Lead concentrations and isotopic ratios in the sediments of the Sea of Galilee.

The isotopic composition and concentrations of Pb in the sediments of the Sea of Galilee (Lake Kinneret) were measured. The studied sediments have been deposited in the lake since the early 1900s (ca. 1920), hence Pb data record the transition from a period when the lake vicinity was sparsely populated to the present (approximately 100,000 people living in the area around the lake). In general, there is either a constant or a relatively slow increase in Pb concentrations from 40 cm depth (3.5-4.4 microg/g; ca. 1920) to 17 +/- 2 cm below the sediment-water interface (3.7-7.2 microg/g;), which was deposited in the mid-1960s. From 17 +/- 2 cm below the surface, there is a much faster increase up to 7 +/- 2 cm below the surface (from 6.5 to 11.5 microg/g; 1982-1983), and from 7 +/- 2 cm there is a gradual decrease in Pb concentrations toward the sediment-water interface. At station G, near the outlet of the Jordan River, Pb concentrations drop between 29 and 25 cm below the surface, probably reflecting changes in the particulate load of the Jordan River due to the drying out of the Hula Swamp in the early 1950s. 206Pb/207Pb values in all the stations record most of the shifts displayed by Pb concentrations in the sediment. The estimated value of total Pb deposited annually in the lake sediment in the early 1990s is very close to the value obtained from measurements of Pb fluxes to the lake from eolian and fluvial sources. On the basis of the linear relationship between 206Pb/207Pb (or 208Pb/207Pb) and 1/[Pb], we argue that two end-members contribute most of the Pb to the lake sediments. Sources of Pb to the lake include (i) the weathering of basalt from the eastern Galilee and the Golan Heights contributing 2.6 +/- 0.5 microg/g Pb to the sediment and (ii) anthropogenic Pb that is affecting both surface and deep (from 30 to 40 cm) lake sediments. At station S, a third source, Pb released from soils developed on carbonates, should be considered as well.

Mechanisms and velocities of anthropogenic Pb migration in Mediterranean soils.

The isotopic composition of Pb measured in soil samples was used to determine rates and mechanisms of anthropogenic Pb migration in the soil. Petrol-Pb found in soluble halogenated aerosols migrates into the soil and is retained in the soil by the stationary soil particles. Lead infiltration velocity is approximately 5 x 10(-1) cm/year, and its retardation factor is estimated to be on the order of 1 x 10(3). The infiltration of Pb into the soil is best described by the advection-dispersion equation under the assumption that the time scale of the longitudinal dispersion is much longer than the time scale of advection. Therefore, the contribution of dispersion to the solution of the advection-dispersion equation is negligible. As a result, the soil profile of petrol-Pb resembles the time-dependent input function of petrol-Pb. The estimated petrol-Pb penetration velocity and the isotopic composition profile of Pb in off-road soil are used for the computation of the fraction of anthropogenic Pb in this soil. It is calculated that the fraction of anthropogenic Pb in the acid-leached soil samples and in the soil residue of this soil profile drops from 60 and 22% near the surface to 6 and 0% at a depth of 33 cm, respectively. The downward migration velocity of Pb in soils of the studied area, which are typically 50 to 100 cm deep, implies a residence time of Pb in the soil of 100 to 200 years.

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.