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

Freshwater Invertebrates
Acute and chronic Pb toxicity data for freshwater invertebrates are summarized in Table
AX7-2.4.1. As described in Section AX7.2.3.5, water hardness is a critical factor governing the
solubility, bioavailability, and ultimately the toxicity of Pb. The acute and chronic toxicity of Pb
increases with decreasing water hardness as Pb becomes more soluble and bioavailable to
aquatic organisms. For example, Borgmann et al. (2005) examined the toxicity of 63 metals,
including Pb, to Hyalella azteca at two levels of water hardness (soft water hardness, 18 mg
CaCO3/L; hard water, 124 mg CaCO3/L). Lead was 23 times more acutely toxic to H. azteca in
soft water than hard water. Besser et al. (2005) found that acute toxicity to H. azteca was also
modified by water hardness.
At a mean pH of 7.97 in soft water (hardness (CaCO3) = 71 mg/L) mortality was >50%
for H. azteca at a dissolved Pb concentration of 151 µg/L. The LOEC for survival in hard water
(hardness (CaCO3) = 275 mg/L) at pH 8.27 was 192 µg/L as dissolved Pb and 466 µg/L as total
Pb. Both waterborne and dietary Pb were found to contribute to reduced survival of H. azteca
(Besser et al., 2005).
Exposure duration may also play an important role in Pb toxicity in some species.
For example, Kraak et al. (1994) reported that filtration in the freshwater mussel Dreissena
polymorpha was adversely affected at significantly lower Pb concentrations over 10 weeks of
exposure than was the case after 48 h of exposure.
The influence of pH on lead toxicity in freshwater invertebrates varies between
invertebrate species. Over a 96-h exposure period, mortality increased with decreasing pH in the
bivalve Pisidium casertanum, while pH-independent mortality was reported for gastropod and
crustacean species under similar exposure conditions (Mackie, 1989). Cladocerans
(Ceriodaphnia dubia), amphipods (H. azteca), and mayflies (Leptophlebia marginata) were also
more sensitive to Pb toxicity at lower pH levels (Schubauer-Berigan et al., 1993; Gerhardt,
1994). Lead was 100 times more toxic to the amphipod, Hyalella azteca, at a pH range of 5.0 to
6.0 (Mackie, 1989) than at a pH range of 7.0 to 8.5 (Schubauer-Berigan et al., 1993).
The physiology of an aquatic organism at certain life stages may be important when
determining the toxicity of metals to test organisms. For example, Bodar et al. (1989) exposed
early life stages of Daphnia magna to concentrations of Pb(NO3)2. The test medium had a pH
of 8.3 ∀ 0.2, water hardness (CaCO3) of 150 mg/L, and temperature of 20 ∀ 1 ΕC. Lead
AX7-184