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

esulted in 91.7% survival (Horne and Dunson, 1995a). Exposure to Pb at high pH and low
water hardness or low pH and high water hardness resulted in 75 and 41.7% survival,
respectively (Horne and Dunson, 1995a). Similar results were reported for Jefferson
salamanders during a 7-day exposure and wood frogs during 7- and 28-day exposures (Horne
and Dunson, 1995c). In some cases, water hardness and pH in the absence of Pb have been
shown to affect survival adversely. Mean acute survival of wood frogs and Jefferson
salamanders exposed to low pH and low water hardness, in the absence of Pb, was 83.3 and
91.7%, respectively. Mean chronic survival of wood frogs and Jefferson salamanders exposed to
low pH and low water hardness, in the absence of Pb, was 79.2 and 41.7%, respectively (Horne
and Dunson, 1995c).
High Ca 2+ concentrations have been shown to protect against the toxic effects of Pb
(Sayer et al., 1989; MacDonald et al., 2002; Hassler et al., 2004; Rogers and Wood, 2004).
Calcium affects the permeability and integrity of cell membranes and intracellular contents
(Sayer et al., 1989). As Ca 2+ concentrations decrease, the passive flux of ions (e.g., Pb) and
water increases. At the lowest waterborne Ca 2+ concentration (150 µmol/L), Pb accumulation in
juvenile rainbow trout (Oncorhynchus mykiss) branchials significantly increased as Pb
concentration in water increased (Rogers and Wood, 2004). At higher Ca 2+ concentrations, Pb
accumulation did not significantly increase with Pb concentration in water. This result
demonstrates the protective effects of waterborne Ca 2+ and supports the suggestion that the Ca 2+
component of water hardness determines the toxicity of Pb to fish (Rogers and Wood, 2004).
Rogers and Wood (2004) reported that the uptake of Ca 2+ and Pb 2+ involves competitive
inhibition of apical entry at lanthanum-sensitive Ca 2+ channels and interference with the function
of the ATP-driven baso-lateral Ca 2+ pump. High mortality was reported in brown trout (Salmo
trutta) fry exposed to Pb at a waterborne Ca 2+ concentration of 20 µmol/L, while negligible
mortality was reported at the same Pb concentration but at a waterborne Ca 2+ concentration of
200 µmol/L (Sayer et al., 1989). Adverse effects to mineral uptake and skeletal development
were observed in the latter test group (Sayer et al., 1989).
The bioavailability of Pb and other metals that can be simultaneously extracted in
sediments may be modified through the role of acid volatile sulfide (AVS) under anoxic
conditions (Tessier and Campbell, 1987; Di Toro et al., 1992; Casas and Crecelius, 1994). The
term AVS (iron sulfide is an example) refers to the fraction of the sediment that consists of a
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