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

In summary, relationships between age, size, and Pb body burden in aquatic invertebrates
and fish are interspecifically variable and depend on many environment-related variables (e.g.,
exposure) (Farkas et al., 2003).
Genetics
There are few studies documenting the effects of Pb on organismal and population
genetics, although rapid advances in biotechnology have prompted recent research in this area
(Beaty et al., 1998). There are two principal effects that sublethal exposure to a contaminant can
have on the genetics of an organism and/or population: (1) a contaminant may influence
selection by selecting for certain phenotypes that enable populations to better cope with the
chemical; or (2) a contaminant can be genotoxic, meaning it can produce alterations in nucleic
acids at sublethal exposure concentrations, resulting in changes in hereditary characteristics or
DNA inactivation (Shugart, 1995). Laboratory studies have shown that exposure to Pb 2+ at
10 mg/mL in blood produces chromosomal aberrations (i.e., deviations in the normal structure or
number of chromosomes) in some organisms (Cestari et al., 2004). Effects of genotoxicity and
toxin-induced selection do not preclude one another, and may act together on exposed
populations. This section reviews Pb genotoxicity and the effects of Pb-induced selection in
aquatic populations.
Selection
Evidence for genetic selection in the natural environment has been observed in some
aquatic populations exposed to metals (Rand et al., 1995; Beaty et al., 1998; Duan et al., 2000;
Kim et al., 2003). Because tolerant individuals have a selective advantage over vulnerable
individuals in polluted environments, the frequency of tolerance genes will increase in exposed
populations over time (Beaty et al., 1998). Several studies have shown that heavy metals can
alter population gene pools in aquatic invertebrates. These changes have resulted in decreased
genetic diversity and are thought to be a potential source of population instability (Duan et al.,
2000; Kim et al., 2003).
Kim et al. (2003) investigated genetic differences and population structuring in the
gastropod Littorina brevicula from heavy-metal polluted and unpolluted environments.
Organisms from polluted sites contained a mean of 1.76 µg Pb/g, while organisms from
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