occupational Safety and Health of the German Social Accident Insurance (IFA) for analysis. Vapours and aerosols of bitumen were analysed according to the BGIA method No. 6305 using tetrachloroethene for extraction and infrared spectroscopy. A mineral oil standard was used for calibration. A factor of 1.47 has been determined for conversion into a bitumen-condensate standard. Statistical analysis Median and interquartile range (IQR) were presented to describe the distribution of airborne bitumen concentrations. Spearman correlation coefficients (rS) were used to evaluate the relationship between the processed asphalt amount and the size of the paved area, and the relationship between the concentrations of vapours and aerosols and the processing temperature. Values below the limit of quantitation (LOQ) were included in analyses as one-half the LOQ. Two multilevel linear regression models (Snijders and Bosker 1999) were applied to determine potential predictors of the concentrations of aerosols of bitumen and of the concentrations of vapours and aerosols of bitumen. The multilevel models had two distinct layers with workers as level-1 units and construction sites as level-2 units. Models were fit using a compound symmetry covariance matrix and restricted maximum likelihood (REML) estimation. We calculated the multilevel version of R2 according to the approach of Snijders and Bosker (1994). Forward variable selection was applied based on changes in R2 bearing in mind the problem of overfitting. Variables considered in the variable selection procedure were processing temperature, ambient air temperature, season, room size, processed asphalt amount, size of paved area, type of asphalt, job tasks and smoking status. All statistical analyses were performed with the log-transformed bitumen concentrations due to the skewness of their distribution. The results are presented re-transformed on the original scale. All calculations were performed with the statistical software SAS, version 9.2 (SAS Institute Inc., Cary, NC, USA).
NLOQa
P25–P75b
N
Median
Results Table 1 depicts the distribution of the personal exposure to aerosols and vapours of bitumen by type of construction site. The majority of bitumen-exposed workers (92%) worked at building construction sites. Furthermore, 14 workers were recruited from three road construction sites and six workers from one tunnel. The median exposure levels were highest in the tunnel (7.84 mg/m3) followed by building construction (2.98 mg/m3) and road construction (1.50 mg/m3). Due to the low number of workers at the road and tunnel construction sites, the following analyses of potential predictors of exposure levels were constrained to the 239 workers at building construction sites. The concentrations of aerosols of bitumen and of vapours and aerosols of bitumen were stratified by various factors that may influence the exposure levels (Table 2). The median processing temperature at the building construction sites was 255°C with a minimum of 216°C and a maximum of 270°C. A higher processing temperature resulted in higher airborne concentrations of vapours and aerosols of bitumen (6.97 mg/m3 as median for temperatures [260°C vs. 2.30 mg/m3 for temperatures B245°C). Additionally, higher exposure levels were observed at higher ambient temperature (3.23 mg/m3 for temperatures [30°C vs. 2.43 mg/m3 for temperatures B20°C). The median exposure levels were highest in summer and lowest in winter (3.99 mg/m3 vs. 2.25 mg/m3). The exposure varied by room size with higher median concentrations in small rooms (3.99 mg/m3) than in large rooms (2.31 mg/m3). Particularly, high concentrations were observed in underground parking sites (5.28 mg/m3), whereas the median concentration in outdoor settings was low (1.25 mg/m3). Another examined predictor of airborne concentration was the amount of asphalt applied during the shift at the construction sites. The processed asphalt amount ranged from seven to about 100 metric tons during a working shift. The surface paved with asphalt ranged from 90 to 10,000 m2. The processed amount and the surface at 36 building construction sites were closely associated (Spearman correlation coefficient
