Characterization and control of bridge workers' exposure to lead during bridge painting tasks

The work done for this thesis is part of a cross-sectional study of bridge painters, aimed at investigating the reasons for persistent elevated blood lead levels. The overall goal of this research was to create and characterize an exposure index for lead for an epidemiologic study, and to identify effective control strategies to reduce workers' exposures to lead.;The first part of this research focuses on the creation and characterization of an exposure index for lead. A task based sampling approach was used to assess workers' exposure to lead during the various paint removal and bridge painting tasks. Daily full-shift time weighted average exposures (TWA) were estimated for each worker on every workday over the two weeks study period. Full shift TWA exposures were calculated by taking the product of the mean task exposure levels and the task duration reported on workers' daily activity-time diaries, and summing the product across all tasks performed on a given day. The above strategy requires tasks which are homogeneous in exposure, and whose means are unbiased and precise. Therefore, the nature of exposure distribution and the sources of exposure variability of short-term task measurements were investigated. The mean task exposure levels were obtained by taking the arithmetic means of the tasks (simple task-am), or by developing a multivariate statistical model to predict mean task exposure levels and then estimate the minimum variance unbiased estimator (MVUE) of the task arithmetic mean (model task-am). Two indices of the full shift TWA exposures were calculated for all the workers and their utility was evaluated by comparing with measured full shift TWA exposures (considered to be the gold standard), and by examination of their relationship with blood lead levels in univariate statistical models. A third exposure index, the Stein estimator, which is hybrid of the individual and group means of the full shift TWA exposures obtained using the simple task-am, performed best in the univariate model explaining worker blood lead levels.;The second part of this research focuses on identifying strategies for controlling worker exposure to lead. The effectiveness of respirator use among bridge workers and the personal, social and work-related factors that affect respirator use by workers were investigated. The effectiveness of the actual respirators used by workers and the effectiveness of the respirators specified by OSHA in the leas in construction standard was evaluated. Comparisons were made of the worker-task exposures to the OSHA PEL for lead, after accounting for the respirators the workers used. The protection factors that would keep the task exposures for 95% of the workers below the PEL for each task were also calculated. The personal, social and work related determinants of respirator use by workers were also investigated to identify factors associated with respirator use among bridge painters. These factors can be used to develop more effective intervention and training strategies to reduce bridge workers exposure to lead.