NORA Manufacturing Sector Strategic Goals
927Z6RT - Welding fume metals exposure matrix determinationStart Date: 10/1/2006
End Date: 9/30/2009
Principal Investigator (PI)Name: Michael Keane
Funded By: NIOSH
Primary Goal Addressed5.0
Secondary Goal Addressed6.0
Attributed to Manufacturing75%
This project addresses the health effects of welding, an important activity in both the Manufacturing and Construction Sectors of the NIOSH Program Portfolio. The objectives of the project include detailed speciation of manganese and chromium forms in the fumes, and investigation of the biologically available metals in simulated biological fluids. This approach will be applied to a spectrum of welding processes including the use of alternate shield gases of higher and lower oxygen content to estimate the effect on toxic entities such as hexavalent chromium and oxidized manganese species. Metal ion content in simulated plasma, lysosomal fluid, and simulated pulmonary surfactant will be measured. Outputs will include peer-reviewed publications, presentations, close collaboration with ongoing toxicology studies already in progress, and communications with welding equipment manufacturers.
The fundamental hypothesis of this project is that all welding fumes are not equivalent, neither from a perspective of exposure composition nor from a disease potential perspective, and a complex exposure assessment strategy is needed to adequately characterize welding fume exposures. The approach will be a general exposure assessment strategy that includes measures of welding fume beyond mass and elemental composition, and will focus on speciation of manganese chemical forms and chromium forms, which are the elements of greatest concern in regard to disease resulting from exposure, namely cancer and neurological disease. In addition to elemental composition and Mn and Cr speciation, the bioavailable levels of metals, including Fe, Ni, Mn, and Cr will be estimated using simulated plasma solutions and simulated lysosomal and pulmonary surfactant fluids. Chemical speciation for Mn will follow the scheme of Thomassen et al., which extracts a soluble fraction, an acetic-acid soluble fraction, and acetic acid/hydroxylamine fraction, and an aqua regia/HF fraction for insoluble Mn alloys, etc. Chromium forms will use solid-phase extraction to separate trivalent Cr from hexavalent Cr, using NIOSH method 7703 adapted for this study, followed by UV-visible spectrophotometry; soluble and insoluble chromium (VI) will be determined. Following Mn and Cr speciation, bioavailable metals will be measured in simulated plasma, a simulated lysosomal fluid, and a simulated pulmonary surfactant. Levels of bioavailable metals will be measured by inductively-coupled plasma/atomic emission spectroscopy (NIOSH method 7300), and Fe, Mn, and Ni solubles will be measured by ion chromatography. This should yield realistic estimates of soluble metal ions in different biological milieu, to inform toxicologists and similar researchers in experimental design. Fluoride content will be measured using ion-selective electrodes, by adapting NIOSH method 7902.
1) Identify and obtain welding fume samples from gas metal arc stainless steel and mild steel processes, and manual metal arc stainless steel processes,
Sector allocations were determined by statistics from the US Dept. of Labor industry population figures. Welding is a very common occupational activity in the US; over 800,000 workers do welding as part of their jobs. Occupational health studies indicate that welders have a high pneumoconiosis (SMR=1.86), and lung cancer (SMR=1.21) death rates; pulmonary function decrements are also associated with welding. A number of studies that have attempted to link welding fume exposures and Parkinson's-like neurological conditions that have been seen in manganese miners and workers, generally called manganism. There have been negative studies on this issue as well as positive ones, and the linkage is controversial at this time. As for manganism in general, the exact causative Mn forms are not well understood. Welding is associated with a number of industrial sectors, including construction and manufacturing, and a wide variety of processes are used, depending on needs, materials, and costs. As well as steel, many other materials are welded, including stainless steel, alloys, aluminum, titanium, and specialty metals. The diversity of metals and processes necessitates a thorough and complex exposure assessment to assure sufficient and competent understanding of the hazards and successful intervention strategies. For example, chromium may be present in stainless steel welding fume in the carcinogenic hexavalent form, may be soluble or insoluble, or may be in the noncarcinogenic form of trivalent Cr. Likewise, manganese in welding fume may be present as the element, as MnO, Mn2O3, Mn3O4, as MnO2, or other chemical forms in the fume; which of these forms contributes to manganism is not known at present. The current analyses for Mn are for total elemental Mn at highly acidic pH; this is not likely to be uniquely related to biologically relevant Mn. The approach will be to measure elemental composition and Mn and Cr speciation in different fumes; the bioavailable levels of metals, including Fe, Ni, Mn, and Cr will be estimated using simulated plasma solutions and simulated lysosomal and pulmonary surfactant fluids. The fumes will be selected based on common processes. One variable will include the oxygen content of shield gas for Gas Metal Arc Welding (GMAW). This may lead to recommendations on shield gas composition to lower the concentration of toxic species.