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Table 2 Exposure to aerosols of bitumen and vapours and aerosols of bitumen by characteristics in 239 bitumen-exposed workers at building construction sites of the Human Bitumen Study Aerosols of bitumen (mg/m3) N
NLOQa
Vapours and aerosols of bitumen (mg/m3)
Median
P25–P75b
NLOQa
Median
P25–P75b
Processing temperature B245°C
72
9
1.26
0.85–2.43
5
2.30
1.65–3.48
136 31
6 0
1.77 3.34
0.74–3.35 2.04–6.45
2 0
3.11 6.97
1.70–5.09 3.86–8.53
B20°C
72
2
1.66
0.70–2.95
0
2.43
1.50–4.20
20–30°C
64
7
1.76
1.00–2.97
3
3.26
2.03–4.92
[30°C
87
4
1.87
1.00–4.30
2
3.23
2.00–6.04
Unknown
16
2
1.84
0.52–3.40
2
2.93
0.97–5.07
35
3
2.23
0.80–5.48
0
3.61
1.80–7.51
Summer
53
1
2.48
1.10–4.90
1
3.99
2.20–6.60
Autumn
117
7
1.61
0.91–2.66
4
2.70
1.85–4.39
Winter
34
4
1.38
0.40–3.00
2
2.25
0.90–4.30
Outdoors
24
9
0.62
0.28–1.04
4
1.25
0.80–1.84
Small room
81
4
2.71
1.52–4.68
3
3.99
2.57–6.54
Large room Underground parking
93 41
2 0
1.40 3.27
0.87–2.23 1.64–4.83
0 0
2.31 5.28
1.70–3.61 3.11–7.28
B25 metric tons
129
13
1.87
0.80–3.40
7
2.84
1.60–4.96
[25 metric tons
110
2
1.72
0.90–3.13
0
3.12
2.07–5.38
B250 m2
121
12
1.70
0.72–3.00
7
2.70
1.50–4.96
[250 m2
118
3
1.92
1.00–3.32
0
3.27
2.10–5.47
160
14
1.46
0.73–2.93
7
2.62
1.51–4.35
AS IC 15
19
0
1.52
0.60–2.26
0
3.86
1.00–5.28
AS IC 40
24
0
1.87
1.14–4.37
0
2.94
2.16–5.98
Others
26
0
4.11
2.31–5.00
0
6.35
3.59–7.26
Unknown
10
1
3.57
2.05–5.92
0
4.77
3.23–7.42
245–260°C [260°C Ambient air temperature
Season Spring
Room size
Processed asphalt amount
Size of paved area
Type of asphalt AS IC 10/AS ICH 10
a
NLOQ, number of measurements below the limit of quantitation
b
P25–P75, interquartile range
of rS = 0.88 (95% CI 0.77–0.94, P \ 0.0001). The concentration of vapours and aerosols of bitumen was slightly lower at construction sites with a processed asphalt amount B25 metric tons (median 2.84 mg/m3) in comparison with construction sites with a processed asphalt amount [25 metric tons (median 3.12 mg/m3). The most frequently applied asphalt types were AS IC 10 or AS ICH 10 (160 workers, 67%). The median exposure levels observed were lower using asphalt type AS IC 10 or AS ICH 10 than AS IC 15 (2.62 vs. 3.86 mg/m3), but the median exposure levels using asphalt type AS IC 40 were lower as well (2.94).
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Figure 1 shows that an increase in the processing temperature is accompanied by an increase in the concentration of vapours and aerosols of bitumen. The concentration correlated with the processing temperature (rS = 0.37, 95% CI 0.25–0.47, P \ 0.0001). Table 3 depicts the exposure levels by job tasks in building construction. A large fraction of the workers (N = 104, 44%) were exposed to mastic asphalt as smoother or in other tasks with direct application. Smoothers had the highest median concentration of vapours and aerosols of bitumen (4.73 mg/m3). Another large fraction of workers (N = 116, 49%) transported the asphalt across the
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variable selection process. The final model for vapours and aerosols of bitumen showed a good fit. The explained proportion of variance within the construction sites (R2Level one) is estimated to be 0.50, and the explained proportion of variance between the construction sites (R2Level two) is estimated to be 0.39. An increase in the processing temperature by 10°C increased the concentration by a factor of 1.2 (P = 0.001) within the range of observed temperatures. An increase in the ambient temperature by 10°C increased the concentration by a factor of 1.1 (P = 0.16). Outdoor settings led to lower exposure levels by a factor of three than underground garages. Jobs in the transport of bitumen were associated with 0.7-fold lower concentrations compared with tasks involving the direct application of bitumen (P \ 0.0001).
