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

designed to model uptake, MINTEQ provides an indication of what forms of the metal are likely
to be encountered by aquatic organisms by estimating the formation of metal ions, complexation
of metals, and the general bioavailability of metals from environmental parameters. More
recently, a mechanistic model centered on biodynamics has been proposed by Luoma and
Rainbow (2005) as a method of tying together geochemical influences, biological differences,
and differences among metals to model metal bioaccumulation. The biodynamic model would
be useful in determining the potential adverse effects on aquatic biota, which species are most
useful as indicators of metal effects, and how ecosystems may change when contaminated by
metals. Two prominent models examine trace metal bioavailability and its link to effects
(Hassler et al., 2004). These include the free ion activity model (FIAM) and the biotic ligand
model (BLM). Specific information on these models, including their limitations, is provided in
Section AX7.2.1.3. These models are useful for advancing our understanding of how metal
uptake occurs in aquatic organisms and how uptake and toxic effects are linked.
Bioconcentration Factors (BCF)
BCFs for Pb are reported for various aquatic plants in Table AX7-2.3.1. The green alga
Cladophora glomerata is reported as having the highest BCF (Keeney et al., 1976). Duckweed
(Lemna minor) exhibited high BCF values ranging from 840 to 3560 depending on the method of
measurement (Rahmani and Sternberg, 1999). Duckweed that was either previously exposed or
not exposed to Pb was exposed to a single dose of Pb-nitrate at 5000 µg/L for 21 days.
Duckweed that was previously exposed to Pb removed 70 to 80% of the Pb from the water, while
the previously unexposed duckweed removed 85 to 90%. Both plant groups were effective at
removing Pb from the water at sublethal levels.
BCFs for Pb are reported for various invertebrates in Table AX7-2.3.2. BCFs for
freshwater snails were 738 for a 28-day exposure (Spehar et al., 1978) and 1,700 for a 120-day
exposure (Borgmann et al., 1978). Other reported values for invertebrates included a BCF of
1930 for the scud during a 4-day exposure (MacLean et al., 1996), and BCFs of 499 and 1120 for
the caddis fly and stonefly, respectively, in 28-day exposures (Spehar et al., 1978). In a 28-day
exposure, midge larvae were reported with a BCF of 3670 (Timmermans et al., 1992).
AX7-150