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

Decomposers
Lack of decomposition has been observed as a particular problem around smelter sites.
Lead concentrations between 10,000 and 40,000 mg/kg soil can eliminate populations of
decomposer bacteria and fungi (U.S. Environmental Protection Agency, 1986a). Lead may
affect decomposition processes by direct toxicity to specific groups of decomposers, by
deactivating enzymes excreted by decomposers to break down organic matter, or by binding with
the organic matter and rendering it resistant to the action of decomposers.
Microorganisms are more sensitive than plants to Pb in soil. Delayed decomposition may
occur at between 750 and 7500 mg/kg soil (depending on soil type and other conditions).
Nitrification is inhibited by 14% at 1000 mg/kg soil.
U.S. Environmental Protection Agency Staff Review of 1986 Criteria Document
The EPA reviewed the 1986 Lead AQCD and presented an overall summary of
conclusions and recommendations (U.S. Environmental Protection Agency, 1990). The major
conclusion was that available laboratory and field data indicated that high concentrations of Pb
can affect certain plants and alter the composition of soil microbial communities. It was noted
that few field studies were available in which Pb exposures and associated effects in wildlife
were reported.
AX7.1.3.2 Recent Studies on the Effects of Lead on Primary Producers
Several studies published since 1986 have reported terrestrial plant exposure to Pb in soil,
many of which were reviewed during the development of the Eco-SSLs (U.S. Environmental
Protection Agency, 2005b). The relevant information from the Eco-SSL document (U.S.
Environmental Protection Agency, 2005b) is summarized below. A literature search and review
also was conducted to identify critical papers published since 2002, which is when the literature
search was completed for Eco-SSL development, and no new papers were identified as critical to
the understanding of Pb toxicity to terrestrial primary producers.
Effects observed in studies conducted since the 1986 Lead AQCD are similar to those
reported previously and include decreased photosynthetic and transpiration rates and decreased
growth and yield (U.S. Environmental Protection Agency, 2005b). The phytotoxicity of Pb is
considered relatively low, due to the limited availability and uptake of Pb from soil and soil
AX7-61