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

Pb is ideally suited for this task. Lead isotopic ratio differences often allow multiple sources to
be distinguished, with an apportionment of the bulk Pb concentration made to those sources.
Lead has four stable isotopes: 204 Pb, 206 Pb, 207 Pb, and 208 Pb in natural abundances of 1.4,
24.1, 22.1, and 52.4%, respectively. The radiogenic 206 Pb, 207 Pb, and 208 Pb are produced by
radioactive decay of 238 U, 235 U, and 232 Th, respectively. Thus, the isotopic composition of Pb
varies based on the U:Pb and Th:Pb ratios of the original ore’s source and age (Faure, 1977).
Because of the small fractional mass differences of the Pb isotopes, ordinary chemical and
pyrometallurgical reactions will not alter their original composition. Therefore, anthropogenic
sources reflect the isotopic composition of the ores from which the Pb originated.
To acquire the Pb isotopes, a sample, generally in aqueous form, is analyzed on an
ICP/MS (quadrapole, magnetic sector, or time-of-flight). Studies reviewing the most common
analytical and sample preparation procedures include Ghazi and Millette (2004), Townsend et al.
(1998), and Encinar et al. (2001a,b). The correction factor for mass discrimination biases is
generally made by analyzing the National Institute for Standards and Technology (NIST),
Standard Reference Material (SRM) 981 and/or spiked 203 Tl and 205 Tl isotopes (Ketterer et al.,
1991; Begley and Sharp, 1997). The overall success of Pb isotope fingerprinting is generally
dependent on analysis precision, which in turn depends on the type of mass analyzer used
(Table AX7-1.1.1).
Table AX7-1.1.1. Relative Standard Deviation (RSD) for Lead Isotope
Ratios on Selected Mass Spectrometers
Single-Focusing
High-Resolution
Magnetic Sector
RSD Quadrapole Double-Focusing Magnetic Sector
ICP/MS
204 206
Pb: Pb 0.0031 0.0032 0.00053 0.0011
207 Pb: 206 Pb 0.0032 0.0027 0.00053 0.00048
208 Pb: 206 Pb 0.0026 0.0024 0.00053 0.00046
An extensive database comprising primarily North American Pb sources can be assembled
from Doe and Rohrbough (1977), Doe and Stacey (1974), Doe et al. (1968), Heyl et al. (1974),
AX7-2