Ann. occup. Hyg., Vol. 47, No. 5, pp. 379-388, 2003
© 2003 British Occupational Hygiene Society
Published by Oxford University Press
Exposure to Dust and Particle-associated 1-Nitropyrene of Drivers of Diesel-powered Equipment in Underground Mining
1 Department of Epidemiology and Biostatistics and 6 Department of Toxicology-Pharmacology, UMC St Radboud, PO Box 9101, NL-6500 HB Nijmegen, The Netherlands; 2 Regional Institute of Hygiene, Partyzanske nam 7, 72892 Ostrava, Czech Republic; 3 Laboratory of Environmental Carcinogenesis, Estonian Institute of Experimental and Clinical Medicine, Hiiu 42, EE-0016 Tallinn, Estonia; 4 Institut für Gefahrstoff-Forschung der Bergbau Berufsgenossenschaft, Waldring 97, D-44789 Bochum, Germany; 5 MRC Environmental Epidemiology Unit, University of Southampton, Southampton SO16 6YD, UK
Received 6 November 2002; in final form 20 February 2003
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSWITHIN-WORKER AND BETWEEN-WORKER...DISCUSSION AND CONCLUSIONSREFERENCES |
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A field study was conducted in two mines in order to determine the most suitable strategy for ambient exposure assessment in the framework of a European study aimed at validation of biological monitoring approaches for diesel exhaust (BIOMODEM). Exposure to dust and particle-associated 1-nitropyrene (1-NP) was studied in 20 miners of black coal by the long wall method (Czech Republic) and in 20 workers in oil shale mining by the room and pillar method (Estonia). The study in the oil shale mine was extended to include 100 workers in a second phase (main study). In each mine half of the study population worked underground as drivers of diesel-powered trains (black coal) and excavators (oil shale). The other half consisted of workers occupied in various non-diesel production assignments. Exposure to diesel exhaust was studied by measurement of inhalable and respirable dust at fixed locations and by personal air sampling of respirable dust. The ratio of geometric mean inhalable to respirable dust concentration was approximately two to one. The underground/surface ratio of respirable dust concentrations measured at fixed locations and in the breathing zones of the workers was 2-fold or greater. Respirable dust was 2- to 3-fold higher in the breathing zone than at fixed sampling locations. The 1-NP content in these dust fractions was determined by gas chromatography–mass spectrometry/mass spectrometry and ranged from 0.003 to 42.2 ng/m3 in the breathing zones of the workers. In mine dust no 1-NP was detected. In both mines 1-NP was observed to be primarily associated with respirable particles. The 1-NP concentrations were also higher underground than on the surface (2- to 3-fold in the coal mine and 10-fold or more in the oil shale mine). Concentrations of 1-NP in the breathing zones were also higher than at fixed sites (2.5-fold in the coal mine and 10-fold in the oil shale mine). For individual exposure assessment personal air sampling is preferred over air sampling at fixed sites. This study also suggests that particle-associated 1-NP much better reflects the ambient exposure to diesel exhaust particles than dust concentrations. Therefore, measurement of particle-associated 1-NP is preferred over measurement of dust concentrations by gravimetry, when linking ambient exposure to biomonitoring outcomes such as protein and DNA adducts and excretion of urinary metabolites of genotoxic substances.
Keywords: black coal mining; nitro-polycyclic aromatic hydrocarbons; oil shale mining; personal air sampling
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSWITHIN-WORKER AND BETWEEN-WORKER...DISCUSSION AND CONCLUSIONSREFERENCES |
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Working conditions in underground mining are associated with a considerable number of health risk factors, such as a high physical workload, radiation exposure, high temperature and humidity conditions and exposure to dust and gas phase hazardous substances. In the mining industry heavy duty diesel-powered equipment is often used as a source of power for lifting heavy loads and transport in narrow spaces, resulting in unfavourable air quality conditions for operators of diesel-powered vehicles and for those working in the vicinity of these vehicles.
Several approaches have been proposed to assess exposure to diesel exhaust. Some investigators have used respirable dust levels as a measure of exposure to diesel exhaust and have corrected these exposure estimates for the contribution of smoking (Hammond et al., 1988; Woskie et al., 1988). In the USA and in Germany different methods have been developed for the determination of elemental carbon (EC) in workplace atmospheres (Birch et al., 1999). However, in many workplaces this approach cannot be used because there are other airborne particles that contain EC.
