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921ZADA - Tungsten Oxide Fiber Dissolution in Artificial Lung Fluids

Start Date: 7/1/2007
End Date: 9/30/2009

Principal Investigator (PI)
Organization: NIOSH
Sub-Unit: DRDS
Funded By: NIEHS

Primary Goal Addressed
5.0

Secondary Goal Addressed
None


Attributed to Manufacturing
100%

Project Description

Short Summary

Tungsten is a dense metal that is used in a range of industrial applications, including non-sag wire for light bulb filaments, pigments for paints, and cemented tungsten carbide (alloyed tungsten carbide and cobalt) cutting tools. Evidence is emerging that tungsten production and possibly hard metal manufacturing workers may be exposed via inhalation to tungsten oxide particulate with fibrous morphology and this morphology could pose a yet unrecognized inhalation hazard. Little is understood regarding the physicochemical properties of occupationally-encountered tungsten oxide fibers or their intrinsic solubility in extracellular lung fluid or lung macrophage phagolysosomes. As such, the aim of this research is measure the relative solubility of three tungsten oxide fiber-containing powders and three non-fiber containing powders in two acellular models of human lung fluids. Resultant solubility and biopersistence data will be used, in part, to support scientific-based decision making regarding the efficacy of current inhalation exposure limits for non-fibrous tungsten forms (oxide, metal, carbide) for tungsten oxide fibers.



Description

To investigate the hypothesis that tungsten oxide fibers are more persistent in the lung than non-fibrous tungsten-containing particles, the following five specific aims were developed:



1. Evaluate the physicochemical properties (morphology, surface area, density, chemical purity, crystallinity, and surface chemistry) of tungsten oxide fiber study materials ("blue" tungsten oxides with stoichiometries WO2.82, WO2.72, and WO2.52) and non-fibrous tungsten particles ("yellow" tungsten trioxide with stoichiometry WO3, "blue" tungsten oxide with stoichiometry WO2.97, and tungsten metal).



2. Determine the relative solubility and biopersistence of tungsten oxide fibers in artificial human extracellular lung fluid and artificial human lung macrophage phagolysosomal fluid.



3. Compare the relative dissolution of individual tungsten oxide fibers to aggregated tungsten oxide fibers in artificial lung fluids.



4. Compare the solubility and biopersistence of tungsten oxide fibers in artificial lung fluids to industrially-important tungsten particles (non-fibrous morphology) and to a known biopersistent fibrous material (amphibole or chrysotile asbestos).



5. Determine if tungsten oxide fiber solubility and biopersistence is enhanced in the presence of cobalt, a common co-exposure material encountered during the manufacture of cemented tungsten carbides.



Specific Aim #1 gas been completed. In FY08 two pilot experiments were completed as part of Specific Aim #2 to measure dissolution of each tungsten oxide material in artificial extracellular lung fluid and lung alveolar macrophage phagolysosomal fluid. These studies evaluated the influence of model constituents on dissolution, determined whether sample masses and exposure durations were sufficient to exceed analytical method detection limits, and estimated dissolution kinetics prior to conducting full dissolution experiments described in Specific Aims #2 through #5.



For Aim #2, we will determine the chemical dissolution kinetics and rate constants of triplicate samples of "blue" tungsten oxide fiber materials WO2.82, WO2.72, and WO2.52 with SUF and PSF at 37°C and evaluate changes in particle physicochemical properties as the result of exposure to these solvents.



For Aim #3, we will determine the chemical dissolution kinetics and rate constants of triplicate samples of dispersed individual fibers and triplicate samples of aggregated fibers of "blue" tungsten oxide fiber materials WO2.82, WO2.72, and WO2.52 with SUF and PSF at 37°C and evaluate changes in particle physicochemical properties as the result of exposure to these solvents.



For Aim #4, we will determine the chemical dissolution rate constants of triplicate samples of amphibole or chrysotile fibers, tungsten oxide particles (WO3, WO2.97), and tungsten metal particles with SUF and PSF at 37°C and evaluate changes in asbestos fiber and non-fibrous particle physicochemical properties as the result of exposure to these solvents.



