Exposures during wet production and use processes of nanomaterials: a summary of 11 worksite evaluations

E. Glassford, N.M. Neu-Baker, K.L. Dunn, K.H. Dunn
SUNY Polytechnic Institute,
United States

Keywords: exposure assessment, air sampling, electron microscopy, direct-reading instruments


From 2011-2015, the National Institute for Occupational Safety and Health (NIOSH) Nanotechnology Field Studies Team conducted 11 evaluations at worksites that either produced engineered nanomaterials (ENMs) via a wet process or used ENMs in a wetted, suspended, or slurry form. While handling ENMs in a wetted, suspended, or slurry form, or as part of a wet process, reduces potential exposure compared to handling of dry nanomaterials, data from these 11 site evaluations indicate exposures may still occur. Workplace information was gathered for each worksite including company descriptions, production processes, nanomaterials of interest, and control measures (including use of personal protective equipment). Exposure assessments were also conducted, following the Nanoparticle Emission Assessment Technique (NEAT)1,2 and the updated Nanomaterial Exposure Assessment Technique (NEAT 2.0).3 This included air sampling via collection onto filter media and real-time particle counting by direct-reading instruments. Additionally, surface wipe samples were collected during 4 of the 11 evaluations. ENMs of interest from the 11 evaluations included silver nanowires, aluminum oxide nanoparticles, silicon dioxide nanoparticles, hafnium oxide nanocrystals, titanium dioxide nanoparticles, and nanocellulose (as fibrils and crystals). The most common processes observed included synthesis reactions in closed vessels; mixing of powders and solvents to form slurries, suspensions, or dispersions; filtering of aqueous suspensions; transfer or manual handling of nanomaterial product; and manual cleaning of equipment. Common engineering controls observed at the sites included the use of laboratory fume hoods, cleanrooms, and closed processes. Personal protective equipment was required during all 11 evaluations, with some form of respiratory protection worn during 9 of the 11 evaluations. Direct-reading data showed potential ENM emissions in 9 of the 11 evaluations. ENMs of interest were confirmed via electron microscopy analysis of air filter samples collected during nearly every evaluation (10 of 11). Elemental mass analysis of air samples was also used for the identification of parent nanomaterials to investigate potential worker exposures. ENMs were identified most often from the area/source air filter samples, but were also identified in worker breathing zone and non-process area samples. ENMs of interest were identified for all 4 evaluations where surface wipe samples were collected, including from non-process areas. Identifying ENMs in the non-process area samples indicates that there is migration of the ENMs out of processing areas and into non-processing areas. The Field Studies Team provided each company with recommendations that, if implemented, could reduce or eliminate the potential for exposures to engineered or incidental nanomaterials, regardless of the nanomaterial used. The Field Studies team encourages the use of the hierarchy of controls to limit and prevent employee exposures in the workplace. Additionally, the use of wet ENMs over dry ENMs is still recommended.