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

The effects of Pb-chloride on the processes of nitrification and nitrogen mineralization
were studied in a 28-day experiment by Wilke (1989). The authors reported that nitrification
was increased by 12 and 16% at levels of 1000 and 4000 mg/kg, respectively, and that nitrogen
mineralization was reduced by 32 and 44% at concentrations of 1000 and 4000 mg/kg,
respectively.
The effects of Pb on arylsulfatase (Haanstra and Doelman, 1991) and urease activity
(Doelman and Haanstra, 1986) in soil were investigated. LC50s for decreases in arylsulfatase
activity were reported at Pb concentrations of 3004 and 4538 mg/kg in a silty loam soil, at pH 6
and 8, respectively. The LC50 for a decrease in urease activity was 5060 mg Pb/kg in a sandy
loam soil.
In laboratory microcosm studies Cotrufo et al. (1995) found that decomposition of oak
(Quercus ilex) leaf litter was reduced at elevated Pb (~20 mg Pb g !1 C) levels after 8 months
compared to controls (~2 mg Pb g !1 C). The researchers found soil respiration and amount of
soil mycelia correlated negatively with soil Pb, Zn and Cr concentration.
AX7.1.3.5 Summary
The current document expands upon and updates knowledge related to the effects of Pb
on terrestrial primary producers, consumers, and decomposers.
Primary Producers
The effects of Pb on terrestrial plants include decreased photosynthetic and transpiration
rates in addition to decreased growth and yield. The phytotoxicity of Pb is considered to be
relatively low, and there are few reports of phytotoxicity from Pb exposure under field
conditions. Recently, phytotoxicity data were reviewed for the development of the Eco-SSL
(U.S. Environmental Protection Agency, 2005b). Many of the toxicity data presented in the Eco-
SSL document (U.S. Environmental Protection Agency, 2005b) are lower than those discussed in
the 1986 Lead AQCD, although both documents acknowledged that toxicity is observed over a
wide range of concentrations of Pb in soil (tens to thousands of mg/kg soil). This may be due to
many factors, such as soil conditions (e.g., pH, organic matter) and differences in bioavailability
of the Pb in spiked soils perhaps due to lack of equilibration of the Pb solution with the soil after
spiking. Most phytotoxicity data continue to be developed for agricultural plant species (i.e.,
AX7-86