Lead content in teeth of three Belgian populations with different exposures are considered in the framework of a three-compartment model describing lead exchanges in the body. The value of the first-order kinetic constant governing the transfer of lead from blood to teeth is shown to be approximately 1.85 yr-1, which is in good agreement with other studies using stable isotope tracers on a few subjects. Application of these findings to bones, where, contrary to teeth, remobilization processes cannot be neglected, leads to a tentative estimation of the rates of lead output from various kinds of bones, on the basis of epidemiologic data on their lead contents reported in the literature.

The level of lead exposure in industrial, urban, and rural populations has been evaluated by sampling permanent teeth gathered from three regions of Belgium. When tooth lead concentrations are plotted against tooth age, a linear function appears to fit the empirical results satisfactorily. On the contrary, comparing only the arithmetical means of the three samples would bring a possible bias of the results because their mean ages are different. The slope of the three best regression lines obtained respectively with data from the three regions increases significantly in the sequence rural < urban < industrial. A simplified mathematical model shows that this slope is directly related to the mean intake of lead under uniform exposure. It is suggested that this slope could be used as an index of the population's exposure to lead.The blood lead (Pb-B) or the free erythrocyte protoporphyrin (FEP) concentrations, or both, are the most commonly used indicators of lead exposure in population surveys. They have both been used to define a "no-effect" lead concentration for children's exposure or a threshold for undue lead absorption. This threshold value has been repeatedly adjusted downwards during the past 20 years as new data have become available on the epidemiology of subclinical effects of low chronic lead exposure.The blood lead concentration is an "instantaneous" indicator that reflects immediate exposure by giving a static picture of a dynamic process that includes intake, excretion, and tissue storage. Changing the conditions of exposure (or intake) leads to a Pb-B variation within about 28 days,' and it is not, therefore, a reliable index of long-term exposure.2 3 The rate at which the free erythrocyte protoporphyrin concentration in blood changes after cessation of exposure is not known.The concentration of lead in teeth, on the contrary, is a cumulative function of earlier exposure. This retrospective look allows the identification of undetected cases of undue lead absorption whenever other indices have returned to normal. In addition, the storage of lead in the teeth of primates has been shown to be dose-dependent.4 Low but continuous lead exposure will thus be shown by the tooth lead Material and methods SAMPLINGSince May 1978 131 permanent teeth, decayed and non-decayed, have been sampled at random from children and adults of both sexes undergoing treatment in private practices or dental schools in Brussels, Hoboken, and Arlon. Clinical data and inquiry cards indicated possible treatments undergone before extraction. Teeth filled with materials suspected to contain lead were discarded. Other information (age, sex, job, home, working or school address, time spent in each place) was noted in order to assess so far as possible sources of lead exposure and their respective contribution to the total exposure of each subject. ANALYSISThe teeth were ashed for 12 hours at 450°C, then crushed. The powders were ashed for a further four hours at the same temperature, then moistened for one hour. Finally, aft...

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