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

and partitioning experiments. This technique has been particularly useful for quantifying the Kd,
or partitioning ratio of Pb in the solid-to-liquid phase (Kd = [total solid-phase metal in mg kg Γ1 ] /
[dissolved metal in mg L !1 ]). While the exact Kd value is a function of pH, organic matter
content, substrate type, total metal burden, and concentrations of competing ligands, such studies
typically show that Pb has very strong solid-phase partitioning. Partitioning ratios determined by
DPASV generally range from 10 3 to 10 6 in soils in the typical pH range (Sauvé et al., 2000b).
Aualiitia and Pickering (1987) used thin film ASV to compare the relative affinity of Pb for
different inorganic particulates. They reported that Mn(IV) oxides completely adsorbed the Pb,
regardless of pH in the range of 3 to 9, and had the highest affinity for Pb in their study. The
adsorption of Pb to pedogenic Fe-oxides, Al-hydroxides, clay minerals, and Fe ores was reported
to be pH-dependent. Sauvé et al. (1998) used DPASV to study the effects of organic matter and
pH on Pb adsorption in an orchard soil. They demonstrated that Pb complexation to dissolved
organic matter (DOM) increased Pb solubility, and that 30 to 50% of the dissolved Pb was bound
to DOM at pH 3 to 4, while >80% of the dissolved Pb was bound to DOM at neutral pH. They
concluded that in most soils, Pb in solution would not be found as Pb 2+ but as bound to DOM.
Sauvé et al. (2000a) compared the relative affinity of Pb 2+ for synthetic ferrihydrite, leaf
compost, and secondary oxide minerals collected from soils. They reported that the inorganic
mineral phases were more efficient at lowering the amount of Pb 2+ that was available in solution
than the leaf compost. Glover et al. (2002) used DPASV in studying the effects of time and
organic acids on Pb adsorption to goethite. They found that Pb adsorption to geothite was very
rapid, and remained unchanged after a period of about 4 h. Lead desorption was found to be
much slower. The presence of salicylate appeared to increase the amount of Pb that desorbed
from goethite more so than oxalate.
AX7.1.2.2 Tracing the Fate of Atmospherically-delivered Lead in Terrestrial Ecosystems
Radiogenic Pb isotopes offer a powerful tool for separating anthropogenic Pb from natural
Pb derived from mineral weathering (Erel and Patterson, 1994; Erel et al., 1997; Semlali et al.,
2001). This has been particularly useful for studying Pb in mineral soil, where geogenic Pb
often dominates. The three radiogenic stable Pb isotopes ( 206 Pb, 207 Pb, and 208 Pb) have a
heterogeneous distribution in the earth’s crust primarily because of the differences in the halflives
of their respective parents ( 238 U, T1/2 = 4.7 × 10 9 year; 235 U, T1/2 = 0.7 × 10 9 year; 232 Th,
AX7-31