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

Source
Although the source of a metal is not directly related to bioavailability, it plays an
important role in risk assessment with the evaluation of metal (1) pathways, (2) background,
and (3) apportionment. It is important to understand a metal’s pathway before any remedial
action can be taken; otherwise, recontamination of the primary pathway and reexposure can
occur. Knowledge of background is important, as an action level cannot be established below
natural background levels.
Plants
When considering the bioavailability of a metal to plants from soils and sediments, it is
generally assumed that both the kinetic rate of supply and the speciation of the metal to either the
root or shoot are highly important. In soils and sediments generally, only a small volume of
water is in contact with the chemical form, and although the proportion of a metal’s
concentration in this pore water to the bulk soil/sediment concentration is small, it is this phase
that is directly available to plants. Therefore, pore water chemistry (i.e., metal concentration as
simple inorganic species, organic complexes, or colloid complexes) is most important.
Tools currently used for metal speciation for plants include (1) in-situ measurements
using selective electrodes (Gundersen et al., 1992; Archer et al., 1989; Wehrli et al., 1994);
(2) in-situ collection techniques using diffusive equilibrium thin films (DET) and diffusive
gradient thin films (DGT) followed by laboratory analyses (Davison et al., 1991, 1994; Davison
and Zhang, 1994; Zhang et al., 1995); and (3) equilibrium models ( SOILCHEM) (Sposito and
Coves, 1988).
AX7.1.1.3 Tools for Bulk Lead Quantification and Speciation
Bulk Quantification
The major analytical methods most commonly used for bulk analyses outlined in the 1986
Lead ACQD included:
• Atomic Absorption Spectrometry (AAS)
• Emission Spectrometry (Inductively coupled plasma/atomic emission spectrometry)
• X-ray Fluorescence (XRF)
• Isotope Dilution Mass Spectrometry (ID/MS)
AX7-9