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

to 15 years after biosolid application. The increase in metal transport is likely the result of
elevated dissolved organic carbon (DOC) in the amended soil. Anodic stripping voltammetry
has indicated that very low percentages (2 to 18%) of the soluble metals are present as ionic or
inorganic complexes (McBride, 1999; Al-Wabel et al., 2002).
AX7.1.2 Distribution of Atmospherically Delivered Lead in
Terrestrial Ecosystems
The 1986 Lead AQCD (U.S. Environmental Protection Agency, 1986a) contains only a
few minor sections that detail the speciation, distribution, and behavior of atmospherically
delivered Pb in terrestrial ecosystems. The document concluded that the majority of Pb in the
atmosphere at that time was from gasoline consumption: of the 34,881 tons of Pb emitted to the
atmosphere in 1984, 89% was from gasoline use and minor amounts were from waste oil
combustion, iron and steel production, and smelting. Lead in the atmosphere today, however, is
not primarily from leaded-gasoline consumption, but results largely from iron and steel
foundaries, boilers and process heaters, the combustion of fossil fuels in automobiles, trucks,
airplanes, and ships, and other industrial processes (Table 2-8, Polissar et al., 2001; Newhook
et al., 2003). The emission source can determine the species of Pb that are delivered to terrestrial
ecosystems. For example, Pb species emitted from automobile exhaust is dominated by
particulate Pb halides and double salts with ammonium halides (e.g., PbBrCl, PbBrCl2NH4Cl),
while Pb emitted from smelters is dominated by Pb-sulfur species (Habibi, 1973). The halides
from automobile exhaust break down rapidly in the atmosphere, possibly via reactions with
atmospheric acids (Biggins and Harrison, 1979). Lead phases in the atmosphere, and
presumably the compounds delivered to the surface of the earth (i.e., to vegetation and soils),
are suspected to be in the form of PbSO4, PbS, and PbO (Olson and Skogerboe, 1975; Clevenger
et al., 1991; Utsunomiya et al., 2004).
There are conflicting reports of how atmospherically derived Pb specifically behaves in
surface soils. This disagreement may represent the natural variability of the biogeochemical
behavior of Pb in different terrestrial systems, the different Pb sources, or it may be a function of
the different analytical methods employed. The importance of humic and fulvic acids (Zimdahl
and Skogerboe, 1977; Gamble et al., 1983) and hydrous Mn- and Fe-oxides (Miller and McFee,
1983) for scavenging Pb in soils are discussed in some detail in the 1986 Lead AQCD. Nriagu
AX7-22