For Aim #5, we will determine the chemical dissolution rate constants of triplicate samples of "blue" tungsten oxide fiber materials WO2.82, WO2.72, and WO2.52 in the presence of cobalt particles (at a ratio of 90:10 by weight) with SUF and PSF at 37°C and evaluate changes in particle physicochemical properties as the result of exposure to these solvents.



Objectives

To investigate the hypothesis that tungsten oxide fibers are more persistent in the lung than non-fibrous tungsten-containing particles, the following five specific aims were developed:



1. Evaluate the physicochemical properties (morphology, surface area, density, chemical purity, crystallinity, and surface chemistry) of tungsten oxide fiber study materials ("blue" tungsten oxides with stoichiometries WO2.82, WO2.72, and WO2.52) and non-fibrous tungsten particles ("yellow" tungsten trioxide with stoichiometry WO3, "blue" tungsten oxide with stoichiometry WO2.97, and tungsten metal).



2. Determine the relative solubility and biopersistence of tungsten oxide fibers in artificial human extracellular lung fluid and artificial human lung macrophage phagolysosomal fluid.



3. Compare the relative dissolution of individual tungsten oxide fibers to aggregated tungsten oxide fibers in artificial lung fluids.



4. Compare the solubility and biopersistence of tungsten oxide fibers in artificial lung fluids to industrially-important tungsten particles (non-fibrous morphology) and to a known biopersistent fibrous material (amphibole or chrysotile asbestos).



5. Determine if tungsten oxide fiber solubility and biopersistence is enhanced in the presence of cobalt, a common co-exposure material encountered during the manufacture of cemented tungsten carbides.



Result of these solubility and biopersistence experiments will: 1) provide a starting point for modeling potential tungsten oxide fiber toxicity in vitro and in vivo; 2) provide data to support scientific-based decision making regarding the solubility of specific suboxides of tungsten oxide fibers relative to tungsten-containing particles; and 3) help to understand the efficacy of current inhalation exposure limits for non-fibrous tungsten forms (oxide, metal, carbide) for tungsten oxide fibers.



Mission Relevance

Tungsten is a dense metal that is used in a wide range of applications, including non-sag wire for filaments in light bulbs and in cemented tungsten carbides. During the production of tungsten metal powder for use as wire filaments or as feedstock for producing cemented carbides, aerosols may be generated which contain tungsten in the form of tungsten oxide fibers. The toxic potential of tungsten oxide in the forms of fibers is poorly understood; however, in one preliminary study of tungsten oxide fibers, the material generated toxic radicals. Thus, a primary question is whether tungsten oxide fibers contribute to development of occupational respiratory diseases, due in part to their persistence in the lung, for which current exposure limits for tungsten compounds are not protective.

To investigate the hypothesis that tungsten oxide fibers are more persistent in the lung than non-fibrous tungsten-containing particles, the following five specific aims were developed: 1) evaluate the physicochemical properties of tungsten oxide fiber study materials and non-fibrous (isometric) tungsten particles; 2) determine the relative solubility and biopersistence of tungsten oxide fibers in artificial human lung fluids; 3) compare the relative dissolution of individual tungsten oxide fibers to aggregated tungsten oxide fibers in artificial lung fluids; 4) compare the solubility and biopersistence of tungsten oxide fibers in artificial lung fluids to industrially-important tungsten particles and to a known biopersistent fibrous material (amphibole or chrysotile asbestos); and 5) determine if tungsten oxide fiber solubility and biopersistence is enhanced in the presence of cobalt, a common co-exposure material encountered during the manufacture of cemented tungsten carbides. Result of these solubility and biopersistence experiments will: 1) provide a starting point for modeling potential tungsten oxide fiber toxicity in vitro and in vivo; 2) provide data to support scientific-based decision making regarding the solubility of specific suboxides of tungsten oxide fibers relative to tungsten-containing particles; and 3) help to understand the efficacy of current inhalation exposure limits for non-fibrous tungsten forms (oxide, metal, carbide) for tungsten oxide fibers.



The aims of this project directly support the RDR cross-sector Intermediate Goal (09PPRDRIG2.3): prevent and reduce "fiber"-induced respiratory diseases.



Page last updated: June 3, 2011
Page last reviewed: May 23, 2011
Content Source: National Institute for Occupational Safety and Health (NIOSH) Office of the Director

 

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