Estimating lung burdens based on individual particle density estimated from scanning electron microscopy and cascade impactor samples

Workplace air is monitored for overall dust levels and for specific components of the dust to determine compliance with occupational and workplace standards established by regulatory bodies for worker health protection. Exposure monitoring studies were conducted by the International Copper Association (ICA) at various industrial facilities around the world working with copper. Individual cascade impactor stages were weighed to determine the total amount of dust collected on the stage, and then the amounts of soluble and insoluble copper and other metals on each stage were determined; speciation was not determined. Filter samples were also collected for scanning electron microscope analysis. Retrospectively, there was an interest in obtaining estimates of alveolar lung burdens of copper in workers engaged in tasks requiring different levels of exertion as reflected by their minute ventilation. However, mechanistic lung dosimetry models estimate alveolar lung burdens based on particle Stoke's diameter. In order to use these dosimetry models the mass-based, aerodynamic diameter distribution (which was measured) had to be transformed into a distribution of Stoke's diameters, requiring an estimation be made of individual particle density. This density value was estimated by using cascade impactor data together with scanning electron microscopy data from filter samples. The developed method was applied to ICA monitoring data sets and then the multiple path particle dosimetry (MPPD) model was used to determine the copper alveolar lung burdens for workers with different functional residual capacities engaged in activities requiring a range of minute ventilation levels.