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NIOSH Program Portfolio

 

Manufacturing

NORA Manufacturing Sector Strategic Goals

927Z6RW - Particle size-distribution and lead content in aerosol exposures from metal processing facilities

Start Date: 10/1/2006
End Date: 9/30/2009

Principal Investigator (PI)
Name: William Chisholm
Phone: 304-285-5977
E-mail: wec6@cdc.gov
Organization: NIOSH
Sub-Unit: HELD
Funded By: NIOSH

Primary Goal Addressed
5.0

Secondary Goal Addressed
8.0


Attributed to Manufacturing
100%

Project Description

Short Summary

The purpose of this research is to asses the standard closed face cassette (CFC) total dust personal sampler as a biologically relevant sampler of lead-containing aerosols in typical occupational exposures. This assessment will be useful to industrial hygiene practice in the Manufacturing Sector, the Exposure Assessment Cross-Sector, and the Cancer, Reproductive, and Cardiovascular Diseases Cross-Sector. The final outcome of this research will be recommendations in sampling procedures to meet the International Standards Organization (ISO) inhalable sampling conventions. The first intermediate outcome is to develop and publish an electron microscope method to measure particle size distributions, (nearly completed). Subsequent intermediate outcomes will be publications of measurements of particle size distributions of the filter catches and wall deposits of samples acquired at a selection of worksites.



Description

The overall purpose of this research is to contribute recommendations in sampling procedures to meet the International Standards Organization (ISO) inhalable sampling conventions. Specifically, the principal goal is to assess the standard closed face cassette (CFC) total dust personal sampler as a biologically relevant sampler of lead-containing aerosols in typical occupational exposures. To achieve this goal, it is necessary to accomplish two specific aims. First, a method to relate measurement of a particle's projected area in a scanning electron microscope image to its aerodynamic equivalent diameter will be developed. Second, the masses and particle size distributions of the filter catches and wall deposits of CFC and IOM samplers will be determined for both laboratory and field samples of lead-containing particles.

The method to relate measurement of a particle's projected area in a scanning electron microscope image to its aerodynamic equivalent diameter starts with assuming that radius estimated from the projected area equals the thickness of the particle. The density of each particle will be calculated from its chemical composition as determined by energy dispersive x-ray spectrometry (EDX). From the density and the spherical equivalent size, the aerodynamic equivalent diameter (AED) of each particle will be calculated. This method should work for all sizes of particles in the inhalable range, whereas the conventional method of direct measurement of AED using cascade impactors cannot distinguish particle sizes from 20µ through the upper limit of 100µ.

Validation of this approach is being done in the laboratory by generating an aerosol from a pure lead compound and characterizing its size distribution with the CFC and IOM samplers, a cascade impactor, and an aerodynamic particle sizing instrument. In the aerodynamic equivalent diameter (AED) range below 20µ, the cascade impactor and aerodynamic particle sizer instrument will provide size distribution data for validation of the particle size distributions determined from SEM-EDX data. For particles larger than 20µ, the size distribution will calculated by extrapolation of the calibration curve determined from the smaller size ranges. This component of the project is near completion.

The field study component of this research will characterize in detail the sampling efficiency of the CFC to lead-containing aerosols by exposing the CFC samplers to dusty atmospheres and analyzing separately the filter catch and wall deposits. Samples acquired simultaneously by an IOM sampler will be compared, assuming the IOM as a standard for inhalable particles. From measurements of relative mass fractions, particle size distributions, and lead contents of the wall and filter deposits, it can be determined if and when the wall deposit must be included to make CFC sampling biologically relevant to lead exposures. The field study worksites chosen for include a bronze foundry, a lead ore concentrate mill, a lead-acid battery recycler, a nickel battery recycler, and a primary copper smelter. Analysis of field samples will be finished in FY 2009.



Objectives

The overall purpose of this research is to contribute recommendations in sampling procedures to meet the International Standards Organization (ISO) inhalable sampling conventions. Specifically, the principal goal is to assess the standard closed face cassette (CFC) total dust personal sampler as a biologically relevant sampler of lead-containing aerosols in typical occupational exposures. To achieve this goal, it is necessary to accomplish two specific aims. First, a method to relate measurement of a particle's projected area in a scanning electron microscope image to its aerodynamic equivalent diameter will be developed. Second, the masses and particle size distributions of the filter catches and wall deposits of CFC and IOM samplers will be determined for both laboratory and field samples of lead-containing particles.

