Exposure to Lead and its Particles Size Distribution

It has been recognized that particle size is a primary determinant of the inhalation and deposition of particulate matter in the human respiratory tract. In this regard, most aerosols have dual Threshold Limit Values (TLV), such as total and respirable particulate mass, in order to consider the difference in absorption due to particle size. It is generally accepted that measurements of airborne lead, an aerosol that could have a diverse size distribution, are taken by means of total mass sampling without particle size selective criteria. Although the Occupational Safety and Health Administration’s Permissible Exposure Limits (OSHA PEL), promulgated in 1978, have contributed to reductions of airborne lead concentrations since their adoption, workers’ exposure to lead in the workplace still remains a major occupational problem . Froines et al.(1986) demonstrated that OSHA PEL did not adequately take into account the effects of the size distribution of the lead aerosol on the absorption of lead. The OSHA model developed by Ashfold et al. was based on a theoretical particle size distribution of lead aerosols as predicted in lead-acid battery manufacturing. Several previous studies had reported that the particle size distribution assumed in the OSHA model was likely found to be incorrect for not only battery plants but also for primary smelter plants, capacitors, and lead powder plants. If the OSHA model was to be directly applied to the actual particle-size distributions, significantly lower levels of lead in the blood would be predicted for a given air lead exposure 5, 7, . It is known that fine lead particle fumes generated in high temperature operations are more easily absorbed into the body than coarse lead particles. Our previous work concluded that the contribution of respirable lead particles to lead absorption would be greater than that of PbA. The present study is designed to compare the size characteristics of lead particles generated in four major lead industries. Our ultimate aim is to suggest that measurement of the respirable fraction of lead is necessary. The specific objectives to obtain this were: 1) to evaluate the worker’s exposure to inhalable (Pb I ), thoracic (Pb T ), respirable (Pb R ) and fine lead particles smaller than 1 ≤ μm (Pb 1μ ), 2) to examine the difference between lead size fractions (Pb I , Pb T , Pb R and Pb 1μ ) with respect to PbA by industry and 3) to compare the relationship between PbA and fractions of lead size (Pb I , Pb T , Pb R and Pb 1μ ) in PbA by industry.