Individual variation in response to lead exposure: a dilemma for the occupational health physician

Subclinical lead poisoning with no clinical symptoms is a dilemma for the occupational health physician. He is supposed to assess when and how to treat workers at risk mainly by the results of biological monitoring. The aim of this study was to demonstrate different responses of biological indices in 50 lead-exposed workers who have been working in the same plant of lead pigment production factory. Twenty-one had normal, that is, permissible blood lead concentrations (PbB), erythrocyte protoporphyrin (EP), and aminolevulinic acid activity (ALAD) measured during regular periodic examinations (group 1). No differences between two measurements were found, although they were continuously working with lead. In 18 of the 50 workers (group 2), PbB and EP concentrations increased, whereas ALAD activity decreased: those parameters improved after a 3- to 6-month cessation of lead exposure. Seven of the 50 workers also had altered values of biological indices, but their condition improved spontaneously without cessation of lead exposure (group 3), while in the remaining four workers, elevated concentrations of biological indices did not change during the observation period. The reasons for such discrepancies and indications for chelation therapy are discussed.