Biology Reference
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techniques in current use. This relationship is often difficult to establish because
of distance to the contaminant source, and of interactions with other stress fac-
tors. Nevertheless, it has been well identified in some examples, such as that of
the imposex in the dog whelk, Nucella lapillus , living in areas contaminated by
tributyltin (Chapter 9). Moreover, responses of the organisms to the pollutants
must be early enough to reveal any potential degradation as soon as it occurs, so
that substantial ecological damage can be avoided and before any remediation
becomes extremely problematic.
• The biology of the species has to be suficiently well known to differentiate the
signal from the background noise (Figure 1.6). Indeed, intraspecific variability of
the biological responses used as biomarkers has been often observed, making the
interpretation of data difficult. Furthermore, it is important to be able to make use
of control organisms held in parallel, in order to differentiate the changes caused
by the contaminants from the natural fluctuations (seasonal, interannual) of the
parameter studied. Finally, the characterization of the individuals must be per-
fectly mastered if the biomarkers to be studied show variation according to sex,
age, etc.
The interest of the general public in particular species is also a criterion sometimes nec-
essarily taken into account for the selection of sentinel species. This interest raises new
criteria such as recreational value fishing of salmonids, sports fishing of swordfish), eco-
nomic value (commercial species), protection status of the species, and any role as flagship
species as in the cases of charismatic megafauna such as dugongs, tortoises, seals and sea
lions, whales and dolphins, or polar bears.
7.1.3 Active Biomonitoring
7.1.3.1 Context
Numerous biotic factors (age, size and weight, sex, stage of sexual maturity) are at the
origin of any increase in the intraspecific variability of the responses of sentinel species
to contaminant exposure. In order to work on statistically homogeneous populations and
to try to be free from this intraspecific variability encountered with individuals taken in
their natural environment, ABM by transplantation can be used (NRC 1991; De Kock and
Kramer 1994; Olivier et al. 2002; Wepener et al. 2005; Ji et al. 2010; Lu et al. 2010). ABM uses
a set of organisms of known age, and thus at the same stage of sexual maturity, homoge-
neous in size and weight. These organisms maintained in enclosures are then placed in
sites of particular interest. Besides promoting a reduced variability in the responses of the
organisms, this methodology also allows control of the period of exposure to contami-
nants and, at least in theory, to have individuals available for easy sampling at designated
times (nevertheless, in the field, incidents such as loss of enclosures during storms or acts
of malevolence are still to be feared!). ABM operations particularly allow the comparison
of various sites, and the distribution of a single species in contaminated sites and/or in
control ones. ABM has been extensively used in environmental toxicology, and has been
shown to give clearer results than passive biomonitoring since organisms already pres-
ent in situ may have adapted to the local pollutants. In aquatic ecosystems, transplanting
mollusks and fish from a reference site to a polluted area is a feasible strategy for bio-
monitoring the effects of environmental changes. For example, this technique has been
used since 1996 in the Biological Integrators Network on the Mediterranean coast (RINBIO
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