Plasma bone lead distribution

Because of its wide distribution in the body, biologic measures of lead dose in a nmnber of tissues—including blood, plasma, umbiUcal cord blood, hair, fingernails and toenails, breast ntilk, urine, semen, soft tissue, and bone— are available (see review by Hu et al. 2007). The excretion of lead in urine can be enhanced by CaNa2EDTA or DMSA, and chelatable lead has been used to estimate lead dose (Schiitz et al. 1987 Tell et al. 1992 Lee et al. 1995, 2000 Schwartz et al. 2001). Because CaNa2EDTA can partially chelate bone lead... 

Among the soft tissues, lead is distributed to the bone marrow, liver and kidney (Barry 1975, Skerfving etal. 1993). Lead does, to some extent, pass the blood-brain barrier into the nervous system and, according to animal experiments, such passage is most likely higher in infants than in adults (Mahaffey 1983). Distribution in the central nervous system (CNS) is uneven, with higher levels in the hippocampus and amygdala. Lead concentrations in the cerebrospinal fluid are very low, and seem to correlate positively with plasma lead concentrations rather than with B-Pb. 

Once absorbed from the intestines, lead enters the blood stream and is rapidly distributed throughout the body, to the erythrocytes, bones, and soft tissue (10). In adults, 90-95% of the total lead body burden is found in bone (5, 435, 436), resulting in a mean level of 14 pg Pb/g of skeletal bone ash (14 ppm) in middle-aged adults in the United States today (27, 437) (Table XVI). In children, the percent of total body lead that resides in bone is closer to 70-80% (436). By contrast, lead concentrations in soft tissues are typically 0.5 ppm (438) and lead concentrations in brain are usually <0.2 ppm, with the highest levels being found in the hippocampus and frontal cortex (10). The average concentration of lead in whole blood for people in the United States in 1999 was 1.6 pg/dL (16 ppb) (18) 94—99% of blood lead is found in the erythrocytes and only 1-6% is in the plasma (10, 27). (Methods for the analysis of lead content in blood are discussed in Section Vl.E.)... 

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