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

or more severe flooding would likely result in increased inputs of Pb and other metals to
floodplain soils.
AX7.1.4.2 Effects of Lead Exposure on Natural Ecosystem Structure and Function
The effects of Pb exposure on natural ecosystems are confounded by the fact that Pb
exposure cannot be decoupled from other factors that may also affect the ecosystem under
consideration. Principal among these factors are other trace metals and acidic deposition.
Emissions of Pb from smelting and other industrial activities are accompanied by other trace
metals (e.g., Zn, Cu, and Cd) and sulfur dioxide (SO2) that may cause toxic effects independently
or in concert with Pb. Reductions in the use of alkyl-Pb additives in gasoline have resulted in
significant decreases in Pb deposition to natural ecosystems in the northeastern United States
(Johnson et al., 1995a). However, the period in which Pb deposition has declined (ca. 1975 to
the present) has also seen significant reductions in the acidity (i.e., increased pH) of precipitation
in the region (Likens et al., 1996; Driscoll et al., 1998). Therefore, changes in ecosystem Pb
fluxes may be the result of reduced Pb inputs and/or reduced acidity.
Experimental manipulation studies do not suffer from these confounding effects, because
Pb can be added in specific amounts, with or without other compounds. Unfortunately,
ecosystem-level manipulations involving Pb additions have not been undertaken. Therefore, we
must use observations from field studies of Pb behavior in sites exposed to various forms of Pb
pollution to assess the effects of Pb on terrestrial ecosystems. This section includes a discussion
of effects of Pb in the structure and function of terrestrial ecosystems. Effects on energy flows
(food chain effects) and biogeochemical cycling are discussed in Section AX7.1.5.3.
Sites Affected by Nearby Point Sources of Lead
Natural terrestrial ecosystems near smelters, mines, and other industrial plants have
exhibited a variety of effects related to ecosystem structure and function. These effects include
decreases in species diversity, changes in floral and faunal community composition, and
decreasing vigor of terrestrial vegetation.
All of these effects were observed in ecosystems surrounding the Anaconda smelter in
southwestern Montana, which operated between 1884 and 1980 (Galbraith et al., 1995). Soils in
affected areas around the Anaconda smelter were enriched in Pb, arsenic, copper, cadmium, and
AX7-95