title: Characteristics of dusts encountered during the production of cemented tungsten carbides.
abstract: Inhalation of cobalt (Co) and tungsten carbide (WC) particles, but not Co or WC alone, may cause hard metal disease, risk of which does not appear to be uniform across cemented tungsten carbide (CTC) production processes. Inhalation of Co alone or in the presence of WC may cause asthma. Hypothesizing that aerosol size, chemical content, heterogeneity, and constituent compaction may be important exposure factors, we characterized aerosols from representative CTC manufacturing processes. Six work areas were sampled to characterize aerosol size distributions (dust, Co) and 12 work areas were sampled to characterize physicochemical properties (using scanning electron microscopy with energy dispersive x-ray spectrometry [SEM-EDX]). Bulk feedstock and process-generated powders were characterized with SEM-EDX and x-ray diffraction. The dust mass median diameter was respirable and the cobalt respirable mass fraction was highest (37%) in grinding. Morphology of particles changed with processing: individual, agglomerate, or aggregates (pre-sintered materials), then mostly compacted particles (subsequent to sintering). Elemental composition of particles became increasingly heterogeneous: mostly discrete Co or W particles (prior to spray drying), then heterogeneous W/Co particles (subsequent work areas). Variability in aerosol respirability and chemical heterogeneity could translate into differences in toxicity and support detailed characterization of physicochemical properties during exposure assessments.
authors.affiliation: Division of Respiratory Disease Studies, National Institute for Occupational Safety and Health, Morgantown, WV 26505, USA.
authors.forename: Aleksandr B
authors.initials: AB
authors.lastname: Stefaniak
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Day
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Harvey
authors.forename: Stephen S
authors.initials: SS
authors.lastname: Leonard
authors.forename: Diane E
authors.initials: DE
authors.lastname: Schwegler-Berry
authors.forename: Steve J
authors.initials: SJ
authors.lastname: Chipera
authors.forename: Nancy M
authors.initials: NM
authors.lastname: Sahakian
authors.forename: William P
authors.initials: WP
authors.lastname: Chisholm
mesh_terms: D000336:Aerosols / Q000032:analysis; D000395:Air Pollutants, Occupational / Q000009:adverse effects / Q000032:analysis*; D000497:Alloys / Q000009:adverse effects / Q000032:analysis*; D001249:Asthma / Q000139:chemically induced; D003035:Cobalt / Q000009:adverse effects / Q000032:analysis*; D004391:Dust / Q000032:analysis*; D004784:Environmental Monitoring / Q000379:methods; D008420:Manufactured Materials; D009784:Occupational Diseases / Q000139:chemically induced; D016273:Occupational Exposure / Q000009:adverse effects / Q000032:analysis*; D010316:Particle Size; D014414:Tungsten / Q000009:adverse effects / Q000032:analysis*
chemical_list: D000336:Aerosols; D000395:Air Pollutants, Occupational; D000497:Alloys; D004391:Dust; C080121:hard metal; D003035:Cobalt; D014414:Tungsten