In the early 1990s 1-nitropyrene (1-NP) was proposed as a chemical marker for diesel exhaust particles (DEP). 1-NP is formed during combustion of fossil fuel at high temperatures with a surplus of combustion air. These conditions are typical of most diesel engines but have been observed in some other domestic combustion processes, such as petroleum gas burners and kerosene heaters (Tokiwa et al., 1985). 1-NP is not formed by photochemical reactions in the atmosphere (although its isomers, 2- and 4-nitropyrene, may be formed under those conditions; Atkinson and Arey, 1994). 1-NP is a major constituent in a mixture of more than 200 different nitro-polycyclic aromatic hydrocarbons (nitro-PAH) associated with diesel exhaust. It has been demonstrated that the content of 1-NP correlates with the mutagenicity of the total dichloromethane extract of DEP (Scheepers et al., 1995), suggesting that 1-NP may be used as a chemical marker for the genotoxic potency of organic compounds associated with DEP.
Underground miners are among the occupational exposure groups most heavily exposed to diesel exhaust (Dahmann et al., 1996). Reliable exposure estimates in the mining industry may help epidemiologists to quantify any risk of lung or bladder cancer from exposure to diesel exhaust more reliably. The objective of this study was to characterize the ambient exposure of workers in the mining industry to diesel exhaust. The study presented here is a part of the BIOMODEM study (Biomarkers for Occupational Diesel Exhaust Exposure Monitoring). The main purpose of this study was to determine adducts of PAH and nitro-PAH with lymphocyte DNA and proteins in blood samples obtained from surface and underground workers. In order to develop a suitable strategy for environmental monitoring, pilot studies were set up in a coal mine and an oil shale mine. Based on the pilot study results, a revised sampling strategy was defined and the most suitable mine for a biological monitoring study was selected. The present results describe the environmental monitoring efforts conducted in the pilot studies and in the main study. Some results of biological monitoring have already been published (Scheepers et al., 2002).
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSWITHIN-WORKER AND BETWEEN-WORKER...DISCUSSION AND CONCLUSIONSREFERENCES |
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Populations studied
The pilot studies were conducted in Ostrava (Czech Republic) at a black coal mine and in Kohtla-Järve (Estonia) at an oil shale mine. Black coal was extracted using a long wall technique, on five production days per week in a three shift system (one maintenance shift followed by two production shifts). In the oil shale mine the room and pillar method was used. The study sample for the pilot study comprised 40 male workers, of whom 20 (10 at each mine) were underground miners and operators of diesel-powered engines (‘underground workers’) and 20 (10 at each mine) were workers engaged in various production assignments above ground that were not associated with the use of diesel-powered engines (‘surface workers’). At the coal mine the 10 surface workers were operators or mechanics in a coal processing plant. At the oil shale mine the 10 surface workers were employed as drivers of non-diesel vehicles, turners and locksmiths in a metal workshop, as operators in an oil shale processing plant or mechanics involved in the maintenance of electrically powered water pumps. The underground workers were drivers of diesel-powered locomotives during the maintenance shift (black coal mine) or drivers of diesel-powered excavators during the production shift (oil shale mine). The underground workers were a priori expected to have ‘high’ exposure to diesel exhaust, whereas the surface workers were anticipated to experience ‘low’ (background) levels of exposure determined by general air quality in the workplace and in the region where they lived.
The main study was conducted in Kohtla-Järve (Estonia) at the oil shale mine. In this study 50 underground workers and 50 surface workers were studied. The oil shale workers came from the same jobs as in the pilot study.
Diesel equipment
In the oil shale mine bulldozers, excavators and loaders were used for transportation of oil shale rock from the blasting site to a chain conveyor belt. Technical specifications of this equipment are shown in Table 1. In the coal mine, trains running on a track and trains hanging from a rail were used for transportation of coal, construction materials and personnel over long distances (1–10 km). Diesel-powered locomotives, which were also equipped with a crane, towed the wagons (for technical specifications see Table 2).
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Study period
Data collection for the pilot study was carried out between 15 and 18 March 1999 and 22 and 25 March 1999 (coal mine), and 12 and 14 April 1999 (oil shale mine). Data collection for the main study was carried out between 5 and 22 June 2000, at which time the oil shale mine was operating 4 days/week. Underground workers were studied during the morning, afternoon or night shift on a Monday, Tuesday and Wednesday (production shift in the oil shale mine) and during the morning shift on a Monday and Thursday (maintenance shift in the coal mine). Workers on the surface were studied during the day shift on a Monday, Tuesday and Wednesday for the oil shale mine and on a Tuesday and Wednesday for the coal mine. During the pilot study the oil shale mine was operating only on Monday, Tuesday and Wednesday. In the main study the workers were followed on Monday, Tuesday, Wednesday and Thursday.
