Exposure to Particles, Elemental Carbon and Nitrogen Dioxide in Workers Exposed to Motor Exhaust

ABSTRACT

Objectives: The main aim of this study was to investigate the personal exposure to diesel and petrol exhaust fumes in occupations when exposure is prevalent and/or high. We also investigated the correlation between the five particle fractions [particles with an aerodynamic diameter <1 mm (PM1), particles with an aerodynamic diameter <2.5 mm (PM2.5), particles in size 0.1–10 mm, elemental carbon (EC) and total carbon (TC)] and nitrogen dioxide (NO2), in the various occupational environments.

Methods: Seventy-one workers were included in the study. They were subdivided into seven groups depending on working area, working indoors, out of doors or in vehicles and type of exposure (diesel or petrol exhaust). Personal measurements were performed during 3 days per worker. We used five indicators of the particle fraction: PM1, PM2.5, particle measured with a real-time monitoring instrument for particles in sizes 0.1 and 10 mm (DataRAM), EC and TC. We used NO2 as an indicator of the gas phase.

Results: Tunnel construction workers showed the highest levels of exposure for all indicators, followed by diesel-exposed garage workers. For the other five groups, the levels were statistically significantly lower, and the differences between the groups were small. The full-shift geometric average of PM1 varied between 119 mg m-3 (tunnel construction workers) and 11 mg m-3 (taxi drivers). For PM2.5, the levels varied between 231 mg m-3 (tunnel construction workers) and 16 mg m-3 (bus and lorry drivers). For the measurements with the real-time monitoring instrument DataRAM, the levels varied between 398 mg m-3 (tunnel construction workers) and 14 mg m-3 (taxi drivers). For EC, the levels varied between 87 mg m-3 (tunnel construction workers) and 4 mg m-3 (other outdoor workers exposed to diesel exhaust), and for TC, the levels varied between 191 mg m-3 (tunnel construction workers) and 10 mg m-3 (taxi drivers). Finally, for NO2, the levels varied between 350 mg m-3 (tunnel construction workers) and 32 mg m-3 (other outdoor workers exposed to diesel exhaust). For the indoor workers exposed to diesel exhaust fumes only, all the indicators correlated comparatively well and statistically significantly to each other (r2 5 0.44–0.89). For the other groups, correlations were lower and showed no consistent pattern.

Conclusions: The tunnel construction workers had exposure levels for all indicator substances that were considerably and significantly higher than for the other groups. The NO2 levels were higher for indoor workers exposed to diesel exhaust than for all other groups (except tunnel construction workers). All particle fractions, as well as NO2 correlated well in occupations with indoor exposure to diesel exhaust.


STUDY SUBJECTS AND METHODS

Seven groups of occupations, with 71 workers altogether, were defined depending on the type of fuel (diesel or petrol) and workplace (indoors, out of doors or in a vehicle).

Group A (tunnel construction workers) included six workers engaged in the construction of a road tunnel in Stockholm. They worked with various installation tasks, using diesel-powered machines and vehicles. Since the tunnel construction was in the final stage, there was no blasting in progress in any part of the tunnel.

Group B (garage workers—diesel) included 20 workers. Fifteen of them worked as lorry or bus mechanics, three worked on other tasks in a bus garage and two worked for the Swedish Vehicle Inspection Company inspecting lorries and buses.

Group C (garage workers—petrol) included six private car mechanics and two parking garage attendants. Since 95% of private cars in Sweden use petrol, we classified them as being exposed to petrol exhaust.

Group D (construction machine operators) included 11 workers. They worked inside or nearby diesel-fuelled construction machines such as excavators, gulley emptiers, etc. The exhaust fumes originated mainly from their own vehicle, but nearby traffic may have contributed.

Group E (other outdoor workers exposed to diesel exhaust) included 12 workers working in or around diesel-fuelled trucks, tractors in agriculture, shunting engines, etc. They all worked in areas with no other traffic close by.

