FREE ERYTHROCYTE PROTOPORPHYRIN AS AN INDICATOR OF BIOLOGICAL EFFECT OF LEAD IN ADULT MALES .3. BEHAVIOR OF FREE ERYTHROCYTE PROTOPORPHYRIN IN WORKERS WITH PAST LEAD-EXPOSURE

The relationship between FEP [free erythrocyte porphyrin] and the indicators of dose (PbB [blood Pb], PbU [urine Pb], PbU-EDTA) was examined in male subjects who had left Pb-exposuring jobs more than 12 mo. previously. FEP, PbB, FEP and PbU were correlated to a distinctly lower degree compared to previous findings in currently exposed subjects, although correlations were still statistically significant. In the previously exposed subjects erythrocyte metabolite displayed definitely higher values than those in currently exposed subjects at the same PbB or PbU levels. Close correlation was found between FEP and PbU-EDTA, as was found in exposed subjects. The regression curve assumed an identical profile in the 2 situations. FEP may persist at high levels for a long time after cessation of exposure due to a direct inhibition of heme synthetase caused by Pb released from tissue deposits. FEP proved a valid test for predicting the amount of Pb storage, even long after cessation of exposure.