Persistence of tungsten oxide particle/fiber mixtures in artificial human lung fluids

BACKGROUND: During the manufacture of tungsten metal for non-sag wire, tungsten oxide powders are produced as intermediates and can be in the form of tungsten trioxide (WO(3)) or tungsten blue oxides (TBOs). TBOs contain fiber-shaped tungsten sub-oxide particles of respirable or thoracic size. The aim of this research was to investigate whether fiber-containing TBOs had prolonged biodurability in artificial lung fluids compared to tungsten metal or WO(3 )and therefore potentially could pose a greater inhalation hazard. METHODS: Dissolution of tungsten metal, WO(3), one fiber-free TBO (WO(2.98)), and three fiber-containing TBO (WO(2.81), WO(2.66), and WO(2.51)) powders were measured for the material as-received, dispersed, and mixed with metallic cobalt. Solubility was evaluated using artificial airway epithelial lining fluid (SUF) and macrophage phagolysosomal simulant fluid (PSF). RESULTS: Dissolution rates of tungsten compounds were one to four orders of magnitude slower in PSF compared to SUF. The state of the fiber-containing TBOs did not influence their dissolution in either SUF or PSF. In SUF, fiber-containing WO(2.66 )and WO(2.51 )dissolved more slowly than tungsten metal or WO(3). In PSF, all three fiber-containing TBOs dissolved more slowly than tungsten metal. CONCLUSIONS: Fiber-containing TBO powders dissolved more slowly than tungsten metal and WO(3 )powders in SUF and more slowly than tungsten metal in PSF. Existing pulmonary toxicological information on tungsten compounds indicates potential for pulmonary irritation and possibly fibrosis. Additional research is needed to fully understand the hazard potential of TBOs.