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

AX7.1.2.7 Summary
The current document expands upon and updates knowledge related to the uptake,
detoxification, physiological effects, and modifying factors of Pb toxicity to terrestrial
organisms.
Surface Deposition onto Plants
Recent work (Dalenberg and Van Driel, 1990; Jones and Johnston, 1991; Angelova et al.,
2004) has supported previous results and conclusions that surface deposition of Pb onto aboveground
vegetation from airborne sources may be significant (U.S. Environmental Protection
Agency, 1986a). Similarly, it has been well documented previously that Pb in soil also is taken
up by plants, although most remains in the roots, there is little translocation to shoots, leaves, or
other plant parts (U.S. Environmental Protection Agency, 1986a). More recent work continues
to support this finding (Sieghardt, 1990), and one study found increased tolerance in species with
bulbs, possibly due to the storage of Pb in the bulb (Wierzbicka, 1999).
Uptake Mechanism into Plants
Lead was thought previously to be taken up by plants via the symplastic route (through
cell membranes), although it was unknown whether some Pb also may be taken up via the
apoplastic route (between cells) (U.S. Environmental Protection Agency, 1986a). Recent work
has shown that the apoplastic route of transport is stopped in the primary roots by the endodermis
(Sieghardt, 1990), supporting the previous conclusion that the symplastic route is the most
significant route of transport into plant cells.
Species Differences in Uptake into Earthworms
Different species of earthworm accumulated different amounts of Pb, and this was not
related to feeding strategy (U.S. Environmental Protection Agency, 1986a). This is supported by
recent work, which has shown Aporrectodea accumulated more than Lumbricus (Terhivuo et al.,
1994; Pižl and Josens, 1995), although this is not consistently observed (Spurgeon and Hopkin,
1996a).
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