A study was undertaken to compare the susceptibility to lead of the heme biosynthetic pathway (blood lead concentration up to 60 μg/100 ml) of male and of female lead workers. At exposures of similar duration and intensity, adult non-pregnant women were more susceptible than men to some biological effects of lead as reflected by an earlier and larger increase of free erythrocyte protoporphyrin (FEP) and urinary δ-aminolevulinic acid (ALAU) levels at comparable blood lead concentrations (PbB). This sex-linked difference is not due to a relative iron deficiency in women (as reflected by plasma iron), since there is no correlation between the lead-induced FEP increase and plasma iron. There is also no correlation between plasma iron concentration and PbB. The most important finding is that at comparable PbB levels the exposed women excreted significantly more lead in urine (PbU) than did the exposed men. It has been hypothesized that sex hormones may influence the distribution of lead between erythrocytes and plasma, which most likely contains the more biologically active fraction of the metal. Preliminary results provided suggestive evidence that plasma lead concentration might be higher in lead-exposed women than in lead-exposed men. Investigation of the potential health significance of protoporphyrin accumulation is urgently needed in order to determine whether or not it must be considered in establishing a biological threshold limit value for lead exposure.
The second part of the paper reports a study of male lead workers, the majority of whom had had several courses of CaNa2-EDTA therapy in recent years. Comparison of the workers who had undergone chelation therapy and of untreated workers from the same plant demonstrated clearly that chelation therapy markedly altered the interrelationships of PbB, PbU, FEP, and ALAU.