Air samples at fixed locations
Samples of airborne particulate matter (‘particles’) were collected on the surface and underground at fixed sampling locations. At each sampling location two samples of inhalable dust and two samples of respirable dust were collected at a height of 
1.5 m above the floor. During the main study one sample of inhalable dust and two samples of respirable dust were collected on each day of the study. Inhalable dust (according to EN 481) was collected using a sampler head developed by the Institut für Gefahrstoff Forschung der Bergbau Berufsgenossenschaft (IGF), Bochum, Germany. Respirable dust (also generally according to EN 481, but using the Johannesburg convention) was collected using an elutriator pre-separator (type MPGII; IGF, Bochum, Germany). Particles were collected on polystyrene membrane filters with a Teflon® coating (type TE38; Schleicher & Schüll, Dassel, Germany). If overloading of the filters occurred during a measurement period the loaded filter was removed and replaced by a new filter. These samples were treated for gravimetrical and 1-NP analysis as separate samples.
Personal air sampling
All of the surface and underground workers who participated in the pilot study were asked to carry personal air sampling equipment during two shifts in the same working week. With an air sampling pump (GSA 2000 or Gilian; GSA, Messgerätebau, Neuss, Germany and Gilian Instruments, Wayne, NJ) operated at an electronically controlled flow of 2.0 l/min, respirable dust was collected in the breathing zones of the workers. The airflow was set by dry calibration before and after air sampling. The dust was collected on the TE38 filters (see above). In the main study, personal air sampling was carried out during just one shift for each worker.
Gravimetry of air samples
The weight of the membrane filters was determined before the start of the air sampling campaign, using a Mettler analytical balance (Sartorius, Göttingen, Germany). Before air sampling, the membrane filters were stored in the weighing room for 24 h to allow adjustment to the temperature and humidity conditions of this room prior to weighing of the filters. This procedure was repeated for the loaded filters and unused blank filters. The procedure fully complies with ISO/DIS 15767 (International Standards Organization, 2002).
Analysis of EC
A sample of oil shale dust was analysed for its EC content using a coulometric method as described by Dahmann et al. (1996).
Analysis of 1-NP
The 1-NP content of the membrane filters was analysed following the method described in Scheepers et al. (1994) with some modifications. The extracts were fractionated on silica cartridges (Bond-Elut LRC; Varian, Harbor City, CA). Nitro-PAHs were reduced using sodium hydrosulphide hydrate (Fluka, Buchs, Germany). The amino analogues were extracted and derivatized using heptafluorobutyric acid (Acros, Geel, Belgium) prior to gas chromatography–mass spectrometry/mass spectrometry (GC-MS/MS) analysis (conditions described by Van Bekkum et al., 1997). Nine-fold deuterated 1-NP (d9-1-NP) was used as an internal standard and was added prior to extraction. SRM 2975 (National Institute for Standardisation and Testing, Gaithersburg, MD) was analysed in duplicate with each series.
Calculations
In a few cases during one sampling period more than one filter was collected (usually if filters were overloaded during the course of sampling they were replaced by new ones). The dust and 1-NP concentrations were calculated by multiplying each concentration by the corresponding sampling time. The total of these products was then divided by the sum of sampling periods. In this way a time-weighted average was determined from reconstitution by calculation of results of gravimetrical and 1-NP determinations of separate samples. The within-worker and between-worker variance ratios (wR0.95 and bR0.95) were calculated from the variance components of the 97.5th and 2.5th percentiles of the log-normally distributed exposures for each group. Significance tests accompanying Pearson correlations were derived from analysis of variance (ANOVA). All analysis was performed with the aid of Stata 7.0 software (Stata, College Station, TX).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSWITHIN-WORKER AND BETWEEN-WORKER...DISCUSSION AND CONCLUSIONSREFERENCES |
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Prior to commencement of the study, raw materials from the coal mine and the oil shale mine were analysed for EC and 1-NP. Black coal and oil shale contained substantial amounts (several weight%) of EC. 1-NP was not detected by GC-MS/MS at a limit of detection of 5 pg on column. Based on these findings it was decided that an exposure assessment for exposure to diesel exhaust would be based on the determination of 1-NP associated with respirable dust.
