Determination of blood‐lead elimination patterns of primary lead smelter workers

Abstract

Data for peripheral blood‐lead (PbB) levels for workers of four primary lead smelters in the United States were analyzed to characterize the patterns of PbB elimination. These workers had been removed from their job under the Medical Removal Protection (MRP) provision of the lead standard promulgated in 1978 by the Occupational Safety and Health Administration (OSHA). For each individual removed under the first or second year of the MRP provision, data for blood‐lead levels in relation to length of time removed were applied to four separate mathematical models, namely, linear regression, power curve fit, exponential curve fit, and logarithmic curve fit. The best model was determined by comparing overall correlation coefficients squared (r²) values derived from each model. Separate analyses were also made to test the relationship of PbB elimination rates to PbB levels at the time of the removal, length of occupational lead exposure, and job category. In addition, the duration of the medical removal time under the third‐year MRP provision for the primary lead smelter workers was estimated on the basis of the mathematical model that best fit the data. Based on analysis of data derived from MRP: (1) The exponential model (first‐order kinetics) most consistently and with the highest degree of correlation described PbB elimination patterns while workers were on MRP. (2) No significant relationship was observed between the rate of PbB decrease and (a) the length of employment prior to removal, (b) the preremoval PbB level, or (c) the job categories (skilled versus less skilled employees). (3) The necessary time period for medical removal under a 60/40 trigger would range from 2 to 4 mo for 50% of those removed and from 3 to 6 mo for 80% of those removed. These estimates are in general agreement with OSHA's 1978 estimate and with recent estimates by others.