The effect of lead-in-air particle size on the lead-in-blood levels of lead-acid battery workers.

The relationship of lead-in-blood (PbB) to lead-in-air (PbA), both with and without consideration of lead aerosol particle size distribution, was examined among 132 lead-acid battery workers with repeated measures over a 30-month period. Longitudinal analyses suggested that PbB levels of a subset of workers with high plant seniority were elevated by past elevated PbA exposures five or more years prior to the study. For workers not exhibiting the effect of past exposure, the slope of the PbB-PbA relationship was 1.50, i.e., PbB ($\mu$g/dl) = 1.50PbA ($\mu$g/m3), a value well above previously reported sloped from other battery plant studies. This difference may be attributable to the relatively low PbA levels (10-20 $\mu$g/m3) seen in this study as compared to the other studies. For workers exhibiting a PbB-PbA relationship, a longitudinal exposure estimate, a modified 30-month PbA arithmetic mean, was found to be a superior predictor of PbB level over any five separate cross-sectional exposure estimates evaluated. The use of the deposition models which fractionated the PbA into portions expected to ultimately be respirable or ingestible resulted in a 25% improvement in the coefficient of determination (R$\sp2$) for PbB over that attributable to only total PbA. In oral inhalation models, the ratio of the coefficients for the respirable to ingestible fractions (range 9.9 to 14.4) appeared to be consistent with the published experimental data. Other findings of interest included: (1) In contradiction to the size distribution model used by the U.S. Government in the selection of the current permissible exposure limit for lead, only the first 1.0 $\mu$g/m3 of PbA, rather than the first 12.5 $\mu$g/m3, was $<$1.0 $\mu$m in aerodynamic diameter (considered "respirable" in the model). (2) Despite the presence of hydroscopic sulfuric acid, the battery plant lead aerosol size distributions did not vary over the environmental relative humidity ranges of 12 to 69%. (3) Fibrous material, collected on cascade impactor stages associated with alveolar deposition, appeared more likely to deposit higher in the respiratory tree based on morphology studies under scanning electron microscopy.