Dorothy M. Settle

Magnitude of lead flux to the atmosphere from volcanoes

Pb/S, Tl/S and Bi/S ratios were measured in eruptive and fumarolic volcanic gases and indexed to the global flux of volcanic S to characterize approximate global volcanic emissions of these three metals to the atmosphere, which are about 1200 tons Pb/yr, 600 tons Tl/yr, and 4000 tons Bi/yr. This volcanic Pb input is similar to the magnitude of natural soil dust Pb input, which is about 1400 tons Pb/yr during the Holocene Interglacial. Both are negligible compared to annual industrial inputs of ~ 300,000 tons Pb/yr which maintain the present tropospheric reservoir of Pb. However, polar ice records indicate that thousands of years ago the atmospheric Pb reservoir was only ~ 1% of its present size, which means that volcanic Pb was the source of about half the Pb in the atmosphere during preindustrial Holocene times.

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 x 10(-5) in rib, ulna, and tooth enamel; and Ba/Ca (wt) = 2.4, 2.4, and 1.8 x 10(-5) in rib, ulna, and tooth enamel, respectively. Mean concentrations of Pb were 11, 19, and 14 micrograms g-1 in rib (ash), ulna (ash), and enamel (dry), respectively. Means for Ba were 8.7, 8.9, and 6.4 micrograms 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.