Group F (bus and lorry drivers) included four bus drivers and six lorry drivers. Two of the bus drivers worked in the city of Stockholm (using ethanol-fuelled buses) and the other two worked in a suburb (on diesel-fuelled buses). All lorry drivers drove in and around Stockholm city, using diesel fuel.

Group G (taxi drivers) included four taxi drivers driving in and around the city of Stockholm. Three of the taxis used diesel fuel and one used petrol.

Of the 71 workers, 68 were men and three were women. All were non-smokers, and smoking was not allowed indoors at any of the workplaces or in any of the vehicles.

We used five exposure indicators for the particle phase of the exhaust: particles with an aerodynamic diameter of <1 lm (PM1), particles with an aerodynamic diameter of <2.5 lm (PM2.5) and particles of sizes between 0.1 and 10 lm (measured with the realtime monitoring instrument DataRAM). We also sampled and analysed EC and organic carbon (OC). Elemental and OCs together represent the total carbon (TC). We used NO2 as an indicator of the gas phase of the exhaust. We used pump units and gravimetric determination for PM1 and PM2.5, a real-time monitoring instrument for particles in size 0.1–10 lm and pump units and chemical analysis for the EC and TC determination. For NO2, we used diffusive samplers. Table 1 gives information about the methods, number of measurements, measuring time and limit of detection for each indicator.

Measurements were done between October 2002 and June 2004, the aim being that they should be representative of normal working conditions. All measurements were based on personal sampling. None of the workers used respiratory protection during work. Three full shifts were measured for all workers. PM1 and EC were measured during 2 days each and NO2 was measured all 3 days. PM2.5 and DataRAM were measured during 1 day. Thus, each day, two different particle fractions and NO2 were measured. The order of the particle fractions was randomly selected. 

Statistical methods

Histograms of the parameters measured showed lognormal distributions both for particle fractions and NO2. Thus, we used logarithmically transformed values for all statistical calculations and expressed our results as geometric mean and geometric standard deviation. We used SPSS version 13.0 for Windows for all statistical calculations. Differences between means were tested by t-test for independent samples, applied to the log-transformed values. A P-value <0.05 was considered statistically significant (two-tailed tests were used).

Pearson’s correlation coefficient was used to investigate the correlations between the exposure indicators. Two-tailed tests were used.

RESULTS

The tunnel construction workers (Group A) showed considerably higher levels of exposure for all indicators than the other groups (Table 2 and Fig. 1). The exposure levels were statistically significantly higher than in the other groups for all six indicators (P < 0.01) (Table 3).

For the other six groups, the levels were lower and the ranking order between them depended on which indicator was used. In Table 3, we have illustrated which of the groups having indicators statistical significant different from others.

The indoor workers in Group B (garage workers—diesel) had statistically higher levels of NO2 than Groups C–G, and for some of the other indicators, both Group B and Group C (garage workers—petrol) had higher levels than the outdoor workers in Group E (other outdoor workers exposed to diesel exhaust) and the drivers in Groups F and G.

Both groups with outdoor exposed workers (Group D = construction machine operators and Group E = other outdoor workers exposed to diesel exhaust) had similar exposure levels except for particles in size 0.1–10 lm (DataRAM), for which Group D had the higher levels.

Both groups of drivers had lower levels than the others for most of the indicators. But for NO2, Group F (bus and lorry drivers) had higher levels than Group E (other outdoor workers exposed to diesel exhaust). Between the drivers themselves, only the particles in size 0.1–10 lm (DataRAM) differed significantly, with higher levels for the bus and lorry drivers (Group F) compared to taxi drivers (Group G).

Correlations between indicators were investigated among indoor exposure to diesel exhaust (Groups A and B), in order to obtain a group with homogenous exposure source (Table 4).

For this pooled Group (A + B), all correlations were statistically significant, most of them with P < 0.01. Correlations were also studied for the other groups but we did not find any uniform pattern for the correlations, except for EC and TC which correlated strongly (P < 0.01) as were expected.

