Various components of machining fluids have been associated with acute airways dysfunction, but the nature and magnitude of these relationships are not completely understood. This work describes an exposure assessment for a study of machining fluid aerosols and acute changes in pulmonary function. The specific objectives were to: (1) obtain indices of personal exposure to machining fluid aerosols in an automotive transmission plant, either directly (by sampling) or indirectly (by estimation), (2) characterize sources of exposure misclassification and adjust for them, where possible, and (3) provide personal exposure data with which to explore the relationship between exposure and respiratory impairment. No prior studies have characterized personal exposures to machining fluid aerosols so extensively. Exposure data were obtained during three principal rounds of data collection over a fifteen month period in conjunction with spirometric testing of 131 subjects. Subjects worked in one of two machining departments, Case and Valve Body, or in a comparison department, Final Assembly. The primary exposure measures for this study were thoracic fraction particulate, thoracic fraction bacteria (viable and non-viable), and total endotoxin. In addition, we collected personal samples of vapor phase nicotine (VPN) to estimate and adjust for the proportion of ambient tobacco smoke in personal thoracic particulate measures. Mean personal air concentrations of thoracic particulate across all study rounds were 0.13 mg/m\sp3 in Final Assembly, 0.32 mg/m\sp3 in Valve Body, and 0.56 mg/m\sp3 in Case. Average personal exposures to thoracic fraction bacteria were 0.38 bacteria/cc in Final Assembly, 0.87 bacteria/cc in Valve Body, and 2.66 bacteria/cc in Case. Average personal endotoxin measurements (Round 3 only) were 16.4 endotoxin units (EU)/m\sp3 in Assembly, 34.7 Eu/m\sp3 in Valve Body, and 234 Eu/m\sp3 in Case. Sump fluid contained on the order of 10\sp8 bacteria/ml, and 10\sp4{-}10\sp5 EU/ml. Since direct quantification of bacterial exposures is costly and time-consuming, mathematical models were developed to estimate personal bacterial concentrations. Generalized estimating equations (GEE) were extremely useful for developing and validating predictive models with correlated (i.e., repeated measures) exposure data. The results demonstrate that it is possible to predict personal levels of airborne bacteria from other measures, including: (1) thoracic particulate concentration, (2) concentration of bacteria in sump fluid, (3) percentage of tramp oil and non-tramp oil in sump fluid, (4) area bacterial concentration, (5) group and individual average exposures, (6) area temperature/humidity, and (7) time and location variables. In exposure-response models, thoracic bacteria measures predicted declines in FEV\sb1 and FVC more consistently and significantly than thoracic particulate. These results strongly suggest that bacteria (or bacterial products) play a role in the causation of respiratory dysfunction. In addition, VPN was significantly associated with cross-shift pulmonary function decrements among non- and ex-smokers, indicating a detrimental effect of passive smoking. We conclude that statistical models proved an effective means of estimating personal bacterial exposures in a metalworking environment. Recommendations for future exposure monitoring, control strategies, and exposure assessment studies are presented.Ph.D.Health and Environmental SciencesOccupational safetyToxicologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/129931/2/9711914.pd