Fig. 1 Association of processing temperature and vapours and aerosols of bitumen in 239 bitumen-exposed workers at building construction sites of the Human Bitumen Study
construction site, for example in buckets. The median concentration of vapours and aerosols of bitumen of workers in transport was lower than in the direct application of asphalt (2.21 mg/m3 vs. 4.37 mg/m3). Among other job tasks, the 19 foremen had a median exposure of 4.08 mg/m3 and a large interquartile range of 1.00–5.16 mg/m3. A large fraction of the asphalt workers at building construction sites were active smokers (62%). Their median exposure of 2.98 mg/m3 (IQR 1.60–5.16 mg/m3) was comparable to that of non-smokers with 3.01 mg/m3 (IQR 2.00–4.90 mg/m3). Statistical modelling of potential predictors of the concentrations of vapours and aerosols of bitumen revealed processing temperature, room size and job task as major influencing factors (Table 4). Smoking status, processed asphalt amount, size of paved area, asphalt type and season were not included in the final model as a result of the
Discussion In the present large cross-sectional study in mastic asphalt workers, we demonstrate that exposure to vapours and aerosols of bitumen varied by several factors, including the construction site, the asphalt processing and the working activities. Exposure levels also differed among the various settings, such as the construction of buildings, roads and tunnels. The majority of workers were engaged in building construction where exposure levels were additionally influenced by the room size. Our work shows that reducing the processing temperature of hot bitumen applications results in a concurrent reduction in airborne exposure to vapours and aerosols of bitumen and thus represents a potential measure to decrease overall exposure.
Table 3 Exposure to vapours and aerosols of bitumen by job task in 239 bitumen-exposed workers at building construction sites of the Human Bitumen Study Job tasks
NLOQa
N Direct application of mastic asphalt
3
Aerosols of bitumen (mg/m3)
Vapours and aerosols of bitumen (mg/m )
Median
P25–P75b
NLOQa
Median
P25–P75b
104
2
2.90
1.69–4.65
1
4.37
2.70–6.89
Smoother
72
0
3.07
1.80–4.92
0
4.73
2.99–7.06
Smoother with additional job tasks
23
1
2.82
1.20–3.90
0
4.46
1.90–6.74
9
1
0.62
0.50–2.04
1
2.40
1.18–2.75
116
11
1.11
0.71–2.17
6
2.21
1.50–3.51
Transport in a bucket
42
8
1.00
0.58–1.61
5
1.91
1.13–2.64
Transport in a barrow
41
0
1.41
0.90–3.13
0
2.45
1.80–4.29
Charger on the mixer or driver of the dumper
31
3
1.29
0.76–2.12
1
2.29
1.70–4.00
2
0
0.45
0.18–0.72
0
0.88
0.41–1.35
Other jobs
19
2
1.56
0.40–2.81
0
4.08
1.00–5.16
Foreman
15
2
1.56
0.30–3.00
0
4.08
0.63–5.16
4
0
1.34
0.55–2.40
0
2.90
1.04–5.35
Other jobs in direct application of asphalt Transport of mastic asphalt
Other jobs in transport
Alongside tasks and other jobs a
NLOQ, number of measurements below the limit of quantitation
b
P25–P75, interquartile range
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Table 4 Determinants of exposure to vapours and aerosols of bitumen in 215 bitumen-exposed workers at building construction sites of the Human Bitumen Study Aerosols of bitumen (mg/m3)
Vapours and aerosols of bitumen (mg/m3)
Exp (b) 95% CI of exp (b) P value
Exp (b)
95% CI of exp (b)
Intercept
0.007
(0.0002–0.098)
0.03
(0.002–0.42)
Processing temperature (per 10°C)
1.24
(1.09–1.41)
0.0013 1.19
(1.07–1.32)
0.001
Ambient air temperature (per 10°C)
1.11
(0.91–1.36)
0.306
1.12
(0.96–1.31)
0.160
Outdoors (Ref = large room)
0.46
(0.32–0.68)
0.0001 0.54
(0.39–0.75)
0.0002
Small room (Ref = large room)
1.70
P value
Fixed Effects
(1.12–2.57)
Underground garage (Ref = large room) 1.87 Bitumen transport (Ref = direct application of asphalt) 0.60
(1.16– 3.03) (0.50–0.72)
Others (Ref = direct application of asphalt)
(0.39–0.76)
0.54
(1.12 – 2.20)
0.009
0.011 1.90 \0.0001 0.65
0.012
1.57
(1.29–2.78) (0.55–0.77)
0.001 \0.0001
0.0004 0.64
(0.47–0.85)
0.002
Random effects
Variance component (S.E.)
