Introduction - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 4

(Mouneyrac and Roméo in Amiard-Triquet et al. 2011). These defense mechanisms have
a positive impact on the health of biota, allowing the survival of organisms in a degraded
environment. In highly contaminated zones, many plant and animal species are indeed able
to cope with the presence of potentially toxic substances (Amiard-Triquet et al. 2011). On the
other hand, development of tolerance through physiological acclimation and genetic adap-
tation can induce energy and fitness costs (Mouneyrac et al. in Amiard-Triquet et al. 2011).
Biomarkers of damage reveal more or less severe biological impairments, potentially
responsible for detrimental effects on reproduction or even survival. The importance
of toxic effects depending on the degree of environmental contamination is quantified
using a dose-effect relationship. The lowest doses do not induce any noxious effect, but
with increasing doses biological impairments are progressively enhanced. The theoretical
dose-effect relationship is depicted in Figure 1.2 for different levels of biological organiza-
tion. The curve is limited to the domain of low doses to show the first observed effects or
initial effects. At the molecular level, the initial effect is observed at a dose X 1 that is lower
than the dose X 2 able to induce a cellular effect, this in turn being lower than X 3 , acting at
the tissue level. The same argument can be expanded to the level of organs, individuals,
populations, etc. This scheme highlights that the lower the level of biological organization,
the more sensitive the biological response will be. The rationale for this is quite evident:
if only a few molecules have suffered a toxicant effect, cell functioning will not be sig-
nificantly disturbed; if only a few cells are no longer functional within a whole organ, the
function of this organ will still be efficient.

Molecular level

X 1 Dose

Cellular level

Dose X

2

Ti Tissular level

X

Dose

3

FIGURE 1.2
Biomarkers of damage: progression of the dose-effect relationship according to the level of biological
organization.