(217a) Assessment of Potential Exposure to Carbon Nanotubes In the Production of Polymer Nanocomposites

Recent animal toxicology studies have shown that carbon nanotubes (CNTs) may pose a significant health risk to those exposed to this nanomaterial in the workplace. However, many questions regarding the toxicology of CNTs still remain unanswered. There has yet to be agreement on which dose metric would not only correlate with the negative health effects but also be able to be successfully implemented in field measurements. The roles of the inclusion of metal catalyst particles in and the morphology of CNTs and/or CNT structures in the toxicology of CNTs are still being investigated. While these matters are being researched further by toxicologists there remains a dearth of information on the actual exposure to CNTs. Even if CNTs are found to be hazardous, there will be no risk without exposure. To fully understand this potential risk effort must be taken to measure the occupational exposure to CNTs.

In this study the potential occupational exposure to CNTs in the production of polymer nanocomposites, where CNTs were used as a filler material, was assessed. The potential exposure to CNTs was quantified by analyzing respirable dust samples collected by personal sampling for elemental carbon. The mass concentration of elemental carbon, of which CNTs mainly consist, was determined by thermal-optical analysis of the sample. Potential exposure sources were identified and characterized by both real-time measurements and area sampling. The potential sources investigated were comprised of both production equipment and production related tasks, which included the handling of unbound CNTs. The real-time measurements were performed by instrumentation which provided number concentration, surface area concentration, respirable mass concentration, and size distributions for micron-sized particles. Area samples were analyzed by transmission electron microscopy to characterize the morphology and to calculate the number concentration of CNT structures. Other samples were taken for analysis by inductively coupled plasma mass spectrometry to measure the concentration of trace metals. The concentration of these metals was then used to estimate the CNT mass concentration based on known impurities. Thermal-optical analysis was performed on additional area samples to measure the elemental carbon mass concentration.