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

chloride and nitrate toxicity has not been found for earthworms (Neuhauser et al., 1985; Bongers
et al., 2004).
Rao et al. (2003) exposed the earthworm Eisenia fetida to Pb-oxide in an artificial soil
with a pH of 6 at the LC50 concentration of 11 mg/kg. Exposure for 14 days resulted in a number
of effects including body fragmentation, protrusions, rupture of the cuticle, etc. Many of these
effects may trigger defensive mechanisms. For example, fragmentation of the affected posterior
region was followed by regeneration and a new ectoderm layer was formed to cover affected
areas, both of which processes may serve to prevent soil bacteria from further affecting the
earthworm (Rao et al., 2003).
Effects on Microorganisms and Microbial Processes
Microorganisms and microbial processes were not included in the Eco-SSL development
process (see Attachment 1-2 of OSWER Directive 92857-55 dated November 2003 in U.S.
Environmental Protection Agency [2005a]). Many reasons were given, including that it is
unlikely that site conditions would only pose unacceptable risk to microbes and not be reflected
as unacceptable risks to higher organisms; that the significance of laboratory-derived effects data
to the ecosystem is uncertain; and that the spatial (across millimeter distances) and temporal
(within minutes to hours) variation makes understanding ecological consequences challenging.
Microbial endpoints often vary dramatically based on moisture, temperature, oxygen, and many
non-contaminant factors. Therefore, the recommendation arising from the Eco-SSL
development process was that risks to microbes or microbial processes not be addressed through
the chemical screening process but that they should be addressed within a site-specific risk
assessment (U.S. Environmental Protection Agency, 2005b).
Few studies on the effects of Pb to microbial processes have been published since 1986.
As the direct toxicity to fungi and bacterial populations are difficult to determine and interpret,
indicators for soil communities are often measured as proxies for toxicity (e.g., urease activity in
soil). Recent studies of this nature (Doelman and Haanstra, 1986; Wilke, 1989; Haanstra and
Doelman, 1991) are summarized in this subsection. The Pb concentrations in these recent
studies (1000 to 5000 mg/kg) are consistent with those reported in the 1986 Lead AQCD (U.S.
Environmental Protection Agency, 1986a) as associated with effects on microbial processes
(750 to 7500 mg/kg).
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