Concentrations of dust and 1-NP at fixed locations
The results of air sampling at fixed sites are presented in Table 3. Geometric mean (GM) concentrations of dust were all <1 mg/m3, except underground in the oil shale mine (pilot study). In the pilot studies the ratio of GM respirable to inhalable dust levels was approximately 0.4–0.5. In the main study this ratio remained the same on the surface but increased to 0.8 in underground workplaces. GM concentrations of inhalable and respirable dust in the coal mine were higher in underground workplaces than in workplaces on the surface. At the oil shale mine this difference was ~5-fold in the pilot study, but in the main study it was reduced to a factor of less than two.
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GM concentrations of 1-NP were higher in underground workplaces than surface locations: approximately 3-fold or more in both mines (pilot phase). In the main study this difference was much greater (two orders of magnitude). In spite of the differences in respirable and inhalable particle concentrations, the GM concentrations of 1-NP associated with the respirable particle fraction were similar to the 1-NP values observed derived from air sampling of the inhalable particle fraction.
Personal exposures to respirable dust and 1-NP
Concentrations of respirable dust observed in the breathing zones of individual workers are presented in Table 4. The measurements of respirable dust in individuals during the first and second shifts were significantly positively correlated (Fig. 1). Respirable particle concentrations observed in the coal mine (maintenance shift) were similar to those obtained in the oil shale mine (production shift). Also, breathing zone concentrations of respirable dust did not change much in the oil shale mine from the pilot phase to the main study. In all of the three studies the observed breathing zone concentrations were roughly 2-fold higher for underground workers, compared with surface workers.
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In the oil shale mine the concentrations of respirable dust observed in the breathing zone were similar to concentrations observed at fixed site sampling locations (differences were <2-fold). In contrast, in the coal mine breathing zone concentrations were 3-fold higher than concentrations at fixed locations.
1-NP associated with the collected respirable dust showed some interesting patterns (see Table 5). In the coal mine 1-NP levels in the breathing zones of the drivers of trains were ~2-fold higher than the levels observed for surface workers. However, in the oil shale mine underground workers appeared to have 10-fold (main study) to at least 20-fold (pilot study) higher concentrations in their breathing zones than surface workers. Results obtained during the first and second shifts (pilot studies) were similar. The correlation coefficient was similar to that observed for respirable dust (0.47), but this was strongly influenced by a single exceptionally high measurement in an underground oil shale miner during the first shift monitored (Fig. 2).
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In the coal mine concentrations of particle-associated 1-NP observed in the breathing zones were 2.5-fold (underground) to 4-fold (surface) higher compared with values observed at fixed locations (1-NP associated with respirable dust). During the pilot study in the oil shale mine, underground breathing zone values were observed to be 10-fold higher than values observed by fixed site sampling. However, on the surface the situation was the reverse: breathing zone values were lower than values obtained by fixed site sampling at surface locations. The concentrations of 1-NP in the breathing zones of the surface workers during the main study were 20-fold higher compared with the observed values at fixed sites. In underground workplaces this difference was smaller (less than a factor of two).
A positive correlation (r = 0.39) was observed between the concentrations of respirable dust and 1-NP (Fig. 3a). For conditions on the surface, respirable dust and 1-NP were not significantly correlated (Fig. 3b).
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WITHIN-WORKER AND BETWEEN-WORKER VARIABILITY |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSWITHIN-WORKER AND BETWEEN-WORKER...DISCUSSION AND CONCLUSIONSREFERENCES |
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Using the criteria suggested by Burstyn and Kromhout (2000) exposure to respirable particles was uniform in the drivers of diesel-powered vehicles underground in the coal mine and the oil shale mine (bR0.95 = 2.6 and 1.6, respectively). 1-NP concentrations in the breathing zones of underground workers indicated that exposure to 1-NP was not uniform (bR0.95 = 5.5 and 4.5, respectively; cf. Table 5). For surface workers exposure to respirable particles or 1-NP was not uniform, except for those working at the surface in the oil shale mine (bR0.95 = 1.0). Within-worker variability was high in all groups of workers in both mines, especially for exposures to 1-NP, and highest for work tasks on the surface (see Table 5).
