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

BLM in AWQC development is the type of dissolved organic matter used in model development
relative to the types of dissolved organic matter at the site of interest. Richards et al. (2001)
demonstrated that natural organic matter (NOM) of different types differentially influenced Pb
and Cu accumulation by gills of rainbow trout. There are also other ligands not accounted for in
the BLM that require more research. Bianchini and Bowles (2002) emphasized the importance
of reduced sulfur as a metal ligand, limitations in scientific knowledge on reduced sulfur, and
provided recommendations for studies necessary to incorporate sulfide ligands into the BLM.
The U.S. EPA is currently revising the aquatic life AWQC for lead, which will include
toxicity data published after the 1985 AWQC were released and incorporation of the BLM is
being evaluated. If an acute BLM is incorporated into the revised AWQC for lead, the chronic
criteria would likely be estimated using an ACR (the same approach used when the acute
criterion is based on empirical toxicity data; see above).
AX7.2.1.4 Sediment Quality Criteria: Development and Bioavailability Issues
As with metals in surface waters, the environmental fate of metal contaminants in
sediments is moderated through various binding processes that reduce the concentration of free,
bioavailable metal. Sediments function as a sink for Pb, as with most metals. Lead compounds
such as Pb-carbonates, Pb-sulfates, and Pb-sulfides predominate in sediments (Prosi, 1989).
Total Pb has a higher retention time and a higher percentage is retained in sediments compared to
copper and zinc (Prosi, 1989). Lead is primarily accumulated in sediments as insoluble Pb
complexes adsorbed to suspended particulate matter. Naturally occurring Pb is bound in
sediments and has a low geochemical mobility (Prosi, 1989). Organic-sulfide and moderately
reducible fractions are less mobile, whereas cation-exchangeable fractions and easily-reducible
fractions are more mobile and more readily bioavailable to biota (Prosi, 1989). Most Pb
transported in surface waters is in a particulate form, originating from the erosion of sediments in
rivers or produced in the water column (Prosi, 1989).
Sediment quality criteria have yet to be adopted by the EPA, but an equilibrium
partitioning procedure has recently been published (U.S. Environmental Protection Agency,
2005c). The EPA has selected an equilibrium partitioning approach because it explicitly
accounts for the bioavailability of metals. This approach is based on mixtures of cadmium,
copper, Pb, nickel, silver, and zinc. Equilibrium partitioning (EqP) theory predicts that metals
AX7-113