Delayed appearance of tracer lead in facial hair

Three adult men were fed 204 Pb - a rare, stable isotope of lead - daily for about 100 days. Simultaneous blood and facial hair measurements of this tracer and of total lead concentrations were made by mass spectrometric isotope dilution analysis. Although the blood showed an immediate response to the intake of the tracer, the facial hair showed a more gradual response and a delay of approximately 35 days. Since the pattern of appearance of lead in hair does not appear to represent a simple time delay of blood lead concentration, the existence of a physiological pool of lead fed by the blood and giving rise to the content in hair is suggested. Hair lead values should, therefore, be interpreted as the integral of the blood lead values over the mean life of this intermediate pool - about 100 days.