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

ecosystems. Just as in the terrestrial environment, the speciation of Pb and other trace metals in
natural freshwaters and seawater plays a crucial role in determining their reactivity, mobility,
bioavailability, and toxicity. Many of the same speciation techniques employed for the
speciation of Pb in terrestrial ecosystems (see Section AX7.1.1 and AX7.1.2) are applicable in
aquatic ecosystems.
There is now a better understanding of the potential effects of sampling, sample handling,
and sample preparation on aqueous-phase metal speciation. Thus, a need has arisen for dynamic
analytical techniques that are able to capture a metal’s speciation, in-situ and in real time. Some
of these recently developed dynamic trace metal speciation techniques include:
• Diffusion gradients in thin-film gels (DGT)
• Gel integrated microelectrodes combined with voltammetric in situ profiling
(GIME-VIP)
• Stripping chronopotentiometry (SCP)
• Flow-through and hollow fiber permeation liquid membranes (FTPLM and HFPLM)
• Donnan membrane technique (DMT)
• Competitive ligand-exchange/stripping voltammetry (CLE-SV)
Various dynamic speciation techniques were compared in a study by Sigg et al. (2006) using
freshwaters collected in Switzerland. They found that techniques involving in-situ measurement
(GIME-VIP) or in-situ exposure (DGT, DMT, and HFPLM) appeared to the most appropriate for
avoiding Pb and other trace metal speciation artifacts associated sampling and sample handling.
AX7.2.1.2 Ambient Water Quality Criteria: Development
The EPA’s procedures for deriving AWQC are described in Stephan et al. (1985) and are
summarized here. With few exceptions, AWQC are derived based on data from aquatic toxicity
studies conducted in the laboratory. In general, both acute (short term) and chronic (long term)
AWQC are developed. Depending on the species, the toxicity studies considered for developing
acute criteria range in length from 48 to 96 hours. Acceptable endpoints for acute AWQC
development are mortality and/or immobilization, expressed as the median lethal concentration
(LC50) or median effect concentration (EC50). For each species, the geometric mean of the
acceptable LC50/EC50 data is calculated to determine the species mean acute value (SMAV).
AX7-108