COMPARISON OF MEASURES OF LEAD-EXPOSURE, DOSE, AND CHELATABLE LEAD BURDEN AFTER PROVOCATIVE CHELATION IN ORGANOLEAD WORKERS

Objectives-To describe 6 h urinary lead excretion (6 h PbU) after 1 g intravenous ethylene diamine tetraacetic acid (EDTA) in organolead man ufacturing workers with mined exposure to organic and inorganic lead; to determine the predictors of lead excretion (PbU); and to determine the extent to which internal lead stores and ongoing external exposure govern blood concentrations of lead (PbB). Methods-A case series of 2 1 active workers were studied. Personal industrial hygiene data, group ed by 29 exposure zones, in combination with personal interviews about work location and times were used to derive several measures of recen t and cumulative exposure to organic and inorganic lead. The average e xposure intensities assigned to the 29 zones ranged from 4 to 119 mu g /m(3) (0.02-0.57 mu mol/m(3) as lead) for organic lead and from 1 to 5 6 mu g/m(3) (0.004-0.27 mu mol/m(3)) for inorganic lead. Results-After controlling for age, 6h PbU was significantly and positively correlat ed with summary measures of PbB-for example, lifetime peak PbB, time w eighted PbB-and zinc protoporphyrin concentrations-for example, lifeti me peak zinc protoporphyrin, time weighted zinc protoporphyrin-but not with measures of estimated external exposure-for example, duration of exposure and cumulative exposure to inorganic or organic lead. Among workers with higher chelatable lead burdens (6 h PbU greater than or e qual to 212.4 mu g (1.03 mu mol) divided at the median), there was no apparent relation between recent inorganic lead exposure and PbB at th e time of chelation. Among workers with lower chelatable lead burdens (6 h PbU < 212.4 mu g (1.03 mu mol) however, there was a significant r elation between exposure and effect between recent exposure to inorgan ic lead and PbBs. Conclusion-These findings are consistent with the co ncept of physiological dampening. The high chelatable lead burden, a s ource of internal exposure, dampens the effect of external exposure on PbBs. The data suggest that in organolead workers with high chelatabl e lead burdens, PbBs may be more influenced by internal lead stores th an by variations in airborne organic and inorganic lead.