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

unpolluted sites contained 0.33 µg Pb/g. They found significant differences in haplotypes
between the test groups and allelic diversity was significantly lower among L. brevicula from
polluted regions. In contrast, Yap et al. (2004) performed a similar experiment with the green-
lipped mussel Perna viridis; they found that mussels from contaminated sites containing between
4 and 10 µg Pb/g, as well as other heavy metals, exhibited a higher percentage of polymorphic
loci and excess heterozygosity compared to those from uncontaminated sites. The higher level
of genetic diversity was attributed to greater environmental heterogeneity (i.e., variation due to
pollution gradients) in contaminated sites (Yap et al., 2004).
Duan et al. (2000) investigated amphipod (Hyalella azteca) selective mortality and
genetic structure following acute exposure to Pb (5.47 mg/L Pb(NO2)2) as well as exposure to
other heavy metals. They found that genetic differentiation consistently increased among
survivors from the original population, supporting the hypothesis that heavy metals, including
Pb, have the potential to alter the gene pools of aquatic organisms.
Genotoxicity
Lead exposure in water (50 µg/L) over 4 weeks resulted in DNA strand breakage in the
freshwater mussel Anodonta grandis (Black et al., 1996), although higher concentrations (up to
5000 µg/L) did not result in significant breakage by the end of the study period. These results
suggest that a threshold effect for DNA damage and repair exists, where DNA repair only occurs
once a certain body exposure level has been reached. More recently, Cestari et al. (2004)
observed similar results in neotropical fish (Hoplias malabaricus) that were fed Pb-contaminated
food over 18, 41, and 64 days. Lead body burdens in H. malabaricus were approximately 21 µg
Pb 2+ /g. Results indicated that exposure to Pb significantly increased the frequency of
chromosomal aberrations and DNA damage in kidney cell cultures, although when assessed at
the end of the longer exposure periods, aberrations were less common.
Environmental Biological Factors
Environmental factors that are biological in origin can alter the availability, uptake and
toxicity of Pb to aquatic organisms. These factors can be grouped into living and non-living
constituents. For example, living organisms may sequester Pb from the water column, reducing
the availability and toxicity of the metal in the water column to other biota, thus reducing
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