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

organism responses to Pb. Section AX7.1.4 outlines and highlights the critical recent
advancements in the understanding of the toxicity of Pb to terrestrial organisms. This section
begins with a summary of the conclusions from the 1986 Lead AQCD (U.S. Environmental
Protection Agency, 1986a) and then summarizes the more recent critical research conducted on
effects of Pb on primary producers, consumers, and decomposers. All concentrations are
expressed as mg Pb/kg soil dw, unless otherwise indicated.
Lead exposure may adversely affect organisms at different levels of organization, i.e.,
individual organisms, populations, communities, or ecosystems. Generally, however, there is
insufficient information available for single materials in controlled studies to permit evaluation
of specific impacts on higher levels of organization (beyond the individual organism). Potential
effects at the population level or higher are, of necessity, extrapolated from individual level
studies. Available population, community, or ecosystem level studies are typically conducted at
sites that have been contaminated or adversely affected by multiple stressors (several chemicals
alone or combined with physical or biological stressors). Therefore, the best documented links
between lead and effects on the environment are with effects on individual organisms. Impacts
on terrestrial ecosystems are discussed in Section 7.1.5 and Annex AX7.1.5.
The summary of recent critical advancements in understanding toxicity relies heavily on
the work completed by a multi-stakeholder group, consisting of federal, state, consulting,
industry, and academic participants, led by the EPA to develop Ecological Soil Screening Levels
(Eco-SSLs). Eco-SSLs describe the concentrations of contaminants in soils that would result in
little or no measurable effect on ecological receptors (U.S. Environmental Protection Agency,
2005a). They were developed by the U.S. EPA for use in screening-level assessments at
Superfund sites to identify contaminants requiring further evaluation in an ecological risk
assessment and were not designed to be used as cleanup target levels. The Eco-SSLs are
intentionally conservative in order to provide confidence that contaminants, which could present
an unacceptable risk, are not screened out early in the evaluation process. That is, at or below
these levels, adverse effects are considered unlikely. Eco-SSLs were derived for terrestrial
plants, soil invertebrates, birds, and mammals. Detailed procedures using an extensive list of
acceptability and exclusion criteria (U.S. Environmental Protection Agency, 2005a) were used in
screening the toxicity studies to ensure that only those that met minimum quality standards were
used to develop the Eco-SSLs. In addition, two peer reviews were completed during the
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