Biology Reference
In-Depth Information
beyond the field of human health. Pollutant-induced changes in genome expression in
natural biota are still being studied through structural alteration of DNA, resulting in
mutations affecting gene sequence and in chromosomal alterations (chromosomal aberra-
tions, DNA breaks, crossing-over, etc.).
Key objectives defined at the onset of genetic ecotoxicology are (1) to explore the extent to
which ecosystems are contaminated with genotoxicants and (2) to identify adverse effects
in individuals and more importantly in populations and communities. In human risk
assessment, cancer is a major fear of exposure to genotoxic agents. As far as environmen-
tal health is concerned, carcinogenic effects in individuals are not analyzed as a threat,
compared to adverse effects on populations and communities. On the other hand, muta-
tions are considered major threats, since they can be transmitted to subsequent genera-
tions when gametes are mutated. Altered fertility, development, and embryonic survival
will reduce reproductive success and thus impair population size or structure. Heritable
mutations, gamete loss due to cell death, embryo mortality resulting from lethal muta-
tions, and abnormal development are environmentally significant. Therefore, linkages
between genotoxic responses, reproduction, and developmental effects justify research on
genotoxic responses as ecologically relevant biomarkers.
The challenge regarding exposure to genotoxic pollutants is to establish thresholds that
will preserve environmental and human health in the long term. Strategies to achieve
this goal will be presented in this chapter. We shall first provide an overview of the main
biomarkers of exposure to genotoxic pollutants, and then the relationships between geno-
toxicity and populational effects established from environmentally relevant experiments
and
in situ
studies.
13.2
In Situ
Biomarkers of Exposure to Genotoxic Pollutants
In their review on genotoxicity biomarkers for environmental biomonitoring published
15 years ago, Rether et al. (1997) underlined the wide use of mutagenicity assays carried
out on environmental samples in the laboratory, as opposed to the few studies focusing
on living species in contaminated environments. Nowadays, the situation has changed
with the development and widespread use of the comet assay for
in situ
investigations
and analyses of exposed populations. Owing to its breadth, this assay has advantages
over the classical methods in use for the survey of populations at risk, namely, mea-
surement of DNA adducts, cytogenetic assays, and the micronucleus (MN) test. The
alkaline unwinding assay has now been replaced by the comet assay for screening
clastogens.
13.2.1 DNA Adducts
The
32
P-postlabeling test described by Randerath et al. (1981) is the reference method
to measure the covalent binding of electrophilic intermediates to DNA,
in vitro
,
in vivo
,
and
in situ
. Detection of adducts provides a way of documenting exposure to genotoxic
chemicals without any knowledge of their identity. The method of quantification is
highly sensitive for detecting bulky hydrophobic xenobiotic-DNA adducts. The latter
are expressed as nanomoles adducts per mole nucleotides, or as the number of adducts
per 10
9
nucleotides.
Search WWH ::
Custom Search