| Abstract |
The aims of this research were to: Identify and evaluate methods to measure airborne nanoparticle concentrations; characterize nanoparticles using a complementary suite of techniques to assess their surface and bulk physical and chemical properties; and determine the collection efficiency of commonly-used respirator filters when challenged with nanoparticles. Aim 1 findings have led to practical proposals for the use of instrumentation by industrial hygienists when evaluating a workplace for the presence, and amount, of nanoparticle aerosols. Our laboratory findings have led to a method for using two hand-held instruments to reproduce the size distribution of an aerosol from the sub-micrometer to micrometer range in order to obtain an understanding of the nanoparticle count and distribution. This is significant because the only alternative methods require very expensive, bench-top instruments. Our field component of Aim 1 led to the development of a method which utilizes the same two hand-held instruments, in conjunction with transmission electron microscopy to also physically and chemically characterize the nanoparticles counter, therefore, their potential source can be identified. Aim 2 findings centered on the best of use of sophisticated analytical instruments to best determine the nature of a nanopowder from a bulk sample. A suite of surface and bulk powder analytical techniques was found to provide the most information including. The findings obtained from these analyses allowed us to distinguish specific characteristics of the nanopowders used from the many possible for each powder type. This result was especially apparent when analyzing carbon nanotubes which can have a wide variety, and concentration, of contaminant compounds that can potentially change its physical properties and toxicological effects. Work associated with Aim 3 involved testing two respirator filter types, and N95 and P100, when challenged with a variety of nanoparticle types. In general, the filters performed within their expected efficiency requirements except when challenged with carbon nanotubes. The principle aspect of our research that can be translated into practice is the development and assessment of a nanoparticle exposure methodology that can be employed by industrial hygienists in the field. This method utilizes field-capable instruments to both enumerate nanoparticles and characterize their morphology and elemental composition. Given that the instruments associated with this method are currently available, the method can be presently utilized by industrial hygienists. The relevance of this work is related to the current need for a method to assess workplaces for nanoparticle exposures. The field of nanotechnology, and the related development of nanopowders in particular, has advanced more rapidly than the steps needed to offer guidance to these industries in terms of both threshold limit values (TLVs) and proper assessment methods. Both the TLVs and related assessment methods for most occupational dust types are based on a mass measurement. These are clearly inadequate when dealing with particles in the submicrometer range which necessarily constitute a very low percentage of the total mass of an aerosol (given a wide distribution) or are undetectable on a mass-basis (given a narrow distribution). The results from this study will aid in the important work needed to develop both TLVs and associated sampling methods for nanoparticle exposures. |
