Variability in quartz exposure in the construction industry: implications for assessing exposure-response relations.

The aims of this study were to determine implications of inter- and intraindividual variation in exposure to respirable (quartz) dust and of heterogeneity in dust characteristics for epidemiologic research in construction workers. Full-shift personal measurements (n = 67) from 34 construction workers were collected. The between-worker and day-to-day variances of quartz and respirable dust exposure were estimated using mixed models. Heterogeneity in dust characteristics was evaluated by electron microscopic analysis and electron spin resonance. A grouping strategy based on job title resulted in a 2- and 3.5-fold reduction in expected attenuation of a hypothetical exposure-response relation for respirable dust and quartz exposure, respectively, compared to an individual based approach. Material worked on explained most of the between-worker variance in respirable dust and quartz exposure. However, for risk assessment in epidemiology, grouping workers based on the materials they work on is not practical. Microscopic characterization of dust samples showed large quantities of aluminum silicates and large quantities of smaller particles, resulting in a D(50) between 1 and 2 microm. For risk analysis, job title can be used to create exposure groups, although error is introduced by the heterogeneity of dust produced by different construction workers activities and by the nonuniformity of exposure groups. A grouping scheme based on materials worked on would be superior, for both exposure and risk assessment, but is not practical when assessing past exposure. In dust from construction sites, factors are present that are capable of influencing the toxicological potency.