Introduction - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 10

(a)
Response
Time
Stress
(b)
Response
Time
Stress
FIGURE 1.6
Relative importance of natural fluctuations of a biomarker response compared to stress-induced response.
(a) Highly variable background masking stress response. (b) Background relatively stable allowing significant
variation due to stress. (After Cairns, J. Jr., Ecotoxicology , 1, 3-16, 1992.)
comparison is essential. However, to date, with the worldwide dispersion of contaminants
evoked above, pristine areas have disappeared and, at best, reference sites can be chosen
in only a few places that remain comparatively clean. To choose a reference site, geographi-
cal proximity and similarity in terms of temperature, granulometry, and organic content
of sediment, salinity regime (in estuaries), etc., are mandatory to mitigate the importance
of confounding factors. This is not an easy task, as described, for instance, in estuaries
(Amiard-Triquet and Rainbow 2009). Potential reference estuaries with low perceived
anthropogenic pressure are generally small, whereas the human activities responsible for
the presence of many chemicals in the environment have historically developed on the
banks of larger main watercourses. This does provide a potential problem when trying
to eliminate comparative differences resulting from hydrodynamic differences between
the estuaries under comparison. Even in the less fluctuating conditions of a freshwater
biomonitoring program, the interpretation of fish biomarker results is strongly influenced
by the selected reference system (Sanchez et al. 2010).
The addition of more than one reference site into any comparative study, however super-
ficially attractive, has significant resource implications. Associated with the need for tem-
poral surveys instead of spot sampling techniques and the development of the need to
analyze a battery of biomarkers (Chapter 2), methodology involving biomarkers is not
always as initially claimed: sensitive, simple, and cost-effective. Even despite this com-
plexification, the biomarker methodology to be proposed to end users—although efficient
in assessing chemical exposure, sediment quality, and the toxic effects of mixed pollut-
ants—still fails at predicting chemical risk at supra-individual levels (Forbes et al. 2006).
The development of an integrated indicator framework using biological effect techniques
remains key to improve the risk assessment of contaminants in aquatic ecosystems (Thain
et al. 2008).
Since pioneering papers (Atrill and Depledge 1997; Clements 2000) underlined the
importance of targeting links between levels of biological integration, certain research
groups have focused their attention on the cascading effects of interrelated biomark-
ers that can be linked to important biological processes and for which changes can be