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DISCUSSION AND CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSWITHIN-WORKER AND BETWEEN-WORKER...DISCUSSION AND CONCLUSIONSREFERENCES |
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The results of comparing air samples taken at fixed sites in duplicate suggest that local conditions in the mine, such as high wind speeds (of up to 5–10 m/s) in the corridors, contributed to considerable variability in dust levels and levels of 1-NP. Respirable and inhalable dust levels were ~2-fold higher in underground workplaces compared with surface workplaces at the coal mine, as indicated by results from fixed site air sampling and personal air sampling. This difference was greater (5-fold) at fixed sampling sites during the pilot study in the oil shale mine. In the main study the difference was reduced to less than 2-fold because inhalable and respirable dust concentrations underground in the oil shale mine were much lower, whereas dust concentrations on surface locations remained the same. GM inhalable dust concentrations were reduced by a factor of four and concentrations of respirable dust by a factor of two. This change might be explained by the much higher humidity (>90% relative humidity) during the main study compared with the pilot study (40–60% relative humidity). These conditions may have reduced the contribution from resuspension of deposited dust particles by moving vehicles because the floors were wet, and sometimes flooded.
The concentrations of 1-NP observed at fixed locations are very dependent on the choice of the sampling location. An important factor is ventilation at the sampling site and the trajectory of moving vehicles relative to the sampling site, especially at underground sampling locations. During the main study it was possible to set up fixed site sampling close to the moving excavators, loaders and bulldozers. Presumably because of this, higher levels of 1-NP were observed in the main study (cf. Table 5). Thus, concentrations of 1-NP measured at fixed locations can be used to characterize general air quality conditions in the underground environment but may not necessarily be reliable indicators of personal exposure of operators of diesel-powered equipment.
The dust concentrations observed in the coal mine were based on measurements during the maintenance shift (not the production shift). Dust concentrations are anticipated to be much higher during production work. In contrast, concentrations of diesel exhaust (and 1-NP) were expected to be similar or even higher in the maintenance shift than in the production shift, because diesel-powered vehicles were used much more for transportation of materials during maintenance work.
The concentration of respirable dust in the breathing zone was ~2-fold higher for workers underground than for workers on the surface. The exposures were uniform for the drivers in both mines, as could be expected because of the similarity of work tasks. With respect to respirable dust in surface operations, exposure was not uniform, presumably because of different job titles included in these groups. Within-worker variability was in the same range as between-worker variability and indicates the contribution of differences in day-to-day task-based emisions of respirable dust and 1-NP and also day-to-day changes in ventilation of the mine.
The finding of enhanced quantities of 1-NP associated with respirable particles in breathing zones indicates that all workers in this study were exposed to DEP to some extent. The results confirm that this exposure was much higher in underground mining activities than in assignments on the surface. Concentrations of 1-NP in workplaces on the surface were similar to levels that have been reported in other workplaces classified as low exposure situations and to outdoor levels of 1-NP in urban areas (Scheepers et al., 1994, 1995, 1999). Changes in background levels between the air quality conditions above ground, specifically between the pilot and main studies, may have resulted from differences in the use of diesel-powered equipment such as forklifts, trucks and tractors and in the more general outdoor air quality at the mine, as determined by meteorological conditions and regional sources of air pollution such as traffic at the time of air sampling.
The exposure groups in both mines were not uniform with respect to 1-NP-associated particles in the breathing zones. However, the exposure of surface workers to 1-NP was uniform, despite different tasks performed. This may indicate that the personal exposures to 1-NP on the surface were determined more by background levels (e.g. general air quality in the region) and not by sources at the workplace. Within-worker variability was very high for exposure to 1-NP in both mines. This may be due to day-to-day differences in the type and intensity of use of diesel-powered vehicles, causing not only differences in the particle emissions but also differences in the 1-NP content of these particles. Previous studies in passenger cars have indicated that the use of the engine (load and r.p.m.) is an important determinant of changes in the 1-NP content of diesel engine emissions and may explain changes of 2- to 10-fold (Scheepers et al., 2001).