Variance component (S.E.)
Level-two variance estimate (full model)a
0.22 (0.08)
0.13 (0.05)
Level-one variance estimate (full model)a
0.38 (0.04)
0.29 (0.03)
Level-two variance estimate (intercept only)b
0.39 (0.13)
0.27 (0.09)
Level-one variance estimate (intercept only)b
0.57 (0.06)
0.42 (0.04)
R2Level two R2Level one
0.37 0.42
0.39 0.50
a
Level-two (between-construction sites) and level-one (within-construction sites) variance estimates from full model
b
Level-two (between-construction sites) and level-one (within-construction sites) variance estimates from intercept-only model
Measuring emissions from hot bitumen are challenging because vapours and aerosols of bitumen represent a complex mixture of numerous organic compounds. Different methods for sampling and analysing bitumen fumes have been developed, for example, the NIOSH method 5042 or the German BGIA method 6305, and differences among the various methods have been explored (Kenny et al. 1997; Ekstrom et al. 2001; Kriech et al. 2004; Kriech et al. 2010). Throughout this study, the German BGIA method No. 6305 was used for personal sampling of emissions from bitumen. A detailed discussion of the method is given in this issue by Breuer et al. (2011). Vapours and aerosols of bitumen and aerosols of bitumen are strongly correlated (Breuer et al. 2011, this issue). Moreover, our results are similar for both variables. As a result, we have focussed the following discussion primarily on vapours and aerosols of bitumen. The type of setting is one of the most important determinants of airborne exposure to vapours and aerosols of bitumen in asphalt workers. Though based on the measurement of six workers at one construction site, we observed high concentrations of vapours and aerosols of bitumen in tunnel workers, supporting results of a previous study (Burstyn et al. 2000). We also found lower concentrations of vapours and aerosols of bitumen in road construction workers compared with those working indoors, but the observed number of workers in road construction
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was small. In road construction, wind and open settings enhanced the ambient air distribution of vapours and aerosols of bitumen. The focus of this study was on building construction sites, where a large number of workers were engaged in the manual application of mastic asphalt. The concentrations of vapours and aerosols of bitumen measured in these workers were about two times higher than concentrations seen in mastic asphalt workers at road construction sites, but less than half of the levels in tunnel workers. However, this comparison was based on small numbers of workers in road construction and tunnels. Our study confirmed that the processing temperature influences the airborne concentrations of vapours and aerosols of bitumen. We observed an increase in the concentrations of vapours and aerosols of bitumen by a factor of 1.2 with a 10°C increase in the mastic asphalt temperature within the observed temperature range. This association is in line with several other studies that reported elevated emissions from bitumen with increasing asphalt temperatures (Burstyn et al. 2000; Heikkila et al. 2002; Ru¨hl et al. 2006; Vaananen et al. 2006; Gasthauer et al. 2008). The concentrations of polycylclic aromatic hydrocarbons (PAH) also increased in a corresponding manner with rising asphalt temperature (Vaananen et al. 2006; Lange and Stroup-Gardiner 2007). Therefore, we support the conclusion of Vaananen and co-workers who suggested that maintaining the asphalt temperature as low as possible
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is a potential way to reduce exposure, also in the case of manual application of asphalt (Vaananen et al. 2006). In addition to the processing temperature, ambient temperature was also described as an influencing factor of the exposure level (Burstyn et al. 2000). In contrast, McClean and co-workers could not confirm that the ambient temperature is a significant determinant of the exposure, which could be explained by the narrow range of the temperatures measured in their study (McClean et al. 2004). Furthermore, weather conditions, such as wind speed and direction (Burstyn et al. 2000) and rain (Burstyn et al. 2002), were described as potential influencing factors at outdoor construction sites. We also observed an increase in the concentrations of vapours and aerosols of bitumen with increasing ambient temperature, although the effect was much smaller than the effect of the processing temperature. Most constructions sites in this study were indoors; therefore, the influence of the weather, with the exception of ambient temperature, was disregarded in this analysis. In our