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

They found that repeated extractions with Na4P2O7 removed between 60 and 100% of the Pb
from their samples. Caution should be used when interpreting the results of pyrophosphate
extractions. Although they are often used to quantify organically bound metals, this reagent can
both disperse and dissolve Fe phases (Jeanroy and Guillet, 1981; Shuman, 1982). Acidified
H2O2 has also been reported to destroy and release elements associated with secondary soil
minerals (Papp et al., 1991; Ryan et al., 2002).
Aside from organic forms, Pb is often found to be associated with secondary oxide
minerals in soils. Pb can be partitioned with secondary oxides by a variety of mechanisms,
including (1) simple ion exchange, (2) inner-sphere or outer-sphere adsorption, and (3) co-
precipitation and/or occlusion (Bargar et al., 1997a,b, 1998, 1999). As discussed above, very
little Pb is removed from soil via dilute acid or salt solutions, so adsorption and co-precipitation
are likely the dominant Pb interactions with secondary mineral phases. Reagents used to
quantify this phase are often solutions of EDTA, oxalate, or hydroxylamine hydrochloride (HH).
Miller and McFee (1983) used an EDTA solution followed by an HH solution to quantify Pb
occluded by Fe and Mn minerals, respectively, in their surface-soil samples from Indiana. They
reported that approximately 30% of the total soil Pb was occluded in Fe minerals, and 5 to 15%
was occluded in Mn phases. In soils from the northeastern United States, Jersak et al. (1997)
used various strengths of HH solutions and concluded that negligible Pb was associated with
Mn-oxides and that 1 to 30% of the Pb was associated with Fe phases in the mineral soils in their
study. Johnson and Petras (1998) reported that no Pb was removed from the Oa horizon at the
Hubbard Brook Experimental Forest (HBEF) by oxalate, but that 5 to 15% of the total Pb in
mineral soils was removed by this extraction, presumably because it was bound to amorphous
oxide minerals. Kaste et al. (2005), however, reported that HH removed 30 to 40% of the Pb
from organic horizons in their study. They concluded that Fe phases were important in
scavenging Pb, even in soil horizons dominated by organic matter.
Synchrotron radiation (X-rays) allows researchers to probe the electron configuration of
metals in untreated soil and sediment samples. This type of analysis has been extremely valuable
for directly determining the coordination environment of Pb in a variety of soils and sediments.
Since different elements have different electron binding energies (Eb), X-rays can be focused in
an energy window specific to a metal of interest. In experiments involving XAS, X-ray energy is
increased until a rapid increase in the amount of absorption occurs; this absorption edge
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