Biological monitoring of workers with past lead exposure. Biochemical findings.

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Abstract
In 56 subjects with Pb exposure that had terminated at least 3 yr previously and in a reference group of nonexposed subjects, the behavior of several biochemical indicators of dose and effect were studied. The mean values for blood Pb (PbB) (1.4 .+-. 0.4 .mu.mol/l), chelatable Pb (PbUEDTA) (3.4 .+-. 1.5 .mu.mol/24 h) and free erythrocyte protoporphyrin (FEP) (62 .+-. 25.2 .mu.g/100 ml red blood cells) were significantly higher in the subjects with past Pb exposure. The cut-off levels (mean + 2 SD calculated for the reference group) of PbB, PbUEDTA and FEP were exceeded in 35.7, 67.9 and 28.6% of the exposed subjects, respectively. A normalization of Pb doses and indicators of effect was reached only when the exposure had not exceeded 2 yr. The time elapsed after termination of exposure did not significantly reduce the PbB level and PbUEDTA excretion; these parameters correlated significantly with the length of exposure. A close correlation was found between the PbB and the PbUEDTA. Due to poor sensitivity at PbUEDTA values < 5.3 .mu.mol/24 h (91% of the cases), PbB and FEP were not useful for subjects whose exposure had terminated > 3 yr earlier. In these cases, only PbUEDTA was capable of revealing elevated active Pb deposits.