The method to relate measurement of a particle's projected area in a scanning electron microscope image to its aerodynamic equivalent diameter starts with assuming that radius estimated from the projected area equals the thickness of the particle. The density of each particle will be calculated from its chemical composition as determined by energy dispersive x-ray spectrometry (EDX). From the density and the spherical equivalent size, the aerodynamic equivalent diameter (AED) of each particle will be calculated. This method should work for all sizes of particles in the inhalable range, whereas the conventional method of direct measurement of AED using cascade impactors cannot distinguish particle sizes from 20µ through the upper limit of 100µ.

Validation of this approach is being done in the laboratory by generating an aerosol from a pure lead compound and characterizing its size distribution with the CFC and IOM samplers, a cascade impactor, and an aerodynamic particle sizing instrument. In the aerodynamic equivalent diameter (AED) range below 20µ, the cascade impactor and aerodynamic particle sizer instrument will provide size distribution data for validation of the particle size distributions determined from SEM-EDX data. For particles larger than 20µ, the size distribution will calculated by extrapolation of the calibration curve determined from the smaller size ranges. This component of the project is near completion.

The field study component of this research will characterize in detail the sampling efficiency of the CFC to lead-containing aerosols by exposing the CFC samplers to dusty atmospheres and analyzing separately the filter catch and wall deposits. Samples acquired simultaneously by an IOM sampler will be compared, assuming the IOM as a standard for inhalable particles. From measurements of relative mass fractions, particle size distributions, and lead contents of the wall and filter deposits, it can be determined if and when the wall deposit must be included to make CFC sampling biologically relevant to lead exposures. The field study worksites chosen for include a bronze foundry, a lead ore concentrate mill, a lead-acid battery recycler, a nickel battery recycler, and a primary copper smelter. Analysis of field samples will be finished in FY 2009.



Mission Relevance

The CDC and NIOSH Adult Blood Lead Epidemiology and Surveillance Program found that in 1998 that some 93 million persons (from 25 States reporting) had elevated blood lead concentrations. The CDC and NIOSH stated "Elevated blood lead levels in adults can damage the nervous, hematologic, reproductive, renal, cardiovascular, and gastrointestinal systems. The majority of cases are workplace-related." The OSHA permissible exposure limit (PEL) to lead dust was promulgated in 1978 and was based on a model relating worker blood lead levels to airborne lead exposure. The model includes average exposure concentration and years of exposure. It also includes lead particle size distribution by assuming that the first 12.5 µg/m3 of exposure are all particles of aerodynamic equivalent diameter (AED) less than one micrometer, and that 37% of these particles are deposited in the body with 100% efficiency. This model reflected conditions in battery manufacturing, but may not accurately describe conditions in other lead industries. Furthermore, there are known inconsistencies in the sampling of lead dust exposures with the widely used closed face cassette (CFC) sampler; Some procedures include the wall deposit with the filter catch, and others address only the filter catch. However, there are very little published data on the distinctions, if any, between the wall deposit and filter catch of the CFC. The most complete data comes from impactor measurements where all particles larger than 12.5 µm aerodynamic diameter fall in a single classification. In that case a single large particle of lead would determine the regulatory concentration, even though it may not be the most physiologically relevant. Given the paucity of relevant data, it was decided that a study to characterize the sizes of airborne lead dusts as sampled by the walls and filters of the CFC and Institute of Occupational Medicine (IOM) samplers in a selection of industries would be valuable.



The proposed research addresses the Manufacturing Sector's "Strategic Goal 5 (09PPMNFSG5): Reduce the number of respiratory conditions and diseases due to exposures in the manufacturing sector." This will occur because the results of this research will enable more accurate determination of lead exposures, which have been linked to numerous health problems." This research similarly addresses Strategic Goal 8 (09PPMNFSG8): Reduce the incidence of injuries, illnesses, and fatalities within specific sub-sectors and small businesses within the manufacturing sector." The particular manufacturing industries which expose workers to lead include ferruginous brass casting; battery recycling and manufacturing; and lead-tin solder manufacturing operations.



The proposed research will address Cancer, Reproductive, and Cardiovascular Sector Strategic Goal 5: Reduce the incidence and mortality of other chronic diseases, including (but not limited to), work-related neurologic (cerebrovascular) and renal disease," Improved measurement of lead exposures will enable accurate evaluation of controls to lead exposure, and hence reduce neurologic, renal, and other diseases associated with them.



The proposed research will result in publications about the use of closed face cassette sampling for lead dust exposures, responding to the Cross Sector Exposure Assessment's Intermediate Goal 2. Develop and evaluate new or improved methods for assessing exposure to workplace chemicals and occupational health stressors either singly or as mixtures, including both prospective and retrospective methods. More specifically, this research addresses 2.3 (09PPEXAIG2.3): Activity/Output 2.3.1 (09PPEXAAOG2.3.1): Development of new or improved methods to measure chemicals or other occupational hazards in the work environment.



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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Manufacturing