In the coal mine the average (GM) concentration of 1-NP in the breathing zone was approximately 2-fold higher in underground workers compared with surface workers, showing the same difference as in levels of respirable and inhalable dust. In contrast, in the oil shale mine with a similar pattern of dust exposures, a large difference in average concentrations of 1-NP in the breathing zones of underground compared with surface workers was observed. This suggests that in the oil shale mine the overall emission of DEP was much higher. It was observed that in the oil shale mine multiple vehicles were operating at a remote production site, involved in many vehicle movements in dead-end corridors, half of the time heavily loaded with oil shale rock. However, in the coal mine, trains were covering (long) distances through main corridors with relatively more efficient ventilation. The difference in 1-NP when comparing underground with surface conditions at the oil shale mine (10-fold to more than 100-fold) was much greater than in the coal mine (2-fold). In addition to differences in the lay-out of the mine and the arrangement of the work (see above), this may be explained by ventilation conditions in the mines and by the total capacity of diesel-powered engines used simultaneously during mining activities, relative to the air volume of the mine (cf. Tables 1 and 2). Also, there may have been a difference in the 1-NP content of emitted DEP of diesel engines in the two mines. In a previous study it has been shown that the specific 1-NP content of diesel fume depends on the type of engine (Scheepers et al., 1994) and the operating conditions (Scheepers et al., 2001).
In both mines the concentrations of 1-NP in the breathing zone tended to be higher than the concentrations at fixed sampling sites, whereas on the surface the reverse situation was observed (pilot phase at the oil shale mine). Underground workers conducted their work in the vicinity of the emission source (as drivers of the diesel-powered vehicles), whereas on the surface, workers were selected that were not employed as drivers and therefore not as close to a diesel emission source. In the main study the personal air samples contained more 1-NP than fixed site air samples in both underground and surface workplaces. The shift that occurred in the ratio of personal versus fixed site concentrations of 1-NP in the shale mine (when comparing the pilot with the main study results) may be explained by the lower background levels of 1-NP and the concurrent rise in 1-NP in the workplace, as indicated by breathing zone values of 1-NP (cf. Tables 3 and 5).
The much lower concentrations of 1-NP observed in the main study in underground shale mine workplaces as opposed to the pilot study may be the result of lower emissions of nitro-PAH from diesel engines. This suggestion is based on the high intake of combustion air from the mine environment. Because of a much higher humidity in the main study period (relative humidity >90%) the water vapour contained in the combustion air may have caused a lower combustion temperature. This leads to lower levels of nitrogen oxides being formed during combustion and consequently to lower levels of nitro-PAH. This hypothesis is supported by a previous report that addition of water to diesel fuel in mining vehicles is used to reduce emissions of nitrogen oxides and PAH (Rosenkranz and Mermelstein, 1985).
In the underground mining workplaces a contribution of respirable particles from smoking was unlikely since smoking underground was prohibited in both mines. In workplaces above ground smoking was prohibited, but permitted outdoors and during breaks. Therefore, on the surface a contribution of tobacco smoke particles to the concentrations of respirable particles may be anticipated. A contribution of tobacco smoke to the concentrations of particle-associated 1-NP is not likely, since 1-NP was not detected in cigarette smoke (Scheepers and Bos, 1992; Scheepers et al., 2001).
In conclusion this study confirms that 1-NP in black coal and oil shale mines is mostly associated with respirable particles and that in mining operations involving the use of diesel-powered engines exposures to DEP may be 3- to 10-fold higher for underground miners than workers on the surface. Furthermore, measurements of particle-associated 1-NP is a more sensitive and discriminating indicator of exposure to DEP than inhalable or respirable particles because of the relatively high concentrations of mine dust in mining operations. Based on observations made during this study, personal air sampling is preferred over collection of air samples at fixed locations because of the great distance of fixed air sampling locations from the sources of DEP emissions and because of possible interference of high wind speeds in mine corridors. Also, it was shown that personal exposures to respirable dust are uniform in drivers of heavy duty diesel-powered vehicles underground, but not exposure to 1-NP. Within-worker variability was high, especially for breathing zone concentrations of 1-NP. As a consequence, positive correlations between estimates of personal inhalation exposure of 1-NP (time-weighted average of one working period) and biomarkers with a short half-life of excretion, such as urinary metabolites, may be anticipated. On the other hand, positive correlations of inhalation exposure with estimates of internal exposures accumulated over several working periods, such as DNA and protein adducts, may be much weaker or non-existent because of considerable within-worker variability.
Acknowledgements—The authors are indebted to E. Väli who supported the study at the oil shale mine and would like to express their gratitude to the workers and the management of the oil shale mine. This study was carried out with support from the EU (contracts nos BMH4-CT98 3458 and ERB IC20 CT98 0211).
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FOOTNOTES |
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* Author to whom correspondence should be addressed. Tel: +31 24 3616878; fax: +31 24 3613505; e-mail: p.scheepers@epib.umcn.nl
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