Air Quality Criteria for Lead Volume II of II - (NEPIS)(EPA) - US ...

T1/2 = 14 × 10 9 year). The result is that the ore bodies from which anthropogenic Pb are typically
derived are usually enriched in 207 Pb relative to 206 Pb and 208 Pb when compared with Pb found in
granitic rocks. Graney et al. (1995) analyzed a dated core from Lake Erie, and found that the
206 Pb/ 207 Pb value in sediment deposited in the late 1700s was 1.224, but in 20th-century
sediment, the ratio ranged from 1.223 to 1.197. This shift in the Pb isotopic composition
represents the introduction of a significant amount of anthropogenic Pb into the environment.
Bindler et al. (1999) and Emmanuel and Erel (2002) analyzed the isotopic composition of Pb in
soil profiles in Sweden and the Czech Republic, respectively, and determined that mineral soils
immediately below the organic horizon had a mixture of both anthropogenic and geogenic Pb.
Anthropogenic Pb has been detected relatively deep into the soil profile (>25 cm) in Europe,
presumably this represents very “old”( i.e., pre-1900) Pb (Steinnes and Friedland, 2005).
Erel and Patterson (1994) used radiogenic Pb isotopes to trace the movement of industrial
Pb from topsoils to groundwaters to streams in a remote mountainous region of Yosemite
National Park in California. They calculated that total 20th-century industrial Pb input to their
study site was approximately 0.4 g Pb m Γ2 . Lead concentrations in organic material were highest
in the upper soil horizons, and decreased with depth. During snowmelt, Pb in the snowpack was
mixed with the anthropogenic and geogenic Pb already in the topsoil, and spring melts contained
a mixture of anthropogenic and geogenic particulate Pb. During base flows, however, 80% of
the Pb export from groundwater and streams was from natural granite weathering (Erel and
Patterson, 1994).
Uranium-238 series 210 Pb also provides a tool for tracing atmospherically delivered Pb in
soils. After 222 Rn (T1/2 = 3.8 days) is produced from the decay of 226 Ra (T1/2 = 1600 years), some
fraction of the 222 Rn escapes from rocks and soils to the atmosphere. It then decays relatively
rapidly to 210 Pb (T1/2 = 22.3 years), which has a tropospheric residence time of a few weeks
(Koch et al., 1996). Fallout 210 Pb is deposited onto forests via wet and dry deposition, similar to
anthropogenic Pb deposition in forests, and is thus useful as a tracer for non-native Pb in soils.
Lead-210 is convenient to use for calculating the residence time of Pb in soil layers, because its
atmospheric and soil fluxes can be assumed to be in steady state at undisturbed sites (Dörr and
Münnich, 1989; Dörr, 1995; Kaste et al., 2003). Atmospheric 210 Pb ( 210 Pbex hereafter, 210 Pb in
“excess” of that supported by 222 Rn in the soil) must be calculated by subtracting the amount of
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