Characterization of exposure to inhalable flour dust in Swedish bakeries

Bakery workers are at risk of developing respiratory symptoms, such as asthma and rhinitis. Exposure to inhalable flour dust in 12 Swedish bakeries was therefore determined: concentrations of airborne inhalable flour dust were measured with the IOM personal inspirable dust sampler and the particle size distribution assessed using the IOM personal inspirable aerosol spectrometer, and the fractions of alpha-amylase, water-soluble protein and total protein in flour dust were determined. A total of 129 measurements were performed of which 77 were repeated measurements. There was a clear hierarchy in geometric mean exposure among bakery workers, with in descending order doughmakers (5.46 mg m-3), bread-formers (2.69 mg m-3), oven workers (1.17 mg m-3), and packers and confectionery workers (0.53 mg m-3). The repeated measurements revealed that within each task group there were considerable differences in mean exposure among the workers: this was demonstrated by geometric standard deviations of between-worker variance of 1.63-1.77. Partitioning of the total variability of inhalable flour dust exposure showed that the task group was the principal source of variance, accounting for 61-69% of the total variability. The optimum grouping strategy was independent of whether the oven workers and the packers were assigned to the same or to different task groups. The doughmakers and the bread-formers are two clearly distinguishable exposure groups with largely overlapping exposure distributions. On average, the flour dust contained 9% total protein, 2.3% water-soluble protein and 0.03% alpha-amylase. The inhalable flour dust was characterized by a substantial proportion of particles with a d(ac) above 10 microns. It was estimated that the thoracic subfraction contributed 39% to the total mass of inhalable dust, and the respirable subfraction 19%.