LEAD - BIOLOGICAL MONITORING OF EXPOSURE AND EFFECTS

The dominant exposure sources of lead, an ubiguitously present metal, include, in many geographical regions, leaded gasoline, water, paint, and industrial emissions. These sources may cause exposure via inhalat ion and ingestion. At inhalation, 10-60% of the particles with a of si ze 0.01-5 mu m will be deposited in the alveolar region. Gastrointesti nal absorption in adults is similar to 10-20%. Lead accumulates in bon e and teeth. The skeleton contains >90% of the total body burden in ad ults, less in children. Turnover in bone is slow, the half-time in tra becular bone being similar to 1 year compared to decades in cortical b one. Other compartments in blood and soft tissues have a half-time of similar to 1 month. Excretion is mainly through urine and feces. Lead toxicity may affect several organ systems, e.g., the hematopoietic sys tem, the peripheral and central nervous system, the kidneys, the gastr ointestinal tract, the cardiovascular system, and the reproducytive sy stem. Lead is an animal carcinogen, but conclusive evidence for carcin ogenesis in humans is lacking. Lead determinations in blood (B-Pb) is presently the prevailing indicator of lead exposure and risk. However, serum/ plasma levels of lead may be more suitable as such an index, m ainly because of the nonlinearity of B-Pb in relation to both exposure and effects.Other, less frequently used indices include lead concentr ations in urine, mobilization tests, and disturbances of heme metaboli sm. During the last two decades in vivo determination of lead in bone, e.g., tibia, calcaneus, and finger bone, by X-ray fluorescence has be en used for biological monitoring of long-term exposure. Recent data i ndicate that there is an accumulation of lead in finger bone, which is related to both time of exposure and B-Pb. In a three-dimensional mod el, lead in finger bone and the exposure time may be used for retrospe ctive estimation of previous B-Pb, reflecting the historic lead exposu re. Such estimates will be of particular value in cross-sectional stud ies of long-term health effects in lead-exposed populations. J. Trace Elem. Exp. Med. 11:289-301, 1998. (C) 1998 Wiley-Liss, Inc.