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

suggested that Cu 2+ may have affected organism physiology through the disruption of cell
membrane integrity. This would allow increased cation (i.e., Pb 2+ ) permeability and, therefore,
substantially increase internalization of Pb and result in effects that were more than additive
(synergistic). Hagopian-Schlekat et al. (2001) examined the impact of individual metals and
complex metal mixtures containing Cd, Cu, Ni, Zn, and Pb to the estuarine copepod Amphiascus
tenuiremis. The copepods were exposed to metal-spiked sediment and pore water. The mixed
metal sediment toxicity tests demonstrated greater than additive toxicity to A. tenuiremis. It was
postulated that the synergism observed was due to two or more metals affecting the same
biological function. Herkovits and Perez-Coll (1991) exposed Bufo arenarum larvae to various
Pb and zinc concentrations in solution. At low zinc concentrations, (2:1 Pb:Zn ratio),
a synergistic toxic effect was observed in the frog larvae relative to the effects observed from
exposure to the individual metals and at higher zinc concentrations. Enhanced Pb toxicity was
attributed to the interference of Pb with cellular activities due to binding with sulfhydryl
polypeptides and nucleic acid phosphates (Herkovits and Perez-Coll, 1991). Allen (1994)
reported on the accumulation of numerous metals and ions into specific tissues of the tilapia
Oreochromis aureus. Tilapia exposed to low concentrations of Pb and mercury (both at
0.05 mg/L) had significantly higher concentrations of Pb in internal organs than those fish
exposed to Pb alone. Similarly, low concentrations of cadmium with low concentrations of Pb
caused increased uptake of Pb in certain organs (e.g., liver, brain, and caudal muscle).
Lead has been shown to complex with Cl ! in aquatic systems. For example, Verslycke
et al. (2003) exposed the estuarine mysid Neomysis integer to six different metals, including Pb,
and a combined metal mixture under changing salinity conditions. At a salinity of 5%, the
reported LC50 for Pb was 1140 µg/L (840, 1440 µg/L). At an increased salinity of 25l, the
toxicity of Pb was substantially reduced (LC50 = 4274 µg/L [3540, 5710 Φg/L]) (Verslycke
et al., 2003). This reduction in toxicity was attributed to the increased concentration of Cl ! ion
due to increased salinity, in that it complexed with divalent Pb in the test system. Exposure of N.
integer to Pb in combination with the other five metals (Hg, Cd, Cu, Zn, Ni) resulted in roughly
strictly additive toxicity (Verslycke et al., 2003).
Long et al. (2006) performed a critical review of the uses of mean sediment quality
guideline quotients (mSQGQs) in assessing the toxic effects of contaminant mixtures (metals and
organics) in sediments. This approach has been used in numerous surveys and studies since
AX7-173