Ultrafine particle number and respirable particle mass concentrations were measured throughout an automotive grey iron foundry during winter, spring and summer using a particle concentration mapping procedure. Substantial temporal and spatial variability was observed in all seasons and attributed, in part, to the batch nature of operations, process emission variability and frequent work interruptions. The need for fine mapping grids was demonstrated, where elevations in particle concentrations were highly localized. Ultrafine particle concentrations were generally greatest during winter when incoming make-up air was heated with direct fire, natural gas burners. Make-up air drawn from roof level had elevated respirable mass and ultrafine number concentrations above ambient outdoor levels, suggesting inadvertent recirculation of foundry process emissions. Elevated respirable mass concentrations were highly localized on occasions (e.g. abrasive blasting and grinding), depended on the area within the facility where measurements were obtained, but were largely unaffected by season. Particle sources were further characterized by measuring their respective number and mass concentrations by particle size. Sources that contributed to ultrafine particles included process-specific sources (e.g. melting and pouring operations), and non-process sources (e.g. direct fire natural gas heating units, a liquid propane-fuelled sweeper and cigarette smoking) were additionally identified.

After decades of research involving numerous epidemiologic studies and extensive investigations in laboratory animals, a causal relationship between diesel exhaust (DE) exposure and lung cancer has not been conclusively demonstrated. Epidemiologic studies of the transportation industry (trucking, busing, and railroad) show a small elevation in lung cancer incidence (relative risks [RRs] generally below 1.5), but a dose response for DE is lacking. The studies are also limited by a lack of quantitative concurrent exposure data and inadequate or lack of controls for potential confounders, particularly tobacco smoking. Furthermore, prior to dieselization, similar elevations in lung cancer incidence have been reported for truck drivers, and in-cab diesel particulate matter (DPM) exposures of truck drivers were comparable to ambient highway exposures. Taken together, these findings suggest that an unidentified occupational agent or lifestyle factor might be responsible for the low elevations in lung cancer reported in the transportation studies. In contrast, underground miners, many of whom experience the highest occupational DPM exposures, generally do not show elevations in lung cancer. Laboratory studies must be interpreted with caution with respect to predicting the carcinogenic potential of DE in humans. Tumors observed in rats following lifetime chronic inhalation of very high levels of DPM may be attributed to species-specific overload mechanisms that lack relevance to humans. Increased tumor incidence was not observed in other species (hamsters or mice) exposed to DPM at very high levels or in rats exposed at lower levels (99% reduction in DPM and other quantitative and qualitative changes in the chemical and physical characteristics of diesel exhaust. Thus, the current database, which is focused almost entirely on the potential health effects of traditional diesel exhaust (TDE), has only limited utility in assessing the potential health risks of new-technology diesel exhaust (NTDE). To overcome some of the limitations of the historical epidemiologic database on TDE and to gain further insights into the potential health effects of NTDE, new studies are underway and more studies are planned.

This study investigated the relationships between particle number, surface area, and respirable mass concentration measured simultaneously in a foundry and an automotive engine machining and assembly center. Aerosol concentrations were measured throughout each plant with a condensation particle counter for number concentration, a diffusion charger for active surface area concentration, and an optical particle counter for respirable mass concentration. At selected locations, particle size distributions were characterized with the optical particle counter and an electrical low pressure impactor. Statistical analyses showed that active surface area concentration was correlated with ultrafine particle number concentration and weakly correlated with respirable mass concentration. Correlation between number and active surface area concentration was stronger during winter (R2 = 0.6 for both plants) than in the summer (R2 = 0.38 and 0.36 for the foundry and engine plant respectively). The stronger correlation in winter was attributed to use of direct-fire gas fired heaters that produced substantial numbers of ultrafine particles with a modal diameter between 0.007 and 0.023 mu m. These correlations support findings obtained through theoretical analysis. Such analysis predicts that active surface area increasingly underestimates geometric surface area with increasing particle size, particularly for particles larger than 100 nm. Thus, a stronger correlation between particle number concentration and active surface area concentration is expected in the presence of high concentrations of ultrafine particles. In general, active surface area concentration may be a concentration metric that is distinct from particle number concentration and respirable mass concentration. For future health effects or toxicological studies involving nano-materials or ultrafine aerosols, this finding needs to be considered, as exposure metrics may influence data interpretation.

Much previous work has suggested that long workhours generate a wide range of adverse outcomes across the employee continuum. This study found no evidence for pervasive workhour effects. Rather, long workhours--especially weekly schedules at the 60 hour or above mark--can lead to problems in certain areas of health and safety. More research is needed that tests group differences across segmented characteristics (eg, poor versus good health) but keeps workhour impact in perspective.