study, seasons had no additional effect, except for the ambient temperature. Furthermore, the room size of the indoor settings had a strong effect on exposure levels of fumes of bitumen, with a threefold difference between small rooms and outdoor settings in building construction. The following ranking with regard to exposure levels of workplaces was possible: Outdoors B Large rooms B Small rooms B Underground garages. This finding is in concordance with the described differences between indoor and outdoor construction sites as previously reported (Ru¨hl et al. 2006). There is a variety of different asphalt types used in bitumen applications (Burstyn et al. 2000), which differs in terms of their volatility, thus influencing the level of exposure to vapours, aerosols and the concentrations of chemical components like PAH. In our study, the mastic asphalt types comprised AS IC 10/AS ICH 10 (hard asphalt for indoors), AS IC 40 (used outdoors) and AS IC 15 (mixture of both types). We could not detect a clear exposure pattern by asphalt type, which may be explained by the use of rather similar mastic asphalt types for the building construction sites. All asphalt types were free of rubber, waste products and Trinidad bitumen. About 90% of the observed construction sites used soap as the release agent, making it difficult to determine the effect of other release agents like oil. McClean et al. (2004) reported that an increase in the amount of asphalt per hour at highway construction sites increased the exposure of the paving workers to polycyclic aromatic compounds (McClean et al. 2004). We could not confirm this result in our setting. The processed asphalt amount and the size of the paved area during a working shift were strongly correlated, but had no additional effect
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on the exposure level of vapours and aerosols of bitumen at building construction sites in our study. This difference might be explained by the lower amounts of asphalt processed in building construction sites with manual application compared with road construction sites with mechanical laying. The placement of the mixer at the construction sites might influence the exposure level of the workers. In our study, the mixer was usually placed outside of the construction sites, and so we did not examine this further. Besides estimates of the variation between construction sites, this large study also allowed the estimation of the variance within construction sites. Workers close to the paving location, for example the smoothers, had higher exposure levels than workers frequently changing their position at the worksite, such as persons transporting asphalt in a bucket or barrow, supporting previous findings (Ru¨hl et al. 2006). Smoking cigarettes had no additional effect on the concentrations of vapours and aerosols of bitumen. Overall, a large fraction of the variance of the airborne measurements was due to differences between construction sites. Asphalt workers in manual applications frequently change their workplace at building construction sites. This implies a high variation in exposure during the lifetime of a worker, making it less feasible to derive an appropriate estimation of the cumulative exposure of asphalt workers with a cross-sectional or retrospective design. Conclusion In conclusion, the exposure of mastic asphalt workers was largely variable between and within the construction sites. The characteristics of construction site, the job tasks and the processing temperature are important determinants of the concentrations of vapours and aerosols of bitumen. To reduce the exposure levels of the workers, the asphalt temperature should be reduced whenever technically possible. Protective measures such as ventilation have to be taken into account, especially at unfavourable settings like tunnels, underground garages or in small rooms. Acknowledgments The Human Bitumen Study was initiated by the German Committee for Hazardous Substances (AGS) and the German Bitumen Forum and financially supported by: German Social Accident Insurance (DGUV), Eurobitume, Deutscher Asphaltverband e.V., Concawe, Zentralverband des Deutschen Dachdeckerhandwerks, Industrieverband Bitumen-, Dach- und Dichtungsbahnen e.V., Berufsgenossenschaft Rohstoffe und Chemische Industrie (BG RCI) and Aksys GmbH, Beratungsstelle Gussasphaltanwendungen (bga), BG BAU, Arbeitsgemeinschaft der Bitumenindustrie (Arbit). We thank all workers participated in the Human Bitumen Study. We gratefully acknowledge the support of the field team especially Anne Flagge, Anja Molkenthin, Bianca Wachter, Gerd Zoubek, and in part Klaus Schott and Hans-Ju¨rgen Schicker.
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