Natural skeletal levels of lead in Homo sapiens sapiens uncontaminated by technological lead

Lead, Ba and Ca concentrations were determined in tooth enamel, femur and rib from buried skeletons of PreColumbian Southwest American Indians, 10 subjects who lived 1000 years ago on the Pacific coast at 34°N, and 13 subjects who lived 700 years ago in a desert valley tributary of the Colorado River at 37°N 111°W, both groups living in environments uncontaminated by technological Pb. For the coastal tribe, average Pb/Ca ratios were 1.1 × 10^(−7) in enamel, 2.3 × 10^(−7) in femur and 4.7 × 10^(−7) in rib, while Ba/Ca ratios were 1.2 × 10^(−5) in enamel, 32 × 10^(−5) in femur and 38 × 10^(−5) in rib (wt ratios). For the desert tribe, average Pb/Ca ratios were 4 × 10^(−7) in enamel, 11 × 10^(−7) in femur and 37 × 10^(−7) in rib, while Ba/Ca ratios were 1.1 × 10^(−5) in enamel, 7.5 × 10^(−5) in femur and 6.2 × 10^(−5) in rib. It is shown that biologic levels of Pb and Ba in buried femur and rib at both burial sites and in buried enamel at the Arizona site are obscured by excessive diagenetic additions of Pb and Ba from soil moisture. It is shown that one-third of the Pb in enamel at the Malibu site is biologic, yielding a skeletal Pb/Ca (wt) ratio of 4 × 10^(−8). This is equivalent to a mean skeletal concentration of 13 ng Pb g^(−1) bone ash, and a mean natural body burden of 40 μg Pb/70 kg adult Homo sapiens sapiens, uncontaminated by technological Pb. This value is about one-thousandth of the mean body burden of 40 mg industrial Pb/70 kg adult American today, which indicates the probable existence within most Americans of dysfunctions caused by poisoning from chronic, excessive overexposures to industrial Pb

Comparative increases of lead and barium with age in human tooth enamel, rib and ulna

Lead and Ba in postmortem tooth enamel, rib and ulna of six contemporary people (67–96 years; ave. 80) were shown to exhibit similar accumulations with age in the three different types of osseous tissue: Pb/Ca (wt) = 3.0, 5.2, and 3.9 × 10^(−5) in rib, ulna, and tooth enamel; and Ba/Ca (wt) = 2.4, 2.4, and 1.8 × 10^(−5) in rib, ulna, and tooth enamel, respectively. Mean concentrations of Pb were 11, 19, and 14 μg g^(−1) in rib (ash), ulna (ash), and enamel (dry), respectively. Means for Ba were 8.7, 8.9, and 6.4 μg g^(−1) in rib (ash), ulna (ash), and enamel (dry), respectively. Comparison of Ba in ulna of our 80-year-old subjects with Ba determined by other investigators in bones of younger contemporary populations indicated that Ba accumulates with age at about half the rate of Pb accumulation in bone. Concentrations of Ba in rib, ulna and enamel were positively correlated and similar within an individual, but varied among subjects in proportion to variations in absorptive uptake in portal blood. Barium may diffuse from a blood-dentine source into enamel, where it replaces Ca and accumulates with age. Because of extreme Pb pollution of our 80-year-old subjects and its variation of intake with age, the correlation of Pb in tooth enamel with Pb in bone was more scattered than for Ba. It is shown by means of stable Pb isotopic tracers that: (i) among the three types of osseous tissue, the residence time of Pb is longest in enamel, where it apparently accumulates with age by diffusion with little loss through exchange; and (ii) the residence time of Pb is longer in compact ulna than in trabecular rib, as it accompanies Ca in its osteoblastic transfer from blood to bone and then in its osteoclastic transfer back to blood from bone