Effect of repeated occupational exposure to lead, cessation of exposure, and chelation on levels of lead in bone

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Abstract
A sensitive K‐X‐ray fluorescence (K‐XRF) instrument was used to measure lead levels in the tibia and patella on a series of twelve subjects who had relatively well‐documented histories of lead exposure and blood lead levels. For some subjects, K‐XRF measurements were taken at multiple points in time, and before and after chelation with EDTA (ethylenediamine tetraacetic acid). Results confirm that K‐XRF measured bone lead levels correspond to cumulative blood lead indices and not to current blood lead levels. Moreover, the data suggest that bone lead levels; (1) correspond to urinary lead following the EDTA mobilization test unless previous chelation has occurred; (2) rise initially after lead exposure ceases and blood lead levels decrease, probably from redistribution from soft tissue, and then fall; and (3) do not decrease with a 3‐ to 5‐day course of therapeutic EDTA chelation. K‐XRF levels in the patella were noted to decrease more rapidly than levels in the tibia after cessation of lead exposure, a finding that probably reflects the greater turnover of lead in trabecular bone than in cortical bone.