History of Biomarkers - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 34

rests on their feasibility within the framework of in situ studies and on a good knowledge
of the risks for the ecosystem (Flammarion et al. 1998). Studies carried out over the past
30 years tend to show that monitoring of pollutant effects by measurement of biomarker
responses in organisms is valid, especially if a battery of biomarkers is analyzed on the
same sample. In contrast to chemical analyses, a biomarker response reflects the physi-
ological state of an organism, examined at the molecular, cellular, or individual organism
level. However, in spite of the acquired knowledge (laboratory experiment and field collec-
tion programs or active biomonitoring), certain points deserve to be underlined: (1) more
chemical analyses are necessary to validate future biomarkers; (2) the sampling strategy of
species of interest still can be improved; (3) comparisons between large geographical areas
can be skewed because the biomarker response in some organisms varies, for example,
along a gradient of salinity or because of seasonal variations in temperature, and of the
physiological processes linked to these factors (assimilation, growth, and reproduction).
Environmental conditions of each studied site have to be well known: (1) it is necessary to
know the basic levels of the biomarkers according to the changes in temperature, salinity,
and sexual maturation in the organisms taken into consideration in a given area; (2) an
excess of pollutants can inhibit certain biochemical responses (e.g., EROD activity or MT
level), just as a mixture of various pollutants.
Novel methods, in particular (eco)toxicogenomics and (eco)toxicoproteomics, provide
integrated approaches to combine the responses of well-established core biomarkers in
response to pollutants. The recent cloning of multiple genes in microalgae (Simon et al.
2008; Hutchins et al. 2010), but also in other species belonging to different phyla, has
revealed several novel features of their transcriptional response, and recent progress
in proteomics indicates that proteome modifications are useful to evaluate the effects
of water pollution (Manduzio et al. 2005; Amelina et al. 2007). Profiles of differentially
expressed genes can also be obtained via transcriptomics studies that have been devel-
oped considerably in recent years. Gornati et al. (2004) reported the coding sequences
of Hsp70 and Hsp90 and a partial sequence of heat shock constitutive protein (HSC70)
in the fish Dicentrarchus labra x. According to Geist et al. (2007), exposure of the striped
bass ( Morone saxatilis ) to the pyrethroid insecticide esfenvalerate had tissue-specific
effects on the transcription of HSP70, HSP90, and CYP1A1. The authors concluded that
stress response at the transcriptome level is a more sensitive indicator for esfenvalerate
exposure at low concentrations than swimming behavior, growth, or mortality. Dowling
and Sheehan (2006) have demonstrated that proteomics could be a route to identifica-
tion of toxicity targets in environmental toxicology. Relationships between the induc-
tion of responses, sensitivity to pollutants, and the possible consequences for exposed
individuals and populations must be characterized; rapid development of genomics and
proteomics tools is promising in this respect. Moreover, more and more work is being
carried out with nonmodel organisms, and gene and protein sequences are increasing
in databases, demonstrating the possibility of using organisms from different phyla
according to their sensitivity to environmental pollutants.
Even if some biomarkers do not permit the assessment of ecological risks, they neverthe-
less give complementary and relevant information compared to chemical analyses because
they take into account the bioavailability of chemical pollutants and not only their total
concentration. Authorities in charge of environmental problems are speaking in terms of
the Precautionary Principle and, in the absence of contrary evidence, any detection of a
biomarker response (e.g., EROD activity, Lopez-Barea 1994, quoted in Flammarion et al.
1998) could be regarded as a signal of a potential risk for living organisms.